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Archive for September, 2008

Discuss among yourselves

Way back when, when I went around interviewing for faculty jobs, there was one particular interview which I really enjoyed. Usually, you get to have a dizzying sequence of brief interviews with faculty members (no, this is not a tribute to David Foster Wallace), but in that one, unusually, I also got to meet with a delegation of graduate students. We had breakfast together and they asked me a few questions, and I got to see an aspect of the department you usually don’t get to see in an interview.

One question they asked stuck in my mind, maybe because I did not provide a good answer. Suppose you have a graduate student, just at the verge of discovering their own voice, maybe after completing their first project. They come to you with their first own idea, but the idea is not that great. It is not terrible, you cannot point out immediately any obvious flaws, but it doesn’t look like it is going to work out, and even if it does it may not be worth the effort. What do you do?

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Some good news for today.

I just stumbled on this article on the New York Times today. The lawsuit against the LHC was dismissed, even if it was based on procedural grounds. At least there is some good news on a day like today.

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Last time I had time to write a detailed physics post, I got to the point of declaring fields as the fundamental entities of nature. Since we can get particles from quantizing (certain kinds of) fields, and since the pointlike particles are confusing and paradoxical, we don’t really need them. Our basic theory of nature is then a (quantum) field theory.

Now, if you are contrarian, which I think everybody should be, you probably immediately think this is a rather dogmatic statement. We don’t really have a complete theory of nature yet, we haven’t unified gravity with quantum mechanics or explained consciousness, not to mention even finding the Higgs. As far as we know the universe may well be a computer, or it is human shaped, perhaps it is elephants (or turtles) all the way down, or angles dancing on a head of a pin. Wasn’t there also that theory of everything, something with a letter and a number? Once we get foundational and stuff, the possibilities are endless really…

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OK, so I admit I occasionally wander around and fill random tests on the web as well. It seems a lot of people do, so what is the harm in admitting it?

This is not a rhetorical question. One might do a bit of social calculus: does filling this test say something about me? What will my colleagues think of me for admitting it? Will I go up or down on their esteem? By how many points? Will they forget quickly or will they remember this and tease me forever?

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I thought I would give you a physics puzzle to solve for a change. This puzzle was posed to me this week right before lunch and we had a fun discussion with my colleagues about it. The great thing about the puzzle, is that you can check for the solution in your kitchen if you have a machine to measure weights. Many cooks do, so you can become an experimental physicist for a day if you want to. The puzzle involves typical things that you can find in your home, like water, and a container for it. It also involves lead (in the original puzzle), which is substituted by a blue egg in the picture. If you have never seen blue eggs, go to a traditional chinese food store near your place and ask for duck eggs. So now you have all the ingredients.

A blue (lead) egg suspended in water hangs by a string


So the idea is that you suspend the egg from a string (you can use superglue), and you lower it slowly into a container of water, but the string supports the weight of the egg. You can hang the string from your favorite support, like your finger. The water is seating atop an instrument that measures its weight. The question is: if you lower the egg in the water, will the weight marked in the register increase, stay the same, or decrease. There is more than one way to think about the puzzle, but in the end you should always arrive at the same answer. The really important question is if the weight on the measuring device changes, by how much does it change?

Incidentally, this reminds me of a time when I was in graduate school when lead was found in the water pipes of the university I was in, many many years ago. The water fountains in the building were closed with yellow warning tape, and right next to them a big water jug dispenser was placed so that people could still get water, but not from the tap. Someone with a good sense of humor (I imagine it was a physics graduate student) put signs on the water fountain from the pipes and the bottled water. The signs said “Leaded” and “Unleaded”.

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Brief note

As expected, I got too busy with the day job. Consequently, this week I was unable to contribute to the type of entertainment and physics fun our 3 readers got used to in the past, er… week or so. This week there is a department review going on, and this means way too much paperwork and politics, and probably some third p I am missing right now (but it sure ain’t physics). Life as faculty member is not always as glamorous as it appears to be in the popular imagination, there will always be weeks like that.

So, in the meantime, something I encountered while browsing the new journal Physics, which seems to be a pretty decent way of keeping up with current stories in, well, physics. Here is a good piece by Stanford’s Shamit Kachru, of KKLT (and Rutgers basketball) fame, writing about one of the very recent developments in string theory, the attempt to find gravitational duals for cold atomic systems. Enjoy!

