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Reversing The Polarity Of The Neutrons

By Nicholas Smeaton

Those of us who have been watching Doctor Who for long enough will remember the days of the Third Doctor (Jon Pertwee). The Third Doctor was something of a scientific tinkerer and he was always fixing a problem by "reversing the polarity of the neutron flow". This practically became his catch phrase (He used it in The Five Doctors.) The phrase appears to be a piece of technobabble, after all as anyone who has done sixth form chemistry or physics knows neutrons have no charge and therefore has no apparent polarity.

One explanation is that the Doctor, sick of giving Jo Grant and the Brigadier long explanations about what he was doing which they probably wouldn't understand anyway, (Let's face it after Liz Shaw the Third Doctor's companions seemed to have a slight problem understanding scientific principles), made up the phrase in order to save himself some bother. But this doesn't hold up because he used the phrase in front of the first two Doctors and they didn't create a fuss, so it is likely that when he talked about reversing the polarity of the neutrons that's what he was trying to do, so a scientific explanation seems necessary.

First of all I'll explain what a neutron is. A neutron is a subatomic particle found in the nucleus of all atoms except Hydrogen. It has an electron mass of 1838.6 i.e. it is equal to 1838.6 electrons in weight, and it has no charge. The other two basic subatomic particles are, the electron with a charge of -1, this is the bit of the atom that does chemistry, and the proton which has an electron mass of 1836.1 and a charge of +1. The proton and neutron stick together to form the nucleus of the atom and the electrons orbit the nucleus. The protons give the electrons a reason to stick around and the neutrons stop the nucleus from flying apart (protons repel each other).

Protons and electrons have charges and therefore polarity, it is possible to produce positively charged electrons (called positrons) and negatively charged protons (called anti-protons) however scientists have also created anti-neutrons. But wait! Neutrons have no electrical charge so how can you have a reversed polarity neutron? Simple, while neutrons don't have an electrical change they do have spin and that generates a magnetic field. An anti-neutron spins in the opposite direction and so generates a magnetic field flowing in the opposite direction. So when the Doctor reverses the polarity of the neutrons what he does is reverse their spin.

To do this the Doctor would need a powerful magnetic field generator that can cause the interference necessary to reverse the spin of the neutrons, since most of the fiddling the Doctor did was with high energy items like stardrives it is likely that the item was fusion powered and fusion reactors are basically particle accelerators using powerful magnetic fields. So the Doctor probably uses that. He would have to be very careful to avoid affecting the protons and electrons as well, (anti-matter is made up of anti-protons, anti-neutrons and positrons.) because The Three Doctors and Arc of Infinity not withstanding when matter and antimatter mix they annihilate each other turning all their mass into energy (Translation: there is an explosion the size of an H-bomb blast, or bigger). The reversal would almost certainly take place inside the reactor and not in the component affected because an atomic nucleus consisting of protons and anti-neutrons would be very unstable, it would fly apart and the anti-neutrons would crash into the nuclei of any nearby normal atoms (neutrons do a lot of this sort of thing, it's how a nuclear reactor works), and when neutrons and anti-neutrons meet they annihilate each other so the nucleus of the normal atom would be blown apart. This would make the area affected very radioactive. (Matter/anti-matter annihilations create a lot of gamma radiation).

So how would reversing the polarity of the neutrons fix a piece of faulty equipment. It is likely that the adjustment of the reactor would cause power fluctuations that could trip a fail safe in the item the Doctor is trying to fix, or even clear the fault itself.

In conclusion I would say that the Time Lords knowledge of physics must be far more advanced then our because when scientists create anti-matter in a laboratory they also create an equal amount of matter, however Time Lords just seem to be able to turn matter into anti-matter by merely bombarding it in a particle accelerator. On the other hand their particle accelerators don't seem to be much more advanced than ours so perhaps in a few years time we'll catch up with them in that area.

This item appeared in TSV 14 (July 1989).

Reprinted in: The Best of TSV 1-20, TSV: The Best of Issues 1-20