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	2022-12-14: How Can Matter Be BOTH Liquid AND Gas? 17:53: So crazy to me that an observatory at the south pole observes the northern hemisphere sky because it needs the Earth to be in the way.
	2022-11-23: How To See Black Holes By Catching Neutrinos 06:34: ... you need to wait until your object sets below the horizon before you can observe ...
	2022-11-16: Are there Undiscovered Elements Beyond The Periodic Table? 17:35: ... says that all other things equal, an observer should reason as if they are randomly selected from the set of all ... 18:25: ... then why can’t I define my reference class as “those who observes an empty universe?” After all, I am my mental experience, and the mental ...
	2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations? 01:46: ... in a location in the universe capable of forming and supporting observers. ... 13:25: The emptiness of our skies and the constraint of making us typical observers is enough to determine all of the parameters of this model. 01:46: ... in a location in the universe capable of forming and supporting observers. ... 13:25: The emptiness of our skies and the constraint of making us typical observers is enough to determine all of the parameters of this model.
	2022-10-26: Why Did Quantum Entanglement Win the Nobel Prize in Physics? 02:18: Opening the box causes the observed ball to have to choose a color state, which then forces the ball on the moon to choose the opposite. 03:22: They only gain specific values when  observed and the wavefunction “collapses”. 02:18: Opening the box causes the observed ball to have to choose a color state, which then forces the ball on the moon to choose the opposite.
	2022-09-28: Why Is 1/137 One of the Greatest Unsolved Problems In Physics? 01:43: ... results in the emission of photons  of specific energies that we observe as spectral lines - sharp peaks in the light observed when we break it ...
	2022-09-21: Science of the James Webb Telescope Explained! 00:19: ... and exoplanet atmospheres to the earliest, most distant galaxies ever observed. ... 04:28: JWST is designed to catch that light and has already observed galaxies much closer to the Big Bang than ever before. 05:57: Most of what the telescope will look at over its hopefully long life will be through the General Observer or GO program.
	2022-08-24: What Makes The Strong Force Strong? 01:41: As physicists tried to understand the aptly named particle zoo, certain peculiar relationships were observed.
	2022-08-17: What If Dark Energy is a New Quantum Field? 03:33: ... out what energy density would be needed to cause the acceleration we observe. That number is around 5x10^-10 Joules/m^3. To give you a sense of the ...
	2022-07-20: What If We Live in a Superdeterministic Universe? 09:01: ... no surprise that Alice and Bob observe opposite spins because we can see that both electron’s spins were ... 09:13: Alice and Bob may observe correlated information if there’s a causal path to both of them. 09:01: ... no surprise that Alice and Bob observe opposite spins because we can see that both electron’s spins were determined by a ... 12:53: ... observed violations of Bell’s inequality with extremely high significance, which ... 00:57: Others - perhaps most - prefer to think of the universe as having a concrete existence independent of the observer. 01:12: Pilot wave theory, objective collapse models, and even the Many Worlds interpretation all seek to describe a reality that exists sans observers. 14:01: The latter has philosophical implications for our own dreams of being detached observers, independent of our subjects. 02:03: Along with Boris Podolsky and Nathen Rosen, he proposed the EPR paradox which was meant to deal a swift death-blow to this observer-centric nonsense. 01:41: ... ad absurdum designed to highlight the ridiculousness of extrapolating observer-dependent indeterminacy to large or macroscopic ... 01:12: Pilot wave theory, objective collapse models, and even the Many Worlds interpretation all seek to describe a reality that exists sans observers. 14:01: The latter has philosophical implications for our own dreams of being detached observers, independent of our subjects.
	2022-06-22: Is Interstellar Travel Impossible? 18:50: ... the no-hair theorem, which tells us that the only things that can be observed about a black hole from its exterior are mass, spin, and ...
	2022-06-15: Can Wormholes Solve The Black Hole Information Paradox? 07:24: ... physics. In a way,   the “classical” and sensible path that we observe is the sum of infinite paths, many ...
	2022-06-01: What If Physics IS NOT Describing Reality? 01:41: ... existence is between the relationship between the observer and the observed. ... 02:20: ... he was careful to note that observer in this context didn't necessarily need to be conscious. Wheeler may ... 11:24: ... does not have a physical   existence independent of the observer. Rather,  the wavefunction and the math that governs it   ... 12:09: ... is.” To learn about something necessarily involves  an observer who is acquiring this knowledge,   so all we can ever know ... 11:24: ... does not have a physical   existence independent of the observer. Rather,  the wavefunction and the math that governs it   describe our ... 12:09: ... famously once asked whether proponents of these   observer-centric interpretations truly believe  the moon isn’t there when nobody ...
	2022-05-04: Space DOES NOT Expand Everywhere 14:34: ... with statements about external factors that they couldn’t directly observe. Unfortunately, practitioners of quantum woo are not so careful and ...
	2022-04-20: Does the Universe Create Itself? 01:59: ... scientist into a superposition of states. And doesn’t the cat get to observe its own state? Perhaps to the cat, the scientists are in a similar ... 09:48: ... was one giant game of negative 20 questions, in which the reality we observe is the only reality that is consistent with the questions asked of it by ... 00:59: ... As Niels Bohr put it “no phenomenon is a phenomenon, until it is an observed phenomenon”. Bohr led the charge with this observer-dependent view, ... 05:56: ... the quantum world appears to live in a state of uncertainty until it’s observed? ... 09:48: ... circuit.” The relationship between the observer (us) and the observed (the universe) brought *both* into existence. Take this yet further and ... 12:27: ... these acknowledge the importance of the observer in defining the observed, while still allowing that there’s some kind of substrate to reality. ... 17:08: ... then it formed by a different process than the black holes that we’ve observed in our universe. The gap between the masses is too enormous for it to ... 00:59: ... As Niels Bohr put it “no phenomenon is a phenomenon, until it is an observed phenomenon”. Bohr led the charge with this observer-dependent view, encapsulated in ... 00:30: ... to the extreme and we imagine the scientist as this perfectly detached observer of the world, capable of monitoring and modeling physical reality ... 00:59: ... in physical particles and quantum fields, nor solely in the mind of the observer, but rather in the interaction of the ... 01:59: ... plays a role in defining reality, how is it possible for separate observers to share a single, consistent reality? Solutions to this seeming paradox ... 04:14: ... Although he started out as a pure realist, he came to believe that the observer must in some way be ... 04:44: ... he saw as the solipsistic view of von Neumann and Wigner, in which the observer was in a sense the primary causal agent and center of its own ... 05:27: ... felt that reality must have its primary existence not in the observer nor in the subject of observation, but rather in the connection between ... 09:48: ... only reality that is consistent with the questions asked of it by all observers. The universe, according to Wheeler, was a giant, closed, “self-excited ... 10:30: ... the present day, the other side of the U. An eyeball here symbolizes the observer. All the astronomers with their telescopes and observatories are aimed ... 12:27: ... about each other. Crucially, these acknowledge the importance of the observer in defining the observed, while still allowing that there’s some kind of ... 13:57: It may be that we live in a participatory universe that’s self-generated by its observers. 14:02: ... with certainty that PBS Space Time is generated by participation of its observers - that’s you guys - and most especially by the participation of our ... 01:59: ... physicists John von Neumann and Eugene Wigner doubled down on the observer-centric view, in which the act of observation in some way creates reality. ... 00:59: ... until it is an observed phenomenon”. Bohr led the charge with this observer-dependent view, encapsulated in his Copenhagen interpretation of quantum ... 01:59: ... plays a role in defining reality, how is it possible for separate observers to share a single, consistent reality? Solutions to this seeming paradox ... 09:48: ... only reality that is consistent with the questions asked of it by all observers. The universe, according to Wheeler, was a giant, closed, “self-excited ... 13:57: It may be that we live in a participatory universe that’s self-generated by its observers. 14:02: ... with certainty that PBS Space Time is generated by participation of its observers - that’s you guys - and most especially by the participation of our ... 01:59: ... objective collapse interpretations. Still others sought to explain the observer’s influence as a sort of selection bias - for example, Hugh Everett’s many worlds ...
	2022-03-23: Where Is The Center of The Universe? 12:19: ... in a sufficiently large cloud that was expanding or contracting would observe an expanding or contracting universe that looks exactly like a FLRW ... 17:32: For example, if a particle races past you you observe its chirality based on its direction of motion. 12:19: ... found that an observer in a sufficiently large cloud that was expanding or contracting would ... 17:22: ... asks whether chirality depend on the observers reference frame, given that it’s defined in reference to the momentum ...
	2022-03-16: What If Charge is NOT Fundamental? 12:31: ... take on a specific combination of values - the combination that we now observe as electric ... 05:57: Charge alone couldn’t explain the patterns of interactions and particle types observed in the particle zoo.
	2022-02-16: Is The Wave Function The Building Block of Reality? 17:42: ... observe an object being frozen at the event horizon if the light emitted at the ... 04:36: ... they’re measured. But the collapse has nothing to do with a conscious observer or any subjective explanation. The wave function and the collapse are ... 16:15: ... point of view of falling matter, but from the point of view of a distant observer. Only the distant observer sees matter approach a state of frozen time, ... 16:48: ... that note Pesila Ratnayaje asks if an outsider observer sees matter slow and freeze at the event horizon, what happens when the ... 18:37: ... nonsensical noise. Which of the two is the case might be relative to the observer. For example Siderite Zackwehdex loves how we ask questions a kid would ... 16:15: ... but from the point of view of a distant observer. Only the distant observer sees matter approach a state of frozen time, and you’re right that from that ... 16:48: ... that note Pesila Ratnayaje asks if an outsider observer sees matter slow and freeze at the event horizon, what happens when the event ... 16:15: ... but from the point of view of a distant observer. Only the distant observer sees matter approach a state of frozen time, and you’re right that from that ... 16:48: ... that note Pesila Ratnayaje asks if an outsider observer sees matter slow and freeze at the event horizon, what happens when the event ...
	2022-02-10: The Nature of Space and Time AMA 00:03: ... showed us i guess that my perception of now could be some other observer's future and yet another observer's past and this leads us to the notion ...
	2022-01-27: How Does Gravity Escape A Black Hole? 04:32: The “speed of space” is just the speed of a free-falling, or inertial observer. 04:38: Falling from very far away, an observer and the patch of space that they occupy reach light speed at the event horizon of the black hole.
	2022-01-12: How To Simulate The Universe With DFT 13:35: ... connected to the narrow sliver of that wavefunction that represents our observed ...
	2021-12-29: How to Find ALIEN Dyson Spheres 02:42: If you were to observe Earth from a distant solar system, you might notice that it looks strangely dark.
	2021-12-20: What Happens If A Black Hole Hits Earth? 15:30: ... made a point that I missed in that MOND episode. And that's that we’ve observed galaxies that seem to be >99% dark matter as well as a few that seem ... 16:33: ... the same as inertial motion in free space. That means that an observer falling through a black hole event horizon shouldn’t notice anything ...
