I’ve traded off my reasons for not blogging much of late. Last week and before it was The Particle at the End of the Universe (in stores November 13!), but that’s now been handed in and I can kick back and catch up on my martini-drinking. Except that instead of doing that, I instantly hopped on a plane for Europe, where I’m now participating in a workshop on philosophy and cosmology. Not that you should feel sorry for me — the workshop is being held at the La Pietra conference center, a beautiful facility owned by NYU in Florence. I’m not sure why NYU owns a conference center in Florence; it could have been a targeted purchase, but it could easily have just been a gift. (Caltech for a while owned an abandoned gold mine. Universities get all sorts of crazy gifts.) But at least temporarily, martinis have been put aside for Chianti and limoncello.
And work, of course. This is my favorite kind of workshop: less than twenty people, gathered around a table, with no fixed agenda, talking about issues of mutual interest as they come up. This group has both scientists and philosophers, although probably more of the latter. So far each day has featured a scientist — Joel Primack, me, Brian Greene, Scott Aaronson — giving some very general remarks, while everyone else takes turns whacking them with (metaphorical) sticks. My own talk started at 11 a.m. and didn’t finish until 5:30 p.m., with breaks for lunch and coffee. So it’s exhausting both intellectually and physically, but very rewarding to have the chance to dig very deeply into difficult issues.
My talk was about — you guessed it — the arrow of time. Most people in the room are already familiar with the basic story that time’s arrow is (at least mostly) a consequence of the increase of entropy over time, and that our current universe has low entropy, but the entropy was even much lower in the past, and that last fact demands cosmological explanation. The central question concerned what would count as an “explanation.” Read More
As I mentioned in my last post, I’m now in Auckland. Richard Easther, a repatriated Kiwi who came here from Yale last year to head up the physics department, has organized a workshop on “The LHC, Particle Physics and the Cosmos“, at which I gave a talk this morning.
This is a very different affair to ICHEP. In Melbourne there were 800 or so participants, filling a gigantic conference hall for the plenary talks, whereas there are
something like 30 44 participants at this workshop, roughly split between New Zealand academics (faculty, postdocs and students), and those of us from abroad. ICHEP was a terrific conference, but more usually I strongly prefer these small, intimate workshops to huge meetings. They tend to be more focused and I typically seem to leave having learned more from the talks.
There were something like 400 people at his talk, and the thing that struck me was the quality of the questions that people asked at the end. There was even a question that was essentially about triggers, and the risk that one might miss important physics due to them. As you’ll have seen discussed before, the sheer volume of data produced by each collision at the LHC, combined with the frequency of these collisions means that it is just impossible to save each individual event. Instead, a decision has to be made extremely rapidly whether to save a given event, understanding that doing this means that many other events will then be missed. This decision is based on the expectations we have of the kind of signals that we expect the new physics to exhibit. Of course, a consequence is that there exist possible signals of new physics that will evade these triggers. This is a subtle question and one that I’m surprised to hear asked in a public lecture.
Yesterday the research talks began. The topics have spanned quite a number of topics, including talks from people on ATLAS and CMS on their Higgs, and other results. There have been talks on dark matter, neutrinos, variance in the Hubble flow in cosmology, and a number of other topics, including one on the Phenomenological Minimal Supersymmetric Standard Model from Tom Rizzo from SLAC. I particularly enjoyed a talk from Pat Scott, who is a postdoc at McGill, about cosmology with ultracompact minihalos of dark matter. These potentially provide a way to probe the extent to which the statistics of structure formation deviates from that expected from gaussian primordial seeds. As such, it seems that it may provide another way to look at non-gaussianity beyond that we usually think of in the microwave background, and about which we hope to see interesting results from the Planck mission.
This morning Tom Appelquist (Yale) and Jay Wacker (SLAC/Stanford) gave interesting theory talks, and our own JoAnne spoke about the physics that may be probed through a program of physics at the intensity frontier. This afternoon Michele Redi from CERN gave an interesting talk on the implications of a light Higgs for composite models. It is one thing to find the object that breaks the electroweak symmetry, but another to pin down whether it is a fundamental or composite particle. Compositeness is attractive in some ways, since it may provide a way to tackle the hierarchy problem, but finding the Higgs at the rather light mass announced last week presents particular challenges to models in which the Higgs is composite, and leads to some specific predictions. Michele is interested in models in which the Higgs is a pseudo-Goldstone boson and showed that in many such models, naturalness, coupled with a 125 GeV Higgs implies that there should also be new fermions in the model that are quite light, and may be within the reach of the LHC.
Well I’m off to have tea and then chair a parallel session in which there will be a lot of theory talks, about which I may report soon.
