Thursday, June 6, 2013

Theoretical physicist seeks revolutions

Here is an interview of a leading physicist:
In the early 1970s, David J. Gross exposed the hidden structure of the atomic nucleus. He helped to reinvent string theory in the 1980s. In 2004, he shared the Nobel Prize in Physics. And today he struggles mightily to describe the basic forces of nature at the Planck scale (billions of times smaller than a proton), where, string theorists hope, the equations of gravity and quantum mechanics mesh. ...

Gross characterizes theoretical physics as rife with esoteric speculations, a strange superposition of practical robustness and theoretical confusion. He has problems with the popularizing of “multiverses” and “landscapes” of infinite worlds, which are held up as emblematic of physical reality. Sometimes, he says, science is just plain stuck until new data, or a revolutionary idea, busts the status quo. But he is optimistic: Experience tells him that objects that once could not be directly observed, such as quarks and gluons, can be proven to exist. Someday, perhaps the same will be true for the ideas of strings and branes and the holographic boundaries that foreshadow the future of physics. ...

Gross: Quantum mechanics remains our latest revolution. That said, some scientists are waiting for an irreducible final theory. Reductionism has proven to be an extraordinary successful method of investigation. The Standard Model is a very precise, reductionist theory. But it wasn’t radical.

Simons Science: When you chaired the 25th Solvay Conference in 2011, you observed, in your opening remarks, that there is “confusion at the frontiers of physics.” Why?

Gross: A scientific “frontier” is defined as a state of confusion. Nonetheless, we have a big problem: Physics explains the world around us with incredible precision and breadth. But further explanation is highly constrained by what we already know. Theories of quantum gravity, for instance, represent serious challenges to our current theoretical framework.

Simons Science: String theory strives to unite all four fundamental forces: electromagnetism, radiation (weak), nuclear force (strong) and gravity.

Gross: First of all, string theory is not a theory. The Standard Model is a theory. String theory is a model, a framework, part of quantum field theory. It’s a set of rules and tricks for constructing consistent quantum states, a lot of them.

Simons Science: At Solvay, you said the hope that string theory would produce a unique dynamical description of reality appears to be a “mirage.”

Gross: String theory is not as revolutionary as we once hoped. Its principles are not new: They are the principles of quantum mechanics. String theory is part and parcel of quantum field theory.

The theoretical structure of modern physics is a lot bigger and richer than we thought, because it’s a theory of dynamical space-time, which must incorporate gravity, a force that is not yet integrated into the Standard Model.

There are frustrating theoretical problems in quantum field theory that demand solutions, but the string theory “landscape” of 10500 solutions does not make sense to me. Neither does the multiverse concept or the anthropic principle, which purport to explain why our particular universe has certain physical parameters. These models presume that we are stuck, conceptually.
Gross is hung up on the idea that physics needs revolutions. He sounds like a Marxist saying stuff like this.

At least he admits that string theory, “landscape”, multiverse, anthropic principle, etc. have flopped. But his reason is that they are not revolutionary enough!
Simons Science: Is it possible to falsify string theory/quantum field theory? Or is that a purely philosophical question?

Gross: The question of how we decide whether our theories are correct or wrong or falsifiable has a philosophical aspect. But in the absence of empirical data, can we really judge the validity of a theory? Perhaps. Can philosophy by itself resolve such an ontological quandary? I doubt it. Philosophers who contribute to making physics are, thereby, physicists!

Now, in the last century, great physicists such as Ernst Mach, Bohr and Einstein were also philosophers who were concerned with developing theories of knowledge. Einstein famously criticized Heisenberg for focusing only on observable entities, when there can be indirect evidence for entities that cannot be seen. It may be the same with string theory.

Simons Science: Is the revolution at hand?

Gross: Those of us in this game believe that it is possible to go pretty far out on a limb, if one is careful to be logically consistent within an existing theoretical framework. How far that method will succeed is an open question.
It sounds as if he is clinging to the silly idea that some hidden variable theory is going to revolutionize physics.

I should credit him with saying that physics already explains the world, that further explanation is constrained by present knowledge, and that all the current revolution attempts are failures.

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