Wednesday, October 24, 2007

Are the laws of physics emergent ?

Last monday I attended a fascinating conference by Robert Laughlin (who won a Nobel Prize for his remarkable work on fractional quantum hall effect). The meadow of his arguments is this: the behavior of the world is ultimately governed by emergent phenomena.

Let's say a kid wants to know how some simple device works, he will surely try one thing: dissasembling the device, look at each part and figure out how they work. This is what Laughlin calls the reductionist approach. Physicis has been carried this way for the past centuries, this is how we arrived to our knowledge of elementary particle physics, by dissambling the matter in to smaller chunks at increasing energies.

Emergent phenomena arraises when collective behavior suddenly becomes different from the behavior of it's individual parts, this pinpoints to one of the fundamenal characteristics of emergent phenomena: universality. This means that the collective behavior is esentially independent of the properties of it's individual parts.

This was exemplified in a funny way by Laughlin who showed Newton burried under a big pile of apples, which is an obviously different behavior from that single apple in Woolsthorpe. Note that for the sake of beeing buried under a big pile of something it won't make a difference to be buried beneath apples, watermelons or potatoes.

One of the really perturbing things mentioned by Laughlin was that Newton's first law is actually emergent and comes from a broken symmetry, this was totally unexpected for me, but maybe one enlightned reader can bring some light to this issue (please!).

But, are fundamental laws of physics emergent? There is no doubt that emergent phenomena is important and quite interesting. And of course, every reasonable physicist will tell you that we don't need to know the detailed behavior of quarks or QED for describing biology or weather.

Whatsoever I don't honestly believe we can have a complete/satisfactory knowledge can be acquired in this way, we actually need to know from where this laws emerge from. As an example, how are we going to figure (say) the properties of fundamental particles? It seems to me that if you keep asking "why?" you eventually need a detailed description, the sort of fundamental physics we have always think about.

And, this might be just a wrong perception but it seems to me that the "reductionist approach" is far more general, at least in the sense we only need to know the law of gravity (and dynamics, of course) to compute the behavior of an arbitrary number of apples, this also applies to any other system where gravity is acting. On the other side you need to have a "lot's of falling things law", "orbital's motion law", "single falling ball law", etc...


Eric Pulido said...

I also find the emergence approach to be pessimistic, but he sure made some interesting points. Apparently power laws are symptoms of some (emergent or non-emergent?) behaviors, and was one of his main points in the conference he gave at unam. However he admitted himself not to be able to show any proof of his theories after 10 years. Sadly as i said in my previous comment we could not hear much on the topic thanks to Mexican bureaucracy, so i am not well informed.

Luis Sanchez said...

Sure, some points are quite interesting. Actually there is no doubt that emergent phenomena exist and that collective "conspiracies" account for some remarkable phenomena, my favorite example is well known: the index of refraction (see Why the speed of light is reduced in a transparent medium. Mary B. James, David J. Griffiths. Am. J. Phys, Vol. 60, No. 4. ).

What concerns me is his attitude that "fundamental (reduccionist) physics" should be abandoned, that all that matters is emergent phenomena and the search for fundamental blocks is similar to the idolatry of a totem (he used a quite a funny drawing for that part). Of course, that is only the impression I got, maybe he is preaching a different attitude!

By the way, do you have some insight in to Newton's first law as an emergent one?

* L i L Y * said...

:D fuiste a la segunda? en el instituto de física? oooh tan cerca y tan lejos, iba a ir! pero se me olvidó tenia mucha tarea, y yo que me la vivia en el instituto aaa qué buena onda pero bueno saludines!

vannern said...

could emergence phenomena explain why meanwhile more and more enthusiam we pour, less and less responses among the CUCEI individuals are showed? :)

Luis Sanchez said...

Well, you probably know my thoughts about CUCEI, unfortunately enough I won't comment any further about it here.

newuniverse said...

An observer on a train sees a ball fall straight down, while one off the tracks looking into a window of the train sees the ball fall on an angled path. General relativity is based on this inertial symmetry breaking and is in part why the term "inertial frames of reference" was coined such. The special case when the dimension of time is asymmetric is Special Relativity.

General Relativity uses spatial transformations to restore symmetry and Special Relativity uses time transformations to restore symmetry.

I know. Your post is 3 years old. But I thought it was interesting!

newuniverse said...

Also, classical Newtonian mechanics can also be considered as emerging from quantum mechanics. Newton's laws are just limiting cases of quantum mechanics applied to bodies with large masses.

So we have emergent behavior based on both Relativity and Quantum Mechanics.