Monday, November 10, 2008

Party String Theory

And of course you go to a party and of course someone asks you what you do and of course you say string theory and of course what is it ? and of course you don't know where to start. // Classic.

So it gets you thinking about how to present string theory and so you find one way and so you feel warm inside and so you post a post. // Classic.

A good way to introduce string theory is as a conceptual framework that unifies the two current pillars of theoretical physics : general relativity and quantum mechanics. To give a feel of what string theory is about, it suffices to focus the explanations on just one specific (but pretty central) aspect of each theory : black holes for GR, the uncertainty principle for QM.

1. The central result of Einstein's general relativity is that a very massive object -- or equivalently a very energetic object, remember E=mc^2 -- has the effect of curving the neighbouring space-time (which in fact implies gravity...). But there is a bound to this phenomenon, since if an object is too massive, it will curve space-time so much that it will end up tearing it apart and creating a black hole. (As an illustration, imagine space-time had only two dimensions, and think about it as a stretched piece of cloth ; putting heavy objects on it will curve it, and if an object is heavy enough it will make a hole in it.)

2. At the heart of quantum physics lies Heisenberg's uncertainty principle, according to which a particle cannot have both a precise position and a precise momentum (mass times speed). There is a tension between the precisions of those two properties : if the position of a particle is determined with great accuracy, unavoidably its momentum becomes very uncertain -- we know precisely where it is but not where it is going nor at which speed it is moving. And inversely, if the momentum is precise, it is the position which becomes uncertain, as if the particle were dissolved into some sort of a fuzzy cloud...

Now if you ask the philosophical question of knowing what is the ultimate building block of reality, and that you undertake to break objects down into little pieces, then in littler pieces, and then yet littler and so on, there will be a point where the piece you consider is so small that by the uncertainty principle its momentum (and so its energy) is so fuzzy that it can produce a black hole. From this point, the division process cannot be carried any further.

String theory aims at describing what is happening at this ultimate scale, where tiny black holes appear and disappear randomly by quantum fluctuations, and where the very notions of space and time lose their pertinence...

[Poetic suspension]

What we call "reality" is nothing but the surface of a chaos of black holes...

[Poetic suspension again]

And hence holography, AdS/CFT, and the like. Good.


On a related note, people are usually amazed when I tell them that I switched from philosophy and art to physics. The most coherent explanation in my bag of tricks has to do with my interest in perception and the essence of reality, but I think I just found a new twist on it, as I was staring at the moon (beautifully speckled tonight). It goes something like this :

At some point in my early life it occurred to me that creation was the purest source of joy (this expression is in fact taken from my application letter to Oxford -- how naive I was...). So that might explain why I was interested in arts and why I even wanted to become a painter. But I was aware (I think) that the product of an artist's creation is not a work of art (although it is, don't get me wrong !), but rather a new perspective on existence.

[Which example could I find to illustrate that ??? I reckon that if you don't already know it, it will be quite impossible to convince you... For example when the Gothic cathedrals started to be built with thinner walls and with more light, it was not (even though maybe ingenuously it was) to make a "pretty" building, but to be in phase with the evolution of the societies from a feudal to a seigniorial organisation. (About this fascinating topic I recommend the brilliant book L'Art féodal et son enjeu social by André Scobeltzine.) But it is not a real good example, because the notion of artist was ill-defined at the time... Anyways !]

OK so the point is that what I am doing currently, namely theoretical physics, is also a creative venture. And what the theoretical physicist creates [notice my emphasis on the "theoretical" bit ? ; )] is not an article, not even a physical theory (although it is, don't get me wrong !), but -- reality itself !

Just like the philosopher in fact... And like the artist as well in fact... I'm afraid I would have utterly lost my party interlocutors by this time in fact... Perhaps that explanation ought to be substantiated more substantially in fact...

Addendum : Well my basic intuition arises roughly from the following type of considerations. Before Galileo the earth was the centre of the universe. It's not just that everybody wrongly thought it was. Go back to Timbuktu : if nobody sees the Dalmatian in the picture then there is no Dalmatian in the picture. Peace.