Ah well, you did of course ask the Physics Van, and so our answer will
be based on what we know about physics. Star Trek is entertainment, and
can depart from known physical principles in order to make stories more
It is true that matter is one of the many different forms of
energy. The conversion is E=mc^2, as found out by Einstein. Over the
years, scientists have been able to change matter into energy and
energy into matter, verifying this and discovering many other rules
that matter and energy obey.
One detail scientists have discovered is that the number of
"baryons" -- that is, the number of protons+neutrons, is constant in
all reactions that we know of. Your typical character on Star Trek has
maybe 5 times 10^28 of these. We're pretty sure you cannot make even
one of those protons or neutrons vanish, even if you heat the Star Trek
character up to many trillions of degrees (we've collided protons
together with effective "temperatures" of about a trillion degrees and
not found any deviations from our predictions). You can convert them
into strange versions of protons and neutrons, but these quickly (and I
mean quickly!) decay back down to the usual protons and neutrons. And a
mess of other stuff.
Another thing you cannot make go away is the number of leptons. An
electron is an example of a lepton. A Star Trek character has about as
many electrons as he has protons. The electrons can be converted into
other leptons (like neutrinos), but you cannot make those go away
So somehow protons, neutrons, and electrons have to be moved from
one place to another. Another alternative is to just look closely at
the character, and write down where all the protons, neutrons and
electrons are and how fast they're going, and send the information
down, where some other machine may attempt to put it back together
(other science fiction shows suggest this way of doing things). This
trick runs into problems with quantum mechanics -- you cannot tell
where something is and how fast it's going at the same time on small
distance scales, like atomic scales.
So no, you cannot convert a Star Trek character into energy no
matter how hot you make him, because everything you have after you try
to run the transporter will still contain baryons and leptons.
The way matter is exchanged for energy in the laboratory is by
creation or destruction of an equal amount of antimatter. If you have
an excess of energy somewhere, you can create an equal amount of matter
and antimatter. Likewise, you can start with some matter and
antimatter, bring them together, and end up with some energy instead.
The baryon and lepton numbers add up properly because the antimatter
has negative values for these.
There is a small asymmetry between how matter and antimatter work
to explain why the universe is made up of mostly matter and very little
antimatter as far as we can tell. We're still working out the details
of that one.
(published on 10/22/2007)