# Search PBS Space Time

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

• 00:03: ... of both space and time okay we start in this description with newtonian physics in which they're the dimensions that form the stage on which ... ### 2022-01-19: How To Build The Universe in a Computer

• 02:23: He’d then adjust the velocities of all according to Newton’s laws.
• 02:56: ... the time of Isaac Newton it had been possible to write down equations describing the trajectories ...
• 03:53: In an N-Body simulation Newton’s laws of motion and gravity are applied over a series of time steps. ### 2022-01-12: How To Simulate The Universe With DFT

• 06:03: In other words, Newtonian mechanics.
• 06:06: When we use Newton to solve, say, the three-body problem, we can solve the equations for each of the 3 particles separately.
• 07:15: In the Newtonian case, particles only interact locally, and that means the Newtonian equations of motion are what we call separable.
• 07:46: ... fact in Newtonian mechanics we can not only write down the equations of motion for each ...
• 08:02: But if we want to keep the quantum behaviour of quantum mechanics we can’t throw away most of configuration space like we do in Newtonian mechanics.
• 10:54: Because they aren’t interacting, the equations of motion for these electrons are separable, just like in Newtonian mechanics. ### 2021-12-20: What Happens If A Black Hole Hits Earth?

• 14:10: ... ways to break general relativity. There was the one on modified newtonian dynamics as an explanation for dark matter, and the one on fuzzballs - ... ### 2021-12-10: 2021 End of Year AMA!

• 00:02: ... the bucket spinning or not spinning referencing um the classic isaac newton thought experiments um but tricky actually gives us an answer and this ... ### 2021-11-10: What If Our Understanding of Gravity Is Wrong?

• 02:02: ... to Isaac Newton’s Law of Universal  Gravitation, the gravitational field drops off ...
• 02:46: But what if gravity doesn’t obey Newton’s law of gravity?
• 02:52: ... Einstein found that Newtonian gravity  breaks down when the gravitational field gets too strong - ...
• 03:08: But Einsteinian gravity looks exactly like Newtonian gravity when gravitational fields get weak.
• 03:18: What if Newtonian gravity breaks down  both for very strong AND very weak fields?
• 03:25: This is the idea behind Modified Newtonian Dynamics, or MOND, proposed by Israeli physicist Mordehai Milgrom in 1982.
• 03:53: ... can be done with a modification to either  Newton’s law of universal gravitation - in which case gravity has a minimum ...
• 06:10: ... Instead it does what it was designed to do - it reproduces good ol’ Newtonian ...
• 09:53: ... acted like Newtonian mechanics on solar system scales, like MOND on galactic scales, and like ... ### 2021-11-02: Is ACTION The Most Fundamental Property in Physics?

• 01:22: ... momentum and kinetic energy - but to no avail. In the meantime Isaac Newton came up with his laws of motion which gave us the instant and miraculous ...
• 05:00: ... you study Newton’s mechanics and then move on to Lagrangian mechanics, it seems almost like ...
• 05:52: ... motivations in developing general relativity was the fact that Newtonian mechanics failed to correctly predict the orbit of Mercury. If you ...
• 11:12: ... wavefunction. This is analogous to how Lagrangian mechanics reproduced Newton’s mechanics. And it’s no coincidence, because the path integral is the ...
• 18:34: ... theory feels like alchemy. Relatedly, Cluebcke says “Rough shade on Newton with that whole "you can't transmute apples into gold" line” - and for ...
• 18:52: ... could Newton have know which lines of inquiry would be “fruitful” without exploring ... ### 2021-10-20: Will Constructor Theory REWRITE Physics?

• 00:00: ... people behind the greatest leaps in physics - Einstein, Newton, Heisenberg, all had the uncanny ability to see the fundamentals - see ...
• 00:46: the laws of thermodynamics or Newton’s laws of motion Step 3.
• 01:43: ... can derive all of thermodynamics and Newtonian mechanics and electromagnetism and so on from two master theories: ...
• 04:55: ... mechanistic philosophy that dominates physics really started with Isaac Newton, so it’s appropriate to start with the falling apple that apocryphally ...
• 05:06: In Newton’s picture, the apple has a current state, stationary and up in the tree. ### 2021-03-09: How Does Gravity Affect Light?

