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	2022-12-08: How Are Quasiparticles Different From Particles? 00:03: ... watching this video on is best understood by thinking about positive and negative charges moving around a circuit of diodes and ... 03:21: This is an n-type semiconductor - n because the flowing charge is negative. 00:03: ... watching this video on is best understood by thinking about positive and negative charges moving around a circuit of diodes and ... 00:12: But the only elementary particle actually flowing in the circuit are the negatively charged electrons. 10:50: At the same time, the negatively charged electrons in a metal lattice attract the positive nuclei. 00:12: But the only elementary particle actually flowing in the circuit are the negatively charged electrons. 10:50: At the same time, the negatively charged electrons in a metal lattice attract the positive nuclei. 00:12: But the only elementary particle actually flowing in the circuit are the negatively charged electrons. 10:50: At the same time, the negatively charged electrons in a metal lattice attract the positive nuclei.
	2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations? 18:50: ... quantum field theory, with the time-reversed signals corresponding to negative frequency ...
	2022-08-24: What Makes The Strong Force Strong? 04:31: With electromagnetism you have one type of charge, which can be positive or negative, with the Strong Force you have three charge types. 09:05: You would have to get really close to an atom to feel the positive electric field of the nucleus, or the negative electric field of the electrons. 10:37: ... like the 3 charges of the strong force, each of which can be positive or negative, and transform into each other additively in the same way, or cancel out ... 11:51: ... in fact they carry two charges at the same time - a positive and a negative of different colours - or more accurately, a superposition of multiple ... 18:36: Those fields have positive and negative frequency modes that cancel each other out to leave a vacuum. 09:05: You would have to get really close to an atom to feel the positive electric field of the nucleus, or the negative electric field of the electrons. 18:36: Those fields have positive and negative frequency modes that cancel each other out to leave a vacuum. 00:28: ... orbitals by the electromagnetic force - opposite charges attract, so the negatively-charged electrons are attracted by the positively charged ...
	2022-08-17: What If Dark Energy is a New Quantum Field? 01:41: ... that the anti-gravitational effect of dark energy is due to it having negative pressure. That’s counter-intuitive because negative pressure is an ... 02:31: ... dark energy is that, on top of the anti-gravitational effect of its negative pressure, it also produces regular attractive gravity due to its ... 12:31: ... omega is between -⅓ and -1 then the outward-pushing negative pressure still dominates over the inward pull of regular gravity, so ... 13:04: ... to get omega less than -1 is for the kinetic energy of the field to be negative. These sorts of negative energy scenarios break the rules in general ... 01:41: ... that the anti-gravitational effect of dark energy is due to it having negative pressure. That’s counter-intuitive because negative pressure is an inward pulling ... 02:31: ... dark energy is that, on top of the anti-gravitational effect of its negative pressure, it also produces regular attractive gravity due to its positive energy ... 12:31: ... omega is between -⅓ and -1 then the outward-pushing negative pressure still dominates over the inward pull of regular gravity, so expansion ...
	2022-06-30: Could We Decode Alien Physics? 02:25: ... - bring together two positive charges or    two negative charges and you get a net positive force - which means a repulsive ... 11:52: ... progression of positive times like we do,   and the past as negative? Or do they do it the other way around? The laws of physics ... 02:25: ... entrenched.   Electrons came to be defined as having  negative charge, and that defined the   relative charge of everything else - ... 00:00: ... through the alien circuitry   is the lightest lepton and has negative  electric charge. Obviously the ... 01:25: ... electric charge in the opposite way - electrons positive, positrons negative.   But how could we make such a blunder? Surely, a quick glance at the ...
	2022-06-22: Is Interstellar Travel Impossible? 19:30: Hawking’s original argument talked about perturbing the positive and negative frequency modes of the quantum vacuum.
	2022-04-20: Does the Universe Create Itself? 08:42: ... Wheeler’s version is a little different. He called it “negative 20 questions,” and it works like this. Unbeknownst to Bob, Alice never ... 09:48: ... came to the view that the universe was one giant game of negative 20 questions, in which the reality we observe is the only reality that ... 15:24: ... because it’s a positive energy density, just like matter. But it’s negative pressure can allow even a closed universe to expand forever. Thanks, ... 08:42: ... Wheeler’s version is a little different. He called it “negative 20 questions,” and it works like this. Unbeknownst to Bob, Alice never ... 09:48: ... came to the view that the universe was one giant game of negative 20 questions, in which the reality we observe is the only reality that is ... 08:42: ... Wheeler’s version is a little different. He called it “negative 20 questions,” and it works like this. Unbeknownst to Bob, Alice never thought of an ... 09:48: ... came to the view that the universe was one giant game of negative 20 questions, in which the reality we observe is the only reality that is consistent ... 15:24: ... because it’s a positive energy density, just like matter. But it’s negative pressure can allow even a closed universe to expand forever. Thanks, dark ...
	2022-03-23: Where Is The Center of The Universe? 04:14: ... on whether the average curvature is positive, negative, or zero, we get one of three shapes- which we call ‘closed’, ‘open’, and ... 11:01: That’s a topic worth it’s own video - although as a spoiler, the answer isn’t as obviously in the negative as you might think.
	2021-12-10: 2021 End of Year AMA! 00:02: ... there a required a type of energy that doesn't exist and that is uh a negative energy density so as far as we know energy can only be positive um ...
	2021-10-05: Why Magnetic Monopoles SHOULD Exist 00:35: ... cut the bar in half and you get a pair of electric charges - one negative and one positive, both of which have electric fields that radiate ...
	2021-09-21: How Electron Spin Makes Matter Possible 05:59: ... Mathematically, a half-cycle phase shift corresponds to putting a negative sign in front of the wavefunction. That makes sense right - because ... 06:49: ... of phase compared to its starting point. So a 360 rotation introduces a negative sign to the spinor ... 07:17: And that little negative sign is ultimately what drives the difference between fermions and bosons. 07:22: ... is the same as doing a 360 degree rotation - so that should put a negative sign in front of the combined wavefunction. And that’s the last piece of ... 12:04: ... that is just the negative of the original. So Psi(B,A) = -Psi(A,B) - swapping electrons flips the ... 05:59: ... Mathematically, a half-cycle phase shift corresponds to putting a negative sign in front of the wavefunction. That makes sense right - because adding ... 06:49: ... of phase compared to its starting point. So a 360 rotation introduces a negative sign to the spinor ... 07:17: And that little negative sign is ultimately what drives the difference between fermions and bosons. 07:22: ... is the same as doing a 360 degree rotation - so that should put a negative sign in front of the combined wavefunction. And that’s the last piece of the ...
	2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe 05:48: ... into the iron nuclei in a process called electron capture. The negatively charged electrons   merge with positively charged protons ...
	2021-08-18: How Vacuum Decay Would Destroy The Universe 02:52: ... and magnetic   fields rise and fall between positive and  negative values, but the average field value   is zero. And after the ...
	2021-08-03: How An Extreme New Star Could Change All Cosmology 17:08: ... earthism - it’s just dressed up a bit nicer. But I don’t want to get all negative at the end of the video - so instead I”ll direct you to the Professor ...
	2021-07-21: How Magnetism Shapes The Universe 01:29: The nuclear forces are short range, and the electrostatic force never adds up to much because its positive and negative charges tend to cancel it out.
