Why do gravitational waves propagate at the speed of light?

In summary: It has not yet been demonstrated that gravity waves propagate faster than the speed of light, but that is the most likely explanation.
  • #1
KarminValso1724
25
1
If things such as quantum entanglement and the expansion of space can travel faster than light, then why can't gravitational waves, which are vibrations of spacetime? I thought that only matter cannot move through space faster than light. Also, has it been 100 percent proven that gravity waves travel at the speed of light?
 
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  • #2
The speed of propagation of gravitational waves is derived in the process of solving a system of equations. In the solution, it turns out they propagate at the speed of light. So it's not a matter of 'could they travel faster?' It's simply that the theory predicts, via the equations, that that's the speed at which they will propagate. If they propagated at any other speed we'd need a new theory of gravity.
 
  • #3
KarminValso1724 said:
If things such as quantum entanglement and the expansion of space can travel faster than light
Neither of those travel faster than light... Because they aren't traveling at all.

(What they are doing is a good topic for another thread, but both have been extensively discussed in older threads please so don't start that thread until you've read what's already out there).
 
  • #4
KarminValso1724 said:
If things such as quantum entanglement and the expansion of space can travel faster than light, then why can't gravitational waves, which are vibrations of spacetime?

In classical electromagnetism, it follows from Maxwell's equations that the propagation of electromagnetic radiation is governed by a certain wave equation which dictates that it does so at the speed of light. Likewise, the Einstein field equations imply that the propagation of gravitational waves is governed by a wave equation which dictates that this happens no faster than the speed of light; that is quite simply what the respective laws of physics demand. I suppose you can think about it as nature's way to ensure that there is no possibility of causality violations.
 
  • #5
KarminValso1724 said:
If things such as quantum entanglement and the expansion of space can travel faster than light, then why can't gravitational waves, which are vibrations of spacetime? I thought that only matter cannot move through space faster than light. Also, has it been 100 percent proven that gravity waves travel at the speed of light?

Saying that entanglement and the expansion of space "travel faster than light" is misleading, because entanglement and the expansion of space can't be used to send faster than light (FTL) signals (that the expansion of space can't be used to send FTL signals is evident, that entanglement can't be used to send FTL signals is a proven result of quantum mechanics).

Gravitational waves are solutions of Einstein's field equations of general relativity, which predict gravitational waves traveling at the speed of light. The recent detection of gravitational waves from merging black holes (LIGO experiment) seems entirely consistent with general relativity.
 

1. Why do gravitational waves propagate at the speed of light?

Gravitational waves are a form of energy that travel through space at the speed of light. This is because they are a type of electromagnetic radiation, and all forms of electromagnetic radiation, including light, travel at the same speed.

2. Is the speed of light the maximum speed at which gravitational waves can travel?

Yes, the speed of light is the maximum speed at which any form of electromagnetic radiation, including gravitational waves, can travel. According to Einstein's theory of relativity, the speed of light is a fundamental constant that cannot be exceeded by anything with mass.

3. How do we know that gravitational waves travel at the speed of light?

Scientists have observed gravitational waves from distant events, such as the collision of two black holes. By analyzing the time it took for the waves to reach Earth, they were able to confirm that the speed of the waves was consistent with the speed of light.

4. Can gravitational waves travel faster than the speed of light?

No, according to Einstein's theory of relativity, nothing can travel faster than the speed of light in a vacuum. This means that gravitational waves, like all forms of electromagnetic radiation, are bound by this speed limit.

5. What implications does the speed of light for gravitational waves have on our understanding of the universe?

The fact that gravitational waves travel at the speed of light has significant implications for our understanding of the universe. It means that they can help us study and observe events that are otherwise invisible to us, such as the collision of black holes. It also confirms the validity of Einstein's theory of general relativity, which predicted the existence of gravitational waves.

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