It’s been a mixed bag so far; while I’ve had great fun interacting with people here in Australia, I’ve also been struggling with a nasty cold I picked up on the flight over. Spent yesterday mostly in bed, too fogged up to even work on my talk for Friday. But when I’ve had the strength to be up and about, it’s been a treat. Here’s an iPhone snap of the University of Sydney; that clocktower in the middle houses, appropriately enough, the Centre for Time.

One of the perks of civilization that hasn’t quite caught on in these parts is affordable internet access in hotel rooms, so don’t expect a lot of blogging over the next week or two. Instead, I can point you to a couple of recent videos. One is an extended interview for Edge, entitled Why Does the Universe Look the Way it Does? It is an interview (presented in text and video), not a carefully pre-planned document, so not all thoughts are arranged as elegantly as one might like. Here is some of the flavor:

We are in a very unusual situation in the history of science where physics has become slightly a victim of its own success. We have theories that fit the data, which is a terrible thing to have when you are a theoretical physicist. You want to be the one who invents those theories, but you don’t want to live in a world where those theories have already been invented because then it becomes harder to improve upon them when they just fit the data. What you want are anomalies given to us by the data that we don’t know how to explain.

The other one is a panel discussion on Time Since Einstein, from the World Science Festival. As the description there says, it features Roger Penrose, David Albert, and some other people it would be too exhausting to list individually. Here’s part 1 of 5:

World Science Festival 2009: Time Since Einstein, Part 1 of 5 from World Science Festival on Vimeo.

Now if only my immune system would finish off the little viral buggers inside me, I could get out and see a bit of this interesting country.

So we rearranged our schedules, met yesterday in Denver, woke up at 6 am this morning, and are now at Kennedy Space Center with 100 space twitterers. They’ve got a full program here with astronauts and a tour today, and the launch of mission STS-129 to the space station at 2:29 pm tomorrow. The event just started… So stay tuned, we’ll keep you posted. We will be blogging as well as loosing our tweeting virginity @cosmicvariance. You can follow the rest of the gang by looking for #nasatweetup.

But the reason I’m blogging about it is because I’ll be giving some public talks, and it would be great if any local CV readers dropped by to say hi. I’ll be hitting three different cities:

• Monday 16 November: Sydney
• Friday 20 November: Melbourne
• Monday 23 November: Adelaide

With all these public talks in a row, you would almost think I’m touring in support of some sort of book. That was part of the original idea, but now the book won’t be officially released until January 7. So instead I’ll just be talking in support of … Science! And trying to stay clear of dangerous creatures.

p.s. Wow, I almost did an incredibly boneheaded thing by showing up at the airport without a visa. Why in the world do you need a visa to go from the USA to Australia? I thought it was like a southern version of Canada. Fortunately, when you check in online you get “reminded” that a visa is required; even more fortunately, there is an online instant-visa service that seems to work. This is why I’m a theoretical physicist and not put in charge of anything important.

Now that I’m basically settled at Penn, I’ve been focused primarily on working on some exciting new projects, while also trying to bring to completion a lot of different research projects that have been languishing somewhat as I got myself settled. I think most of these are back on track now (although some of my collaborators, whose Skype calls I’ve moved several times, may have a different opinion), which is a nice feeling to have after a few months of concerted effort. I even managed to get a conference proceedings finished. I’ll probably post about some of these projects when they’re done.

But over the last few weeks, I’ve also been traveling a little, starting with a colloquium at the University of Wisconsin, Milwaukee, where I talked about modifying gravity to a very knowledgeable audience, and where I was treated to a wonderful (and very late) Friday night out, courtesy of Luis Anchordoqui and Patrick Brady, to whom I owe many thanks. That trip was followed by a colloquium at NASA Goddard Space Flight Center, which seems to employ an inordinate number of people I went to graduate school with. I certainly enjoyed the talk, but particularly enjoyed the meetings they had set up for me during the day. I learned about the long-term possibility of using observations of gravitational wave sources by the LISA experiment, accompanied by optical follow-ups, as a new way to construct a Hubble diagram to trace the cosmic expansion history. While not feasible right now, I found this a fascinating possibility for the future, and I’m hoping that our resident expert may tell us more about it some time.

My final two trips of the recent period were both to New York, and both to NYU. The first was to deliver a seminar at the Center for Particle Physics and Cosmology. The second was for the first of a set of one day meetings that the Center for Particle Cosmology has begun with the NYU Center. That took place a week ago, and featured talks by my colleagues Justin Khoury and Daniel Wesley, and NYU speakers Neal Weiner and Roman Scoccimarro. This was a very fun intellectual exchange, with talks on modified gravity, cyclic cosmologies, and interacting dark matter. Certainly the NYU people set the hospitality bar pretty high for us for when they visit us at Penn next semester.

However, perhaps the most time consuming activity of the last few weeks, in comparison with the rest of the year, has been writing and editing letters of recommendation. This is something I think everyone realizes professors do, but usually doesn’t realize the amount of time it takes.

I don’t know what it is like for everyone, but the first time I was asked to write a serious letter of recommendation was when I was a postdoc, and one of the graduate students I’d been working with asked me if I’d be one of his letter writers as he applied for his first postdoc. This first letter keeps you up at night. One wants to be enthusiastic about the candidate, while realizing that your letter is supposed to provide a service for your colleagues who will evaluate the application, as well as for the candidate. Thus one gets excessively stressed about painting a balanced picture of the candidate’s strengths and weaknesses, while competing with some of the glowing letters that one knows other people will write for their candidates. Nevertheless, you get over it, and you write the best letter you can and hope that it is helpful.

As a faculty member, one rather rapidly comes to realize that writing letters of recommendation is a crucial and time-consuming part of one’s job. So how does one go about it? Well, suppose that someone has asked you for a letter. They might be an undergraduate, a graduate student or a postdoc, asking for a letter for positions ranging from an REU position to a faculty job. The first thing to decide is whether you are prepared to write for them. For me, I tell a person I will write if I think my letter will leave a better impression than receiving no letter at all. If not, then I turn them down and tell them they would do better asking someone else. I also like to tell people roughly the type of letter they can expect. Obviously I don’t give details, but I don’t want there to be any confusion. They might decide they can get a better letter from someone else, or that they just don’t want me to write, and I like them to have enough information to make that decision.

But assuming you’ve made the decision to write for someone, and that they still want you to write, then you have a lot of work ahead of you. There’s some basic stuff to get out of the way up front – how long have you known the person and in what capacity? This is where you lay out why you have sufficient experience with them to be able to provide a complete and authoritative account of their skills, track record and potential. When one is rather junior and writing, this part is important to demonstrate your qualifications before you discuss the applicant’s. As a physicist becomes more senior and well-known, this part of the letter remains just as important, although now it is more because it reassures the reader that the writer actually does know this person well, as opposed to them just being another of the presumably huge number of people clamoring for letters.

