Cosmic Natural Selection
|Apr30-05, 10:22 AM||#69|
Cosmic Natural Selection
If a theory about nature makes false predictions it normally gets chucked out. But its mathematical machinery, if valid as mathematics, could be re-applied elsewhere and might indeed prove useful, even though the theory for which it was originally invented has been ruled out.
I think your point confirms what many of us suspect (or I do at least) which is that progress can be made by formulating and testing physical theories even when they fail. It is not a pure loss for a theory to be formulated, made to predict something, and then checked. Even if it doesnt check out in the end, something is learned, and (as your post reminds us) the mathematical machinery may be useful in other applications.
|Apr30-05, 10:50 AM||#70|
At one point string/M inspired hope that it might eventually develop into a theory explaining the parameters of the Standard Model. Now many string researchers have given up on that hope and accepted the inevitability of something which Lubos Motl calls the "Haystack" of possible versions each with its own physics. There was a recent article about this---I don't have a subscription to the N.S. but maybe someone else does and has seen it:
Earlier this year there was an article by the San Francisco Chronicle's science writer, Keay Davidson. The title was:
"'Theory of everything' tying researchers up in knots"
This did quote major scientists outside string, including Nobel laureates. But there was no leader from within string expressing criticism of the way the field has been going. There certainly was no quote like this from Witten!
For example David Gross has been an outspoken, even impassioned, opponent of Landscape/Anthropery but only in house. He has not come out in as public a medium as the New Scientist. And in the 14 March SF Chronicle article he breathed no word of string self-criticism.
so maybe the current (30 April) New Scientist article about the
string theory "road trip from hell" does represent a bit of progress towards getting more forthcoming public recognition of the crisis by string leadership.
|Apr30-05, 11:23 AM||#71|
This article seems to set a new benchmark for open expression of dissatisfaction by a string leader. It is not much compared with what is heard inhouse. but for a wide-circulation magazine it is something. Here's the link again:
The theory of everything: Are we nearly there yet?
"The hunt for the theory of everything is turning into a road trip from hell..."
This current New Scientist article was discussed some today and yesterday at Peter Woit's blog
Here are a couple of posts by Thomas Larsson
---quotes from Larsson---
This pessimism about string theory over the last year or two, seems to be quite different and more ominous than what happened during the temporary lull string theory experienced around 1990 (before D-branes, duality, AdS/CFT, etc ...).
Another reason why the present situation is much worse than 1990 is that we know more now. In particular, we know that the cosmological constant is positive (so AdS is ruled out) and that supersymmetry requires fine-tuning at the percent level (which in some sense means that the odds that SUSY is realized in nature is down to the percent level). Since SUSY and a non-positive CC are the main soft-predictions of string theory, it seems rather problematic that both are ruled out by experiments. Not surprisingly, it is precisely these two results that have triggered the recent anthropic excuses.
Hence I disagree somewhat with the premise of this blog. I don't think that string theory is not even wrong, but rather that it in fact is wrong.
Posted by: Thomas Larsson at April 29, 2005 04:11 AM
There are many potential signals of supersymmetry, some of which should already have been triggered. Apart from direct discovery of sparticles, we could have seen e.g. a light Higgs, proton decay, muon g-2 deviation, permanent electric dipole moment, WIMPs, and probably many other things that I don't know about. An arxiv search for the keywords "tuning supersymmetry" gave 35 hits during the past year, the most recent one being hep-ph/0504246. Let me quote from the introduction
"Another problem comes from the fact that LEP II did not discover any superparticles or the Higgs boson. In most supersymmetric theories, this leads to severe fine-tuning of order a few percent to reproduce the correct scale for electroweak symmetry breaking. This problem is called the supersymmetric fine-tuning problem".
I am no expert on SUSY phenomenology and never claimed to be. But if the experts say that there is a fine-tuning problem, I see no reason to doubt that.
It was, I believe, the need for SUSY fine-tuning that motivated the introduction of split supersymmetry. For almost 20 years, Witten used to say that string theory makes one prediction, supersymmetry (and one postdiction, gravity), but I haven't heard him make this claim for a couple of years. One cannot help noting that string theory apparently stopped predicting SUSY once this claim became accessible to experimental tests.
Posted by: Thomas Larsson at April 30, 2005 06:42 AM
|May1-05, 12:33 AM||#72|
Strong words from inside the camp. I admit being a critic of ST. It has always been too mushy for me.
|May1-05, 06:24 AM||#73|
Witten saying (for New Scientist) that he hopes Landscape "isn't on the right track". But not strong enough, I fear, to give critics like Lubos any protection. At String 2003 conference David Gross took a much stronger stand against appealing to Anthropery, quoting a churchill WW2 speech about "never never never give up". It was just in house rather than out in the open.
Do you get the impression that the reason Lubos Motl has been disciplined is because his outspoken rejection of the Landscape? In his "Kennedy Landscape" blog I hear him say flatly that it isnt even interesting enough to disagree with. And I hear him say that it is gradually becoming string dogma that you have to at least consider it, or treat it as worth discussing.
When he says "heresy" I hear him say that now you can't treat it as mere Landfill without getting into trouble.
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