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2022-09-28: Why Is 1/137 One of the Greatest Unsolved Problems In Physics?

  • 11:33: ... the relationship  between the uncertainty in measuring position and velocity. ...

2022-09-14: Could the Higgs Boson Lead Us to Dark Matter?

  • 08:48: ... of momentum tells us that the product of velocity times mass of all particles going into a collision has to be the same as ...

2022-07-27: How Many States Of Matter Are There?

  • 03:20: ... single water molecule doesn’t really have a temperature, it has a velocity - but the average energy of motion of all water molecules is its ...

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

  • 07:38: ... called the cross product. Force equals   charge times velocity cross magnetic field.  This is a type of vector multiplication ...

2022-06-22: Is Interstellar Travel Impossible?

  • 08:19: The kinetic energy deposited by each particles is 1/2 times mass times velocity squared.

2022-05-25: The Evolution of the Modern Milky Way Galaxy

  • 18:41: ... horizon of a black hole   at the speed of light - that’s the velocity  of an inertial frame that falls from infinite   distance ...

2022-05-04: Space DOES NOT Expand Everywhere

  • 01:24: ... expand your view to large enough scales, that local motion or “peculiar velocity” is small compared to the fact that distant points are moving apart - ...

2022-03-08: Is the Proxima System Our Best Hope For Another Earth?

  • 04:38: This way of finding exoplanets is called the radial velocity method.
  • 04:42: ... the Doppler effect is only  produced by the component of the star’s velocity that’s either directly towards us or away from us - in the “radial” ...
  • 05:37: Now that we know this, the radial velocity method can step in and potentially catch many more systems - as long as they’re not perfectly face-on.
  • 05:46: ... radial velocity method is emerging as a competitor to the transit approach due to rapid ...

2022-02-16: Is The Wave Function The Building Block of Reality?

  • 14:52: ... absorbed. The absorbed energy can go into changing the black hole’s velocity, but also can be added to the black hole’s mass. BuzzBen’s also asks ...

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

  • 00:03: ... the same way as objects moving relative to each other due to their velocities in special relativity okay so the answer is that two types of motion ...

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.
  • 02:28: Finally, he’d allow time to tick forward - he’d move the bulbs according to their new velocities.
  • 06:16: It works like this: you start with a volume full of particles, each with its starting position and velocity.
  • 11:13: ... typical simulation,  which just tracks particle  positions and velocities. ...

2022-01-12: How To Simulate The Universe With DFT

  • 15:14: The minimum velocity it could have on reaching the Earth is the solar system’s escape velocity at Earth’s orbit, or around 42 km/s.
  • 15:49: Either way, it’ll still have solar system escape velocity after the passage through the earth and we would never see it again.

2021-11-10: What If Our Understanding of Gravity Is Wrong?

  • 02:18: That means the orbital velocities of stars out there should be lower in order to keep them in orbit.
  • 06:47: ... Tully-Fisher Law  is such a tight relationship because the rotation velocity depends on the dark matter halo  while the luminosity depends on ...

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

  • 01:22: ... body at each time, which lets you calculate its exact vector positions, velocities, and accelerations at each ...

2021-10-20: Will Constructor Theory REWRITE Physics?

  • 00:32: describe some aspect of the universe with numbers - like the temperature, pressure, etc of a gas or the position, velocity, etc. of a particle Step 2.

2021-09-07: First Detection of Light from Behind a Black Hole

  • 07:17: This means this extreme velocity gas - the far ends of the broad line - should respond first as our flare reverberates out.

2021-06-23: How Quantum Entanglement Creates Entropy

  • 01:02: ... least not in the same way. Instead, that molecule has a   velocity and a mass and so on, which define how it bounces off the walls or ...
  • 16:39: ... Lorentz invariant.   The distances have to depend on the velocity of the observer. Moving fast should then collapse the   ...

2021-06-09: Are We Running Out of Space Above Earth?

