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Most recent answer: 10/22/2007
Q:
When matter comes into contact with antimatter there is a ginourmous explosion. Do ’particles’ in the electromagnetic spectrum count as matter? If not, couldn’t a magnetic field be used to contain positrons or antiprotons? Another thing that bugs me is: Why should the big bang have happened in the first place if it was all down to chance?
- Muhammed (age 17)
Sir George Monoux College, London
A:
1. When matter comes into contact with antimatter there is a ginourmous explosion.

Yes, but what happens depends on how much kinetic energy the matter and antimatter particles have. High-energy particle colliders such as the ones at smash particles and antiparticles together at very high energies, in the hopes of producing exotic, not-before-detected particles, and of measuring precisely the properties of ones we already know about.

But see the answer below about the photons:

2. Do 'particles' in the electromagnetic spectrum count as matter?

Photons are their own antiparticles: an anti-photon is just a photon. To a good approximation, photons do not interact with each other (but you can search this web site for our explanations of how much they do and under what circumstances). So a photon meeting an anti-photon does not result in a ginormous explosion -- they just go past each other nearly all of the time.

3. If not, couldn't a magnetic field be used to contain positrons or antiprotons?

Very good! This is exactly how antiprotons and other antiparticles are stored at particle-physics research laboratories. Charged particles feel forces when traveling through magnetic fields. In practice, beams of antiprotons (or protons, or electrons, or positrons, or lots of other goodies) can be made to travel in circular paths with the help of magnets. Fermilab's Tevatron ring, for exmaple, is four miles in circumference and consists of a pipe with a very good vacuum in it. Very strong magnets supply a field perpendicular to the plane of the ring. A beam of antiprotons whirls around in one direction and a beam of protons whirls around in the other. These beams can be stored in this way for days on end (but collisions between the protons and antiprotons, and between the beams and residual gas molecules will eventually make the beams get weaker and weaker -- same energy, but fewer particles).

4. Another thing that bugs me is: Why should the big bang have happened in the first place if it was all down to chance?

Don't expect a definite or reliable answer to this one. Just for fun, I'll run one of the many possible answers by you. It may be that the 'chance' in quantum mechanics has nothing to do with randomness of which event will occur but rather is a subjective impression because ALL the events which quantum mechanics allows do occur. Any one version of you can only experience one little chain of these possibilities, so it feels chancy. That seems to be the most natural reading of the quantum time-dependence equations, although like other ways of looking at quantum mechanics it has serious problems. It may be that one piece of the quantum state underwent the big bang simply because that's one possibility and all possibilities occur.

Mike W. and Tom J.

(published on 10/22/2007)

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