To me this is the most important question in physics. Of course, interactions are exchanges of gauge bosons. But what is happening? How do the exchanges take place?

In the past weeks, I read everything I could find about this topic. A sobering experience that I can summarize thus: white, English-speaking men know nothing about the answer. And they are even afraid of speculating about it. Other humans do not write anything about it.

Wikipedia's article http://en.wikipedia.org/wiki/Fundamental_interaction is funny: "fundamental interactions are the ways that elementary particles interact with one another". One has to be drunk to write such a definition.

Most researchers only say that interactions are "particle exchanges described by a gauge group". They speculate about various gauge groups, or about supersymmetry, or about BRST. But no one speculates about how interactions appear in the first place.

Established researchers do not explore the question. But why? They do not even speculate about it. Are they afraid? I only found the spaghetti model as candidate proposal. What a poor harvest. And of course, it is written by a white, English-speaking man. What about black women speaking Swahili? Or South-American women speaking Quechua? And what shall we do before they come along?

One friend told me about a possible background. She said that white men are so nasty among each other that anybody daring to speculate is not invited any more to talks, to committees or to conferences. "Speculators" are discarded from the academic community. They know it and they fear it. They behave among themselves in the same way that they behave towards students in examinations.

Men have organized modern physics in a way that speculation has become impossible. Progress is impossible in modern theoretical physics. Dear sisters, please come along!

Clara,

ReplyDeleteWhat is wrong with stating that gauge interactions follow from demanding that physics stays invariant to arbitrary transformations of space-time and/or field space? After all, physics cannot depend on any particular "frame of reference" chosen to describe coordinates and operators. Quoting Weinberg:

"Symmetry principles have moved to a new level of importance in this century and especially in the last few decades: there are symmetry principles that dictate the very existence of all the known forces of nature."

Cheers,

Ervin

Ervin,

ReplyDeleteinteractions do not follow from your requirement! You cannot deduce U(1), SU(2) or SU(3) in this way.

I guess I am missing your point.

DeleteGroup theory is relevant precisely because it describes symmetries. In particular, unitary groups of transformations preserve the probabilities of state transitions in quantum field theory. This is why the most important groups in particle theory are U(1), SU(2) and SU(3).

Ervin,

DeleteU(1), SU(2) and SU(3) are experimental results. Of course they preserve probabilities. But that is valid for many Lie groups. There is NO argument explaining where these particular gauge groups (instead of, e.g., SU(5), SO(10), E(6)) come from.

Dear Ervin,

ReplyDeleteElectrodynamics was formulated as a phenomenological physical theory in terms of field strengths E and B. Gauge stuff appeared later, after introducing an ambiguous function - a potential. Reading backwards is not always fruitful. "All the known forced of Nature" is a too brave and self-confident statement.

Well, in order to conserve probabilities, interactions must have symmetry groups. But these specific groups are not deduced in this way. Nor do such arguments explain why interactions exist at all. This was the point of my post.

ReplyDeleteClara,

DeleteThanks for the follow-up clarifications.Your question can be reformulated as follows:

Why does nature comply with U(1), SU(2) and SU(3) from the large set of possible Lie groups?

I concur with you that this is a foundational puzzle for which we don't have a compelling answer.

My own point of view, published in several papers, is that the source of these groups is entirely dynamical and stems from the multifractional topology of space-time at large energy scales. Albeit preliminary, this viewpoint falls in line with the concept of scale invariance in continuous dimension and leads to a number of post-dictions on SM parameters that match fairly well experimental data available to-date.

In S-matrix approach all interactions are introduced on ad hoc basis. This is because S-matrix is an ad hoc theory. All events in S-matrix approach take place inside a black box, and no one cares of what is happening inside. Only initial and final states at infinities are considered.

ReplyDeleteThe Big black box can further be decomposed into several smaller black boxes, but it is not very helpful.

The theroy that answers Clara's question should contain something more than algorithm for transforming inputs to outputs.

Let us wait for a smart woman ...

ReplyDeleteClara,

ReplyDeleteSorry if my comment is off topic, but I wish to direct your attention to Phil's blog:

http://blog.vixra.org/2012/12/05/fqxi-results/

You find there a representative sample of how theoretical physics struggles nowadays. Many researchers in Quantum Gravity associated with the Perimeter Institute have been recognized as contest winners. But NONE of these essays offer the slightest hint for how to build models that are falsifiable!

I share your disappointment.

ReplyDelete