5 ms·

Is there a theory for what "effect" would be produced by a theoretical object going faster than light? The relevance is that, I thought a "sonic boom" was defin

by tabeth 10y ago

Is there a theory for what "effect" would be produced by a theoretical object going faster than light? The relevance is that, I thought a "sonic boom" was defined as what happens to an object and its surroundings after going faster than sound. A "sonic boom" of light seems nonsensical, even after reading the article. Isn't this just a cone shaped wave?

whatshisface 10y ago
No, there's no (experimentally supported) theory that would work at all with an object going faster than light. It just isn't in the geometry - asking for a hyperbolic rotation that stretches your motion's vector past c is like trying to turn an apple around in your hand in a way that makes it twice as big. What they're doing here is based on the fact that you can make light move at under c if you force it to travel through a dielectric material. The c in E=mc^2 is the speed of light in a vacuum: not necessarily through a carefully designed atomic obstacle course.
- ianai 10y ago
  Light always travels at c. It may appear to an observer to travel slower than c if it is being absorbed and emitted through media along the way.
  - snarfy 10y ago
    It's not due to absorption/re-emission. The vacuum permittivity and permeability of free space is different than a medium. https://en.wikipedia.org/wiki/Vacuum_permittivity https://en.wikipedia.org/wiki/Vacuum_permittivity https://en.wikipedia.org/wiki/Vacuum_permeability https://en.wikipedia.org/wiki/Vacuum_permeability Free space has an electrical resistance of about 376 ohms. https://en.wikipedia.org/wiki/Impedance_of_free_space https://en.wikipedia.org/wiki/Impedance_of_free_space
    - passwd 10y ago
      >Free space has an electrical resistance of about 376 ohms. Impedance, to be precise. If free space had electrical resistance of 376 ohms, our world would be much stranger place than it is now.
cjslep 10y ago
Cherenkov radiation[0] is when a photon is travelling faster than the speed of light through water. To overly simplify, the speed of light in a vacuum is different than the speed of light through a medium. [0] https://en.m.wikipedia.org/wiki/Cherenkov_radiation https://en.m.wikipedia.org/wiki/Cherenkov_radiation
- sdx23 10y ago
  Beware the usage of the term "speed of light" here. There is two things: the phase velocity and the group velocity.
- symmetricsaurus 10y ago
  I think you mean when an electron (or other charged particle) travels through water.
- FreeFull 10y ago
  It doesn't happen with photons. Photons themselves always travel exactly at the (vacuum) speed of light, even in water, and they aren't charged particles. Cherenkov radiation happens with charged particles like electrons.
  - delecti 10y ago
    A photon's net speed through a medium is not always the vacuum speed of light. > For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. Light travels at about 0.75c in water. https://en.wikipedia.org/wiki/Refractive_index https://en.wikipedia.org/wiki/Refractive_index
    - posterboy 10y ago
      I guess that's relative, depending on which photon is referenced. The corollary is that from the photon POV, not its speed changes, but spacetime is warped, so it sees time in its own frame of reference going faster and/or distances shorter than we. You are both correct, but on different levels.
valarauca1 10y ago
Is there a theory for what "effect" would be produced by a theoretical object going faster than light? There really isn't an effect. The speed of light (in a vacuum) is just the speed of causality. The fabric of space-time will bend around you to ensure you can never get there. Objects without mass move at the speed of light, and no other speed. Now if you don't mean in a vacuum but in a medium like water, or air, or ice, etc. That is https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation
dotancohen 10y ago
The speed that light propagates is not always C. Light travels at C in a vacuum, but at a slower speed in any medium, e.g. water. Objects, and light itself, can travel faster than "the speed of light in water" in water. https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation
acqq 10y ago
> A "sonic boom" of light seems nonsensical The experiment specifically used mediums, where the speeds are not the speed through through the vacuum, the report from which smithsonianmag took the info and provides the link is somewhat more precise: http://www.livescience.com/57572-ultrafast-camera-captures-sonic-booms-of-light.html http://www.livescience.com/57572-ultrafast-camera-captures-s... "study lead author Jinyang Liang, an optical engineer at Washington University in St. Louis, and his colleagues designed a narrow tunnel filled with dry ice fog. This tunnel was sandwiched between plates made of a mixture of silicone rubber and aluminum oxide powder." "Then, the researchers fired pulses of green laser light — each lasting only 7 picoseconds (trillionths of a second) — down the tunnel. These pulses could scatter off the specks of dry ice within the tunnel, generating light waves that could enter the surrounding plates." "The green light that the scientists used traveled faster inside the tunnel than it did in the plates. As such, as a laser pulse moved down the tunnel, it left a cone of slower-moving overlapping light waves behind it within the plates."

