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	2022-03-16: What If Charge is NOT Fundamental? 09:52: ... can have right-handed chirality if their spin is clockwise relative to their momentum vector and left-handed chirality if it's ...
	2022-02-10: The Nature of Space and Time AMA 00:03: ... same answers and we did a recent episode on how it is the slowing of clocks as you descend into a gravitational field actually causes uh our ...
	2022-01-27: How Does Gravity Escape A Black Hole? 09:36: According to relativity, that means its clock slows.
	2021-11-02: Is ACTION The Most Fundamental Property in Physics? 06:47: ... relativity, clocks run at different rates depending on things like relative speed and ...
	2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light 10:35: For a real, physical experiment, we need a clock that’s physically measurable. 10:40: In 2020, a paper was published in the journal Nature that used the swiveling axis of a particle’s quantum spin as the clock hand. 10:59: The rate of rotation can be used as an internal clock. 11:38: They were just trying to verify whether using spins as an internal clock would work at all, and they were successful. 11:50: ... for the faster-than-light Hartman effect, because the spin-based clocks that they were working with should still show the effect under FTL ... 10:40: In 2020, a paper was published in the journal Nature that used the swiveling axis of a particle’s quantum spin as the clock hand. 11:50: ... for the faster-than-light Hartman effect, because the spin-based clocks that they were working with should still show the effect under FTL ...
	2021-07-21: How Magnetism Shapes The Universe 07:43: ... circularly polarized - and it can be left- or right-polarized, meaning clockwise or counterclockwise ...
	2021-06-16: Can Space Be Infinitely Divided? 03:14: ... distance measure has an uncertainty because   you can only clock the instant of the return to within one wave-cycle of the ...
	2021-05-19: Breaking The Heisenberg Uncertainty Principle 10:03: ... demonstrated this same principle in other systems like entangled atomic clocks, which may one day massively enhance the precision of our GPS ...
	2021-03-09: How Does Gravity Affect Light? 03:56: ... process that generates a photon can be thought of as a clock - be it an electric charge pulsing up and down a radio antenna, or an ... 04:10: These are the ticks of a clock, and the frequency dictates the frequency and the wavelength of the photon produced by that motion. 04:18: But from a great distance away, those clocks run slow, and so the frequency of light emerging from within a gravitational field is lower. 04:37: ... horizon of the black hole, gravitational time dilation is so strong that clocks stop and the frequency of photons trying to escape is brought to ... 06:15: Well, tricky - because there’s no change in clock speed in the horizontal direction - only the vertical. 06:22: But we saw in our previous episode that a gradient in clock speed across the vertical extent of the object is enough to drag it downwards. 10:19: ... because of two effects: your clock is ticking faster than clocks in the gravitational field, and space ... 03:56: ... process that generates a photon can be thought of as a clock - be it an electric charge pulsing up and down a radio antenna, or an atom ... 06:15: Well, tricky - because there’s no change in clock speed in the horizontal direction - only the vertical. 06:22: But we saw in our previous episode that a gradient in clock speed across the vertical extent of the object is enough to drag it downwards. 04:18: But from a great distance away, those clocks run slow, and so the frequency of light emerging from within a gravitational field is lower. 04:37: ... horizon of the black hole, gravitational time dilation is so strong that clocks stop and the frequency of photons trying to escape is brought to ... 10:19: ... because of two effects: your clock is ticking faster than clocks in the gravitational field, and space within the gravitational field is ...
	2021-02-24: Does Time Cause Gravity? 00:25: Clocks run slow in gravitational fields. 01:05: We know that gravity must cause clocks to run slow on the basis of logical consistency. 01:11: And we know that gravity DOES cause clocks to run slow based on many brilliant experiments. 02:46: We can show this as a bunch of identical clocks. 02:51: Clocks closer to the Earth take longer to tick for every tick on a distant clock. 03:32: We can think of any object as being made of many tiny clocks. 03:41: And each of those clocks has a velocity vector in time. 05:50: On the other hand, light itself travels at the speed of light through space only, and not at all through time - a photon’s clock is frozen. 05:57: ... have a 4-velocity, which is defined according to the ticking of your own clock - your proper time - which is zero for the timeless ... 06:21: To us currency exchange looks favorable for space - a teapot gains a rapid plummet to its doom for an imperceptible slowing of its clock. 07:29: It’s enough to imagine clocks that are infinitesimally separated and we still have our time gradient. 05:57: ... have a 4-velocity, which is defined according to the ticking of your own clock - your proper time - which is zero for the timeless ... 00:25: Clocks run slow in gravitational fields. 01:05: We know that gravity must cause clocks to run slow on the basis of logical consistency. 01:11: And we know that gravity DOES cause clocks to run slow based on many brilliant experiments. 02:46: We can show this as a bunch of identical clocks. 02:51: Clocks closer to the Earth take longer to tick for every tick on a distant clock. 03:32: We can think of any object as being made of many tiny clocks. 03:41: And each of those clocks has a velocity vector in time. 07:29: It’s enough to imagine clocks that are infinitesimally separated and we still have our time gradient. 02:51: Clocks closer to the Earth take longer to tick for every tick on a distant clock.
