Search PBS Space Time


2022-10-12: The REAL Possibility of Mapping Alien Planets!

  • 06:05: ... their own fuel have hard constraints   on payload size and acceleration period because they’re weighed down by their own fuel supply. ...
  • 07:45: ... it doesn’t blow out our mass budget.   Solar sails experience more acceleration  the closer they are to the Sun. To reach   the speeds we need, ...

2022-08-17: What If Dark Energy is a New Quantum Field?

  • 01:41: ... creation of dark energy, and so on, ultimately leading to exponential acceleration. Exactly why the creation of dark energy accelerates expansion requires a ...
  • 03:33: ... true we can figure out what energy density would be needed to cause the acceleration we observe. That number is around 5x10^-10 Joules/m^3. To give you a ...
  • 07:31: ... Caldwell, Rahul Dave and Paul Steinhardt in 1998, the same year as the acceleration of the universe was ...
  • 10:08: ... are within a factor of a few of each other, at exactly the time when the acceleration begins? This could be a crazy coincidence, or perhaps there are ...

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

  • 11:09: ... happens to be electrically charged, then the constant jiggling and acceleration caused by this Brownian motion means it will emit radiation. Last year, ...

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

  • 03:35: The idea is straightforward enough - what if there exists a minimum possible acceleration that can be produced by the gravitational force?
  • 03:44: In MOND, force or acceleration drop off with distance squared until, at very low values they start to plateau out.
  • 03:53: ... - or by a modification to Newton’s 3rd law of motion, in which case the acceleration produced by a force has a minimum ...
  • 04:17: ... need to tune a single parameter -  which is effectively the minimum acceleration - to get the correct rotation curves for nearly all ...

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

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

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

  • 08:28: ... processing its surface methane into hydrocarbons. This also explains the acceleration - it would be due to outgassing of the nitrogen-ice, abundant on such ...

2021-04-21: The NEW Warp Drive Possibilities

  • 03:20: Objects in that warp bubble move with that patch without themselves ever feeling any acceleration.
  • 07:11: Bobrick and Martire is that no past warp solution has in-built mode of acceleration.
  • 08:14: But this acceleration isn’t actually derived from his warp field solution.

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

  • 05:19: This time you fire your laser across the deck perpendicular to the direction of acceleration.

2021-02-24: Does Time Cause Gravity?

  • 00:34: ... of light is constant for all observers, and that the weight induced by acceleration is fundamentally the same as that induced by gravity - the so-called ...
  • 05:03: ... velocity in the down direction - it accelerates - and it pays for that acceleration by losing velocity - Decelerating in the time ...

2021-02-17: Gravitational Wave Background Discovered?

  • 00:00: ... no way that experiment can tell the difference between gravity or acceleration or between free fall or the absence of gravity earth's gravitational ...

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

  • 06:11: If we set it rotating at the right speed then centripetal acceleration leads to some nice artificial gravity.
  • 08:25: The source of acceleration doesn’t matter.
  • 08:54: The equivalence principle demands that there’s no experiment that can distinguish between acceleration and gravity.
  • 09:00: ... in a circle at the right radius and speed, or accelerated with linear acceleration equal to the gravitational ...
  • 09:16: ... are true - the constancy of the speed of light and the equivalence of acceleration and gravity, then time must run slow in gravitational ...
  • 09:25: ... the gravitational time dilation for the equivalent gravitational acceleration. ...
  • 09:53: ... the traveling twin to be in a gravitational well with a constant acceleration equal to her spaceship’s ...
  • 10:08: Well, as deep as the distance back to Earth - which is why the time dilation in this case is so huge, even if the acceleration is mild.

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

  • 14:59: ... the difference between the traveling and stay-at-home twin is actually acceleration, so shouldn’t acceleration be used to account for the time ...
  • 15:11: ... again to turn around, and according to Einstein’s equivalence principle, acceleration is fundamentally the same as gravitation as far as the laws of physics ...
  • 15:25: ... were standing on the surface of a planet with the same gravitational acceleration? ...

2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing?

  • 10:56: ... the trap and free-fall for some time. The CPT theorem states that the acceleration of an anti-atom in Earth’s gravitational field should be exactly the ...

2019-03-28: Could the Universe End by Tearing Apart Every Atom?