• 01:17: ... assumed that Isaac Newton’s theory of gravity was the full picture, and that light behaves like any ...
• 01:34: We now know that both gravity and light are much weirder than Newton thought.
• 07:16: Einstein was in the business of overturning the ideas of Newton, so it’s not surprising that he turns to one of Newton’s great rivals.
• 07:24: The Dutch physicist Christiaan Huygens disagreed with Newton on many things - including the idea that light is a particle.
• 11:28: The number he got was exactly twice the deflection calculated by Cavendish based on Newton’s gravity. ### 2020-11-18: The Arrow of Time and How to Reverse It

• 02:31: ... Newton’s laws of motion combined with Coulomb’s law perfectly describe how the ... ### 2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time

• 00:34: ... When John Mitchell and Pierre-Simon Laplace explored Newton’s law of universal gravitation,   they realized the possibility ... ### 2020-10-13: Do the Past and Future Exist?

• 01:17: As with many ideas in physics, this one originates with Isaac Newton.
• 01:21: Newton was the first to come up with a set of laws that allow us to predict the motion of all objects in the universe.
• 01:27: ... Newton’s revelations led to the notion of the deterministic universe - the idea ...
• 01:54: Newton’s picture of the universe included one other assumption that we know for sure is wrong.
• 02:08: Newton assumed that all particles, all observers, all points in space were ruled by a single, constantly ticking clock.
• 02:27: Here’s a nice way to represent Newton’s picture of space and time.
• 05:33: The representation of the block universe that I showed you is very Newtonian.
• 05:47: Newton says there’s only one way to slice the universe. ### 2020-09-08: The Truth About Beauty in Physics

• 02:19: There IS an extremely simple, elegant law underlying planetary motion - it's Newton’s Law of Universal Gravitation.
• 02:27: Not only can Kepler’s complicated laws be derived from Newton, but Newtonian gravity makes predictions far beyond the motion of the planets.
• 02:35: But even Newtonian gravity proved to be a special case of a much deeper law.
• 02:41: Einstein’s equations of general relativity give even better precision than Newton’s law - perhaps perfect precision - in their description of gravity.
• 02:50: And general relativity is also more explanatory than Newton - it tells us that gravity results from the warping of space and time.
• 03:13: Ptolemy, Copernicus, Kepler, Newton, Einstein - each followed their own sense of mathematical beauty in this long quest to understand gravity.
• 05:59: ... Newton’s law of gravitation is a great example, and we can be sure that Newton ...
• 06:35: The step from Kepler to Newton suggests so, but then why does complexity seem to increase when you go one level deeper from Newton to Einstein?
• 09:23: Same with Newton’s gravity, derived from observations of apples and the moon, but it predicts the motions of galaxies. ### 2020-07-28: What is a Theory of Everything: Livestream

• 00:00: ... have challenged this and started asking those questions anyway isaac newton came along and said hey wait a minute it's a perfectly legit question ... ### 2020-06-08: Can Viruses Travel Between Planets?

• 14:22: ... theory is modified newtonian dynamics - MONDS - in which gravity doesn’t drop off as quickly as the ... ### 2020-05-27: Does Gravity Require Extra Dimensions?

• 00:33: ... was the first force to get a decent mathematical description with Isaac Newton’s Law of Universal Gravitation back in the 17th ...
• 01:37: But even Newton’s old theory works great in almost all situations.
• 01:42: And deviations from Newton’s description may point the way to an understanding deeper than Einstein’s.
• 01:53: ... Newton’s law of gravitation is an example of such a law - basically, the strength ...
• 02:38: That’s where the r^2 comes from on the bottom of Newton’s law of gravitation.
• 03:36: Newton’s inverse square law for gravity tells us there are 2+1 = 3 spatial dimensions.
• 07:36: It’s actually the OG - the experiment first used to measure the strength of the force of gravity - or the G in Newton’s law of gravitation. ### 2020-05-11: How Luminiferous Aether Led to Relativity

• 04:06: ... only 5 years before his death. Across the channel, a much younger Isaac Newton was sitting in Cambridge making life difficult for Huygens. First his ...
• 05:08: ... versus Newton. Light as a wave versus a particle. Most accepted Newton - as most always ...
• 06:22: ... so we get to the end of the 19th Century. With Newton’s mechanics and gravity, Huygen’s optics, Maxwell’s electromagnetism, ...
• 07:19: ... using the Galilean transformation, which is part of the foundation of Newton’s mechanics. I were a smug 19th century physicist, I’d wanna hope Galilean ...
• 11:20: ... contradicts Galilean relativity, and so revealed a crack in the sacred Newtonian mechanics. This directly inspired Hendrik Lorentz to derive his Lorentz ...
• 11:42: ... and then his general theory of relativity that ultimately overthrew Newton’s theory of gravity, and, according to Einstein, it revealed the cracks in ... ### 2020-02-18: Does Consciousness Influence Quantum Mechanics?

