Mass–energy equivalence, 2

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.

— Koji Mukai, with David Palmer, Andy Ptak and Paul Butterworth

— for the Ask an Astrophysicist

— The National Aeronautics and Space Administration (NASA)

2012.10.10 Wednesday ACHK