	2021-12-10: 2021 End of Year AMA! 00:02: ... which would give us dark energy i don't know if it agrees with what is observed um paseo achilles asks is my beer painted uh yes this is actually ...
	2021-11-17: Are Black Holes Actually Fuzzballs? 01:14: ... no-hair theorem, which says that the only properties that we can observe from outside a black hole are its mass, electric charge, and angular ...
	2021-11-10: What If Our Understanding of Gravity Is Wrong? 01:22: The expected rotation rates of galaxies come  from applying our laws of gravity based on the observed mass. 04:08: If you tune the modification right you recover  the observed rotation curves for spiral galaxies very nicely without the need for extra mass. 01:22: The expected rotation rates of galaxies come  from applying our laws of gravity based on the observed mass. 04:08: If you tune the modification right you recover  the observed rotation curves for spiral galaxies very nicely without the need for extra mass.
	2021-11-02: Is ACTION The Most Fundamental Property in Physics? 18:13: ... the particular equation that describes the precise details of a given observed phenomenon - usually by trial and error - we come at in from the other ... 07:09: ... to understand. Action is now just how much time is perceived by an observer in their own frame of reference. All objects moving through space time ...
	2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light 03:44: ... improbable isn’t impossible, and so if you then observe the nucleus, it’ll “collapse” into one of those two states - either ... 06:41: And then when you observe the train, all but one of the carriages would vanish! 16:08: As it is, the magnetic fields we observe around black holes seem more consistent with regular dipole fields, with both north and south poles.
	2021-09-21: How Electron Spin Makes Matter Possible 08:21: ... probability distribution is the square of that. We can never, ever observe Psi - all we can do is map Psi^2 by making multiple measurements. The ... 09:45: ... - no observable property is changed by the swap. Remember, that we only “observe” the square of the wavefunction, and in that square the minus sign goes ... 08:21: ... probability distribution is the square of that. We can never, ever observe Psi - all we can do is map Psi^2 by making multiple measurements. The ... 05:59: ... that holds information about the probability of a given property being observed. For example, the wavefunction representing the position of a particle ...
	2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe 02:00: ... and their motion in those jets results in  the radiation that we observe as ...
	2021-09-07: First Detection of Light from Behind a Black Hole 13:34: For communication the warp bubble can be much much smaller, so probably wouldn’t be able to observe those.
	2021-08-03: How An Extreme New Star Could Change All Cosmology 00:00: ... but instead by murmurs of “huh, that’s weird”. Well, we’ve just observed a faint point of light on the sky whose weirdness could change the way ... 09:51: ... turbulent motion to jump start a dynamo powerful enough to produce the observed magnetic ...
	2021-07-21: How Magnetism Shapes The Universe 11:54: ... - in the polarized light surrounding the M81 supermassive black hole observed by the event horizon ... 17:10: ... for each quantum outcome - because in the many worlds interpretation, an observer is more likely to see the most probable outcomes simply because there ...
	2021-07-13: Where Are The Worlds In Many Worlds? 09:48: OK, so you’ve observed the result of the experiment. 09:52: Different yous have observed all results.
	2021-07-07: Electrons DO NOT Spin 03:48: ... - but that has huge problems. For example, in order to produce the observed magnetic moment they’d need to be spinning  faster than the speed ... 06:10: ... between due to all the random orientations. But that's not what’s  observed. Instead, the atoms hit the screen in only two spots corresponding  ... 12:13: ... intrinsic angular momenta can only be observed as plus or minus a half times the reduced Planck constant,   ... 03:48: ... - but that has huge problems. For example, in order to produce the observed magnetic moment they’d need to be spinning  faster than the speed of light. ...
	2021-06-23: How Quantum Entanglement Creates Entropy 11:00: ... the quantum and classical world.   Our capacity to observe quantum  effects like superposition   depends on being ... 16:39: ... Planck length in   that direction, which is also wrong - the observed Planck length should be independent of velocity.   Michal asks ...
	2021-05-25: What If (Tiny) Black Holes Are Everywhere? 04:26: ... with a very distant zero-gravity region where the Hawking radiation is observed. ... 02:17: To a distant observer it would look like the black hole is radiating particles.
	2021-05-19: Breaking The Heisenberg Uncertainty Principle 05:58: the recombined laser no longer perfectly cancels, and so flashes of light are observed.
	2021-05-11: How To Know If It's Aliens 00:52: ... samples were first heated to 160 Celsius, in which case no response was observed - as you might expect if the microbes had been fried It seemed like a ... 01:55: ... Now when this is done with Earth samples, new bursts of gas are always observed as the microbes wake up and start feeding. But not so in the Martian ... 00:52: ... samples were first heated to 160 Celsius, in which case no response was observed - as you might expect if the microbes had been fried It seemed like a slam ...
	2021-04-21: The NEW Warp Drive Possibilities 02:38: That effectively means that it’s impossible to observe a massive object cross this speed barrier.
	2021-03-23: Zeno's Paradox & The Quantum Zeno Effect 02:44: Rather, each state has an amplitude that determines the probability of finding the arrow in that state were you to try to observe it. 03:47: ... you observe the arrow now, most likely it’ll “collapse” to the starting position, ... 14:17: And the value we get is different to what we observe in the modern universe.
	2021-03-16: The NEW Crisis in Cosmology 06:22: ... our good-ole Cepheid variables   in galaxies where both are observed. But those distant Cepheids are in turn calibrated based ...
	2021-03-09: How Does Gravity Affect Light? 02:49: The spider still observes the laser traveling at the speed of light - because the speed of light is invariant to all observers. 05:28: Let’s look at it from the perspective of a non-accelerating observer outside the ship. 02:49: The spider still observes the laser traveling at the speed of light - because the speed of light is invariant to all observers. 09:46: The only thing that’s not relative is the speed of light - everyone observes the same local speed of light - 300,000 km/s in a vacuum.
	2021-02-24: Does Time Cause Gravity? 00:34: ... relativity theory: that the speed of light is constant for all observers, and that the weight induced by acceleration is fundamentally the same as ...
	2021-02-10: How Does Gravity Warp the Flow of Time? 00:25: ... it himself - he described his happiest thought as the following: “For an observer falling freely from the roof of a house, the gravitational field does ... 04:48: ... - that the speed of light is always measured to be the same for all observers, no matter their personal ... 05:25: For an observer in the moving lab, it appears that the stationary clock is ticking slow. 06:52: Both observers see the other’s time has slowed. 06:55: But after a full revolution, both observers ask each other how many ticks their clock ticked. 07:14: The summary is this: two observers moving in straight lines to each other do perceive the other as time-dilated - slowed. 07:22: But as soon as one of those observers changes direction, the symmetry is broken. 09:49: You do have to be careful to choose the right relative distances between observers. 00:25: ... it himself - he described his happiest thought as the following: “For an observer falling freely from the roof of a house, the gravitational field does not ... 04:48: ... - that the speed of light is always measured to be the same for all observers, no matter their personal ... 06:52: Both observers see the other’s time has slowed. 06:55: But after a full revolution, both observers ask each other how many ticks their clock ticked. 07:14: The summary is this: two observers moving in straight lines to each other do perceive the other as time-dilated - slowed. 07:22: But as soon as one of those observers changes direction, the symmetry is broken. 09:49: You do have to be careful to choose the right relative distances between observers. 07:14: The summary is this: two observers moving in straight lines to each other do perceive the other as time-dilated - slowed.
	2021-01-26: Is Dark Matter Made of Particles? 13:52: Cezar Catalin asks what if the ladder traveling through the barn stops when the outside observer sees both doors closed?
	2021-01-19: Can We Break the Universe? 15:40: This is the first time the flourescence has been directly observed, so it lends credence to the theory. 00:17: ... that the speed of light was the fastest speed possible, and that all observers should measure the same speed of light, regardless of their ... 00:26: But from that can the inevitable conclusion that space and time themselves were relative - depended on the velocity of the observer. 01:09: ... will appear to tick more slowly from the point of view of a stationary observer back on the ... 01:42: ... seeming contradictions only become paradoxes if the different observers - on the spaceship and on Earth - can compare the results of an ... 01:52: ... example, there IS a disagreement between the astronaut and an observer back on Earth about the relative passage of time and the distance ... 02:08: ... observer on Earth thinks the astronaut’s clock ticked slow, but the astronaut ... 02:54: But in the frame of a stationary observer, the ship is just moving ridiculously fast, and doesn’t destroy itself. 04:27: One of the consequences of special relativity is that different observers give different accounts of what events are simultaneous. 04:33: ... the spacetime diagram, the set of simultaneous events for a motionless observer lie on a horizontal line - all events corresponding to your notion of a ... 09:09: One observer says the ladder fits, the other says no. 09:18: In this case, the different observers disagree on when the ends of the ladder enter and exit the barn. 09:41: The ladder’s observer perceives the front of the ladder exiting the barn before the base enters. 04:33: ... the spacetime diagram, the set of simultaneous events for a motionless observer lie on a horizontal line - all events corresponding to your notion of a ... 09:41: The ladder’s observer perceives the front of the ladder exiting the barn before the base enters. 00:17: ... that the speed of light was the fastest speed possible, and that all observers should measure the same speed of light, regardless of their ... 01:42: ... seeming contradictions only become paradoxes if the different observers - on the spaceship and on Earth - can compare the results of an ... 04:27: One of the consequences of special relativity is that different observers give different accounts of what events are simultaneous. 09:18: In this case, the different observers disagree on when the ends of the ladder enter and exit the barn. 01:42: ... seeming contradictions only become paradoxes if the different observers - on the spaceship and on Earth - can compare the results of an experiment ... 09:18: In this case, the different observers disagree on when the ends of the ladder enter and exit the barn.
	2021-01-12: What Happens During a Quantum Jump? 01:56: ... theory, and it very neatly explained the specific frequencies of light observed in emission spectra of hydrogen - although it failed for more complex ... 06:21: And in 1986, almost simultaneously, three different teams observed quantum jumps in such an atom.
	2020-12-22: Navigating with Quantum Entanglement 09:49: ... to observe the strange behavior of the quantum world we need to perform incredibly ... 13:17: I was gratified that you were all so excited about this thing that no one will ever, ever observe. 09:32: Although birds do have cryptochromes, the mechanism itself has not been directly observed in a bird, and it remains only the most likely explanation. 13:37: ... are entirely based on the observational properties - what elements are observed as emission or absorption lines, the way the light decays over time, and ...