  • 00:25: ... and that expansion is accelerating and we don't know what's causing that acceleration but that hasn't stopped us from giving it a name we call this unknown ...
  • 03:05: ... of Newton's law of gravity for the whole universe describing the acceleration or deceleration of the expansion rate which depends on how much stuff ...
  • 05:32: ... acceleration is therefore positive which means dark energy is pushing outwards to ...
  • 06:20: ... expands, but it actually increases. The result would be that the acceleration increases over time offhand, that doesn't sound so much crazier than ...
  • 12:40: ... acceleration rate measured using distant quasars hints at an equation of state ...

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

  • 01:30: First it’s the property of an object that resists acceleration.
  • 01:34: This is encapsulated in Newton’s second law, which defines the connection between the amount of force applied and the acceleration that results.
  • 01:42: This type of acceleration-resisting mass is called inertial mass.
  • 02:46: ... you calculate the acceleration of an object in a gravitational field, inertial and passive ...
  • 03:08: ... property that defines the response to gravity also defines resistance to acceleration by all forces – including ...
  • 06:04: ... that there’s no experiment that can distinguish between the feeling of acceleration in empty space and the feeling of weight in a gravitational ...
  • 06:17: ... equivalence principle only works if all masses experience the same acceleration in a given gravitational field, so passive gravitational mass and ...
  • 10:39: We then happily plugged our negative inertial mass into Newton’s 2nd law to get acceleration.
  • 11:52: ... inertial mass implies flipping the sign of the acceleration when any force is applied to exotic matter, and it also means flipping ...

2019-01-09: Are Dark Matter And Dark Energy The Same?

  • 01:57: That acceleration matches the effect you would get if empty space itself had a tiny bit of energy.
  • 02:03: As more space comes into existence because of that expansion thing the more“dark energy” you get, which causes more acceleration.
  • 02:47: That’s the solution to the Einstein equations that tells you the rate of acceleration of the expansion of the universe.
  • 05:23: For a positive inertial mass, direction of acceleration is the same as direction as the applied force.
  • 05:29: For a negative mass, this equation suggests that acceleration is in the opposite direction to the applied force.

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

  • 00:37: ... second that's the escape velocity at Earth's surface that requires an acceleration of up to hundreds of thousands of GS and hundreds of thousands of Earth ...

2018-11-21: 'Oumuamua Is Not Aliens

  • 03:04: This non-gravitational acceleration was reported in a nature paper in June.
  • 03:09: The extra acceleration is tiny, but it's clear.
  • 03:20: Comets show the same sort of acceleration on their way out from the sun.
  • 04:36: In fact, the observed acceleration seems to be following an inverse square law.
  • 04:41: The acceleration is decreasing with the square of the distance from the sun.
  • 04:49: ... this inverse square acceleration is also what you'd expect from outgassing, because outgassing also ...
  • 05:09: ... a highly reflective material would produce the observed brightness and acceleration. ...
  • 05:32: The lightsail hypothesis potentially explains the acceleration and the weird shape.
  • 06:39: The acceleration is the weirdest thing so we'll start there.
  • 06:59: Without reflective dust, outgassing would be invisible to our telescopes but could still cause the observed acceleration.
  • 07:07: The paper that first reported the unusual acceleration proposes some plausible scenarios.

2018-10-03: How to Detect Extra Dimensions

  • 07:44: But there's another way to get this type of acceleration.

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

  • 04:08: Finally, it will detect radio waves from processes responsible for the acceleration of particles in the solar wind.
  • 04:14: Hopefully, teaching us about how that acceleration occurs.

2018-07-11: Quantum Invariance & The Origin of The Standard Model

  • 01:24: An example would be a ball rolling down a hill under a constant gravitational acceleration.

2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!)

  • 11:49: ... accelerating observer and the quantum field which should inhibit that acceleration by creating a type of ...
  • 12:13: The accelerating observer must expend more energy to produce the same acceleration.

2018-04-04: The Unruh Effect

  • 00:51: They found that the simple act of acceleration cuts off your causal access to a region of the universe.
  • 03:13: That's the world line of an observer undergoing constant acceleration.
  • 03:17: Acceleration means change in speed, so an accelerating world line is curved.
  • 03:33: They fire their rockets and begin a constant acceleration in the opposite direction.
  • 03:42: Just before they reach my space-time location, that constant acceleration brings them to a halt, and they start moving back in the opposite direction.
  • 03:57: That constant acceleration world line traces out a hyperbola, and it has a very interesting property.
  • 04:28: In reality, eternal constant acceleration would take infinite energy.
  • 04:59: In fact, the active acceleration does create a type of event horizon called a Rindler horizon.
  • 05:28: The distance of a Rindler horizon is inversely proportional to acceleration.
  • 05:32: The larger the acceleration, the closer the horizon.
  • 05:46: Even momentary acceleration generates a Rindler horizon.
  • 05:54: It's like the projected future acceleration gives you a Rindler horizon in the present.
  • 06:36: The vacuum should appear warm with a temperature proportional to the acceleration.
  • 08:36: ... friction turn between the detector and the field that results from the acceleration. ...
  • 08:55: The source of that energy is the acceleration itself.
  • 09:58: According to Einstein's equivalence principle, remaining stationary in a gravitational field is equivalent to acceleration in free space.
  • 10:12: ... there's one place in the universe where the gravitational acceleration can get that high, and that's right above the event horizon of a black ...