I’m about to leave Melbourne for Auckland, where I’ll be speaking at and participating in a workshop Richard Easther is organizing, called The LHC, Particle Physics and the Cosmos.
I’ll have a little bit more to say about the ICHEP conference, but for now, I’ll leave you with a link to a very brief interview I did on the Australian Broadcasting Corporation’s Radio National Drive Radio show a couple of days ago. I found it hard to get much across in the short time, but it is nice to think that people driving home from work might have been hearing about ICHEP, the Higgs and dark matter.
As you may have seen from our live-blogging of the CERN seminars on Wednesday morning, after having told Sean and John I would be asleep, I woke up anyway and watched the announcement live at 3am my time. I don’t regret it for a moment – you don’t get to watch historic events like that every day! But the reason I’d originally intended to stay asleep was that I had a very long day ahead of me, since Wednesday evening I flew out to Melbourne to take part in the 36th International Conference on High Energy Physics (ICHEP). This is the major high-energy physics conference every two years; and this year, given the Higgs announcement, it is particularly exciting.
I landed in Melbourne on Friday morning (local time), but couldn’t attend a lot of the conference that day because I had to deal with a lost bag (thanks United!) and then shop for a shirt, underwear, etc. Enough about that though. For the last year or so the University of Melbourne has been the primary institution in a new Australian Center of Excellence in Particle Physics (CoEPP) at the Terascale, and I am fortunate to be one of their international partner investigators and on the International Advisory Committee. Friday evening there was a small reception and dinner for members of the Center and the IAC. Geoff Taylor (head of CoEpp), my friend Ray Volkas, Rolf Heuer (Director General of CERN and Chair of the IAC), and others were all there, dressed nicely in their suits. And I was there in the jeans I’d worn continually (and slept in on the plane) for two and a half days (thanks United! OK, I’ll stop mentioning it now). In any case, this was a lovely start to what I”m hoping will be one of the more exciting conferences of my career.
We are very close to the end of the semester here at Penn, and the last couple of weeks have been the usual flurry of activity as teaching comes to an end, exam period begins, and a few late semester/early summer meetings all take place at the same time.
A week or so ago, I spent a couple of days back at Syracuse University, where I was a faculty member for quite a few years. I was there primarily to participate in a special event that preceded the East Coast Gravity Meeting being held there on the following weekend. The event was a celebration – GoldbergFest – of the career of Josh Goldberg, a good personal friend, and an eminent relativist at Syracuse, who has been an emeritus professor there for many years now.
Josh began as a graduate student at Syracuse in the early 1950′s, working on conservation laws in General Relativity (GR) and on canonical quantization. At the time Syracuse had one of the few well-known relativity groups in the world, led by Peter Bergmann, and an impressive group of young people were trained under him, and later under Josh, as students and postdocs; people like Ted Newman, Ray Sachs, Art Komar, Roger Penrose, and many others. I’m certainly no expert on the precise history of the Syracuse group, but fortunately, as part of a special issue of General Relativity and Gravitation dedicated to Josh, to which I was honored to also contribute, Ted Newman describes it wonderfully. The Fest was a lovely event. I enjoyed the other speakers’ talks – John Stachel, Rafael Sorkin and Peter Saulson, and Ted Newman’s hilarious and touching after dinner speech, and the reminiscences of the other people at the dinner made for what I hope Josh thought was a wonderful day.
Over the next two days quite a few of our students and postdocs from Penn gave talks at the East Coast Gravity Meeting, and I was delighted to hear that our very own Godfrey Miller won the award for the best student presentation.
Returning To Penn, I just about had enough time to finish putting together the take-home final exam for my graduate General Relativity course, before heading off to NYU on Wednesday with our whole group for our semesterly joint meeting. We were joined, as usual, by a nice crowd from Columbia and Case Western for a day of talks and discussion. I always find these meetings to be incredibly useful scientifically, because the group is so interactive, boisterous and interested in the material, while being such warm and friendly hosts. It makes for an enjoyable day every time. Beyond the obvious exchange of ideas, these meetings also provide an opportunity for our students to get used to giving talks on their work. This time my student – Garrett Goon – and one of my colleague Justin Khoury’s students – Austin Joyce – gave our student talks, leading to some healthy discussion Wess-Zumino terms in new field theories and conformal cosmology, respectively. Both did a terrific job, although they’re becoming old pros at this point, rather than beginning students in need of practice.
To close out last week, Greg Gabadadze from NYU came down on Friday so that we could try to finish up some details in a project that is close to completion, before we start dispersing for various summer conferences. I’ll discuss these soon, I expect.
Today my final exam will be turned in and grading starts, an old friend is delivering a seminar in our group, and Sean’s student Kim Boddy arrives for a week so that the three of us can try to finish up a paper. The end of the semester always seems to go this way. While all these things are fun, life becomes excessively hectic for two weeks, and then travel begins.