	2020-12-15: The Supernova At The End of Time 14:17: The point here is that even the idea of "it has happened" is a relative concept - relative to the observer. 14:24: And WE observers ride the wave of time in a particular direction. 14:35: John Ring correctly summarizes that observers in a reverse-time universe wouldn't know the difference. 15:49: ... is a time-reversed observer from a Many Worlds multiverse, and complains they actually can remember ... 14:24: And WE observers ride the wave of time in a particular direction. 14:35: John Ring correctly summarizes that observers in a reverse-time universe wouldn't know the difference. 14:24: And WE observers ride the wave of time in a particular direction.
	2020-11-11: Can Free Will be Saved in a Deterministic Universe? 12:24: It's an emergent phenomenon, and it's the most directly verifiably real thing you will ever observe. 00:36: In it, the past and future have a sort of eternal timeless existence from the point of view of some god-like observer outside both space and time.
	2020-11-04: Electroweak Theory and the Origin of the Fundamental Forces 12:39: The very existence of those symmetries requires a family of fields and particles that we now observe in nature.
	2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time 13:38: ... in one of those branches. The problem isn’t that we can’t observe the other branches at all - just   that we can’t observe them ...
	2020-10-20: Is The Future Predetermined By Quantum Mechanics? 04:57: ... than choosing one reality out of many, when we observe a quantum system, we sort of just become part of one of the realities ... 14:31: In fact, it's the only thing we can observe directly. 02:53: ... states that, that chunk of the universe could be in, if it were to be observed. ... 03:50: ... that a quantum system is literally in a state of undefined-ness until observed. ... 00:47: But different observers will slice the block at different angles that depend on their velocities. 00:52: ... means that for every observer it's possible to imagine another observer who lives in their definition ... 01:10: ... if we accept a unique reality for those other observers in our present and we accept that their perception of the present is as ... 02:00: ... or everything outside our past light cone is undefined, including other observers and the room around you in what you would normally think of as the ... 06:09: But now let's say we believe that other observers in the universe can also collapse the same universal wave function with their observations. 06:17: Well, no problem so far, you can imagine this fleet of observers collapsing the universe all the way up to what you perceive as the present. 06:34: A fast moving observer defines the present very differently to you. 06:38: In fact, any part of spacetime, not in your future light cone is potentially the past for another observer in your present. 06:46: ... that observer can imagine a third observer on their different present for whom your ... 06:58: ... to define an absolute definition of the past, and if we believe in other observers there's no way to keep the wave function of your future from being ... 07:20: It could be observers as in the Von Nuemann-Wigner Interpretation. 07:24: That's the hardest to gel with a non-deterministic universe, unless you are the only observer in the universe. 10:59: There are still other observers in your slice of reality for whom you are now is their past or future. 12:54: ... maybe, but two observers can certainly construct a map of events across the universe that they ... 13:27: ... can ascribe actual existence to one slice of the block universe, to one observer's definition of the present, then you should ascribe existence to the ... 13:44: The alternative seems to be to not ascribe reality to any observer's present but then what exists? 13:50: Just the one observer? 06:34: A fast moving observer defines the present very differently to you. 00:47: But different observers will slice the block at different angles that depend on their velocities. 01:10: ... if we accept a unique reality for those other observers in our present and we accept that their perception of the present is as ... 02:00: ... or everything outside our past light cone is undefined, including other observers and the room around you in what you would normally think of as the ... 06:09: But now let's say we believe that other observers in the universe can also collapse the same universal wave function with their observations. 06:17: Well, no problem so far, you can imagine this fleet of observers collapsing the universe all the way up to what you perceive as the present. 06:58: ... to define an absolute definition of the past, and if we believe in other observers there's no way to keep the wave function of your future from being ... 07:20: It could be observers as in the Von Nuemann-Wigner Interpretation. 10:59: There are still other observers in your slice of reality for whom you are now is their past or future. 12:54: ... maybe, but two observers can certainly construct a map of events across the universe that they ... 13:27: ... can ascribe actual existence to one slice of the block universe, to one observer's definition of the present, then you should ascribe existence to the ... 13:44: The alternative seems to be to not ascribe reality to any observer's present but then what exists? 06:17: Well, no problem so far, you can imagine this fleet of observers collapsing the universe all the way up to what you perceive as the present. 13:27: ... can ascribe actual existence to one slice of the block universe, to one observer's definition of the present, then you should ascribe existence to the slice of the ...
	2020-10-13: Do the Past and Future Exist? 03:17: Time is just a dimension like space, and we only observe a flow of time if we play the slices in sequence like a flip-book. 12:07: ... of the world within that cone - exist in a state of indeterminacy until observed. ... 02:08: Newton assumed that all particles, all observers, all points in space were ruled by a single, constantly ticking clock. 08:14: The upshot is that the moving observer builds an entirely different map of that time slice - they define the present differently. 08:21: In fact, it’s possible for another observer to be in your slice of the present, but for you not to be in theirs. 08:29: ... relativity - space and time tilt into each other, so that different observers will slice up block time at different angles depending on their ... 10:03: Consider the time-slice of our present; we can imagine other observers on that time slice that we surely must “exist”. 10:19: ... them. Just like it does for us. So now fill our present time slice with observers and their remains no part of the block universe that couldn't be ... 08:14: The upshot is that the moving observer builds an entirely different map of that time slice - they define the present differently. 02:08: Newton assumed that all particles, all observers, all points in space were ruled by a single, constantly ticking clock. 08:29: ... relativity - space and time tilt into each other, so that different observers will slice up block time at different angles depending on their ... 10:03: Consider the time-slice of our present; we can imagine other observers on that time slice that we surely must “exist”. 10:19: ... them. Just like it does for us. So now fill our present time slice with observers and their remains no part of the block universe that couldn't be ...
	2020-10-05: Venus May Have Life! 07:23: The abiotic production rate of phosphine is expected to be 10,000 to a million times too low to produce the amount of phosphine that was observed.
	2020-09-08: The Truth About Beauty in Physics 05:43: ... heart, Occam’s Razor comes from the idea that the extreme complexity we observe in our world - in which there are many, seemingly disconnected phenomena ...
	2020-09-01: How Do We Know What Stars Are Made Of? 08:36: Cecilia Payne set about analyzing the many spectra of stars that had been observed at Harvard Observatory.
	2020-08-24: Can Future Colliders Break the Standard Model? 01:55: ... collision experiments, all sorts of never-before-seen particles were observed allowing physicists to begin to map out the subatomic ...
	2020-08-17: How Stars Destroy Each Other 07:38: He observed these objects using visible wavelength of light - and found one object was indeed pulsing.
	2020-07-28: What is a Theory of Everything: Livestream 00:00: ... here's so-and-so's theory let's work out what observers will actually observe if it were stefan's way if it were james way etc and to do that you ...
	2020-07-20: The Boundary Between Black Holes & Neutron Stars 03:34: ... that case it corresponded to an explosion observed across the electromagnetic spectrum - energy released as the neutron ... 09:33: So far we’ve never observed a black hole with masses lower than around 5 times that of the Sun.
	2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing? 03:38: ... baryogenesis.” But, at least at the level of CP violation that we’ve observed, this isn’t enough to explain the level of baryon asymmetry that does ...
	2020-06-30: Dissolving an Event Horizon 13:11: ... between atoms in one aeon would be infinite from the point of view of observers from the previous ...
	2020-06-22: Building Black Holes in a Lab 06:33: ... in fact Hawking-like radiation has been observed in these analog black holes. Or at least, the perturbations in the ...
	2020-06-15: What Happens After the Universe Ends? 11:18: ... cosmology gives a natural explanation for the extreme smoothness that we observe in the early ... 03:28: Remember, the universes contain only light - no observers and no clocks. 04:57: Lines representing constant distance or simultaneous times shift with the velocity of the observer. 05:12: They show how time will tick for any constant-velocity observer passing through this point. 03:28: Remember, the universes contain only light - no observers and no clocks.
	2020-05-18: Mapping the Multiverse 15:51: No indication has ever been found that the speed of light depends on the speed of the device or of the observer.
	2020-05-11: How Luminiferous Aether Led to Relativity 06:42: The key was to observe a change in the speed of light depending on the direction of motion. 07:06: ... - depends in a simple way on the velocity and direction of motion of the observer. This is Galilean relativity - after Galileo ... 11:04: ... The speed of light appeared to be independent of the motion of the observer. ... 07:19: ... calculate what velocity everyone observes using the Galilean transformation, which is part of the foundation of ...
	2020-05-04: How We Know The Universe is Ancient 11:07: ... and also by tracking the past expansion history of the universe to observe the slowing effect of all of those galaxies on the whole universe. It ... 03:24: ... and Jesuit priest, Georges Lemaître, suggested that Vesto Slipher’s observed redshifts could be a sign of the universe’s expansion. Lemaitre put ... 07:40: ... had observed a brighter variety of Cepheids in distant galaxies, but he then used a ... 03:24: ... and Jesuit priest, Georges Lemaître, suggested that Vesto Slipher’s observed redshifts could be a sign of the universe’s expansion. Lemaitre put forward the ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... that's there is an unavoidable observer bias in the universe that we observe okay and so I mean this is there's some interesting stuff in there ...
	2020-04-22: Will Wormholes Allow Fast Interstellar Travel? 09:17: ... these energy conditions are more guidelines than rules, and have been observed to be violated in some cases - for example in dark energy and in the ... 14:59: ... Willenberg asks whether we've observed Fermi Bubbles in other galaxies. Actually yes. Google image search for ...
	2020-04-14: Was the Milky Way a Quasar? 02:48: Before I get to what the team observed, let me describe what they expected to see.
	2020-03-31: What’s On The Other Side Of A Black Hole? 01:53: ... horizon, time appears to freeze from the point of view of a distant observer. And the Schwarzschild metric is defined in terms of that observer’s ...
	2020-03-24: How Black Holes Spin Space Time 10:51: ... rotational energy of the black hole. It’s hypothesized that some jets observed from accreting black holes may be powered by this ...
	2020-03-16: How Do Quantum States Manifest In The Classical World? 01:48: ... seems to provide a partial answer - we talked about it last time - to observe a superposition there needs to be a knowable phase relation between two ... 13:22: ... states - weird superpositions are not. It still doesn't tell us why we observe one pointer state over another unless of course there are multiple of ... 17:40: ... states that all branches survive, and the measurement result that we observe depends on which branch we find ourselves in. However not all ...
