Tuesday, August 5, 2008

LH but no C

While there is obviously much excitement about the Large Hadron Collider here at CERN, I also sense a certain fatigue related to it. It has been talked about to death by now. Apparently all possibilities about what it will discover, from the most exotic to the most banal, have been analysed. Pessimists have predicted the death of particle physics. Optimists have predicted a resurgence of the field and a renewed thrust towards a "final theory" of all fundamental particles. There seems not much more to say until it starts gathering data.

This situation profoundly brings home to me the role of experiment in science. Most things that can be said about LHC before it starts running have been said. And yet we cannot know what it will find, or not find, until it happens. What better proof - if any were needed - that all the words in the world are not a substitute for an experimental result?

One thing I particularly like is that here the pessimists could well be proved wrong. In everyday life, pessimists usually take the "safe" option and too easily end up looking "cool". If you are pessimistic about politics, or human behaviour, or the environment, you are usually right. But about the Higgs, or supersymmetry - sure, be pessimistic if you like, but you could have to eat your words and they may end up more indigestible than all the blue cheese in Gex!

In a comment on a previous blog I was asked if there is any betting going on. I don't know if there is -- it hasn't come up in discussions at which I've been present, at least so far. But if there's one thing to bet on right now, it would be the date on which the machine is turned on. Current gossip indicates late August/early September. But all that will happen then is that a single proton beam will circulate in one direction through the tunnel. So it will be a case of Large Hadron, but no Collider! Of course it will be a crucial test for the magnets and everything else, but having two beams circulating in opposite directions, and then making them collide, and then collecting the data, and analysing it... It's all a long way off. Till then, we have only our words for company.

6 comments:

Ramanan said...

In particle physics (actually in Physics), whatever is allowed is compulsory... we dont ask why particles have to decay, rather we ask whats keeping them from decaying... everything seems to exist .. internal symmetries, symmetry breaking, etc. Its natural for supersymmetry to exist and if supersymmetry is not found, we will be left with difficult questions on why it doesn't exist. Plus of course the meeting of the coupling constants at the unification scale and the weak-mixing angle in supersymmetric models are good indicators. I think those who think that nothing can be found do not know enough field theory and cant appreciate the renormalization group and effective field theory gyaan. And they apply "sophist" logic that since string theory is wrong.. superparticles will not be found!

Sunil Mukhi said...

Ramanan, While it's nice of you to be optimistic (and so am I), the point I made in my blog could equally well be used to critique your view: yes we think a lot of things are natural, but only experiment can decide which ones are true.

I know I'm sounding a bit like a graduate student who's just woken up to the reality of experimental physics (and that is not true of me - I enjoyed my lab course in Stony Brook some decades ago and actually performed well in it too!). But the thing that I find exciting is the extent to which human pride and vanity can go up in flames when an experiment is performed. And this is just as true for optimists as pessimists...

Ludwig said...

One set of speculations is here. What do you think, reasonable? :)

alobela said...

Well said Sunil. The role of experiments in Physics is understated, I strongly feel, in our Physics curricula. When I was an undergrad I had an impression that it was natural for the most brilliant students to work on Theoretical Physics. (The tension among first year graduate students in TIFR Physics to get admission in DTP is quite well known.) Of course there are exceptions.

Ramanan said...

Yeah Sunil, of course experiments will decide what will be found but what I am saying is that there is no rational reason to dismiss supersymmetry apriori.

Ludwig, that link had an interesting item - God! Someone in the media can make an interesting headline "Scientists think that new experiments will disprove God"!

Sunil Mukhi said...

Ludwig, thank you for posting a link to Sean Carroll's comments on the Cosmic Variance blog - they are typically insightful.