*[W]hen we formulate the laws of mechanics so that they, too, are invariant under Lorentz transformations, we get the formula above for kinetic energy, with E=mc*

^{2}in the limiting case of zero velocity.Image: Wallpaper Safari |

Source/Credit: Quora

By Viktor T. Toth | September 30, 2015

OK, let me challenge the theory right here on the spot. That's because

*E*=

*mc*is no theory. It is just a limiting case of another formula, the formula for the kinetic energy of a particle of mass

^{2}*m*in the limit of zero velocity:

But this formula is no theory either. The actual theory is a set of two postulates: that the laws of physics are the same in all inertial systems regardless of their velocities, and that there exists an invariant velocity, which is the same for all observers, and which happens to be the vacuum speed of light.

The second assumption was actually inspired by another theory, Maxwell's theory of electromagnetism, which predicted just such an invariant velocity, making it incompatible with the pre-relativity concepts of space and time. So arguably, we only need the first assumption for relativity: the laws of physics (including Maxwell's theory) must be the same for all observers. It so happens that Maxwell's theory is invariant when inertial systems are related to each other by Lorentz transformations. And when we formulate the laws of mechanics so that they, too, are invariant under Lorentz transformations, we get the formula above for kinetic energy, with

*E*=

*mc*in the limiting case of zero velocity.

^{2}So then, you might wonder... are the laws of relativity challenged by physicists? And the answer is... all the time. Not a day goes by without new papers appearing on arXiv.org, proposing theories that violate Lorentz invariance, or theories that otherwise change, alter, expand or otherwise modify the postulates of special relativity.

There are a variety of motivations behind these attempts: to challenge the status quo, to explain, or improve the explanations for, hard to explain phenomena, to simply probe the limits of validity of the theory. But these proposals also face a great challenge: the body of experimental/observational evidence confirming the predictions of relativity is huge, and quite obviously, any new proposal has to be at least as good as the one it purports to replace when it comes to explaining away existing observations.

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**Written by Viktor T. Toth**, IT pro, part-time physicist - Written Sep 30, 2015 ·

Upvoted by Abhijeet Borkar, PhD in Physics (Astrophysics) and Jesse Raffield, Master's degree in physics

Read original post here: Why is E=mc2 so universally accepted as accurate?

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