Now one moves on to the meat of the matter – evaluating the technical talents of the applicant. Are they deep, broad, sophisticated, creative, and calculationally skilled? There are many nuances involved in this part. Obviously, one wants to be accurate, while highlighting the skills that have impressed you most about the person. If you have written papers with the candidate, then this is the place you’ll write about some of the details and what the candidate brought to the project. If there are relevant weaknesses, you may want to point them out; but in my case, if I’ve decided to write, then I will typically think that these are outweighed by strengths, and you want to make that clear. Perhaps the most important thing to bear in mind here is that these are just your opinions. Yes, they are informed opinions; and yes, they have been solicited by both the candidate and/or the hiring institution because they feel you are qualified to give them. Nevertheless, there is no way around the fact that there is a significant subjective component to a recommendation letter, and it is important to make sure that you recognize this and consider it carefully before making any strong statements.

This, of course, makes letter writing somewhat terrifying (naturally, having to ask for them is also scary). Of course, one doesn’t resent students, postdocs and colleagues for asking for letters (not least because we have all relied on others to do this for us many times), and you want to see your talented colleagues succeed. It’s just that because of this you owe it to everyone involved to do a good job, and this is what makes for the required time commitment. October and November are the time when most letters are requested, and so if you find yourself writing for many people (ten or more people sometimes, at various levels), then it comprises a significant portion of your work over those weeks. It’s a not-often-mentioned, but important part of an academic’s job.

Yes, that’s a pretty suave picture of me on the image capture. What can I say? I’m just one of those lucky folks with an effortless magic in front of the camera.

If you prefer to get your talks about entropy unadulterated by voice and motion, and don’t mind a more technical presentation, I’ve put the slides from my recent Caltech colloquium online. These are aimed basically at grad students in physics, so there is an equation or two, and the caveats are spelled out more clearly. But the punchline is the same.

Then it’s off to the Francophone sector with me, where I’ll be visiting McGill University in Montreal to give another public talk on Monday night. I don’t know of any recordings there, but the talk won’t be that different from Saturday’s. But if there are any CV readers in Montreal, be sure to say hi!

It’s become clear along the way that I am not as accurate when I’m trying to represent philosophers as opposed to physicists; the vocabularies and concerns are just slightly different and less familiar to me. So take things with an appropriate grain of salt.

Tuesday morning: The Case for Multiverses

9:00: Bernard Carr, one of the original champions of the anthropic principle, has been instructed to talk on “How we know multiverses exist.” Not necessarily the title he would have chosen. Of course we don’t observe a multiverse directly; but we might observe it indirectly, or infer it theoretically. We should be careful to define “multiverse,” not to mention “exist.”

There certainly has been a change, even just since 2001, in the attitude of the community toward the multiverse. Quotes Frank Wilczek, who tells a parable about how multiverse advocates have gone from voices in the wilderness to prophets. That doesn’t mean the idea is right, of course.

Carr is less interested in insisting that the multiverse does exist, and more interested in defending the proposition that it might exist, and that taking it seriously is perfectly respectable science. Remember history: August Comte in 1859 scoffed at the idea we would ever know what stars were made of. Observational breakthroughs can be hard to predict. Rutherford: “Don’t let me hear anyone use the word `Universe’ in my department!” Cosmology wasn’t respectable. For what it’s worth, the idea that what we currently see is the whole universe has repeatedly been wrong.

So how do we know a multiverse exists? Maybe we could hop in a wormhole or something, but let’s not be so optimistic. There are reasons to think that multiverses exist: for example, if we find ourselves near some anthropic cutoff for certain parameters. More interesting, there could be semi-direct observational evidence — bubble collisions, or perhaps giant voids. Discovering extra dimensions would be good evidence for the theories on which the multiverse is often based.

The only direct observations that currently exists that might bear directly on multiverses is the prediction of giant voids and dark flows by Laura Mersini-Houghton and collaborators.

Carr believes that the indirect evidence from finely-tuned coupling constants is actually stronger. Existence of planets requires a very specific relationship between strength of gravity and electromagnetism, which happens to exist in the real world. There is a similar gravity/weak tuning needed to make supernovae and heavy elements. Admittedly, many physicists dislike the multiverse and find it just as unpalatable as God. But ultimately, multiverse ideas will become normal science by linking up with observations; we just don’t know how long it will take.

9:45: George Ellis follows Carr’s talk with what we’ve been waiting for a while — a strong skeptical take on the multiverse idea.

There are lots of types of multiverses: many-worlds, separated by space or time, or completely disjoint. Anthropic arguments are what make the idea go. The project is to make the apparently improbable become probable.

The very nature of the scientific enterprise is at stake: multiverse proponents are proposing that we weaken the idea of scientific proof. Science is about two things: testability and explanatory power. Is it worth giving up the former to achieve the latter?

The abstract notion of a multiverse doesn’t get you anything; you need a specific model, with a distribution of probabilities. (Does Harry Potter exist somewhere in your multiverse?) But if there is some process that generates universes, how do you test that process? Domains beyond our particle horizon are unobservable. How far should we expect to be able to extrapolate? Into a region which, in principle, we will never be able to observe.

In the good old days we accepted the Cosmological Principle, and assumed things continued uniformly forever beyond our observable horizon. Completely untestable, of course. If all the steps in the extrapolation are perfectly tenable, extrapolations are fine — but that’s not the case here. In particular, the physics of eternal inflation (gravity plus quantum field theory, Coleman-de Luccia tunneling) has never been tested. It’s unknown physics used to infer an unobservable realm. Inflation itself is not yet a well-defined theory, and not all versions of inflation are eternal. We haven’t even found a scalar field!

There is a claim that a multiverse is implied by the fine-tuning of the universe to allow life. At best a weak consistency test. Can never actually do statistical tests on the purported ensemble. Another claim is that the local universe, if it’s inside a bubble, should have a slight negative curvature — but that’s easily avoided by super-Hubble perturbations, so it’s not a strong prediction. We could, however, falsify eternal inflation by observing that we live in a “small” (topologically compact) universe. But if we don’t, it certainly doesn’t prove that eternal inflation is right. Finally, it’s true that we might someday see signatures of bubble collisions in the microwave background. But if we don’t, then what? Again, not a firm prediction.

Ultimately: explanation and testability are both important, but one shouldn’t overwhelm the other. “The multiverse theory can’t make any prediction because it can explain anything at all.” Beware! If we redefine science to accommodate the multiverse, all sorts of pseudo-science might sneak inside the tent.

There are also political/sociological issues. Orthodoxy is based on the beliefs held by elites. Consider the story of Peter Coles, who tried to claim back in the 1990’s that the matter density was only 30% of the critical density. He was threatened by a cosmological bigwig, who told him he’d be regarded as a crank if he kept it up. On a related note, we have to admit that even scientists base beliefs on philosophical agendas and rationalize after the fact. That’s often what’s going on when scientists invoke “beauty” as a criterion.

