Doppler Law in Light: Seeing the Light Barrier

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Discussion Overview

The discussion revolves around the application of the Doppler effect to light, particularly in relation to the concept of breaking the "light barrier." Participants explore whether such a phenomenon can be observed in everyday life and how it compares to sound waves and their associated shockwaves.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the Doppler law applies to light similarly to sound, questioning if a "light barrier" can be observed when light is emitted.
  • Others argue that breaking the light barrier in a vacuum is impossible, but within a material, particles can exceed the speed of light, leading to Cherenkov radiation.
  • One participant suggests that to create a shockwave effect with light, the light source itself must travel faster than light, rather than just emitting light at the speed of light.
  • There is a comparison made between sound and light, with some participants questioning if light should produce a shockwave similar to sound when the speed of light is exceeded.
  • Participants clarify that turning on a flashlight does not produce a burst of light akin to a sonic boom, as it does not involve exceeding the speed of light.

Areas of Agreement / Disagreement

Participants generally disagree on the applicability of the Doppler effect to light in the context of breaking the light barrier, with multiple competing views on the nature of light and sound waves.

Contextual Notes

There are unresolved assumptions regarding the definitions of "light barrier" and the conditions under which light behaves differently in various media. The discussion does not reach a consensus on the analogy between sound and light in this context.

bassplayer142
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I'm sure that the doppler law would come into effect in light as it does in sound. Not the changing of light color but breaking the light barrier as I'll call it. I'm just wondering if we ever see it or if we never see it in life. Even when you turn on a light shouldn't you be seeing this light barrier as a flash of light because it is going the speed of light or not.
 
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Breaking the light barrier in vacuum is impossible, since nothing (physical) can go faster than light.
But within a material it is possible to break the "light barrier".
Within a material, light can go slower that in vacuum.
Therefore a fast energetic particle can go faster than the speed of light in the given material.
This procudes some light emission called "Cerenkov radiation".

http://www.physics.upenn.edu/balloon/cerenkov_radiation.html
http://en.wikipedia.org/wiki/Cherenkov_radiation

You could observe it as a faint blue light in nuclear fuel storage pools.
 
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So in order to break the light barrier you can't just go the speed of light but faster.
 
I'm not sure what analogy you are trying to draw here, but do you hear a blast of sound when someone starts talking? Or are you saying that since light goes the speed of light, it should form some shockwave? Does sound do that?

There is a regular doppler effect for light that changes it's color, but I'm not sure how that relates to your question - it doesn't make much sense to me.
 
Yes, when you hit the speed of sound there is a shockwave. If you went faster then light wouldn't it be a light wave. A huge burst of light that goes off from the object.
 
It's the light source that must be traveling faster than light for the kind of "shock wave" effect I think you are talking about (and which lalbatros explained). Just turning on a flashlight does nothing.
 
Right - turning on a flashlight doesn't produce a burst of light just like talking doesn't produce a burst of sound.
 
Bassplayer; The Cerenkov radiation lalbatros mentioned is the optical analogy of a sonic boom (which I'm guessing is what you refer to when you say "shock wave").

Claude.
 

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