Quantum Physics - Matter is not what we think it is
When we turn our attention from the outer reaches of the cosmos to the realms of the incredibly small, things get very strange indeed, so weird in fact that physicists exploring the insides of atoms used to go home scratching their heads and thinking they must have got their results wrong. But the results were repeatable and led to the Standard Model of Quantum Physics, one of the most successful theories ever, which has allowed us to make huge leaps in our understanding of the universe and has supported the development of new kinds of technology including new methods of encryption for internet security.
So what do we know about the atom?
We'll start by asking ourselves how small an atom is. To get some idea of how many atoms there are inside a cricket ball, imagine that cricket ball the size of the planet earth. On that scale, an atom is the size of a grape. So if you imagine the whole Earth packed with grapes, that's about how many atoms there are in a cricket ball!
Next, let's look at what's inside an atom. They come in various sizes but basically they have a central nucleus containing particles called protons and neutrons (which in turn are made from smaller particles called quarks and gluons) and, whizzing around this nucleus, there are electrons. In some ways, it's a bit like a miniature solar system with the nucleus like a little sun and electrons like planets in orbit around it. There are over a hundred different elements, classified by the number of protons in their nucleus.
Protons are positively charged, electrons are negatively charged, so atoms generally have an equal number of both in order to maintain neutrality. If they don't balance, the atom becomes a charged ion which happily couples up with ions of opposite charge to form a neutral molecule. Electrons occupy shells or orbitals around the nucleus and each shell can contain a particular number of electrons. The shells fill up with electrons from the inside out. When there are vacancies in the outside shell, the atom can get together with neighbouring atoms so its outer shell feels full. So for example, a carbon atom has four vacancies in its outer shell so it might get together with four Hydrogen atoms (which have one vacancy each) to form methane, or two oxygen atoms (which have two vacancies each) to form Carbon Dioxide, etc.. That's the basis of chemistry. Carbon can also link to other carbon atoms to form long chains and rings, which give rise to organic chemistry and life on Earth.
For the purposes of learning chemistry and biology in school, the little solar system image holds up quite well, so this is the kind of thing we are generally taught as chilldren. However, it's much weirder than that and I have to say that I was a bit mortified when, in later life, I learned about the stuff I'm about to describe and found out that scientists have known about this since the beginning of the twentieth century but my school science teachers just had not thought fit to share this information with us during the sixties and seventies. Discovering this information is potentially life changing.
So what's so special about atoms? Well, lets take a look at the smallest atom, a hydrogen atom, which has only one proton and one electron. If you imagine a hydrogen atom the size of the dome of St. Paul's Cathedral, then on that scale the nucleus in the middle is the size of a grain of salt, and the electron whizzing round it is about two thousand times smaller than that!
If you have not heard about this before, just take a few moments to take it in.
What we're saying here is that atoms are almost entirely empty space! The only reason we are not currently falling through the floor is because of electromagnetic fields which prevent our atoms from passing through those of other substances such as floors (in much the same way that like poles of magnets repel each other). The electron itself is whizzing around so fast that it seems to occupy the whole dome, like a rotating helicopter blade appearing as a disc. It's going so fast that we can't know its position without stopping it and if we measure its speed we can't know where it is because it's not in any one place long enough. And of course, at that scale, if we tried to see what was going on by shining a light on it, a photon of light would interfere so much that we couldn't really say what would have happened without our observation messing it up. All we can know about an electron is the probability of it being in a particular place.
Particles, waves and "waveicles"
All that would be strange enough if we actually knew what an electron is. But we don't really.
There have been countless experiments carried out during the last century which have tried to find out whether an electron is a particle or a wave of energy. One electron can pass through either one slit in a screen (like a particle) or two slits at the same time, causing an interference pattern (like a wave). You can read about these experiments in some of the books on the reading list but, in a nutshell, what they found was that an electron can behave as either a particle or a wave, depending on what the scientist conducting the experiment is looking for!
Now again, think about the implications of this. It suggests that what goes on inside the atoms that make up our universe can be influenced by the mere presence of an observer. Not all physicists agree with this but a substantial number do, including the great-granddaddies of quantum physics, most of them Nobel Prize Winners, who met in Copenhagen early last century to discuss these implications. This idea is therefore often referred to as the Copenhagen interpretation.
So, you may rightly ask, if the electron is so insubstantial, what is it that gives the material world its hard substance? Is it the proton in the middle that is a solid particle?
Well, actually no. Protons and neutrons are no more substantial than electrons; they are bound together so strongly that when you split open an atomic nucleus it releases a vast amount of energy, as evidenced by the atomic bomb. They are composed of tiny entities called quarks, three quarks per "particle", and these are bound together incredibly strongly, a process which seems to involve other particles called "gluons". These paricles in the nucleus whizz around at close to the speed of light, where our ordinary notions of time break down, and it's incredibly difficult to separate them because the force between them actually increases with distance, unlike gravity.