Multiverse theories invoke “a profligate excess of existential multiplicity” in order to explain a small number of features of the universe we actually see. It’s a possible explanation of fine tuning, but is not uniquely defined, is not scientifically testable, and in the end “simply postpones the ultimate metaphysical question.” Nevertheless — if we accumulated enough consistency tests, he’d be happy to eventually become convinced.

11:00: After coffee, we reconvene for a panel discussion on “the views of physicists,” featuring Pedro Ferreira, George Efstathiou, and Sean Carroll.

Ferreira talks about the paradigm shift we’ve seen over the last decade. Driven by three factors: inflation, the accelerating universe, and the string landscape. What are the alternatives? Inflation has almost no robust alternatives, unlike twenty years ago. Still not very precisely predictive, too many models. The cosmological constant is a good explanation of the accelerating universe. There are viable alternatives, but they all require severe fine tuning; the story isn’t yet finished. The landscape has been around since the 80’s, but didn’t take off until the vacuum energy became a pressing issue. It might be good if more people were digging into properties of specific compactification schemes. Is it premature to worry about the multiverse when we understand so few compactifications?

Efstathiou pulls out a white board and starts writing equations! Which I will not reproduce here (it’s basic Bayesian probability). The point is that we can only test models against other models, not in some abstract theoretical vacuum. When you don’t have well-defined alternatives, you must take what you can get. He then tells a parable about the promiscuous astronomer, which I also won’t reproduce here. (A close relative of the Sleeping Beauty puzzle well-known to philosophers.)

Carroll explains that it’s difficult to explain the low entropy of our early universe if we stick to unitary autonomous evolution of a comoving patch of space; if we don’t want to give up on conventional quantum mechanics and we don’t want to invoke ad hoc boundary conditions, we’re led directly to a multiverse. He is interrupted frequently by spontaneous applause and finishes to a standing ovation, several audience members smacking their palms to their foreheads and crying “Brilliant! Why didn’t I think of that?”

During the question period, Max Tegmark puts even money on the proposition that the Planck satellite will find evidence for an inflationary gravitational-wave background from B-mode polarization of the cosmic microwave background. Carroll quickly turns it into a formal bet, and the stakes are set at $100. Max will be paying up three or four years from now.

Tuesday afternoon: Philosophical Assessment of the Scientific Case

1:45: The afternoon session is given over to the philosophers. We begin with a panel discussion featuring John Norton, David Wallace, Wayne Myrvold, and Henrik Zinkernagel.

Norton points out that we’re all looking for ultimate explanations of everything — looking down on the idea of brute inexplicable facts. If you go down that road, you run the danger of accepting more metaphysics that you were originally planning to. Don’t get too wedded to particular criteria for distinguishing science from non-science; it leads to later regrets when you want to do something perfectly scientific that doesn’t quite fit your criterion. The problem with pseudosciences is not that they don’t make predictions; it’s that they always change to accommodate new information. “Falsifiability” is a great slogan and an irresistible sound bite, but not a reliable rule to separate science from non-science.

Wallace talks about observable vs. unobservable things. We can’t observe electrons, dinosaurs, or the interior of the Sun. We nevertheless accept them because they are non-optional parts of theories that are very tightly coupled to data. You can’t have a theory that explains dinosaur fossils without believing in dinosaurs. Multiverses come in a variety of forms — from practically useless to quite specifically useful. Not all created equal, and we need to be a bit careful.

Myrvold dislikes the very idea of a “philosophical assessment” of scientific cases; that’s a job for the people who are deeply involved with the theories and the data. Nevertheless (unsurprisingly) there is something to say. Trying to explain things at the edge of knowledge is part of the practice of science, but there is certainly some inductive risk. Hypothetico-deductive method: deduce consequences of an hypothesis and some auxiliary assumptions, go out and test these consequences, reject hypothesis if consequence is falsified. That can’t possibly be the whole story. Do we reject hypothesis or auxiliary assumptions? Quine: maybe we were just hallucinating. Process is often underdetermined.

Zinkernagel talks about the role of time in the multiverse. Could our universe be just a patch in a much older and larger structure? Depends on what you mean by “time.” We could define “supercosmic time” that orders different patches, or we could simply extrapolate from within our observable patch. General relativity allows for all sorts of time coordinates, but under special circumstances we can define a unique notion of time. To do this in the real world, you need a physical clock, and something to set the scale.

The discussion session gets into the question of policing the boundaries of respectable science, and whether the truth will eventually win out regardless of how well we do the policing. Brian Greene takes a poll: do people think that 200 years from now the truth or falsity of the multiverse (or whatever) will basically shake itself out regardless of our current investigation of what does or does not count as science? Almost everyone agrees that it will except for Julian Barbour, who doesn’t believe in time anyway (Brian’s joke).

4:00: We go right into another panel discussion, this time about “Cosmology as a Science,” featuring William Stoeger, Jean-Philippe Uzan, Jeremy Butterfield, and Huw Price.

Stoeger dives into the thicket of the demarcation problem: what is science, and what is not? It wasn’t all that long ago that cosmology itself had a doubtful status as science. There’s only one observable universe; can’t do repeatable experiments. But cosmology is not only a science, but has extended beyond the observable part of the universe. Ernan McMullin: induction moves backwards from observed effects to inferred causes. Continued success of an hypothesis leads us to conclude that “something very much like the content of the hypothesis exists in reality.” Always trying to fit our hypotheses into larger explanatory systems. A bit more optimistic than Ellis about bringing multiverses into cosmology as long as they continue to provide fruitful hypotheses.

Price has three comments for us. First, why are we asking “Is the multiverse science?” rather than simply “Is the multiverse true?”, or at least “Is it a reasonable hypothesis?” Second, there is a close analogy between the current multiverse ideas and the Steady State cosmology (details for the reader to work out). Third, think about the notion of “explanatory relief.” The inflationary multiverse provides relief for the puzzle of why the universe allows life; but we don’t think that the Everett multiverse provides relief for the puzzle of why some particular person exists. The Lewisean multiverse (all logically possible worlds exist) provides relief for all sorts of questions — but what good is that? There’s a slippery slope here, trading off explanatory power for triviality. TIme for a fourth comment: In everyday life, we explain the future in terms of the past (asymmetric in time). But what is the justification for that in the context of cosmology?

Uzan wants to talk about cosmology with a lower-case “c,” what we call “physical cosmology.” Standard cosmological model relies on assumptions about gravity, matter, symmetry, and global structure of the universe. All should be subjected to empirical tests. For general relativity, it would be nice to have more tests on cosmological scales (low acceleration, low curvature). For example, using various forms of large-scale structure data — weak lensing, galaxy maps, velocities, integrated Sachs-Wolfe effect. We can also imagine testing the assumed symmetries of space, as embodied in the Copernican principle. With precise spectra, we could measure the change in the redshift of an object over time. And of course, we can look for a compact topology to the universe.