	2020-03-03: Does Quantum Immortality Save Schrödinger's Cat? 01:29: ... interpretation, which says that the wavefunction branches that we don’t observe somehow vanish at the moment of ... 02:33: ... equally - the atom is simultaneously decayed and not decayed until we observe ... 13:07: It ensures that sensible and consistent macroscopic realities are observed across each branch. 09:36: ... probability arguments including Bayesian analysis or thinking in “observer years” rather than observer ... 12:03: ... configurations between experimental aparatus and the brain of different observers means decoherence should proceed differently along those ... 12:14: So why do different observers always agree on the result of the experiment? 12:19: Well, Vampyricon answers this partically, saying that each observer will be on one decohered branch of the wavefunction. 12:29: Each decohered branch will have its own set of observers. 12:33: In other words, not all observers agree on experimental outcomes - it's just you never meet the ones who don't agree with you. 12:46: ... have sets of observers who make consistent observations, and who are unaware of observers on ... 09:36: ... including Bayesian analysis or thinking in “observer years” rather than observer lifetimes. ... 12:03: ... configurations between experimental aparatus and the brain of different observers means decoherence should proceed differently along those ... 12:14: So why do different observers always agree on the result of the experiment? 12:29: Each decohered branch will have its own set of observers. 12:33: In other words, not all observers agree on experimental outcomes - it's just you never meet the ones who don't agree with you. 12:46: ... have sets of observers who make consistent observations, and who are unaware of observers on ... 12:33: In other words, not all observers agree on experimental outcomes - it's just you never meet the ones who don't agree with you.
	2020-02-24: How Decoherence Splits The Quantum Multiverse 06:53: And this is one of the weird, multiple history aspects of quantum mechanics that we can directly observe. 09:04: By the way, this is why any attempt to observe which slit the photon passes through destroys the interference pattern. 09:18: ... some magical effect whereby the wavefunction “knows” that it has been observed and so ... 10:01: ... of signals traveling from those pixels ultimately to the brain of the observer. ... 12:31: So you shouldn’t think of yourself as this gods-eye observer, capable of seeing the whole wavefunction and causing it to collapse.
	2020-02-18: Does Consciousness Influence Quantum Mechanics? 11:24: You talk to each other and agree that you observed the same result - the wavefunction collapses in the same way for both of you. 07:38: So there’s the conflict - different observers say the wavefunction collapses at different times. 11:37: ... maybe you are the only observer and you’re inventing your friend and, well, the rest of reality and ... 11:46: ... for the consistency of experimental results between different observers seems to be that the result of the experiment - and reality - exists ... 07:38: So there’s the conflict - different observers say the wavefunction collapses at different times. 11:37: ... your friend and, well, the rest of reality and there are no other observers in the universe to give conflicting ... 11:46: ... for the consistency of experimental results between different observers seems to be that the result of the experiment - and reality - exists ...
	2020-02-11: Are Axions Dark Matter? 02:35: ... In fact they almost demand it - and yet no such violation has ever been observed. ...
	2020-01-13: How To Capture Black Holes 00:24: ... stunning enough, but the real promise lay ahead. Every time we learn to observe the universe in a new way we discover new things. When we figured out ... 08:27: ... it may explain why so many surprisingly massive black hole mergers are observed. And if we spot more and more high-mass mergers that will be further ...
	2019-12-17: Do Black Holes Create New Universes? 16:03: Step 2: Observe that the internet has existed for approximately 30 years.
	2019-12-09: The Doomsday Argument 03:31: ... to be the value that most astronomers across the multiverse would observe, with a few assumptions like that the number of astronomers in a universe ... 08:39: ... “what sort of cosmological constant is the typical astronomer likely to observe - so reference class was an astronomer - or really any observer capable ... 03:03: He got a value that was a factor of 10 higher than what would be observed 10 years later when dark energy was discovered. 03:48: Weinberg calculated that the density of dark energy should most typically be observed to be around 5-10 times the density of matter. 03:03: He got a value that was a factor of 10 higher than what would be observed 10 years later when dark energy was discovered. 03:24: He realized that we should instead assume that we are the most common type of observer. 04:15: ... refinement of the anthropic principle to talk about observers rather than environments is essentially using the Self-Sampling ... 08:39: ... likely to observe - so reference class was an astronomer - or really any observer capable of measuring the cosmological ... 09:03: ... example, if you define our reference class as all observers in our past and future evolutionary chain, then we could still be in the ... 08:39: ... likely to observe - so reference class was an astronomer - or really any observer capable of measuring the cosmological ... 04:15: ... refinement of the anthropic principle to talk about observers rather than environments is essentially using the Self-Sampling ... 09:03: ... example, if you define our reference class as all observers in our past and future evolutionary chain, then we could still be in the ... 01:20: ... can use: our existence selects for a particular type of potentially-rare observer-supporting environments, but we should expect to find ourselves in the most typical ...
	2019-12-02: Is The Universe Finite? 15:15: There's no reason they need to be in any way happy about the universe they observe. 15:29: Regis Bodnar has a great point: while it may be technically possible to observe a typical universe, it's perhaps impossible to define one. 02:06: ... expansion rate for the universe that does not match the expansion rate observed today - particularly the modern expansion rate determined from supernova ... 14:35: ... mean by "reference class" - as in, how do you choose the sample of observers from which you consider yourself randomly ... 15:04: ... anthropic seletion only demands that our universe be able to produce observers who think about the nature of the ... 14:35: ... mean by "reference class" - as in, how do you choose the sample of observers from which you consider yourself randomly ... 15:04: ... anthropic seletion only demands that our universe be able to produce observers who think about the nature of the ...
	2019-11-18: Can You Observe a Typical Universe? 01:55: ... have been able to produce us - to give rise to living creatures that can observe ... 03:10: ... just call it the anthropic principle: we necessarily observe from an environment capable of producing observers; be that environment ... 06:32: We certainly don’t observe the universe in a typical, observer-hostile state, and and so it’s tempting to use the anthropic principle here. 07:19: By the Copernican principle, we are most likely to observe a very typical environment - this is just a statement of probability. 11:41: The anthropic principle in its proper form is without question an important thing to take into account whenever we observe the universe. 02:35: ... we must live in a place and time in the universe capable of supporting observers - in our case, a habitable biosphere, and the strong anthropic ... 03:10: ... we necessarily observe from an environment capable of producing observers; be that environment a planet within a universe or a universe within a ... 04:37: ... the strong anthropic principle to mean that the evolution of observers somehow had some causal influence on the initial formation of the ... 05:00: The principle is NOT causal - it just tells us to account for an observer selection bias when interpreting the nature of our environment. 07:32: ... anthropic principle tells us we must account for our status as observers when we interpret our environment - including the probability of being ... 07:42: ... in a typical region of the cosmos that is consistent with us being observers. ... 08:48: ... one galaxy to spawn a life-bearing planet - so there should be many more observers in small entropy fluctuations than in large ... 10:08: ... self-sampling assumption, which states that “All other things equal, an observer should reason as if they are randomly selected from the set of all ... 10:33: That means you’re most likely a common type of observer, and in a common environment in which observers can exist. 10:55: The prior is that we are an observer. 10:59: But proper Bayesian thinking requires careful definition of priors - for example, Bostrom talks about “observers in their reference class”. 13:03: ... about your universe, given your privileged status as a typical conscious observer of space ... 14:21: ... they say that the universe isn't really fine-tuned for life or for observers because there could be many types of observer very different to ... 14:43: ... can probably assume that for an intelligent observer to emerge in any universe, that universe must be capable of forming ... 15:16: ... while there may be many small parts of that parameter space where observers can arise, most of it - hence most universes - should be devoid of ... 16:43: ... self-sampling assumption says we should assume we're a typical observer - so maybe the most typical observers are in relatively barren ... 17:53: In other words, find all possible combinations of constants that can produce observers. 16:43: ... self-sampling assumption says we should assume we're a typical observer - so maybe the most typical observers are in relatively barren universes, ... 05:00: The principle is NOT causal - it just tells us to account for an observer selection bias when interpreting the nature of our environment. 07:58: That allows us to be in a rare, observer-friendly environment, but tells us that we should be in the most typical of such environments. 06:32: We certainly don’t observe the universe in a typical, observer-hostile state, and and so it’s tempting to use the anthropic principle here. 02:35: ... we must live in a place and time in the universe capable of supporting observers - in our case, a habitable biosphere, and the strong anthropic ... 03:10: ... we necessarily observe from an environment capable of producing observers; be that environment a planet within a universe or a universe within a ... 04:37: ... the strong anthropic principle to mean that the evolution of observers somehow had some causal influence on the initial formation of the ... 07:32: ... anthropic principle tells us we must account for our status as observers when we interpret our environment - including the probability of being ... 07:42: ... in a typical region of the cosmos that is consistent with us being observers. ... 08:48: ... one galaxy to spawn a life-bearing planet - so there should be many more observers in small entropy fluctuations than in large ... 10:08: ... as if they are randomly selected from the set of all actually existent observers (past, present and future) in their reference class." If there are a ... 10:33: That means you’re most likely a common type of observer, and in a common environment in which observers can exist. 10:59: But proper Bayesian thinking requires careful definition of priors - for example, Bostrom talks about “observers in their reference class”. 14:21: ... they say that the universe isn't really fine-tuned for life or for observers because there could be many types of observer very different to ... 15:16: ... while there may be many small parts of that parameter space where observers can arise, most of it - hence most universes - should be devoid of ... 16:43: ... we should assume we're a typical observer - so maybe the most typical observers are in relatively barren universes, and there are just way more of those ... 17:53: In other words, find all possible combinations of constants that can produce observers. 02:35: ... we must live in a place and time in the universe capable of supporting observers - in our case, a habitable biosphere, and the strong anthropic principle, ...
	2019-11-11: Does Life Need a Multiverse to Exist? 09:49: If fact, that’s true if the strength of vacuum energy were only a little larger than is observed. 02:50: We must find ourselves at a place and time in the universe capable of producing observers. 03:05: Well, Carter also has a strong version. The universe must be such as to admit the creation of observers within it at some stage. 03:27: ... strong anthropic principle tells us that there’s an observer selection bias that may help us understand why we live in such a ... 02:50: We must find ourselves at a place and time in the universe capable of producing observers. 03:05: Well, Carter also has a strong version. The universe must be such as to admit the creation of observers within it at some stage.
	2019-11-04: Why We Might Be Alone in the Universe 00:57: ... strong anthropic principle tells us that an observed universe must be able to produce observers - and we’ll get to the ... 13:48: And this was NOT observed in the light from a distant gamma ray burst, which presents a challenge for the theory. 00:57: ... strong anthropic principle tells us that an observed universe must be able to produce observers - and we’ll get to the implications of ... 00:38: The anthropic principle tells us that we shouldn’t expect to find ourselves in some random corner of the multiverse - there’s an observer bias. 00:57: ... principle tells us that an observed universe must be able to produce observers - and we’ll get to the implications of that soon - including the ... 01:29: ... may seems tautological, but accounting for this observer selection bias is important to understanding why the universe looks the ... 01:54: To get to this, let's think about what it means to be an intelligent observer. 00:38: The anthropic principle tells us that we shouldn’t expect to find ourselves in some random corner of the multiverse - there’s an observer bias. 01:29: ... may seems tautological, but accounting for this observer selection bias is important to understanding why the universe looks the way it ... 00:57: ... principle tells us that an observed universe must be able to produce observers - and we’ll get to the implications of that soon - including the ...
	2019-09-30: How Many Universes Are There? 06:15: That residual field might be what we observe as dark energy.
