Friday, February 19, 2010

Fine tuning solved....or not?

I was interested this week to see the blurb for an article in the January 2010 edition of ‘Scientific American’; the U.S equivalent of ‘the New Scientist’. Like it’s UK doppelganger this mag has had something of a reputation among grouches like Peter Woit for ‘multiverse pseudo-science stories’ including ‘Parallel Universes, The Great Cosmic Roller-Coaster Ride and Does Time Run Backwards in Other Universes?’. Now they have produced an article by Alejandro Jenkins and Gilad Perez purporting to address the issue of so called cosmic ‘fine tuning’. The article description reads:

Multiple other universes—each with its own laws of physics—may have emerged from the same primordial vacuum that gave rise to ours. Assuming they exist, many of those universes may contain intricate structures and perhaps even some forms of life. These findings suggest that our universe may not be as “finely tuned” for the emergence of life as previously thought.

It begins:

'Remarkably, we have found examples of alternative values of the fundamental constants, and thus of alternative sets of physical laws, that might still lead to very interesting worlds and perhaps to life. The basic idea is to change one aspect of the laws of nature and then make compensatory changes to other aspects

Or ‘very few’ examples as it transpires. The rest is a quite interesting discussion of alternative biochemistry, with an abundance of ‘maybe’s, ‘could’s and ‘possibly’s. I have to say I was more impressed by how little you could actually change rather than the alternate scenarios that could work. In fact you can’t alter any of the values of many of the forces without compensating in other areas. Some of the conclusions seemed more than a little dodgy, for instance they reckon you could knock out the weak nuclear force and still produce a habitable universe (you would still have to fiddle with the standard model to get the remaining forces to work properly).

The fundamental problem the 'weakless' universe is going to have is that the stars produced are only going to churning out energy at a few percent that of our sun. Secondly the elements would not be spread by supernovas as these would fail (but they could still be spread to a lesser extent by thermo-nuclear explosions caused by accretion). Earth like planets would have to be a lot closer to suns and they would have no plate tectonics (that has implications serious for evolutionary processes). If any complex life did eventually evolve it would doubtless be bored out of it’s mind as the lack of heavy elements would make this alternate earths landscape flat and dull; a bit like the Midwest.

These objections however pale in comparison to that raised by Dr. Robert Piccioni on his blog:

“Contrary to the cover story in Scientific American's January 2010 issue, life would NOT be possible in a universe without the weak nuclear force, because then matter and antimatter would have completely annihilated each other, leaving no atoms to make life. Only the weak force treats matter and antimatter asymmetrically, allowing slightly more matter to develop in the first second after the Big Bang. Everything we see, and are made of, comes from that slight excess that the weak force enabled.”

On the other hand it looks like you can fiddle with the values of the three lightest quarks and still get some kind of functioning chemistry (but not by very much).

If quark masses were adjusted to make the proton heavier than the neutron, then the proton in a hydrogen nucleus would capture the surrounding electron and turn into a neutron, so that hydrogen atoms could not exist for very long. But deuterium or tritium (hydrogen 3) might still be stable, and so would some forms of oxygen and carbon. Indeed, we found that only if the proton became heavier than the neutron by more than about 1 percent would there cease to be some stable form of hydrogen. With deuterium (or tritium) substituting for hydrogen 1, oceans would be made of heavy water, which has subtly different physical and chemical properties from ordinary water. Still, there does not appear to be a fundamental obstacle in these worlds to some form of organic life evolving.

This seems like a fair conclusion on the surface but I suspect it's not that simple. Heavy water in large quantities has the effect of slowing down a great many chemical reactions occurring in biological systems. Smaller forms of cellular life can adapt to this pretty well but more complex lifeforms get into difficulties.

Yet all this speculation proves to have been of no avail since, following this discussion of cosmological ‘what ifs’, the authors still go back to arguing for the multiverse at the end on the basis of the 'cosmological constant' problem.

Our work did not address the most serious fine-tuning problem in theoretical physics: the smallness of the “cosmological constant,” which our universe neither recollapsed into nothingness a fraction of a second after the big bang, nor was ripped part by an exponentially accelerating expansion. Nevertheless, the examples of alternative, potentially habitable universes raise interesting questions and motivate further research into how unique our own universe might be.… the late 1990s, astronomers discovered that the universe is indeed expanding at an accelerating rate, pushed by a mysterious form of “dark energy.” The observed rate implied that the cosmological constant is positive and tiny—within the bounds of Weinberg’s prediction—meaning that dark energy is very dilute. Thus, the cosmological constant seems to be fine-tuned to an exceptional degree. Moreover, the methods our teams have applied to the weak nuclear force and to the masses of quarks seem to fail in this case, because it seems impossible to find congenial universes in which the cosmological constant is substantially larger than the value we observe. Within a multiverse, the vast majority of universes could have cosmological constants incompatible with the formation of any structure.

So having read all the way through an article purporting to have solved the fine tuning problem you find at the end that the problem is just as intractable as ever and it’s full speed ahead to the multiverse. Bottom line is, if you read the blurb for an article of scientific paper, take it with a pinch of salt.

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Al Moritz said...

Yes, the 'weakless' universe does nothing to the fine-tuning issue, as you rightly point out -- in fact, it is just another example of fine-tuning since other parameters need to be adjusted. I have discussed that also in my article "Cosmological arguments for the existence of God":

Unknown said...

I think I have to agree with Peter Woit on this one.

Rob O said...

I'm forced to agree with those who counter that the Many Worlds hypothesis is 'ad hoc' and contrived. It does not qualify as science, for starters, because it cannot be tested. In our current physical forms and with our measuring instruments we cannot probe outside our space-time manifold. The physics of other universes (if they exist) would destroy us and our instruments even if it were possible to transcend the boundary of ours. Those proposing it ought to at least admit that it is a metaphysical hypothesis - one which violates Occam's razor, and is dispensable from the get-go.

Anonymous said...

To be honest, I don't even think ANYONE approves of the multiverse theory, it's just that they like making cool pictures depicting it. Case in point: the SciAm cover.