	2021-04-21: The NEW Warp Drive Possibilities 04:48: We can summarize this by saying that it requires a negative energy density, which should be impossible except perhaps on the tiniest, quantum scales. 04:59: ... people talk about the drive requiring negative mass - also called exotic matter - and yeah, that would do the trick too ... 05:30: ... studies demonstrated that any superluminal warp drive MUST use negative energy ... 06:58: ... the authors: Warp drives are inertially moving shells of positive or negative energy material which enclose a `passenger' region with a flat ... 08:44: ... note that even a subluminal reaction-less warp drive would still require negative energy and an enormous amount of it for any decent sized ... 09:11: Lentz claims to have found an actual superluminal warp field solution that does NOT require the impossible negative energy densities. 09:54: When you calculate the total energy with only this component than it’s alway negative. 04:48: We can summarize this by saying that it requires a negative energy density, which should be impossible except perhaps on the tiniest, quantum scales. 05:30: ... studies demonstrated that any superluminal warp drive MUST use negative energy ... 06:58: ... the authors: Warp drives are inertially moving shells of positive or negative energy material which enclose a `passenger' region with a flat ... 08:44: ... note that even a subluminal reaction-less warp drive would still require negative energy and an enormous amount of it for any decent sized ... 09:11: Lentz claims to have found an actual superluminal warp field solution that does NOT require the impossible negative energy densities. 05:30: ... studies demonstrated that any superluminal warp drive MUST use negative energy densities. ... 09:11: Lentz claims to have found an actual superluminal warp field solution that does NOT require the impossible negative energy densities. 04:48: We can summarize this by saying that it requires a negative energy density, which should be impossible except perhaps on the tiniest, quantum scales. 06:58: ... the authors: Warp drives are inertially moving shells of positive or negative energy material which enclose a `passenger' region with a flat ... 04:59: ... people talk about the drive requiring negative mass - also called exotic matter - and yeah, that would do the trick too - ...
	2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time 05:01: ... matter   always produce this convergence. It would take negative mass or negative pressure   to cause light rays to diverge. ...
	2020-09-08: The Truth About Beauty in Physics 08:35: ... allowed the electron to have states with negative energy levels - not technically possible, but we now understand these as ...
	2020-08-10: Theory of Everything Controversies: Livestream 00:00: ... what chose the asymmetry to to break left or to the right positive or negative that's not a problem no that's not a problem why is that a problem ...
	2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing? 02:12: ... should be unchanged. We have charge conjugation, where positive and negative charges are swapped; we have parity inversion, where the universe is ... 08:00: ... to a number of different experiments, including ALPHA. There, the negatively-charged anti-protons are trapped by a combination of electric and magnetic ...
	2020-06-30: Dissolving an Event Horizon 04:10: ... the central singularity - which point-like in this case - results in a negative pressure that again resists the inward pull of ...
	2020-06-22: Building Black Holes in a Lab 05:25: ... and are separated - one escapes and one falls in, somehow converting to negative energy and so decreasing the mass of the black hole. A more technical ... 06:33: ... hole because the infalling particles-slash-vibrations themselves acquire negative energy. This effect on the black hole is called the backreaction of the ... 05:25: ... and are separated - one escapes and one falls in, somehow converting to negative energy and so decreasing the mass of the black hole. A more technical ... 06:33: ... hole because the infalling particles-slash-vibrations themselves acquire negative energy. This effect on the black hole is called the backreaction of the Hawking ...
	2020-05-27: Does Gravity Require Extra Dimensions? 11:58: This is the negative pressure due to the exclusion of quantum vacuum modes, or virtual particles, between two very closely separated plates.
	2020-05-18: Mapping the Multiverse 07:34: For one thing, the ring singularity becomes entirely repulsive - as though it had negative mass. 10:37: ... not the bizarro negative time traveling universe either - here, the laws of physics are the same ... 12:06: ... time carries a current of positive energy, while the backwards carries negative ... 13:13: ... black holes the electromagnetic field within causes massive tension, or negative pressure that produces an antigravitational ... 12:06: ... time carries a current of positive energy, while the backwards carries negative energy. ... 07:34: For one thing, the ring singularity becomes entirely repulsive - as though it had negative mass. 13:13: ... black holes the electromagnetic field within causes massive tension, or negative pressure that produces an antigravitational ... 10:37: ... not the bizarro negative time traveling universe either - here, the laws of physics are the same as ...
	2020-05-04: How We Know The Universe is Ancient 14:36: ... that does not have an event horizon, but you need the non-existent negative energy to do so and keep it open long enough to traverse. The reality is ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... the fact that as the universe gets bigger it acquires more and more negative gravitational potential energy okay and so if energy can be negative ...
	2020-04-22: Will Wormholes Allow Fast Interstellar Travel? 08:42: ... common way to think of exotic matter is anything with negative energy density. Something with negative mass could produce the required ... 09:44: ... existing in that region. The gap between the plates will then have a negative energy density relative to surroundings. Unfortunately, the Casimir ... 10:15: ... if you could create a Casimir negative energy wall in the center of a wormhole that should keep it open. ... 08:42: ... common way to think of exotic matter is anything with negative energy density. Something with negative mass could produce the required ... 09:44: ... existing in that region. The gap between the plates will then have a negative energy density relative to surroundings. Unfortunately, the Casimir effect is ... 10:15: ... if you could create a Casimir negative energy wall in the center of a wormhole that should keep it open. Unfortunately ... 08:42: ... common way to think of exotic matter is anything with negative energy density. Something with negative mass could produce the required negative ... 09:44: ... existing in that region. The gap between the plates will then have a negative energy density relative to surroundings. Unfortunately, the Casimir effect is very, ... 10:15: ... the wormhole would have to pass through this region of extremely high negative energy density, which probably wouldn’t be healthy. Matt Visser, who literally wrote the ... 08:42: ... energy density. Something with negative mass could produce the required negative gravity. But actually “exotic matter” is a broader class of weirdness than that. ...
	2020-03-24: How Black Holes Spin Space Time 09:37: ... Kerr metric of the ergosphere allows one half of the object to acquire negative energy, which is transferred to the black hole, while the other half ...
	2020-02-11: Are Axions Dark Matter? 01:05: ... axes. Another example is flipping the charges of particles - positive to negative and vice versa - most of the equations of physics hold under that flip. ... 03:02: ... exhibit an electric field like you’d get from a pair of positive and negative charges - an electric dipole field. Our very sensitive measurements have ...
	2019-12-09: The Doomsday Argument 14:06: ... finite or infinite because it may be that there's a slight positive or negative curvature just beyond the sensitivity of our ... 14:02: If it turns out to the universe is negatively curved then well it's infinite.
	2019-12-02: Is The Universe Finite? 04:26: Rapid expansion tends to give negative curvature and open the universe - make it infinite. 04:56: ... curvature COULD have been very slightly positive or very slightly negative - just as the surface of the Earth appears flat if you’re standing on ... 04:26: Rapid expansion tends to give negative curvature and open the universe - make it infinite. 03:36: Then there’s 2) the negatively curved universe, analogous to a hyperbolic plane - an infinite saddle shape.
