A lot of posts in this thread are old, but it might be worth clearing up some confusion... This stuff is from my old University physics and chemistry days...
Scientists normally distinguish
chemical change from
physical change, and
neither of these is what we need to create matter from energy, but they're a good starting point, so here they are:
Chemical change: a change that produces a new substance. Burning wood changes molecules of wood into molecules of smoke. Eating food changes molecules of food into molecules of people. You can tell when a substance is new because it acts differently in contact with other substances. Photosynthesis is an example of chemical change.
Chemical changes often either consume energy (e.g. baking bread) or produce energy (e.g. burning wood), but the energy that goes into these changes is normally locked in the molecule. One principal of chemical changes is that the total amount of mass doesn't change. If you burn a tonne of wood you will produce a tonne of wood-smoke, ash and steam. If you eat a half-pound meal then you'll gain weight by half a pound (less whatever what you excrete)
Physical change:a change that alters the physical properties of a substance, but keeps the chemical properties. Cutting a log into sawdust doesn't stop the sawdust from acting like wood (it'll still burn, for instance, and termites will still eat it). Freezing or boiling water doesn't make it poisonous to us. Physical changes often either consume energy (e.g. boiling water), or release energy (e.g. a hot oven cooling). The total mass of substances undergoing physical change doesn't alter either. Freeze 1kg of water and you get 1kg of ice (except for some air bubbles that escape while you're freezing it, but these add up to the total).
Point is: neither physical nor chemical changes are an example of energy converting into matter - because the total mass of the substances doesn't change.
For our purposes, energy only converts into matter with great difficulty, and only in tiny quantities. The most common way this occurs on Earth is via a
particle accelerator, where small particles of matter are smashed together at high speed (the energy is in the speed), to produce
more particles of matter that actually
weigh more than the original particles. If you can imagine a high-speed smash between two Minis that manages to produce an SUV and two bicycles, that's pretty much what scientists are trying to do with particle accelerators.
Unfortunately, these collisions
don't produce even a single atom -- just fragments of atoms. And you can't really 'aim' one single particle at another - you have to fling a
lot together and hope that a few of them crash together in the right way. Then you find a clever way to whisk away the original, light particles, and see if there are any heavy ones left.
What does this mean for the universe?
Well, it's all speculative, but here's a popular view:
Whatever created all the matter in our Universe, it was an extraordinary event, and it seemed to happen all at once. A lot of matter was created and flung outward with a lot of excess energy. This matter collided and made
more matter, and eventually made atoms which were heavy enough to combine into molecules, which got big enough to attract one another through gravity. This matter is still flying apart. Last time I read anything on this, the idea was that it would
keep flying apart -- never to come back together and explode again.
If that happened, then eventually galaxies would move so far apart that we couldn't see them, and so the night sky would lose most of its stars. I'm not sure what would happen to our own galaxy - would it fly apart, or get pulled back in to smash together again? If the latter, it might create some more matter, but it's not the sort of thing you could see from earth, because our solar system would get mooshed to atomic paste too.
So, no Instaburgers?
Back to Science Fiction and Instant Mass, the energy-mass equation (E = mc[SUP]2[/SUP]) is not your friend if you want to turn electricity into a hamburger, say - even if you had machinery clever enough to do it. Converting a single sugar cube into pure energy could light a small city for a whole year, so to get the sugar cube
back, you'd have to drain that city's lighting for a year. And nanotechnology
won't help you get a sugar-cube rather than atomic paste, since nanotech is made of
big molecules, and we're talking about assembling splinters of a single
atom.
If you want instant food, you're much better off assembling it from existing molecules - via
chemical change. That's essentially what nanotech is meant to do - just the same thing we do in a kitchen or a chemistry lab, only on a smaller scale and with more efficiency.
Hope this helps.