Butterfield wants to keep his remarks short so that he doesn’t say anything incriminating that ends up on this blog. [Ed. note: everyone knows about the live-blogging and there is a slight undercurrent of distrust, although Jeremy was just joking. I think.] He congratulates the cosmology community in general, and George Ellis in particular, on their endogenous amphetamines. Wants to encourage plucky theories being studied by small groups of researchers (”weeds in the garden,” in a nomenclature from a previous session). How much do/should controversies in the foundations of statistics interact with debates in fundamental cosmology? In particular, how do they impact the measure problem?

In discussion, George Ellis quotes G.K. Chesterton: “the only people who have an explanation for everything are madmen.”

Tuesday evening: Why is there Something Rather than Nothing?

9:30: The conference closes with a posh dinner at Balliol College, featuring a talk by John Hawthorne on the primordial existential question. Then we have a response by Max Tegmark. Apparently my principled refusal to go to talks after 9:00 p.m. is no more reliable than my refusal to attend meetings that receive funding from the Templeton Foundation.

But I didn’t actually bring my laptop to the talks, so the summaries will be short and sweet. Hawthorne didn’t offer an answer to the question, but tried to provide a roadmap to possible answers. He distinguished between different notions of “nothing,” from true non-existence to an empty and involving universe. Then he distinguished between explanations from law — something exists because there is a deep principle of nature which, perhaps among other things, requires something to exist — and explanations from probability — there is a measure on the space of things that might possibly exist, and the measure assigned to the empty set is zero or at any rate small. Long story short, metaphysicians have not reached a consensus on this question.

Tegmark decided to tackle the question of what kinds of things there could be, rather than why at least one of them was real. He has a classification of multiverses: Type I is just a really big space that is pretty similar throughout, Type II is an inflationary kind of multiverse with distinct (although perhaps connected) bubbles, Type III is different branches of the wave function. His favorite option is the Type IV, in which all possible mathematical structures exist; that’s closely related to David Lewis’s ideas about modal realism.

I had a question I wanted to ask, as follows. Imagine that we agreed that any universe could be described by some sort of mathematical structure; perhaps a wave function evolving in Hilbert space, or a discrete cellular automaton, or a single point, or even the empty set (”nothing”). The question is, what kind of possible answer to the question “Why is the actual universe this structure rather than that structure?” could one imagine providing that would be more fruitful, give us more information, than a simple statement of the brute fact of which structure it was? Isn’t it necessarily like trying to discern a pattern from a single event?

But I was sensible enough to recognize that going to sleep was a higher priority than figuring out the meaning of existence. Maybe some other time.

Monday morning: The Case for Multiverses

9:00: We start today as we ended yesterday: with a talk by Martin Rees, who has done quite a bit to popularize the idea of a multiverse. He wants to argue that thinking about the multiverse doesn’t represent any sort of departure from the usual way we do science.

The Big Bang model, from 1 second to today, is as uncontroversial as anything a geologist does. Easily falsifiable, but it passes all tests. How far does the domain of physical cosmology extend? We only see the universe out to the microwave background, but nothing happens out there — it seems pretty uniform, suggesting that conditions inside extend pretty far outside. Could be very far, but hard to say for sure.

Some people want to talk only about the observable universe. Those folks need aversion therapy. After all, whether a particular distant galaxy eventually becomes observable depends on details of cosmic history. There’s no sharp epistemological distinction between the observable and unobservable parts of the universe. We need to ask whether quantities characterizing our observable part of the universe are truly universal, or merely local.

So: what values of these parameters are consistent with some kind of complexity? (No need to explicitly invoke the “A-word.”) Need gravity, and the weaker the better. Need at least one very large number; in our universe it’s the ratio of gravity to electromagnetic forces between elementary particles. Also need departure from thermodynamic equilibrium. Also: matter/antimatter symmetry, and some kind of non-trivial chemistry. (Tuning between electromagnetic and nuclear forces?) At least one star, arguably a second-generation star so that we have heavy elements. We also need a tuned cosmic expansion rate, to let the universe last long enough without being completely emptied out, and some non-zero fluctuations in density from place to place.

If the amplitude of density perturbations were much smaller, the universe would be anemic: you would have fewer first-generation stars, and perhaps no second-generation stars. If the amplitude were much larger, we would form huge black holes very early, and again we might not get stars. But ten times the observed amplitude would actually be kind of interesting. Given an amplitude of density perturbations, there’s an upper limit on the cosmological constant, so that structure can form. Again, larger perturbations would allow for a significantly larger cosmological constant — why don’t we live in such a universe? Similar arguments can be made about the ratio of dark matter to ordinary matter.

Having said all that, we need a fundamental theory to get anywhere. It should either determine all constants of nature uniquely, in which case anthropic reasoning has no role, or it allows ranges of parameters within the physical universe, in which case anthropics are unavoidable.

10:00: Next up, Philip Candelas to talk about probabilities in the landscape. The title he actually puts on the screen is: “Calabi-Yau Manifolds with Small Hodge Numbers, or A Des Res in the Landscape.”

A Calabi-Yau is the kind of manifold you need in string theory to compactly ten dimensions down to four, picked out among all possible manifolds by the requirement that we preserve supersymmetry. There are many examples, and you can characterize them by topological invariants as well as by continuous parameters. But there is a special corner in the space of Calabi-Yau’s where certain topological invariants (Hodge numbers) are relatively small; these seem like promising places to think about phenomenology — e.g. there are three generations of elementary particles.

Different embeddings lead to different gauge groups in four dimensions: E₆, SO(10), or SU(5). Various models with three generations can be found. Putting flux on the Calabi-Yau can break the gauge group down to the Standard Model, sometimes with additional U(1)’s.

11:15: Robert Brandenberger steps up to talk about probability measures and initial data for inflation. The title was assigned by the organizers, and he claims that he got scared by it and started having sleepless nights, so he changed it: “Initial Conditions for Early Universe Scenarios.” He wants to consider alternatives to inflation.

Inflation is great; solves lots of problems, and provides a mechanism for density perturbations. But it’s not the only way to produce primordial perturbations, and there are problems, such as the need to consider modes with wavelengths shorter than the Planck length.

One alternative is string gas cosmology. Predicts a slight red tilt for density perturbations, but a slight blue tilt for gravitational waves. String theory has a maximum temperature (the Hagedorn temperature); when you squeeze strings to sufficiently high density you enter a dual phase where the temperature goes down. We could loiter in a metastable phase at constant temperature before the universe began expanding. Might explain why only three dimensions become large.

Another alternative is a matter bounce, in which the universe first contracts and then bounces back to expansion. Predicts scale-free perturbations for both density and gravitational waves, but the bispectrum can be large.

The final idea is the ekpyrotic/cyclic scenario. Three large dimensions of space appear to bounce, while branes are crashing together in extra dimensions. Predictions are hard to make because we’re not really sure how to resolve the singularity — but a scale-invariant spectrum is conceivable.

