# E=mc^2, backwords

1. Mar 17, 2005

### oldunion

If matter can be converted into energy, why then can energy not be converted into matter?

2. Mar 17, 2005

### Staff: Mentor

Energy is converted into matter every day at high-energy particle physics laboratories such as Fermilab and CERN. Smash together particles with lots of kinetic energy, and some of that energy goes into the mass of the particles that are created in the collision.

3. Mar 17, 2005

### HallsofIvy

Staff Emeritus
The point is that BECAUSE e= mc2, and c is a very large number, a small amount of mass produces a huge amount of energy but it takes a huge amount of energy to produce a small amount of mass- energy to mass conversion happens all the time- you just don't notice it because it produces such a small mass!

4. Mar 18, 2005

### pmb_phy

The term "matter" is too ill defined to correctly answer your question. But for the most part, in SR, ditates that energy of a closed system is always conserved as observed in in inertial frame of reference.

Pete

5. Mar 18, 2005

### oldunion

how could energy be conserved if you went from it to mass. you would be losing it all over the place, thermal, light, friction

6. Mar 18, 2005

### chroot

Staff Emeritus
"Energy" is a very generic term. Mass and energy are really essentially the same thing -- that's what E=mc^2 is all about in the first place. If you convert one kind of energy, like radiation, into mass, you're not destroying the energy -- you're locking it up in the form of mass. You could later turn that mass back into the same amount of energy you started with.

In General Relativity, the scientific theory which describes gravitation, energy and mass are treated quite directly as different kinds of the same "stuff." They both, in fact, produce gravitational forces in the same way.

- Warren

7. Mar 18, 2005

### Staff: Mentor

Because we define an object to have a certain amount of energy (its "rest energy") simply because it has a certain amount of mass, according to $E = mc^2$.

8. Mar 23, 2005

### eNathan

I think he wants to know this.
if $E= mc^2$ then m= $\frac {E} {c^2}$

Last edited by a moderator: Mar 27, 2005
9. Mar 26, 2005

### 1123581321

energy can be converted into matter, you just neet a lot of energy to make matter (just look at the formula e=mc2, the speed of light is a very large number, which means very large amounts of energy)

Fibonacci

10. Mar 27, 2005

### eNathan

the latex of my above post did not work out. So here goes using ASCII :)
if e=cm^2 then m=c^2/e

11. Mar 27, 2005

### moving finger

Excellent example (if one accepts the inflation hypothesis) is the end of inflation during the Big Bang, when the energy contained in the inflaton field quickly decayed into other particles and fields until eventually the universe consisted mainly of long-lived forms of energy such as protons, neutrons, electrons, neutrinos, photons etc.

MF