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Author Topic: What is the relevence of c squared in Einstein's famous equation?  (Read 6456 times)

Paul Young

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Paul Young  asked the Naked Scientists:
Hi my name is Paul from Woldingham in Surrey and my question relates to Einstein's famous E=MC^2 formula
What is the relevance of the C-squared piece? Since you can't travel faster than the speed of light why would you need to square it in the formula.
It's always confused me?
Thanks for your help
Paul Young

What do you think?
« Last Edit: 07/02/2011 04:30:02 by _system »


Offline syhprum

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C squared occurs because special relativity is mostly concerned with Lorenz contraction's and the solution of geometric equations, you think this complex ? wait till you get to general relativity where you will encounter c^4

Offline Eric A. Taylor

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E=MC2 isn't actually part of Relativity, It's sort of an addendum. The equation basically states that matter, the stuff that makes all physical objects, and energy are the same thing in different forms. C which is the speed of light important because it states something about energy. Energy MUST move at the speed of light. If a bit of energy slows down it will become matter.

Some science fiction stories describe being of "pure energy". If you had a being made of nothing but energy then they could never stop nor interact with matter in any way without changing.

Offline yor_on

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"Einstein's insight was to see that E=mc^2 was the proper energy of mass m, the energy associated with mass m, independent of its motion. When it had relative speed, its energy was increased from γ(0)mc^2 to γ(v)mc^2, the difference between them being its kinetic energy. Look here for more of it.

There is one thing I don't agree with in that link though. They have a movie in where they define the energy in a compressed spring as 'potential'. As far as I know that 'energy' is not 'potential' at all, it's real, also expressed as a added mass as long as the spring is compressed. A 'potential energy' is better expressed as the relation between a 'photon' propagating, and the 'energy' people will define to it, before meeting it. That will depend on how they move relative the photon, from it or towards it, and as long they haven't meet that photon its 'energy' will indeed only be potential to them, not real. But otherwise it's a cool link.
« Last Edit: 07/02/2011 21:16:10 by yor_on »

Offline Bill S

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Since you can't travel faster than the speed of light why would you need to square it in the formula.

Paul, this seems to be a part of your question that has not been addressed.
In my very non-expert opinion, I would say that this has nothing directly to do with the inability to travel faster than light.  As Eric pointed out, "c" is relevant because of its link to energy, while the fact that it has to be squared for the calculation is simply a measure of the amount of energy "contained" in each unit of mass.

Offline Geezer

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I think Bill is right. c˛ just happens to be the proportion between matter and energy (for reasons that I do not understand).

What I do understand is that c is a very big number, and c˛ is an incredibly big number, so converting mass into energy creates an enormous amount of energy. Going in the other direction, it takes an enormous amount of energy to create any mass. 

Offline colarris

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I have no idea what any of you just said. :D

Offline grizelda

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I have no idea what any of you just said. :D

That's just Yor_on. I think he mixes his frames of references sometimes.

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