Not Even Wrong

Arizona State University’s new Origins Initiative is starting off this year with some mind-expanding programs, including an Origins Symposium that will start tomorrow. The number and quality of speakers who will be making the trip to Tempe is remarkably high. The event will be webcast, so the rest of the world can get the inside dope by following along here.

Cosmology will be the main topic on the first full day of the Symposium, with Science Friday broadcasting live at 11am a panel discussion on “Physicists and the Origin of the Universe”. The afternoon program will be in three parts, with the last part about new observational methods. The first two deal more with the chronic heady topics and pipe dreams of theorists (“How Far Back Can We Go?” and “Is our Universe Unique, and how can we find out”), and will have a break for tea and brownies, finishing up at 4:20 with Glashow (whose title is the blunt “Is Particle Physics Over?”) and Vilenkin (“Mediocrity as a principle”).

I hear that refreshments will be provided by Tempe’s own ChebaHut and there will be an exhibit featuring work of local artists. Arizona is putting on quite a show, with a major effort to attract cutting-edge researchers in physics to the state, including the recent announcement of proposed new legislation.

Update: The final paragraph above was inspired by the posting date, and is pure fantasy. In addition, I have no idea whether brownies will be served during the break tomorrow, or what might or might not be in them. I do look forward to seeing what the various speakers will have to say, and am sure they will be addressing the multiverse/pre-big-bang topic without the aid of any mind-altering substances, difficult as that may be to believe.

Yesterday at the KITP Wati Taylor gave a talk entitled Freedom and Constraints in the Landscape of Intersecting/Magnetized Branes. During the talk he explained in detail the problem of lack of predictivity caused by the landscape. As far as anyone knows, to the extent you can calculate anything, you can get whatever you want: “Anything Goes”, and string theory is useless for ever predicting anything. He was looking at some particular classes of vacua, chosen for their computational tractability, and hoping to find some constraints among the quantities one can compute. There’s no known reason to expect this, but one can compute anyway and hope. The end result was the expected one: you can get whatever you want. Here are some quotes from the talk:

So, We’re really in a very challenging situation where we don’t really know how to define the theory, we don’t know what the set of solutions are, and even if we did we would have a very hard time making a sensible statement about what that means for predictions…

Every piece of data we have so far I would say is consistent with the notion that everything is pretty much uniformly and randomly distributed in the landscape.

There was extensive discussion of the predictivity problems and overwhelming evidence string theory can’t ever predict anything below the Planck scale (this wasn’t discussed, but I don’t see how it predicts much above the Planck scale either). For some reason there was no drawing of the obvious conclusion that one should just give up on the idea and try something else.

Seed Magazine has a video and transcript up of a discussion between cosmologist Paul Steinhardt and philosopher of science Peter Galison advertised as The physicist and the historian discuss the nature of truth as theoretical models of the universe become increasingly difficult to test.

Steinhardt is no fan of the anthropic landscape and makes a general attack on the idea of eternal inflation, explaining why he prefers his cyclic model:

The original idea — the way it’s often talked about in literature and textbooks, even the way we talk to students — is that inflation makes everything in the universe the same. What we’ve learned is that inflation actually divides the universe up into little sectors that are all different from one another. Some regions of space would be habitable like ours, but others would be inhabitable; still others would be habitable but would not have the same physical laws or the same distributions of matter that we see here…

Because you have an infinite number of everything, you have no rigorous mathematical or statistical way of computing a probability — it’s not even a sensible question to ask. So people are in the process of trying to regulate this infinity. For example, they try to invent a rule for deciding probability that makes what we see likely. But there’s no way of deciding why that rule instead of some other one. They simply keep trying until they’ve found the answer they wanted. Some people are going down that path and are prepared to declare victory if they find something they think works.

Others take a different path. They accept the infinity of infinities and the fact that they can’t find any measure for deciding whether our circumstance is more probable or not. They’ll be satisfied with the fact that at least some patches look like what we see, and will declare victory on that basis.

Personally, I don’t find either of these approaches acceptable, which is why I have developed an alternative picture in which the big bang is not the beginning. A big bang repeats at regular intervals of a trillion years or so, and the evolution of the universe is cyclic.

The two then get into a philosophy and history of science discussion, starting with Steinhardt’s:

We’ve been talking about an example in which you have a complex energy landscape and an infinite number of possibilities for the universe. But we have no real explanation as to why things are the way they are, because it could have been different.

So it has no power. And without real explanatory power, it’s not interesting to me. But I’d be interested to hear how this has played out in the history of science.

and Galison’s response:

We have that sort of split right now among the string theorists. One side says, “Look, what’s really scientific is to say there’s this infinite or very huge number of craters to be imagined in some landscape, each of which carries different physical particles and different physical laws and so on. And we happen to live in one of them.”

But the other says, “You’ve given up! You’ve given up the historical project of science. We went into string theory because we wanted to produce a theory that had one parameter, or very few movable parts. And now instead of a glider you’ve got a helicopter with 10,000 little pieces that have to move exactly the same way. If the slightest thing goes off, it falls to the ground in a heap of burning aluminum.”

It’s really an interesting moment in that way.

Steinhardt describes the current situation as follows:

I think it’s historic. There’s a certain community that feels, “This is an ‘aha’ moment. Science has to change. We have to accept that science has limits. There’s only a certain amount that we’ll be able to predict. Beyond that we’re going to accept that we live in some special corner of space in which seemingly universal laws — including Newton’s law of gravity — are just local environmental laws that aren’t really characteristic of the whole.”

Other groups say, “Hold it, this is failure. We either find ways of fixing the problems in those theories, or we scrap them and replace them with something else.”

The source of the problem here is not actually eternal inflation, but string theory. It is the fact that one needs to postulate a huge landscape in string theory in order to have something complicated and intractable enough to evade conflict with experiment that is the problem. Once one has this, and populates it with eternal inflation, then one has a pseudo-scientific framework with no explanatory or predictive power. Galison notices that string theorists are dividing up into those who follow this path, and those unhappy with it, but it is only Steinhardt who makes the obvious point that what’s going on here is just garden-variety scientific failure. The failure though is not attributable to the general idea of inflation, but rather to the string theory-based assumption that fundamental physical theory involves a hopelessly complicated set of possibilities for low-energy physics.