Sunday, March 25, 2007

Physics, then and now

I get into a tin can, and make a long flight to my parents' home. While trying to keep awake to get over jetlag, I see an oldie in my father's bookshelf - "Elementary Particles - A Short History of Some Discoveries in Atomic Physics - The Vanuxem Lectures, 1959", by Chen Ning Yang.

It begins thus (emphasis added by me):

"AT THE TURN of the century the world of physics was clearly coming into the dawn of a new era. Not only did the brilliant achievements of classical mechanics and of the Faraday-Maxwell theory of electromagnetism bring to a successful termination the era of classical macroscopic physics, but there were already in the air everywhere new phenomena, new puzzlement, new excitement, and new anticipation. Cathode rays, photoelectriciy, radioactivity, the Zeeman effect, X-rays, and the Rydberg law of spectral lines were all recent discoveries. What the new era would have in store was of course difficult to predict at that time. Among other things, there was much discussion of the possible atomic structure of electricity. But let us recognize that although the concept of the atomic structure of matter had been speculated upon since early times, such speculation could not be entered into the books of scientific knowledge. For without quantitative experimental verification, no philosophical discussions can be accepted as scientific truth. For example, as late as 1897, Lord Kelvin, a giant in the world of physics in the latter part of the nineteenth century, still wrote that the idea that "electricity is a continuous homogenous liquid" (rather than having an atomic structure) deserved careful consideration."

Physics, now, via Peter Woit's Not Even Wrong, where Peter does a great job of recording the atrocities:

Physicist Mark Srednicki:

"We see that the big issue for Brian, and for just about all scientists (though with the apparent exceptions of Lee Smolin and Peter Woit), is what is TRUE. Not what corresponds to some philosophy of what science is or is not. Lee writes that the landscape must be rejected because “it would mean the end of our field” (page 165). It should be obvious that this is not the basis that is traditionally used for accepting or rejecting a theory! Peter’s (essentially the same) argument that string theory must be rejected because (at the moment) it does not appear to be sufficiently predictive (for Peter) is also irrelevant to the question of whether or not string theory is TRUE.

If the landscape is right, we may never get anything more than circumstantial evidence that it’s right. But that’s often the case in science. We’ve been spoiled in particle physics by having extremely precise data and highly predictive and quantitative theories for the past few decades. Most of the rest of science has not been so lucky. Perhaps we will not be so lucky going forward. The only way to find out is to do more work and see where it leads."


Bears repeating:

"For without quantitative experimental verification, no philosophical discussions can be accepted as scientific truth."


I'll also venture to say that particle physics faces the prospect of a new generation of physicists who actually know less than their predecessors. For all the personal knowledge of the interplay of experiment and theory may vanish as one generation retires, and is replaced by a new generation that knows mainly extremely sophisticated mathematics. We have to hope that Nature is more providential.


nige said...

What's interesting for me is the contrast in the way maths is used.

My understanding of "physics" is that you proceed from data to formulate laws, and then you check those laws by making predictions well outside the range of the data which suggested the laws. If the predictions are right, you then try to come up with a theory to unify the laws and perhaps explain them in terms of a deeper underlying concept.

This holds for most of the advances in physics.

Hence, particle physics was first sorted out by the eigthdold way when it was realised that particles could be arranged into symmetric patterns if their strangeness was plotted against their isotopic spin.

This was an abstract symmetry, but it left an empty space in one of the plots, which predicted the omega minus with its properties in 1961, and the omega minus was discovered in 1964.

Then the eightfold way was explained by quark theory, which in turn was checked in high energy scattering experiments, and led to QCD, which led to asymptotic freedom, explaining the size of nucleons and other particles, and leading to more checks.

String theory is the very opposite. The string theorist decides to explain a few unobserved speculations (spin-2 gravitons, unification of standrad model forces into an unobservable superforce near the unobservable Planck scale), using more unobservables (supersymmetry with an unobservable supersymmetric partner for every observable particle, extra dimensions, etc.), in the process requiring a complex Calabi-Yau compactification of the extra dimensions which makes for a landscape of an incredible number of solutions, preventing checks.

So string theory is worse than any other theory, not just because it doesn't make checkable predictions, but because nothing factual has gone into it.

Even if it worked, it isn't based on facts, just speculations. Suppose string theory was a perfect success and really did unify spin-2 graviton theory with the theory of Planck scale unification. So what? Neither of these have been observed. Even if the theory was a complete unification of these speculations, it would still be a speculation.

It's just not addressing any physical facts in the first place.

String theory has been accorded so much hype and celebration prematurely, that it's invincible.

The irony is that even those string theorists who are relatively willing to discuss the problem, are duped. Over on Asympotia, one says that if alternative theory was as good or better than string theory, people would take it seriously and work on it.

String theory being a complete religion, any alternative which addresses the facts should be considered better than string theory. They are just completely deluded, and it's a genuine self-brainwashing on the part of these string theorists. They believe in their cause religiously.

The proof string theory is a religion is really to be seen in the way they either ignore or attack all alternative ideas, including those of Smolin, as being non-serious.

It's not the "string" that the problem, it's the way they are trying to put ideas together.

What evidence is there that strings vibrate at different frequencies to produce different types of particles?

Why not just have loops of string (energy, field lines) of different combinations to give different particles, or some kind of preon idea? There are so many layers of abject speculation involved in string theory, it's inconceivable it could be anything but a massive gamble, yet without the risk of a gamble because it can't be falsified.

I think people should be working from the data and trying to formulate empirical models, then trying to unify these empirical models theoretically. This is the proper way to do physics. Even Dirac's equation was not a complete guess, because he was unifying two empirically validated theories, quantum mechanics and special relativity.

String theory is really a mathematical philosophy, and you have to go right back to Plato's theory that atoms are geometric constructions, to get an analogy to the methods and thinking of string theory. They're really following the mentor of Plato, Aristotle, who claimed that physics is about pure reasoning, not working from experimental data.

(I apologise for the length of this comment.)

nige said...

"Even if the theory was a complete unification of these speculations, it would still be a speculation."

Just to clarify, my point here is that string theory has got to unify or explain something observed before it even qualifies as a speculative theory.

If string theory did explain say the facts of the Standard Model, then it would at least be an ad hoc model. It doesn't.

This is why I think Smolin and Woit, who do at least model observables without requiring extra dimensions, are more successful than string theorists.

Luboš Motl said...

Thanks God that even at the level of the blogosphere, things are getting a little bit sane and crackpots like you, Nigel Cook, Peter Woit, Roger Schlafly (the creationoist) and many others are getting irrelevant. Needless to say, Mark Srednicki is right on the money. Neither of the crackpots' pseudoarguments have nothing to do with the main question, namely what is the right theory and whether the theory we deal with is correct or not.

Arun said...


String theory in principle offers a unification of quantum field theory and general relativity.

What it has also demonstrated is that the physical principles we know of so far are insufficient constraints to specify the universe in the experimental domain that is available to us.

Like Democritus' atoms, string theory might be true, but it may be twenty centuries before it enters the realm of physics.