by tabeth 10y ago

whatshisface 10y ago

No, there's no (experimentally supported) theory that would work at all with an object going faster than light. It just isn't in the geometry - asking for a hyperbolic rotation that stretches your motion's vector past c is like trying to turn an apple around in your hand in a way that makes it twice as big. What they're doing here is based on the fact that you can make light move at under c if you force it to travel through a dielectric material. The c in E=mc^2 is the speed of light in a vacuum: not necessarily through a carefully designed atomic obstacle course.

ianai 10y ago
Light always travels at c. It may appear to an observer to travel slower than c if it is being absorbed and emitted through media along the way.
- snarfy 10y ago
  It's not due to absorption/re-emission. The vacuum permittivity and permeability of free space is different than a medium. https://en.wikipedia.org/wiki/Vacuum_permittivity https://en.wikipedia.org/wiki/Vacuum_permittivity https://en.wikipedia.org/wiki/Vacuum_permeability https://en.wikipedia.org/wiki/Vacuum_permeability Free space has an electrical resistance of about 376 ohms. https://en.wikipedia.org/wiki/Impedance_of_free_space https://en.wikipedia.org/wiki/Impedance_of_free_space
  - passwd 10y ago
    >Free space has an electrical resistance of about 376 ohms. Impedance, to be precise. If free space had electrical resistance of 376 ohms, our world would be much stranger place than it is now.

cjslep 10y ago

Cherenkov radiation[0] is when a photon is travelling faster than the speed of light through water. To overly simplify, the speed of light in a vacuum is different than the speed of light through a medium. [0] https://en.m.wikipedia.org/wiki/Cherenkov_radiation https://en.m.wikipedia.org/wiki/Cherenkov_radiation

sdx23 10y ago
Beware the usage of the term "speed of light" here. There is two things: the phase velocity and the group velocity.
symmetricsaurus 10y ago
I think you mean when an electron (or other charged particle) travels through water.
FreeFull 10y ago
It doesn't happen with photons. Photons themselves always travel exactly at the (vacuum) speed of light, even in water, and they aren't charged particles. Cherenkov radiation happens with charged particles like electrons.
- delecti 10y ago
  A photon's net speed through a medium is not always the vacuum speed of light. > For example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. Light travels at about 0.75c in water. https://en.wikipedia.org/wiki/Refractive_index https://en.wikipedia.org/wiki/Refractive_index
  - posterboy 10y ago
    I guess that's relative, depending on which photon is referenced. The corollary is that from the photon POV, not its speed changes, but spacetime is warped, so it sees time in its own frame of reference going faster and/or distances shorter than we. You are both correct, but on different levels.

valarauca1 10y ago

Is there a theory for what "effect" would be produced by a theoretical object going faster than light? There really isn't an effect. The speed of light (in a vacuum) is just the speed of causality. The fabric of space-time will bend around you to ensure you can never get there. Objects without mass move at the speed of light, and no other speed. Now if you don't mean in a vacuum but in a medium like water, or air, or ice, etc. That is https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation

dotancohen 10y ago

The speed that light propagates is not always C. Light travels at C in a vacuum, but at a slower speed in any medium, e.g. water. Objects, and light itself, can travel faster than "the speed of light in water" in water. https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation

acqq 10y ago

> A "sonic boom" of light seems nonsensical The experiment specifically used mediums, where the speeds are not the speed through through the vacuum, the report from which smithsonianmag took the info and provides the link is somewhat more precise: http://www.livescience.com/57572-ultrafast-camera-captures-sonic-booms-of-light.html http://www.livescience.com/57572-ultrafast-camera-captures-s... "study lead author Jinyang Liang, an optical engineer at Washington University in St. Louis, and his colleagues designed a narrow tunnel filled with dry ice fog. This tunnel was sandwiched between plates made of a mixture of silicone rubber and aluminum oxide powder." "Then, the researchers fired pulses of green laser light — each lasting only 7 picoseconds (trillionths of a second) — down the tunnel. These pulses could scatter off the specks of dry ice within the tunnel, generating light waves that could enter the surrounding plates." "The green light that the scientists used traveled faster inside the tunnel than it did in the plates. As such, as a laser pulse moved down the tunnel, it left a cone of slower-moving overlapping light waves behind it within the plates."