	2019-10-21: Is Time Travel Impossible? 05:17: We need to counter gravity, and to do that we need another probably-non-existent form of mass – negative mass – also referred to as exotic matter. 05:27: As far as we know, mass can only take on positive, real values, so a requirement of negative mass seems a non-starter. 05:37: Really what we need to open the wormhole is a negative energy density. 05:51: However there’s no clear path to translating this to a large-scale negative energy distribution that could keep a wormhole open. 05:59: And in fact we'd need entire planets – perhaps entire stars converted to negative energy to do this. 06:05: Some other time travel options also involve using negative energy densities - for example the Alcubierre warp drive, which we already covered. 06:19: But is negative mass-energy as much of a non-starter as imaginary mass? 06:36: They’re a set of requirements that do things like prevent negative energies and enforce energy conservation. 06:58: And as it turns out, there may be other ways to build time machines without either negative or imaginary masses. 07:55: Stephen Hawking showed that unless the cylinder is infinitely long this doesn’t work – unless you also modify the spacetime with negative energy. 06:36: They’re a set of requirements that do things like prevent negative energies and enforce energy conservation. 05:37: Really what we need to open the wormhole is a negative energy density. 05:51: However there’s no clear path to translating this to a large-scale negative energy distribution that could keep a wormhole open. 05:59: And in fact we'd need entire planets – perhaps entire stars converted to negative energy to do this. 06:05: Some other time travel options also involve using negative energy densities - for example the Alcubierre warp drive, which we already covered. 07:55: Stephen Hawking showed that unless the cylinder is infinitely long this doesn’t work – unless you also modify the spacetime with negative energy. 06:05: Some other time travel options also involve using negative energy densities - for example the Alcubierre warp drive, which we already covered. 05:37: Really what we need to open the wormhole is a negative energy density. 05:51: However there’s no clear path to translating this to a large-scale negative energy distribution that could keep a wormhole open. 05:17: We need to counter gravity, and to do that we need another probably-non-existent form of mass – negative mass – also referred to as exotic matter. 05:27: As far as we know, mass can only take on positive, real values, so a requirement of negative mass seems a non-starter. 06:19: But is negative mass-energy as much of a non-starter as imaginary mass?
	2019-08-26: How To Become an Astrophysicist + Challenge Question! 10:46: ... increased by a factor of 10 to the power of 26 Every 10 to the power of negative 32 seconds and an extra credit question at that rate How close to our ...
	2019-08-06: What Caused the Big Bang? 03:48: ... by a factor of 10 to the power of 25 in less than 10 to the power of negative 30 ...
	2019-07-18: Did Time Start at the Big Bang? 01:56: ... observational evidence that the time before around 10 to the power of negative 32 seconds Included a period of extremely rapid expansion called cosmic ...
	2019-07-01: Thorium and the Future of Nuclear Energy 15:29: ... that this whole black hole killing star formation thing seems like a negative feedback Interaction more gas equals more active black hole equals more ...
	2019-04-10: The Holographic Universe Explained 11:15: While the original space was flat, the new space had negative curvature – it was a hyperbolic, anti-de Sitter or AdS space. 16:40: KI9 asks whether the things we learn from AdS/CFT are applicable to the universe we live in given that our universe doesn't have negative curvature. 16:50: ... we don't know for sure that it doesn't have negative curvature - just that any curvature - negative or positive - is very ... 11:15: While the original space was flat, the new space had negative curvature – it was a hyperbolic, anti-de Sitter or AdS space. 16:40: KI9 asks whether the things we learn from AdS/CFT are applicable to the universe we live in given that our universe doesn't have negative curvature. 16:50: ... we don't know for sure that it doesn't have negative curvature - just that any curvature - negative or positive - is very weak compared ... 13:41: ... represent THIS universe, because our universe doesn’t appear to be negatively curved AdS space, nor does it have 4 spatial dimensions as in ...
	2019-04-03: The Edge of an Infinite Universe 03:25: Finally there’s the universe with negative curvature, and the 2-D analog of that is the hyperbolic surface, like an infinite saddle or pringle. 17:01: ... energy is conserved and that dark energy is created from the increasing negative potential energy of the cosmic gravitational field, but I think at that ... 03:25: Finally there’s the universe with negative curvature, and the 2-D analog of that is the hyperbolic surface, like an infinite saddle or pringle. 17:01: ... energy is conserved and that dark energy is created from the increasing negative potential energy of the cosmic gravitational field, but I think at that level this ... 09:16: For the holographic principle we need the infinite boundary of a negatively-curved universe – an anti-de Sitter, AdS universe.
	2019-03-28: Could the Universe End by Tearing Apart Every Atom? 03:05: ... density and no real pressure leaves the right side of the equation negative so negative acceleration matter on its own can only cause deceleration ... 04:32: ... definition of the cosmological constant. So now the pressure term is A, negative and B because of this factor of 3 it's a bigger influence than the ... 06:03: ... the limit: What if we make the equation of state parameter smaller than negative ... 11:35: ... first, it seems too much of a coincidence that it should be so close to negative one without being negative ... 12:11: ... violates the same energy conditions of general relativity that prohibit negative mass and time ... 12:40: ... quasars hints at an equation of state parameter slightly less than negative 1 well they're not yet with enough significance to overturn all other ... 04:32: ... influence than the density so this whole party in the brackets becomes negative - so, emo - that cancels this negative sign and makes the right side of ... 12:40: ... quasars hints at an equation of state parameter slightly less than negative 1 well they're not yet with enough significance to overturn all other ... 03:05: ... and no real pressure leaves the right side of the equation negative so negative acceleration matter on its own can only cause deceleration the expansion rate what ... 12:11: ... violates the same energy conditions of general relativity that prohibit negative mass and time ... 04:32: ... party in the brackets becomes negative - so, emo - that cancels this negative sign and makes the right side of the equation ...
	2019-03-06: The Impossibility of Perpetual Motion Machines 09:54: ... to come up with a perpetual motion machine based on the funky notion of negative ... 10:06: According to some interpretations, negative mass should be attracted to positive mass, but positive mass should be repelled by negative mass. 10:15: The result is that a positive and negative mass should accelerate indefinitely, potentially powering an infinite energy device. 10:58: We have a rare non-dynamo device from Adrien Romeo, who uses cogs with negative and positive mass teeth. 09:54: ... to come up with a perpetual motion machine based on the funky notion of negative mass. ... 10:06: According to some interpretations, negative mass should be attracted to positive mass, but positive mass should be repelled by negative mass. 10:15: The result is that a positive and negative mass should accelerate indefinitely, potentially powering an infinite energy device.
	2019-02-20: Secrets of the Cosmic Microwave Background 07:42: ... effect On the other hand an expanding universe with no energy would have negative curvature So a flat universe must have exactly the right amount of ...
	2019-02-07: Sound Waves from the Beginning of Time 13:19: Today, it's the 'Crisis in cosmology' and 'Negative mass perpetual motion' episodes. 15:16: Ergo, time will prove negative mass' existence. 16:03: flux_capacitor notes an alternate model for how negative mass might behave. 16:08: In so-called bimetric gravity, you can have positive and negative masses, but each is described by its own set of Einstein field equations. 16:18: That's kind of like having parallel spacetimes, one with positive and one with negative masses, which can still interact gravitationally. 16:26: ... get the crazy runaway motion that occurs if you put both positive and negative masses in the same ... 13:19: Today, it's the 'Crisis in cosmology' and 'Negative mass perpetual motion' episodes. 15:16: Ergo, time will prove negative mass' existence. 16:03: flux_capacitor notes an alternate model for how negative mass might behave. 15:16: Ergo, time will prove negative mass' existence. 13:19: Today, it's the 'Crisis in cosmology' and 'Negative mass perpetual motion' episodes. 16:08: In so-called bimetric gravity, you can have positive and negative masses, but each is described by its own set of Einstein field equations. 16:18: That's kind of like having parallel spacetimes, one with positive and one with negative masses, which can still interact gravitationally. 16:26: ... get the crazy runaway motion that occurs if you put both positive and negative masses in the same ...
