# What is the experimental basis for using the speed-of-light, $c,$ as the maximum speed in the universe? [closed]

Doppler effect, mass changes of objects, and all relativistic effects (v^2/c^2) are based on $c$ as the maximum velocity ($Vt$) in the Universe. We have a fairly good understanding of relativity (I will stop at SR). If $Vt$ was only slightly higher than $c$ (say 0.001%), then certain conflicts in physics could be resolved. For example, photons could then have a very insignificant rest mass, which would then match all the other photon physical characteristics and properties.

Therefore my question is - What is the experimental and/ or measured data for setting that ultimate velocity limit? Keep in mind that assuming 'nothing goes faster than the speed of light' is not what I am asking as it is generally agreed that we have not seen anything yet. Nor am I asking for mathematical assumptions that were then incorporated into the interpretation of the measured data, as this is circular logic.

## closed as unclear what you're asking by knzhou, CuriousOne, heather, John Rennie, Qmechanic♦Aug 4 '16 at 21:45

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• Special and general relativity along with all the measurements validating them? – Sanya Aug 3 '16 at 21:26

You see, the Lorentz transformation arises as one of the symettries of electromagnetism, and the speed of light appears as powers of $\epsilon_0$ and $\mu_0$ (the permittivity and permiability of free space), which were measured with some attention to detail in the development of electromagnetism.