# B C as a Energy conversion constant

1. Jun 17, 2017

### xcom2112

I was thinking about the law of conservation of energy, states that energy can neither be created nor destroyed.

Then I thought about it more broadly, it actually states that the universe was created with a fixed amount of energy (and this energy only transforms from one form to another)

And then I thought a little more, in the big bang the universe was formed from energy, part of that energy became matter, according to the famous equation E = mc2

or Electromagnetic waves

so C is not the speed of electromagnetic waves (in a vacuum) or anything like that, it is simply the ratio in which energy becomes something else.

And if the energy in the universe is constant (as I assumed at the beginning), which for me is the only axiom, then if the waves will move faster than C , the energy conservation law will simply be violated.

Maybe someone already put it this way? (I've never seen, at least not at university, a way of looking at things like that)

2. Jun 17, 2017

### Staff: Mentor

Conservation of energy does not apply to the universe as a whole - there is no global energy conservation in general relativity.
It is related to both. But more fundamentally, it is the universal speed limit.
That doesn't make sense.

3. Jun 17, 2017

### Staff: Mentor

That's a natural assumption, but it turns out not to be correct. It's not so much that energy isn't conserved (it is - see below) but that there is no unambiguous way of defining "the total amount of energy in the universe" so nothing we can point to and say "this quantity is conserved".

We can reword the law of conservation of energy to be more precise: Imagine an arbitrarily small box. At some moment it contains a certain amount of energy, and a moment later it contains a different amount. The difference between the two will be exactly equal to the amount of energy that left or entered the box. In this form the law of conservation of energy works just fine, but it is also clear that it cannot be extended to cover the entire universe. For a bit more detail, you might be interested in http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

4. Jun 17, 2017

### Mister T

The $m$ in the expression $mc^2$ represents mass, not matter. The Einstein mass-energy equivalence teaches us that mass is not a measure of the quantity of matter because the mass of a composite body is made up in at least part by the energies of the constituents.

And $mc^2$ is not equal to the total energy of a body. It's equal to the rest energy.