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2022-11-23: How To See Black Holes By Catching Neutrinos

  • 02:05: ... reference, if you want to stop a low-energy neutrino with a wall of lead, the wall ...

2022-11-16: Are there Undiscovered Elements Beyond The Periodic Table?

  • 17:35: ... of all actually existent(past, present and future) observers in their reference ...
  • 17:49: So the trick is figuring out what your reference class is.
  • 17:53: For example, if I define my reference class as a biological being then I don’t have to be surprised that I don’t find myself somewhere uninhabitable.
  • 18:14: ... if I define my reference class as those who are able to formulate anthropic arguments then it’s ...
  • 18:25: ... then why can’t I define my reference class as “those who observes an empty universe?” After all, I am my ...
  • 18:46: You could say that this is too restrictive a way to define your reference class, but the fact is there is no clearly correct way to do that.

2022-06-30: Could We Decode Alien Physics?

  • 00:00: ... for building a faster-than-light  propulsion device, along with a reference manual   containing what amounts to all physics known by ...

2022-04-20: Does the Universe Create Itself?

  • 14:50: ... reference to the question “What is the universe expanding into?”, John Retherford ...

2022-03-23: Where Is The Center of The Universe?

  • 17:22: ... asks whether chirality depend on the observers reference frame, given that it’s defined in reference to the momentum vector of ...
  • 17:54: That spin projection is actually called helicity, and it does change depending on your reference frame.

2022-02-10: The Nature of Space and Time AMA

  • 00:03: ... two uh dimensions have the tendency to morph together depending on reference frame the best place to explore that is the episode we did on the ...

2021-11-02: Is ACTION The Most Fundamental Property in Physics?

  • 06:47: ... field. Proper time is the time that an object will perceive in its own reference frame. If you plug the relativistic Lagrangian into the Euler-Lagrange ...
  • 07:09: ... now just how much time is perceived by an observer in their own frame of reference. All objects moving through space time move through paths that minimize ...
  • 16:26: ... between them with graphs. But for details check my previous reference - the internet. Chapter 7.4 I think. But as far as I understand, ...

2021-05-11: How To Know If It's Aliens

  • 06:27: ... There’s a certain Harvard Astrophysicist who’s fond of saying this in reference to his many claims that some new astrophysical phenomenon might be ...

2021-03-09: How Does Gravity Affect Light?

  • 02:14: ... distinguish between the backwards pull due to being in an accelerating reference frame and the downward pull of gravity of the same ...
  • 12:17: It’s a matter of perspective, and how you define your reference frames.

2021-02-24: Does Time Cause Gravity?

  • 09:10: ... on my comment “the time before the big bang” - which I mentioned in reference to a potential component of the gravitational wave ...

2021-02-10: How Does Gravity Warp the Flow of Time?

  • 00:25: ... that there’s no experiment that you can do to distinguish a frame of reference in freefall within a gravitational field from a frame of reference ...
  • 06:24: They’re in a non-accelerating, or inertial frame of reference.
  • 06:46: Over that brief interval we know perfectly well what the time difference is between the two frames of reference.
  • 09:25: ... pure special relativity with its kinematic time dilation plus shifting reference frames, OR you can use general relativity to calculate the gravitational ...
  • 10:29: So is it some sort of cosmic coincidence that you get the same number with shifting reference frames as with artificial gravity?

2021-01-26: Is Dark Matter Made of Particles?

  • 14:05: Well that's awesome question - the answer looks different depending on your reference frame.

2021-01-19: Can We Break the Universe?