Now about initial conditions. It can be hard to get inflation to start, but it becomes easier if we start in a false vacuum and then tunnel to inflation. For the string gas, thermal equilibrium looks like a local attractor, so that’s also okay. For the matter bounce, on the other hand, the assumed background is unstable — so that’s a problem. Maybe you can do it if the bounce is generated by gravity rather than by matter. Likewise for the ekpyrotic universe. Cyclic universe is a bit better; essentially we are currently going through “inflation” at a very low scale.

12:00: Now we have a panel of “critical commentaries,” featuring Brian Greene, Jean-Philippe Uzan, and Andrei Linde.

Brian Greene begins by breaking the overhead projector, so he has to speak without slides. “Can the multiverse” be tested is an unanswerable question, because it depends on what kind of multiverse theory you actually have. E.g. if we live in some specific part of the string landscape, we could in principle probe details of the compactification manifold, to figure out which one it is. If there are bubble universes, we might observe collisions between bubbles. The landscape might predict relationships between observable quantities. Or, if you had a microphysical theory that you had tested well enough to accept it, and it predicted a multiverse, that would be a sensible conclusion to accept. On the other hand: eternal inflation undermines many of the successes of inflation, because it removes the possibility of unique predictions. Need to have a measure. In quantum mechanics, a measure can emerge directly from a theory; maybe inflation will eventually get to that point.

Jean-Philippe Uzan brings up the example of general relativity — why do we pick the Einstein-Hilbert action over any others? We take it as a simple choice, but we can also look for deviations, and constrain them experimentally. When do we simply accept a theory, vs. putting great effort into looking for modifications of it?

Andrei Linde laments that he is playing the role of Big Brother — watching you in case you claim to have a better theory than inflation. He studied string gas cosmology some time ago, but found it to be somewhat ill-defined. We don’t really know enough about it to say what it predicts. The bouncing cosmologies studied within Horava-Lifshitz gravity are very new, and haven’t been studied carefully. He has looked carefully at ekpyrotic models, but they are also a moving target. It seems difficult for perturbations to travel smoothly through a singularity.

Monday afternoon: Fine Tuning and Anthropic Arguments

2:00: We kick off the afternoon with Sir Roger Penrose talking about entropy issues for cosmology. Penrose has enough clout that they have brought out the overhead projector so he can show his famous hand-drawn slides.

The Second Law of Thermodynamics is mysterious. Part of it is perfectly clear: entropy increases because there are more high-entropy states than low-entropy ones. The mystery is why entropy was lower in the past — all the way back to the Big Bang. Why did the Bang have such a low entropy? What was the nature of the constraint on those early conditions? Things were very smooth. Sounds high-entropy, but not when you take gravity into account. In a fixed box, the highest-entropy state will often be a black hole (maximally non-uniform).

Inflation purportedly explains the smooth conditions of the early universe. However, there are many more non-inflationary initial conditions corresponding to our current universe than inflationary ones. Anthropic principle doesn’t really help; it’s much easier to make a tiny region of universe suitable for life than to make a patch ready to undergo inflation.

The Weyl Curvature Hypothesis conjectures an explicit time-asymmetry in the laws of nature: singularities in the past are smooth (have zero Weyl curvature), while singularities in the future can be arbitrarily chaotic. That would determine the arrow of time. After all, at high temperatures particles are essentially massless (compared to their energies), and therefore nearly conformally invariant. Maybe we can extend that conformal structure to before the Big Bang. In fact, we could imagine a conformal cyclic cosmology, matching the smooth far future onto the smooth early past. We can even think of observational consequences: perhaps calculate density perturbations induced by the fact that the “late” empty universe is not precisely de Sitter. David Spergel at Princeton has a student looking for circles in the CMB, which might be predicted by this model.

3:00: Now we have a panel on “explaining fine tuning,” featuring Alex Vilenkin, Lawrence Hall, and David Wallace.

Despite all the talks that have alluded to measures on the multiverse, Vilenkin is the first to talk very specifically about different proposals and their problems. The problem is that spacetime (in a typical multiverse model) is infinitely big. One generally chooses some cutoff to define a finite region of spacetime, calculate ratios of different conditions in that finite region, then let the cutoff go to infinity. That only makes sense if the result is not sensitive to the specific cutoff; but usually it is sensitive. The only measure that works is the scale factor cutoff; but Vilenkin admits that other people (even within the room) have very different ideas. Of course the right answer should be derived from a deeper theory, not simply postulated. He has hopes for the holographic measure.

Hall is the first particle phenomenologist we’ve heard at the conference. He wants to ask whether we can use the multiverse to make predictions about particle properties. Evidence might be quantitative (mass of the electron) or structural (why three gauge forces?). An old-school particle physicist would try to invent new symmetries; a new-school multiverse physicist calculates probability distributions and places anthropic cutoffs. If we lie near an anthropic boundary, that might be taken as evidence for a multiverse. Low-scale supersymmetry is a possible explanation for the hierarchy between the weak scale and the Planck scale; however, there is also an anthropic bound which really isn’t all that different. And note that we certainly could have — one might say “should have” — already detected low-scale supersymmetry if it existed. Similarly, there is an anthropic boundary in Higgs/top-quark parameter space; being pushed near that boundary suggests that we will find the Higgs near 112 GeV and the top near 177 GeV. If the Higgs is there, that’s a quantitative prediction good at the 5% level. If we then don’t find supersymmetry, the multiverse would be the only known explanation. Many aspects of the multiverse theory can’t be tested, but that’s true for any theory. The right question is, “Can we obtain sufficient evidence to be convinced?”

Wallace is a philosopher who was asked to talk about the Everett interpretation of quantum mechanics, and possible connections to the multiverse idea. But he’s not sure what those connections are, so he apologizes for being a bit vague. The Everett (a/k/a many-worlds) interpretation is simply the idea that we should take unitary quantum mechanics (evolution obeying the Schrodinger equation) as literally true and complete — no wave-function collapse. It implies a kind of multiverse: many mutually decohering histories. A bit different from the kind of spatial multiverse discussed in cosmology, but there are some similarities. Encouragingly, we used to be very confused about how to calculate probabilities within many-worlds, but we’ve lately made great strides toward figuring that out. We might be optimistic that the right measure in the cosmological multiverse might simply be the quantum-mechanical measure, properly applied.

4:30: Another panel! Featuring more critical commentaries, this time from John Barrow, Alex Pruss, and Robin Collins.

Barrow points out that many apparent fine-tunings are ultimately explained by theory. Most particles in nature are identical; that’s explained by quantum field theory. Inertial mass equals gravitational mass; explained by general relativity. If there was any random element in the early universe, anthropic considerations are needed. Barrow and Tipler put an anthropic upper bound on the cosmological constant back in 1986. Maybe the vacuum energy is changing with time, as Sorkin suggested.

