Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: yamo on 28/02/2010 19:12:49

can e=mc˛ be solved to give a value for t, time and d, space? what are the values of time and space?
mod edit: Please make your topic titles a question. Because i'm simply gorgeous I have done it for you.

No.

The relation e=mc^{2} is valid for any value of t and d.
In other words, it was valid yesterday and so it is today.
It is valid here in my place and everywhere in universe.
Or, if you wish, if I move an object with rest mass m from here to there,
the total energy stored in the rest mass will still be e=mc^{2}.

Umm.. e=mc^{2} is not valid for any value of t & s (where s= displacement) because the result of s/t must always be <= 'c'
However, t & s are just different qualities of spacetime, where t can be equated to s, so you essentially end up trying to deal with s/s. The difference between s & t is really just down to our point of view.

E=mc^{2} just tells you how to relate mass and energy for a stationary object (one that isn't moving) at a single point in spacetime. It's valid for any single point in spacetime that you want to choose, as long as the object isn't moving, so that you can't tell the exact position and time just by looking at the equation.
By the way, the full equation is E^{2}=m^{2}c^{4}+p^{2}c^{2},
where p is momentum, which tells you about how the object is moving in space. This is usually the one you want to use, since it's valid no matter how fast you or the object is moving. If the object isn't moving, p=0 and this equation becomes E=mc^{2}.
Edit: to fix a sign error.

well c is a velocity delta d over delta t. so what i am looking for is a definition for t or d in terms of e and m. mebbe the limit as delta t(or d) approaches 0.

If you care about velocity, which is delta d/delta t, then you can get it from the energy and momentum: v=pc^{2}/E. You can't get position of time themselves because the equations are valid at any spacetime point you want to choose, so there's nothing to tell you which one you're using.

Try working with this one, M = hf/c^2

Yamo: no, you can't "solve" this. That's because c is just a conversion factor between our measures of space and time. It's the speed of light, so it's a speed, which is distance over time, and both of these measures are defined using light.
JP: pair production and annihilation demonstrates a kind of "flip flop" between the p^{2}c^{2} and the m^{2}c^{4}.