From The Daily Show, via Why Evolution is True, here’s a hard-hitting expose on the slick con called “science” that is scamming America.
| The Daily Show With Jon Stewart | Mon – Thurs 11p / 10c | |||
| Weathering Fights – Science – What’s It Up To? | ||||
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I am generally a fan of the two-party system. Sadly, at the moment in this country, one of the parties is completely crazy.
Update: Sorry that the video isn’t available outside the U.S. Note that Lisa Randall was a guest earlier on the show.
Following the guest post from Tom Banks on challenges to eternal inflation, we’re happy to post a follow-up to this discussion by Don Page. Don was a graduate student of Stephen Hawking’s, and is now a professor at the University of Alberta. We have even collaborated in the past, but don’t hold that against him.
Don’s reply focuses less on details of eternal inflation and more on the general issue of how we should think about quantum gravity in a cosmological context, especially when it comes to counting the number of states. Don is (as he mentions below) an Evangelical Christian, but by no means a Young Earth Creationist!
Same rules apply as before: this is a technical discussion, which you are welcome to skip if it’s not your cup of tea.
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I tend to agree with Tom’s point that “it is extremely plausible, given the Bekenstein Hawking entropy formula for black holes, that the quantum theory of a space-time , which is dS in both the remote past and remote future, has a finite dimensional Hilbert space,” at least for four-dimensional spacetimes (excluding issues raised by Raphael Bousso, Oliver DeWolfe, and Robert Myers for higher dimensions in Unbounded entropy in space-times with positive cosmological constant) if the cosmological constant has a fixed finite value, or if there are a finite number of possible values that are all positive. The “conceptual error … that de Sitter (dS) space is a system with an ever increasing number of quantum degrees of freedom” seems to me to arise from considering perturbations of de Sitter when it is large (on a large compact Cauchy surface) that would evolve to a big bang or big crunch when the Cauchy surface gets small and hence would prevent the spacetime from having both a remote past and a remote future. As Tom nicely puts it, “In the remote past or future we can look at small amplitude wave packets. However, as we approach the neck of dS space, the wave packets are pushed together. If we put too much information into the space in the remote past, then the packets will collide and form a black hole whose horizon is larger than the neck. The actual solution is singular and does not resemble dS space in the future.”
So it seems to me that, for fixed positive cosmological constant, we can have an arbitrarily large number of quantum states if we allow big bangs or big crunches, but if we restrict to nonsingular spacetimes that expand forever in both the past and future, then the number of states may be limited by the value of the cosmological constant.
This reminds me of the 1995 paper by Gary Horowitz and Robert Myers, The value of singularities, which argued that the timelike naked singularity of the negative-mass Schwarzschild solution is important to be excluded in order to eliminate such states which would lead to energy unbounded below and instabilities from the presumably possible production (conserving energy) of arbitrarily many possible combinations of positive and negative energy. Perhaps in a similar way, big bang and big crunch singularities are important to be excluded, as they also would seem to allow infinitely many states with positive cosmological constant.
Now presumably we would want quantum gravity states to include the formation and evaporation of black holes (or of what phenomenologically appear similar to black holes, whether or not they actually have the causal structure of classical black holes), which in a classical approximation have singularities inside them, so presumably such `singularities’ should be allowed, even if timelike naked singularities and, I would suggest, big bang and big crunch singularities should be excluded. (more…)
Videos from our Setting Time Aright conference are gradually filtering online, courtesy of the Foundational Questions Institute. Perhaps the very first question that should be asked, of course, is whether the subject of the conference actually exists. So we recruited two well-known partisans on this issue to hash things out. Tim Maudlin is a philosopher of science who has argued forcefully that time is real — and furthermore that the arrow of time is an intrinsic part of reality, not just a byproduct of the low-entropy Big Bang. (Crazy talk.) Julian Barbour is a physicist who is well known for arguing that time doesn’t really exist, we can happily eliminate it from all of our equations of physics. (Even crazier.)
So we asked them to go at it, with a twist: here Tim defends the proposition that time doesn’t exist, while Julian argues that it is real. I was not the only one to conclude that these guys were just as good at arguing this side as the one they actually believed.
Well worth watching — both talks are quite brilliant, in very different ways.
