Tuesday, August 19, 2008

Coolest place on earth

I've not blogged for over a week because life has been getting busy here at CERN. The buildup to the Strings 2008 conference kept me rather occupied. Alas my attempt to go down into the LHC tunnel (with the help of Indian experimentalists working at one of the detectors) narrowly failed because it's now officially closed to visitors.

The Strings 2008 conference had - unusually for a Strings conference, but understandably given the location - an entire session devoted to the LHC, yesterday afternoon. In three successive talks we learned about the design and construction of the machine, the design and construction of the detectors and the new physics that we anticipate learning about once the machine starts taking data.

One striking fact is that because such strong magnets need to be superconducting to function, the insides of the LHC are cooled to 1.9 Kelvin. That's not just colder than anywhere on earth - it is actually colder than outer space! That's because (for those readers not familiar with physics) the entire universe is at a minimum temperature of 2.7 Kelvin, the temperature of the so-called Cosmic Microwave Background Radiation found everywhere and believed to be the residue of the Big Bang in which the universe originated.

Now there are certainly laboratories where much colder temperatures than 1.9 Kelvin are achieved (it's hard to be "much colder" than 1.9K since one can't go below absolute zero, but in this range tiny changes make a big difference on physics). The world record as far as I know is 100 picoKelvin or a ten-billionth part of a Kelvin above zero.

However the LHC isn't just a very very cold little box in the lab, but achieves its temperature over its entire 27 kilometre circumference. That certainly makes it unique and CERN's media-savvy publicists now describe the laboratory as "the coolest place on earth".

As for the functioning of the machine - last week a test beam was sent around one-eighth of the ring, approximately 3 km, and we were told that it worked on the first shot. On September 10 a test beam will be sent all the way around (I mentioned this in a previous posting "LH but no C", but now the date is known). Finally the first collisions will take place after the official inauguration, which is to be accompanied by huge fanfare and loads of European politicians, on October 21 2008.

As a tailpiece - in the last three weeks I've heard countless "scenarios" about what the LHC will find, and every speaker has had an item like "Totally unexpected result" as one of the possibilities. Obviously they don't spend much time on this item as - by definition - there isn't anything to say about it. But this raises a new question - or perhaps meta-question. Will the LHC find any of the wide spectrum of phenomena that has been predicted, or something that all the theorists somehow missed? I feel this can have a major impact on the enterprise of theoretical physics - at least that part of it that deals with regimes of energy not yet subjected to experiment.

Either it's good to keep working on theories and hope experiments will later vindicate them, or else we humans lack the ability to make progress without experiment as a guide. Clearly the former possibility will please theorists and the latter one will please experimentalists. I wonder if the LHC will (at least in particle physics) tilt the balance in one direction or the other.

1 comment:

Rahul Basu said...

Much as I look forward to what the LHC will find (my future as a high energy phenomenologist might depend on it, unlike those of condensed matter physicists or string theorists) this publicity blitz about 'colder than outer space' from CERN, while technically true, is getting to be a bit over the top. (I even used it in my talk on the LHC 2 years ago but it sounds too hackneyed now even though I have left it in). And as might be expected, some condmat people have started taking pot shots at it e.g here is Doug Natelson:

I understand that the folks at CERN feel like it's important for people
to be aware of the LHC and get excited about it - at this point, it
looks like it's going to be the only game in town in a few years for the
frontier of high energy physics. Still, the steady stream of publicity
(much of it arguing that they're going to unlock the secrets of the
universe, prove string theory, find evidence of extra dimensions, etc.)
is getting to be a bit much. Today comes this article discussing the
cooldown of the magnets for the collider and the detector.
Technologically impressive to be sure, but the whole "colder than deep
space" angle is pretty lame - people have been able to reach these
temperatures for nearly 100 years, and superconducting magnets are used
in thousands of MRI machines the world over. We get it - it's a big
machine. If this is the level of publicity hounding that's going on
before they even have a single piece of data, the coverage of the actual
physics runs is going to be really oppressive.

True, its over a bigger scale than MRI machines which Mr Natelson seems to have overlooked or not understood, but as I said, repetition is not making it more impressive. Perhaps it's time to cool down (!) and wait for the actual results which I have no doubt will be exciting enough. We have not had a significant discovery machine in a long time.
Precision tests are hardly as exciting, except to the cognoscenti.