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The Question

(Submitted July 24, 1997)

Why is it impossible, at this point in time, to convert energy into matter?

The Answer

It happens all the time. Particle accelerators convert energy into subatomic particles, for example by colliding electrons and positrons. Some of the kinetic energy in the collision goes into creating new particles.

It's not possible, however, to collect these newly created particles and assemble them into atoms, molecules and bigger (less microscopic) structures that we associate with 'matter' in our daily life. This is partly because in a technical sense, you cannot just create matter out of energy: there are various 'conservation laws' of electric charges, the number of leptons (electron-like particles) etc., which means that you can only create matter / anti-matter pairs out of energy. Anti-matter, however, has the unfortunate tendency to combine with matter and turn itself back into energy. Even though physicists have managed to safely trap a small amount of anti-matter using magnetic fields, this is not easy to do.

Also, Einstein's equation, Energy = Mass x the square of the velocity of light, tells you that it takes a huge amount of energy to create matter in this way. The big accelerator at Fermilab can be a significant drain on the electricity grid in and around the city of Chicago, and it has produced very little matter.

Koji Mukai, with David Palmer, Andy Ptak and Paul Butterworth
for the Ask an Astrophysicist

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