Now that we’ve softened you up by explaining a bit about eternal inflation and its puzzles, we’re very happy to host a guest post by Tom Banks in which he really hits on some of these problems hard.
Tom is a professor at Rutgers and UC Santa Cruz, an extremely accomplished researcher in field theory and string theory, and the author of a textbook on quantum field theory. In collaboration with Fischler, Shenker, and Susskind, he proposed the (M)atrix Theory non-perturbative formulation of string theory. Most recently, he (often working with Willy Fischler) has been exploring the connections between holography and cosmology, developing a detailed model of the evolution of the universe that is compatible with the holographic principle. Here is video of a lecture Tom recently gave on holographic cosmology.
This post is at a more technical level than most of our entries here at CV, and we’re going to try to keep the discussion useful for workers in the field. Sincere questions are welcome, but we’ll be deleting any unproductive philosophical gripes or advertisements for anyone’s personal outsider theories.
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Why I Don’t Believe in Eternal Inflation
A lot of research in high energy theory has been devoted to the topic of eternal inflation. More and more, over the last few years, I’ve come to regard this as an enormous waste of intellectual resources and I’ve chosen Cosmic Variance as a very public way to make my objections to this theoretical mistake clear. The theory was developed in the 1980s, when it seemed plausible that quantum field theory in curved space-time was a good approximation to a real theory of quantum gravity whenever the energy densities and curvatures of the background geometry were small in Planck units. This idea is simply wrong. The fact that its falsification came through a back door, the rather philosophical discussion of whether black hole evaporation violates the rules of quantum mechanics, has led to a widespread but unfortunate tendency to ignore this FACT.
There are two other psychological reasons for the widespread interest in Eternal Inflation, which I will discuss below. They have led even the inventors of the resolution of the black hole information paradox through the notion of holography, to try to find a sensible holographic theory which incorporates the notion of EI. While this attempt itself is subject to a number of objections, I will not go into them here. Instead, I’ll concentrate on evidence from the seminal Coleman-De Luccia (CDL) theory of tunneling in quantum gravity, which is one of the two biggest clues to what the theory of quantum gravity really is.
There are, in my opinion, two serious conceptual errors behind the theory of EI. The first is the notion that space-time geometry is a fluctuating quantum variable. The second is that de Sitter (dS) space is a system with an ever increasing number of quantum degrees of freedom. The increase is supposed to take place as the global dS time coordinate, or the time coordinate in flat coordinates, goes to future infinity. I’ll end this post with a brief discussion of the formalism of Holographic Space Time (HST), in which both of these ideas are seen to be false, in a very explicit manner. The fact that the HST formalism is able to give an approximate description of particle physics in a curved space-time background is by itself enough to falsify any claim that the semi-classical ideas that lead to EI are inevitable consequences of ANY sensible theory of quantum gravity. For this purpose, it’s not even necessary that HST be right, only that it have a limit in which it reduces to QFT in curved space-time.
There are two flavors of EI. (more…)
My inaugural column for Discover discussed the lighting-rod topic of the inflationary multiverse. But there’s only so much you can cover in 1500 words, and there are a number of foundational issues regarding inflation that are keeping cosmologists up at night these days. We have a guest post or two coming up that will highlight some of these issues, so I thought it would be useful to lay a little groundwork. (Post title paraphrased from Andrei Linde.)
This summer I helped organize a conference at the Perimeter Institute on Challenges for Early Universe Cosmology. The talks are online here — have a look, there are a number of really good ones, by the established giants of the field as well as by hungry young up-and-comers. There was also one by me, which starts out okay but got a little rushed at the end.
What kinds of challenges for early universe cosmology are we talking about? Paul Steinhardt pointed out an interesting sociological fact: twenty years ago, you had a coterie of theoretical early-universe cosmologists who had come from a particle/field-theory background, almost all of whom thought that the inflationary universe scenario was the right answer to our problems. (For an intro to inflation, see this paper by Alan Guth, or lecture 5 here.) Meanwhile, you had a bunch of working observational astrophysicists, who didn’t see any evidence for a flat universe (as inflation predicts) and weren’t sure there were any other observational predictions, and were consequently extremely skeptical. Nowadays, on the other hand, cosmologists who work closely with data (collecting it or analyzing it) tend to take for granted that inflation is right, and talk about constraining its parameters to ever-higher precision. Among the more abstract theorists, however, doubt has begun to creep in. Inflation, for all its virtues, has some skeletons in the closet. Either we have to exterminate the skeletons, or get a new closet.