	2021-02-17: Gravitational Wave Background Discovered? 00:00: ... to that individual pulse so nature has graced us with these perfect clocks scattered across the galaxy but how do we use them to detect ...
	2021-02-10: How Does Gravity Warp the Flow of Time? 01:37: Mass and energy change the lengths of rulers and the speeds of clocks - and somehow those changes lead to objects being attracted to each other. 03:17: But to do that I need to give you a quick refresher on regular old time dilation, which tells us moving clocks must appear to tick slowly. 03:48: Einstein’s thought laboratory - his gedankenlab - was filled with many incredible imaginary devices, but one of his favorites was the photon clock. 04:07: The photon clock represents the simplest possible clock, and anything that we conclude for it also applies to any other clock. 04:23: ... amount of time taken for one tick of the photon clock is the distance the photon travels divided by its speed - so twice ... 04:40: They see the photon clock ticking, but the photon travels a longer path. 05:09: Add an identical but stationary photon clock. 05:12: It seems to tick more than once for a single tick of the moving clock. 05:25: For an observer in the moving lab, it appears that the stationary clock is ticking slow. 06:29: We have a photon clock in the lab and an identical one with the physicist. 06:35: One tick of either clock is very short, which means that over that interval the lab moves only a tiny arc of the full circle. 06:55: But after a full revolution, both observers ask each other how many ticks their clock ticked. 07:01: And it turns out that the stationary clock did tick more - time slowed for the rotating case. 07:27: In the twin paradox, the twin traveling to a nearby star and back has aged less even though both could see the other’s clock ticking slowly. 07:42: ... point, so that she misses a bunch of the ticks of her brothers clock. ... 08:15: ... lines of constant time for the moving clock tilt back and forth, and as that line tilts it fast-fowards over the ... 08:31: The photon in the accelerating clock has to chase the upper mirror some, increasing the distance it needs to travel. 11:14: So that photon clocks and matter do evolve more slowly in gravitational fields. 04:07: The photon clock represents the simplest possible clock, and anything that we conclude for it also applies to any other clock. 06:55: But after a full revolution, both observers ask each other how many ticks their clock ticked. 04:40: They see the photon clock ticking, but the photon travels a longer path. 07:27: In the twin paradox, the twin traveling to a nearby star and back has aged less even though both could see the other’s clock ticking slowly. 08:15: ... tilt back and forth, and as that line tilts it fast-fowards over the clock ticks of the stationary ... 01:37: Mass and energy change the lengths of rulers and the speeds of clocks - and somehow those changes lead to objects being attracted to each other. 03:17: But to do that I need to give you a quick refresher on regular old time dilation, which tells us moving clocks must appear to tick slowly. 11:14: So that photon clocks and matter do evolve more slowly in gravitational fields. 01:37: Mass and energy change the lengths of rulers and the speeds of clocks - and somehow those changes lead to objects being attracted to each other.
	2021-01-19: Can We Break the Universe? 01:09: ... relativity tells us that the clocks on the spaceship will appear to tick more slowly from the point of view ... 01:35: That means it sees clocks back on the Earth ticking more slowly, and the Earth and the distance traveled being squished. 02:08: ... observer on Earth thinks the astronaut’s clock ticked slow, but the astronaut thinks they traveled a shorter distance - ... 03:31: According to the twin back on Earth, his sister’s clock has been ticking slower than his own. 03:42: And during that time she sees her brother’s clock ticking slower. 03:45: So if both perceive the other’s clocks ticking slow, who has experienced less time by the time they reunite? 06:11: Both twins still perceive the other’s clock to be ticking slower - so which twin is older when they reunite? 02:08: ... observer on Earth thinks the astronaut’s clock ticked slow, but the astronaut thinks they traveled a shorter distance - and ... 03:42: And during that time she sees her brother’s clock ticking slower. 01:09: ... relativity tells us that the clocks on the spaceship will appear to tick more slowly from the point of view ... 01:35: That means it sees clocks back on the Earth ticking more slowly, and the Earth and the distance traveled being squished. 03:45: So if both perceive the other’s clocks ticking slow, who has experienced less time by the time they reunite?
	2020-12-08: Why Do You Remember The Past But Not The Future? 01:43: ... also have internal clocks that give a sense of time elapsed, but to understand why the ... 07:56: Just rewind the clock to the moment before the asteroid’s very last interaction with the outside universe. 01:43: ... also have internal clocks that give a sense of time elapsed, but to understand why the ...
	2020-10-13: Do the Past and Future Exist? 02:08: Newton assumed that all particles, all observers, all points in space were ruled by a single, constantly ticking clock. 02:16: ... universal clock meant it was possible to define a notion of “now” that everyone would ...
	2020-07-28: What is a Theory of Everything: Livestream 00:00: ... general in in the 20th century is that it was this really kind of like clockwork uh uh you know progression of sort of like strange observation uh ...
	2020-06-22: Building Black Holes in a Lab 01:29: ... study analog black holes - and by analog, I don’t mean old fashioned clockwork black holes - I mean analogies. Physical systems that aren’t black holes ...
