Hot Topics on sci.physics.research

chroot

Hello all,

It's time for a little experiment.

As part of my constant quest to stimulate discussion and bring more technical content to physicsforums.com, I am going to occassionally provide links to posts from the usenet newsgroup sci.physics.research, which is a moderated internet-based discussion group used by a quite a number of professional physicists.

What I am attempting to do is to present to you something like what an "operating theater" is to medical students. In operating theaters, medical students watch professional surgeons work through a pane of glass, and are able to carry on their own discussion about what's happening.

My first link will appear below. Feel free to make comments!

- Warren

chroot

http://groups.google.com/groups?dq=&...ogle.com#link1

Central topics for discussion:

• The latest trends in physics are departing from the hard, cold rigor idealized by the scientific method.
  
• As difficult as these departures are to swallow, are they the natural course of physical theory? How long must we, the scientific community, be patient with theories that cannot produce predictions?
  
• How much emotion is there, or should there be, in science? As Arno Penzias said of scientists, "Of course we champion our theories! Of course we believe in them with our hearts! If we didn't, how could we bring ourselves to go to work every morning?"

- Warren

Ambitwistor

When has the trend in physics ever been towards "cold, hard rigor"? If anything, cutting-edge physics is a messy, seat-of-the-pants, guessing kind of business. The cold, hard rigor comes later, after the mathematicians jump in.

As long as nothing that can produce predictions comes along.

That's rather overstating things. Sure, if you're working in a field, it's probably because you think it's better than the alternatives. But that doesn't mean you have to lose your self-skepticism.

selfAdjoint

I believe we already have a couple of threads going on this topic over on Strings Branes and LQG. Let me throw this out; there is no branch of theoretical physics at all that is satisfactorily grounded in mathematical rigor. None.

And in my opinion that isn't the fault of the physicsts, who are not overimpressed with rigor, but of the mathematicians and mathematical physicsts, who have taken up the task of supplying the rigor and have failed.

Ambitwistor

Oh, sure there is. Newtonian mechanics. Electromagnetism. General relativity. Most of statistical mechanics and quantum mechanics. These fields have rigorous axiomatic definitions, and there are rigorous theorems concerning the existence and uniqueness of solutions, etc. It's just that physicists rarely bother to make use of the available rigor. Rigor is lacking mostly in quantum field theory. It's also lacking in fluid mechanics; a Millenium Prize goes to the person who can rigorously prove existence/uniqueness theorems for the Navier-Stokes equations.

selfAdjoint

When you say quantum mechanics is rigorously based, beware. There are mathematical objections to the way it handles Hilbert Space. And the more I get into GR the more I see statements like, well this spacetime wouldn't be well-defined unless we ---- but we can't. And don't forget those singularities.

One theory you left out war special relativity. In its own little world, separated from everything else, it's rigorous. Sort of like thermodynamics. No existence theorems though.

As for Newton, what about those theorems in which massive bodies get hurled to infinite distances in finite times? Is this a feature of a well-posed theory?

Ambitwistor

I don't think so. There may be mathematical objections to how some physicists handle Hilbert space.

Like what?

What about them? You can speak rigorously of a manifold with singularities; cf Hawking and Ellis.

I included it in general relativity, which is also rigorous.

The Saari and Xia result? It's a feature of a mathematically rigorous theory (and it was published by mathematicians, in a mathematical journal). Whether it makes physical sense is another matter. Equations can have singular solutions, you know: that doesn't mean that there is anything non-rigorous about defining or solving them.

Adam

Seems to me that science and eng people are out there doing their thing. But the net is allowing a load of crackpots and Arts student philosophers to throw out barely educated opinions about everything. Sagan was cool, but the popularisation of science by him and Hawking has got a lot of people into coffee table books about semi-science. Sure, I'm only a beginner myself, but even I sometimes get miffed at some of the idiocy out there.

There will always be whacky theories. I think we in fact need some emasure of whackiness, just to make sure we don't get stuck in a rut. Allow imagination, inspiration, et cetera. Just never allow it to gather any authority until it proves its value in each case.

