Quantum mechanics tells us that there are limitations to what we can know about reality. A particle appears to be in two places at the same time. Where is it "really"? Particles can be "entangled," so that one particle "knows" instantaneously what happens to another particle, no matter how far apart they are. How does it do that? When we try to look at these particles, to find out exactly what's going on with them, our doing so instantly removes the odd quantum effects. The quantum effects "collapse," so that the particle examined appears to be acting perfectly "normally."
In other words, we know weird things are going on, and we can see the statistical result of those weird things when we observe numerous particles. But when we try to observe what's actually happening to any one particle -- well, we simply can't.
Are the limitations of quantum mechanics epistemological or ontological? In other words, does quantum mechanics describe limits on our ability to observe reality, or does it describe the very weird nature of reality itself?
This week's New Yorker contains a lengthy article discussing the work of a British physicist who has spent his life thinking about these matters. He concludes that the limitations are ontological. Most physicists don't even like to think about the question -- it's too "philosophical." They'd prefer just to accept the theory as an accurate description of the data, and see what they can accomplish with it. Focus on building a better transistor.
But the British physicist -- David Deutsch -- who is the subject of the New Yorker article, believes that quantum mechanics can best be understood by accepting a "Many Worlds" theory of reality. This theory, well-known in physicist circles, hypothesizes that an incredibly large number of parallel universes exist, side by side, and that incredibly large numbers of new universes are being created every second, every time one of two possible outcomes of an event occurs. To simplify this idea, consider my flipping a coin. In our universe, we see it as coming up either heads or tails. In "Many Worlds," flipping the coin creates a split of universes -- it comes up heads in one and tails in the other.
Deutsch believes that quantum mechanics seems bizarre to us because most of what happens is happening in parallel universes. In the laboratory, for example, we shoot photons at a pair of openings or slits. We know the initial trajectory of the particles when we fire them off, and we see a wave diffraction distribution created by the particles when they hit a detector on the other side of the slits, a result not predicted by classical mechanics. But if we try to follow each particle, to see which slit it passes through, we immediately lose the wave distribution, and the pattern on the detector is the same as though we were firing BBs at the slits.
This result makes no sense under classical mechanics. Photons should act either as particles or waves -- they shouldn't change their nature based on whether they are being observed from origin to destination. Deutsch would contend that between the firing off of the particles, and the impact on the detector, the particles follow a trajectory that leads through parallel universes. He suggests that once one accepts the Many Worlds hypothesis, much of what seems weird about quantum mechanics then becomes more logical and undertandable.
[T]he quantum theory of parallel universes is not the problem -- it's the solution. ... It is the explanation -- the only one that is tenable -- of a remarkable and conterintuitive reality.
Deutsch's speculations would be merely a somewhat curious mind problem if quantum mechanics were not so important in today's world. Virtually all of our high tech equipment since the invention of the transistor depends on quantum mechanics. We have become dependent on the acceptance and use by scientists and engineers of data that make no sense under classical mechanics.
Do they make no sense because we haven't yet developed the technology to obtain additional data needed to understand reality? Or is that the way reality is -- what we see is all we'll ever get? Deutsch would argue the latter.
It would be fun to locate that parallel universe where I became an architect rather than a lawyer -- my alter ego probably has developed a more relaxed and less contentious personality.
No comments:
Post a Comment