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We all like to play darts occasionally, and some others like buying lottery tickets. Although there is some skill that needs to be acquired when playing darts (we could call this the aim), playing the lottery requires no skill at all. In both of these situations a natural mathematical object comes to the fore. We usually call it the odds of winning. In some sense, the odds describe how you should bet money on the different possible outcomes of one of these games. If you do your analysis carefully you will find that betting on the lottery is always (statistically) a losing proposition, unless you could bet against winning.

Given that we are in the middle of a financial crisis, essentially because the odds of something happening were not calculated correctly, I thought this might be nice place to talk about the odds of stuff happening at another place: the Large Hadron Collider (I will use the standard acronym: LHC). Sadly, the odds were not in favor last week where there was a Helium leak.
Failures of these kinds are considered routine and they tend to happen more at the beginning, so there should be no alarm. It’s just that the schedule for collisions gets pushed back and the eager collective of particle physicists have to wait longer for new data. This gives us theoretical folk just a little more time to place bets as to what we will see come out of the LHC accelerator.

I want to describe the ‘bets’ that are made to find the missing link of the Standard Model: the Higgs particle. So if you want to hear about some odds, follow me through some reading of specs.

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About a couple of years ago I received, to my surprise, an invitation to be the token string theorist in the annual conference “Loops 2007″. Over the years, especially during my long term stays at the Perimeter Institute, I befriended quite a few people from the loop community. Mexico is always a pleasure to visit, and there is practically no jet lag involved, so I could just fly in and out of there, in between getting a few days to go around with my camera and enjoy a picturesque colonial town. So, I thought to myself, why not?

Of course, there was also the small issue of what to talk about. Previous such talks involved string theorists reviewing recent developments in the field, and where progress has been made. Nothing is wrong with that, but I thought I’d go a different route. Years ago Lee Smolin asked me why I don’t work on LQG (Lee is a true believer, and a direct sort of guy, I respect that), so I thought I’d use my hour to give a detailed answer. Without being overly obnoxious, of course, I would not want people having the wrong impression of us string theorists…

Naturally, one hour is not enough for such a large topic, so I had to narrow it down to cover just one major issue, and I chose to talk about background independence. Among all the fundamental differences between different approaches to quantum gravity (including for example, what does it mean to quantize gravity), this to me seems like the one needing most clarification. It is the one expression most likely to be used as a mantra, or as the one answer fitting almost any question, so basic and primary that evidently no elaboration is needed.

So, I’ve done my part now, I have given the talk, which was a real pleasure, and I have now expanded it to this writeup. In the process I have learned that writing a polemic is not as easy as it looks…I hope someone enjoys reading this, and it provokes a few useful discussions. I’d be happy to answer questions if it is evident they are formed after reading what I wrote.

Update: I guess the link to the writeup is not going to be available till tomorrow, apologies for the bad planning. In the meantime anyone interested can play the traditional lunch-time game of trying to guess what is in a paper you haven’t read. Oftentimes you discover things more interesting than the actual paper, that may well be the case here.

Update (September 23rd): I am not sure how much I would trust someone who cannot manage to submit a simple PDF file to the arXiv, but here it is finally, knock yourselves out.

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Yarr, ye scurvy dogs. Me here talkin’ pirate, seeing as it’s talk like a Pirate day (Thanks Todd) and me thinkin what would Pirate’s physics must look like. Being prone to long explanations and other yarring expletives, methinks we shall talk about proper designs of planks fer walking the plank.

Seeing as planks are ye olde version of good ole trampolines, we should be talking about trampolines and other springy designs to entertain the pirate, modern and old, yarr. And we be seein’ you turned into chum, yarr. So stay hooked fer we wil talk endlessly about our honorary Pirate, ye olde Robert Hooke, friend and chum of ye olde Captain Hook.

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Essay contest

The always enigmatic FQXI foundation (try to guess the acronym!) announced a while ago its first essay competition. The topic is “the nature of time” and it has the potential to be very interesting (or not). From the perspective of a string theorist, this is truly a foundational question, one that needs much more work, and could use a couple of new ideas. With some luck I may write something here about the issues involved in the future.

In the meantime go and read, vote and contribute! At the moment many of the essays there seem to have lots of cut and paste marks all over them, but it is still early…

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