## Wednesday, June 06, 2007

### Landscape 2007

A notorious critic of physics wrote the following:
There seems to be a peculiar trend going on in the particle theory community. Just about all theorists I talk to, correspond with, argue with on blogs, etc. claim to be quite unhappy with the Landscape, and insist that most of their colleagues share this view. On the other hand, all evidence is that Landscape research is becoming increasingly influential at the highest levels of the string theory community.
A long list of talks about the landscape and hints that some people find it important follows.

Well, indeed, most high-energy theorists dislike the anthropic principle. A poll at a previous Strings conference revealed that about 80% of the folks oppose notion that the anthropic selection will be an essential feature of the right solution to the vacuum selection problem. There is obviously no consensus and the majority dislikes the anthropic setup.

But what is equally important to realize is that the landscape is, at present, the only concrete solution to the vacuum selection problem that can be combined with the cutting edge understanding of particle physics as well as gravity into a coherent whole that has also the ability to produce the right value of the cosmological constant problem. Whoever denies the statement of the previous sentence because of some preconceptions is a bigot and a denier. ;-)

The absence of a concrete alternative is why there can't obviously be too many serious papers that would approach these important questions - and the vacuum selection problem is even more important today than it was in the past - from a different perspective than the anthropic one. Such a perspective is simply not yet available. This fact makes it unsurprising that the relative representation of the anthropic principle in literature and at the conferences and summer schools keeps on growing.

Is the actual probability that the anthropic principle is correct increasing, too? Or is the effect in the previous paragraph just an irrational artifact of sociology?

I have somewhat mixed feelings about this question. How does it really work? Those who think that the right answer to the vacuum selection problem is not anthropic - like myself - spend a part of their time by thinking about conceivable alternatives, for example attempts to refine the Hartle-Hawking wavefunction within string theory. We believe in the assumption that it was only due to a lack of imagination that people have only found the anthropic answer so far; more creative people will find a better solution in the future. However, no one has so far found such a concrete enough alternative which makes our belief system somewhat vague.

The assumption that the situation will change in the future is a nice assumption but it can't be a dogma as long as we're scientifically inclined people. I think that it is pretty clear that the more unsuccessful man-hours the community has invested to the search for quantitative but non-anthropic laws controlling the vacuum selection problem, the less likely it is that such a better solution exists. If you have been searching for a cup in your bedroom for three days, you should start to consider the possibility that the cup is actually not there.

I don't know how quickly the perceived probability that another solution - which may even be a non-stringy solution, if you want to be even more speculative - exists is decreasing or should be decreasing. But it is decreasing anyway. While I believe that the probability is still very high (the probability of a non-anthropic, but of course stringy solution), it would be foolish to think that the probability of a completely different theory that no one has been able to write down for decades can be kept constant. The only question is a quantitative one: how quickly it goes down.

On the other hand, the anthropic approach is continuing to perform all kinds of analyses. People like me don't believe that a huge majority of these things will be relevant for the ultimate understanding of the vacuum selection problem. People like me think that some of the ideas used in the anthropic research are even irrational and wrong and that no material progress in increasing the explanatory power of the theory takes place. But despite these facts, there is also an increasing amount of knowledge based on the anthropic thinking that is scientifically legitimate and logical. At least, the people find correct solutions to some mathematically well-defined problems even though these problems may be proven to be physically irrelevant in the future.

Right now we can't prove that the anthropic framework is wrong in all of its forms: the difficulty with proving that it's wrong is one of the main reasons why we hate it so much. :-) There is a very small chance that something could go very wrong with the vague anthropic framework which makes the survival of the anthropic framework unimpressive as a consistency check. Nevertheless, I think that the scientific approach obviously dictates that the people who believe the anthropic principle - and be sure that people like Raphael Bousso and others who give talks about it do believe it and expectations of a universal consensus are silly - have the unquestionable right to continue to do what they're doing while others will continue to believe that this whole direction will be replaced by something much more satisfactory in the future. This majority will wait for a better alternative - hopefully not just passively wait.

If I summarize this situation, it may be frustrating but there is simply nothing so terribly peculiar about it. The anthropic answer is disappointing but more concrete which is why it is rather straightforward to find problems in this setup and write papers about it. The hypothetical non-anthropic alternative is surely more attractive but it is mostly ill-defined at present. This asymmetry implies that the number of anthropic papers exceeds the number of non-anthropic papers even though most people believe that physics is ultimately not anthropic. There's nothing wrong with this asymmetry as long as the anthropic papers correctly admit that they still don't have any proof - and they do admit it. They may find a proof in the future but I find it unlikely.

There is no law that would say that the distribution of papers or talks should copy the opinions of scientists about the underlying questions. It would be a silly law: in reality, the number of papers and talks reflects not only the beliefs but also the actual ability of a given framework to be concretely or even quantitatively analyzed. And in science (as opposed to theology), the results of the papers can actually influence the beliefs.

In junk sciences, the number of papers about a given topic is also determined by the potential of this topic to scare the society and secure funding and by the political opinions of the scientists but I don't think that in the case of the high-energy questions, the society cares in one way or another and I don't think that politics is correlated too much with physics which is why the distribution of papers is determined almost exclusively by objective factors. But the a priori beliefs of scientists are not the only objective factor. In fact, it is not exactly one of the most objective factors here!

But if you're an opponent of the anthropic principle, don't forget: no one can guarantee that the anthropic principle will be replaced by something else. There have been many people in the past who had various reasons to dislike various theories - for example evolution, probabilistic nature of quantum mechanics, or string theory - and who were simply waiting for the theory to die. They have always been using big words to attack the theories they disliked. But these three theories, among hundreds of other examples, simply haven't died and they almost certainly never will. But concerning the anthropic landscape as an explanation of the low-energy parameters of Nature, we just don't know for sure.

The vacuum selection problem is an important problem and many people from both sides of the anthropic divide feel that this is the right moment when we should try to solve it. No one can promise that a solution will be found in 5, 15, or 50 years. And we're not confident about any solution today. The anthropic people are in advantage because they have a bad but very concrete framework to address all these issues. The anti-anthropic people are in disadvantage but the last thing they should do is to invent idiotic sociological conspiracy theories a la Woit or Smolin. Only fresh ideas and actual working theories and explanations can make science more exciting, powerful, true, and predictive - and their case stronger.

And that's the memo.