Copyright 1996-2002 by Donald R. Tveter, http://www.dontveter.com, commercial use is prohibited. This material cannot be quoted at length or posted elsewhere on the net or included in CD ROM collections. Short quotations are permitted provided proper attribution is given. But better yet, since I'm hardly an expert on the subject, don't quote me.
The typical way to approach Quantum Mechanics had been to give a history of all the odd experiments that have been done over the years and then announce the solution. There are good books that do this like John Gribbin's Schrodinger's Kittens and the Search for Reality and they certainly are worth reading. Here, I am going to break with this tradition and simply give the "answer" according to Physicist John Cramer, then go on to show how the solution works in the famous experiments. Gribbin has a short WWW file that includes this interpretation as one of its topics. Cramer also has a larger hypertext explanation.
The equations used to predict quantum mechanical processes give the right answers, answers as right as anyone can possibly ask for in all the situations in which they have been tested. Yet the interpretation of what "really" happens has been very confusing and a number of famous paradoxes have come up. There are many ways to interpret what is happening in quantum mechanical events and when you go to make equations out of all of these theories they all give the same equations, the equations that so far seem to be perfect! Which of these interpretations should you pay attention to? One answer is to use whichever interpretation works best for a given problem so you need to know them all. Another answer is that the interpretation of QM by Physicist John Cramer is the best one so far. This recommendation comes from John Gribbin in his recent book, Schrodinger's Kittens and the Search for Reality who praises the simplicity of Cramer's interpretation. As Gribbin says, this explanation may not be the final one yet it has a great deal of simplicity and it explains various QM paradoxes that have worried Physicists for up to 70 years. This interpretation requires a long description and you really should get it from a better source than me however I will now try to get you somewhat oriented about what is going on.
For quite a long time Physicists have been trying to figure out if light is a wave or a particle. First Isaac Newton had most people convinced that light was a stream of particles. Later it became clear that light behaved like a wave. Then it appeared to be both! Then, things got even more confusing when those things that definitely seemed to be particles, like electrons, protons and atoms turned out to behave like waves as well! Physicists then worked out an equation, the famous Schroedinger wave equation that accurately predicted how all these particles behave. Unfortunately it made such crazy predictions about how particles behave that to this day they are still very confused. One result of all this confusion is that most Physicists no longer try to figure out what is "really" happening, they just look for formulas that get the right answers. Thus now no one worries about what a photon or electron or whatever really is. In fact these things behave like things no one has ever seen before.
The most important force that determines what our world looks like is the electromagnetic force. The quantum version of electromagnetism is the theory of Quantum Electrodynamics (QED). This theory supersedes the classical theory of electromagnetism found by James Clerk Maxwell. QED is simply concerned with the probability that a particle (typically an electron) will exchange a photon, the particle of light with a second particle. In Cramer's interpretation of QED every particle that wants to give up a photon looks deep into the future to find another particle that will accept the photon. These elementary particles "know" the layout of the future. When a deal is "negotiated" the first particle lets the photon fly off on its path knowing full well where the other particle that accepts the photon will be when it finally gets there. So go out and look at a nearby star, say Sirius if you're in the northern hemisphere. Sirius is 10 or so light years away. The photons that hit your eye "knew" that at the time they left the star 10 years ago that they would hit electrons in your retina. Now when you go back inside the photons coming from Sirius "knew" 10 years ago that they will hit the sidewalk or the grass or wherever, rather than hitting your eye. These "deals" were "negotiated" 10 years ago with particles in a star ten light years away, long before you ever thought to look at the star.
So far this interpretation has been confirmed in experiments done wholly on Earth. Particles are sent through a device where the layout of the device is changed at random when the particles are part way through. The particles "know" what to do before they started out through the device, they know just after they enter the device AND before the random change is made to the device. In fact just so you take me seriously (I'm thinking of my telling you not to take me seriously, only take the experts seriously.) I'm going to give a quote about this experiment from Schrodinger's Kittens by Physicist John Gribbin, page 140. The experiment done by a group headed by Alain Aspect involves photons traveling through a "beam-splitter" in the middle of the device and the layout of the device is changed at random by a computer. The results were:
The behaviour of the photons at the beam-splitter is changed by how we are going to look at them, even when we have not yet made up our own minds about how we are going to look at them!.The photons had to know ahead of time what the computer was going to decide at random, it had to know what the experimental appratus was going to look like. Gribbin says that it may soon be possible to do this experiment with light coming from a quasar on the order of a billion light years away.
Notice how this contrasts with our usual way of thinking about the world. Normally we look at where particles are now, notice which way they are moving and then try and figure out where they will be a little while from now. Things are simply flying into the future in an uncoordinated way. Photons emitted from a source don't know where they're going they just go and where they end up is just where they happen to end up. If they hit a bit of dust in space, a molecule in the atmosphere of a planet, the planet itself or the eye of a person on a planet that is it, a completely unplanned process. Things move forward from here and now and there is no future out there yet to influence the here and now.
I'm not sure but I don't think Science has been able to digest these strange results yet and we're still stuck trying to explain the world in pre-quantum terms. One person who has been thinking about such strange results is philosopher Huw Price who has written a book called Time's Arrow and Archimedes' Point. Price especially got to his viewpoint not by looking at the Aspect experiments but by considering the treatment of time in physical theories. Price's conception of the universe is that it is finished from beginning to end and that we should think about it as if it were an object we could step outside of and view whole. But this certainly fits nicely with the interpretation of quantum mechanics produced by Cramer.