	2019-01-30: Perpetual Motion From Negative Mass? 00:31: Matter with negative mass - has long been the pipedream of science fiction writers, futurists, and certain rather. 00:59: And we also recently covered a very new use for negative mass: as “dark fluid”, a proposed explanation for both dark matter and dark energy. 01:10: That episode really got me thinking about the subtleties of negative mass and how it should really behave gravitationally. 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. 04:45: A repulsive force on a negative mass becomes an attractive force and vice versa. 04:51: ... this in the dark fluid episode, but to recap: this suggests that two negative masses produce an attractive force which actually drives them ... 05:02: Even weirder, a positive mass should attract a negative mass while at the same time being repelled by it. 05:08: A negative mass apple would still fall to the Earth, and you wouldn’t notice Earth’s infinitesimal repulsion from the apple. 05:17: But put equal positive and negative masses next to each other and they should accelerate uniformly forever. 07:13: That should mean that a negative mass behaves the same in a gravitational field as a positive mass. 07:50: This suggests that a positive gravitational field attracts everything, including negative masses. 07:57: So what about negative gravitational fields? 08:01: Negative mass causes negative curvature, which in our sheet analogy looks like pulling the sheet up. 08:13: That suggests that everything, regardless of mass, should be repelled from a negative mass. 08:21: It suggests that positive masses attract everything and negative masses repel everything, including each other. 08:29: A positive mass attracts and is repelled by a negative mass. 08:51: So a positive and a negative mass apple placed side by side should chase each other across the cosmos, accelerating forever. 09:06: ... mass apple gains positive momentum and energy as it speeds up, while the negative mass apple balances that with negative momentum and negative ... 09:37: They are a set of conditions against negative energies that seem necessary in order for general relativity to describe a sensible universe. 09:46: ... fact the mere existence of negative mass breaks certain energy conditions, but the prospect of a bottomless ... 10:03: In particular, with the idea of negative and positive masses accelerating each other to infinite energies? 10:18: In this case, the basic nature of the positive versus negative gravitational fields – the way the fabric of spacetime gets stretched has to be right. 10:26: Much less clear is the way a negative mass responds to an applied force. 10:39: We then happily plugged our negative inertial mass into Newton’s 2nd law to get acceleration. 11:42: The real nonsense seems to be the idea of negative inertial mass. 11:48: By comparison, negative gravitational mass is kind of ok. 11:52: ... Negative inertial mass implies flipping the sign of the acceleration when any ... 12:28: ... if we conclude that negative inertial mass can’t exist and we want to save the equivalence principle ... 12:55: Some say negative mass can’t exist, some say it can. 12:59: ... say that, if they do, then positive mass always attracts while negative mass always repels, while others say that like mass signs always attract ... 13:18: ... it is: assuming that positive mass both attracts and is repelled by negative mass, come up with a way to use a pair of infinitely accelerating ... 13:59: Make the subject line negative mass challenge question. 03:28: In fact, in Newtonian gravity, any like masses – both positive or both negative - should produce a mutually attractive force. 08:01: Negative mass causes negative curvature, which in our sheet analogy looks like pulling the sheet up. 09:37: They are a set of conditions against negative energies that seem necessary in order for general relativity to describe a sensible universe. 09:06: ... while the negative mass apple balances that with negative momentum and negative energy. ... 09:46: ... energy conditions, but the prospect of a bottomless well of infinite negative energy breaks them all very badly, and has implications for the stability of ... 07:57: So what about negative gravitational fields? 10:18: In this case, the basic nature of the positive versus negative gravitational fields – the way the fabric of spacetime gets stretched has to be right. 11:48: By comparison, negative gravitational mass is kind of ok. 07:57: So what about negative gravitational fields? 10:18: In this case, the basic nature of the positive versus negative gravitational fields – the way the fabric of spacetime gets stretched has to be right. 11:48: By comparison, negative gravitational mass is kind of ok. 04:37: Newton’s second law seems to say that negative inertial masses respond oppositely to the applied force. 10:39: We then happily plugged our negative inertial mass into Newton’s 2nd law to get acceleration. 11:42: The real nonsense seems to be the idea of negative inertial mass. 11:52: ... Negative inertial mass implies flipping the sign of the acceleration when any force is ... 12:28: ... if we conclude that negative inertial mass can’t exist and we want to save the equivalence principle and the ... 10:39: We then happily plugged our negative inertial mass into Newton’s 2nd law to get acceleration. 11:42: The real nonsense seems to be the idea of negative inertial mass. 11:52: ... Negative inertial mass implies flipping the sign of the acceleration when any force is applied ... 12:28: ... if we conclude that negative inertial mass can’t exist and we want to save the equivalence principle and the rest ... 04:37: Newton’s second law seems to say that negative inertial masses respond oppositely to the applied force. 00:31: Matter with negative mass - has long been the pipedream of science fiction writers, futurists, and certain rather. 00:59: And we also recently covered a very new use for negative mass: as “dark fluid”, a proposed explanation for both dark matter and dark energy. 01:10: That episode really got me thinking about the subtleties of negative mass and how it should really behave gravitationally. 04:45: A repulsive force on a negative mass becomes an attractive force and vice versa. 05:02: Even weirder, a positive mass should attract a negative mass while at the same time being repelled by it. 05:08: A negative mass apple would still fall to the Earth, and you wouldn’t notice Earth’s infinitesimal repulsion from the apple. 07:13: That should mean that a negative mass behaves the same in a gravitational field as a positive mass. 08:01: Negative mass causes negative curvature, which in our sheet analogy looks like pulling the sheet up. 08:13: That suggests that everything, regardless of mass, should be repelled from a negative mass. 08:29: A positive mass attracts and is repelled by a negative mass. 08:51: So a positive and a negative mass apple placed side by side should chase each other across the cosmos, accelerating forever. 09:06: ... mass apple gains positive momentum and energy as it speeds up, while the negative mass apple balances that with negative momentum and negative ... 09:46: ... fact the mere existence of negative mass breaks certain energy conditions, but the prospect of a bottomless well ... 10:26: Much less clear is the way a negative mass responds to an applied force. 12:28: ... equivalence principle and the rest of physics, we need to conclude that negative mass of any type can’t ... 12:55: Some say negative mass can’t exist, some say it can. 12:59: ... say that, if they do, then positive mass always attracts while negative mass always repels, while others say that like mass signs always attract and ... 13:18: ... it is: assuming that positive mass both attracts and is repelled by negative mass, come up with a way to use a pair of infinitely accelerating positive and ... 13:59: Make the subject line negative mass challenge question. 00:31: Matter with negative mass - has long been the pipedream of science fiction writers, futurists, and certain rather. 05:08: A negative mass apple would still fall to the Earth, and you wouldn’t notice Earth’s infinitesimal repulsion from the apple. 08:51: So a positive and a negative mass apple placed side by side should chase each other across the cosmos, accelerating forever. 09:06: ... mass apple gains positive momentum and energy as it speeds up, while the negative mass apple balances that with negative momentum and negative ... 07:13: That should mean that a negative mass behaves the same in a gravitational field as a positive mass. 09:46: ... fact the mere existence of negative mass breaks certain energy conditions, but the prospect of a bottomless well of ... 13:59: Make the subject line negative mass challenge question. 13:18: ... come up with a way to use a pair of infinitely accelerating positive and negative mass objects to build a perpetual motion ... 10:26: Much less clear is the way a negative mass responds to an applied force. 03:19: OK, so how do negative masses work in Newtonian mechanics? 04:51: ... this in the dark fluid episode, but to recap: this suggests that two negative masses produce an attractive force which actually drives them ... 05:17: But put equal positive and negative masses next to each other and they should accelerate uniformly forever. 07:50: This suggests that a positive gravitational field attracts everything, including negative masses. 08:21: It suggests that positive masses attract everything and negative masses repel everything, including each other. 04:51: ... this in the dark fluid episode, but to recap: this suggests that two negative masses produce an attractive force which actually drives them ... 08:21: It suggests that positive masses attract everything and negative masses repel everything, including each other. 03:19: OK, so how do negative masses work in Newtonian mechanics? 09:06: ... energy as it speeds up, while the negative mass apple balances that with negative momentum and negative ... 00:13: Because you could use negative-mass apples to build warp drives, travel in time, and construct a perpetual motion machine.