	2020-06-15: What Happens After the Universe Ends? 03:28: Remember, the universes contain only light - no observers and no clocks. 04:06: To really compare the sizes of two chunks of spacetime we need to grid them up with rulers and clocks. 05:36: ... interval, and it’s equal to the amount of time that passes on the clock of the traveler - or the proper time of the ... 05:48: So it turns out that we grid up the universe by the rate of ticking of the clocks of its travelers. 05:55: But what if the universe has no clocks? 06:03: Light follows these tracks in between the time grid, and never, ever cross contours that mark even a single tick of a clock. 06:20: As Roger Penrose puts it: in order for time, and hence space to be meaningful, a universe must be able to build a clock. 06:26: A clock must see the spacetime grid - and to do that it must travel at sub-light speed. 06:32: And in order to do that, the clock must have mass. 06:36: ... if you have even a single electron in the universe you can build a clock and can tell the difference between the one light-second and the billion ... 07:27: The photons and gravitons are massless - you can’t build clocks with them. 03:28: Remember, the universes contain only light - no observers and no clocks. 04:06: To really compare the sizes of two chunks of spacetime we need to grid them up with rulers and clocks. 05:48: So it turns out that we grid up the universe by the rate of ticking of the clocks of its travelers. 05:55: But what if the universe has no clocks? 07:27: The photons and gravitons are massless - you can’t build clocks with them.
	2020-05-04: How We Know The Universe is Ancient 03:24: ... universe is expanding now, then in the past it was smaller. Rewind the clock according to the raw Friedman equations and there’s no alternative - the ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... reading I'm building a concrete coffee table I'm working on this crazy clock puzzle that's one there going to be this cool wooden clock it's taking ...
	2020-04-22: Will Wormholes Allow Fast Interstellar Travel? 02:50: ... were accelerated into a circular path at near the speed of light, its clock would freeze compared to the other end. By entering the non-moving end ...
	2020-04-07: How We Know The Earth Is Ancient 06:07: ... the progress of evolution by mapping the fossil record to the geological clock. The ordering of the appearance of ancient species is found when we date ...
	2020-03-31: What’s On The Other Side Of A Black Hole? 01:53: ... So if they try to trace a path across the horizon in terms of their own clock, the moment of crossing never happens. It’s like Achilles chasing the ...
	2020-01-27: Hacking the Nature of Reality 02:16: ... search for the underlying clockwork of reality led to quantum field theory, in which all particles are ...
	2020-01-20: Solving the Three Body Problem 00:20: ... transformed our erratic-seeming cosmos into a perfectly tuned machine of clockwork predictability. Given the current positions and velocities of the bodies ...
	2019-10-21: Is Time Travel Impossible? 01:45: The spaceship’s clock slows down as it speeds up, and it stops completely at the speed of light.
	2019-09-23: Is Pluto a Planet? 03:19: That same motion almost perfectly reflected the clockwork predictions of Newtonian mechanics.
	2019-07-18: Did Time Start at the Big Bang? 04:20: So when I talk about rewinding the expansion, I mean running the clock backwards to track a shrinking scale factor. 06:02: ... get that you can't think about the universe as having one big clock that Rewinds and then winks out of existence of the Big Bang or into ... 04:20: So when I talk about rewinding the expansion, I mean running the clock backwards to track a shrinking scale factor. 06:02: ... to think about time in the way Einstein Intended there is no universal clock time is relative Clocks are attached to each observer each moving frame of ...
	2019-07-15: The Quantum Internet 10:57: ... distributed quantum computers, as well as achieve new levels of atomic clock synchronization and extreme precision in our interferometric ...
	2019-05-01: The Real Science of the EHT Black Hole 04:45: It can do this because the telescopes are synchronized with atomic clocks. 10:01: ... the jet and we have the rotation direction of the black hole – roughly clockwise from our perspective, with an axis pretty close to our line of ...
	2019-01-24: The Crisis in Cosmology 15:22: The T in CPT symmetry isn't a literal rewinding of the clock.
	2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe 00:29: ... in the mirror for it to be parity symmetric he invites us to imagine a clock in a mirror ... 00:42: ... and then he asks us to imagine building that same mirror clock in reality everything is constructed as though reflected - numbers get ... 02:02: ... detector is placed to intercept those electrons and the clock ticks with every captured electron. In our reflected clock we need to ... 03:02: ... what a switch to antimatter means how does this work in our Antion on a clock well antimatter atoms have negatively charged nuclei which means their ... 10:26: ... to Feynman diagrams maybe that's why he was so into building antimatter clocks. So, yeah the universe is not symmetric under this simple version of T ... 10:54: ... broken the CPT theorem looks safe Feynman's mirror reflected antimatter clock will work just fine but as well as ticking backwards every atom every ... 02:02: ... taken to its literal extreme a perfectly constructed mirror reflected clock behaves differently so what's the big deal well the violation of parity symmetry ... 03:02: ... parity conservation well that sucks our mirror reflected antimatter clock doesn't work right after all nice one Fineman and that's not the worst of it the ... 02:02: ... detector is placed to intercept those electrons and the clock ticks with every captured electron. In our reflected clock we need to replace ... 03:02: ... leaves the electrons traveling in the original direction down and the clock ticks as normal so even though the universe isn't parity symmetric maybe it is ... 00:42: ... - our intuition would be wrong. The laws of physics and so the laws of clocks are not symmetric to this sort of parity transformation as we saw in our ... 03:02: ... first glance this CP symmetry appears to hold not just in an imaginary clocks but also in the particles of the standard model the great parity ... 10:26: ... to Feynman diagrams maybe that's why he was so into building antimatter clocks. So, yeah the universe is not symmetric under this simple version of T ...