  • 07:09: ... a collision velocity of 11.6km/s, it was less a smash than a splash, creating hundreds of ...
  • 14:38: Give them any velocity at all and they stream right through matter as though it isn’t there.

2021-04-21: The NEW Warp Drive Possibilities

  • 07:16: All of them, including Alcubierre’s, move with whatever velocity they started at.
  • 08:20: The velocity of the bubble is baked into the equation for the field geometry, but it’s not clear how you change that velocity.
  • 16:32: Raven Lord always thought that the idea of "instantaneous velocity" that solves this paradox is just a theoretical artifact of calculus.
  • 16:40: Actually, in quantum mechanics, velocity isn’t just change in position with time.
  • 16:45: Momentum, which incorporates velocity, is as fundamental as position.
  • 16:49: So a particle at an instant in time really does have an instantaneous velocity.

2021-03-23: Zeno's Paradox & The Quantum Zeno Effect

  • 00:50: ... the “vanishingly small” part cancels out and the arrow’s instantaneous velocity is very ...

2021-03-16: The NEW Crisis in Cosmology

  • 13:38: ... of light in here to give time the same dimentions as space. Your velocity through   spacetime - also called your 4-velocity - is ...

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

  • 06:31: To get technical: any massive object has a component of its 4-dimensional spacetime velocity - its 4-velocity in the time direction.
  • 06:51: It has no time-component to its velocity.
  • 10:47: And even if this change in velocity isn’t “real”, it’s enough to let us use Huygen’s principle.

2021-02-24: Does Time Cause Gravity?

  • 00:04: If even a tiny bit of your breakneck temporal velocity leaks into one of the dimensions of space.
  • 02:21: You could say that it has a positive velocity through time, and zero velocity through space.
  • 02:55: Velocity through time increases away from the Earth.
  • 02:58: ... we move particles through time according to those velocities, we have this sense of time flowing in a gradient - faster streams ...
  • 03:41: And each of those clocks has a velocity vector in time.
  • 03:45: So what’s the temporal velocity of the entire object?
  • 03:54: Objects don’t just have a velocity through space or through time - they have a velocity through spacetime.
  • 04:26: ... think of the two objects as becoming one object, and the difference in velocities across its length causes a torque that rotates the overall velocity ...
  • 04:41: The gradient of velocities cause the overall 4-velocity of the object to be rotated.
  • 05:03: ... motion of any object in a gravitational field - it gradually picks up velocity in the down direction - it accelerates - and it pays for that ...
  • 06:13: In this picture, a falling object trades some of its enormous velocity through time to pay for a small velocity through space.
  • 07:45: They have no “velocity through time” to trade.

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

  • 04:33: But let’s say the gerdankenlab is moving at a constant velocity past a stationary physicist.

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

  • 15:33: ... the same answer as if we just have the traveling twin instantly flip its velocity around with no slowing down or speeding ...

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

  • 00:17: ... observers should measure the same speed of light, regardless of their velocities. ...
  • 00:26: But from that can the inevitable conclusion that space and time themselves were relative - depended on the velocity of the observer.

2020-12-08: Why Do You Remember The Past But Not The Future?

  • 03:15: ... omniscient supergenius physicist could measure the exact positions and velocities of every particle comprising the asteroid and calculate their paths ...

2020-11-18: The Arrow of Time and How to Reverse It

  • 05:10: ... low entropy. You can do low entropy by having a weird distribution of velocities, but you can also do it by clustering the particles in one spot in the ...
  • 05:43: ... look like going backwards in time? Uh, exactly the same actually. Random velocity directions will tend to spread this cluster apart in both time ...
  • 07:17: ... particles” to illustrate evolving entropy. When we measure the velocities of particles across our universe - in the form of galaxies - we don’t ...
  • 08:11: ... particles backwards in time to this original “special” slice, at which velocities are all random, and keep tracing out the other side then you should see ...

