Just left a great little workshop at the Perimeter Institute in Canada, organized by Justin Khoury. It was a focused but relaxed meeting, with plenty of opportunity for interaction; every speaker had at an hour and a half or two hours to speak, and discussion during the talks was actively encouraged. Not hard to figure out what people are interested in from looking over the talks:
- Robert Brandenberger: String Gas Cosmology. Proposed an alternative mechanism to inflation for generating cosmological perturbations.
- Me: Spontaneous Inflation and the Arrow of Time. (See a report on my talk by Yidun Wan, a graduate student who blogs at Road to Unification.) Proposed a way to make inflation respectable in the context of a multiverse, but tried not to mention the anthropic principle or the landscape.
- Rocky Kolb: Acceleration from Cosmological Perturbations. Proposed an alternative to dark energy in the form of back-reaction from cosmological perturbations. Made fun of the anthropic principle.
- Frank Wilczek: Particle Physics and Dark Matter. Used the anthropic principle (but not the string-theory landscape) to make predictions about the density of dark-matter axions.
- Burt Ovrut: The Heterotic Standard Model. Proposed a very specific compactification of string theory that gives the Minimal Supersymmetric Standard Model (and nothing else) at low energies, with stabilized moduli and a (fine-tuned) positive cosmological contant. Made fun of the landscape.
- Neil Turok: Perturbations in the Cyclic-Universe Scenario. Proposed an alternative mechanism to inflation for generating cosmological perturbations. Made fun of the landscape.
- Paul Steinhardt: Ways to Calculate the Cosmological Constant, and Ways Not To. Proposed a dynamical mechanism for obtaining a small cosmological constant. Made fun of the landscape.
The themes should be clear: cosmological perturbations, inflation and alternatives thereto, dark energy, the anthropic principle and the landscape.
It’s remarkable how polarizing the whole idea of the string-theory landscape and the anthropic principle really is. It’s not a simple split of string theorists vs. cosmologists vs. everyone else; there are string theorists who love the lanscape, as well as ones who hate it, and likewise for cosmologists or anyone else paying attention. I’ve been arguing that the landscape/multiverse might very well exist and is interesting to think about, but that it’s absolutely impossible right now (and might always be) to use it to calculate anything, or even to sensibly re-calibrate our notions of what is “natural.” I was happy to learn that Paul Steinhardt and Neil Turok are basically in agreement with this view, and are even writing a paper that attempts to make it crystal clear that the landscape does not correctly predict the cosmological constant ala Weinberg. In fact, if we’re allowed to take it seriously at all, it makes quite a strong and vividly different prediction altogether: the cosmological constant should be quite large (many times the matter density, although presumably not at the Planck scale), and we should live in a single lonely galaxy in an empty universe dominated by vacuum energy. Their paper is in preparation, and I hope to say more about it when it comes out. In the meantime, there is serious and hard work to be done to understand the generation and evolution of cosmological perturbations, so it hasn’t all devolved into a shouting match over whether talking about unobservable parts of the universe should count as science.
Peripherally related, I got a chuckle out of the cover of Lee Smolin’s forthcoming book. It’s a pair of shoes with the laces tied together.
I heard you got married!
Dear other Elliot (comment #2), can you distinguish your name with a last name or letter? Otherwise it is going to get confusing around here.
Thanks,
Sean, do you know if this talks from this conference are archived (in video)
as PI often records seminars/conference talks? If so could you provide a link?
Thanks
Shantanu
shantanu– since this meeting wasn’t announced and was by invite only, i suspect that these talks will not have been archived. at any rate, talks which double up as dicussion sessions are poorly recorded as you can only really make out what the speaker is saying while the audience members remain inaudible… but yes sean, if there is a link, let us know because there aren’t any obvious links on the p.i. website…
On the subject of the widely revered “Landscape”, I’ve just finished “Not Even Wrong”. It has a balanced analysis of the “Landscape” from chapter 13, On Beauty and Difficulty, onward. (Chapter 13 begins by quoting Leibniz’ Discourse on Metaphysics.)
Sean and Clifford are cited on the acknowledgements page, as is Lubos. The book is entirely different from both the blog and the Woit articles in arxiv and elsewhere. The first hundred pages should be put in school physics textbooks. It introduces all the experimentally validated particle physics very nicely, including a detailed history of particle accelerators. It introduces the essential mathematical parts of quantum field theory and the Standard Model in a historical context and explains the key mathematical concepts. It explains for instance how Weyl worked out the representation theory of Lie groups, spinors, etc. There are many historical and recent funny episodes quoted. Example:
“The weblog includes a comment section … One of the more excitable … superstring theorists, a Harvard faculty member, used this comment section to express the opinion that those who criticised the funding of superstring theory were terrorists who deserved to be eliminated by the United States military. I’m afraid he seemed to be serious …’ (page 227)
😉
By the way, on the problem with the cosmological constant from the string theory perspective, the N.E.W. book on page 179 calculates that supersymmetry predicts a vacuum energy density of between 10^56 and 10^113 times higher than what is believed to be true from observation, because energy density is proportional to the fourth power of the scale for spontaneous symmetry breaking.
These errors are smaller than the predicted landscape of ground states due to the Calabi-Yau manifold in string theory (which N.E.W. estimates at 10^100 to 10^1000).
However, if Phil Anderson is right and the final quantum gravity theory simply doesn’t have the universal dynamics to retard expansion, then the CC will be zero, and the error factor for string theory vacuum energy density will presumably be infinite (the fourth power of spontaneous symmetry breaking energy, divided by zero). For Anderson, see http://blogs.discovermagazine.com/cosmicvariance/2006/01/03/danger-phil-anderson/
Shantanu: The talks in this workshop were not videoly recorded.