	2019-09-16: Could We Terraform Mars? 04:06: The ablation of what is left of the Martian atmosphere has now been directly observed by NASA’s MAVEN spacecraft, as we’ve also discussed before.
	2019-08-06: What Caused the Big Bang? 01:31: ... to rise after it leaves your hand. This is the Hubble expansion that we observe ... 03:04: Now, we know that something like this exists because we've observed it in the accelerating expansion produced by dark energy.
	2019-07-18: Did Time Start at the Big Bang? 06:02: ... there is no universal clock time is relative Clocks are attached to each observer each moving frame of reference to see what time does at the Big Bang We ...
	2019-06-20: The Quasar from The Beginning of Time 00:04: ... event that built this land has provided another window: it allows us to observe a time when the universe was still cooling from the fire of its own ... 07:27: ... can see the universe beyond the electromagnetic spectrum that we observe with traditional ...
	2019-05-01: The Real Science of the EHT Black Hole 03:31: ... to observe the event horizon of the M87 black hole you need to resolve one ... 10:33: ... that seemed too outlandish to be real, and certainly too difficult to observe to ever ... 02:51: ... points separated by an angle that is the same as the ratio between the observed wavelength and the separation of the telescopes – also called the ... 03:19: ... for the resolution of any telescope – it’s the diffraction limit – the observed wavelength divided by the diameter of the ... 02:51: ... points separated by an angle that is the same as the ratio between the observed wavelength and the separation of the telescopes – also called the ... 03:19: ... for the resolution of any telescope – it’s the diffraction limit – the observed wavelength divided by the diameter of the ... 07:43: Remember that the EHT observes radio light with a wavelength of around a millimeter.
	2019-04-24: No Dark Matter = Proof of Dark Matter? 00:03: ... the effect of dark matter dark matter and baryons should never be observed separately the first piece of evidence that baryons and dark matter can ...
	2019-04-10: The Holographic Universe Explained 03:03: ... the point of view of outside observers, its contents is smeared into 2-D on the surface, but from the PoV of ...
	2019-03-28: Could the Universe End by Tearing Apart Every Atom? 00:25: ... us from giving it a name we call this unknown influence dark energy. the observed acceleration is for the most part nicely described with a constant ...
	2019-03-20: Is Dark Energy Getting Stronger? 09:29: When compared to observed UV brightness that gives you distance.
	2019-01-24: The Crisis in Cosmology 12:18: ...that could explain why we observe a higher H0 in the modern universe... 03:39: ...whose observed brightness, therefore, tells us their distance. 09:18: ...could give the power spectrum observed by Planck. 03:39: ...whose observed brightness, therefore, tells us their distance.
	2019-01-09: Are Dark Matter And Dark Energy The Same? 12:07: Which is good for string theorists, as Farnes notes, but not for observers because that’s not consistent with what we see.
	2018-12-06: Did Life on Earth Come from Space? 00:37: ... come swooping in and shout aliens every time something inexplicable is observed and we have at least one counterpoint mark gibble says that no it's ...
	2018-11-21: 'Oumuamua Is Not Aliens 03:48: But no coma or tail was observed in Oumuamua. 04:36: In fact, the observed acceleration seems to be following an inverse square law. 05:09: ... thick and made of a highly reflective material would produce the observed brightness and ... 06:59: Without reflective dust, outgassing would be invisible to our telescopes but could still cause the observed acceleration. 04:36: In fact, the observed acceleration seems to be following an inverse square law. 06:59: Without reflective dust, outgassing would be invisible to our telescopes but could still cause the observed acceleration. 05:09: ... thick and made of a highly reflective material would produce the observed brightness and ...
	2018-11-14: Supersymmetric Particle Found? 09:49: It may also be that there were some gigantic bursts of regular neutrinos at the time of the observed events. 10:05: In fact, one of the two events may have been associated with a distant supernova that was observed around the same time and location. 09:49: It may also be that there were some gigantic bursts of regular neutrinos at the time of the observed events.
	2018-10-31: Are Virtual Particles A New Layer of Reality? 14:28: ... majority of every civilization that ever developed would have to observe all of these conditions in order for us to see ...
	2018-10-18: What are the Strings in String Theory? 14:03: Roman R. asks whether computation at an event horizon would experience massive time dilation relative to an outside observer.
	2018-10-03: How to Detect Extra Dimensions 09:22: Just observe a gravitational wave and figure out how much its intensity dropped off over the distance traveled. 00:59: The key to this breakthrough was the gravitational wave event observed in August of 2017, GW170817. 01:29: The resulting kilonova is first observed in gravitational waves and then as a gamma ray burst.
	2018-09-20: Quantum Gravity and the Hardest Problem in Physics 00:47: Together, general relativity and quantum mechanics have allowed us to explain nearly every fundamental phenomenon observed. 02:25: It describes particles as waves of infinite possibility whose observed properties are intrinsically uncertain.
	2018-08-30: Is There Life on Mars? 02:06: ... allowed him to observe a dark patch on the Martian surface, and so measure Mars's 24-hour ... 04:05: ... observed streaks on the surface of the planet that he named "canali." That's ...
	2018-08-01: How Close To The Sun Can Humanity Get? 02:07: ... the Carrington Event, after British astronomer Richard Carrington who observed ...
	2018-07-25: Reversing Entropy with Maxwell's Demon 05:41: The demon has the ability to observe speed and trajectories of individual particles in the system. 01:31: ... or microstates in physics-speak-- that could produce the same observed set of macroscopic observables, or the same ...
	2018-07-11: Quantum Invariance & The Origin of The Standard Model 03:18: The position that we observe when we look at the particle is picked randomly from that distribution. 04:23: It's that magnitude squared that we can observe.
	2018-07-04: Will A New Neutrino Change The Standard Model? 05:46: Every neutrino we've ever observed was spotted using the weak interaction. 06:33: We've observed a neutrino's flavor can change.
	2018-06-20: The Black Hole Information Paradox 06:07: The motivation for this idea is the fact that, from the point of view of an outside observer, nothing ever actually crosses the event horizon. 07:25: From the point of view of an observer falling into the black hole, they aren't frozen at the horizon. 07:55: No observer can ever see both. 07:25: From the point of view of an observer falling into the black hole, they aren't frozen at the horizon.
	2018-06-13: What Survives Inside A Black Hole? 13:30: More likely is that the observer and the observation are a small part of a global wave function that continues to evolve in a unitary manner.
	2018-05-02: The Star at the End of Time 02:41: ... figure out the lifespan of red dwarf stars, also known as "M dwarfs." We observe that a red dwarf with 10% of the Sun's mass is about 1,000 times fainter ...
	2018-04-18: Using Stars to See Gravitational Waves 03:49: ... black holes that live in the centers of galaxies, we need to observe gravitational waves in the 0.1 million hertz to 0.1 hertz ... 07:52: ... it may be possible to observe this effect in the dense star fields of galactic cores if those galaxies ... 03:49: ... black holes that live in the centers of galaxies, we need to observe gravitational waves in the 0.1 million hertz to 0.1 hertz ... 00:46: In its two and a half years of operation, LIGO has observed five certain black hole-black hole mergers. 01:47: Perhaps we've observed the merging of primordial black holes formed in the instant after the Big Bang.
	2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!) 10:57: Last week, we talked about the mysterious Unruh effect, in which accelerating observers find themselves bathed in a sea of particles. 11:07: ... Diagrams points out that from the point of view of an inertial observer, an accelerating particle detector emits particles instead of absorbing ... 11:23: ... in short, the inertial observer sees the accelerating particle detector click as though it registered a ... 11:49: ... inertial observer sees that there's a type of friction between the accelerating observer ... 11:59: But the accelerating observer doesn't directly see that friction. 12:05: The answer is that the accelerating observer perceives themselves to be plowing through a bath of Unruh particles, and these produce the drag. 12:13: The accelerating observer must expend more energy to produce the same acceleration. 11:59: But the accelerating observer doesn't directly see that friction. 12:05: The answer is that the accelerating observer perceives themselves to be plowing through a bath of Unruh particles, and these produce the drag. 11:23: ... in short, the inertial observer sees the accelerating particle detector click as though it registered a ... 11:49: ... inertial observer sees that there's a type of friction between the accelerating observer and ... 10:57: Last week, we talked about the mysterious Unruh effect, in which accelerating observers find themselves bathed in a sea of particles.
	2018-04-04: The Unruh Effect 09:46: ... difficult to directly observe Unruh particles, although analogies have been observed even in classical ... 00:44: They were independently studying how the nature of quantum fields appears to change depending on whether or not an observer is accelerating. 01:14: It tells us that accelerating observers find themselves in a warm bath of particles. 02:16: ... of light, so the world line of a massive object, which includes any observer, has to be less than 45 degrees from the ... 02:26: ... light ray world lines backwards from our observer defines what we call the past light cone, the region of space-time that ... 02:38: ... because photons fired from anywhere in the past light cone can reach our observer either at the current point or at some point in their past world ... 02:47: ... our observer moves forward in time, as long as they don't travel faster than light, ... 03:13: That's the world line of an observer undergoing constant acceleration. 04:50: This means that any events happening to the left of that diagonal line will never affect the accelerating observer, which sounds pretty horizon-like. 05:06: ... after the coordinate system we use to describe a constantly accelerating observer in special relativity, Rindler coordinates, devised by Austrian ... 05:20: The Rindler horizon flows at a fixed distance behind a constantly accelerating observer. 05:25: Let's call them Rindler observers from now on. 05:36: All parts of the universe beyond that horizon are out of causal connection with the Rindler observer as long as they continue to accelerate. 06:47: In the case of Hawking radiation, an inertial observer far from the black hole sees the radiation. 07:00: The only observers who don't see Hawking radiation are those plummeting in freefall towards the event horizon. 07:06: ... if an accelerating Rindler observer is in the same location as an inertial observer, the former will see ... 07:23: What if the Rindler observer accelerates fast enough that they are burned to a crisp by Unruh radiation? 07:29: Does the inertial observer see some sort of spontaneous combustion? 07:37: A little less gruesomely, imagine the Rindler observer has a particle detector. 07:45: And the inertial observer would agree that it clicked, but they wouldn't see the particle that triggered it. 09:13: An inertial observer sees the charged particle itself radiating, its energy extracted from the magnetic field. 09:19: But an observer accelerating with that charged particle sees it absorbing Unruh particles and then spitting them out again. 09:27: The Rindler and inertial observers disagree on the source of the energy even if they agree on the final result. 10:29: ... event horizon and the particles of Hawking radiation seen by a distant observer? ... 07:23: What if the Rindler observer accelerates fast enough that they are burned to a crisp by Unruh radiation? 09:19: But an observer accelerating with that charged particle sees it absorbing Unruh particles and then spitting them out again. 02:26: ... light ray world lines backwards from our observer defines what we call the past light cone, the region of space-time that can have ... 02:47: ... our observer moves forward in time, as long as they don't travel faster than light, their ... 09:13: An inertial observer sees the charged particle itself radiating, its energy extracted from the magnetic field. 03:13: That's the world line of an observer undergoing constant acceleration. 08:58: The upshot is that the very existence of particles is observer-dependent. 01:14: It tells us that accelerating observers find themselves in a warm bath of particles. 05:25: Let's call them Rindler observers from now on. 07:00: The only observers who don't see Hawking radiation are those plummeting in freefall towards the event horizon. 09:27: The Rindler and inertial observers disagree on the source of the energy even if they agree on the final result.