Greetings from Norway, where we’re about to embark on what is surely the most logistically elaborate conference I’ve ever attended. Setting Time Aright starts here in Norway, where we hop on a boat and cross the North Sea to Copenhagen. The get-together is sponsored by the Foundational Questions Institute, although it came together in an unusual way; I was part of a group that was organizing a conference, and we applied to FQXi for funding, at which point they mentioned they were planning almost exactly the same conference at the same time. So we joined forces, and here we are. Unity ’11!
The topic, if you haven’t guessed, is time. That’s a big subject, one that can hardly be done justice by sprawling books with hundreds of (admittedly quite charming) footnotes. You can see why the conference has to spread over two countries. We’re trying an experiment in interdisciplinarity: while the conference is a serious event meant for researchers, we have a wide variety of specialties represented, including biologists, computer scientists, philosophers, and neuroscientists, as well as the inevitable physicists and cosmologists. (There is also a public event, for those of you who find yourselves in Copenhagen next week.) I can’t wait to hear some of these talks, it should be a blast.
My job is to open the conference with an introductory talk that hits on some of the big questions. Here are the slides, at least as they are right now; last-minute editing is always a possibility. I think I put enough in there to provoke almost everyone at the conference one way or another.
In my last post I described the workshops and conferences – research travel – that I’ve been on during the first part of the summer. But when I returned from Brazil there was one other science trip I went on before taking a few weeks off. In mid June, Sean, Jennifer, Risa, Janna Levin and I were invited speakers at the first of a new initiative – the Discovery Retreats.
These are the brainchild of John Hendricks, the founder of the Discovery Channel and a host of science and education related programming. Taking place at Gateway Canyons Resort (yes, I know, sometimes we’re spoiled), these are several day events at which people come for vacation time in a stunning environment, mixed with lectures, panel discussions, star-gazing, and open discussion events. This inaugural retreat was titled “Secrets of the Universe”, at which Sean (who was organizing the scientific part of the event) gave the introductory overview of cosmology, Janna spoke about black holes, Risa discussed dark matter in the universe, I talked about dark matter and cosmic acceleration, and Jennifer gave a fascinating and fun talk on science and hollywood.
For me, by far the most enjoyable science part of the event was the panel discussion. Janna had left at this point, but we were joined by Nick Sagan, who provided his perspective as a science fiction author. Jennifer moderated this, and had a well thought out sequence of questions that guided us through a set of popular topics. However, it is always interesting to see what topics the audience is most fascinated by, even though they are often the ones you would have suspected. We were led through the nature of the big bang singularity, the ideas of inflation, string theory, the question of whether the universe has an edge, and a bunch of other big issues that frequently arise when one gets into chats about cosmology. We certainly had a great time – I hope the audience did.
One of the more fun non-science events was a tour of John’s extensive car museum at the resort. Here are Janna and I sitting in front of one of the many beautiful exhibits
In many ways this first retreat was a bit of a dry run, in which we were feeling out the right format and exploring the mix of scheduled and free time. There are going to be more of these events, not just focused on cosmology but on the frontiers of other scientific areas. Hopefully our first attempt wasn’t just fun, but also gave enough feedback that these future attempts work as well as possible.
Like many physicists, I spend a reasonable portion of the summer months traveling, delivering talks at conferences and workshops, and taking the opportunity to meet with colleagues and gain first-hand experience of the range of research being done in my field. For me, this began a couple of hours after my classes ended for the semester (congratulations to my General Relativity class, all of whom did very well at the end of the day), when I headed off to California to hang out with Sean for a few days and to give the Caltech physics colloquium.
I always enjoy visiting Caltech, and I find colloquia particularly fun talks to deliver, since they provide the opportunity to explain what’s going on at the frontiers of the field to physicists who spend most of their time working in their own, different areas. But this talk was particularly exciting to give, because of the location. I hadn’t realized, but the Caltech physics colloquia take place in a rather old lecture hall (201 E. Bridge) in which I was told Richard Feynman delivered his renowned lectures on physics. This part of Caltech is about to undergo a round of renovations, which meant that this was probably my last chance to speak in the same place that Feynman did – a wonderful experience. With most academic travel, the main payback from a trip like this is the chance to develop some new ideas with one’s collaborators. This time was no exception, and Sean, a student of his and I started discussions about a new dark matter idea that I’ll attempt to blog about here should it come to anything.
