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Can Light Travel Faster Than Speed of Light

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Svensken
#1
Mar25-10, 04:55 AM
P: 29
Hey!

If you fire a gun standing still the bullet will travel at a certain velocity.
If you fire a gun sitting in an airplane, the bullet's velocity will be speed of plane plus the the velocity due to the gun.

If you fire a bullet with a light being emitted from it: will the velocity of the light be:
The light plus the velocity of the bullet?
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guerom00
#2
Mar25-10, 05:04 AM
P: 93
No, the speed of light will be the same, whatever frame of reference :)
The reason : when you say that “If you fire a gun sitting in an airplane, the bullet's velocity will be speed of plane plus the the velocity due to the gun.” you simply add the two velocities (the one from the plane plus the one from the bullet). This law (adding the two velocities) is only an approximation when the velocities are small wrt the speed of light; it is incorrect when you have to deal with near-speed-of-light velocities.
When you use the correct composition of velocities law, you see that the speed of light stays the same whatever frame of reference :)
Redsummers
#3
Mar25-10, 08:26 AM
P: 163
Quote Quote by Svensken View Post
If you fire a bullet with a light being emitted from it: will the velocity of the light be:
The light plus the velocity of the bullet?
No, that could never happen, since photons are massless particles and they will always have that same speed, as for:

[tex]c = \nu\lambda[/tex]

And you could check the ranges of both the wavelength and the frequency in a electromagnetic radiation table and see how they concur on maintaining the [tex]c[/tex] constant. Which, however, must not to be confused with the energy of the photon:

[tex] E = \frac{hc}{\lambda} = h\nu[/tex]

Ali Inam
#4
Mar25-10, 12:52 PM
P: 99
Can Light Travel Faster Than Speed of Light

the bullet's velocity will travel with the velocity of light, but it wont attain its velocity, will it ? !

Obviously, the speed of light is far too much greater to make the velocity of gun compatible with that of light
Redsummers
#5
Mar25-10, 01:17 PM
P: 163
Quote Quote by Ali Inam View Post
the bullet's velocity will travel with the velocity of light, but it wont attain its velocity, will it ? !

Obviously, the speed of light is far too much greater to make the velocity of gun compatible with that of light
I don't think I understand your question, but an object such as a bullet to reach the speed of light, infinite energy would be needed. No matter how fast is the bullet traveling, the speed of light c will be the same for any inertial frames of reference moving with the relative velocity [tex]V[/tex]. According to the velocity transformations of Lorentz:

[tex]v' = \frac{v - V}{1 - vV/c^2}[/tex]

So, again you can see from here that if you set [tex]v = c[/tex], one can only say that the speed of light is the largest, since for [tex]V > c[/tex] would lead you to imaginary numbers as a result, if we regard the other lorentz transformations of the velocity.
Frame Dragger
#6
Mar25-10, 07:17 PM
P: 1,540
I realize this isn't "physics", but the title of this thread is a tautology; light can't travel faster than light, because then light would be traveling that fast.

So, maybe thinking about the issue long enough to formulate a thread title would be a good idea?

As for the basic question you're posing, NO. This is the what SR was about, with light flashes on trains and such. I suggest basic research into first SR, and then GR. Your question is the premise upon which relativity is BASED; that invariant of "bullet", the light ALWAYS moves at local light-speed (c in a vacuum). You can't "add" velocity to light, or subtract it, except insofar as the velocity changes in a given medium, which has nothing to do with your question.