I know I only do well in subjects I enjoy. I am more eager to read and learn if/when I like the subject. I wish I could forget about further classes and simply leap straight into funded research. I have some nifty ideas. But research funding is virtually non-existent in Australia.

Nereid

Here's a somewhat oblique comment: There are far, far more really, really bright people working on leading edge physics today than at any time in the past, and they have to hand tools and techniques which earlier generations of physicists could hardly have dreamed of, let alone use.

And yet, and yet, ... these people are still all just people, who live in communities where careers, money, jealousy, spite, altruism, and the whole nine yards are alive and kicking just as they were one to ten (and more) generations ago.

As the thread you posted, Warren, shows there is the same process of myth formation ('little else left for physics at the turn of the century') and its coincidental relationship to what actually happened; similar debates about predictions and refutations, proofs and consensus; experiment and theory; ...

Apart from some (early?) work to apply scientific methods to the study of the real process of physics itself (the myth* gives Kuhn much kudos), has there been a qualitative change? If we can get far enough away, does today's landscape look 'just like' that of any other time (in western societies, since the Dark Ages)?

*I mean 'myth' in the sense of the widely held perceptions/beliefs; no intent to imply anything - one way or the other - about history.

James

Its a requirement of a physical theory to make predictions. I can't think of a 'hot topic' in theoretical physics which doesn't make predictions. Testable predictions is another matter. By testable I mean having the capability to experimentally test.

Haelfix

Quantum Mechanics is rigorously defined nowdays, with the Wiener measure.

There are some fishy things with certain physicist solutions to particular problems, but they have been solved rigorously (albeit in more complicated language).

One has to be careful with domain and range issues with unbounded, noncompact operators for instance. Indeed the Bra-Ket formulation can lead to some pretty nasty errors if you are not careful.

But more or less, its solved.

QFT otoh, can be rigorously constructed, however huge classes of acceptable experimentally verified solutions are sometimes excluded. Its very puzzling in many ways, you have to play around with particular problems to try to make sense of them. Then you have problems with landau poles, operator ordering, careless use of complex structures (you do damage to your geometry if your not careful) and abuse of wicks theorems. Also canonical quantization and the path integral seems more and more likely to not be the same thing, unless you are very very careful..

S = k log w

"Cold Hard Rigor" v theories that do not produce results?

It is curiosity that drives people to invent ideas, be they irreproducible or proven. It is the discipline of science tests in reality the validity of an idea. Sometimes there is no proof. They remain theory. "Proof" is subjective. Something can be proven and accepted as the body of knowlege as "Truth" until, that is, someone else disproves the convention. Sometimes it is not based on science, rather in spite of it. The man who had invented the starter motor for the automobile did not know that it was theoretically impossible for a 'dead short' to work. Historically it was the invention of the prism and of the telescope, which at first were considered toys for children that was the big ahh haa! That led to the age of discovery.
Many silly ideas, and silly inventions, such as perpetual motion machines had been attempted. But significantly was the concept that the unverse might be understandable, and controlled by man. It led to experiments which eventually became scientific discipline. It also caused the industrial revolution. The parents of science technology are sand, doubt, child's play, wonder, awe, and ego. Perhaps a poet had worded it best.

To see the world in a grain of sand
And Heaven in a wild flower
Hold Infinity in the palm of your hand
And Eternity in an hour

William Blake

Nereid

Surely this is one of the most enduring of the myths of science! Why? Because, if true, the Mayans, Aztecs, Incas, Harappans, Dravidians, Chinese, ... would have discovered all the early post-Dark Ages things we mostly attribute to modern physics. And they would have done so at least 2,000 years ago! Even in astronomy and mathematics, even starting as late as the Greeks, there should have a Kepler and a Leibitz well before 0 BC.

Just to take the 'concept that the unverse might be understandable, and controlled by woman', didn't the ancient Greeks and Chinese have this, in spades?