Of Particular Significance

Blog – Of Particular Significance

It’s hard to know quite what to say about the verdict in Italy convicting scientists — experts on earthquakes — for having… for having… well, what, exactly did they do?  That’s the whole question.  They made pronouncements that tried to state that risks of a big quake, following a swarm of smaller earthquakes in the L’Aquila area of Central Italy, were low, although of course not zero.  But their wording and their calls for calm led to some people staying in their homes instead of remaining outdoors, and consequently losing their lives when, in fact, the big quake did take place soon after.   The issue is not whether they failed to predict the quake — no one is arguing they could have done that.  The issues are whether they did enough to make clear that there was a small risk of a big quake, and also, who is ultimately responsible — the experts, the government, or the public — for making the final cost-benefit analysis about the risks to individuals’ lives?

And of course, following the conviction, and a sentence of six years in prison for manslaughter, the next question is: even if this sentence is overturned on appeal, what scientist, or expert of any type, will dare to give advice to the Italian public in future, knowing that if the advice proves incomplete or unwise in retrospect, the result may be incarceration? Has Italy lost its wisest advisors?  (Four members of the “Great Risks Commission” have already resigned, including one of Italy’s greatest theoretical particle physicists, and I doubt they’ll return without new legal protections.) Will other countries lose theirs?

The issue at stake is clearly not Italian earthquakes; it is expert advice.  Sometimes I feel that we in modern society are forgetting how to be grown-ups and take responsibility for our own actions, and how to accept that bad things do just happen sometimes and it isn’t always someone’s fault.  When we go and get advice from anyone — whether it be medical advice,  financial advice,  advice about the weather or advice about the risks from earthquakes — we need to remember it’s provided by a human being.  Ideally that human being has access to the best information available and understands the odds, and will give us a recommendation based on the odds — on the probabilities for various things to happen.  But even when it is the best available advice, it’s based on odds… on statistics.  It’s an educated guess — yes, it’s educated, but also yes, it’s a guess.

And one thing that is dead certain, given that it is a guess based on odds, is that occasionally — rarely, perhaps, but not never — that guess will be wrong.   It’s inevitable, even if the expert is making the best possible recommendation, based on the best available information and the most accurate possible assessment of the odds.  When that bad guess happens, property may be lost, and people may die.  It’s sad, but it is inherent in the nature of odds and probabilities. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON October 25, 2012

Robert Garisto sent me a reply to my previous post; here it is.  [A “vev” is shorthand for a non-zero value in the vacuum of space, what I call a “non-zero average value”.]

—

Matt – Thanks for your extensive reply to my comment! Of course I agree that a scalar field without a vev can have a hard mass term. And I do agree that how the Higgs boson gets mass is at least somewhat different than how the W does.

Let’s agree to define a Higgs as a scalar field with a vev. Then I think you agree that the mass of the excitation about the vev, the Higgs boson, is not a hard mass term, one obtains it by finding the minimum of the potential as you did above. Now if there are other scalars with vevs, the mass of the Higgs boson we are concentrating on can depend on those too. But isn’t it correct to say that the mass of such a Higgs boson goes to zero in the limit that all of those vevs go to zero? If so, I would say that the Higgs boson mass is provided by the Higgs fields (all scalars with nonzero vevs).

Anyway, the main reason I made the comment is that for the purposes of explaining to the public electroweak symmetry breaking, I think it makes sense to say that the Higgs boson mass comes from the Higgs field, because it is, in the SM, proportional to the vev.  It’s also kind of neat, I think.

—

We disagree, that’s all there is to it.  What Garisto says about the Standard Model is a simple consequence of dimensional analysis, not a fundamental relation that applies widely. And no, it is not correct to say that the mass of a Higgs boson always goes to zero in the limit that all vevs go to zero; there can be first order phase transitions in which, as the parameters change, the Higgs field’s vev jumps from non-zero to zero abruptly, and the mass of the Higgs particle is never zero.  So I think to tell the public that the Higgs particle gets its mass from the Higgs field is to confuse them into thinking that the Higgs particle gets its mass the same way the other known particles do — which is false.

But in any case, we agree it’s not that big a deal.  The thing which is important for the public to understand is that the Higgs field does not give mass to all massive objects — such as atomic nuclei and black holes.  And the thing which it is important for particle physics students to understand is that the Higgs mass is not generically proportional to the vev of the Higgs field.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON October 24, 2012

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. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON October 23, 2012

With my series of articles on Fields and Particles complete, I’m continuing my series of articles on How the Higgs Field Works.  (These sets of articles require a little math and physics background, the sort you’d get in your first few months of a beginning university or pre-university physics class.)

The first article in the new series was an overview of The Basic Idea behind how the Higgs field works. (In these articles I’m mainly concentrating on the simplest type of Higgs, the Standard Model Higgs field and particle.) Then came an article about why and how the Higgs field becomes non-zero.  And the newest article explains how the Higgs particle arises as the quantum of waves that oscillate around the non-zero value of the Higgs field, and how its mass is determined by the equation of motion of the Higgs field.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON October 22, 2012

This Wednesday I was visiting the University of Massachusetts, in the currently colorful town of Amherst, where I gave a colloquium (an hour-long talk aimed at a physics department’s undergraduate majors, graduate students and faculty who are not themselves experts in particle physics) entitled The Quest for the Higgs Boson.  It’s similar to the one I gave two weeks ago at the University of Toronto, which is available on-line now. There’s audio and there are slides, but no video, so I’m afraid you’ll have to figure out on your own how the slides and audio fit together; but I think it should be fairly obvious.

If, however, you’re not a physicist or physics student, but you have been following particle physics a little bit, perhaps by reading this blog or Scientific American articles or books for laypeople by, say, Brian Greene or Lisa Randall, then you might instead want to try listening to this lecture I gave recently, which is also in the form of an audio feed plus slides.  It makes far fewer assumptions about what audience members are familiar with.  And of course there’s always my [in]famous video clips from my March 2011 public lecture on the Large Hadron Collider; a bit out of date since they were made before the new Higgs-like particle was found, but still basically covering what you need to know.

Please note these presentations are under copyright.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON October 19, 2012

Following on my series of articles on Fields and Particles, I’m building my next series of articles, on How the Higgs Field Works.  (These sets of articles require a little math and physics background, the sort you’d get in your first few months of a beginning university or pre-university physics class.)

The first article in the new series was an overview of The Basic Idea behind how the Higgs field works.  I recently revised it to make it easier to read.

The next article, just completed, is about why and how the Higgs field becomes non-zero — to the extent that we understand it.  (The following article will explain how the Higgs particle arises.)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON October 17, 2012

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