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Can Light Travel Faster Than Speed of Light 
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#1
Mar2510, 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? 


#2
Mar2510, 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 nearspeedoflight velocities. When you use the correct composition of velocities law, you see that the speed of light stays the same whatever frame of reference :) 


#3
Mar2510, 08:26 AM

P: 163

[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] 


#4
Mar2510, 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 


#5
Mar2510, 01:17 PM

P: 163

[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. 


#6
Mar2510, 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 lightspeed (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 subforum, because you really need to be starting at first principles here. (at least, in terms of Relativity and QM) 


#7
Mar2710, 11:53 AM

P: 2,158

Light can travel faster than c in the Casimir vacuum:
http://arxiv.org/abs/hepth/9810221 This does not lead to causal paradoxes, as explained in detail here: http://arxiv.org/abs/grqc/0107091 


#8
Mar2710, 12:08 PM

P: 136




#9
Mar2710, 12:10 PM

P: 136




#10
Mar2710, 12:13 PM

P: 93

I am not aware of the fact that the Casimir force violates “the most wellknown conservation law of energy” Could you clarify this point ?



#11
Mar2710, 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 ZeroPoint 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. 


#12
Mar2710, 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 


#13
Mar2710, 12:23 PM

P: 136

I can assure you there is. It's a wellknown 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. 


#14
Mar2710, 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) 


#15
Mar2710, 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. 


#16
Mar2710, 02:09 PM

Mentor
P: 16,162

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


#17
Mar2710, 02:30 PM

P: 136

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 zeropoint field. 


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