After a week back in Philadelphia, I was on a plane once more, this time for a short hop to my old stomping grounds in Cleveland, to take part in a workshop on gravity being held at Case Western Reserve University. The last decade or so have seen a resurgence of efforts to seek a sensible way in which General Relativity (GR) might be modified, either in ways that might yield new physics of the early universe, or in a manner that might explain phenomena at late times. The main original impetus for this work has been the possibility that the phenomenon of cosmic acceleration might be signaling a modification of gravity on the largest scales. However, among many researchers the current thrust is to gain a comprehensive understanding of the ways in which gravity may differ from GR, and at what scales one might expect any allowed modifications to appear.
It is, in fact, an extremely tricky proposition to modify GR, with almost any idea one might think of running into trouble either with established tests of the theory within the solar system, or with serious theoretical inconsistencies such as the appearance of particles with negative energies, known as ghosts. Many of the more interesting ideas involve models arising from extra dimensions, which have led not only to interesting modified gravity models, but also to new ideas about field theories in four dimensions, that I will discuss in another post soon. The gravity workshop focused on many of these new ideas, and, as often happens at small intense meetings, I left with lots of new ideas about my own work.
In June, I left for a lightning trip to Brazil, to speak at the very first meeting of the whole of the Brazilian Physical Society. This conference was held in the beautiful location of Iguassu Falls. Although I was, unfortunately, too ill from a flu I had caught to be able to travel to the falls themselves, I was lucky enough to see them from the air a couple of times. I will clearly have to go back! The meeting had several thousand people, and it was clear that Brazilian physics is undergoing a period of rapid expansion, something it is heartening to see given the pressures science is facing in many other parts of the world. One of the highlights was an event launching the new South American branch of the International Center for Theoretical Physics (ICTP). The ICTP, in Trieste, Italy, was founded in 1964 by Abdus Salam, with the goal of providing educating scientists from developing countries. Their new branch, in Sao Paulo, will be directed by Nathan Berkovitz and should extend the great work of the original. It’ll be interested to see how this endeavor develops – I wish them all the best.
I’d intended three days in Brazil, but ended up there for an extra twenty-four hours because the airport at Iguassa Falls was closed for a day by particulates from the Chilean volcano. I get delayed many times every year and find myself cursing airlines (I’d missed an important meeting in Cambridge a few weeks earlier thanks to USAir), but it’s hard to be furious at a volcano. The people at the Brazilian Physical society were wonderfully helpful and I’d like to thank them as publically as I can for taking such good care of us, dealing with our hotel rooms, and getting us rebooked on new flights.
Now I’m back to work, taking a few weeks without travel and trying to get new projects up and running, while finishing writing up a few papers before the new semester creeps up on me.
Not much blogging this week, as I’m at the World Conference of Science Journalists in Doha, Qatar. I’m informed that the technical term describing my role here is that of trailing spouse. But I did give a little talk on upcoming discoveries we should be looking forward to in particle physics and cosmology.
I’ll try to put up a more full report later. Right now I’ve just been guilted into blogging because I’m listening to a sexy and exciting panel about science blogs, staring Mo Costandi, Maryn McKenna, Jennifer Ouellette, Ed Yong, and Mohammed Yahia. And just to prove I’m here, I can show you what a sign inside Starbucks looks like in an Arab country.
Afterwards I’ll be headed to the souk to shop for scimitars.
Yesterday’s talks were devoted to the idea of dark matter, which as you know is the hottest topic in cosmology these days, both theoretically and experimentally.
Eric Armengaud and Lars Bergstrom gave updates on the state of direct searches and indirect searches for dark matter, respectively. John March-Russell gave a theory talk about possible connections between dark matter and the baryon asymmetry. The density of dark matter and ordinary matter in the universe is the same, to within an order of magnitude, even though we usually think of them as arising from completely different mechanisms. That’s a coincidence that bugs some people, and the last couple of years have seen a boomlet of papers proposing models in which the two phenomena are actually connected. Tracy Slatyer gave an update on proposals for a new dark force coupled to dark matter, which could give rise to interesting signatures in both direct and indirect detection experiments.
This is science at its most intense. A big, looming mystery, a bounty of clever theoretical ideas, not nearly enough data to pinpoint the correct answer, but more than enough data to exclude or tightly constrain most of the ideas you might have. It wouldn’t be at all surprising if we finally discover the dark matter in the next few years; unfortunately, it wouldn’t really be surprising if it eluded detection for a very long time. If we knew the answers ahead of time, it wouldn’t be science (or nearly as much fun).
Today is our last day in Avignon, devoted to cosmic acceleration. My own talk later today is on “White and Dark Smokes in Cosmology.” (The title wasn’t my idea, but I couldn’t have done better, given the context.) It’s the last talk of the conference, so I’ll try to take a big-picture perspective and not sweat the technical details, but (following tradition) I will admit that it’s an excuse to talk about my own recent papers and ideas I think are interesting but haven’t written papers about. At least it should be short, which I understand is the primary criterion for a successful talk of this type.