• 15:59: ... for not nerding hard enough because you corrected my pronunciations of Newton's book while missing my questionable taxonomic identify of apes versus ...
• 16:17: ... roman or princhipia like a modern Italian or latin mass, and whether Newton himself would have said the latter - it seems probably he ... ### 2020-02-11: Are Axions Dark Matter?

• 16:00: ... last week's comment responses I corrected my pronundiation for Newton's book - and then lots of people corrected my correction. Principia ... ### 2020-02-03: Are there Infinite Versions of You?

• 12:40: The solutions only exist in special cases for Newtonian gravity.
• 15:56: Also I mispronounced the name Newton's great work - it's PrinKipia - hard K, not soft principia. ### 2020-01-20: Solving the Three Body Problem

• 00:20: ... - and arguably all of science changed forever in 1687 when Isaac Newton published his Principia. Within it were equations of motion and gravity ...
• 01:24: ... does it mean to find a solution to the three-body problem? Newton’s laws of motion and his law of universal gravitation give us a set of ...
• 02:06: ... the case of two gravitating bodies, the solutions to Newton’s laws are just the equations for the path traveled by the bodies - be it ...
• 03:18: ... motion of many bodies. For most of the three centuries since Newton, predicting the motion of the planets and the moon was critical for ... ### 2019-10-15: Loop Quantum Gravity Explained

• 15:35: ... counters the gravitatinally attraction - if you'll forgive my crude Newtonian ... ### 2019-09-23: Is Pluto a Planet?

• 02:20: This picture was cleaned up by the observations of Galileo and Brahe and the mathematical models of Kepler and Newton.
• 02:27: Newton’s Laws of Gravity led to consistent predictability of the motion of the heavenly spheres.
• 03:06: New wandering stars were discovered in the centuries following Newton.
• 03:19: That same motion almost perfectly reflected the clockwork predictions of Newtonian mechanics. ### 2019-04-24: No Dark Matter = Proof of Dark Matter?

• 00:03: ... of gravitational theory itself the first such proposal was Mons modified Newtonian dynamics proposed by Mordecai Milgram in the early 80s the idea is the ... ### 2019-03-28: Could the Universe End by Tearing Apart Every Atom?

• 03:05: ... thing is the second Friedman equation it's basically the equivalent of Newton's law of gravity for the whole universe describing the acceleration or ... ### 2019-03-06: The Impossibility of Perpetual Motion Machines

• 06:14: After all, Newton tells us, an object in motion tends to remain in motion unless acted on by an outside force. ### 2019-01-30: Perpetual Motion From Negative Mass?

• 01:34: This is encapsulated in Newton’s second law, which defines the connection between the amount of force applied and the acceleration that results.
• 01:52: It appears in Newton’s Law of Universal Gravitation.
• 02:35: ... Newton’s second law with the law of gravitation and you see that although massive ...
• 02:57: ... with very different masses fall at the same rate, and that was before Newton came even ...
• 03:19: OK, so how do negative masses work in Newtonian mechanics?
• 03:28: In fact, in Newtonian gravity, any like masses – both positive or both negative - should produce a mutually attractive force.
• 04:37: Newton’s second law seems to say that negative inertial masses respond oppositely to the applied force.
• 05:47: ... fact Newton’s law of gravitation is really only approximation of a much more complete ...
• 08:18: So far this seems to echo the Newtonian prediction.
• 08:42: But this should crudely translate to the case of two equal-sized objects, although not in the simple, linear style of Newtonian mechanics.
• 10:39: We then happily plugged our negative inertial mass into Newton’s 2nd law to get acceleration.
• 10:58: ... carved into the geometry of Einstein’s spacetime – are the GR analogs of Newton’s second law and give the equations of motion of ...
• 11:10: ... principle, or from Lagrangian mechanics – a more modern version of Newton’s laws of ... ### 2019-01-09: Are Dark Matter And Dark Energy The Same?

