Could information travel faster than C

In summary: So the wave front would move at the speed of light in a vacuum.In summary, information can't travel faster than the speed of light.
  • #1
127
5
I've heard a few times that information can't travel faster than C, but what if you have an extremely dense metal rod that extends for 1 light year in length, the moment you move it here, wouldn't it instantaneously move at the other end 1 light year away? Or would the electrons that make it up cause it to take time?
 
Physics news on Phys.org
  • #2
  • #5
You have asked about a specific example using a rigid rod. But it can be shown in general that if a signal could travel faster than c, there would be frames of reference in which causality would be violated i.e. the effect of the signal would occur before the signal was generated.
 
  • #6
According to a PRL letter, superluminal communications have been well demonstrated experimentally:

“We note that such a superluminal phenomenon ... should consist with the causality and special relativity. Our experiments show that the group velocity of the signal pulse does exceed c ... provides a new way of opening up superluminal communications via optical fibers."

L. Zhang, L. Zhan, K. Qian, J. Liu, Q. Shen, X. Hu, S. Luo, Superluminal propagation at negative group velocity in optical fibers based on Brillouin lasing oscillation, Phys. Rev. Lett. 107 (2011) 093903).
 
  • #7
PFfan01 said:
According to a PRL letter, superluminal communications have been well demonstrated experimentally:

“We note that such a superluminal phenomenon ... should consist with the causality and special relativity. Our experiments show that the group velocity of the signal pulse does exceed c ... provides a new way of opening up superluminal communications via optical fibers."

L. Zhang, L. Zhan, K. Qian, J. Liu, Q. Shen, X. Hu, S. Luo, Superluminal propagation at negative group velocity in optical fibers based on Brillouin lasing oscillation, Phys. Rev. Lett. 107 (2011) 093903).
First, this paper is not relevant to the OP who is asking about superluminal information transfer in a rigid rod.

Second, Zhang is infamous for performing rather mundane experiments and then grossly mis-representing the results of those experiments, usually with the clear goal to disprove something about relativity. He is a highly biased author and, to my knowledge, none of his outlandish claims have ever been reproduced. This paper demonstrates a clear misunderstanding of basic signal properties. Specifically, he reports the group velocity as -0.151 c, decidedly sub-luminal. The group velocity is the velocity that carries the signal pulse and is useful for information transfer. A superluminal phase velocity is well-known and also known to not carry information.
 
  • Like
Likes russ_watters, QuantumQuest, PeterDonis and 2 others
  • #8
Well, well, well... It's a PRL ;-)) SCNR.
 
  • #9
victorhugo said:
I've heard a few times that information can't travel faster than C, but what if you have an extremely dense metal rod that extends for 1 light year in length, the moment you move it here, wouldn't it instantaneously move at the other end 1 light year away? Or would the electrons that make it up cause it to take time?
You would set up a longitudinal wave in the rod. The speed of that wave front is given by v = √(λ/ρ), where λ is the stiffness constant in Hooke's law and ρ is the linear density of the rod.
 

1. Is it possible for information to travel faster than the speed of light?

No, according to the theory of relativity, the speed of light, denoted by "c", is the maximum speed at which all matter and information can travel. It is considered a fundamental constant of the universe and cannot be exceeded.

2. Can anything else travel faster than light?

No, as mentioned before, the speed of light is the ultimate speed limit in the universe. Nothing, including particles, energy, or information, can travel faster than light.

3. What about quantum entanglement? Doesn't that allow for instantaneous communication?

While quantum entanglement does allow for instantaneous correlation between two particles, it does not allow for communication. This is because the information transmitted through entanglement is random and cannot be controlled or manipulated in a specific way.

4. Is there any evidence that information has traveled faster than light in the past?

No, there is no scientific evidence to support the claim that information has traveled faster than light. All experiments and observations have consistently shown that the speed of light is the ultimate speed limit.

5. Could there be any loopholes or exceptions to the speed of light limit?

Based on our current understanding of physics, there are no known exceptions or loopholes to the speed of light limit. However, as science and technology continue to advance, our understanding of the universe may change and reveal new possibilities.

Similar threads

Replies
6
Views
1K
  • Special and General Relativity
Replies
9
Views
1K
  • Special and General Relativity
Replies
6
Views
1K
  • Special and General Relativity
Replies
2
Views
831
  • Special and General Relativity
Replies
19
Views
1K
Replies
3
Views
264
  • Special and General Relativity
Replies
6
Views
680
  • Special and General Relativity
2
Replies
36
Views
2K
  • Special and General Relativity
Replies
20
Views
2K
  • Special and General Relativity
Replies
8
Views
1K
Back
Top