What converts energy to mass and vice versa

Question

I understand the mass-energy equivalence theory but I'm just not sure how mass is 'converted' to energy.

Answer 1

It can be fascinating.  You might like to go read about the subject.

First, when a body rises in energy, its mass increases!  Just like that.  It happens all the time.  When you go up in an airplane your energy increases because of the potential energy of height, and that increases your mass.  The plane goes at 300 mph, and THAT kinetic energy also increases your mass.  When a pitcher throws a fastball, the ball is heavier at 90 mph than at rest.  Of course, all of these mass increases are miniscule, as you can calculate with E=mc^2.    

It really comes into play with nuclear processes.  Energy is released by radioactive decay, and that release decreases the mass of the nucleus that is decaying.  Nuclear fusion releases a relatively high percentage of the initial mass of the hydrogen isotopes to produce a lot of energy.   Even then, the actual percentage of mass that converts to energy is pretty small.

When an electron accelerator gets electrons up to close to the speed of light, they get a LOT heavier, because most of the input energy at those speeds goes into mass, and because they start out so light in the first place.  

When matter and antimatter meet (proton-antiproton, electron-positron (look up Positron Emission Tomography, PET) they annihilate and ALL of there rest mass is converted to energy.  That's a special case.

But 'Mr.Fusion' from Back to the Future?  Implying complete conversion of mass to energy, of ordinary matter?  No.  

Answer 2

there really is no conversion. its easier just to say that mass is converted to energy or visa versa, but thats not really right. mass is the interaction of energy with the higgs field/higgs boson. certain particles interact with the higgs field, others do not. photons do not. so in certain reactions photons are created, which carries away energy, and therefore mass.

think of everything as energy, because thats what it is. energy is in particle form no matter what. but sometimes it is in photons, sometimes it is in other particles that interact with higgs bosons.

so there really is no conversion.

EDIT: and the kid the posted before me is an idiot. mc^2 has nothing to do with relativistic mass, that is an entirely different and more complicated equation. all mass is energy. if rest mass werent energy nuclear reactions wouldnt be able to happen since they are a difference between the mass of individual nucleons and nuclei.

Answer 3

In most atomic reactions, a small amount of mass dissappears, and large amounts of energy appear.  This can be balanced in an equation.  

The reverse is harder, because large amounts of energy would need to be condensed into matter.  Possibly using a beam to split helium up into hydrogen would convert energy to mass.  

In *chemical* reactions, even smaller amounts of mass are in play.  Practically undetectible.

Answer 4

Energy is equivalent actually to relativistic mass, not rest mass actually.  If the rest mass of a body is m, its relativistic mass is mc^2.  The process appears to happen whenever fast moving objects seem to accelerate around you (you consider yourself stationary and see the world around your measurements of other people's mass will change as you observe them changing in energy).  This is the relativistic interaction between mass and energy, and it was in this context (changing frames of reference) that Einstein first came up with the theory, and this is still how it is still derived usually now.

This also happens on the small scale whenever fundamental particles interact.  When fast particles like energetic electrons or photons are given off by nucleon reactions, you would see the total mass of the system go down slightly.  The examples of fusion or beta decay are the most commonly given examples of mass/energy conversion and fall into this grouping.

However, to a physicist, the relativistic example, with what are called 'boosts, or hyperbolic rotations in the Minkowski metric' is the most natural way of seeing where E=mc^2 comes from.