EDIT: This is also a question about Relativity, not Quantum Physics. May I suggest you ask a staff member to move this thread to the appropriate forum? In your case, I would suggest the Acadmic Guidence sub-forum, because you really need to be starting at first principles here. (at least, in terms of Relativity and QM)
Count Iblis
#7
Mar27-10, 11:53 AM
P: 2,157
Light can travel faster than c in the Casimir vacuum:

http://arxiv.org/abs/hep-th/9810221

This does not lead to causal paradoxes, as explained in detail here:

http://arxiv.org/abs/gr-qc/0107091
ManyNames
#8
Mar27-10, 12:08 PM
P: 136
Quote Quote by Count Iblis View Post
Light can travel faster than c in the Casimir vacuum:

http://arxiv.org/abs/hep-th/9810221

This does not lead to causal paradoxes, as explained in detail here:

http://arxiv.org/abs/gr-qc/0107091
The difference are virtual photons. I've not read the link, but i know a fair bit to realize i think this is the type of superluminosity of particles of light. For a short time virtual particles can travel faster than light under the uncertainty principle.
ManyNames
#9
Mar27-10, 12:10 PM
P: 136
Quote Quote by Count Iblis View Post
Light can travel faster than c in the Casimir vacuum:

http://arxiv.org/abs/hep-th/9810221

This does not lead to causal paradoxes, as explained in detail here:

http://arxiv.org/abs/gr-qc/0107091
Moreover, whilst it may not lead to causal paradoxes, the Casimir Force does, because it violates the most well-known conservation law of energy; This is the fine line between which is classical, and which obeys the uncertainty principle.
guerom00
#10
Mar27-10, 12:13 PM
P: 93
I am not aware of the fact that the Casimir force violates “the most well-known conservation law of energy” Could you clarify this point ?
ManyNames
#11
Mar27-10, 12:16 PM
P: 136
Sure.

The Casimir Force is a direct experimental result of which is believed to be a background energy of virtual particles; also known as the Zero-Point Field. It is from here, energy is released spontaneously and created even in a lab. The conservation in which states energy can only change states and cannot be created is therefore violated, since energy apparently can be created from the virtual vacuum which is a resavior of negative energy - an infinite amount presumably.
guerom00
#12
Mar27-10, 12:20 PM
P: 93
I know what the Casimir force is since it is my research field
I can assure you that there is no violation of any energy conservation principle
ManyNames
#13
Mar27-10, 12:23 PM
P: 136
I can assure you there is. It's a well-known fact.

The classical theory states no energy can be created. But we can create energy from the vacuum, from virtual to real.

It stands to reason this is a violation of the classical sense.
guerom00
#14
Mar27-10, 12:38 PM
P: 93
There is no energy created, don't trust those QED mumbo jumbo
Rather, consider Casimir interaction as usual van der Waals interaction (which it is)
ManyNames
#15
Mar27-10, 12:42 PM
P: 136
Au contrare;

In a recent discussion on this forum, i repeatedly told a person that there is no general consensus whether van der Waals interaction was literally the case of reality. The ZPF is still highly respected, and one must remember that the ZPF was proposed to exist according to the rules of quantum mechanics long before there was any confirmation of its theoretical evidence in the form of the attractive and repulsive Casimir Force.

One can choose either theory - but the ZPF is still i would estimate, the leader of the pack over this new interpretation, which i am not fond of.
Vanadium 50
#16
Mar27-10, 02:09 PM
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Quote Quote by ManyNames View Post
I can assure you there is. It's a well-known fact.
No, it's not. (And it takes quite some chutzpah to argue this point with someone who does this for a living!)

There is no more a violation of conservation of energy than finding a rock on a hilltop and rolling it down.
ManyNames
#17
Mar27-10, 02:30 PM
P: 136
Quote Quote by Vanadium 50 View Post
No, it's not. (And it takes quite some chutzpah to argue this point with someone who does this for a living!)

There is no more a violation of conservation of energy than finding a rock on a hilltop and rolling it down.

Yes there is. Taking for granted that the total energy of the universe is still zero, sporadic appearances of energy from the vacuum which is a creation process goes directly against the idea that energy cannot be created by the classical law.

I'm not going to argue about it. You can agree to disagree if this is what it will consist of. I've studied physics for many years now, and i am positive i have a clear grasp on the subject of the zero-point field.
dx
#18
Mar27-10, 03:34 PM
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P: 1,961
There is no violation of conservation of energy in quantum mechanics, and quantum mechanics fully accounts for the Casimir force.


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