David Gross has in the past invoked the phrase “never, never, never give up”, attributed to Churchill, to describe his view about claims that one should give up on the traditional goals of fundamental physics in favor of anthropic arguments invoking a multiverse. Steven Hawking has a new book out this week, called The Grand Design and written with Leonard Mlodinow, in which he effectively announces that he has given up:
We seem to be at a critical point in the history of science, in which we must alter our conception of goals and of what makes a physical theory acceptable. It appears that the fundamental numbers, and even the form, of the apparent laws of nature are not demanded by logic or physical principle. The parameters are free to take on many values and the laws to take on any form that leads to a self-consistent mathematical theory, and they do take on different values and different forms in different universes.
Thirty years ago, in his inaugural lecture as Lucasian professor, Hawking took a very different point of view. He argued that we were quite close to a final unified theory, based on N=8 supergravity, with a 50% chance of complete success by the year 2000. A few years after this, N=8 supergravity fell into disfavor when it was shown that supersymmetry was not enough to cancel possible ultraviolet divergences in the theory. There has been a recent revival of interest as new calculational methods show unexpected and still not completely understood additional cancellations that may fully eliminate ultraviolet divergences. Hawking shows no interest in this, instead signing on to the notion that “M-theory” is the theory of everything. The book doesn’t even really try to explain what “M-theory” is, we’re just told that:
People are still trying to decipher the nature of M-theory, but that may not be possible. It could be that the physicist’s traditional expectation of a single theory of nature is untenable, and there exists no single formulation. It might be that to describe the universe, we have to employ different theories in different situations
The book ends with the argument that
M-theory is the unified theory Einstein was hoping to find. The fact that we human beings – who are ourselves mere collections of fundamental particles of nature – have been able to come this close to an understanding of the laws governing us and our universe is a great triumph.
This isn’t exactly an air-tight argument…
The book begins in a more promising manner, with a general philosophical and historical discussion of fundamental physical theory. There’s this explanation of what makes a good physical model:
A model is a good model if it:
1. Is elegant
2. Contains few arbitrary or adjustable elements
3. Agrees with and explains all existing observations
4. Makes detailed predictions about future observations that can disprove or falsify the model if they are not borne out.
The fact that “M-theory” satisfies none of these criteria is not remarked upon.
The book is short (about 100 pages of actual text, interspersed with lots of color graphics and cartoons), and contains rather little substantive science. There are no references of any kind to any other sources. The discussion of supersymmetry and M-theory is often highly misleading. For example, we are assured that
various calculations that physicists have performed indicate that the [super]partner particles corresponding to the particles we observe ought to be a thousand times as massive as a proton, if not even heavier. That is too heavy for such particles to have been seen in any experiments to date…
With no references, one has no idea what these “various calculations” might be. If they are calculations of masses based on the assumption that the supersymmetry and electroweak-symmetry breaking scales are similar, they typically predict masses visible at the Tevatron or LEP. I suspect that the logic is completely backwards here: what is being referred to are calculations based on the Tevatron and LEP limits that require masses in the TeV range.
As for the fundamental problem of testability of M-theory, here’s the only thing we get:
The theory we describe in this chapter is testable…. The amplitude is reduced for universes that are more irregular. This means that the early universe would have been almost smooth, but with small irregularities. As we’ve noted, we can observe these irregularities as small variations in the microwaves coming from different directions in the sky. They have been found to agree exactly with the general demands of inflation theory; however, more precise measurements are needed to fully differentiate the top-down theory from others, and to either support or refute it. These may well be carried out by satellites in the future.
This looks like one of many dubious claims of “testability” of multiverse theories, which tend to founder on the measure problem and the fact that one has no idea what the underlying theory actually is. Without any details or references though, it’s hard to even know exactly what the claim is here.
One thing that is sure to generate sales for a book of this kind is to somehow drag in religion. The book’s rather conventional claim that “God is unnecessary” for explaining physics and early universe cosmology has provided a lot of publicity for the book. I’m in favor of naturalism and leaving God out of physics as much as the next person, but if you’re the sort who wants to go to battle in the science/religion wars, why you would choose to take up such a dubious weapon as M-theory mystifies me. A British journalist contacted me about this recently and we talked about M-theory and its problems. She wanted me to comment on whether physicists doing this sort of thing are relying upon “faith” in much the same way as religious believers. I stuck to my standard refusal to get into such discussions, but, thinking about it, have to admit that the kind of pseudo-science going on here and being promoted in this book isn’t obviously any better than the faith-based explanations of how the world works favored by conventional religions.
For some reviews of the book showing a bit of skepticism, see ones by Craig Callender, Fred Bortz, and Roger Penrose. For much more credulous reviews, see for example James Trefil (who evidently has his own multiverse book coming out). The Economist has a news story about this, which assures us that Hawking is
a likely future recipient of the Nobel prize in physics (if, as expected, his 1974 theory that black holes emit radiation despite their notorious all-engulfing gravitational pull is confirmed by experiments at the Large Hadron Collider in CERN).
Update: There’s a new posting at physicsworld.com by Hamish Johnston that brings up the issue of the potential damage caused by this to the cause of science funding in Britain:
This morning there was lots of talk about science on BBC Radio 4’s Today Programme — but I think it left many British scientists cringing under their duvets.
Hawking explained that M-theory allows the existence of a “multiverse” of different universes, each with different values of the physical constants. We exist in our universe not by the grace of God, according to Hawking, but simply because the physics in this particular universe is just right for stars, planets and humans to form.
There is just one tiny problem with all this — there is currently little experimental evidence to back up M-theory. In other words, a leading scientist is making a sweeping public statement on the existence of God based on his faith in an unsubstantiated theory…
Physicists need the backing of the British public to ensure that the funding cuts don’t hit them disproportionately. This could be very difficult if the public think that most physicists spend their time arguing about what unproven theories say about the existence of God.
Update: Today’s Wall Street Journal has a quite positive review of the book by Sean Carroll.
Update: See here for John Horgan’s take on the Hawking book:
I’ve always thought of Stephen Hawking—whose new book The Grand Design (Bantam 2010), co-written with Leonard Mlodinow, has become an instant bestseller—less as a scientist than as a cosmic, comic performance artist, who loves goofing on his fellow physicists and the rest of us…
Toward the end of the meeting [in Sweden, 1990], everyone piled into a bus and drove to a nearby village to hear a concert in a Lutheran church. When the scientists entered the church, it was already packed. The orchestra, a motley assortment of blond-haired youths and wizened, bald elders clutching violins, clarinets and other instruments, was seated at the front of the church. Their neighbors jammed the balconies and seats at the rear of the building.
The scientists filed down the center aisle to pews reserved for them at the front of the church. Hawking, grinning ear to ear, led the way in his motorized wheelchair. The townspeople started to clap, tentatively at first, then passionately. These religious folk seemed to be encouraging the scientists, and especially Hawking, in their quest to solve the riddle of existence.
Now, Hawking is telling us that unconfirmable M-theory plus the anthropic tautology represents the end of that quest. If we believe him, the joke’s on us.