Next up, Alex Pruss discusses the different meanings of “fine tuning” between physicists and philosophers of religion. Physicists are thinking of parameters taking on unlikely values within some presumed distribution; philosophers of religion are thinking about parameters that are tuned to allow for the existence of life. Philosophers of religion, of course, don’t worry about testability. But the fact that so many physicists at this conference keep insisting that it’s okay if some aspects of the multiverse are not testable is evidence that there must be people who don’t think it’s okay. The move by the scientists is to say that only specific models are testable. That’s a respectable move, and one that philosophers of religion might want to emulate. Is there some specific theory of what God is trying to maximize? Simplicity of laws, for example? On the other hand, philosophers of religion do something worthwhile, in that they consider a wider variety of allowed explanations.

Robin Collins digs into a foundational question: what does probability mean? One necessary criterion: a notion of probability must conform to rational expectation. In cosmology, this is hard to get right. Consider the flatness problem: we look at the density parameter at early times, and ask why it’s so close to one. But why look at that, rather than some crazy function of that parameter? We should also think carefully about the purported feature of philosophy of religion that it considers a wider variety of explanatory schemes. Can we really separate out these schemes from the search by ordinary science for simple and robust explanations of observed phenomena? Inflation is not a panacea — you might want to go the the “unrestricted multiverse,” where all possibilities are real. The problem is that it doesn’t explain the world we see, because it “explains” anything you could possibly see. Even a multiverse needs restrictions.

Monday evening there was a scheduled talk by Paul Davies, with a response by George Ellis, on “Cosmology, Ultimate Causation, and Multiverses.” But I’m pretty sure that an all-powerful and all-beneficent deity would never have intended jet-lagged scientists to attend talks that started later than 9:00 p.m., so that’s it for today.

The proximate reason for this particular conference is George Ellis’s 70th birthday party. Ellis is of course a well-known general relativist, cosmologist, and author. Although the idea of a birthday conference for respected scientists is quite an established one, Ellis had the idea of a focused and interdisciplinary meeting that might actually be useful, rather than just bringing together all of his friends and collaborators for a big party. It’s to his credit that they invited as many multiverse-boosters as multiverse-skeptics. (I would go for the party, myself.)

George is currently very interested and concerned by the popularity of the multiverse idea in modern cosmology. He’s worried, as many others are (not me, especially), that the idea of a multiverse is intrinsically untestable, and represents a break with the standard idea of what constitutes “science.” So he and the organizing committee have asked a collection of scientists and philosophers with very different perspectives on the idea to come together and hash things out.

It appears as if there is working wireless here in the conference room, so I’ll make some attempt to blog very briefly about what the different speakers are saying. If all goes well, I’ll be updating this post over the next three days. I won’t always agree with everyone, of course, but I’ll try to fairly represent what they are saying.

Saturday night:

Like any good British undertaking, we begin in the pub. I introduce some of the philosophers to Andrei Linde, who entertains us by giving an argument for solipsism based on the Wheeler-deWitt equation. The man can command a room, that’s all I’m saying.

(If you must know the argument: the ordinary Schrodinger equation tells us that the rate of change of the wave function is given by the energy. But for a closed universe in general relativity, the energy is exactly zero — so there is no time evolution, nothing happens. But you can divide the universe into “you” and “the rest.” Your own energy is not zero, so the energy of the rest of the universe is not zero, and therefore it obeys the standard Schrodinger equation with ordinary time evolution. So the only way to make the universe real is to consider yourself separate from it.)

Sunday morning: Cosmology

9:00: Ellis gives the opening remarks. Cosmology is in a fantastic data-rich era, but it is also coming up against the limits of measurement. In the quest for ever deeper explanation, increasingly speculative proposals are being made, which are sometimes untestable even in principle. The multiverse is the most obvious example.

Question: are these proposals science? Or do they attempt to change the definition of what “science” is? Does the search for explanatory power trump testability?

The questions aren’t only relevant to the multiverse. We need to understand the dividing line between science and non-science to properly classify standard cosmology, inflation, natural selection, Intelligent Design, astrology, parapsychology. Which are science?

9:30: Joe Silk gives an introduction to the state of cosmology today. Just to remind us of where we really are, he concentrates on the data-driven parts of the field: dark matter, primordial nucleosynthesis, background radiation, large-scale structure, dark energy, etc.

Silk’s expertise is in galaxy formation, so he naturally spends a good amount of time on that. Theory and numerical simulations are gradually making progress on this tough problem. One outstanding puzzle: why are spiral galaxies so thin? Probably improved simulations will crack this before too long.

10:30: Andrei Linde talks about inflation and the multiverse. The story is laden with irony: inflation was invented to help explain why the universe looks uniform, but taking it seriously leads you to eternal inflation, in which space on extremely large (unobservable) scales is highly non-uniform — the multiverse. The mechanism underlying eternal inflation is just the same quantum fluctuations that give rise to the density fluctuations observed in large-scale structure and the microwave background. The fluctuations we see are small, but at earlier times (and therefore on larger scales) they could easily have been very large — large enough to give rise to different “pocket universes” with different local laws of physics.

Linde represents the strong pro-multiverse view: “An enormously large number of possible types of compactification which exist e.g. in the theory of superstrings should be considered a virtue.” He said that in 1986, and continues to believe it. String theorists were only forced to take all these compactifications seriously by the intervention of a surprising experimental result: the acceleration of the universe, which implied that there was no magic formula that set the vacuum energy exactly to zero. Combining the string theory landscape with eternal inflation gives life to the multiverse, which among other things offers an anthropic solution to the cosmological constant problem.

Still, there are issues, especially the measure problem: how do you compare different quantities when they’re all infinitely big? (E.g. number of different kinds of observers in the multiverse.) Linde doesn’t think any of the currently proposed measures are completely satisfactory, including the ones he’s invented. A big problem with Boltzmann brains.

Another problem is what we mean by “us,” when we’re trying to predict “what observers like us are likely to see.” Are we talking about carbon-based life, or information-processing computers? Help, philosophers!

Linde thinks that the multiverse shows tendencies, although not cut-or-dried predictions. It prefers a cosmological constant to quintessence, and increases the probability that axions rather than WIMPs are the dark matter. Findings to the contrary would be blows to the multiverse idea. Most strongly, without extreme fine-tuning, the multiverse would not be able to simultaneously explain large tensor modes in the CMB and low-energy supersymmetry.

12:00: Raphael Bousso talks about the multiverse in string theory. Note that “multiverse” isn’t really an accurate description; we’re talking about connected regions of space with different low-energy excitations, not some metaphysical collection of completely distinct universes. The multiverse is not a theory — need some specific underlying dynamics (e.g. string theory) to make any predictions. It’s those theories that are tested, not “the multiverse.” Predictions will be statistical, but that’s okay; everyone’s happy with statistical mechanics. “Even if you were pretty neurotic about it, you could only throw a die a finite number of times.” We do need to assume that we are in some sense typical observers.

