Sep 25, 2006

Lee Smolin on the temporality of physical laws

The non-inciting part of the Pope's speech--the part that got less radio play--involved faith and reason in conflict and combination. Quoth Benedict, as noted by my brother:
Modern scientific reason quite simply has to accept the rational structure of matter and the correspondence between our spirit and the prevailing rational structures of nature as a given, on which its methodology has to be based.
Compare that with Lee Smolin, in the latest NewScientist [subs. req.]:
In science we aim for a picture of nature as it really is, unencumbered by any philosophical or theological prejudice. Some see the search for scientific truth as a search for an unchanging reality behind the ever-changing spectacle we observe with our senses. The ultimate prize in that search would be to grasp a law of nature - a part of a transcendent reality that governs all change, but itself never changes.

The idea of eternally true laws of nature is a beautiful vision, but is it really an escape from philosophy and theology? For, as philosophers have argued, we can test the predictions of a law of nature and see if they are verified or contradicted, but we can never prove a law must always be true. So if we believe a law of nature is eternally true, we are believing in something that logic and evidence cannot establish.

Of course, laws of nature are very useful, and we have in fact been able to discover good candidates for them. But to believe a law is useful and reliable is not the same thing as to believe it is eternally true. We could just as easily believe there is nothing but an infinite succession of approximate laws. Or that laws are generalisations about nature that are not unchanging, but change so slowly that until now we have imagined them as eternal.

These are disturbing thoughts for a theoretical physicist like myself. I chose to go into science because the search for eternal, transcendent laws of nature seemed a lofty goal. However, the possibility that laws evolve in time is one that recent developments in theoretical and experimental physics have forced me, and others, to consider....

Here is the question that keeps me awake these days: is there a way to represent the laws of physics mathematically that retains the notions of the present moment and the continual unfolding of time? And would this allow us - or even require us - to formulate laws that also evolve in time?...

It is not impossible to achieve time-bound laws in physics. There are logicians who have proposed alternative systems of logic that incorporate a notion of time unfolding. In these logics, what is true and false is assigned for a particular moment, not for all time. For a given moment some propositions are true, others false, but there remains an infinite list of propositions that are yet to become either true or false. Once a proposition is true or false, it remains so, but at each moment new propositions become decided. These are called intuitionalist logics and they underlie a branch of mathematics called topos theory.

Some of my colleagues have studied these logics as a model for physics. Fotini Markopoulou of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, has shown that aspects of space-time geometry can be described in terms of these logics. Chris Isham of Imperial College London and others propose to reformulate physics completely in terms of them.

Looking at biology, it seems there are advantages to what are, essentially, time-bound laws. Evolving laws might make computer systems similarly robust and less likely to do what the laws of natural selection, it seems, never do: crash. The universe, too, seems to function rather well, operating without glitches and fatal errors. Perhaps that's because natural selection is hard at work in the laws of nature.
I'd love to republish the whole thing, because it's hidden behind a subscriber-only firewall, but I'm too respectful of copyright. I'll poke around and see if anyone else has written about it, and link to their (more learned) opinions.

Added: LuboŇ° Motl, for one, isn't very happy.

Lee Smolin promotes his cosmological natural selection. Just during the last month, five independent people have mentioned this issue in discussions with me or in their own articles; the list included famous names like L.S. or A.V. All of them are convinced that it is trivial to falsify Smolin's hypothesis and it has, in fact, been done immediately when Smolin proposed it.

A decade ago, Smolin had conjectured that the laws of our universe are optimized for black hole production because every new black hole is a new baby whose properties are similar to the parent universe but it is not quite identical because there is also a cosmological mutation going on. The most prolific universes - those who create many black holes - are going to dominate the ensemble of the universes. Lee Smolin has written a whole book whose content is isomorphic to this paragraph.

It is easy to see that if you change some parameters in our universe, for example if you reduce the hierarchy between the electroweak scale and the Planck scale, many more black holes will be created. The theory is dead. Trivially dead. Period. Why does Smolin revive this nonsense all the time, without having any new arguments or mechanisms? Does a lie become the truth when it is repeated 100 times?

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