  • 01:23: But in relativity, every non-accelerating frame of reference should be considered equal.
  • 03:57: ... the fact that the traveling twin hasn’t been in a single moving frame of reference, but rather in two separate moving frames - one moving away and one ...
  • 04:15: Let’s say we’re in Earth’s reference frame so the Earth doesn’t move in space - just straight up, which means forward in time.
  • 06:07: And if she travels in a straight line she sticks to a single reference frame.
  • 07:25: It seems that in this closed universe there IS a fundamental difference between frames of reference.
  • 07:31: There’s a stationary frame of reference where lines of constant time are closed loops, while in every other frame they are endless helices.
  • 07:45: Relativity tells us that there’s not a preferred LOCAL frame of reference.
  • 08:06: That’s the frame of reference in which the cosmic microwave background appears still - or un-Doppler-shifted.
  • 10:22: Those lines are the x-axis in the ladder’s frame of reference, which means the ladder sees its present state as this line.

2020-10-20: Is The Future Predetermined By Quantum Mechanics?

  • 15:50: And for those uninitiated it into "Rick and Morty", there are other funny pop culture references in the comments.

2020-08-24: Can Future Colliders Break the Standard Model?

  • 04:38: Which is, for reference, a lot of energy.

2020-06-30: Dissolving an Event Horizon

  • 15:36: ... it's low." And a gratifying number of Hitchhikers Guide to the Galaxy references: "The answer is 42." "Goodbye and thanks for all the fish." "We apologize ...

2019-12-17: Do Black Holes Create New Universes?

  • 15:50: ... highlights this trickiness in defining reference class with a great example: Step 1: Define reference class as "homo ...
  • 16:46: ... this really highlights the challenge in identifying our "reference class" for this sort of anthropic reasoning. Now, the Prince of France ...
  • 17:20: The point is that you need to take into account prior knowledge when you're defining your reference class.

2019-12-09: The Doomsday Argument

  • 04:15: ... of all actually existent observers (past, present and future) in their reference class." If a type of environment or type of universe produces more ...
  • 08:17: ... through the self-sampling assumption and the definition of your reference ...
  • 08:35: Choosing your reference class depends on the question you’re asking.
  • 08:39: ... cosmological constant is the typical astronomer likely to observe - so reference class was an astronomer - or really any observer capable of measuring ...
  • 08:54: In the doomsday argument, the assumption is that our “reference class” is all past and future humans.
  • 09:01: But is that the right reference class?
  • 09:03: ... example, if you define our reference class as all observers in our past and future evolutionary chain, then ...
  • 09:28: I for one welcome the doomsday if it means graduating out of our reference class into some sort of cybernetic, gene-spliced ultra-human.
  • 09:37: ... general, it’s the fuzziness of this notion of reference class that makes this idea seem far less mathematically precise - far ...
  • 10:23: Speaking of which, what about this idea that your reference class is exactly you?
  • 12:52: John, you are in a reference class of your own: reference class supremely awesome.
  • 12:57: ... moved over to the doom-never box . If anyone wishes to join John S in reference class awesome, any level of contribution is a big ...
  • 17:22: ... you for Douglas Adams - and thank god most people got the hitchhikers reference in that last episode - you really are the hoopiest froods on the ...

2019-12-02: Is The Universe Finite?

  • 14:35: ... answer your question P.S.Y - what exactly DOES Nick Bostrum mean by "reference class" - as in, how do you choose the sample of observers from which you ...
  • 14:48: In order to save ourselves from imminent doom we may have to hope future generations are NOT in our reference class. Tune in next week.

2019-11-18: Can You Observe a Typical Universe?

  • 10:08: ... of all actually existent observers (past, present and future) in their reference class." If there are a bajillion observers in the entire cosmos, you ...
  • 10:59: But proper Bayesian thinking requires careful definition of priors - for example, Bostrom talks about “observers in their reference class”.
  • 11:08: But how do we know what our reference class is?

2019-07-18: Did Time Start at the Big Bang?

  • 03:27: ... in space at some moment in time Relative to their distance at some other reference moments that reference moment is typically taken to be right now So the ...
  • 06:02: ... is relative Clocks are attached to each observer each moving frame of reference to see what time does at the Big Bang We have to trace a path through ...

2019-03-13: Will You Travel to Space?

  • 06:08: ... space flights took it to around 83 and 90 kilometers respectively. For reference 80 kilometers above sea level is the boundary of space used by the ...
  • 15:26: A couple of you referenced Ginsberg's Theorem.

