Thursday, July 23, 2009

Sorting the Physics from the Metaphysics

Physics world has recently released a couple of interesting articles from sometime adversaries Lee Smolin and Leonard Susskind. Susskind’s article is an attempt to cheerlead for the String Theory Anthropic landscape by invoking Darwin and the science-religion 'conflict'. He remarks that:

In successfully explaining the origin of species, he eliminated superstition and set a new standard for what an explanation of nature should be like. As I wrote in my book The Black Hole War (Little Brown, 2008), Darwin’s masterstroke was to have “ejected God from the science of life”..... In other words, before Darwin, even the greatest physicists had little alternative to a supernatural explanation of the origin of life, and therefore of nature itself. It was the success of Darwinism that forced the issue and set the standard for future theories of origins, whether it be it of life or of the universe. Explanations must be based on the laws of physics, mathematics and probability — and not on the hand of God.

Unfortunately Darwin merely appears to have evicted God into the cosmologist’s territory, a fact bemoaned by Susskind.

what is less noted is that physics and cosmology pose very similar questions, such as why the universe seems so incredibly fine-tuned for the existence of life. The only explanation, if we can call it an explanation, is that if it were less fine-tuned, intelligent observers like ourselves would have been impossible. I am, of course, referring to the cosmological constant, L. Theoretically, one would expect L to be unity in natural Planck units. But if it were anything bigger now than it is known to be — 10–123 — it would have prevented the evolution of galaxies, stars and us. Like Paley, we encounter what appears to be an extremely unlikely Paley might have complained, accidents involving 123 decimal places are too unlikely.

Luckily, just as the ‘faith-heads’, ‘theocrats’, ‘fidophiles’ and ‘sky-fairy aficionados’ let out a triumphant yell of glee, the string theorists gallop over the horizon to save the day.

‘Just as the details of DNA determine the biological details of a living organism, so the details of the fluxes, branes and other elements determine the properties of the universe. Again, the numbers are so staggering that even if the world as we know it seems extremely unlikely, there will be many ways of arranging the elements to make the constants of nature consistent with life. In particular, there will be many configurations in which the cosmological constant will be fine-tuned to 123 decimal places......Whether string theory with its huge landscape, and eternal inflation with its reproducing pockets of space, will prove to be correct is for the future to decide. What is true is that as of the present time, they provide the only natural explanation of the universe that lives up to the standard set by Darwin.

The problem being that String Theory find itself in a lot of trouble with the publication of Peter Woit’s ‘Not Even Wrong’ and Lee Smolin’s ‘The Trouble with Physics’. Peter Woit on his blog was less than impressed, complaining that:

Lenny Susskind gives new depth and meaning to the word “chutzpah” with an article in Physics World on Darwin’s Legacy. It seems that Darwin’s legacy for physics is the field of string theory anthropic landscape pseudo-science. Luckily, I don’t think creationists normally read Physics World.

Perhaps Susskind’s article was prompted by last month’s article by Smolin entitled ‘The Unique Universe’ in which he argues against the excesses of String Theory Anthropic Reasoning and argues that the timeless multiverse does not lend itself to predictive models and effectively does not exist:

there has been a gradual shift, during which it first became acceptable to work on theories that described not only our universe, but other possible universes, universes with less or more dimensions, or universes with different kinds of particles and forces. In the last few years, we have moved further away from theories of our one universe, as these other worlds went from being logically possible to hypothetically actual. It is now common to hear about the multiverse — a quantum cosmology that takes for granted that the visible universe that we see around us is just one of a vast or infinite number of universes..... the combination of the multiverse assumption and the timeless assumption effectively gives us a static meta-universe. Even if our own universe evolves in time, at a deeper level it is part of a timeless, eternal, ensemble of universes.

This is part of the problem highlighted by Paul Davies in a 2007 article:

The multiverse theory is increasingly popular, but it doesn’t so much explain the laws of physics as dodge the whole issue. There has to be a physical mechanism to make all those universes and bestow bylaws on them. This process will require its own laws, or meta-laws. Where do they come from? The problem has simply been shifted up a level from the laws of the universe to the meta-laws of the multiverse.

Smolin identifies the problems with this multiverse and meta laws. The first is that the relationship between the fundamental laws that would govern the theoretical multiverse and the effective laws we observe in our universe is fraught with difficulties:

...In a timeless world in which our universe is just one of many equally real universes, the laws of physics must be very different from those that most physicists can ever have conceived. This is because the laws of physics are no longer determinable by what we observe in our own universe, for they must apply to all of the vast en¬semble of universes. A fundamental law then no longer proscribes what happens in our universe; instead it gives probability distributions for properties of the ensemble of universes.... given that the characteristics of the ensemble can be postulated at will and are not subject to experimental tests, the result is that we cannot make precise and unambiguous predictions about anything observable in our own universe.

The second is that ‘without time, and without the assumption that what exists is the single universe that we observe, it is hard to make sense of statements about probability relevant to what we observe in our universe. Since quantum mechanics is a probabilistic theory, we then run into trouble by trying to extend it to a realm where probability appears to make no sense’. In other words, theories that do not posit time to be a fundamental property fail to reproduce the space—time that we are familiar with.

