Of Particular Significance

Why the Higgs Particle Matters

Matt Strassler, July 2, 2012

[Updated slightly, to reflect the fact that a Higgs of some type has been discovered, as announced at the LHC on July 4th, 2012.]

Most of us learned in school, or from books, that all the materials around us — everything we eat, drink and breathe, all living creatures, and the very earth itself — are made from atoms. These come in about 100 types, called “the chemical elements”, and are typically found arranged into molecules, as letters can be arranged into words. Such facts about the world we take almost for granted, but they were still hotly debated late into the 19th century. Only around 1900, when the actual size of atoms could finally be inferred from multiple lines of reasoning, and the electron, the subatomic particle that inhabits the outskirts of atoms, was discovered, did the atomic picture of the world come into focus.

But even today, some lines in this picture are still fuzzy. Puzzles dating back a century still remain unresolved. And the “Higgs boson” hullabaloo that you’ve been hearing about has everything to do with these deep questions at the heart of our own existence. Some of these blurry areas may soon become clearer, revealing details about the world that we cannot yet discern.

We learned in school that the mass of an atom comes mostly from its tiny nucleus; the electrons that form a broad cloud around the nucleus contribute less than a thousandth of an atom’s mass. But what most of us didn’t learn, unless we took a college class in physics, is that an atom’s size — the distance across it — depends mainly on the electron’s mass. If you managed somehow to decrease the mass of the electron, you’d find atoms would grow larger, and much more fragile. Reduce the electron’s mass by more than a factor of a thousand or so, and atoms would be so delicate that even the leftover heat from the Big Bang that launched our universe could break them apart. And so the very structure and survival of ordinary materials is tied to a seemingly esoteric question: why does the electron have a mass at all?

The mass of the electron, and its origin, has puzzled and troubled physicists since it was first measured. Complicating and enriching the puzzle are the many discoveries, over the past century, of other apparently elementary particles. First it was learned that light is made from particles too, called photons, that have no mass at all; then it was learned that atomic nuclei are made from particles, called quarks, that do have mass; and recently we found strong indications that neutrinos, elusive particles that stream from the sun in droves, have masses too, albeit very small ones. And so the question about the electron became subsumed in larger questions: Why do particles like electrons, quarks and neutrinos have mass, while photons do not?

In the middle of the last century, physicists learned how to write equations that predicted and described how electrons behaved. Even though they didn’t know where the electron’s mass came from, they found it easy to put the mass, by hand, into their equations, figuring that a full explanation of its origin would turn up later. But as they began to learn more about the weak nuclear force, one of the four known forces of nature, a serious problem emerged.

The physicists already knew that electric forces are related to photons, and then they realized further that the weak nuclear force is related, similarly, to so-called “W” and “Z” particles. However, the W and Z differ from the photon, in that they do have a mass — they are as massive as an atom of tin, over a hundred thousand times heavier than are electrons. Unfortunately, the physicists found they could not put masses for the W and Z particles by hand into their equations; the resulting equations gave nonsensical predictions. And when they looked at how the weak nuclear force affected electrons and quarks and neutrinos, they discovered that the old way of putting in the electron mass by hand wouldn’t work anymore; it too would break the equations.

To explain how the known elementary particles could possibly have mass at all required fresh ideas.

This conundrum emerged gradually in the late 1950s and early 1960s. Already in the early 1960s a possible solution emerged — and here we meet Peter Higgs, and the others (Brout, Englert, Guralnik, Hagen and Kibble.) They suggested what we now call the “Higgs mechanism.” Suppose, they said, there is an as yet unknown field of nature — like all fields, a sort of substance present everywhere in space — that is not zero, and uniform across all of space and time. If this field — now called the Higgs field — were of the right type, its presence would then cause the W and Z particles to develop masses, and also would allow physicists to put the electron mass back into their equations — still putting off the question of why the electron’s mass is what it is, but at least allowing equations to be written down in which the electron’s mass isn’t zero!

Over the ensuing decades the idea of the Higgs mechanism was tested in many different ways. We know, today, through exhaustive studies of the W and Z particles, among other things, that something like this is the right solution to the conundrum posed by the weak nuclear force. But the details? We don’t know them at all.