	2019-01-24: The Crisis in Cosmology 13:26: ...about negative mass dark fluid... 14:06: ...will give the exact opposite results if dark matter is due to this negative mass fluid... 14:48: Marik Zilberman's distaste for negative masses... 16:31: And a negative mass particle, moving backwards in time,... 13:26: ...about negative mass dark fluid... 14:06: ...will give the exact opposite results if dark matter is due to this negative mass fluid... 16:31: And a negative mass particle, moving backwards in time,... 13:26: ...about negative mass dark fluid... 14:06: ...will give the exact opposite results if dark matter is due to this negative mass fluid... 16:31: And a negative mass particle, moving backwards in time,... 14:48: Marik Zilberman's distaste for negative masses...
	2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe 03:02: ... how does this work in our Antion on a clock well antimatter atoms have negatively charged nuclei which means their nuclear magnetic fields point in the ...
	2019-01-09: Are Dark Matter And Dark Energy The Same? 00:32: And it’s pretty wild: negative mass particles continuously popping into existence between the galaxies. 00:58: Farnes 2018, “A unifying theory of dark energy and dark matter: Negative masses and matter creation within a modified Lambda-CDM framework”. 02:53: But here’s the punchline: if empty space has a constant, positive energy density then it also has a negative pressure. 03:02: For obscure reasons that we delve into those episodes, negative pressure produces an anti-gravitational effect. 03:10: ... positive energy density gives it a positive gravitational effect but its negative pressure is ... 03:58: He tried to do this in very different way: with negative mass. 04:15: So what about negative masses? 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. 04:45: Two negative masses should cancel each other’s signs so also give you an attractive force. 04:51: But with one negative and one positive mass, the final force of gravity has the opposite sign - that makes it repulsive. 05:29: For a negative mass, this equation suggests that acceleration is in the opposite direction to the applied force. 05:36: Push a negative mass away from you it’ll move towards you, pull it and it’ll move away. 05:45: So Farnes argues that the “attractive” gravitational force between two negative masses should actually drive them apart. 05:56: At the same time, the repulsive force between a negative and positive mass should repel the positive and attract the negative mass. 06:15: The author uses these ideas about the interactions of negative and positive mass particles to create an N-body simulation. 06:22: ... he programs a virtual universe into his computer with both positive and negative mass particles, along with his interpretations of Newton’s ... 06:32: Those simulations showed that galaxies do indeed spin more quickly when surrounded by negative mass particles. 06:39: ... is because the positive mass in the galaxy attracts a halo of negative mass, but at the same time that positive mass is repelled inwards by the ... 06:59: To make the same negative mass stuff also emulate dark energy requires an extra gigantic assumption. 07:07: The problem is that our negative masses will dilute away as the universe expands. 07:12: To fix this, Farnes proposes that these negative masses are constantly created as the universe expands. 07:20: That keeps the density of negative masses constant, even as the density of positive masses falls. 07:26: The result is a very diffuse negative mass fluid that fills the universe and constantly replenishes itself. 07:57: And that a positive Lambda results in an antigravitational negative pressure? 08:02: Well a constant NEGATIVE energy density – like the one proposed by Farnes, gives a negative cosmological constant. 08:18: ... really the analog of Newton’s law of gravity for the whole cosmos, this negative mass fluid – as a negative cosmological constant – has the same ... 08:35: The direct effect is repulsive – antigravitational – which I guess was the original motivation for using negative matter. 08:50: ... Farnes acknowledges that his proposal gives a negative cosmological constant that ultimately decelerates, but there’s some ... 09:06: And yet a negative cosmological constant gives you an extremely different universe. 09:10: Dr. Farnes does a couple of calculations that are consistent with a negative lambda. 09:15: ... – that’s this thing - to correctly conclude that a universe with a negative cosmological constant should have a sinusoidal scale ... 09:43: The negative cosmological constant is the source of that slow-down and for the subsequent accelerating collapse. 09:55: Plugging negative masses into general relativity allows you to break causality. 10:07: This is a strong indication that negative mass can’t exist. 10:16: Does a universe with a constant negative energy density fit the observations? 10:48: ... a negative cosmological constant and this sinusoidal expansion, any slowdown ... 11:00: ... an age for his universe of 13.8 billion years assuming a very low negative energy density, but that really just corresponds to the very first ... 12:59: ... all, it’s easy to get confused by the compounding negatives in what is probably not a negative mass, anti-gravitational, positive ... 08:02: Well a constant NEGATIVE energy density – like the one proposed by Farnes, gives a negative cosmological constant. 08:18: ... law of gravity for the whole cosmos, this negative mass fluid – as a negative cosmological constant – has the same competing effects as regular dark energy, but in ... 08:50: ... Farnes acknowledges that his proposal gives a negative cosmological constant that ultimately decelerates, but there’s some contradiction ... 09:06: And yet a negative cosmological constant gives you an extremely different universe. 09:15: ... – that’s this thing - to correctly conclude that a universe with a negative cosmological constant should have a sinusoidal scale ... 09:43: The negative cosmological constant is the source of that slow-down and for the subsequent accelerating collapse. 10:48: ... a negative cosmological constant and this sinusoidal expansion, any slowdown happens near the ... 08:02: Well a constant NEGATIVE energy density – like the one proposed by Farnes, gives a negative cosmological constant. 08:18: ... law of gravity for the whole cosmos, this negative mass fluid – as a negative cosmological constant – has the same competing effects as regular dark energy, but in the ... 08:50: ... Farnes acknowledges that his proposal gives a negative cosmological constant that ultimately decelerates, but there’s some contradiction because he ... 09:06: And yet a negative cosmological constant gives you an extremely different universe. 09:15: ... – that’s this thing - to correctly conclude that a universe with a negative cosmological constant should have a sinusoidal scale ... 09:43: The negative cosmological constant is the source of that slow-down and for the subsequent accelerating collapse. 10:48: ... a negative cosmological constant and this sinusoidal expansion, any slowdown happens near the turnaround ... 08:02: Well a constant NEGATIVE energy density – like the one proposed by Farnes, gives a negative cosmological constant. 10:16: Does a universe with a constant negative energy density fit the observations? 11:00: ... an age for his universe of 13.8 billion years assuming a very low negative energy density, but that really just corresponds to the very first straight ... 08:02: Well a constant NEGATIVE energy density – like the one proposed by Farnes, gives a negative cosmological constant. 10:16: Does a universe with a constant negative energy density fit the observations? 11:00: ... an age for his universe of 13.8 billion years assuming a very low negative energy density, but that really just corresponds to the very first straight part in the ... 09:10: Dr. Farnes does a couple of calculations that are consistent with a negative lambda. 00:32: And it’s pretty wild: negative mass particles continuously popping into existence between the galaxies. 03:58: He tried to do this in very different way: with negative mass. 05:29: For a negative mass, this equation suggests that acceleration is in the opposite direction to the applied force. 05:36: Push a negative mass away from you it’ll move towards you, pull it and it’ll move away. 05:56: At the same time, the repulsive force between a negative and positive mass should repel the positive and attract the negative mass. 06:22: ... he programs a virtual universe into his computer with both positive and negative mass particles, along with his interpretations of Newton’s ... 