• 04:18: The answer is complicated - it’s not always obvious how weird stuff like negative masses translates from general relativity to Newton’s laws.
• 04:26: But for now let’s follow the paper’s argument, which is based on Newtonian physics.
• 04:31: In Newtonian gravity, you multiply the two masses together along with some other stuff to get the strength of their mutual gravitational attraction.
• 04:58: Dr. Farnes takes the Newtonian argument a step further.
• 05:09: It also determines the way objects respond to forces via Newton’s 2nd Law.
• 05:43: According to this Newtonian interpretation.
• 06:22: ... positive and negative mass particles, along with his interpretations of Newton’s ...
• 08:18: ... we look at the second Friedmann equation, which is really the analog of Newton’s law of gravity for the whole cosmos, this negative mass fluid – as a ... ### 2018-12-12: Quantum Physics in a Mirror Universe

• 00:02: ... get flipped the laws of physics should be unaltered in that mirror world Newton's laws will still give the balls trajectory those laws work the same no ... ### 2018-11-07: Why String Theory is Right

• 02:33: Everyone knows that Isaac Newton discovered gravity when he fell out of an apple tree, or something like that. ### 2018-10-03: How to Detect Extra Dimensions

• 04:07: In our universe, gravity appears to diminish according to the inverse square law, as reflected in Newton's law of universal gravitation. ### 2018-09-20: Quantum Gravity and the Hardest Problem in Physics

• 02:06: ... the earlier ideas of Isaac Newton, in which space and time are treated as separate and universal, special ...
• 02:49: But the Schrodinger equation treats space and time as fundamentally separate in the old-fashioned Newtonian way. ### 2018-07-18: The Misunderstood Nature of Entropy

• 03:57: This theory explained thermodynamic behavior as the summed result of the individual motion of tiny particles under Newton's laws of motion.
• 10:22: ... the laws of motion, whether Newtonian or quantum mechanical, don't care about the direction of time, and yet, ... ### 2018-07-11: Quantum Invariance & The Origin of The Standard Model

• 02:03: Newton's laws of motion and gravity, Maxwell's equations for electromagnetism, Einstein's general relativity, and of course, the standard model. ### 2018-06-20: The Black Hole Information Paradox

• 11:54: They were glimpsed as dark stars in the mathematics of Isaac Newton's law of universal gravitation.
• 12:01: So, to continue your own mathematical journey into black holes, Newton's gravity is the place to start.
• 12:07: ... comprehensive series on gravitational physics that will take you from Newton's law all the way through gravitational field and celestial ... ### 2018-06-13: What Survives Inside A Black Hole?

• 06:26: ... Newton's law of universal gravitation and Coulomb's law for electrostatics say ... ### 2018-05-23: Why Quantum Information is Never Destroyed

• 00:36: Newton's equations for classical mechanics, Maxwell's equations for electromagnetism, and the Schrodinger equation for quantum mechanics. ### 2018-05-16: Noether's Theorem and The Symmetries of Reality

• 05:00: The law of conservation of energy is fundamental in Newtonian mechanics, in which space and time are unvarying and eternal. ### 2018-04-18: Using Stars to See Gravitational Waves

• 08:40: ... the existence of gravitational waves, he had to master it precursor, Newtonian ...
• 08:51: He needed to understand Newton's theory of gravity well enough to see where it failed.
• 08:56: ... already done some serious university-level physics, then mastering Newtonian gravity is also your next step toward understanding Einstein's view of ...
• 09:10: ... from the basics of classical mechanics through the intricacies of Newtonian ... ### 2018-02-28: The Trebuchet Challenge

• 01:43: ... Newton's laws tell us that when two objects with different masses are accelerated ...
• 04:46: ... to figure out the equations of motion of a trebuchet in terms of Newton's laws, with a complicated series of force vectors, some gnarly geometry, ... ### 2018-02-14: What is Energy?