2019-03-06: The Impossibility of Perpetual Motion Machines

  • 16:13: ... need 5 letters of reference from Nobel Laureates, be in the top 0% on your GREs, and yeah, first ...

2018-12-12: Quantum Physics in a Mirror Universe

  • 00:02: ... even that new dark energy dark matter is a negative mass fluid thing reference to seem heavily and yeah we'll be covering that after we do why string ...

2018-06-20: The Black Hole Information Paradox

  • 15:10: ... a very certain special frame of reference, like when you're trying to throw together a quick graphic and forget ...
  • 15:20: In these frames of reference, sometimes 21 months takes 8 minutes due to "ran out of time" dilation.

2018-04-04: The Unruh Effect

  • 06:20: ... of positive and negative frequency modes in the accelerating frame of reference, which leads to the creation of particles in that accelerating ...

2018-01-17: Horizon Radiation

  • 03:44: ... equations describing the interaction transform cleanly between inertial reference frames in a way that leaves the laws of physics and the nature of the ...

2017-09-13: Neutron Stars Collide in New LIGO Signal?

  • 15:42: And Hot Fuzz is obviously a reference to black hole singularities in string theory.

2017-08-02: Dark Flow

  • 01:20: Galilean relativity tells us that there is no preferred frame of reference to define absolute stillness.
  • 01:31: And yet, there is one frame of reference that, in some ways, is a little more preferred, or at least special, than all of the others.
  • 01:39: It's the frame of reference of the cosmic microwave background radiation, the CMB.
  • 02:28: ... if the CMB is asymmetric due to our motion, there must be some reference frame, some velocity, in which there's no observed Doppler shift in any ...
  • 02:38: If you were in that reference frame, you would be still with respect to the CMB.
  • 02:43: In that reference frame, if you added together the peculiar velocities of all galaxies in the universe, you'd expect them to cancel out.
  • 04:36: It sort of resets the apparent velocity, the frame of reference of that patch of the CMB to the peculiar velocity of the cluster.

2017-07-19: The Real Star Wars

  • 15:06: ... resulting from high energy loops "ultraviolet divergences," in reference to the ultraviolet ...

2017-07-07: Feynman's Infinite Quantum Paths

  • 13:28: Just like air, the medium was imagined to have some preferred reference frame in which it was motionless.
  • 13:56: The crucial difference is that this field has no preferred reference frame.

2017-06-21: Anti-Matter and Quantum Relativity

  • 01:47: In relativity, the dimensions of space and time are intrinsically connected and they float into each other as frames of reference change.
  • 01:56: ... function according to one and only one clock, typically the clock in the reference frame of the ...

2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer

  • 01:07: ... choosing the right path and the right reference frame, any superluminal motion can lead to information or objects ...
  • 08:39: Let's return to the reference frame of the Earth to do this.
  • 08:58: Now we transform back to the near lightspeed reference frame.
  • 09:30: We constructed this time traveling path using two different reference frames.

2017-03-15: Time Crystals!

  • 01:35: The name time crystal is somewhat out there, but Wilczek wasn't the first to use it in reference to a regularly repeating system.

2017-03-08: The Race to a Habitable Exoplanet - Time Warp Challenge

  • 01:04: In fact, there's only one possible way to map between different observers' reference frames.
  • 03:55: That'll let you transform between reference frames.

2017-02-02: The Geometry of Causality

  • 06:03: The traveler infers a set of simultaneous events that, to me, are not simultaneous, but there is no preferred reference frame.
  • 06:34: Moving between these reference frames is now a simple matter of squaring up our traveler's axes.
  • 07:03: This transformation allows you to calculate how properties, like distance, time, velocity, even mass and energy, shift between reference frames.
  • 07:27: They will always land on the same hyperbola, no matter the observer's reference frame.

2017-01-19: The Phantom Singularity

  • 02:34: Some singularities come about from your choice of reference frame or coordinate system.
  • 03:09: I mean, the curvature and the density are infinite from any frame of reference.