06:32: Those simulations showed that galaxies do indeed spin more quickly when surrounded by negative mass particles. 06:39: ... is because the positive mass in the galaxy attracts a halo of negative mass, but at the same time that positive mass is repelled inwards by the ... 06:59: To make the same negative mass stuff also emulate dark energy requires an extra gigantic assumption. 07:26: The result is a very diffuse negative mass fluid that fills the universe and constantly replenishes itself. 08:18: ... really the analog of Newton’s law of gravity for the whole cosmos, this negative mass fluid – as a negative cosmological constant – has the same competing ... 10:07: This is a strong indication that negative mass can’t exist. 12:59: ... to get confused by the compounding negatives in what is probably not a negative mass, anti-gravitational, positive pressure, anti-deSitter space ... 07:26: The result is a very diffuse negative mass fluid that fills the universe and constantly replenishes itself. 08:18: ... really the analog of Newton’s law of gravity for the whole cosmos, this negative mass fluid – as a negative cosmological constant – has the same competing effects ... 00:32: And it’s pretty wild: negative mass particles continuously popping into existence between the galaxies. 06:22: ... he programs a virtual universe into his computer with both positive and negative mass particles, along with his interpretations of Newton’s ... 06:32: Those simulations showed that galaxies do indeed spin more quickly when surrounded by negative mass particles. 06:59: To make the same negative mass stuff also emulate dark energy requires an extra gigantic assumption. 00:58: Farnes 2018, “A unifying theory of dark energy and dark matter: Negative masses and matter creation within a modified Lambda-CDM framework”. 04:15: So what about negative masses? 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. 04:45: Two negative masses should cancel each other’s signs so also give you an attractive force. 05:45: So Farnes argues that the “attractive” gravitational force between two negative masses should actually drive them apart. 07:07: The problem is that our negative masses will dilute away as the universe expands. 07:12: To fix this, Farnes proposes that these negative masses are constantly created as the universe expands. 07:20: That keeps the density of negative masses constant, even as the density of positive masses falls. 09:55: Plugging negative masses into general relativity allows you to break causality. 07:20: That keeps the density of negative masses constant, even as the density of positive masses falls. 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. 08:35: The direct effect is repulsive – antigravitational – which I guess was the original motivation for using negative matter. 02:53: But here’s the punchline: if empty space has a constant, positive energy density then it also has a negative pressure. 03:02: For obscure reasons that we delve into those episodes, negative pressure produces an anti-gravitational effect. 03:10: ... positive energy density gives it a positive gravitational effect but its negative pressure is ... 07:57: And that a positive Lambda results in an antigravitational negative pressure? 03:02: For obscure reasons that we delve into those episodes, negative pressure produces an anti-gravitational effect. 11:57: If you replace both dark energy and dark matter with negative-energy stuff, then the universe becomes negatively curved. 12:59: ... all, it’s easy to get confused by the compounding negatives in what is probably not a negative mass, anti-gravitational, positive ...
	2018-12-20: Why String Theory is Wrong 03:43: Shrink it down to around 10 to the power of negative thirtieth of a meter, so it's only visible to things equally miniscule.
	2018-12-12: Quantum Physics in a Mirror Universe 00:02: ... transformation followed by a flipping of electric charge positive to negative and vice-versa and a reversal in the direction of the flow of time will ...
	2018-09-20: Quantum Gravity and the Hardest Problem in Physics 05:57: ... to an accuracy better than a Planck length around 10 to the power of negative 35 of a meter, the amount of energy you would need to put into that ... 06:46: Try to measure any time period shorter than 10 to the power of negative 43 seconds, the Planck time, and boom-- black hole. 05:57: ... to an accuracy better than a Planck length around 10 to the power of negative 35 of a meter, the amount of energy you would need to put into that region ... 06:46: Try to measure any time period shorter than 10 to the power of negative 43 seconds, the Planck time, and boom-- black hole.
	2018-09-12: How Much Information is in the Universe? 02:48: ... smallest meaningful measure of distance, at around 1.6 times 10 to the negative 35 ...
	2018-08-30: Is There Life on Mars? 06:12: Three of the tests were negative, but the fourth was positive. 12:16: With enough of this stuff, the freezing point of water could be as low as negative 75 Celsius.
	2018-07-04: Will A New Neutrino Change The Standard Model? 03:20: So an electron has a charge of negative 1 and an antielectron has a charge of plus 1. 05:05: ... example, both left and right chiral negatively charged electrons have their own positively charged antimatter ...
	2018-06-20: The Black Hole Information Paradox 13:20: ... electric charge within the black hole produces a negative pressure that actually halts the cascade of space within the black hole ...
	2018-06-13: What Survives Inside A Black Hole? 08:15: ... quickly attract particles with the opposite charge until positive and negative charges within the black hole balance out and the black hole becomes ...
	2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!) 04:19: ... as a struggle for entropy, well, more accurately, against entropy or for negative ... 04:29: Erwin Schrodinger, in his 1944 book, "What is Life," describes life as a process feeding on negative entropy. 04:19: ... as a struggle for entropy, well, more accurately, against entropy or for negative entropy. ... 04:29: Erwin Schrodinger, in his 1944 book, "What is Life," describes life as a process feeding on negative entropy.
	2018-04-04: The Unruh Effect 06:20: ... here they also lead to a mixing of positive and negative frequency modes in the accelerating frame of reference, which leads to ...
	2018-03-15: Hawking Radiation 03:32: One way that quantum fields are very different to guitar strings is they can have both positive and negative frequencies. 03:39: A negative frequency can be thought of as a mode that travels backwards in time and can be interpreted as corresponding to antimatter. 03:51: ... field is in a vacuum state, there's a balance between positive and negative frequency modes, which you can crudely think of as a balance between ... 06:30: They describe a sort of mixing of the positive and negative frequency vibrational modes that are caused by that curved space. 08:13: So Hawking's math describes splitting or mixing of these pure positive and negative frequency modes. 10:05: We can think about positive and negative frequency modes being mixed due to scattering, perhaps, by the as yet undiscovered graviton. 03:32: One way that quantum fields are very different to guitar strings is they can have both positive and negative frequencies. 03:39: A negative frequency can be thought of as a mode that travels backwards in time and can be interpreted as corresponding to antimatter. 03:51: ... field is in a vacuum state, there's a balance between positive and negative frequency modes, which you can crudely think of as a balance between virtual ... 06:30: They describe a sort of mixing of the positive and negative frequency vibrational modes that are caused by that curved space. 08:13: So Hawking's math describes splitting or mixing of these pure positive and negative frequency modes. 10:05: We can think about positive and negative frequency modes being mixed due to scattering, perhaps, by the as yet undiscovered graviton. 03:51: ... field is in a vacuum state, there's a balance between positive and negative frequency modes, which you can crudely think of as a balance between virtual matter and ... 08:13: So Hawking's math describes splitting or mixing of these pure positive and negative frequency modes. 10:05: We can think about positive and negative frequency modes being mixed due to scattering, perhaps, by the as yet undiscovered graviton. 06:30: They describe a sort of mixing of the positive and negative frequency vibrational modes that are caused by that curved space.