2020-11-11: Can Free Will be Saved in a Deterministic Universe?

  • 00:57: ... knowledge of the current state of the universe, like the positions and velocities of all particles, and perfect knowledge of the laws of nature could ...

2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time

  • 13:38: ... end up at different times depending   on your relative velocities. Your velocities  determine your definition of the present.   ...

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

  • 00:47: But different observers will slice the block at different angles that depend on their velocities.
  • 12:47: It depends on relative velocities.

2020-10-13: Do the Past and Future Exist?

  • 01:27: ... universe - the idea that, by knowing the current position and velocity of every particle in the universe, as well as the forces that act ...
  • 08:29: ... will slice up block time at different angles depending on their velocities. ...

2020-08-17: How Stars Destroy Each Other

  • 11:14: ... - but if that core is above a certain mass it shrinks so that the escape velocity at its surface is greater than the speed of ...

2020-07-20: The Boundary Between Black Holes & Neutron Stars

  • 05:34: And much more difficult to escape the neutron star - the escape velocity at the surface is up to half the speed of light.
  • 05:42: ... on the verge of being black holes, which by definition have an escape velocity at the event horizon equal to the speed of ...
  • 05:51: If only you could cram a little more matter into the neutron star, the escape velocity would increase and it would become a black hole.
  • 06:36: So more mass in a neutron star means higher surface gravity means higher escape velocity.

2020-06-15: What Happens After the Universe Ends?

  • 04:57: Lines representing constant distance or simultaneous times shift with the velocity of the observer.
  • 05:23: ... something taking the most direct path between them - a path of constant velocity that reaches that point in space at the right instant in ...

2020-05-18: Mapping the Multiverse

  • 15:08: ... the Michelson Morley experiment has been performed at much higher velocities to get a better reading - say 10% the speed of ...

2020-05-11: How Luminiferous Aether Led to Relativity

  • 07:06: ... apparent velocity of an object - or a wave - depends in a simple way on the velocity and ...
  • 07:19: ... calculate what velocity everyone observes using the Galilean transformation, which is part of ...
  • 11:20: ... that now allowed the speed of light to remain constant, no matter your velocity. ...

2020-05-04: How We Know The Universe is Ancient

  • 02:44: ... Slipher’s velocities or redshifts and Hubble’s distances, we learned that essentially ...
  • 04:40: ... fields of nearby galaxies and clusters. We can deal with these “peculiar velocities” just by averaging over many ...
  • 06:22: ... over lots of galaxies - and that averages out those pesky peculiar velocities. ...

2020-02-03: Are there Infinite Versions of You?

  • 03:19: ... universe, the starting conditions in any given region - like positions, velocities, etc of all particles - perfectly determines the future history of any ...

2020-01-20: Solving the Three Body Problem

  • 00:20: ... machine of clockwork predictability. Given the current positions and velocities of the bodies of the solar system, Newton’s equations could be used in ...
  • 01:24: ... equation and its solved. Those numbers are the starting positions and velocities of your gravitating bodies, plus a value for ...
  • 10:30: ... we call a phase space - a space of possible arrangements of position and velocity. Well, for a pseudo-random system, statistical mechanics lets us ...

2019-07-25: Deciphering The Vast Scale of the Universe

  • 04:50: ... combined his distances with Vesto Slipher’s velocities to discover that the galaxies all appear to be racing away from the ...
  • 06:34: ... we’ve only mapped the locations and velocities of around 1% of those stars, that gives us an incredible understanding ...
  • 07:10: Every dot we see is a known galaxy, it’s position, velocity, and even stellar content measured and cataloged.

2019-06-17: How Black Holes Kill Galaxies

  • 00:08: ... in their random orbits within galactic bulge the so called, Stellar Velocity ...

2019-04-24: No Dark Matter = Proof of Dark Matter?