2018-02-14: What is Energy?

  • 02:47: ... Chatelet's gravitational potential energy, mass times the gravitational acceleration times height, is just a statement about how much kinetic energy, 1/2 mv ...
  • 03:26: ... as long as the downward gravitational acceleration doesn't change over time, the ball should lose speed on its way up at ...
  • 04:19: That's true even if the gravitational acceleration changes from one point in space to the next.

2017-11-08: Zero-Point Energy Demystified

  • 06:02: The fact is, any acceleration of a real particle involves a transfer of momentum between real particles via virtual particles.

2017-10-19: The Nature of Nothing

  • 10:22: ... so, then the amount of vacuum energy needed to produce the observed acceleration is tiny, around one one hundred millionth of an erg per cubic ...

2017-04-19: The Oh My God Particle

  • 06:41: But they may come from magnetic acceleration in quasars, or perhaps they're blasted out in gamma ray bursts.

2017-04-05: Telescopes on the Moon

  • 03:08: Subject them to the few G's of acceleration during a rocket launch, and you risk seven billion years of bad luck.

2017-01-19: The Phantom Singularity

  • 01:14: Infinite force means infinite acceleration, which means-- well, physics breaks.
  • 01:21: According to Newton's law, in order to fuel that infinite gravitational acceleration you need to get zero distance from an object's center of mass.

2016-11-09: Did Dark Energy Just Disappear?

  • 02:26: ... and Sarkar published a paper titled "Marginal Evidence for Cosmic Acceleration from Type IA Supernovae." It appeared in the prestigious Nature journal, ...
  • 03:08: The new guys claim that the much larger sample is consistent with there being no acceleration, and more data equals more confidence, right?
  • 03:38: ... and that range now includes a history in which there never was any acceleration. ...

2016-10-19: The First Humans on Mars

  • 06:19: ... slightly curved outer wall so that the centrifugal and gravitational accelerations work together to give you the right direction of down on that ...

2016-05-18: Anti-gravity and the True Nature of Dark Energy

  • 03:18: It's about the acceleration or deceleration of that expansion.
  • 03:41: It's the acceleration of the scale factor.
  • 04:00: Positive acceleration outwards, negative inwards.
  • 06:09: So acceleration will always be inwards.
  • 06:34: So he added to his field equations that would give a positive outward acceleration in the second Friedmann equation.
  • 08:12: A negative p here cancels this minus sign and can result in outward acceleration.

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

  • 06:23: Everything will have to withstand tens of thousands of G's of acceleration and impact from interstellar dust or cosmic rays.

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

  • 12:08: The orbiting object is subject to the full acceleration caused by gravity, which is what causes it to move in an orbit.
  • 12:17: In that reference frame, it's the velocity perpendicular to the centripetal acceleration that resists radial infall.

2016-03-16: Why is the Earth Round and the Milky Way Flat?

  • 07:55: ... the Equator the upward acceleration we feel due to the Earth's rotation is 0.03 meters per second squared, ...

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

  • 11:14: That change in motion is an acceleration.
  • 11:23: To account for the effect of acceleration, you need to use general relativity.
  • 11:47: So for the Alcubierre warp metric, there's actually no time dilation either due to motion or acceleration.

2016-01-13: When Time Breaks Down

  • 08:55: Shouldn't the resistance to acceleration produced by a compressed spring only take effect along the length of the spring, as opposed to the side?

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

  • 02:40: But as long as acceleration continues, the pressure differential persists.
  • 02:45: Acceleration is resisted in a way that feels exactly like mass.
  • 03:14: And you can derive the famous E equals Mc squared just by looking at how momentum transfers between the photons in the box under acceleration.
  • 05:52: Is it just the result of massless particles and fields bumping and sloshing around inside things resisting acceleration?
  • 06:01: This acceleration resisting mass, inertial mass, seems to be an emergent property of the ensemble.
  • 08:55: It gives them inertia-- a resistance to acceleration.