	2018-12-20: Why String Theory is Wrong 16:28: ... filming that episode in a mirror universe apparently balls were spinning clockwise when I said counter clockwise left became right and vice-versa on ...
	2018-12-12: Quantum Physics in a Mirror Universe 00:02: ... flipping the sign of the electric charge and time reversal sending the clock ticking backwards we'll come back to both of these they are going to ...
	2018-07-04: Will A New Neutrino Change The Standard Model? 03:50: Helicity can be right-handed, which means clockwise rotation, or left-handed or anticlockwise.
	2018-05-23: Why Quantum Information is Never Destroyed 02:33: If they allow us to rewind the clock and figure out a single unique history.
	2018-05-09: How Gaia Changed Astronomy Forever 05:53: ... current velocities and positions of the stars, we can actually wind the clocks backwards and forwards, to see where they came from and where they're ...
	2018-04-18: Using Stars to See Gravitational Waves 03:35: ... orbits just before merger, which for black holes and neutron stars clocks in at a few to maybe 1,000 orbits per second in the last ... 05:41: ... resulting in a sequence of flashes more regular than an atomic clock. ... 03:35: ... orbits just before merger, which for black holes and neutron stars clocks in at a few to maybe 1,000 orbits per second in the last ...
	2017-11-08: Zero-Point Energy Demystified 06:59: Vacuum energy is real, and it's part of the fundamental clockwork of the universe.
	2017-09-28: Are the Fundamental Constants Changing? 09:26: We're also trying to develop atomic clocks accurate enough to track changes in Alpha in real time. 10:50: ... of telescopes, more refined cosmological models, and better atomic clocks will also help scientists shave down those experimental errors little by ... 09:26: We're also trying to develop atomic clocks accurate enough to track changes in Alpha in real time. 10:50: ... of telescopes, more refined cosmological models, and better atomic clocks will also help scientists shave down those experimental errors little by ... 09:26: We're also trying to develop atomic clocks accurate enough to track changes in Alpha in real time.
	2017-08-16: Extraterrestrial Superstorms 00:43: Meanwhile, the fastest winds ever measured, clocking 1,500 miles per hour, once raged in Neptune's Great Dark Spot. 02:34: The result is a raging vortex in the same direction as the Earth's rotation, clockwise in the southern hemisphere and counterclockwise in the north. 03:42: However, that vortex rotates in the opposite direction, clockwise in the north and counterclockwise in the south. 02:34: The result is a raging vortex in the same direction as the Earth's rotation, clockwise in the southern hemisphere and counterclockwise in the north. 03:42: However, that vortex rotates in the opposite direction, clockwise in the north and counterclockwise in the south. 02:17: ... a clockwise-spinning surface, there's a pull, a Coriolis force, to the left, while on a ...
	2017-08-10: The One-Electron Universe 04:43: ... actually goes backwards, just that if you reverse the ticking of the clock in the particles coordinate frame, its direction of motion appears ... 05:15: T is time reversal, changing the direction of the coordinate clock.
	2017-07-12: Solving the Impossible in Quantum Field Theory 13:41: In Schrodinger's equation, all of the particles are tracked according to one universal master clock. 13:48: ... approach, each particle is tracked according to its own proper time clock, which can vary in its tick speed depending on how fast the particle is ...
	2017-07-07: Feynman's Infinite Quantum Paths 04:58: In relativity, it's proportional to the proper time, so the time measured by the clock on a given trajectory.
	2017-06-21: Anti-Matter and Quantum Relativity 01:56: ... evolution of a particle's wave function according to one and only one clock, typically the clock in the reference frame of the ...
	2017-03-29: How Time Becomes Space Inside a Black Hole 04:32: It carries you with it and drives your personal clock forward as it does so.
	2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer 01:54: ... in time at a constant rate for all observers, governed by one global clock. ... 02:16: Einstein showed us that there is no universal clock. 02:19: Instead, every space time traveler carries their own clock. 02:22: The tick rate of your clock and your perception of simultaneity depends on your velocity. 02:42: The tick marks on that time axis also depend on velocity and represent the speed of everyone's personal clock in their proper time.