  • 00:03: ... Rubin discovered dark matter in the first place by observing that the velocities were too fast in clusters and in galaxies indicating an unseen source of ...

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

  • 06:32: ... minutes in space the craft re-enters and lands. It never reaches orbital velocity so it's low speed reentry is less fraught than say the space ...

2019-01-30: Perpetual Motion From Negative Mass?

  • 06:56: At first glance this tells us that any object, no matter its mass, will follow the geodesic determined by its starting position and velocity.
  • 07:40: But those trajectories only depend on the active gravitational mass of the central object, and on the velocity and starting position of the apple.

2019-01-24: The Crisis in Cosmology

  • 00:49: Combined with the Doppler shift velocity measurements of Vesto Slipher,...
  • 02:54: ...meant measuring the recession velocity and distance for as many galaxies as possible.
  • 02:59: The velocity part is relatively easy.

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

  • 00:02: ... or position vectors point in the opposite direction same with the velocity / momentum through our board the mirror away from yourself and its ...

2018-12-06: Did Life on Earth Come from Space?

  • 00:37: ... to a minimum of eleven point two kilometers per second that's the escape velocity at Earth's surface that requires an acceleration of up to hundreds of ...

2018-10-18: What are the Strings in String Theory?

  • 06:22: These resonant frequencies depend on the length of the string, also its tension, which defines wave velocity and so relates frequency to wavelength.

2018-09-05: The Black Hole Entropy Enigma

  • 03:46: ... describe the system's internal state like all the particle positions, velocities, et ...

2018-08-01: How Close To The Sun Can Humanity Get?

  • 04:33: It'll make detailed measurements of their kinematic properties like velocity temperature and density.
  • 07:06: ... each pass, Venus will tug on Parker in just the right way to reduce its velocity, causing it to fall into a more stretched out elliptical orbit that will ...
  • 10:42: ... some physical system that can detect incoming particles, measure their velocity, and then open the door based on a decision about that ...

2018-07-18: The Misunderstood Nature of Entropy

  • 04:22: By configuration, I mean the exact arrangement, of positions, velocities, et cetera of all microscopic particles.

2018-07-04: Will A New Neutrino Change The Standard Model?

  • 04:17: However, chirality is fundamental to the particle and doesn't depend on your own velocity.

2018-05-16: Noether's Theorem and The Symmetries of Reality

  • 10:39: But Gaia is really optimized for extreme astrometry-- phenomenally accurate position data that actually allows measurements of velocities.

2018-05-09: How Gaia Changed Astronomy Forever

  • 01:15: As we'll see, this precision allows Gaia to measure true distances and true velocities for 1.3 billion of its stars.
  • 04:23: Moving on to stellar velocities, the galaxy is a dynamic place.
  • 04:45: This gives the velocities of the stars in the plane of the sky.
  • 05:00: Combining motion on the sky and Doppler shift, gives the full three-dimensional velocities for these billion stars.
  • 05:07: ... putting such complete velocity measurements together with our position data, it's now possible to model ...
  • 05:16: On the large scale, we see the distribution of stellar velocities through the spiral structure of our part of the Milky Way.
  • 05:53: ... the current velocities and positions of the stars, we can actually wind the clocks backwards ...
  • 06:46: We can even potentially, detect exoplanets by looking at the star's radial velocities and measuring shifts to a planet tugging on the star.

2018-04-25: Black Hole Swarms

  • 03:18: The ultimate result is that the black hole slows down and no longer has the velocity it needs to maintain its circular orbit.

2018-04-04: The Unruh Effect

  • 01:45: For an object with a constant velocity, an inertial object, these world lines are just straight lines, and the slope gives their velocity.