2016-12-21: Have They Seen Us?

  • 16:31: ... at the speed of light relative to the black hole's stationary frame of reference as recorded by a distant ...

2016-11-16: Strange Stars

  • 11:19: I referenced a previous video when I made that statement in last week's dark energy episode.

2016-06-08: New Fundamental Particle Discovered?? + Challenge Winners!

  • 04:12: There are links to references to all of these possibilities in the description.

2016-06-01: Is Quantum Tunneling Faster than Light?

  • 07:50: Reference link below.

2016-05-04: Will Starshot's Insterstellar Journey Succeed?

  • 11:03: ... points out that we must need some sort of luminosity reference point before we can start using white dwarf supernovae or Type 1a ...

2016-03-23: How Cosmic Inflation Flattened the Universe

  • 11:40: It emerges in a rotating reference frame as a force-like term that resists inward motion.
  • 11:47: It doesn't exist in the inertial reference frames for which Newton's laws are valid.
  • 11:52: ... example, in a reference frame of an unmoving center of mass, you have a center-pointing or ...
  • 12:17: In that reference frame, it's the velocity perpendicular to the centripetal acceleration that resists radial infall.

2016-02-17: Planet X Discovered?? + Challenge Winners!

  • 03:49: ... a slower tick rate compared to a clock that's stationary in your own reference ...

2016-02-03: Will Mars or Venus Kill You First?

  • 09:16: ... worth of interaction and change since the Big Bang for things in our reference ...

2016-01-27: The Origin of Matter and Time

  • 04:50: There's no preferred inertial, or non-accelerating, reference frame.
  • 04:53: Now that means that in the frame of reference of the moving clock, it is stationary.
  • 11:28: [INAUDIBLE] tells us that accelerating reference frame feels a slower passage of time.
  • 11:59: Bruno JML would like to know in what reference frame Pink Floyd's "Dark Side of the Moon" syncs to when time breaks down.

2016-01-13: When Time Breaks Down

  • 04:57: ... similar arguments will show us that a photon clock in an accelerating reference frame-- say on a rocket ship in empty space-- will also tick slower ...

2015-11-25: 100 Years of Relativity + Challenge Winners!

  • 02:28: First, let's do the calculation in the frame of reference of Apophis' 2029 orbital velocity.
  • 02:49: We just need to add enough velocity to Apophis to move it 25,000 kilometers relative to the frame of reference of its initial motion.

2015-10-28: Is The Alcubierre Warp Drive Possible?

  • 01:40: ... even if the galaxies are relatively still in their local frames of reference. ...

2015-10-07: The Speed of Light is NOT About Light

  • 01:37: ... of the velocity of your non-accelerating, or inertial, frame of reference. ...
  • 03:49: The two work together to give you the same electromagnetic, the Lorentz, force, regardless of reference frame.
  • 04:06: ... that will allow Maxwell's equations to jump seamlessly between reference frames-- the transformation that represents space and time in our ...
  • 04:24: And it'll bump you between reference frames Harry Potter style.
  • 05:58: Next, no preferred inertial reference frame.
  • 06:26: Require that we can consistently transform between reference frames.
  • 06:37: I should also be able to jump consistently through multiple frames of reference and back again.
  • 07:59: With it, we can write down one law for electromagnetism that works in all frames of reference.

2015-09-23: Does Dark Matter BREAK Physics?

  • 09:26: And so in its reference frame, the rate of Hawking radiation is not time dilated.

2015-08-19: Do Events Inside Black Holes Happen?

  • 03:01: ... us out here cannot consistently be assigned a "when." From our frame of reference outside the black hole, those events just don't occur, even if we wait ...

2015-08-05: What Physics Teachers Get Wrong About Tides!

  • 02:31: ... and how it manifests itself from the perspective of a frame of reference attached to Earth's ...
  • 03:11: It's an artifact of Earth's frame of reference.
  • 13:18: In the Newtonian sense, acceleration would mean put a frame of reference at Earth's center.
  • 14:46: Finally, I do want to reference one individual comment.

