When I was reading Susskind’s book The Cosmic Landscape, I was paying close attention to the main problem with the whole multiverse/anthropic string landscape idea: is there any sort of experimental prediction that emerges from this that would justify calling it science? One thing that kind of mystified me was Susskind’s claim, in the Introduction and Chapter 12, that the “cosmic horizon” beyond which other parts of the multiverse live is like a black hole horizon and in principle information about what is beyond the horizon is accessible in the analog of Hawking radiation. This seemed to be a rather vague idea, which Susskind goes on to drop, never mentioning it in the chapter he devoted to possible experimental tests of the landscape. Since I’d never heard of anyone claiming this anywhere else, and Susskind didn’t seem himself to take it very seriously, I just ignored it.
Cosmologist G. F. R. Ellis, in a new preprint entitled On horizons and the cosmic landscape has decided to take it seriously, and show that it is wrong. Ellis’s paper is rather peculiar; I’ve never before seen an arXiv paper that argues against not another scientific paper, but some vague statements in a popular book. I haven’t tried to follow Ellis’s argument, partly because it seems rather vague itself, with not a single equation in it. Perhaps this is unavoidable, given the vagueness of Susskind’s argument that he is challenging. Anyway, at the present time, the situation seems to be that neither Susskind nor anyone else has come up with a calculation that would show how to detect information about other parts of the multiverse hidden in some sort of Hawking radiation from a cosmic horizon, and now we have an argument from Ellis that this is in principle impossible.
Some people have been giving me grief about writing blog entries with no equations, but here no one seems to have any.
If you want to hear more from Susskind about the multiverse, he’s giving the colloquium next week at MIT with title The Landscape and the Megaverse, and the abstract of this talk is:
A new paradigm for the origin of the laws of physics may (or may not) be emerging out of observational cosmology and theorists efforts to understand string theory. The ordinary 15 billion light-year universe is being replaced by a vastly bigger “megaverse” consisting of a huge number of what Guth calls “pocket universes.” If this is true then many of the Laws of Physics that we normally think of as “written in stone” will be local environmenal facts. I will explain the evidence for this controversial view, its implications, and the various views of leading physicists and cosmologists.
Susskind is also giving a talk here in New York on April 10 at the New York Academy of Sciences. The description of the talk tells us that
Several decades ago, Susskind introduced the revolutionary concept of string theory to the world of physical science. In doing so, he inspired a generation of physicists who believed that the theory would uniquely predict the properties of our universe. Now Susskind argues that the very idea of such an “elegant theory” no longer suits our understanding of the universe….
… Susskind believes that string theory, rather than reaching a dead end, has led to a vastly expanded concept of the universe, which he calls “the lanscape,” where the anthropic principle makes perfect sense.
Attending the talk would cost $20, so I think I’ll skip this one.
The last issue of the NYAS publication Update Magazine has an article by Lee Smolin on all of this entitled A Crisis in Fundamental Physics. Later this year Smolin will have a new book out, entitled “The Trouble With Physics”.
There is something I would very much like to attend, but will be out of town so will have to miss. The American Museum of Natural History each year organizes a debate in honor of Isaac Asimov. This year the topic will be Universe: One or Many?, and the blurb goes:
Join a panel of cosmologists to argue and debate the possibility that our Universe is just one of many universes that comprise the “multiverse.” This notion invokes dimensions beyond our everyday experience and draws from the leading edge of our conception of the cosmos. The presence or absence of data in support of these ideas forms a central theme for the evening.
I’m not sure who is going to argue for the presence of data in support of these ideas since I’ve never heard of any. The panelists are Michio Kaku and Andrei Linde, presumably pro-megaverse, Lawrence Krauss, who I’m guessing is on the anti-side, and Lisa Randall and Virginia Trimble, about whose views on the subject I know nothing.