2018-03-28: The Andromeda-Milky Way Collision

  • 03:01: Hubble went on to combine distance measurements to many galaxies with measurements of their velocities to discover the expansion of the universe.
  • 03:09: Those velocities were found by another astronomer, Vesto Slipher, by measuring Doppler shifts of spectral lines.
  • 03:32: But Doppler shift measurements only gives the line of sight velocity, the component of the galaxy's motion directly towards or away from us.
  • 03:44: If the galaxy has enough sideways or transverse velocity, then it could miss us completely.
  • 03:49: For a long time, we had no idea about Andromeda's transverse velocity.
  • 04:01: ... with a transverse velocity equal to its line of sight velocity, Andromeda's motion over several ...
  • 04:16: So how do we measure Andromeda's transverse velocity?
  • 04:47: They calculated a transverse velocity of 17 kilometers per second.

2018-03-21: Scientists Have Detected the First Stars

  • 08:13: Then, half mv squared gives us its velocity, around 80 meters per second.

2018-02-28: The Trebuchet Challenge

  • 01:43: ... by the same force over the same path, the quantity half mass times velocity squared has to be ...
  • 02:35: Kinetic and potential energy are defined as combinations of more basic quantities, for example, position, velocity, and mass.

2018-02-14: What is Energy?

  • 01:15: He realized that the sum of mass times velocity squared for a system of particles bouncing around on a flat surface is conserved.
  • 03:07: ... for the student, see if you can show that the square of the change in velocity of a falling ball is proportional to the distance it ...

2018-01-31: Kronos: Devourer Of Worlds

  • 02:56: And they then made spectroscopic observations to measure Doppler shift velocities.
  • 03:29: The stars' velocities tell us that they're moving in lockstep together around the galaxy.

2018-01-10: What Do Stars Sound Like?

  • 04:31: Well, for the sun, we can map these oscillations in two ways-- changes in brightness and changes in velocity.
  • 04:45: At the same time, gas moves vertically in and out during the same oscillation, reaching velocities of 0.1 meters per second.
  • 08:12: ... holography, the visible wave field-- so the distribution of Doppler velocities across the visible surface of the sun-- is used to infer the current ...

2017-12-13: The Origin of 'Oumuamua, Our First Interstellar Visitor

  • 04:00: Another way to think of this is in terms of escape velocity.
  • 04:03: That's the velocity an object would need to have to escape a gravitational field.
  • 04:18: The escape velocity at that closest approach was a little over 80 kilometers per second.
  • 05:47: ... would have been over 100 kilometers per second, higher than the escape velocity at the distance of closest approach to that ...
  • 10:14: That factor, the square root of one minus V squared on C squared, approaches 0 as velocity approaches the speed of light.
  • 10:42: In the case of matter, uncertainty in momentum can manifest in both velocity and mass.

2017-08-16: Extraterrestrial Superstorms

  • 10:16: Besides size, velocity is a good measure of storm strength.

2017-08-10: The One-Electron Universe

  • 11:13: OKFFF1 comments that data flow must have a constant velocity and not be accelerating.
  • 11:50: ... the direction of dark flow, given that we can only really measure the velocity components that are towards us or away from ...
  • 12:04: ... a slight preferred direction to one point on the sky, then the way those velocity vectors map onto our line of sight to those galaxies should change in a ...

2017-08-02: Dark Flow

  • 02:28: ... asymmetric due to our motion, there must be some reference frame, some velocity, in which there's no observed Doppler shift in any ...
  • 02:43: In that reference frame, if you added together the peculiar velocities of all galaxies in the universe, you'd expect them to cancel out.
  • 04:24: ... a galaxy cluster has some extra peculiar velocity in addition to the Hubble flow, then the SZ effect adds an extra Doppler ...
  • 04:36: It sort of resets the apparent velocity, the frame of reference of that patch of the CMB to the peculiar velocity of the cluster.
  • 04:49: And that shift can tell us the peculiar velocity of the cluster.
  • 04:54: ... really tiny, and it can only tell us the component of the peculiar velocity that's either towards or away from us, not side to ...
  • 05:17: ... observations of the cosmic microwave background to build up a peculiar velocity map of around 700 clusters in all directions on the sky and out to ...