Sean said, “…a shouting match over whether talking about unobservable parts of the universe should count as science”
Do people still have shouting matches about that? Surely not? Aren’t the shouting matches about other things?
Gosh, an unannounced invitation-only ‘workshop’.
Why the secrecy?
Will there be any public record at all of who was there and what was said?
I don’t see why anyone should feel it necessary to say something about ‘the landscape’ or as it used to be known the ‘vacuum selection problem’. It is nothing new, very similar issues surfaced as soon as the huge number of Calabi-Yau manifolds was known of. Back then people didn’t have very much useful to say about it… now has very much changed apart from a slight technical improvement in constructing models?
Four to seven different cosmological models and all agree that perturbations are important because entropy is less than it should be.
No it isn’t.
If entropy was greater, then pockets of energy would be wasted to an inert, “cold-death”, and energy is not conserved when the systems ability to do work is not maximized.
Perurbations are important, alright, but not as a backreaction, rather, as a natural stabilizing mechanism that prevents the quantum harmonic oscillator from wasting energy before work is maximized.
See: Lindblad form of the master equation.
Fine-Tuning From First Principles
Fine-Tuning From First Principles… again
Anthropic Dogma
Once Upon A Spacetime
I really don’t mean to seem rude, but on the face of it it seems that all these talks are about things that appeared on the arxiv long ago. Is that really the way of conferences and workshops — one wanders about, giving the same talk about old stuff? Is that useful? I’m honestly not being sarcastic — maybe people really get something useful out of this activity? Perhaps in the discussions at the end? For myself, and for most people I know, the submission of a paper essentially means the end of my interest in it. And I can’t really say that I have ever learned anything useful from discussions at conferences, where people’s interest in one’s talk is strictly proportional to whether you seem likely to cite them, and nobody really understands what anyone else is talking about. But perhaps other people’s mileages vary.
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More on name.
The article is good in creating more questions as it should be? 🙂
Of course it is important that the universe in expression be understood from “certain conditions?” Microstate blackholes, some how important to the larger development and incentive of the motivations behind the universe in creation?
This does not in anyway limit what had already been worked at in regards to the group rehashing things, but adds perspectve to what really began in the beginnning?
Is this not the objective, to understand how the universe came into being?
Sean ,when you say that the “multiverse/landscape” might exist, do you mean “string theory might have many solutions” or “the universe we live in might be one of several different ones”?
I’ve been going back and forth in my head about whether things that are unobservable should be considered science. When I parse this it comes down to what the definition of unobservable is. If unobservable means that there can be no quantifiable measurement whatsoever of the phenomenon directly or indirectly in principle or practice, then I think it is not science. On the other hand if the “unobservables” have explanatory power for phenomena that are quantifiable then I waver a bit. I wonder if this isn’t a deep semantic issue.
(of course the same argument could be applied to religious explanations for things as well.)
Elliot
Johan, I mean both/either. String theory may have many vacua, and there may be many “universes” (either truly disconnected, or just far away beyond our ability to see), and those things may or may not be related. We don’t know at the moment, but I’m perfectly happy to contemplate the possibilities.
Jack, the talks referred to some things that had already appeared, but were mostly about new work that extended those results. Conferences are a mixed bag; the big lecture talks are often wastes of time, but the small conversations can be immensely useful. This was a very small and focused workshop, so it was more useful than most.
Sean,
By and large, I find it more appealing to contemplate an infinite range of Cosmological Constants within a boundless array of Hubble-Bubbles within an endless landscape. In contrast, I find it less appealing to contemplate a single finite Cosmological Constant within the confines of an isolated, self-contained Hubble-Bubble devoid of an endless landscape. Unfortunately, the more appealing scenario is purely nebulous without the backbone of science.
Best regards,
Elliot,
On the Effects of External Sensory Input on Time Dilation.” A. Einstein, Institute for Advanced Study, Princeton, N.J.
I just thought it might be important for some? 🙂
In Einstein’s book on “Relativity” (1952)he writes,
May be useful, or not?
Plato,
Thanks for the reference but I am in no way speaking about the observer/observable duality here.
Dear Prof. Carroll,
Thanks a lot for linking to my blog and the report on your talk! The brief notes on Prof. Wilczek’s talk is already available too.
Best,
Yidun
Elliot,
If you could not include “dynamcial thinking” into the world around us, then what use the statement, “about what is real or not?”
Perimeter’s Institute Principal Mandate
We can’t see a lot of things, yet we know “particle creations” are really important to the way we talk about the very beginning of the universe? Some may “color” particle creations in a different way?
That’s not real?:)
OK Sean, I will take your word for it that some people get something useful out of conferences. But a lot of people sure don’t…….
So what’s new with the arrow of time? Now *there’s* something that a lot more people could be thinking about!
I wonder what Andrei Linde thinks about this? He can usually be relied upon to blow several fuses at the hint that there is something that Inflation can’t do….
Approaches to the Quantum Theory of Gravity by the PI Institute
Sometimes, this is taken to another level of actual “feuding,” yet, it is understood, that they are all working towards the same end?
Wouldn’t this be a good prerequisite of knowledge as to what makes a “good scientist?”
Or is it “a game” that fuels each other with which to encourage advancingly so “more roads and tools of math” by developing the “expert relations” on Quantum Gravity? 🙂
Thus, Lee Smolin may be a “moderate of sorts,” while being criticized? A well balanced approach?