	2018-03-28: The Andromeda-Milky Way Collision 02:36: He observed Cepheid variables, which have a pulsation rate that depends on their energy output. 04:40: Then they averaged the observed motion of all of those stars and removed the effects due to the rotation of Andromeda and the motion of the sun. 02:36: He observed Cepheid variables, which have a pulsation rate that depends on their energy output. 04:40: Then they averaged the observed motion of all of those stars and removed the effects due to the rotation of Andromeda and the motion of the sun.
	2018-03-15: Hawking Radiation 05:44: A distant future observer sees radiation coming from the black hole. 09:12: In fact, an observer in freefall through the horizon sees nothing. 09:22: This radiation is visible only to distant observers. 05:44: A distant future observer sees radiation coming from the black hole. 09:22: This radiation is visible only to distant observers.
	2018-01-31: Kronos: Devourer Of Worlds 05:01: So why are their chemical differences much higher than ever observed for a wide binary pair? 06:06: Oh et al. calculated that 15 Earth masses of raw Earth material would produce the observed abundances very nicely.
	2018-01-24: The End of the Habitable Zone 10:49: Last week we talked about how slicing a piece out of space time caused different observers to disagree on the nature of the vacuum. 11:14: The vacuum state of all fields are redefined in the vicinity of a black hole or for an accelerating observer. 10:49: Last week we talked about how slicing a piece out of space time caused different observers to disagree on the nature of the vacuum.
	2018-01-17: Horizon Radiation 12:54: These are observed as X-ray flares. 00:17: Even so, every observer agrees on whether a particle exists or not, right? 00:26: [MUSIC PLAYING] Both theories of relativity, special and general, tell us that many things are observer dependent. 00:37: Different observers might disagree about speeds, lengths, or times, but the laws of physics should be the same for everyone. 00:46: And for two observers with very different, but constant speeds-- inertial observers, the vacuum itself should appear the same. 01:24: It limits an observer's causal connection to a part of the universe. 01:45: As it turns out, what gives is the nature of the vacuum, and in fact, the notion of what a particle is becomes observer dependent. 01:53: ... the Unruh effect, both of which are very similar and are results of this observer dependent ... 02:22: ... get at this idea of observer dependent particles and vacua, we're going to need some quantum field ... 03:00: For the laws of physics to be consistent, the fundamental properties of these fields must be the same for all observers. 03:14: ... observers, be they floating in empty space or accelerating or orbiting a black ... 03:33: There's no conflict for constant speed inertial observers. 03:55: ... when an observer who sees a horizon tries to write down these equations, in order to ... 11:23: It appears to be bathed in thermal particles-- particles that don't exist for an observer who doesn't see that horizon. 00:17: Even so, every observer agrees on whether a particle exists or not, right? 00:26: [MUSIC PLAYING] Both theories of relativity, special and general, tell us that many things are observer dependent. 01:45: As it turns out, what gives is the nature of the vacuum, and in fact, the notion of what a particle is becomes observer dependent. 01:53: ... the Unruh effect, both of which are very similar and are results of this observer dependent ... 02:22: ... get at this idea of observer dependent particles and vacua, we're going to need some quantum field theory, and ... 01:53: ... the Unruh effect, both of which are very similar and are results of this observer dependent vacuum. ... 00:37: Different observers might disagree about speeds, lengths, or times, but the laws of physics should be the same for everyone. 00:46: And for two observers with very different, but constant speeds-- inertial observers, the vacuum itself should appear the same. 01:24: It limits an observer's causal connection to a part of the universe. 03:00: For the laws of physics to be consistent, the fundamental properties of these fields must be the same for all observers. 03:14: ... observers, be they floating in empty space or accelerating or orbiting a black ... 03:33: There's no conflict for constant speed inertial observers. 01:24: It limits an observer's causal connection to a part of the universe.
	2017-12-20: Extinction by Gamma-Ray Burst 03:25: The observed faint flash of gamma rays from exploding stars can last anywhere from a couple of seconds to a few minutes.
	2017-12-13: The Origin of 'Oumuamua, Our First Interstellar Visitor 00:51: ... it became abundantly clear that we were looking at the first object ever observed that came from outside our solar ... 03:00: ... previously observed asteroid-- indeed, every previously observed everything in our solar ...
	2017-12-06: Understanding the Uncertainty Principle with Quantum Fourier Series 02:06: The uncertainty principle exists alongside this observer effect.
	2017-11-29: Citizen Science + Zero-Point Challenge Answer 00:33: ... but as an amateur astronomer, he discovered Uranus and was the first to observe binary star systems, among other ... 02:20: ... American Association of Variable Star Observers, founded in 1911, has generated an archive of variable star data taken ...
	2017-11-22: Suicide Space Robots 03:37: But then inexplicably, sporadic recoveries in power were observed. 12:20: ... has a lot of trouble explaining why it produces the tiny energy density observed as dark energy, as opposed to either 0 or very high energy ...
	2017-10-19: The Nature of Nothing 07:40: ... the same year that the Lamb shift was first observed, German physicist Hans Bethe successfully explained it in terms of a ... 09:42: Now while there are potentially other explanations for the observed force, this has been taken as strong evidence that vacuum energy is real. 10:22: ... so, then the amount of vacuum energy needed to produce the observed acceleration is tiny, around one one hundred millionth of an erg per ... 09:42: Now while there are potentially other explanations for the observed force, this has been taken as strong evidence that vacuum energy is real. 07:40: ... the same year that the Lamb shift was first observed, German physicist Hans Bethe successfully explained it in terms of a fluctuating ...
	2017-10-04: When Quasars Collide STJC 03:59: ... short the target is observed with radio telescopes on opposite sides of the planet, and phase ... 06:47: The extreme energy densities observed are also what you'd expect from the bases of two distinct jets.
	2017-09-28: Are the Fundamental Constants Changing? 00:30: [MUSIC PLAYING] The laws of physics are the relationships we observe between space and time, and the fields and particles that occupy it. 04:48: We see this effect in the sharp spikes or dips in light at specific wavelengths when we observe the spectrum of a gas.
	2017-09-20: The Future of Space Telescopes 04:18: With the starshade, we may soon directly observe terrestrial exoplanets with cameras and spectrographs. 10:12: What once seemed like fundamental limits to our ability to observe the universe are now being overcome by some incredible human ingenuity. 04:18: With the starshade, we may soon directly observe terrestrial exoplanets with cameras and spectrographs.
	2017-09-13: Neutron Stars Collide in New LIGO Signal? 13:56: ... life by observing extraterrestrial atmospheres, Alex asks whether we can observe the atmosphere of Proxima Centauri B. Well, the answer is no, at least ... 07:09: The observed gamma ray burst, GRB, was of that type.
	2017-08-30: White Holes 08:02: However, it's not one that we can ever observe for two reasons. 03:24: ... the perspective of an outside observer, any events occurring at the event horizon, including folding into it, ...
	2017-08-24: First Detection of Life 03:10: A set of non-equilibrium chemical abundances must be observed that can't possibly be explained without life. 04:25: While there are non-biological ways of making nitrous oxide, like lightning, these aren't nearly enough to account for the amount observed. 06:06: Galileo also observed the spectrum of Earth's surface and took color photographs. 08:06: The parent star was observed using the Hubble and Spitzer Space Telescopes during a transit. 01:29: But first, let's talk about what life on Earth looks like to an observer in space.
	2017-08-16: Extraterrestrial Superstorms 02:09: Any object moving over a spinning surface will appear to follow a curved path relative to an observer moving with that surface.
	2017-08-02: Dark Flow 02:28: ... there must be some reference frame, some velocity, in which there's no observed Doppler shift in any ...
	2017-07-12: Solving the Impossible in Quantum Field Theory 04:37: If we observe two electrons bouncing off each other, all we really see is two electrons going in and two electrons going out.
	2017-07-07: Feynman's Infinite Quantum Paths 13:40: That should cause different observers to measure a different speed of light.
	2017-06-21: Anti-Matter and Quantum Relativity 03:34: However, we actually observe two electrons per orbital. 15:28: ... greatest talents was his uncanny ability to see the fundamentals beneath observed ... 01:56: ... and only one clock, typically the clock in the reference frame of the observer. ...
	2017-06-07: Supervoids vs Colliding Universes! 06:21: ... of reduction in temperature in the CMB, which is a mere 1/5 of the observed 150 microkelvin ... 06:38: McKenzie et al. also observed a control region, G23, in the direction of the star [INAUDIBLE].. 07:01: And that's actually a good match to the observed deviation of 15 microkelvins. 06:21: ... of reduction in temperature in the CMB, which is a mere 1/5 of the observed 150 microkelvin ... 07:01: And that's actually a good match to the observed deviation of 15 microkelvins.
	2017-05-03: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson 08:47: We must observe a universe or a part thereof that can have observers. 08:51: ... tells us that we should be the most typical, the most common type of observer, that could possibly be having our current ... 09:03: ... our own experience, then it's more likely that we are those more typical observers. ... 12:11: Just for now, I strongly recommend that we proceed as though we are real life observers, part of the original space time. 08:47: We must observe a universe or a part thereof that can have observers. 09:03: ... our own experience, then it's more likely that we are those more typical observers. ... 12:11: Just for now, I strongly recommend that we proceed as though we are real life observers, part of the original space time.
	2017-04-26: Are You a Boltzmann Brain? 04:01: ... than the age of the universe for it to happen, so in practice we never observe the second law of thermodynamics being broken on macroscopic ... 05:41: Nonetheless, it shouldn't really be so surprising that we observe a low-entropy blip in an otherwise mostly high-entropy universe. 05:57: What other time could we possibly observe? 06:02: We can only observe an environment capable of producing observers. 06:58: We observe the universe from as typical a vantage point as is consistent with our experience. 06:02: We can only observe an environment capable of producing observers. 07:05: So, aren't there more probable, smaller dips in entropy that could lead to conscious observers? 07:23: And so should the conscious observers that evolve in them. 06:02: We can only observe an environment capable of producing observers. 07:05: So, aren't there more probable, smaller dips in entropy that could lead to conscious observers? 07:23: And so should the conscious observers that evolve in them.