• 01:38: Fun side note, Leibniz was famously arrival of Isaac Newton.
• 01:43: Besides the whole co-inventing calculus thing, Leibniz's vis viva seen as a competition to Newton's idea of conservation of momentum.
• 01:53: Newtonian mechanics had only recently revolutionized physics.
• 03:04: But that's just Newtonian mechanics.
• 06:55: Just adding conservation of energy to Newton's mechanics gives an extra constraint that allows us to solve problems we couldn't otherwise.
• 07:08: Newtonian mechanics is great at describing the motion of simple systems of a few rigid objects.
• 07:56: ... its conservation has led to new types of mechanics that have supplanted Newtonian mechanics, for example Lagrange mechanics, which, in its simplest form, ...
• 08:12: It produces the same equations of motion as Newtonian mechanics but without having to keep track of those innumerable fiddly force vectors. ### 2017-11-29: Citizen Science + Zero-Point Challenge Answer

• 06:38: Multiply those together and you get that a gecko can support something like 40 newtons, or four kilograms, in Earth gravity. ### 2017-09-28: Are the Fundamental Constants Changing?

• 03:11: The dimensions behind, say, Newton's gravitational constant-- or the mass of the electron-- all have arbitrary human definitions. ### 2017-01-19: The Phantom Singularity

• 00:16: [MUSIC PLAYING] Isaac Newton's universal law of gravitation was an incredible insight when he figured it out in the late 1600s.
• 00:39: Newton's equation gives you the gravitational force exerted between two masses, m1 and m2 that are a distance R apart.
• 01:21: According to Newton's law, in order to fuel that infinite gravitational acceleration you need to get zero distance from an object's center of mass.
• 04:04: So, does the fact that it includes a singularity mean there's something fundamentally wrong with Newton's law of gravitation?
• 04:16: ... gravitational field is too strong-- say, near a star or a black hole-- Newton's law gives the wrong answers, and we need Einstein's general theory of ...
• 04:30: So does general relativity rid us of Newton's pesky singularity?
• 06:47: r, the distance to the center of mass, remains in the denominator just as it was in Newton's law.
• 07:00: This gives us the same infinite gravitational pull as the Newtonian singularity.
• 07:05: And just as with the Newtonian case, this gravitational singularity can only exist if infinite densities are possible.
• 07:13: But unlike Newton's laws of gravity, the Schwarzschild metric actually tells us whether or not that infinite density is expected.
• 07:22: To see how, we need to look at the second singularity in this equation, a singularity that Newton's law does not contain. ### 2017-01-04: How to See Black Holes + Kugelblitz Challenge Answer

• 10:26: Well, here, we're saved by Newton's shell theorem, which states that the gravitational force inside a perfectly symmetric shell is zero. ### 2016-12-21: Have They Seen Us?

• 16:17: ... the escape velocity at the surface of the Earth because we're used to Newtonian approximations ...
• 16:49: ... happen to get exactly the right size for the event horizon if you use Newtonian gravity to calculate the distance at which the escape velocity reaches ... ### 2016-12-14: Escape The Kugelblitz Challenge

• 05:22: ... Newton's shell theorem tells us that the entire inside of a spherically symmetric ... ### 2016-09-14: Self-Replicating Robots and Galactic Domination

• 00:41: Space stuff gravitates around in slow, stately arcs that would make Newton proud. ### 2016-06-22: Planck's Constant and The Origin of Quantum Mechanics

• 04:13: It was Sir Isaac Newton who first analyzed this heat glow in the 1660s when he used a prism to split sunlight into its component colors. ### 2016-05-25: Is an Ice Age Coming?

• 13:58: ... that the law of conservation of energy, as we learned when we studied Newtonian mechanics, is a feature of flat ...
• 14:12: ... gravity from a Newtonian perspective requires the invention of a new quantity-- gravitational ... ### 2016-05-18: Anti-gravity and the True Nature of Dark Energy

• 04:04: This thing is in a real way just Newton's law of gravitation for the whole cosmos.
• 11:35: This law is a property of a Newtonian universe, in which space and time are fixed static dimensions. ### 2016-04-13: Will the Universe Expand Forever?