The cosmological constant problem (why is the vacuum energy so small?) is an obvious candidate for anthropic explanation. String theory is unique at a deep-down level, but features jillions of possible compactifications down to four dimensions, each with different low-energy parameters. Challenges to making predictions: landscape statistics (how many of each kind of vacua?), cosmological dynamics (how does the universe evolve?), measure problem (how do we count observers?). Each is hard!

For the cosmological constant, the distribution of values within the string landscape is actually relatively understandable: there is basically a uniform distribution of possible vacuum energies between minus the Planck scale and plus the Planck scale. Make the right vacua via eternal inflation, which populates the landscape. Our universe decayed from a previous vacuum, an event that must release enough energy to produce the hot Big Bang. That’s a beneficial feature of the multi-dimensional string landscape: “nearby” vacua can have enormously different vacuum energies.

The measure problem is trickier. In the multiverse, any interesting phenomenon happens an infinite number of times. Need some sort of way to regularize these infinities. A problem for eternal inflation; not only for the string landscape. Bousso’s favorite solution is the causal patch measure, which only counts events that happen in the past light cone of any particular event, not throughout a spacelike surface. In that measure, most observers see a cosmological constant comparable to the age of the universe they observe — that’s compatible with what we see, and directly solves the coincidence problem.

Sunday afternoon: Philosophers’ turn

2:00: John Norton talks about the “Bayesian failure” of cosmology and inductive inference. (He admits off the bat that it’s kind of terrifying to have all these cosmologists in the audience.) Basic idea: the Bayesian analysis that cosmologists use all the time is not the right tool. Instead, we should be using “fragments of inductive logics.”

The “Surprising Analysis”: assuming that prior theory is neutral with respect to some feature (e.g. the value of the cosmological constant), we observe a surprising value, and then try to construct a framework to explain it (e.g. the multiverse). This fits in well with standard Bayesian ideas. But that should worry you! What is really the prior probability for observing some quantity? In particular, what if our current theory were not true — would we still be surprised?

We shouldn’t blithely assume that the logic of physical chances (probabilities) is the logic of all analysis. The problem is that this framework has trouble dealing with “neutral evidence” — almost everything is taken as either favoring or disfavoring the hypothesis. We should be talking about whether or not a piece of evidence qualifies as support, not simply calculating probabilities.

The disaster that befell Bayesianism was to cast it in terms of subjective degrees of belief, rather than support. A prior probability distribution is pure opinion. But your choice of that prior can dramatically effect how we interpret particular pieces of evidence.

Example: the Doomsday argument — if we are typical, the universe (or the human race, etc.) will probably not last considerably longer than it already has (or we wouldn’t be typical). All the work in that argument comes from assuming that observers are sampled uniformly. But the fact that 60 billion people have lived so far isn’t really evidence that 100 trillion people won’t eventually live; it’s simply neutral.

Heretical punchline: cosmic parameters can’t be judged as “improbable,” so long as they’re consistent with theory and observation.

[David Wallace, during questions: Do you really mean to say that if we observed the stars in the sky spelling out the message "Oxford is better than Cambridge," all we could say is "Well, it's consistent with the laws of physics, so we can't really conclude anything from that"?]

2:45: Simon Saunders talks about probability and anthropic reasoning in a multiverse. Similar issues as the last talk, but he’ll be defending a Bayesian analysis.

Sometimes we think of probability objectively — a true physical structure — and sometimes subjectively — a reflection of the credence we give to some claim.

Problems with anthropic arguments involve: linguistics (what is included in “observer” and “observed”?), theory (how do we calculate the probability of finding certain evidence given a particular theory?), and realism (why worry about what is observed?). On the latter point: do we conditionalize on the existence of human life, or the existence of some observers, or simply on the existence of conditions compatible with observers? Saunders argues for the latter: all we care about are physical conditions, not whether or not observers come into existence. Call this “taming” the anthropic principle.

Aside on vacuum energy: are we really sure it’s finely-tuned? Condensed-matter analogues give a different set of expectations — maybe the vacuum energy just adjusts to zero after phase transitions.

For branches of the wavefunction, there exist formal axioms (e.g. Deutsch-Wallace) for evaluating the preferences of a rational observer which recover the conventional understanding of Copenhagen probabilities even in a many-worlds interpretation. For a classical multiverse, the argument is remarkably similar; for a fully quantum inflationary multiverse, it’s less clear.

4:00: Panel discussion with Alex Vilenkin, Wayne Myrvold, and Christopher Smeenk. It’s a series of short talks more than an actual discussion. Vilenkin goes first, and discusses — wait for it — calculating probabilities in the multiverse. The technical manifestation of the assumption that we are typical observers is the self-sampling assumption: assume we are chosen randomly from within some reference class of observers. The probability that we observe something is just the fraction of observers within this class that observe it. But how do we choose the class? Vilenkin argues that we can choose the set of all observers with identical information content. (Really all information: not just “I am human” but also “My name is Alex,” etc.) That sounds like a very narrow class, but in a really big multiverse there will be an infinite number of members of each such class. (This doesn’t solve the measure problem — still need to regulate those infinities.) In fact we should use the Principle of Mediocrity: assume we are typical in any class to which we belong, unless there is evidence to the contrary.

Myrvold is next up, and he chooses to respond mostly to John Norton’s talk. Most of the time, when we’re evaluating theories in light of evidence, we don’t need to be too fancy about our background analytical framework. The multiverse seems like an exception. More generally, theories with statistical predictions are tricky to evaluate. If you toss a coin 1000 times, any particular outcome is highly improbable. You have to choose some statistics ahead of time, e.g. the fraction of heads. Cosmological parameters might be an example of where we don’t know how to put sensible prior probabilities on different outcomes.

Smeenk wants to talk about how big a problem “fine-tuning” really is. Sometimes more than others: when some parameter (e.g. the vacuum energy) is not just chosen from a hat, but gets various contributions about which we have sensible expectations, it’s giving up on too much to simply take any observed value as neutral with respect to theory evaluation. He’s reacting against Norton’s prescription a bit. Nevertheless, we should admit that choosing measures/probability distributions in cosmology is a very different game than what we do in statistical mechanics, if only because we don’t actually have more than one member of the ensemble in front of us.

Sunday evening: “Ultimate Explanation”

After dinner we reconvene for a talk and a response. The talk is by Timothy O’Connor on Ultimate Explanation: Reforging Natural Philosophy.” He reminds us that Newton insisted that he did not “feign hypotheses” — he concentrated on models that he claimed were deduced from the phenomena, and thought that any deeper hypothetical explanations had “no place in experimental philosophy.” The implication being that Newton would not have approved of the multiverse.

O’Connor says that a fully complete, “ultimate” explanation cannot possibly be attained through science. Nevertheless, it’s a perfectly respectable goal, as part of the larger project of natural philosophy.

