gravity

Conclusion of the Higgs Symposium

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By almost all measures, the Higgs Symposium at the University of Edinburgh, as part of the new Higgs Centre for Theoretical Physics, was a great success.  The only negative was that Professor Peter Higgs himself had a bad cold this week, and had to cancel his talk, as well as missing the majority of the talks by others.  Obviously all of us in attendance were very disappointed not to hear directly from him, and we wish him a speedy recovery.

Other than this big hole in the schedule, the talks given at the symposium seemed to me to form a coherent summary of where we are right now in our understanding of the Higgs field and particle.  They were full of interesting material, and wonderfully complementary to one another.  This motivates me to try to provide, for non-experts, some future articles on what the conference attendees had to say.  But to write such articles well takes time.  So for now, here’s the quick version summarizing the last few talks, along the lines of the summaries I wrote (here and here) of the earlier talks.  The slides from all the talks are posted here.

Here we go:

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Two Days of Polchinski Puzzles

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One of the most prominent theoretical physicists of our time, Professor Joe Polchinski of the University of Santa Barbara, who has made lasting contributions to our understanding of quantum field theory, of gravity, and of string theory, gave a couple of talks at the Institute for Advanced Study in Princeton this week.  The two presentations manifested a certain amusing (anti-)parallel; the first was on a puzzle that was thought to have been mostly solved 20 years ago, but turns out to have only been partly resolved; the second was related to a puzzle that was thought to have been solved last year, but turns out to have been partly solved over 20 years ago.

In the middle of all of this, it was announced that Polchinski was one of several people awarded one of these new-fangled Fundamental Physics Prizes that are getting lots of attention — specifically, one of the Frontiers Prizes, if you’re keeping score.  You can read about that elsewhere.  Here we’ll try to keep our focus on the science.

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Does the Higgs Field Give the Higgs Particle Its Mass, or Not?

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When I wrote my article last week about the relation between the Higgs and gravity, emphasizing that there really was no relation at all, I said that the Higgs field is not the universal giver of mass. I cited four reasons:

  1. The Higgs field does not give an atomic nucleus all of its mass, and since the nucleus is the vast majority of the mass of an atom, that means it does not provide all of the mass of ordinary matter.
  2. Black holes appear at the centers of galaxies, and they appear to be crucial to galaxy formation; but the Higgs field does not provide all of a black hole’s mass. In fact the Higgs field’s contribution to a black hole’s mass can even be zero, because black holes can in principle be formed from massless objects, such as photons.
  3. There is no reason to think that dark matter, which appears to make up the majority of the masses of galaxies and indeed of all matter in the universe, is made from particles that get all of their mass from the Higgs field.
  4. The Higgs field, though it provides the mass for all other known particles with masses, does not provide the Higgs particle with its mass.

Although it doesn’t matter too much to the main point of the Higgs-and-gravity article (since the first three points are not in question), the editor of a leading physics journal, Robert Garisto, took issue with the fourth point, arguing that I was making a statement that really wasn’t right, or at least is too strong. His argument has some merit, though in the end, I stick with my statement. I think it’s worth describing what he had in mind (as best I understand it) and why I feel strongly that one should think about it differently. There are some semantic aspects to the disagreement, but there are also some interesting and important subtle scientific points.  I don’t want to suggest that this discussion is really that big a deal — the very fact that we can argue about whether the Higgs field does or doesn’t provide the Higgs particle with its mass distinguishes the Higgs particle from, say, the W particle, whose mass indisputably arises from the Higgs field. But there’s something to learn here about quantum field theory and how the Higgs mechanism works.

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Why the Higgs and Gravity are Unrelated

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One of the questions I get most often from my readers is this:

  • Since gravity pulls on things proportional to their mass, and since the Higgs field is responsible for giving everything its mass, there obviously must be a deep connection between the Higgs and gravity… right?

It’s a very reasonable guess, but — it turns out to be completely wrong. The problem is that this statement combines a 17th century notion of gravity, long ago revised, with an overly simplified version of a late-20th century notion of where masses of various particles comes from.  I’ve finally produced the Higgs FAQ version 2.0, intended for non-experts with little background in the subject, and as part of that, I’ve answered this question.  But since the question is so common, I thought I’d also put the answer in a post of its own.

As preface, let me bring out my professorial training and correct the question above with a red pen:

  • Since gravity pulls on things proportional to their mass to a combination of their energy and momentum, and since the Higgs field is responsible of giving everything not everything, just the known elementary particles excepting the Higgs particle itself its mass, there obviously must be a deep connection between the Higgs and gravity… right? wrong.

Now let me explain these corrections one by one.

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Quick Post: More on Extra Dimensions and Gravity

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Quick post today: First, there were rumors about the Higgs particle search on Monday that got a lot of attention.  Caveat emptor: the experimentalists can’t possibly have their data in presentable form yet, so the rumors can’t be correct in every detail.   But if you are interested in a reasonable analysis of what the rumors … Read more

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