What's even weirder still is that, in the world of particle physics, these basic elementary particles can flit in and out of existence in fractions of a second and can transform into different things. Matter and energy are interchangeable so lots of energy of motion can form a particle, as if out of nothing, and particles can break down into energy.
This is a lot to take in, but we're just getting started. Perhaps the weirdest thing we have learned about the sub-atomic world is a phenomenon called non-locality.
We have already said that electrons move around the nucleus of an atom in discrete shells or orbitals. Moving from an inside shell to one further out requires energy, and falling back to an inner shell gives off energy. The energy is released or absorbed in discrete packets called quanta. Absorbing a quantum of energy allows an electron to jump up to the next shell outwards while dropping down a level gives off a quantum of energy. (That's why this branch of science is called quantum physics). When an electron switches from one orbital to another, it doesn't travel there, it just instantaneously stops being in the one it was in and appears in the other one.
Before it makes this quantum leap, it appears to smear itself out over a large region of spacetime and then collapse back into its chosen orbital. This would be like, for example, the planet Venus smearing itself out across the galaxy and then disappearing from its own place in the solar system and immediately popping up in the orbit of Jupiter. Thankfully, large things like planets don't behave the same way as they do in the sub-atomic world!
Now electrons, apparently, like to go around in pairs. They have a quality which physicists have called "spin" and in any pair of electrons, one spins one way while the other spins the opposite way. (In fact, weirder still, they can be in both states at once, which we'll come back to later when we talk about quantum computers). Scientists have managed to separate pairs of electrons and put large distances between them. Once they have been separated, if the spin of one of the electrons is deliberately changed, the spin of the other immediately reverses as well. By immediately, I mean that there is no time delay which would allow any physical message to be passed through space from one to the other, even at the speed of light. It's instantaneous. It's called quantum entanglement, and it seems to work however much space is between them, so in theory an electron on one side of the universe would be instantly affected by a change in its partner on the other side of the universe.
Einstein called this "spooky action at a distance" and he did not like it at all. We don't know how it works, (see a suggestion in g theory and read more about it in Shroedinger's Kittens) but we do know it happens and quite a bit of modern technology exists because of it, including new types of encryption for internet security. It's not only electrons that do this. Other sub-atomic particles, including photons, can also behave in this way. It's possible that it implies the existence of a fifth dimension that we are unable to see. Imagine two coins on the surface of a baloon. You coud move one and instantly affect the other if, underneath the inside surface, each was attached to a hidden magnet and the magnets were connected by a piece of string. This would not be visible to a two-dimensional baloon surface-dweller who would consider it to be spooky action at a distance or be convinced that they had got their experiments wrong.
The upshot of all of this is that we don't fully understand what matter is. It's certainly a lot stranger than it appears at face value. We don't even have a good theory to explain why it has mass without invoking a new type of field called the Higgs Field, which may or may not exist. We have spent billions constructing the Large Hadron Collider to test this and other theories. Scientists at the LHC have narrowed the search down and may yet find the Higgs (or "God particle") sometime soon. If they don't find it at all, we may need to completely re-think everything we thought we knew about the universe.
When you really start to think about all of the above, the universe becomes a very strange and fascinating place. What appears substantial and predictable becomes more of a sea of energy, vibrations and possibilities. Particles seem to be elusive clouds of probability which are only collapsed into something we can measure when an observer looks at them (a phenomenon called "decoherence" or "collapsing the wave function"). So, in theory, it's possible that the whole universe is only there when someone is looking at it.
Makes you think, doesn't it?
Two extra bits of information and some interesting thoughts
1. According to New Scientist 26.6.10, in an article called "Quantum Machines", it is not only subatomic particles such as electrons, photons etc that exhibit quantum weirdness. While Schrodinger famously explained that something as big as a cat could not be expected to be in two states at once (eg dead and alive both at the same time), scientists at the Universitiy of Vienna have found that Carbon-70 molecules (about ten million times bigger than an electron and visible through a microscope) do appear to go through two slits at once and interfere with themselves like waves in much the same way as electrons do. The latest theory about the difference between tiny objects and larger ones is that the larger an object becomes, the more it interacts with some kind of cosmic background field which we have so far been unable to detect, which gives it mass and brings about it's decoherence from the "cosmic soup" of overlapping superpositions and gives it a particular position in spacetime.
2.The phenomenon of "decoherence" of a "superposition of states" (sometimes also known as collapsing the wave function), as we have seen above, is influenced by the presence of an observer. In other words, an electron or photon is both a wave and a particle and can exist in two places at once as long as nobody is watching but when a measurement is taken, it becomes one or the other, like a cat in a box being both alive and dead until somebody takes the lid off. This is interesting in itself but it has also been noticed that if more than one observer is present, there is only one outcome for a particular experiment. They don't each notice different outcomes from the same experiment. It has been suggested that this implies that there is only one consciousness in the room, however many people are present. Could this be something to do with the undetectable "background field" we mentioned above? Are we necessarily talking about two different things here?
Perhaps, as they say, there is nobody else in the room!
Perhaps: "There can be only One", and we are all it!
Return Home Return to Reality