• 02:16: ... let's develop intuition a bit by thinking about gravity from a Newtonian perspective-- as a force, rather than as an Einsteinian spacetime ...
• 02:58: Now this escape velocity comes right out of Newton's universal law of gravitation, which itself can be derived from the Einstein equations.
• 03:07: The mathematical step from Newton's gravity to escape velocity comes from thinking about energy.
• 03:40: ... this Newtonian analogy-- and, remember, ignoring dark energy-- the universe also has an ...
• 09:29: And to understand how does so will take us far beyond the capacity for Newtonian analogy. ### 2016-03-23: How Cosmic Inflation Flattened the Universe

• 11:47: It doesn't exist in the inertial reference frames for which Newton's laws are valid. ### 2016-03-16: Why is the Earth Round and the Milky Way Flat?

• 02:15: Here it's fine to think about gravity Newtonianly as a force rather than as an Einsteinian warping of space time.
• 02:23: ... Newton's Universal Law of Gravitation tells us that the strength of gravity drops ... ### 2016-01-06: The True Nature of Matter and Mass

• 02:20: The photons exert a force on the box, the box also exerts a force on the photons-- Newton's Third Law, which gives us the conservation of momentum. ### 2015-11-25: 100 Years of Relativity + Challenge Winners!

• 01:32: But for now we have some math to do and it's all going to be Newtonian.
• 01:37: Newton was OK, too, I guess.
• 02:13: ... some Newtonian mechanics to see how much mass is needed to accelerate Apophis to get ...
• 04:12: Newton's law of universal gravitation tells us the force between two massive objects. ### 2015-11-11: Challenge: Can you save Earth from a Killer Asteroid?

• 01:43: To do this, you'll need lots of Newton.
• 01:49: You'll need Newton's law of universal gravitation as well as basic mechanics and kinematics. ### 2015-10-07: The Speed of Light is NOT About Light

• 01:46: This Galilean Relativity is an incredible insight that Isaac Newton would later codify into his Laws of Motion.
• 02:11: By the late 1800s, we have Maxwell's equations, Newton's mechanics, various other awesome theories.
• 02:38: In fact, we now know that even Newton's mechanics were using assumptions that implied an infinite speed of light, which is really bad.
• 03:16: Galileo and Newton tell us that total monkey speed equals pony blade speed plus monkey skate speed.
• 04:37: Newton's mechanics use it.
• 05:06: The transformation underpinning Newton's mechanics is wrong. ### 2015-09-23: Does Dark Matter BREAK Physics?

• 03:32: According to Newton, gravity weakens proportional to distance from its source squared.
• 03:50: Well, it turns out that if you make a simple change to Newton's gravity, things work out.
• 04:05: The original modified Newtonian dynamics hypothesis, and it's a general relativity extensions, tries to give us this basic relationship for gravity. ### 2015-08-27: Watch THIS! (New Host + Challenge Winners)

• 00:09: There was a Newtonian and an Einsteinian version of the challenge.
• 00:15: ... key to the Newtonian challenge was getting an expression for the gravitational force on the ...
• 01:26: This is kind of a coincidence of the specific situation of a uniformly dense planet and Newtonian mechanics.
• 05:05: But remember, the Newtonian solution is also there. ### 2015-08-19: Do Events Inside Black Holes Happen?

• 00:37: ... treat gravity Einsteinially rather than Newtonianially from the outset, it will help a lot if I can rely on technical terms ...
• 07:03: ... Newtonian gravity, a projectile on the surface of a planet or a star needs a ... ### 2015-08-12: Challenge: Which Particle Wins This Race?

• 00:17: For the purposes of this challenge, I want you to treat gravity and all physics Newtonianly.
• 00:59: ... Newtonian gravity, you can work out an expression for the orbital speed of this ...
• 03:35: Use the subject line "Two-particle Newtonian gravity challenge".
• 05:09: You can only enter one challenge, though, Newton or Einstein.
• 05:16: ... can enter the Einsteinian challenge at all, that means you can solve the Newtonian challenge in about 60 seconds, which isn't much of a ...
• 05:29: But you also have more time, and both the Newtonian and Einsteinian versions of the question are pretty fun exercises. ### 2015-08-05: What Physics Teachers Get Wrong About Tides!

