Saturday, January 10, 2015

Stephen W. Hawking. The Theory of Everything (2002)

     Stephen W. Hawking. The Theory of Everything (2002) Originally published as The Cambridge Lectures: Life Works in 1996. The title is a sly joke: Hawking is not offering a grand unified theory, but an  account of “The Origin and Fate of the Universe”.
     There have been a few advances or improvements in that account since he wrote it. There’s now definite evidence of the Higgs boson, which will add to the detail of the first few femtoseconds of the Universe’s existence. Some progress has been made in deducing the state of the universe while it was still a dense opaque soup of elementary particles and energy quanta, before it became transparent. The notion of a singularity at the inception of time as we know it is being modified: it may be sensible to talk of a time before our universe’s expansion from almost nothing, but any information from that time is inaccessible. But these are details: the grand picture is the same now as it has been for a couple of decades: our universe (or our bit of it) began in an unimaginably dense region which expanded very rapidly in a few seconds, and has been expanding much more slowly ever since. It will likely continue to expand “forever”,  which makes one think about what that term may mean.
      Hawking writes concisely, his disability forces him to choose his words carefully. He has a lovely sly sense of humour, noticing sideways and loopy connections between what he’s saying about abstract models and the actual life we live. It feels good to think that he’s managed to remain cheerful despite the ravages of ALS.
     Cosmology is an iffy science. It’s essentially speculative. Models are proposed, they are massaged until they produce some prediction, and the experimentalists and observers look for matches. Matches winnow the number of candidates, and may suggest new ones. Since sometime around the 1970s, cosmologists have included quantum physics (QP) in their models, Hawking chief among them. (He’s very careful to give credit where it’s due, and to admit his errors and oversights). Including QP raises some questions.
     There is a temptation to interpret models as pictures of reality, to use them as justifications of claims about what reality is. But QP is notorious for prompting incompatible or metaphysically absurd interpretations. Is our universe one among hugely many in a multiverse? Is the number of universes increasing because random bubbles in space-time appear and expand, or do human choices have something to do with it? There is no way, absent more complete models, to arbitrate between the answers. But I doubt that more complete models will do away with such interpretations. The reason is the way physicists talk about reality.
      What many physicists say about what QP tells us about “reality” suggests to me that they forget that they are talking about models. A scientific theory is a model of reality, it’s not reality. The experimenter tries to simplify the interaction as much as possible, on the assumption is that simplification will reveal some essential properties of the observed object. And that is certainly the case. But there is an additional assumption: that an object is some kind of stable combination of its properties. I think this is a misleading assumption. All we can know of any object is our interactions with it. The uncertainties intrinsic to QP are uncertainties about what we are able to know about those interactions. To put it bluntly: Observations are interactions. An object is the history of our interactions with it.
     For example, I don’t think it makes sense to say that photons are somehow both waves and particles, some weird combination of what we see on the surface of a pond and what we see on the surface of a billiard table. It does make sense to say that their behavior is like that of a wave or that of a particle, depending on how we interact with them. They may even exhibit both behaviours in some situations.  Someone has even invented the term “wavicle”, kinda cute. It’s that dual behaviour which persuades some people that photons are somehow both wave and particle.
     But it doesn’t persuade me. I’d rather say that we can’t imagine an object that is both wave and particle, the best we can do is use wave and particle mathematics to describe and predict the behaviour of photons. Just what a photon is in and of itself is a meaningless question.  “Wavicle” is a gap-filling belief.
     The same can be said of our theories of the universe. Mathematics is a wonderfully precise language for describing and predicting our interactions with the world. But to think that these descriptions are anything more than that is I think a  delusion.
     Read Hawking’s book. It’s a bit outdated, but it’s an easy read for anyone who’s kept up with cosmology, and a not too difficult introduction for the newcomer. It lacks diagrams, a minor fault. ***½

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