2015-07-29: General Relativity & Curved Spacetime Explained!

  • 00:14: [THEME MUSIC] Newton's and Einstein's dispute over gravity comes down to competing notions of what constitutes an inertial frame of reference.
  • 07:07: ... the free fall orbits of satellites looks spatially circular in frames of reference that cover too big a space time ...

2015-07-22: SPECIAL ANNOUNCEMENT + Flat Spacetime Geometry Comments

  • 04:05: ... in Part 3-- namely, how would everything have looked from the frame of reference of the accelerating ...
  • 04:16: Dan Fox, in particular, asked whether the accelerating car's own worldwide, wouldn't that look straight from the car's frame of reference?
  • 04:24: It is tricky to talk about the car's frame of reference in special relativity.
  • 04:44: If you try to draw the accelerating car's frame of reference, things get really messy.
  • 04:48: ... general way of talking about the world that would work for any frame of reference, including the accelerating ...
  • 05:15: ... even if we can't talk about the accelerating car's entire frame of reference, we can talk about a sequence of inertial frames of reference, relative ...

2015-07-15: Can You Trust Your Eyes in Spacetime?

  • 00:18: Today's episode will reference information from three of our earlier episodes.
  • 01:55: My clock and my axis together make a frame of reference, which should also have y and z-axes, but I want to keep things visually simple.
  • 02:35: Is my frame of reference inertial?
  • 03:49: But it's only vertical for my frame of reference.
  • 03:51: Red guy also has a frame of reference.
  • 05:52: So the visual criterion for parallelism works since it's either met or not met in every frame of reference.

2015-06-17: How to Signal Aliens

  • 06:20: First off, Blackmark52 and Gary Oak both pointed out that the frames of reference video that we linked to is from University of Toronto and not MIT.
  • 07:17: ... Euan Johnson, Josh Mullins, and danx505 all asked how two frames of reference falling on opposite sides of Earth can both the inertial when they're ...

2015-06-10: What Happens to a Helium Balloon in Freefall?

  • 00:19: ... our gravity episode-- that you can click over here to view-- we referenced the balloon video from Smarter Every Day, which you should check out if ...

2015-06-03: Is Gravity An Illusion?

  • 00:59: To analyze motion, you need what's called a frame of reference.
  • 01:06: The reason you need a frame of reference is that you can only measure motion relative to other things.
  • 01:11: ... super awesome 1960s black and white video from MIT all about frames of reference. ...
  • 01:25: ... Newton's laws can't tell you whether a frame of reference is really at rest or really moving at constant velocity because that ...
  • 01:34: However, interestingly, Newton's laws can tell you whether your frame of reference is really accelerating or not.
  • 01:44: If it stays right where it is, then your frame of reference is not accelerating and we call it an inertial frame.
  • 02:17: So inside the train car, F decidedly does not equal ma and the train car's frame of reference is not inertial.
  • 02:55: All right, let's look at things from the train car's frame of reference though a little more carefully.
  • 03:44: So accelerated frames of reference mimic a gravitational field in the opposite direction of the frames acceleration.
  • 05:05: ... fact, the accelerated frame of reference of Destin's car is completely indistinguishable from having that car ...
  • 07:27: ... a gravitational force is an artifact of being in an accelerated frame of reference. ...
  • 08:27: Second, by your criterion, Einstein, orbiting frames of reference-- like on the space station-- should also be considered inertial.

2015-05-06: Should the First Mars Mission Be All Women?

  • 09:22: ... why O'Neill Cylinder, which I've already referenced in the comments, would have two counter-rotating sections, so that there ...

2015-04-29: What's the Most Realistic Artificial Gravity in Sci-Fi?

  • 03:56: That apparent departure from straight line motion in rotating reference frames is called the Coriolis effect.

2015-02-11: What Planet Is Super Mario World?

  • 04:24: You can compute it with the following formula, using Earth's mass and radius as a reference.
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