	2017-11-08: Zero-Point Energy Demystified 05:02: ... is that the reduction of energy between Casimir plates can be considered negative energy and so could be useful for all of those wonderful things that ... 05:18: Well, if we define the average vacuum energy as 0, then the Casimir Effect produces negative energy. 05:36: That means the vacuum energy between Casimir plates still produces positive spatial curvature, not the negative curvature required for warp drives. 05:02: ... is that the reduction of energy between Casimir plates can be considered negative energy and so could be useful for all of those wonderful things that negative ... 05:18: Well, if we define the average vacuum energy as 0, then the Casimir Effect produces negative energy.
	2017-11-02: The Vacuum Catastrophe 06:07: ... positive zero point energies, then perhaps others have extremely large negative zero point energies that cancel them ... 07:31: Assuming vacuum energy is to blame, dark energy weighs in at 10 to the power of negative 8 ergs per centimeter cubed. 07:59: ... or a vacuum energy of exactly 0 if we assume symmetry of positive and negative zero points between different fields, but a very small non-zero vacuum ... 08:19: Gigantic positive and gigantic negative zero point energies would need to cancel each other out down to a very tiny non-zero value. 07:31: Assuming vacuum energy is to blame, dark energy weighs in at 10 to the power of negative 8 ergs per centimeter cubed.
	2017-10-19: The Nature of Nothing 14:10: Flo Striker was wondering about the idea of negative kelvin temperatures. 14:17: It's not very intuitive, though, because having a negative temperature means the substance is hotter than any substance with a positive temperature. 14:38: But at negative temperatures, most particles are excited towards the highest possible energy states. 14:52: So why call them negative temperature? 15:29: So if temperature is change in thermal energy over entropy, then temperature is negative. 14:10: Flo Striker was wondering about the idea of negative kelvin temperatures. 14:17: It's not very intuitive, though, because having a negative temperature means the substance is hotter than any substance with a positive temperature. 14:52: So why call them negative temperature? 14:38: But at negative temperatures, most particles are excited towards the highest possible energy states. 14:44: This means that a negative-temperature substance can only lose thermal energy to a positive-temperature substance, not gain it.
	2017-10-11: Absolute Cold 00:42: This state of absolute cold is the zero point in the Kelvin temperature scale corresponding to negative 273.15 Celsius.
	2017-08-10: The One-Electron Universe 03:58: ... example, if a negatively charged electron is moving to the left, it produces some current, I. ...
	2017-07-26: The Secrets of Feynman Diagrams 05:04: Similarly, if a photon creates a negatively charged electron, it must also create a positively charged positron.
	2017-06-28: The First Quantum Field Theory 13:50: ... Mr. Diagrams points out, the resulting Klein Gordon equation gives negative energy solutions just like the Dirac equation does, but Schrodinger ...
	2017-06-21: Anti-Matter and Quantum Relativity 06:30: It allowed electrons to exist in states of negative energy. 06:38: ... energy as light infinitely, and sink lower and lower, to infinite negative energy ... 07:06: These electrons occupy all of the negative energy states, all the way from negative infinity, up to zero. 09:13: Paul Dirac's negative energy solutions describe anti-matter, not holes in the Dirac sea. 10:06: They are two sides of the same coin, positive and negative energy solutions of the same type of vibration in the electron field. 10:37: It's not negative mass despite this negative energy description. 06:30: It allowed electrons to exist in states of negative energy. 06:38: ... energy as light infinitely, and sink lower and lower, to infinite negative energy ... 07:06: These electrons occupy all of the negative energy states, all the way from negative infinity, up to zero. 09:13: Paul Dirac's negative energy solutions describe anti-matter, not holes in the Dirac sea. 10:06: They are two sides of the same coin, positive and negative energy solutions of the same type of vibration in the electron field. 10:37: It's not negative mass despite this negative energy description. 09:13: Paul Dirac's negative energy solutions describe anti-matter, not holes in the Dirac sea. 10:06: They are two sides of the same coin, positive and negative energy solutions of the same type of vibration in the electron field. 06:38: ... energy as light infinitely, and sink lower and lower, to infinite negative energy states. ... 07:06: These electrons occupy all of the negative energy states, all the way from negative infinity, up to zero. 10:37: It's not negative mass despite this negative energy description.
	2017-04-05: Telescopes on the Moon 11:33: ... singularity is expected to produce an antigravitational effect through negative pressure, in a way that's mathematically similar to dark ...
	2017-03-29: How Time Becomes Space Inside a Black Hole 01:34: If one event causes a second event, the spacetime interval must be 0 or negative. 02:00: In fact forward temporal evolution requires a negative spacetime interval. 02:05: In flat space time, that negative sign in front of the delta t drives that forward evolution. 03:48: A negative spacetime interval still means causal movement. 04:01: Then both of these brackets become negative. 04:04: The entire delta r stuff is now negative. 04:36: In the mathematics the coordinate r, which once represented distance, now grants the negative sign needed to maintain your causal flow. 04:50: Meanwhile the coordinate previously known as time, t, lost its negative sign and become space-like. 02:05: In flat space time, that negative sign in front of the delta t drives that forward evolution. 04:36: In the mathematics the coordinate r, which once represented distance, now grants the negative sign needed to maintain your causal flow. 04:50: Meanwhile the coordinate previously known as time, t, lost its negative sign and become space-like. 04:36: In the mathematics the coordinate r, which once represented distance, now grants the negative sign needed to maintain your causal flow. 02:00: In fact forward temporal evolution requires a negative spacetime interval. 03:48: A negative spacetime interval still means causal movement. 02:00: In fact forward temporal evolution requires a negative spacetime interval. 03:48: A negative spacetime interval still means causal movement.
	2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer 03:37: ... we write the spacetime interval for flat space with a negative sign in front of the time part, then changes in your space interval have ...
	2017-02-02: The Geometry of Causality 09:08: ... way I define the spacetime interval, it becomes increasingly negative in the forward time direction, so we can represent this as a valley ...
	2016-10-12: Black Holes from the Dawn of Time 12:16: ... also a dipole, meaning it has more positive charge on one side and more negative on the ...
	2016-05-25: Is an Ice Age Coming? 12:01: Last week, we wrapped up our conversation on dark energy, talking about anti-gravity, negative pressure, and conservation of energy.
