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I understand why the speed of light is a constant in all reference frames, and the reason behind why the mass of an object increases as it approaches the speed of light.( Since the added energy has to go somewhere it turns out to be just mass.) Now, due to this and the fact that we require infinite energy to reach the speed of light, we will never be able to do that. But, people also seem to be talking about information and forces(like the electrostatic force) not being able to travel faster than the speed of light. I dont understand this statement.It is not mass anyway, then why is it restricted by the speed of light? (I AM NOT TALKING ABOUT QUANTUM ENTANGLEMENT, SINCE WE DON'T KNOW MUCH ABOUT IT;ALL CLASSICAL)

Qmechanic
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Chandrahas
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    and the reason behind why the mass of an object increases as it approaches the speed of light This is not the way to view this situation. Please read: Invariant Mass –  Jan 27 '17 at 18:28
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    The invariance of the speed of light is a restriction on causality itself! Nothing to do necessarily with mass or energy! –  Jan 27 '17 at 18:49
  • But I don't understand why? for particles with mass its quite simple but why does it restrict the electrostatic force?gravity? etc. – Chandrahas Jan 28 '17 at 02:51
  • Mass and energy are similar. A force comes from a field, and it has energy. As for information, it's always about the physical means of having it go from here to there. It needs to be carried by some physical thing, i.e. Energy. So it also doesn't go faster than light. – Bob Bee Jan 28 '17 at 04:30
  • If you can send information, in any form, faster than light, then it is trivial to send it into your own past. –  Jan 28 '17 at 14:43

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In very simple words: One of interesting hypotheses assumes, that it impossible to send a beam of light (or photon) back and forth immediately, because mass less particles (force carriers) move inside material bodies with a speed of light and create interactions in these material bodies.

Since force carriers move inside material bodies with the same velocity as they move outside material bodies, certain amount of interactions will take place inside material body ANYWAY, while flying photon will travel back and forth to a distant point. Thus, speed of light is determined by inner properties of matter.

It means, it is impossible to send a photon to a distant point and back instantly, even if we wish to send it with “infinitely large velocity”. As I understand, it is roughly the same as to measure velocity of light using ordinary light clock. We cannot measure any other velocity than c.

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Instead of calling it the speed of light what if it were called "the speed at which information travels" or "the speed of cause and effect" or "the speed of anything without mass." Any of these could have been the name for "C." The equations you are thinking of when you say, "the added energy has to go somewhere it turns out to be just mass," is just one example of an outcome; it is not the underlying reason that C is the speed limit and light is not the only thing the speed limit applies to.

Paul B
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I was about to post the same question as this. I have read through the responses but, for me, the question is not answered.

I was reading about entanglement and it was suggesting instantaneous communication between entangled particles. But then it said communication cannot exceed the speed of light. I'm sure this is true, but why, what physical principle would be violated.

john
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  • This is actually an entanglement question that has been discussed a number of times here already. A few examples: https://physics.stackexchange.com/questions/203831/ftl-communication-with-quantum-entanglement or https://physics.stackexchange.com/questions/504879/can-quantum-entanglement-provide-a-faster-way-of-transfer-of-information-than-th/504907#504907 – DrChinese Dec 19 '23 at 15:36