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Q & A: Matter and Energy

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Most recent answer: 10/22/2007
Q:
Hello. I have always been fascinated with the interrelationship of matter and energy. In the excellent book entitled, "The Physics of Star Trek" by Lawerence Krauss, he discusses about the transporter and how it works. It basically converts crew members into energy and once that energy is sent to it’s appointed destination, the energy is reconverted back into matter. Granted Star Trek creator Gene Roddenberry created the transporter as a means of speeding up storytelling but let’s focuse on the matter-energy conversion process itself for the sake of argument. Krauss stated that in order to convert matter into energy, one must heat it up to 1000 billion degrees!!! 1) If we were to accept the premise of the show, why would heating the crew members up to 1000 billion degrees be necessary in order to convert them into energy? 2) Is there another way to theorically convert them into energy without heating them up?
- Julian (age 14)
Bayside High, NY
A:
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 interesting.

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 either.

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.

Tom

(published on 10/22/2007)

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