• 02:01: Assumption one-- we're going to use Newtonian gravity.
• 03:09: And in Newtonian physics, it's fake.
• 03:13: Remember, Earth itself is accelerating towards the Moon, so according to Newton, Earth's frame is non-inertial.
• 12:39: ... what the geodesics should be-- that resemble-- that basically give you Newton's laws of motion as if there were a gravitational force-- are just the ...
• 13:18: In the Newtonian sense, acceleration would mean put a frame of reference at Earth's center. ### 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.
• 00:27: ... Newton says that a frame on earth's surface is inertial, and relative to that ...
• 01:11: Today we're finally going to show how curved spacetime makes Einstein's model of the world just as self consistent as Newton's.
• 01:18: ... one is to express both Newton's and Einstein's viewpoints in geometric spacetime terms, since that's the ...
• 02:03: This captures Newton's idea that inertial observers shouldn't accelerate relative to other inertial observers.
• 02:08: ... Newtonian gravity would just be an additional force we introduced, like any other ...
• 03:18: OK, Einstein's position is that Newton is making the same mistake as the ant.
• 04:27: Now according to Newton, that happens because the apples fall radially instead of down.
• 05:09: But then again, so does Newton's flat spacetime picture that has gravity injected as a kicker.
• 06:34: And that means game over for Newton.
• 06:36: ... and time separately at all, most of the everyday effects on earth that Newton would attribute to gravity are due to curvature in ...
• 08:22: So we often think in Newtonian gravitational terms, because it's easier, and because the resulting errors are usually small. ### 2015-07-22: SPECIAL ANNOUNCEMENT + Flat Spacetime Geometry Comments

• 02:58: Remember, in Newtonian physics, there's no unambiguous answer to that question, because you can only talk about motion relative to other things.
• 03:22: Those are the guys that, it turns out, corresponds to inertial observers in Newtonian physics. ### 2015-07-15: Can You Trust Your Eyes in Spacetime?

• 01:30: Pretend the world has no gravity, Newtonian or otherwise.
• 06:38: In Newtonian mechanics, we distinguish inertial and noninertial observers dynamically by using the floating ball test. ### 2015-07-08: The Leap Second Explained

• 00:30: Thus, in 1960, the second was redefined to be whatever would make the motions of multiple objects in the solar system fit Newton's laws of motion. ### 2015-07-08: Curvature Demonstrated + Comments

• 06:34: ... the curves and vectors in that space mean, and how it helps explain away Newtonian ... ### 2015-07-02: Can a Circle Be a Straight Line?

• 01:21: ... how it lets you account for the motion we observe even if there's no Newtonian force of ... ### 2015-06-17: How to Signal Aliens

• 06:35: ... by the terms "acceleration" an "inertial frame." That means reexamining Newton's first and second laws and so ...
• 07:26: ... pointed out that you can distinguish ordinary celebration from real Newtonian gravity, because real gravity will vary in strengths slightly at both ...
• 09:42: All directions are equivalent in the absence of some kind of real gravity in the Newtonian sense picking out some direction. ### 2015-06-03: Is Gravity An Illusion?

• 00:00: ... PLAYING] Isaac Newton said that an apple falls because a gravitational force accelerates it ...
• 00:18: ... to Isaac Newton, the ground can be considered at rest, Earth applies a gravitational ...
• 00:54: OK, bear with me for a minute because we need to begin with some Physics 101 and Newton's laws of motion.
• 01:25: ... Newton's laws can't tell you whether a frame of reference is really at rest or ...
• 01:34: However, interestingly, Newton's laws can tell you whether your frame of reference is really accelerating or not.
• 01:49: Now in Newtonian physics, inertial frames are special because Newton's second law, F equals ma, is only valid in inertial frames.
• 02:41: Inertial frame and non-accelerating frame are synonyms in Newtonian physics.
• 03:26: There's something else familiar that makes people, books, and elephants accelerate in lockstep-- the Newtonian force of gravity.
• 05:31: Now in Newtonian physics, this is just an accounting trick that has no broader significance.
• 05:49: Now, you know what Newton would say.
• 06:29: Well because, Newton says, that frame can't be inertial.
• 06:51: Really, Newton?
• 07:11: More to the point, Newton, if you're inside the box, there's no way for you to know that you're not in intergalactic space.
• 07:59: Now Newton says, nice try, Einstein, but you forgot something-- Earth is round.
• 09:19: It makes several predictions that Newton's theory of gravity does not, and so far, it has passed all its experimental tests. ### 2015-04-29: What's the Most Realistic Artificial Gravity in Sci-Fi?

• 00:53: Whether you want to think of gravity in the Newtonian or the Einsteinian sense, the problem persists.
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