	2017-02-02: The Geometry of Causality 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. 01:51: Everyone agrees on the number of ticks that occurred on everyone else's clock. 02:00: ... time measured by a moving observer on their own clock is called proper time, but counting those clock ticks isn't the best way ... 03:06: If I don't move through space, I still travel forward in time at a speed of exactly one second per second according to my proper time clock. 03:48: My world line is only through time, and the tick marks on the time axis correspond to my own proper time clock ticks. 04:03: To me, their clocks tick slow. 04:06: They time their journey on these slow clocks, so I perceive them traveling for longer. 04:20: Drawing a connecting line at the tick of every traveler's proper time clock gives a set of nested hyperbola, but these aren't just [INAUDIBLE]. 05:33: ... every future tick of my clock, a signal arrives from the left and the right, and I use that to build up ... 05:44: Our traveler does the same thing, but from my point of view, their clock is slow, so I see them register signals at a different rate. 07:33: ... told you that these contours show where clocks moving from the origin reach the same proper time count, but more ... 02:00: ... observer on their own clock is called proper time, but counting those clock ticks isn't the best way for everyone to agree on spacetime ... 03:48: My world line is only through time, and the tick marks on the time axis correspond to my own proper time clock ticks. 02:00: ... observer on their own clock is called proper time, but counting those clock ticks isn't the best way for everyone to agree on spacetime ... 04:03: To me, their clocks tick slow. 04:06: They time their journey on these slow clocks, so I perceive them traveling for longer. 07:33: ... told you that these contours show where clocks moving from the origin reach the same proper time count, but more ... 04:03: To me, their clocks tick slow.
	2017-01-19: The Phantom Singularity 08:37: No clock ticks can't ever happen there. 09:08: An object at the event horizon has to change its distance from the black hole to keep its clock ticking. 09:17: And once inside, inward spatial movement continues to be the only way to fuel the ticking of an object's proper time clock. 09:08: An object at the event horizon has to change its distance from the black hole to keep its clock ticking. 08:37: No clock ticks can't ever happen there.
	2017-01-11: The EM Drive: Fact or Fantasy? 09:38: Joel, we're considering buying a lightly used EmDrive with your contribution, only 1,000 light years on the clock, apparently.
	2016-09-29: Life on Europa? 12:25: ... with not just inanimate objects running on behind-the-scenes clockwork, but with our behavior-- including our belief that we are free to choose ...
	2016-06-01: Is Quantum Tunneling Faster than Light? 05:27: It's actually extremely hard to test this because we can't make clocks accurate enough to time such a ridiculously quick event.
	2016-02-17: Planet X Discovered?? + Challenge Winners! 03:10: OK, time for the answer to our photon clock challenge question. 03:14: ... asked you whether according to your perception, a clock, or a photon clock, traveling towards you at 50% of the speed of light, ... 03:47: But it also affects clock rate. 03:49: ... see, special relativity tells us that a clock that's moving relative to you will have a slower tick rate compared to a ... 03:59: However, that's based on a sort of instantaneous comparison of the timelines of the two clocks. 04:21: So a photon clock that stationary on the spacetime diagram moves straight up. 04:30: ... a clock that first moves towards the observer and the stationary clock, ... 04:48: To understand that, you need to draw lights like photon paths between the moving clock and the stationary observer. 05:06: When the clock is approaching, its ticks are more clustered than when it's moving away. 05:11: So the approaching clock ticks faster than the receding clock. 05:14: ... this is just a complicated way of saying that the approaching clock sort of chases after its own photons, condensing the distance between ... 05:25: ... the receding clock is backing away from the photons traveling in your direction, stretching ... 05:38: Does the approaching clock appear to tick faster, slower, or at same rate compared to a stationary clock? 05:48: One effect, time dilation, slows down the tick rate of the approaching clock. 05:58: Time dilation will slow a moving clock down by this, 1 over the square root of 1 minus velocity squared over c squared. 06:08: The relativistic Doppler effect will speed up an approaching clock by 1 over 1 minus v on c. 06:20: The length of the observed second decreases by this factor for an approaching clock and increases for a receding clock. 06:28: Our clock is moving at 50% the speed of light. 06:34: The approaching clock appears to tick around 73% faster than your own stationary clock. 06:40: While the receding clock appears to tick 42% slower than your clock. 06:46: ... the time dilation, and not the Doppler effect, you get that the moving clock is always around 13% percent slower than your clock, whether approaching ... 06:34: The approaching clock appears to tick around 73% faster than your own stationary clock. 06:40: While the receding clock appears to tick 42% slower than your clock. 03:10: OK, time for the answer to our photon clock challenge question. 04:30: ... a clock that first moves towards the observer and the stationary clock, overtakes, and then moves away, will have ticks that occur at a less frequent rate ... 03:47: But it also affects clock rate. 05:14: ... this is just a complicated way of saying that the approaching clock sort of chases after its own photons, condensing the distance between the ... 05:11: So the approaching clock ticks faster than the receding clock. 03:14: ... asked you whether according to your perception, a clock, or a photon clock, traveling towards you at 50% of the speed of light, would seem to have a tick rate ... 03:59: However, that's based on a sort of instantaneous comparison of the timelines of the two clocks.
	2016-02-03: Will Mars or Venus Kill You First? 08:54: ... imagine a clock that magically appeared at the moment of the Big Bang and somehow ... 09:11: That clock would now read around 13.8 billion years.