What is the Higgs field, and how should we conceive of it? It is as invisible to us, and as unnoticed by us, as air is to a child, or water to a fish; in fact even more so, because although we learn, as we grow up, to become conscious of the flow of air over our bodies, as detected by our sense of touch, none of our senses provide us with any access to the Higgs field. Not only do we lack a means to detect it with our senses, it proves impossible to detect directly with scientific instruments. So how can we hope to tell for sure that it is there? And how can we hope to learn anything about it?

There is one additional way in which the analogy between air and the Higgs field works well: if you disturb either of them, they will vibrate, forming waves. In the case of air, it’s easy to make these waves — just shout, or clap your hands — and our ears can easily detect these waves, in the form of sound. In the case of the Higgs field, it’s harder to create the waves, and harder to observe them. To make them requires a giant particle accelerator, called the Large Hadron Collider or LHC, at the CERN laboratory outside Geneva, Switzerland; and to detect them demands the use of building-sized scientific instruments, which go by the names of ATLAS and CMS.

How is it done? Clapping your hands will reliably make loud sound waves. Smashing two very energetic protons together, using the LHC, can make very quiet Higgs waves, and very unreliably — only about one in every ten billion collisions will do this. The wave that emerges is the quietest possible wave in the Higgs field (technically, a single “quantum” of this type of wave.) We call this quietest possible wave a “Higgs particle”, or “Higgs boson”.

Sometimes you will see the media call this the “God particle”. This term was invented by a publisher to sell a book, and thus has its origin in advertising, not in science or religion. Scientists do not use the term.

Making a Higgs particle is the relatively easy half of the process; detecting the Higgs particle is the hard part. While a sound wave will travel freely from your clapping hands across a room to someone else’s ear, a Higgs particle disintegrates into other particles faster than you can say “Higgs boson”… in fact, in less time than it takes for light to travel across an atom. All that ATLAS and CMS can do is measure the debris from the exploding Higgs particle as carefully as possible, and try to work backwards, like detectives using clues to solve a crime, to determine whether a Higgs particle could have been the source of that debris.

It’s even harder than this. It’s not enough to make one Higgs particle, because its debris isn’t sufficiently distinctive; often a collision of two protons will in some other way create debris that resembles what might emerge from a fragmenting Higgs particle. So how can we hope to determine that Higgs particles have been formed? The key is that Higgs particles are rare but their debris is relatively regular in appearance, while the other processes are common but more random; and just as your ear can gradually pick out the singing tone of a human voice even above heavy static on a radio, so experimenters can pick out the regular ringing of the Higgs field amid the random cacophony created by the other similar-looking processes.

Carrying this out is extremely complex and difficult. But in a triumph of collective human ingenuity, it has been done.

Why was this Herculean task even attempted? Because the profound importance of the Higgs field for our very existence is matched by our profound ignorance of its origin and properties. We do not even know that there is only one such field; there may be several. The Higgs field may itself be a complicated thing, built somehow out of other fields. We do not know why it is not zero, and we do not know why it interacts differently with different particles, giving the electron a very different mass from, say, the type of quark we call the “top quark”. Given the importance of mass not only in determining the size of atoms but in a whole host of other properties of nature, our understanding of our universe and ourselves cannot be complete and satisfactory while the Higgs field remains so mysterious. Studying the Higgs particle — the waves in the Higgs field — will give us our first profound insights into the nature of this field, just as one can learn about air from its sound waves, about rock by studying earthquakes, and about the sea by watching waves upon the beach.

Some of you will inevitably (and fairly) ask: This may be inspirational, but what good is all this to society, in a practical sense? You may not like the answer, but you should. History shows that the societal benefits of research into fundamental questions often do not emerge for decades, even a century. I suspect you used a computer today; I doubt that, when Thompson discovered the electron in 1897, anyone around him could have guessed at the huge change in society that electronics would bring about. We cannot hope to imagine the technology of the next century, or to envision how seemingly esoteric knowledge gained today may impact the distant future. An investment into fundamental research is always a bit of an educated gamble. But at worst, we are very likely to learn something about nature that is deep, and has many unforeseen implications. Such knowledge, though without clear monetary value, is (in both senses) priceless.

