What happens if you go faster than light?

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Discussion Overview

The discussion revolves around the implications of traveling faster than light, particularly in different media such as water. Participants explore theoretical scenarios, the concept of Cerenkov radiation, and the limitations imposed by the laws of physics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that if one travels faster than light in a medium, such as water, they would experience phenomena related to Cerenkov radiation.
  • Others argue that the laws of physics dictate that no object can exceed the speed of light in a vacuum, but it is possible for particles to exceed the speed of light in a medium.
  • One participant asserts that traveling faster than light would result in infinite mass and energy requirements, leading to catastrophic consequences.
  • A later reply questions the application of relativistic mass, suggesting that an observer does not perceive their mass increasing while moving.
  • Some participants clarify that the speed of light in a medium is not a universal limit and that certain particles can exceed this speed under specific conditions.
  • There is a discussion about the definitions of group velocity and phase velocity in dispersive media, and how these concepts relate to the speed of light.
  • One participant shares a personal experience witnessing Cerenkov radiation, highlighting its visual characteristics.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the implications of exceeding the speed of light in different media. The discussion remains unresolved, with differing interpretations of the laws governing light speed and particle behavior.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about relativistic effects, the definitions of speed in different contexts, and the specific conditions under which particles may exceed light speed in a medium.

mathlete
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Let's say you are in water where light travels at a speed of [tex]\frac{c}{n_w}[/tex] where [tex]n_w = 1.5[/tex] and you travel faster than this speed - what happens? What do you see?
 
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The laws of the speed of light apply to any medium, not just vacuum. If the speed of light were 1m/s in a certain material, that speed would be unattainable in that same medium.
 
whozum said:
The laws of the speed of light apply to any medium, not just vacuum. If the speed of light were 1m/s in a certain material, that speed would be unattainable in that same medium.

Yes, it can. That's the whole principle behind the Cerenkov radiation - charged particles moving in a medium at a faster velocity than light in that medium. Huge detectors are used to detect neutrinos this way.

Zz.
 
you will die, no seriously, you will. you will be of infinite weight and will require infinite energy to move, and will die. talk about letting yourself go. it is impossible to go faster than light, no matter what (unless you are a universe that just happens to be expanding, then, i read, it is possible. i don't know exactly how, but i will trust my reading skills

Fibonacci
 
1 said:
you will die, no seriously, you will. you will be of infinite weight and will require infinite energy to move, and will die. talk about letting yourself go. it is impossible to go faster than light, no matter what (unless you are a universe that just happens to be expanding, then, i read, it is possible. i don't know exactly how, but i will trust my reading skills

Fibonacci

This is a faulty application of relativistic mass. Take a look at how it is applied with respect to ANOTHER observer. Pay attention to the fact that a person does NOT see his/her mass increasing since he/she is always in the same proper frame and does not observe his/her mass moving.

Zz.
 
ZapperZ said:
This is a faulty application of relativistic mass. Take a look at how it is applied with respect to ANOTHER observer. Pay attention to the fact that a person does NOT see his/her mass increasing since he/she is always in the same proper frame and does not observe his/her mass moving.

Zz.

you didn't get that 'physics guru' for nothing, did you Zz.

Fibonacci
 
Fibonacci,

Please refrain from responding to question unless you are quite sure you are giving a correct answer.

- Warren
 
ZapperZ said:
Yes, it can. That's the whole principle behind the Cerenkov radiation - charged particles moving in a medium at a faster velocity than light in that medium. Huge detectors are used to detect neutrinos this way.

Zz.

Isn't that more of an exception than the rule?
 
offcourse it's an exception
 
  • #10
Then my answer to the OP is more or less correct. :D
 
  • #11
whozum said:
Then my answer to the OP is more or less correct. :D
No, it wasn't. It was completely wrong.

- Warren
 
  • #12
Care to explain why?
 
  • #13
You said that objects cannot exceed the speed of light in a medium. That is completely false.

- Warren
 
  • #14
Wont argue with you. How do objects go faster than the speed of light in a medium?
 
  • #15
By covering a greater distance in the same amount of time. I suspect you are looking for a good reason why they 'can'. Well, there is simply nothing that prevents something (often an electron) from doing so. Laws of physics are generally written according to what restricts movement or any other characteristic. It's just the way we interpret them - if it's not restricted to move a certain way, then it can.

Cerenkov radiation does not need to be explained here - http://en.wikipedia.org/wiki/Cerenkov_effect
and scroll to "Physical Origins"
 
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  • #16
Isn't it restricted by the same reasons its restricted in vacuum?
 
  • #17
whozum,

No. The speed of light in vacuum is a universal 'speed limit,' but the speed of light in an arbitrary medium is not.

- Warren
 
  • #18
whozum said:
Isn't it restricted by the same reasons its restricted in vacuum?

"in our world" there exists a universal speed limit c. From the Maxwell's equations we see that in vacuum light wave propagates with c. In the media this velocity is reduced due to existing wave impedance, but this doesn't mean that a universal constant is changed ;) just the EM wave propagates slower.
 
  • #19
whozum said:
Isn't that more of an exception than the rule?

I'm not sure what you mean by an "exception"? You said that NOTHING can travel faster than light in a particular medium with index of refraction greater than vacuum. I said no, this is not true. A neutrino, and the charged particle that it generates when it collides with other particles, CAN travel faster than light in a particular medium, such as water, ice, quartz plate, etc. This is how we detect neutrinos (see SuperKamiokande, MINOS, AMANDA, ICE CUBE, quartz plate in the linear accelerator that I work with, etc...).

This isn't an "exception" nor the rule. It is ALLOWED.

Zz.
 
  • #20
whozum said:
Wont argue with you. How do objects go faster than the speed of light in a medium?

This is because in a dispersive media other than a vacuum, we define "speed of light" as being the GROUP VELOCITY. In a vacuum, the group velocity and the phase velocity are IDENTICAL. When light enters a medium, these two are dispersed (thus, the term dispersive medium) and they are no longer identical.

Again, it is instructive for many people learning this subject to ALWAYS go back and figure out how we define things, and how certain things are measured. This is especially true when we get to the really exotic things and properties, such as "stopping light" in a medium to 0 m/s. Why would that be any different than having light falls onto a black piece of paper? That's stopping it, isn't it?

To appreciate such things, one must learn the intrinsic properties of light and how we define/measure these properties.

Zz.
 
  • #21
No object can go faster than the speed of light in vacuum. In a medium such as water, the speed of light is reduced. It is possible for an object, such as an electron or positron, to move faster than the speed of light in that medium but slower than the speed of light in vacuum.
 
  • #22
chroot said:
Fibonacci,

Please refrain from responding to question unless you are quite sure you are giving a correct answer.

- Warren

actually i thought i was right. :frown:
 
  • #23
The first time that I saw Cherenkov radiation was during a tour when they opened the Douglas Point nuclear reactor in the late '60s. The uranium storage pool is full of it. (Caused by neutrons exceeding c in water.) It's kind of eerie to look at, but a really beautiful colour.
 
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