	2016-01-27: The Origin of Matter and Time 00:37: This clock is a thing. 01:43: You put something-- say this clock-- on this diagram. 02:16: The slope tells you how much position is changing for each tick of the clock. 03:31: But what does this look like if we replace our regular clock with a photon clock? 03:37: Now remember, a photon clock marks time with a particle of light bouncing between two mirrors. 03:42: Each back and forth bounce is one tick of the clock. 03:50: Stationary, the world line of the photon clock looks like this. 03:54: The clock travels smoothly straight upward in time. 04:08: A second photon clock with a constant speed with respect to the first, travels a steeper time light path. 04:20: Regardless of the speed of that clock, the internal photons always do those 45 degree paths back and forth. 04:28: On the timeline of the stationary clock, the ticks of the moving clock don't match up. 04:34: The moving clock appears to tick at a slower rate. 04:53: Now that means that in the frame of reference of the moving clock, it is stationary. 04:58: And from that frame, the first clock appears to be moving. 05:01: The whole space time diagram can be transformed to give the second clock's world line a constant location in space. 05:20: So the second clock is still. 05:22: But the first clock is moving. 05:31: The now stationary frame sees the now moving frame as having a slower clock rate. 06:13: First, let's think more carefully about what these clock ticks really are. 06:42: In this analogy, those clock ticks become interactions between the internal parts of our atoms and nucleons. 07:15: Just as with the photon clock, it's only the ensemble that can travel slower than light, or be still. 10:21: What happens when an astronaut does a round trip at a large fraction of the speed of light, and returns to compare her clock to one left on Earth? 10:29: From both perspectives, the other clock was moving, and so should have ticked slower. 10:35: But which clock has the time lag when they get back together? 11:08: In order to compare clocks, the astronaut has to turn around at the end of the journey and come home. 11:33: So the answer is that the astronaut's clock, or the traveling twin, has experienced less time. 12:07: ... in order to fit the whole album into the episode, you need to slow your clock by accelerating uniformly from rest to 99% of the speed of light by the ... 12:17: The start of the song time should sync with the appearance of the photon clock. 04:34: The moving clock appears to tick at a slower rate. 04:58: And from that frame, the first clock appears to be moving. 04:28: On the timeline of the stationary clock, the ticks of the moving clock don't match up. 03:37: Now remember, a photon clock marks time with a particle of light bouncing between two mirrors. 05:31: The now stationary frame sees the now moving frame as having a slower clock rate. 06:13: First, let's think more carefully about what these clock ticks really are. 06:42: In this analogy, those clock ticks become interactions between the internal parts of our atoms and nucleons. 03:54: The clock travels smoothly straight upward in time. 05:01: The whole space time diagram can be transformed to give the second clock's world line a constant location in space. 11:08: In order to compare clocks, the astronaut has to turn around at the end of the journey and come home.
	2016-01-20: The Photon Clock Challenge 00:12: ... a recent episode, we showed you how the ticking of a clock-- and in particular a photon clock-- slows down if that clock is moving ... 00:21: The photon in the clock has further to travel from your stationary perspective. 00:35: And the resulting slowing of clock ticks due to motion is the time dilation of Einstein's theory of special relativity. 00:50: Imagine observing a clock moving toward you at 50% the speed of light. 00:55: As the light from that clock reaches you, you see the hands of the clock tick. 00:59: Eventually the clock reaches you, passes by, and continues to move away at the same speed. 01:06: ... the clock was moving toward you, do you observe its hands to be ticking slower, ... 01:22: ... the clock is moving toward you, do you see its hands ticking slower, faster, or at ... 01:33: Submit your answers to the email on the screen, using the subject line Photon Clock Challenge Answer. 00:50: Imagine observing a clock moving toward you at 50% the speed of light. 00:55: As the light from that clock reaches you, you see the hands of the clock tick. 00:59: Eventually the clock reaches you, passes by, and continues to move away at the same speed. 00:12: ... we showed you how the ticking of a clock-- and in particular a photon clock-- slows down if that clock is moving with respect to ... 00:55: As the light from that clock reaches you, you see the hands of the clock tick. 00:35: And the resulting slowing of clock ticks due to motion is the time dilation of Einstein's theory of special relativity.