In the interest of brevity, I have oversimplified; things needn’t have turned out quite this way. It was possible that the waves in the Higgs field wouldn’t have been discoverable, much as an attempt to make waves in a lake of asphalt or thick syrup will end in failure, for the waves will die away before they ever really form. But we know enough about the particles of nature to know this could only have happened if there were other particles and forces as yet undiscovered, and some of these would have been accessible to the LHC. Alternatively, even though the Higgs particle (or particles) existed, they might have been somewhat harder to produce than expected, or might have typically disintegrated in somewhat unexpected ways. In all of these cases, it might have been several more years before the Higgs field began to reveal its secrets. So we were prepared to be patient, though hoping we wouldn’t have to explain these complexities to the media.

But we needn’t have worried.

The discovery of the Higgs particle represents a historic turning point — a triumph for those who proposed the Higgs mechanism, and for those who operate the LHC and the ATLAS and CMS detectors. Yet it does not represent the end to our puzzles about the masses of the known particles, only the beginning of our hope of solving them. As the energy and collision rate at the LHC increase over the coming years, ATLAS and CMS will be pursuing exhaustive and systematic studies of the Higgs particle. What they learn may allow us to resolve the mysteries of this mass-giving ocean in which we swim, and will propel us forward on our epic journey begun over a century ago, whose end may yet lie decades, perhaps centuries, beyond our current horizon.

89 Responses

  1. But why a Higgs particle? Relativity tells us that no signal can travel faster than light. Incorporating this into quantum mechanics tells us that forces which we think of as being due to fields are actually transmitted between objects by the exchange of particles. The way particles transmit forces is a bit like a game of catch if I throw a ball and you catch it, I will be pushed backwards by the act of throwing and you will be pushed backwards by the act of catching. Thus we act as if we repel each other.

  2. The questions of Higgs field should be remained hypothetically until the human brain being transformed by the Creator
    In our universes, there is a divine forces which scientiests could’nt materialize unless the Higgs creator permit them to see it’s forces. There is no time limits for Higgs. It is not a kind of particles but a divine forces.

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  4. It is a really amazing site.
    There is only one small matter. I guess the one who first discovered the electron is “Thomson”, not “Thompson”.
    But the rest is simply terrific. I have learned so much from this website and am still learning. Thank you so much.

  5. Thanks, I’m trying to get a grasp of, somewhat anyways, of what this universe entails as well as trying to learn a little of the Magyar language my parents often used when they didn’t want us to know what they were talking about, neither of which is an easy task. Köszönöm

  6. I thought it was a very good explanation, however, I did not get goose bumps. Is something wrong with me? So, the Higgs is a little like molasses increased force is met with increased resistance? Is it like fish swimming up steam in a river, small fish meet with less resistance and large fish more. What is it about the particles themselves, why do some interact with the Higgs more than others and some not at all?

    1. 🙂 No, nothing’s wrong with you. Aside from the fact that different people get goosebumps about different things, I do think you’ve identified that one problem with my article is that it doesn’t let you see where the goosebumps really come from for scientists like me. They don’t come from the Higgs field anyway — the Higgs field is really, really important, but it isn’t the thing that drives me. The goosebumps come from the larger context in which the Higgs field arises, and that I didn’t have time to explain in such a short article. Maybe I should think about revising it so that this becomes clearer. I was aiming at a good explanation, not so much at a goosebump generator

      But I think I did a better job of bringing out the “goosebumps” aspects of nature in my recent class and in my recent one-hour-long public talk. If you do have the time, give it a shot. http://profmattstrassler.com/2013/07/03/my-public-talk-on-the-higgs-now-online/

      The Higgs field is not like molasses, however, and not like fish swimming upstream. Those analogies are just wrong; if they were right, the Higgs field wouldn’t affect anything that is standing still, whereas in fact the electron has its mass no matter what it is doing. The right way to think about the Higgs field is not familiar from everyday life, but not that complicated either. And I did explain in my public talk, so you might find that useful.

      As to why some particles interact more strongly with the Higgs field than others — we have no idea. Or more accurately, we have dozens of ideas, and no clue as to which idea is right, or whether we’ve thought of the right idea yet. Talk about goosebumps — that’s one of the most important unsolved mysteries in particle physics. We’re hoping the LHC will help us figure this out, though we also know that it may not do so. So finding the Higgs particle isn’t the end of this story; it’s maybe the “end of the beginning”, at best.

  7. Bravo! Thank you so much for taking the time to write this article in a clear and simple way. This article will change the way I look at the world. I’m sure it has done the same for many.