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

  • 02:57: ... force between the spacecraft and Apophis is providing all of the acceleration and hence velocity change needed to pull Apophis that extra ...
  • 03:06: How much mass do we need to provide the necessary acceleration?
  • 03:16: But we can just calculate the average acceleration based on the average mass of the spacecraft plus fuel over the seven years.
  • 03:24: ... average acceleration will give us the same change in velocity as we'd get using calculus to ...
  • 03:41: ... basic kinematic equations, the one relating change in position, average acceleration, and time, with a starting velocity of zero in the frame of Apophis in ...
  • 03:53: ... this equation, the average acceleration comes out to around 10 to the power of minus 9 meters per second squared ...
  • 04:03: What mass is needed to produce this acceleration?
  • 04:18: It also gives us the acceleration experienced by Apophis due to the mass of the spacecraft and the fuel.
  • 04:43: So the average mass needed to achieve the acceleration we calculated earlier comes to 1,600 metric tons.

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

  • 02:49: A starship inside the bubble is carried along for the ride while feeling no acceleration at all.

2015-10-22: Have Gravitational Waves Been Discovered?!?

  • 10:18: Now, the trip is going to take decades, so this is pretty good acceleration.

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

  • 03:41: ... object's resulting acceleration relative to Earth's surface is called the total acceleration of that ...
  • 04:14: ... tidal acceleration on objects due to the Moon's differential gravity along the Earth/Moon ...
  • 04:28: Plus, even if you turned Earth's gravity off, you would never notice an outward acceleration of one micron per second per second.
  • 04:41: The key is to look at the tidal acceleration of objects that are not on the Earth/Moon line.
  • 04:54: So relative to the Earth's surface, the block's tidal acceleration is almost radially inward-- in other words, down.
  • 05:01: In fact, if we map out the tidal acceleration vectors that you'd see at different points on Earth's surface, they look like this.
  • 05:26: Remember, the radially inward acceleration caused by Earth's own gravity on objects is 10 million times bigger.
  • 13:13: We're using the word acceleration here in two different and mutually exclusive senses.
  • 13:18: In the Newtonian sense, acceleration would mean put a frame of reference at Earth's center.
  • 13:41: And acceleration in that context means, is your tangent vector being parallel transported along your worldline?

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

  • 01:02: ... familiar meanings of terms like a constant velocity straight line and acceleration will become ...

2015-06-17: How to Signal Aliens

  • 06:35: ... what we even mean in the first place or think we mean by the terms "acceleration" an "inertial frame." That means reexamining Newton's first and second ...
  • 07:39: ... end up being resolved by, among other things, the facts that, one, acceleration does not mean what you think it means and, two, once we get the meaning ...

2015-06-03: Is Gravity An Illusion?

  • 01:57: ... the net force on an object will equal that object's mass times its acceleration only if you're measuring that acceleration using an inertial ...
  • 02:45: In fact, you can think of inertial frames as the standard against which you measure true acceleration.
  • 03:07: You, a book, and an elephant will all lurch toward the back of the car with the same acceleration.
  • 03:44: So accelerated frames of reference mimic a gravitational field in the opposite direction of the frames acceleration.
  • 04:37: You can also think that the car's forward acceleration is mimicking some extra gravity pointing backward.
  • 05:52: ... would remind us that inertial frames are the standard for measuring true acceleration, so you can only say Earth is really accelerating upward if you can ...
  • 06:35: ... interior just seems like zero G because the downward acceleration acts like a fake extra upward gravitational field that, from the ...

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

  • 08:21: So go 9.8 meters per second per second acceleration in one direction.
  • 08:25: ... in God's Eye." The problem is, where do you get the fuel to keep that acceleration ...

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

  • 04:01: An object's Coriolis acceleration will be proportional to its speed, relative to the rotating frame and the rotation rate of the frame itself.

2015-04-01: Is the Moon in Majora’s Mask a Black Hole?

  • 02:52: Now, on its own, this differential acceleration tends to separate rocks from the planet, even on the side of the planet opposite the moon.

2015-02-18: Is It Irrational to Believe in Aliens?

  • 07:19: But think about how much fuel it would take to keep that acceleration going.

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

  • 00:58: ... per second per second, or 10 meters per second squared, is called the acceleration due to gravity, or the surface gravity of ...
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