origin":wozhmsek said:

Fallingstar1971":wozhmsek said:

So C2=E/M is invalid?

So M= E/C2 is invalid?

So E=MC2 is invalid?

Star

Yes the first 2 equations are invalid in a physical sense even if they are mathematically they are correct. If you think about it for a minute it would be clear to you that the first equations has no physical relevence. What in the world could this mean in a physical sense:

If I take the square root of a quantity of energy and divide it by a square root of a mass I will end up with the speed of light.

That is competely meaningless in a physical sense, but mathematically it is correct.

I'm not sure I would call those equations invalid myself.

The second and the third are used in nuclear calculations. The third gives you the energy released based on a known mass deficit. The second can be used to figure out the magnitude of mass deficit you would need to release a certain amount of energy. Roughly ... much more complicated in practice.

Now the first (c^2=E/m) I think is probably fundamental in ways we don't quite understand yet. The fundamental constant c seems to be much more than just the speed of light, IMHO.

For example, in Special Relativity, space and time are now viewed as one single "entity". So, an object can be viewed as having motion through space AND time. And, for any object, its motion through time PLUS it's motion through space EQUALS the speed of light. For example, in the twin paradox, one twin is at rest (i.e. motion through time only). The other twin, which is on the interstellar trip, has motion through time AND space RELATIVE to the twin at rest. So, his time is slowed, or dilated, relative to the other twin, since some of his motion is now directed to displacing himself in space. Another way of looking at the twin paradox.

Anyhow, in special relativity, c is a fundamental quantity determining relationships of motion.

I view that first eq (c^2 = E/m ) as another fundamental relation between mass and energy. If one is "converted" from one to another, the universe WORKS IN SUCH A WAY, that the ratio is ALWAYS equal to c^2.

It's like the Lagrangian formulation of classical mechanics. The Lagrangian is equal to the kinetic energy minus the potential energy (L = T - V). Why does the Universe work in such a way that the time integral of this quantity, known as the action, is ALWAYS a minimum (really an extremum for the mathematicall precise). This is the least action principle and the equation used is [d/dt(dL/dqdot) - dL/dq = 0]. We don't fully know, but it's a fundamental way the Universe seems to work, and it comes in REALLY, REALLY, REALLY handy for solving many problems in physics

anyhow, sorry for the long winded post.