	2016-01-13: When Time Breaks Down 00:35: We have internal clocks, neural processors dedicated to the counting of seconds and hours. 00:57: And a perfectly engineered clock will always tick at the same right. 01:03: Any clock is just an arrangement of matter. 01:28: But do the individual components of the clock feel the same flow of time? 01:36: The most accurate clocks in the world are atomic clocks, which can drift by less than a billionth of a second each day. 01:43: All of the atoms in such a clock feel the same length of a second. 01:59: The faster an object moves relative to you, the slower its clock appears to tick. 02:08: Its clock is frozen. 03:02: We're going to use a very close cousin to the photon box to explore time-- a thought experiment of Einstein's that we'll call the photon clock. 03:11: Imagine a clock made from two mirrors and a photon bouncing between them. 03:16: Every back and forth bounce of the photon results in a tick of the clock. 03:26: The rate of ticks is consistent, time flows smoothly, until the clock starts moving relative to me. 04:05: ... me, it appears as though the ticks take longer in the moving clock compared to an identical photon clock standing still right next to me, ... 04:15: ... other guy who is riding along with the moving clock would see it ticking at the normal rate, and quite bizarrely, will see ... 04:25: After all, my clock is moving relative to them. 04:35: Now what if the clock is traveling at the speed of light? 04:38: The apparent distance that the photon needs to travel to reach that top mirror becomes larger and larger as the clock speed increases. 04:45: And that distance is infinite when the clock reaches the speed of light. 04:49: From our point of view, the photon clock could never complete a tick because the photon could never reach that mirror. 04:57: ... the way, similar arguments will show us that a photon clock in an accelerating reference frame-- say on a rocket ship in empty ... 05:29: And so clocks must also tick slower the deeper they are in their gravitational field. 05:39: So what does this odd example of the photon clock have to do with real time and real matter? 05:44: Well, if our photon clock behaves this way, then so does the photon box. 06:29: So as an atom races past you at high speed, you would see all its internal bits ticking slower, just like the photon clock. 01:59: The faster an object moves relative to you, the slower its clock appears to tick. 05:44: Well, if our photon clock behaves this way, then so does the photon box. 04:05: ... me, it appears as though the ticks take longer in the moving clock compared to an identical photon clock standing still right next to me, which ... 01:28: But do the individual components of the clock feel the same flow of time? 01:43: All of the atoms in such a clock feel the same length of a second. 04:45: And that distance is infinite when the clock reaches the speed of light. 04:38: The apparent distance that the photon needs to travel to reach that top mirror becomes larger and larger as the clock speed increases. 04:05: ... ticks take longer in the moving clock compared to an identical photon clock standing still right next to me, which ticks at the normal ... 03:26: The rate of ticks is consistent, time flows smoothly, until the clock starts moving relative to me. 04:15: ... see it ticking at the normal rate, and quite bizarrely, will see my clock ticking ... 00:35: We have internal clocks, neural processors dedicated to the counting of seconds and hours. 01:36: The most accurate clocks in the world are atomic clocks, which can drift by less than a billionth of a second each day. 05:29: And so clocks must also tick slower the deeper they are in their gravitational field. 00:35: We have internal clocks, neural processors dedicated to the counting of seconds and hours.
	2016-01-06: The True Nature of Matter and Mass 07:55: Their clocks are frozen.
	2015-12-16: The Higgs Mechanism Explained 02:27: Their clocks should be frozen. 02:35: ... of intrinsic quantum spin that we call chirality, and this can either be clockwise or counterclockwise relative to the direction of ...
	2015-12-09: How to Build a Black Hole 07:45: Clocks run noticeably slower. 10:05: On our clock, the singularity forms infinitely far in the future. 07:45: Clocks run noticeably slower.
	2015-09-30: What Happens At The Edge Of The Universe? 09:11: No monkeys were harmed in the making of "SpaceTime" and any events that can be consistently assigned to our clocks at PBS.
	2015-09-23: Does Dark Matter BREAK Physics? 08:02: ... the monkey were to calculate the clock time of an external observer as it fell, then that calculated time would ... 09:54: ... falling through the event horizon, the monkey's clock, its universe, now contains events that happen at the horizon, including ... 08:02: ... the monkey were to calculate the clock time of an external observer as it fell, then that calculated time would ...
	2015-08-27: Watch THIS! (New Host + Challenge Winners) 04:55: You don't know how clocks work.
	2015-08-19: Do Events Inside Black Holes Happen? 01:29: ... clocks in high-altitude orbit will get ahead of clocks on the ground by a few ... 02:43: But everyone else insisted he never does, even after an infinite amount of time on any of our clocks. 01:29: ... clocks in high-altitude orbit will get ahead of clocks on the ground by a few ... 02:43: But everyone else insisted he never does, even after an infinite amount of time on any of our clocks.
	2015-08-12: Challenge: Which Particle Wins This Race? 00:22: ... means clocks run at the same rate everywhere, space and time are two separate things, ... 04:13: ... if the particles depart simultaneously as measured by the clock at one end of the planet, which one arrives first according to the clock ... 04:44: ... the radial geodesics, and work out who arrives first according to the clock on the other side of the ... 00:22: ... means clocks run at the same rate everywhere, space and time are two separate things, ...
	2015-08-05: What Physics Teachers Get Wrong About Tides! 12:21: ... that you take a frame attached to Earth's center, with clocks-- that frame's not going to be inertial-- and then you work out what the ... 13:22: ... a clock as if it runs-- pretending that it runs the same rate everywhere and ... 12:21: ... that you take a frame attached to Earth's center, with clocks-- that frame's not going to be inertial-- and then you work out what the ...