	2016-05-18: Anti-gravity and the True Nature of Dark Energy 03:58: That's this negative sign here. 04:00: Positive acceleration outwards, negative inwards. 06:01: So it looks like as long as there's anything in the universe whatsoever, that whole right side is negative. 08:10: It's negative. 08:12: A negative p here cancels this minus sign and can result in outward acceleration. 08:24: It's negative pressure. 08:26: What does negative pressure even mean? 08:33: So negative pressure would pull inwards. 08:49: Negative pressure pulls in. 09:05: The direct effect of dark energy's negative pressure doesn't do anything, because that negative pressure is the same everywhere in the universe. 09:14: But even though the negative pressure has no direct effect, it has its relativistic effect. 09:19: Relativistically, negative pressure has to do the opposite of positive pressure and results in anti-gravity, because math. 09:29: The relativistic effective of negative pressure is actually really, really hard to describe intuitively. 09:38: Part of the problem is that negative pressure doesn't come from the motion of dark energy particles, whatever they might be. 10:09: That's exactly how we define negative pressure. 10:12: A volume has negative pressure if it takes work to expand, just like a volume with positive pressure takes work to compress. 10:22: Negative pressure means energy is gained on expansion. 10:35: That looks like negative pressure, and yet this abstract-sounding negative pressure has a very real physical effect. 11:01: But both agree that a constant energy density and the resulting negative pressure leads to accelerating expansion. 04:00: Positive acceleration outwards, negative inwards. 08:24: It's negative pressure. 08:26: What does negative pressure even mean? 08:33: So negative pressure would pull inwards. 08:49: Negative pressure pulls in. 09:05: The direct effect of dark energy's negative pressure doesn't do anything, because that negative pressure is the same everywhere in the universe. 09:14: But even though the negative pressure has no direct effect, it has its relativistic effect. 09:19: Relativistically, negative pressure has to do the opposite of positive pressure and results in anti-gravity, because math. 09:29: The relativistic effective of negative pressure is actually really, really hard to describe intuitively. 09:38: Part of the problem is that negative pressure doesn't come from the motion of dark energy particles, whatever they might be. 10:09: That's exactly how we define negative pressure. 10:12: A volume has negative pressure if it takes work to expand, just like a volume with positive pressure takes work to compress. 10:22: Negative pressure means energy is gained on expansion. 10:35: That looks like negative pressure, and yet this abstract-sounding negative pressure has a very real physical effect. 11:01: But both agree that a constant energy density and the resulting negative pressure leads to accelerating expansion. 09:05: The direct effect of dark energy's negative pressure doesn't do anything, because that negative pressure is the same everywhere in the universe. 09:38: Part of the problem is that negative pressure doesn't come from the motion of dark energy particles, whatever they might be. 11:01: But both agree that a constant energy density and the resulting negative pressure leads to accelerating expansion. 08:49: Negative pressure pulls in. 03:58: That's this negative sign here. 00:46: Two, such an underdense universe should be geometrically weird, a negatively curved hyperbolic hyperplane.
	2016-04-27: What Does Dark Energy Really Do? 10:11: The universe could be positively or negatively curved below that level.
	2016-04-20: Why the Universe Needs Dark Energy 03:43: And we call that a "closed geometry." If k is minus 1, the universe is the 3D version of a negatively curved hyperbolic plane.
	2016-04-13: Will the Universe Expand Forever? 06:48: And if the left-hand side is negative, in that case there was never a high-enough expansion rate to reach that extreme size.
	2016-04-06: We Are Star Stuff 10:58: ... about the geometry of the universe and describe it as flat positive or negatively curved, I should say that the curvature of space at a single, constant ...
	2016-03-23: How Cosmic Inflation Flattened the Universe 02:00: On a negative curvature hyperbolic plane-- a saddle-like structure-- they add up to less. 03:35: If the center of the alley represents a flat universe, then the gutters represent extreme curvature in the positive or negative directions. 02:00: On a negative curvature hyperbolic plane-- a saddle-like structure-- they add up to less. 03:35: If the center of the alley represents a flat universe, then the gutters represent extreme curvature in the positive or negative directions. 02:48: It should be larger if the universe is positively curved, smaller if negatively curved.
	2015-11-05: Why Haven't We Found Alien Life? 10:55: ... bubble can traverse the walls in any direction besides forwards and our negative mass matter may also end up on the ...
	2015-10-28: Is The Alcubierre Warp Drive Possible? 03:24: ... do this for the warp field, you find that you need to produce a ring of negative energy density in a band around the ship to produce the right warp ... 03:38: Unfortunately, it may not even be possible to make negative energy densities on large enough scales. 03:44: We can create something like it, a negative pressure, on quantum scales via Casimir effect. 03:49: ... on macroscopic scales, you'd probably need some sort of exotic negative mass matter, like element zero, which is tricky, because there may be no ... 04:37: ... that you can even make negative mass matter, to make a warp field, some of it would need to go outside ... 04:46: ... are some proposed solutions, one of which is to lay down the external negative energy conditions along the path before you leave, sort of like a warp ... 05:02: Last tricky thing-- as Alcubierre devised the warp bubble, he figured it would take a lot of negative energy. 05:08: In fact, it would take significantly more negative energy than there is positive mass/energy in the entire observable universe. 05:25: Thicken the walls of the warp field, and you get the negative mass/energy requirement down to the equivalent of maybe the moon or even an asteroid. 05:46: ... Tardis style, which could get us down to needing only milligrams of negative ... 06:18: Now, this would be a field created by positive, not negative, energy density. 03:24: ... do this for the warp field, you find that you need to produce a ring of negative energy density in a band around the ship to produce the right warp ... 03:38: Unfortunately, it may not even be possible to make negative energy densities on large enough scales. 04:46: ... are some proposed solutions, one of which is to lay down the external negative energy conditions along the path before you leave, sort of like a warp ... 05:02: Last tricky thing-- as Alcubierre devised the warp bubble, he figured it would take a lot of negative energy. 05:08: In fact, it would take significantly more negative energy than there is positive mass/energy in the entire observable universe. 06:18: Now, this would be a field created by positive, not negative, energy density. 04:46: ... are some proposed solutions, one of which is to lay down the external negative energy conditions along the path before you leave, sort of like a warp ... 03:38: Unfortunately, it may not even be possible to make negative energy densities on large enough scales. 03:24: ... do this for the warp field, you find that you need to produce a ring of negative energy density in a band around the ship to produce the right warp ... 06:18: Now, this would be a field created by positive, not negative, energy density. 03:49: ... on macroscopic scales, you'd probably need some sort of exotic negative mass matter, like element zero, which is tricky, because there may be no such ... 04:37: ... that you can even make negative mass matter, to make a warp field, some of it would need to go outside the ... 05:46: ... Tardis style, which could get us down to needing only milligrams of negative mass. ... 03:49: ... on macroscopic scales, you'd probably need some sort of exotic negative mass matter, like element zero, which is tricky, because there may be no such ... 04:37: ... that you can even make negative mass matter, to make a warp field, some of it would need to go outside the warp ... 05:25: Thicken the walls of the warp field, and you get the negative mass/energy requirement down to the equivalent of maybe the moon or even an asteroid. 03:44: We can create something like it, a negative pressure, on quantum scales via Casimir effect.
	2015-05-20: The Real Meaning of E=mc² 05:29: It's because potential energy can be negative. 05:48: So the potential energy of the electron and proton in a hydrogen atom is negative. 05:58: ... as it turns out, the potential energy is negative enough that the sum of the kinetic and potential energies still comes ... 06:22: ... and potential energies of those atoms once they form a chemical bond is negative. ...
	2015-05-13: 9 NASA Technologies Shaping YOUR Future 08:46: ... might be long term negative effects to which women are more susceptible that we haven't even seen ... 08:56: ... asks why I didn't bring up osteoporosis as a bigger negative for women, and the reason is that spaceflight basically gives everyone ... 08:46: ... might be long term negative effects to which women are more susceptible that we haven't even seen yet, and a ...
	2015-05-06: Should the First Mars Mission Be All Women? 02:37: So while it's a negative for women, radiation risk might be one of those things that you have to solve for everyone in order to send anyone.
	2015-04-29: What's the Most Realistic Artificial Gravity in Sci-Fi? 01:10: Or you need something exotic, like gravitationally repulsive negative mass, which doesn't exist. 09:53: ... could have been present at both events, which corresponds to a zero or negative space time interval between those ... 01:10: Or you need something exotic, like gravitationally repulsive negative mass, which doesn't exist. 09:53: ... could have been present at both events, which corresponds to a zero or negative space time interval between those ...
	2015-04-22: Are Space and Time An Illusion? 03:12: We'll notice that since it involves subtraction, a spacetime interval can be positive, zero, or negative. 03:27: When it's zero or negative, signals or things can get from one event to the other and everyone agrees on their sequence.

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