  8. One might eventually want to know what is the gene map of the Higgs particle. One day most people will understand that the universe is not one, but eternal. It has neither a beginning, nor an end. Imagine everything were the size of a tennis ball. Now imagine the ball. It cannot be done. Because if you did imagine the ball, it would be inside of something else and that could not be if the ball were everything or the universe. Uni means one and verse from the Greek Logos means Word. So it is One Word and in religion The Word of God. Hence, the opening statement of the Gospel of John. In the beginning was The Word and The Word was God. Notice ‘in the beginning” is not “at the beginning. That particular gospel was written for the Greeks while the Gospel of Mark witj a vocabulary of around 2,000 or less was written for simple fishermen and other town folk .

  9. thanks very much …
    I want to understand more about higgs fields when the mass is zero and non-zero
    please … kindly help me more ….

  10. Thank you for this article! This is the best explanation of the Higgs Field/Particle I’ve read so far! I try to stay informed on science developments but I find that I have to do a lot of work reading from multiple sources and translating everything into layman terms that my brain can get a handle on. Good visuals & metaphors are always useful, and your metaphor of homing in on a singer’s voice over background noise is highly instructive & elegant.

  11. Could it be that “the massgiving ocean in which we swim” has a Higgs system based on the opposite oscillations of TWIN ( massless but energetic) Higgs particles making the ocean not massive for motion, but giving mass to Fermions by the relativistic production rate of gravitons?

  12. Absent the Higgs, the gauge theory of radioactive decay is all wet. Do you have smoke detectors at home ? Have you had a PET scan or a SPECT scan?

  13. Thanks so much for the wonderful blog. It’s the best place on the internet to read this material. Crystal clear exposition and a great pleasure every time. Compelling, understandable and inspiring. A dramatic improvement on the dry and boring majority of articles that I just can’t get through.

      1. Will do Matt! Hope to hear you give some talks and looking forward to your book!

  14. I have read it three times, and got goosebumps every time. The content is thrilling, and the execution is flawless.

  15. This is the best scientific article I have ever read. Some of the questions and responses make my head spin. But the article, so clearly written and filled with humility and humanity, is a work of art.

  16. I believe this one is pretty easy. I’ll be the first to admit I have the mathematical prowess of a broken sliderule, but E=mc^2 is what this is all about. As you add (copious quantities of) energy to an electron (which by some theories is just a convergence of various undulating fields – consonant resonance), its mass increases ever so slightly. If you go back to the equation, C is a constant, so if you increase E(energy), m(mass) must also increase.

    There are some really good texts written by folks like the guy who writes this blog. May I suggest reading Michio Kaku, John Gribbin, Lawrence Krauss, everything ever written by Richard Feynman (RIP), and of course, Stephen Hawking.

  17. I am not familiar with this field except what little I learned years ago in school. This might be a basic question but I’m going to ask anyway: why is “why does an electron have mass at all” a question? I don’t understand why an electron having mass is so difficult to reconcile with. Also, how does one modify the mass of an electron so that the atom grows larger? If this isn’t practically possible then the issue does not exist at all.

    I hope to get some understanding here of concepts that have changed since I went to school. This probably isn’t a forum for curious laypeople but no one I know in real life can answer my questions. I have more questions but i’ve started with the first one that occurred me while reading this article. Thanks!!

    1. This is most definitely a forum for curious laypeople!

      The issue is this: It is **impossible** to write equations that both give the electron a mass AND allow it to behave as it does when affected by the weak nuclear force… unless there is a Higgs field, or something like it, added to the equations.

      In short, what cannot be reconciled is two facts about nature obtained from data: (a) an electron having mass, and (b) electrons and neutrinos interacting as they do with the weak nuclear force — unless a third fact is true — that (c) something like a Higgs field (and possibly a Higgs particle, too) exists.

  18. As a layperson, I really enjoyed this article. My love for Science brought me here. Tomorrow it’s back to Waly-Mart where I’m living the dream…

  19. Mike, if gravity doesn’t exist without mass, then you can state that mass is THE causative effect of gravity, correct? So by studying mass you are studying gravity by default since the one does not exist without the other. I’ll bet my 8th grade education on it! Please feel free to correct me as I realize the limits of my educational upbringing. Anyone?… Bueller?