	2017-03-29: How Time Becomes Space Inside a Black Hole 01:22: Different observers may report that two events are separated by different distances delta x and by different amounts of time delta t. 01:30: However all observers record the same spacetime interval. 01:22: Different observers may report that two events are separated by different distances delta x and by different amounts of time delta t. 01:30: However all observers record the same spacetime interval.
	2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer 01:54: ... now, and that all points move forward in time at a constant rate for all observers, governed by one global ...
	2017-03-08: The Race to a Habitable Exoplanet - Time Warp Challenge 00:51: In that episode, we talked about the spacetime diagram and how it transforms between observers traveling at different speeds. 01:04: In fact, there's only one possible way to map between different observers' reference frames. 01:11: It lets us figure out what spacetime looks like for every observer, no matter what his or her velocity is. 01:17: If two events happen in spacetime, observers with different velocities will report different separations between them, in both space and time. 00:51: In that episode, we talked about the spacetime diagram and how it transforms between observers traveling at different speeds. 01:04: In fact, there's only one possible way to map between different observers' reference frames. 01:17: If two events happen in spacetime, observers with different velocities will report different separations between them, in both space and time. 01:04: In fact, there's only one possible way to map between different observers' reference frames. 00:51: In that episode, we talked about the spacetime diagram and how it transforms between observers traveling at different speeds.
	2017-02-15: Telescopes of Tomorrow 03:29: The finest detail any telescope can observe is given by the diffraction limit, which increases with wavelength. 07:23: ... allow to take photographs of planets in other solar systems and even to observe the spectra of the atmospheres of some ...
	2017-02-02: The Geometry of Causality 05:28: To observe those points, I just wait around until their light had time to reach me. 01:31: An observer I leave behind with an amazing telescope, observes me traveling the entire original distance but will perceive my clock as having slowed. 01:41: ... length contraction and time dilation allows both moving and stationary observers to agree on how much older every one looks at the end of the ... 02:00: ... time measured by a moving observer on their own clock is called proper time, but counting those clock ticks ... 02:13: ... this thing called the spacetime interval that relates observer dependent perspectives on the length and duration of any journey that ... 07:27: They will always land on the same hyperbola, no matter the observer's reference frame. 02:13: ... this thing called the spacetime interval that relates observer dependent perspectives on the length and duration of any journey that all ... 01:41: ... length contraction and time dilation allows both moving and stationary observers to agree on how much older every one looks at the end of the ... 02:13: ... perspectives on the length and duration of any journey that all observers will agree on, even if they don't agree on the delta x and delta t of ... 07:27: They will always land on the same hyperbola, no matter the observer's reference frame. 01:31: An observer I leave behind with an amazing telescope, observes me traveling the entire original distance but will perceive my clock as having slowed.
	2017-01-25: Why Quasars are so Awesome 03:19: Its light must have been traveling from two billion light years away to acquire the observed redshift.
	2017-01-19: The Phantom Singularity 15:55: A vacuum test out of TU Dresden in Germany observed a thrust, but found the thrust was the same even if they stood the EM drive vertically. 05:17: The Schwarzschild metric allows us to compare two points or events in space time around a massive object from the perspective of different observers. 05:50: Every inertial, so non-accelerating observer, will agree on the same space time interval for every pair of events and for every world line. 05:17: The Schwarzschild metric allows us to compare two points or events in space time around a massive object from the perspective of different observers.
	2017-01-11: The EM Drive: Fact or Fantasy? 03:41: The main criticism of all non-vacuum tests is that thermal convection in the surrounding air may have produced the observed force. 04:36: The thrusts were reported to be the same as those observed in a non-vacuum. 04:42: The average thrust to input power observed was around 1.2 millinewton per kilowatt. 04:50: That's vastly smaller than the thrust observed by Shawyer's experiments, but still much, much larger than for a photon thruster. 08:42: All of that said, if the observed effect really is a thrust, then something is causing it. 03:41: The main criticism of all non-vacuum tests is that thermal convection in the surrounding air may have produced the observed force.
	2016-12-21: Have They Seen Us? 14:32: So a distant immortal observer, with a ridiculously good telescope, will detect photons from the falling monkey at all future times. 16:31: ... the black hole's stationary frame of reference as recorded by a distant observer. ...
	2016-12-14: Escape The Kugelblitz Challenge 03:41: Any observers within this extended event horizon are cut off from any future causal connection with the rest of the universe. 03:51: OK, in the case of the collapsing start, that's still a core, is going to be an insanely hot, dense place and not great for observers. 03:41: Any observers within this extended event horizon are cut off from any future causal connection with the rest of the universe. 03:51: OK, in the case of the collapsing start, that's still a core, is going to be an insanely hot, dense place and not great for observers.
	2016-12-08: What Happens at the Event Horizon? 07:08: Our space-faring simian begins its journey and emits a regular light signal that we observe from a safe distance.
	2016-11-16: Strange Stars 08:00: ... all, the pulsar in the Crab Nebula was also observed as a supernova by Chinese astronomers in 1054, except something was ...
	2016-11-09: Did Dark Energy Just Disappear? 06:19: We can't yet observe dark energy directly; we can only infer its existence based on how it affects the expansion of the universe. 02:52: However, in the 18 years since the first studies, we've observed a lot more of these exploding white dwarfs.
	2016-11-02: Quantum Vortices and Superconductivity + Drake Equation Challenge Answers 02:11: ... in topology were the culprit behind a strange quantized magnetic field observed in the mysterious "quantum hole effect." These findings will lead to ...
	2016-10-26: The Many Worlds of the Quantum Multiverse 02:55: And so until it's observed, it exists in a superposition of states. 03:29: And what about the entire rest of the universe that's not currently being observed by physicists or cats? 05:23: ... extends beyond the radioactive decay, beyond the cat, and includes the observer and, indeed, the entire universe, ... 06:20: ... trajectories, of histories, merges into the single timeline of the observer's ... 10:23: It explains the apparent randomness of quantum mechanics with a sort of observer bias. 06:20: ... trajectories, of histories, merges into the single timeline of the observer's ...
	2016-09-29: Life on Europa? 11:37: ... and its partner with a macroscopic system so complex that we no longer observe clean quantum ... 11:08: Alex Trusk very reasonably asks me to define what I mean by observer. 11:18: The definition of observer sort of depends on what interpretation of quantum mechanics you're going with.
	2016-09-21: Quantum Entanglement and the Great Bohr-Einstein Debate 05:31: We always find that the observed quantum spin aligns itself with our chosen measurement axis. 08:36: The instantaneous influence has been observed over many kilometers at this point. 05:31: We always find that the observed quantum spin aligns itself with our chosen measurement axis. 00:08: Or is that reality an illusion in the eye of the observer? 01:19: This notion that the universe exists independent of the mind of the observer is called realism in physics.
	2016-09-07: Is There a Fifth Fundamental Force? + Quantum Eraser Answer 01:59: Well, in short, it's because the anomaly was observed for a very particular transition between the beryllium nuclear states.
	2016-08-24: Should We Build a Dyson Sphere? 09:43: Admittedly, the fading that the Kepler Space Telescope observed in Tabby's star is sort of consistent with a partial swarm.
	2016-08-17: Quantum Eraser Lottery Challenge 02:25: ... or a single pile distribution, the information regarding whether the observer knows the path appears to travel back in time, even if was only a tiny ...
	2016-08-10: How the Quantum Eraser Rewrites the Past 02:12: But it's still pretty interesting to see what happens if we try to observe the wave function at different points in the double slit experiment. 07:22: The observer lost the info of which slit we went through. 09:43: Perhaps this thing we call observation is just entanglement between the observer and the experiment. 07:22: The observer lost the info of which slit we went through.
	2016-07-27: The Quantum Experiment that Broke Reality 00:06: One of the strangest experimental results ever observed has got to be that of the single particle double-slit experiment. 01:43: This double-slit interference of light was first observed by Thomas Young back in 1801. 04:56: This crazy effect has even been observed with whole atoms, even whole molecules. 05:02: ... are gigantic spherical molecules of 60 carbon atoms and have been observed to produce double-slit interference under special ...
	2016-07-20: The Future of Gravitational Waves 01:54: It's calculated that LIGO would need to observe for over 200,000 years to see the same signal arise from random vibrations. 01:09: On December 26, LIGO again observed the merger of two different black holes. 03:59: It's kind of amazing that the signals observed look exactly like what we expect them to from the predictions of general relativity.
	2016-07-06: Juno to Reveal Jupiter's Violent Past 11:00: But this observed whiteness is a result of the fact that our color sensitivity is limited.
	2016-06-22: Planck's Constant and The Origin of Quantum Mechanics 08:59: ... to do this just by varying the constant until the Planck law matched the observed ...
	2016-06-15: The Strange Universe of Gravitational Lensing 12:16: The wave function that we calculate defines the probability that we will observe a particular set of physical properties. 08:58: This ultimate gravitational lensing has not yet been observed. 11:28: The idea is that a physical system doesn't have the familiar classical properties like position, momentum, spin, et cetera, until it is observed. 12:13: But from the standpoint of us, the observer, the effect is the same. 13:09: However, one view that's not really favored is the idea that a conscious observer is needed to collapse a wave function.
	2016-06-01: Is Quantum Tunneling Faster than Light? 02:16: Observe me and you'll collapse my wave function and probably find me pretty much exactly where you expect to. 00:35: Each specific state has a certain probability of being true when the object is observed.
	2016-02-17: Planet X Discovered?? + Challenge Winners! 04:06: To determine the observed tick rate, you also have to factor in the travel time of light. 04:57: Where those paths intersect the vertical world line tells you the observed time interval between the ticks. 06:20: The length of the observed second decreases by this factor for an approaching clock and increases for a receding clock. 04:06: To determine the observed tick rate, you also have to factor in the travel time of light. 04:57: Where those paths intersect the vertical world line tells you the observed time interval between the ticks. 04:30: ... a clock that first moves towards the observer and the stationary clock, overtakes, and then moves away, will have ... 04:48: To understand that, you need to draw lights like photon paths between the moving clock and the stationary observer.
	2016-02-11: LIGO's First Detection of Gravitational Waves! 00:27: It opens a whole new window through which we can now observe our amazing universe. 05:55: ... long, we will observe one of these mergers simultaneously using multiple telescopes that span ... 06:35: ... of this spectrum, much lower frequencies, opening the possibility to observe completely new ...
	2016-01-27: The Origin of Matter and Time 06:02: It's defined locally for any observer, or indeed, thing.
	2016-01-20: The Photon Clock Challenge 01:06: ... the clock was moving toward you, do you observe its hands to be ticking slower, faster, or at the same rate compared to ...
	2016-01-13: When Time Breaks Down 03:46: All observers, regardless of their own speed, will report seeing the same speed for any particle of light-- any photon.