He defines an “ultimate explanation” as something that involves no brute givens — “such that one could not intelligibly ask for anything more.” That’s not attainable by science. If nothing else, “the most fundamental fact of existence itself” will remain unexplained, even if we knew the theory of everything and the wave function of the universe. Alternatively, if we imagine “plenitude” — everything possible exists — it would still be possible to imagine something less than that, so a contingent explanation is still required.

We are led to step outside science and consider the idea of an ultimately necessary being — something whose existence is no more optional than that of mathematical or logical truths. We could endorse such an idea if it provided explanations without generating insoluble puzzles of its own, and if we thought we had considered an exhaustive list of alternatives, all of which fell short. Spinoza and Leibniz are invoked.

Note the peculiar logic: if a necessary being does not exist, it was not simply an optional choice; it must necessarily not exist. (Because if a necessary being is conceivable, it must necessarily exist. Get it?)

Punchline: Science is independent of any/most metaphysical claim. But that means it can’t possibly “explain” everything; there must be metaphysical principles/assumptions. Some of these might be part of the ultimate explanation of the actual world in which we live.

The response comes from Sir Martin Rees. He opens by quoting John Polkinghorne: “Your average quantum mechanic is no more philosophical than your average motor mechanic.” But maybe cosmologists are a bit more sympathetic. He then recalls that Dennis Sciama — who was the thesis advisor of George Ellis, Stephen Hawking, and Rees himself — was committed as a young scientist to the Steady State model of cosmology, primarily for philosophical reasons. He did give up on it when confronted with data from the microwave background, but it was an anguished abandonment.

Searching for “explanations,” we should recognize that different fields of science have autonomous explanatory frameworks. People who study fluid mechanics would like to understand turbulence, and they don’t need to appeal to the existence of atoms to do so — atoms do exist, and one can derive the equations of fluid mechanics from them, but their existence sheds no light whatsoever on the phenomenon of turbulence.

Note also that, even if there is an ultimate explanation in the theory-of-everything sense, it may simply be too difficult for our limited human minds to understand. “Many of these problems may have to await the post-human era for their solution.”

Continued at Day Two.

Central Krakow emerged from World War II, which began nearly exactly 70 years ago, nearly unscathed. The central square is one of the more beautiful in Europe, similar in a way to that of Prague. But it was hard to avoid waling there without imagining what it must have looked like during the war, occupied by German soldiers who had made Krakow the center of their regional government during the war.

From the square one can take tours in little golf-cart-like jitneys, and see some of the interesting historical sites, including the Jewish Quarter (Kazimierz) and Schindler’s famous enamelware factory. Some of the apartment buildings in Kazimierz are still in the state they were at the end of the war, a rather grim reminder of the central role Krakow played in the Holocaust.

From Krakow one can take day trips to a number of interesting places, and we visited the spectacular salt mines of Wielicka, a UNESCO World Heritage site, which have amazing, huge rooms carved out of the rock.

But there was another interesting place to tour that we were hesitant about – Auschwitz. Others who took the tour came back saying that it was well worth the journey, over an hour by bus each way, but tended not to say much more about it…hmmm.

So on our last free day we took the plunge, signed up for the tour, and went. The bus traveled through quite rural countryside on two-lane roads, past farms and villages, roughly following the Vistula river, until reaching the town of Oswiecim, which the Germans called Auschwitz.

There are in fact two concentration camps there, called Auschwitz and Birkenau, the latter actually being Auschwitz II. Birkenau is twenty times larger than the original camp, which was in fact a Polish army installation before the war. Auschwitz I was turned into a labor camp by the Germans shortly after the start of the war, and tens of thousands lost their lives there, working in nearby armaments factories, and on the construction of the Birkenau camp, starving to death on a 500-calorie-a day diet, or in the original gas chamber there.

The camps are still plainly visible from the air, as you can see in the photo. Auschwitz I is now a museum and living memorial to those who died there. Our tour of the museum included rooms filled with the personal effects taken from the prisoners: shoes, clothing, eyeglasses, and, perhaps most shockingly, human hair, which was used to make clothing for the German army. It’s actually hard to write about this, forcing myself to remember touring the housing blocks and the infamous Block 11, where, as an experiment, the SS first tested Cyclon B as a means of mass murder on 600 Soviet prisoners of war and 250 sick Poles.

After touring the museum, we went a few kilometers to Birkenau. The entry to the camp, along the rail line through the brick block house, is the same as the entry was for over a million people who were murdered there, predominantly Jews (most from Hungary), but also Gypsies. In late 1944 and early 1945, the fleeing Germans tried to destroy as much of the camp as they could, blowing up the crematoria and burning the wooden barracks, leaving only the brick chimneys standing behind the once-electrified barbed wire fences. The pictures we took say it all.

Throughout the tour of both places, everyone was hushed and, I think, awestruck by the sheer scale of the evil perpetrated there, and duplicated at so many other camps in eastern Europe and Germany. You can watch Sophie’s Choice or Schindler’s List, or read about the Holocaust, but until you stand there and see for yourself the actual crematoria and barracks, the mile-long rail line inside the camp, and the electrified fences with guard towers, you may not have truly appreciated what happened. AllI could think about was how anyone with an ounce of goodness in their hearts could have perpetrated this, but some 70,000 SS members did exactly that. Only 10,000 or so were ever brought to justice.

In an attempt to understand the mindset of the perpetrators, at the Auschwitz bookstore I bought a book called “KL Auschwitz seen by the SS” with the written reminiscences of the commandant of the camp, Rudolf Hoess, the diary of one of the camp doctors who participated in many of the “selections” of prisoners upon arrival. Hoess’ memoir was chilling, to say the least. It was written while he was in prison, before being hanged at Auschwitz in April, 1947. He describes the process of creating and operating the camp, and carrying out the Final Solution, in terms which are more reminiscent of large project management than mass murder. He had a very tight budget, and had to be ruthlessly efficient in meeting the SS quotas for labor production and human destruction. He was a problem solver at heart…that’s what made it so chilling. As for the diary of the doctor, Paul Kremer, it was particularly difficult to swallow his diatribes against the Allied bombing of Germany after his clinical discussion of his work at the camp.

How can people do this to other people?

We also bought the book “Hope is the Last to Die” by Halina Birenbaum, who describes her teen years spent in the Warsaw ghetto and then a series of concentration camps, somehow managing to survive through numerous near-death events. She is still alive, as far as I can tell, living in Israel. This book is a must-read.

This one-day tour, and the books we read, had a profound affect on me this past summer. And there are two things that I really have to say at this juncture. Firstly, it has been tremendously disturbing to see Obama (or any US president) seriously compared to or equated with Hitler or the Nazi party. Anyone who does such a thing is, to my mind, a sick human being, and doing a terrible disservice to the memories of the victims of the Holocaust.

Secondly, earlier today in Iran the world was treated to the annual sight of Iranians marching in the street, chanting “Death to America! Death to Israel!”, with Ahmadinejad denying the Holocaust, as we have come to expect. I guess it’s not realistic to ask them to do the reading on this one, much less visit a place like Auschwitz.