  20. Is there a non-zero energy density or momentum associated with the Higgs field? If there is what are implications for gravity? If there isn’t- why not? Do the equations allow for it?

    Another question – is the mechanism of an electron acquiring mass in the Higgs field in any way similar to how an electron gets an effective mass in a semiconductor? I.e. getting “dressed” in excitations of the field caused by electron-field coupling?

    Thank you! Cannot express how much I appreciate your postsx

  21. It seems to me that ‘mass’ is a measure of the effect of gravity. If we wish to understand mass, I think we need to fully understand gravity. My reading suggests that we know hardly more about the force of gravity than we do about the Higgs boson. To me, gravity is the big mystery.

    1. “Mass” isn’t a measure of gravity: it’s a measure of inertia. The more massive an object is, the “harder” gravity has to pull to accelerate said object, or the harder you have to work to lift said object off the ground. Conversely, gravity is a measure of mass because the more massive an object is, the more it warps space-time, i.e., what we colloquially call “gravity.”

    2. You need to consider that mass is also related to inertia, the inertial mass, which is seems to be the same as the gravitational mass. So you don’t necessarily need gravity to understand mass.

  22. A small comment: using the word ‘massive’, which has a specific technical meaning for physicists–non-zero mass–is not helpful in a colloquial essay such as this, as it can be very easily misconstrued in the sense ‘enormous’. As such, phrases like “massive particles called quarks” look like they mean ‘really big particles called quarks, when in fact they are ‘very small’ (though heavy) – speaking loosely here.

  23. In “Putting the Higgs Boson in its place” http://gu.com/p/2zftz/tw John Butterworth quoted Ian Sample that “the Higgs is only responsible for about 1% of the mass of everyday stuff. The rest comes from the binding energy of the strong nuclear force. So there”. On the same subject (although not directly commenting on that particular statement) you told Tim Preece in a reply to your Higgs FAQ on January 12, 2012 that ” … in fact there is an important quantum mechanical effect that this leaves out. And if you account for it, the Higgs field contributes almost all of the mass (of a basketball)”. Assuming there is nothing special fundamental physics-wise about basketballs, I would love to get you and John together for a panel discussion on the subject. Have I missed anything more recent in your blogs about this important quantum mechanical effect or is this an explanation challenge you have yet to tackle?

    1. Matt, this effect you quoted. Did you mean the ’empowerment’ of the strong nuclear force by the Higgs Field? If not, what is it?
      Curious 🙂

    2. Hi Matt, Thanks for the on-line response on the Nature live Q&A this week. For the record I am putting our discourse in-line here. Hopefully to be expanded upon later?

      Prof. John Butterworth (ATLAS and UCL) said “the Higgs is only responsible for about 1% of the mass of everyday stuff” true or false?

      Matt Strassler:
      This is a great question — because the answer is true and false! Butterworth is absolutely right that in an ordinary atom, only the electrons get their mass completely from the Higgs; the proton’s mass comes from effects of the strong nuclear force (long story).

      BUT — if you really think about it carefully, the Higgs gives mass to many particles, and indirectly, if you were to turn off the Higgs field (it’s the field, not the particle, that provides the mass, by the way) it would change the strength of the strong nuclear force — and would indirectly change the proton mass.

      1. Definitely will write a post on this someday. But I have to explain it a how particle masses can indirectly affect the strength of the strong nuclear force, which is not a short article and requires some real thought.

  24. “The key is that Higgs particles are rare but their debris is relatively regular in appearance, while the other processes are common but more random; and just as your ear can gradually pick out the singing tone of a human voice even above heavy static on a radio, so experimenters can pick out the regular ringing of the Higgs field amid the random cacophony created by the other similar-looking processes.”

    Phenomenal metaphor btw. Thanks for all the hard work you do to help us explain this process to our laymen friends and family-members.

  25. Matt, Jay Carlson here, simon’s rocker and ex husband of Caitlin. Hey, congratulations on the discovery I am reading about today. I know that this is a huge deal in your field, and I believe that you have done some work relating to CERN during your own career. Anyway, I thought of you when I read the articles, and I thought I would reach out and say well done.

  26. Higgs field is a contemporary and likely real version of the old-fashioned ether…Not like it, however, in the sense the Higgs field is in some sense “relativistic” and “quantum”…

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