By Frederic Friedel
When I first met Vera, one of the smartest people I know, she was in her early twenties, a pretty and effusive young girl, really. I asked her casually what she did. “I’m a physicist, and doing a doctorate in string theory,” she replied. “What??” I said, with such a look of surprise that she had to elucidate: actually it was two doctorates, one in string and one in the theory of time. That only intensified my expression of incredulity, and so she asked: “Why do you find that so surprising?” “Because,” I replied, “quantum physics and string theory are hard!” So hard in fact that it seemed impossible that a bubbly young thing could be an advanced expert in this field.
Well, Vera’s answer has stuck in my mind ever since: “Actually it is not so hard, mathematically, but is is very hard to imagine what you are proposing, very hard to visualize your results.” That is the crux of the matter: it is possible, for the mathematically gifted, to do all the calculations that make up quantum theory, but it is almost impossible, even for them, to understand or imagine what they are saying.
Now as a skeptic and debunker I would in a flash label quantum theory a classical pseudoscience, one that has all the characteristics of purely invented fields of discourse. It makes use of suitably complex verbiage, the methods of discovery are nebulous and obscure, and nobody understands what the proponents are talking about. Aside: we must never forget how the great quantum physicist Richard Feynman put it, back in 1965. “I think I can safely say that nobody understands quantum mechanics” and, most famously, “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”
But I don’t (label it a pseudoscience). Why? Because there are experiments and there are practical applications that derive from this apparent mathematical nonsense that are so powerful, so precise, that there is only one way to explain: it has to be real. It is as if someone is using divining rods and mysterious chants to measure the distance between continents. We can only dismiss it with laughs of derision until we find that his results are consistently accurate to one tenth of a millimeter. No, you would build billion-dollar laboratories, like the Large Hadron Collider, to support his research.
I want to give you just one example of how far and how subtle quantum physics has become. I hope that in this case I will be able to describe the experiment in a way that is short and reasonably understandable. See if you can believe what I am saying.
The neutron is one of the elementary particles that make up the nucleus of atoms. It has mass, 939.57 million electron volts (as opposed to 938.28 MeV for protons and 0.511 MeV for the electron), but no charge.
When it resides in the nucleus of an atom the neutron has a lifetime of trillions of year — maybe forever. It is not prone to radioactive decay, which is the case when it is floating around by itself, outside an atom. Then it breaks up into other lighter subatomic particles, a proton, an electron, and an antineutrino, in a little under fifteen minutes. This is known, but quantum physicists are trying to find the exact number. Some say it is 878.5 seconds, on average, while others come up with 887.7 seconds. The difference is vexing and heartbreaking to physicists.
How did they find these numbers? Well, one group put free neutrons into a bottle and counted how many remained after various intervals of time. The other sent a beam of neutrons through an electromagnetic trap — they pass straight through, unless one decays, when the proton is captured in the trap. The bottle method yielded an average lifetime of 878.5 seconds, the beam experiment 887.7 seconds The systematic and statistical uncertainty of the first was 0.8 seconds, of the second it was 2.2 seconds. So the theoretical spread was three seconds, whereas the actual results differed by 9.2 seconds.
Now that does not seem like a lot, but the theoretical chance of such a deviation is less than 1:10,000. So quantum physicists are left with the task of further refining and repeating the experiment. But even if one of the numbers is confirmed the problem remains why other measurement was different. One possibility, that is being seriously considered, is that the neutrons generally decay into protons, electrons and antinutrinos, but very occasionally into other exotic, as yet unknown particles. The bottle experiment only counts the number of neutrons that have vanished, while the beam method counts the number of protons that have resulted from the decay. So if occasionally there are unknown and undetectable particles resulting from neutron decay, then the beam experiment would miss some of the decay events and assume a longer lifetime of free neutrons, while the bottle setup would count them all.
Why is this so important? Because it involves one of the four forces known in nature, the weak force, which is responsible for all radioactive decay, including the nuclear fusion that keeps the sun burning. Neutron decay is a very simple and pure form of the process, and calculating the exact rate at which it happens will help us understand the early evolution of the universe. More precisely: it will help us understand what happened after the first second of the Big Bang, when the universe was still too hot — about ten billion degrees — for particles to stick together, until about three seconds in, when it had cooled enough for protons and neutrons to stick together and stop neutron decay. If neutron decay was faster then there would have been less neutrons available to bind with protons and produce helium, leaving a universe with much more hydrogen (which has no neutrons), and if it were slower there would be a greater abundance of neutrons available three seconds after the Big Bang, and hence a greater amount of helium (which contains one or two neutrons). Am I losing you here?
The most exciting prospect is that the decay experiments described above provide evidence that unknown particles are being produced, particles that do not interact with normal matter and thus are (for now) undetectable. They would be prime candidates for dark matter, which we need to assume constitutes a substantial part — over 80% — of our universe. We need dark matter to explain a number of observable features of space, galaxies and galaxy clusters, like a problem that has bothered me since early childhood (well, for many years now): why do galaxies — all galaxies — spin as though the stars and gasses they contain were glued together, like a solid plate, rather then the outer regions moving much slower than the inner parts, as is the case in the solar system.
One explanation is that everything is held together by dark matter, which is assumed to consist of weakly interacting massive particles (shortened WIMPs, would you believe it?) that interact only through gravity and the weak force. It’s either that or we have to modify the standard laws of physics and general relativity to account for the observations, which some physicists are attempting to do.
I’m on the dark matter side, and so following the neutron decay experiments and voting for the beam side. Is that a popular enough way of putting it?