What does "E eqals m c squared" mean?

On Wed, 1 Mar 2000, ba wrote:

> I've been trying to find a "layman's term" definition
> of what exactly e equals mc squared (e=mc2) means. I
> know that e is energy, m is mass and I'm pretty sure
> c2 is the speed of light but I'm not sure how it all
> fits together. Any input would be greatly
> appreciated.

Hello,

While Einstein's equation seems very simple, it is, in fact, a very
complicated concept. First, you have all the parts labeled correctly. c
is the speed of light, and c^2 is c times c. M is the "rest mass", or how
much mass an object has if it is not moving.

What this equation means is that it is possible to transform mass into
energy, and it is possible to transform energy into mass. In other words,
mass is just a special form of energy, just like heat and motion are both
forms of energy.

An example of this is nuclear fusion, the reaction that powers the sun.
In the first step of this process, two hydrogen atoms smash together and
stick together, releasing energy in the process. If you weigh the two
hydrogen atoms at the beginning and the deuterium atom that is the result
at the end, you will find that the deuterium is a fraction of a percent
lighter than the two hydrogen atoms! If you use Einstein's equation, the
energy that the "missing" mass is equal to is exactly the amount of energy
that came out of the reaction! If you want to split deuterium back into
two hydrogen atoms, you need to put the same amount of energy back into
the deuterium, at which point the energy turns into mass and the two
hydrogen atoms come apart.

I hope this helps to clear up Einstein's equation some. I know it doesn't
explain WHY the equation has the form that it does, but the equation is
correct!

Thanks for writing.

Sincerely,
Kurtis Williams

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