To solve this problem, Smolin suggests positing a time as something fundamental, rather than seeing it as an emergent property. He also suggests that science should proceed with the following metaphysical principles:

1) There is only one universe. There are no others, nor is there anything isomorphic to it.

2) All that is real is real in a moment, which is a succession of moments. Anything that is true is true of the present moment.

3) Everything that is real in a moment is a process of change leading to the next or future moments. Anything that is true is then a feature of a process in this process causing or implying future moments – this would reject the idea of eternal laws and the existence of a platonic world of mathematical forms

4) Mathematics is derived from experience as a generalization of observed regularities when time and particularity are removed.

Smolin concludes by saying that the “notion of transcending our time-bound experiences in order to discover truths that hold timelessly is an unrealizable fantasy. When science succeeds, we do nothing of the sort; what we physicists really do is discover laws that hold in the universe we experience within time. This, I would claim, should be enough; anything beyond that is more a religious urge for transcendence than science’. He also plugs his cosmological natural selection theory by claiming that the laws of nature could evolve with time.

Whether Smolin's metaphysical edicts will be the modern day equivalent of the 1277 condemnations remains to be seen. While his principles will go some way to tidying up all the speculation rife in physics they are unlikely to satisfy those who wonder why this particular model of universe exists.

For those that are interested, there is an article about the theological implications here.

Discuss this post at the Quodlibeta Forum


knowingthomas said...

I'm guessing "string theory anthropic landscape" and "String Theory Anthropic Reasoning" is just another way of saying "Explaining away the fine tuning with String Theory", not fine tuning in general right?

Tor Hershman said...

Here, wait a'll take care of the god/devil thingy(s), thus.....

unkle e said...

Very interesting! Smolin's suggested principles are a big step forward from the generally unstated metaphysical assumptions often made. And they illustrate that much has to be assumed, or postulated, before one can have a basis for any worldview and for science. Many scientists want to assume positivism. So let's hope there is some good discussion of these principles.

Matthew said...

Great entry.

Humphrey said...

String theory anthropic landscape refers to the fact that String theory indicates there are 10 to the 500 ‘vacua’ with varying parameters and features. With some sort of appropriate mechanism - i.e cosmic inflation, these vacua could be actualised and this would solve such things as the cosmological constant problem. We observe what we observe because this is the part of the landscape we happen to be in.

Problems (borrowing heavily from David Gross)

1) The ‘vacua’ of string theory are all meta-stable, most are uncontrollable and none constitute a consistent cosmology. They are nothing more than approximate solutions.

2) The mechanism of eternal inflation and the multiverse is technically and conceptually shaky. Postulating a series of causally disconnected regions of some kind of configuration space is something that would have challenged medieval theology.

3) We still do not know what String Theory is. Does it even deserve the name theory?. Should be called a’ framework’. Many suspect there is something important missing.

4) Space and Time are thought to be emergent. How does this multiverse and it's meta-laws operate if it is not within space or time?. How do we even conceive of something like that? or infer what it must be like from the properties of our universe?.

Xavier Terri said...

I read Lee Smolin's book ‘Las dudas de la física en el siglo XXI’, 2007, Ed. Crítica. Wonderful. I have seen that Lee Smolin are looking for a new big idea, the fundamental simply idea for the progress and unification of physics. Seems that Smolin got the conviction that both quantum mechanics and GR theorys don’t understand the deep nature of time (page 355). It is right for GR unless.

Here is what i say:
No more Lorentz’s Transformations. The new alternatives transformations (’relational transformations’) are deduced on ‘La paradoja de los gemelos de la teoría de la relatividad especial de Einstein’, f.i., equations (22) and (23) with “C” and “D” given by (42) and (43) , pages (33) to (36). From them arises the ‘teoría relacional’, an alternative to special relativity.
The generalitation of this ‘teoría relacional’, the unique possible classic alternative to GR, appears on ‘Extracto de la Teoría Conectada’. 3 are the fundamental equations. (84), (171) and (172), pages (146) and (182). This 3=24 equations are necessary in order to eliminate the Newton-Einstein’s absolute space. There are not absolutes accelerations (neither absolutes velocities, of course).

The Dark Matter problem is solved in ‘Apéncice C’, page 205 (Exponential factor gets important at large distance from the center).

What about a “quantum teoría conectada”? I believe that you can say something important about it.

Xavier Terri
Terrassa 2009 august 6

P.D.: Smolin are completely certain when he tell that the great historic mistake comes from Descartes-Galileo ('Las dudas de la física en el s.XXI', pages 355-356). This great historic error is the Principle of Inertia (movement is a relational concept. It is completely false that the movement of ALL free bodies is a straight line. Some of them move, respect the SAME reference system, in a curved way. Spacetime metric defines a specific relationship betwen bodies and reference system.Pure evidence beyond the reason: at night, see the stars). Also, Principle of Inertia leads us to the inertial-non inertial dichotomy. Where is INVARIANCE of physical laws? (pages 45 on 'Paradoja' and 141, eq. (77), on 'Teoría Conectada').

Teoría Conectada: The best physic's theory since 1687

Xavier Terri said...

"Sorting the Physics from the Metaphysics", the 'teoría conectada' solution of the dark matter problem can be found in the e-print 1002.0007: