Why is the maximum speed the speed of light

Transferred from a reply .

　　 In fact, we are not very accurate about the speed of light , This involves what is light . What we are talking about in physics is actually the dissemination of information （ The interaction of matter ） Is there an upper limit on speed , That is, whether there is over distance effect . At present, all human experiments have not found the over distance effect , Therefore, we believe that there is a limit to the speed of information transmission in the world .

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　　 Mathematically, such a system becomes Poincare symmetry . Mathematically, we can prove , The upper limit of velocity in Poincare symmetric system is conserved . For all inertial reference frames , The upper speed limit is exactly the same . We use it c To represent the highest speed .

　　 Generative element in Poincare Group P Corresponding invariants , Four dimensional momentum Satisfy the mass energy equation ： , Or use a more familiar way of writing . When momentum is zero , That is, when still , The mass energy equation becomes the one printed all over the street .

　　 From the Lagrange equation of free particles

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　　 When the mass of the particle is 0 When , , therefore . That is to say , If there is a maximum value for the spread of information , Then the highest value is the same in all inertial frames , And all particles without mass must move at the highest speed . And photon is such a particle without mass . Because the speed of light is easy to measure , So we call it the highest speed “ The speed of light ”. And the speed of light we measured is finite , This confirms the assumption that there is the highest transmission speed of information

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　　 Poincare symmetry has another meaning . If there is no highest speed in the world , The laws of physics will satisfy the symmetry of Galileo Group , In this case, the laws of physics change with the moving speed of the coordinate system , That is to say, there is an absolute stationary coordinate system in the world , Will be different from other inertial frames . Etheric thought is based on this assumption . This hypothesis was rejected by Michelson interference experiment . This is another proof that speed has limits .