2017-07-19: The Real Star Wars

  • 02:01: Despite definitely being in space, these are called suborbital trajectories because they don't actually reach orbital velocity.

2017-07-12: Solving the Impossible in Quantum Field Theory

  • 15:03: Feynman didn't limit particle velocity to the speed of light.

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

  • 00:44: Knowing a particle's location perfectly means its velocity is unknowable.

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

  • 02:06: Relativity tells us that the passage of time depends on velocity.

2017-05-03: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson

  • 15:06: ... to take such an expanded cloud of particles and exactly reverse their velocities, then they would all end up back in their original ...
  • 15:57: ... principle, a perfect set of particle positions and velocities could be found such that the subsequent series of interactions leads to ...

2017-04-26: Are You a Boltzmann Brain?

  • 02:14: Entropy is just a measure of the specialness, or the degree of order, in the current arrangement of positions and velocities of a system's particles.
  • 03:18: Entropy increases because particle positions and velocities get randomized over time.

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

  • 02:22: The tick rate of your clock and your perception of simultaneity depends on your velocity.
  • 02:28: There's no absolute notion of velocity, so everyone can be considered motionless from their perspective.
  • 02:42: The tick marks on that time axis also depend on velocity and represent the speed of everyone's personal clock in their proper time.
  • 06:23: ... interval is invariant to Lorentz transformations, when we shift to the velocity frame of the Annihilator, we just make sure events stay on the contours ...

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

  • 01:11: It lets us figure out what spacetime looks like for every observer, no matter what his or her velocity is.
  • 01:17: If two events happen in spacetime, observers with different velocities will report different separations between them, in both space and time.

2017-02-02: The Geometry of Causality

  • 03:16: Motion at a constant velocity appears as a sloped line, and the time axis is scaled so that the speed of light is a 45 degree line.
  • 05:06: They see themselves as stationary, so their time axis is just their own constant velocity world line.
  • 07:03: This transformation allows you to calculate how properties, like distance, time, velocity, even mass and energy, shift between reference frames.
  • 09:23: I can change that path by expanding energy to change my velocity, although doing so realigns the contours so I always slide down the steepest path.

2016-12-21: Have They Seen Us?

  • 15:59: Some people complained about my use of the expression "escape velocity greater than the speed of light" at the beginning of the episode.
  • 16:17: ... it receives in nerd circles, it's accepted to talk about the escape velocity at the surface of the Earth because we're used to Newtonian ...
  • 16:39: That's the velocity you need to escape.
  • 16:43: The reason that people poo-poo the expression "escape velocity" is that it reminds us of a strange coincidence.
  • 16:49: ... you use Newtonian gravity to calculate the distance at which the escape velocity reaches the speed of ...
  • 17:06: But the concept of escape velocity at the event horizon is still as meaningful as it is from the surface of the Earth.

2016-12-08: What Happens at the Event Horizon?

  • 00:29: Black holes, objects with densities so high that there's this region, the event horizon, where the escape velocity reaches the speed of light.
  • 16:16: Vacuum Diagrams correctly points out that to know the future trajectory of a particle, you only need position, not velocity, as I had stated.
  • 16:26: That velocity information is in the guiding wave.

2016-11-30: Pilot Wave Theory and Quantum Realism

  • 04:51: ... of path isn't random-- if you know the exact particle position and velocity at any point, you could figure out its entire future ...
  • 05:01: Apparent randomness arises because we can't ever have a perfect measurement of initial position, velocity, or other properties.
  • 09:07: The entire wave function knows the location, velocity, and spin of each particle.

2016-07-20: The Future of Gravitational Waves

  • 06:16: To do this, you needed to assume that the alpha particle bounces back and forth between the walls of the nucleus with a constant velocity.
  • 06:32: ... get the alpha particle velocity from its kinetic energy, which I gave you, and you get the size of the ...