Many of you may know that Discover is not only a web site that hosts a diverse collection of entertaining blogs, but also publishes a monthly “magazine” printed on paper. Wild, right? Just ask this baby, who can tell you that a magazine is kind of broken when compared to an iPad.
Nevertheless, people read these things like crazy. I have recently started contributing an occasional column to the print magazine, known as “Out There.” (Our blog neighbor Carl Zimmer has been columnizing about the brain for a while now.) My first column appeared in the October issue (which comes out in September), and is now online — check it out.
The issue I’m tackling, under the draconian word count limit of an actual print magazine, is whether it’s scientific to talk about the multiverse. (Spoiler: it is!) Let me know what you think.
Here’s a blast from the somewhat-recent past: a set of five lectures I gave at CERN in 2005. It looks like the quality of the recording is pretty good. The first lecture was an overview at a colloquium level; i.e. meant for physicists, but not necessarily with any knowledge of cosmology. The next four are blackboard talks with a greater focus; they try to bring people up to speed on the basic tools you need to think about modern early-universe cosmology.
Obviously I’m not going to watch all five hours of these, so I’ll just have to hope that I’m relatively coherent throughout. (I do remember being a bit jet-lagged.) But I do notice that, while it was only a few years ago, I do appear relatively young and enthusiastic. Ah, the ravages of Time…
Lecture One: Introduction to Cosmology
Technology Review has temporarily made their archives openly available, and one of their recent features is this fascinating plot of the number of space launches over time. (Via FlowingData.) This is a cropped and shrunk version; see the original article for the full glory.
The authors offer an explanation for why the Soviet Union had so many more military launches in the 70’s and 80’s than the US did: their satellites tended not to last as long. I didn’t find a reason for the uptick and subsequent downturn in US commercial launches in the late 90’s.
There’s no danger that we’re going to stop going into space altogether, but we don’t go as often as we once did. We’ll probably need a phase transition of some sort to change that situation dramatically. That could be sparked by private companies, or if China lands someone on the Moon. (Not equally good reasons to re-commit to space, but reasons nonetheless.)
I have my answer (“yes, but not by finding meaning `out there’ in the world”), which I hope to write about more soon. In the meantime, listen to a great conversation between philosophers Owen Flanagan and Alex Rosenberg from Philosophy TV. “What there is, and all there is, are bosons and fermions.”
Both discussants have written really good books. Rosenberg recently came out with The Atheist’s Guide to Reality: Enjoying Life Without Illusions, while I very much enjoyed Flanagan’s earlier book The Really Hard Problem: Meaning in a Natural World.
Empirically, of course, naturalists often lead very enjoying and fulfilled lives. Here’s a great profile of newly minted Laureate Brian Schmidt, in his capacity as a cook and winemaker as well as an astronomer. And here’s Bob Kirshner, writing to the NYT from Friendship, Maine, about the meaning of dark energy.
To celebrate my birthday today, I’m heading back into Second Life to do a chat with Alan Boyle of MSNBC.com fame. Alan has previewed some of the topics we’ll be discussing in a post at Cosmic Log. It’s possible the Nobel Prize will be mentioned. (The physics one. Don’t expect any insight from me on quasicrystals, except that they’re awesome.)
We’ll be chatting at 9pm Eastern/6pm Pacific, at the Stella Nova Theater. If you’re not already on Second Life, it’s super easy (and free) to join. (Here’s some very useful information for beginners.) And you get to design an avatar that looks like you would want to look, rather than your inevitably-disappointing real self.
The chat is part of the Virtually Speaking series hosted by FireDogLake, in this case co-produced with the Meta Institute for Computational Astrophysics. Alan does a regular series of interviews on science, so you may get hooked. Our chat will be a multi-media extravaganza, so you can choose to listen in various ways:
Yes I know, very complicated. If simplicity is more your bag, here’s a guest video on dark energy that I did for the wonderful Minute Physics series.