	2015-07-29: General Relativity & Curved Spacetime Explained! 01:33: But even in a world without gravity, we already know that clocks, rulers, and our eyes can all mislead us. 03:22: Inertial frames, that means axes plus clocks, are the spacetime equivalent of the ant's xy grid. 03:47: ... world lines will be geodesics, and their axis and clocks can serve as local inertia frames, provided that we think of them as ... 05:59: Now if spacetime is flat, then clocks on the ground and on the roof should run at the same rate. 06:15: The excess time is less than a second, but any discrepancy means that clocks are running at different rates. 06:59: Remember, a frame consists of axes and clocks. 07:02: And around Earth, spacetime curvature manifests itself in clocks much more than in rulers. 01:33: But even in a world without gravity, we already know that clocks, rulers, and our eyes can all mislead us. 03:22: Inertial frames, that means axes plus clocks, are the spacetime equivalent of the ant's xy grid. 03:47: ... world lines will be geodesics, and their axis and clocks can serve as local inertia frames, provided that we think of them as ... 05:59: Now if spacetime is flat, then clocks on the ground and on the roof should run at the same rate. 06:15: The excess time is less than a second, but any discrepancy means that clocks are running at different rates. 06:59: Remember, a frame consists of axes and clocks. 07:02: And around Earth, spacetime curvature manifests itself in clocks much more than in rulers. 01:33: But even in a world without gravity, we already know that clocks, rulers, and our eyes can all mislead us.
	2015-07-15: Can You Trust Your Eyes in Spacetime? 01:42: To record when and where events in this world happen I've got a clock to tell time, nice. 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. 02:01: To represent this set up in a diagram, let's copy my x-axis onto a blackboard and add a vertical axis to show the time on my clock. 02:09: ... axis is showing the distance ct that light travels per tick of my clock, which is interchangeable with clock ticks since I know the speed of ... 02:28: Rather, they are events, each of which occurs somewhere along my axis in a one-dimensional physical space and at some moment according to my clock. 02:42: All right, now, some weirdo in a red shirt carrying his own clock and x-axis approaches me from the left at constant speed. 02:49: He passes me just as my clock reads zero. 02:58: Anyway, say I plot the values of ct on my clock as the photon passes different marks on the x-axis. 03:13: In the same amount of time on my clock, he passes fewer marks on my x-axis. 07:58: ... changes in the monkey's position on my axis with respect to ticks of my clock-- that's ordinary velocity-- I'm going to track two hybrid quantities ... 02:49: He passes me just as my clock reads zero. 07:58: ... position on my axis relative to the monkey's clock and the time on my clock relative to the monkey's ... 02:09: ... that light travels per tick of my clock, which is interchangeable with clock ticks since I know the speed of ...
	2015-07-08: The Leap Second Explained 00:41: ... 1967, we redefined the SI second again based on atomic clocks since they're more stable, but the atomic clock second was calibrated to ... 01:16: The atomic clock second just inherited this discrepancy. 01:28: That means right now, we're measuring the day and keeping actual time on our clocks using slightly different concepts of a second. 01:34: Thus, 12:00 PM on our clocks is continually getting ahead of when the sun is directly over us. 01:40: ... and grows to around one second and we insert leap seconds to force our clocks back into sync with the ... 00:41: ... 1967, we redefined the SI second again based on atomic clocks since they're more stable, but the atomic clock second was calibrated to ... 01:28: That means right now, we're measuring the day and keeping actual time on our clocks using slightly different concepts of a second. 01:34: Thus, 12:00 PM on our clocks is continually getting ahead of when the sun is directly over us. 01:40: ... and grows to around one second and we insert leap seconds to force our clocks back into sync with the ...
	2015-07-02: Can a Circle Be a Straight Line? 09:40: ... since those discrepancies are measurable with atomic clocks, this has to be taken into account when you calibrate time systems, or ...
	2015-06-24: The Calendar, Australia & White Christmas 05:17: ... we'll just reckon time in atomic clock seconds or something like the Stargate system on "Star Trek," which, ... 05:40: Before we sign off, I want to comment quickly on the leap second that we'll all be adding to our clocks this coming June 30. 05:17: ... we'll just reckon time in atomic clock seconds or something like the Stargate system on "Star Trek," which, yes, I know ... 05:40: Before we sign off, I want to comment quickly on the leap second that we'll all be adding to our clocks this coming June 30.
	2015-06-03: Is Gravity An Illusion? 01:02: That's just some X-Y-Z axes to label points in space and a clock to track time.
	2015-03-25: Cosmic Microwave Background Explained 02:51: To answer that and to see why space used to be orange, we need to turn the clock back to about 400,000 years after the Big Bang, give or take.
	2015-03-18: Can A Starfox Barrel Roll Work In Space? 02:19: So say you want to do a barrel roll that's clockwise, as viewed from the rear. 02:30: Now, on a planet, the clockwise and subsequent counter-clockwise torques required to do this are provided by the atmosphere. 03:42: That flywheel is spinning clockwise, as seen from the rear of the ship, or counterclockwise as seen from the nose. 02:19: So say you want to do a barrel roll that's clockwise, as viewed from the rear. 02:30: Now, on a planet, the clockwise and subsequent counter-clockwise torques required to do this are provided by the atmosphere. 03:42: That flywheel is spinning clockwise, as seen from the rear of the ship, or counterclockwise as seen from the nose.
	2015-02-25: How Do You Measure the Size of the Universe? 05:03: One of those beams of raisin light would be just switching as the clock hits 13.8 billion years.

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