2016-06-29: Nuclear Physics Challenge

  • 02:46: You'll also need the velocity of the alpha particle.
  • 02:56: And you can calculate the velocity using the equation for kinetic energy and the mass of the alpha particle.

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

  • 02:23: See an object's de Broglie wavelength depends on its momentum, so mass times velocity.
  • 05:21: That suggests a velocity faster than light, which sounds problematic.

2016-04-20: Why the Universe Needs Dark Energy

  • 04:56: ... with exactly the right density, that's expanding at exactly its escape velocity, one that will slow to a stop over infinite time, should be flat, with ...

2016-04-13: Will the Universe Expand Forever?

  • 02:45: ... I throw it at 11 kilometers per second, which is the escape velocity on Earth's surface, then, by the time it almost stops moving, it will be ...
  • 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.
  • 03:36: That minimum kinetic energy tells you the escape velocity.
  • 03:40: ... and, remember, ignoring dark energy-- the universe also has an escape velocity that lets distant galaxies escape each other's gravitational ...
  • 04:05: How do we calculate the escape velocity for the whole universe?
  • 06:22: Essentially, that's if the expansion is exactly equal to the escape velocity.

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

  • 12:17: In that reference frame, it's the velocity perpendicular to the centripetal acceleration that resists radial infall.

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

  • 05:58: Time dilation will slow a moving clock down by this, 1 over the square root of 1 minus velocity squared over c squared.

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

  • 05:48: We can draw that time axis along any constant velocity time-like path, and just Lorentz transform to get a valid perception of space time.

2016-01-06: The True Nature of Matter and Mass

  • 01:58: But let's give the box a little nudge-- increase its velocity.

2015-12-09: How to Build a Black Hole

  • 06:40: Very, very large neutron velocities become part of the possibility space.
  • 09:17: Well, momentum space expands accordingly, with the corresponding enormous velocities all inward pointing.
  • 12:18: ... problem is that changing its velocity enough to hit the sun, or even to fall into Earth's orbit-- which was ...

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

  • 02:28: First, let's do the calculation in the frame of reference of Apophis' 2029 orbital velocity.
  • 02:35: That way we don't need to worry about the asteroid's initial 30 kilometer per second velocity at all.
  • 02:39: In the asteroid's frame, its starting velocity is zero.
  • 02:49: We just need to add enough velocity to Apophis to move it 25,000 kilometers relative to the frame of reference of its initial motion.
  • 02:57: ... spacecraft and Apophis is providing all of the acceleration and hence velocity change needed to pull Apophis that extra ...
  • 03:24: ... average acceleration will give us the same change in velocity as we'd get using calculus to determine the acceleration at every point ...
  • 03:41: ... change in position, average acceleration, and time, with a starting velocity of zero in the frame of Apophis in ...
  • 05:01: ... tells us the relationship between delta v, the total change in velocity, to the exhaust velocity of the fuel and the ratio of fueled to unfueled ...
  • 05:45: OK, but what about the exhaust velocity?
  • 05:49: We know that our pulsed fusion drive has an exhaust velocity of 500 kilometers per second.
  • 06:08: The angle of the thrusters ends up being around 30 degrees, so the effective exhaust velocity is the backwards or reverse component of the thrust.
  • 06:29: The reverse component of the exhaust velocity ends up being 427 kilometers per second.
  • 07:11: ... regular rocket fuel has less than 1% of the exhaust velocity of our pulsed future drive and so we need almost as much initial fuel ...

2015-11-11: Challenge: Can you save Earth from a Killer Asteroid?

  • 01:23: ... we have a state of the art post-fusion rocket engine capable of exhaust velocities of 500 kilometers per second ready by the launch data, can we feasibly ...
  • 01:54: ... also need the rocket equation which relates velocity change to the propellant exhaust velocity and the ratio of wet to dry, ...

