# Can energy be converted into mass?

1. Mar 24, 2008

### manjuvenamma

I know mass has been converted into energy in fission and fusion bombs. But the converse - i.e., converting energy into mass - has been achieved? Please let me know.

2. Mar 24, 2008

### pmb_phy

Its not that mass is converted into energy or vice-versa. What actually happens is that the form of (inertial) mass changes. What happens is that the proper mass increases as does the mass due to motion (aka relativistic mass) since the atom will recoil in order to take up the photon's momentum.

Pete

3. Mar 24, 2008

### Staff: Mentor

High-energy particle physicists produce more-massive particles by colliding less-massive particles together with the help of accelerators like the ones at CERN and Fermilab.

4. Mar 24, 2008

### manjuvenamma

Pete,

I always read in books that E = mc^2 conserves mass plus energy rather than mass and energy separately as held by the Newtonian principles. I always read that the equation relates conversion of mass into energy. Perhaps they are oversimplified statements that I read.

I will try to understand your answer better. Can you give me some link that explains this equation more accurately and allows me to understand your answer better.

5. Mar 24, 2008

### Schrodinger's Dog

6. Mar 24, 2008

### Staff: Mentor

Yes, the creation of an electron-positron pair is one of the most important interactions for photons with a little more than 1 MeV energy.

7. Apr 1, 2008

### superdirt

Calling them equivalent is not really correct.

You could perhaps say that matter is a type of energy or matter has energy, but some types of energy do not have mass and thus could not be matter.

Scott

8. Apr 1, 2008

### belliott4488

manjuvenamma:

I might have misunderstood Pete, but if not, then I'd have to disagree with his earlier statement. It sounded to me as if he was describing the effect of relativistic mass, which is where the mass of an object increases as its velocity increases.

In nuclear fission, mass is most certainly destroyed and converted to energy. Actually, this happens any time matter and antimatter annihilate. The reverse process is precisely what other posts have referred to, e.g. production of e+/e- pairs.

9. Apr 1, 2008

### JesseM

All forms of energy in the rest frame of a bound system (say, an atom, or a collection of particles in a box) do contribute to the inertial mass of the system as a whole as measured in its rest frame, though. A box containing some system will have inertial mass proportional to the sum of the rest mass energy, kinetic energy, and potential energy of all of the particles that make it up (including the ones in the wall of the box of course).

10. Apr 1, 2008

### superdirt

That is correct, all energy has inertial or relativistic mass. What I meant and should have said, is that not all energy has rest mass.

Mass and energy can't be equivalent, because they are defined so differently.

Scott

11. Apr 2, 2008

### Schrodinger's Dog

Ok e doesn't equal mc^2 then. Mass and energy are not convertable, that's not what I meant.

They are as equivalent as the $\equiv$ sign. No they are not the same thing.

Good gravy. :tongue:

Instead of $E=mc^2 \rightarrow E\simeq mc^2$

Last edited: Apr 2, 2008