	2015-12-16: The Higgs Mechanism Explained 06:36: However, if we observe the particle, then it means the field also exists. 07:55: ... although an outside observer can never witness anything cross the event horizon, as something falls ... 08:06: ... infalling stuff does vanish, and the event horizon that an outside observer sees does grow because anything falling into the black hole adds to its ...
	2015-12-09: How to Build a Black Hole 09:37: From the point of view of an outside observer-- so, us-- this never happens.
	2015-11-05: Why Haven't We Found Alien Life? 01:48: Of course we're going to observe at least one instance of intelligent life happening because we are that one instance. 01:58: As long as it happens once, it will be there to observe itself. 02:01: ... on the anthropic principle, which states that an observer will always observe a universe that can make observers or a planet that ...
	2015-10-22: Have Gravitational Waves Been Discovered?!? 01:03: However, there's one last, incredible prediction that has never been directly observed-- gravitational waves.
	2015-10-15: 5 REAL Possibilities for Interstellar Travel 12:26: Ed Stephan asks why we're even talking about gravitational waves when none have ever been observed.
	2015-10-07: The Speed of Light is NOT About Light 00:14: ... speed but 300,000 kilometers per second in a vacuum-- according to any observer-- and, two, keep anything from traveling faster than that ... 00:51: Causal connections give us the only ordering of events that all observers will agree on. 08:48: In fact, it's the maximum speed at which any observers can see two parts of the universe talk to each other. 00:51: Causal connections give us the only ordering of events that all observers will agree on. 08:48: In fact, it's the maximum speed at which any observers can see two parts of the universe talk to each other.
	2015-09-23: Does Dark Matter BREAK Physics? 01:16: From this, we can figure out exactly how much mass is needed to cause the observed lensing. 04:35: But they ultimately have a hard time getting all of the observed effects. 01:16: From this, we can figure out exactly how much mass is needed to cause the observed lensing. 01:01: Place a strong gravitational field on an axis between a light source and an observer and voila, you basically have a lens. 08:02: ... the monkey were to calculate the clock time of an external observer as it fell, then that calculated time would approach infinity as the ... 08:59: ... is eternally frozen on the event horizon with respect to a distant observer, shouldn't the black hole evaporate beneath ... 10:07: The distant observer does witness the instance that the black hole evaporates, with a huge burst of Hawking radiation. 10:21: It never even happens in the distant observer's universe, either before or after the black hole's evaporation. 08:59: ... is eternally frozen on the event horizon with respect to a distant observer, shouldn't the black hole evaporate beneath ... 10:21: It never even happens in the distant observer's universe, either before or after the black hole's evaporation.
	2015-08-27: Watch THIS! (New Host + Challenge Winners) 03:34: Which quasar is the most distant object ever observed?
	2015-08-19: Do Events Inside Black Holes Happen? 02:24: In fact, so would any observer, inertial or otherwise, who is always outside the black hole's edge. 03:24: According to observers like the monkey who are at those events, those events take place at spatial locations inside that black blob we see in the sky. 03:37: It's all the events that have ever or will ever take place there, according to observers who are physically there. 03:58: ... temporal terms when you delete entire occurrences from every external observer's self-consistent record of the history of the ... 06:38: So a freefalling observer inside that cutoff, like the monkey, will go radially inwards. 08:20: That means that to external observers, black holes are black because light that gets emitted just outside the horizon is redshifted into invisibility. 09:52: So to external observers, most of the matter never crosses the horizon. 02:24: In fact, so would any observer, inertial or otherwise, who is always outside the black hole's edge. 06:38: So a freefalling observer inside that cutoff, like the monkey, will go radially inwards. 03:24: According to observers like the monkey who are at those events, those events take place at spatial locations inside that black blob we see in the sky. 03:37: It's all the events that have ever or will ever take place there, according to observers who are physically there. 03:58: ... temporal terms when you delete entire occurrences from every external observer's self-consistent record of the history of the ... 08:20: That means that to external observers, black holes are black because light that gets emitted just outside the horizon is redshifted into invisibility. 09:52: So to external observers, most of the matter never crosses the horizon. 08:20: That means that to external observers, black holes are black because light that gets emitted just outside the horizon is redshifted into invisibility. 03:58: ... temporal terms when you delete entire occurrences from every external observer's self-consistent record of the history of the ...
	2015-08-12: Challenge: Which Particle Wins This Race? 04:31: ... fluid whose energy density is the same when measured locally by an observer that's instantaneously at rest at any location in that ...
	2015-07-29: General Relativity & Curved Spacetime Explained! 01:54: ... think about it, on the flat spacetime diagrams of inertia observers, the world lines of other inertial observers are straight, indicating ... 02:03: This captures Newton's idea that inertial observers shouldn't accelerate relative to other inertial observers. 03:32: ... when an observer in deep space says that the falling apple is accelerating, he's pushing ... 03:43: However, global inertial observers do. 03:45: They're observers that have no forces on them. 01:54: ... think about it, on the flat spacetime diagrams of inertia observers, the world lines of other inertial observers are straight, indicating ... 02:03: This captures Newton's idea that inertial observers shouldn't accelerate relative to other inertial observers. 03:43: However, global inertial observers do. 03:45: They're observers that have no forces on them. 02:03: This captures Newton's idea that inertial observers shouldn't accelerate relative to other inertial observers.
	2015-07-22: SPECIAL ANNOUNCEMENT + Flat Spacetime Geometry Comments 02:48: Inertial observers will see each other dynamically, moving with a constant three-dimensional velocity. 02:54: But does that mean that inertial observers are really moving with a constant three-dimensional velocity? 03:05: ... moving at constant three-dimensional velocity, sort of-- which is those observers whose world lines in space time are straight-- i.e., that are geodesics ... 03:22: Those are the guys that, it turns out, corresponds to inertial observers in Newtonian physics. 03:27: And they are distinguishable from non-inertial observers in a geometric way in space time. 04:32: ... that I drew in the last episode were from the point of view of inertial observers-- Blue Gabe, Red Gabe, the ... 05:01: Imagine a family of inertial observers, all of whom are moving with different speeds relative to each other. 05:06: That accelerating car, at any given moment, from its point of view, is always stationary instantaneously relative to one of those inertial observers. 02:48: Inertial observers will see each other dynamically, moving with a constant three-dimensional velocity. 02:54: But does that mean that inertial observers are really moving with a constant three-dimensional velocity? 03:05: ... moving at constant three-dimensional velocity, sort of-- which is those observers whose world lines in space time are straight-- i.e., that are geodesics ... 03:22: Those are the guys that, it turns out, corresponds to inertial observers in Newtonian physics. 03:27: And they are distinguishable from non-inertial observers in a geometric way in space time. 04:32: ... that I drew in the last episode were from the point of view of inertial observers-- Blue Gabe, Red Gabe, the ... 05:01: Imagine a family of inertial observers, all of whom are moving with different speeds relative to each other. 05:06: That accelerating car, at any given moment, from its point of view, is always stationary instantaneously relative to one of those inertial observers. 04:32: ... that I drew in the last episode were from the point of view of inertial observers-- Blue Gabe, Red Gabe, the ...
	2015-07-15: Can You Trust Your Eyes in Spacetime? 04:18: ... to be present at two events represented by points on such a line an observer or a photon would have to be moving faster than light, which normal ... 04:34: ... like time dilation, or length contraction, or disagreements between observers about event ... 06:38: In Newtonian mechanics, we distinguish inertial and noninertial observers dynamically by using the floating ball test. 06:44: But in spacetime, we can also distinguish those classes of observers geometrically. 06:49: Inertial observers have geodesic world lines and noninertial ones don't. 08:30: In fact, every observer's 4-velocity always has a length of minus the speed of light squared, even the accelerating car's 4-velocity. 08:37: ... vector a spacetime speed, then the world line of every inertial observer is a constant-speed straight ... 08:49: And accelerated observer's world lines are constant-speed non-straight lines. 04:34: ... like time dilation, or length contraction, or disagreements between observers about event ... 06:38: In Newtonian mechanics, we distinguish inertial and noninertial observers dynamically by using the floating ball test. 06:44: But in spacetime, we can also distinguish those classes of observers geometrically. 06:49: Inertial observers have geodesic world lines and noninertial ones don't. 08:30: In fact, every observer's 4-velocity always has a length of minus the speed of light squared, even the accelerating car's 4-velocity. 08:49: And accelerated observer's world lines are constant-speed non-straight lines. 08:30: In fact, every observer's 4-velocity always has a length of minus the speed of light squared, even the accelerating car's 4-velocity. 06:38: In Newtonian mechanics, we distinguish inertial and noninertial observers dynamically by using the floating ball test. 06:44: But in spacetime, we can also distinguish those classes of observers geometrically.
	2015-07-02: Can a Circle Be a Straight Line? 01:21: ... last statement, and to explain how it lets you account for the motion we observe even if there's no Newtonian force of ...
	2015-05-20: The Real Meaning of E=mc² 02:59: ... for talking this way, among them that rest mass is a property all observers agree about, much like the space-time interval that we discussed in a ...
	2015-04-22: Are Space and Time An Illusion? 01:01: Suppose two observers are moving relative to each other, and particles count as observers. 01:08: Fact-- those observers don't agree about how much time passes between events. 01:25: And yet, each observer measures things properly and is entirely consistent, which means neither of them is wrong. 01:57: If two observers can't agree on the sequence of events, it means that at present, someone's past is in someone else's future. 02:40: And as luck would have it, all observers do agree about this thing. 02:52: ... though two observers in relative motion will measure different distances and different ... 03:18: When it's positive, nothing can get from one event to the other, and there are always observers who disagree about which one happens first. 01:25: And yet, each observer measures things properly and is entirely consistent, which means neither of them is wrong. 01:01: Suppose two observers are moving relative to each other, and particles count as observers. 01:08: Fact-- those observers don't agree about how much time passes between events. 01:57: If two observers can't agree on the sequence of events, it means that at present, someone's past is in someone else's future. 02:40: And as luck would have it, all observers do agree about this thing. 02:52: ... though two observers in relative motion will measure different distances and different ... 03:18: When it's positive, nothing can get from one event to the other, and there are always observers who disagree about which one happens first. 01:08: Fact-- those observers don't agree about how much time passes between events.
	2015-04-01: Is the Moon in Majora’s Mask a Black Hole? 08:49: With each passing moment of time, any observer sitting anywhere will see photons that were emitted from progressively more distant locations.
	2015-03-25: Cosmic Microwave Background Explained 00:50: Problem is, we don't know of any source anywhere that would emit this observed pattern of microwave emission, so where's it coming from? 02:32: The CNB is one of the closest things to a mathematically perfect thermal spectrum that has ever been observed. 00:50: Problem is, we don't know of any source anywhere that would emit this observed pattern of microwave emission, so where's it coming from?
	2015-03-04: Should We Colonize Venus Instead of Mars? 07:11: What the Hubble Bubble offers is a potential alternative to the currently observed, accelerated expansion of space.

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