2015-10-15: 5 REAL Possibilities for Interstellar Travel

  • 02:18: The rocket equation tells us that maximum speed is based on exhaust velocity, fuel mass, and spacecraft mass.
  • 02:38: But there are two ways to achieve high velocities, propel a lot of mass backwards or propel less mass at much higher speeds.

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

  • 01:30: Not only is Earth or, indeed, any other location not special, but Galileo posits that no velocity is special, either.
  • 01:37: ... way, all experiments should give the same results regardless of the velocity of your non-accelerating, or inertial, frame of ...
  • 03:08: And I can figure out the field strength from Maxwell's equations based on what I see is the monkey's total velocity.
  • 03:15: But what is that velocity?
  • 03:45: See, there's a velocity-dependent trade-off between the electric and magnetic fields.
  • 03:56: This tells us that the electromagnetic force holds clues to the fundamental interplay between space, time, and velocity.
  • 04:28: An example is the Galilean transformation, which basically says that velocities add together and space and time don't depend on velocity.
  • 05:49: First, we're not going to pretend that we know how velocities add.
  • 06:00: Under our new transformation, the laws of physics will work the same regardless of position, orientation, or velocity.
  • 06:17: Position, orientation, and velocity are changing massively.
  • 06:30: ... frame as I use to get to the pony's frame just by using the different velocities. ...
  • 06:48: And I can also get back to my frame by putting a minus sign on the velocities.

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

  • 07:03: ... surface of a planet or a star needs a minimum speed called the escape velocity in order to get really far and not turn back as it's pulled by the ...
  • 07:15: If a planet's radius equals the Schwarzschild radius of the equivalent-mass black hole, it turns out that the escape velocity is the speed of light.

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

  • 01:54: ... of other inertial observers are straight, indicating constant spatial velocity. ...

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

  • 02:36: ... so we would ordinarily see moving with a constant three-dimensional velocity through ...
  • 02:48: Inertial observers will see each other dynamically, moving with a constant three-dimensional velocity.
  • 02:54: But does that mean that inertial observers are really moving with a constant three-dimensional velocity?
  • 03:05: ... a way to discern who's really moving at constant three-dimensional velocity, sort of-- which is those observers whose world lines in space time are ...
  • 04:41: They're moving at constant spatial velocity.

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

  • 07:16: ... see in a physics 101 class, tangent vectors to trajectories represent velocities, how fast you're going and in what ...
  • 07:30: In my frame, my own velocity is zero, but in the red guy's frame it isn't.
  • 07:34: So ordinary velocity would not be a frame invariant geometric vector in spacetime.
  • 07:58: ... position on my axis with respect to ticks of my clock-- that's ordinary velocity-- I'm going to track two hybrid quantities instead, the monkey's position ...

2015-07-02: Can a Circle Be a Straight Line?

  • 01:02: ... a curved spacetime, then the familiar meanings of terms like a constant velocity straight line and acceleration will become ...

2015-06-03: Is Gravity An Illusion?

  • 01:25: ... a frame of reference is really at rest or really moving at constant velocity because that distinction is meaningless and simply a matter point of ...

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

  • 05:31: ... achieve 1 g, Ringworld's rotational velocity would be small enough that, just like on Earth, Coriolis effects would ...

2015-04-08: Could You Fart Your Way to the Moon?

  • 01:01: Now if you push the ball forward hard, the ball also pushes backward on you, giving you and the skateboard a backward velocity in the process.
  • 02:48: In truth, even starting out from low Earth order, you'd be short of Earth's escape velocity by a factor of about a billion.
  • 03:11: Let's start with the exhaust velocity of a fart.
  • 04:59: About 500 to 700 times higher recoil velocity, a little over 77 meters per hour, or enough to get you back to the ISS in under eight minutes.
  • 05:14: ... required exit velocity would exceed Mach 4, over 3,000 miles per hour, which is over 50% faster ...
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