Category Archives: History of Science

In Memoriam: Gerry Guralnik

For those who haven’t heard: Professor Gerry Guralnik died. Here’s the New York Times obituary, which contains a few physics imperfections (though the most serious mistake in an earlier version was corrected, thankfully), but hopefully avoids any errors about Guralnik’s life.  Here’s another press release, from Brown University.

Guralnik, with Tom Kibble and Carl Hagen, wrote one of the four 1964 papers which represent the birth of the idea of the “Higgs” field, now understood as the source of mass for the known elementary particles — an idea that was confirmed by the discovery of a type of “Higgs” particle in 2012 at the Large Hadron Collider.  (I find it sad that the obituary is sullied with a headline that contains the words “God Particle” — a term that no physicist involved in the relevant research ever used, and which was invented in the 1990s, not as science or even as religion, but for $$$… by someone who was trying to sell his book.) The other three papers — the first by Robert Brout and Francois Englert, and the second and third by Peter Higgs, were rewarded with a Nobel Prize in 2013; it was given just to Englert and Higgs, Brout having died too early, in 2011.  Though Guralnik, Hagen and Kibble won many other prizes, they were not awarded a Nobel for their work, a decision that will remain forever controversial.

But at least Guralnik lived long enough to learn, as Brout sadly did not, that his ideas were realized in nature, and to see the consequences of these ideas in real data. In the end, that’s the real prize, and one that no human can award.

What if the Large Hadron Collider Finds Nothing Else?

In my last post, I expressed the view that a particle accelerator with proton-proton collisions of (roughly) 100 TeV of energy, significantly more powerful than the currently operational Large Hadron Collider [LHC] that helped scientists discover the Higgs particle, is an obvious and important next steps in our process of learning about the elementary workings of nature. And I described how we don’t yet know whether it will be an exploratory machine or a machine with a clear scientific target; it will depend on what the LHC does or does not discover over the coming few years.

What will it mean, for the 100 TeV collider project and more generally, if the LHC, having made possible the discovery of the Higgs particle, provides us with no more clues?  Specifically, over the next few years, hundreds of tests of the Standard Model (the equations that govern the known particles and forces) will be carried out in measurements made by the ATLAS, CMS and LHCb experiments at the LHC. Suppose that, as it has so far, the Standard Model passes every test that the experiments carry out? In particular, suppose the Higgs particle discovered in 2012 appears, after a few more years of intensive study, to be, as far the LHC can reveal, a Standard Model Higgs — the simplest possible type of Higgs particle?

Before we go any further, let’s keep in mind that we already know that the Standard Model isn’t all there is to nature. The Standard Model does not provide a consistent theory of gravity, nor does it explain neutrino masses, dark matter or “dark energy” (also known as the cosmological constant). Moreover, many of its features are just things we have to accept without explanation, such as the strengths of the forces, the existence of “three generations” (i.e., that there are two heavier cousins of the electron, two for the up quark and two for the down quark), the values of the masses of the various particles, etc. However, even though the Standard Model has its limitations, it is possible that everything that can actually be measured at the LHC — which cannot measure neutrino masses or directly observe dark matter or dark energy — will be well-described by the Standard Model. What if this is the case?

Michelson and Morley, and What They Discovered

In science, giving strong evidence that something isn’t there can be as important as discovering something that is there — and it’s often harder to do, because you have to thoroughly exclude all possibilities. [It's very hard to show that your lost keys are nowhere in the house --- you have to convince yourself that you looked everywhere.] A famous example is the case of Albert Michelson, in his two experiments (one in 1881, a second with Edward Morley in 1887) trying to detect the “ether wind”.

Light had been shown to be a wave in the 1800s; and like all waves known at the time, it was assumed to be a wave in something material, just as sound waves are waves in air, and ocean waves are waves in water. This material was termed the “luminiferous ether”. As we can detect our motion through air or through water in various ways, it seemed that it should be possible to detect our motion through the ether, specifically by looking for the possibility that light traveling in different directions travels at slightly different speeds.  This is what Michelson and Morley were trying to do: detect the movement of the Earth through the luminiferous ether.

Both of Michelson’s measurements failed to detect any ether wind, and did so expertly and convincingly. And for the convincing method that he invented — an experimental device called an interferometer, which had many other uses too — Michelson won the Nobel Prize in 1907. Meanwhile the failure to detect the ether drove both FitzGerald and Lorentz to consider radical new ideas about how matter might be deformed as it moves through the ether. Although these ideas weren’t right, they were important steps that Einstein was able to re-purpose, even more radically, in his 1905 equations of special relativity.

In Michelson’s case, the failure to discover the ether was itself a discovery, recognized only in retrospect: a discovery that the ether did not exist. (Or, if you’d like to say that it does exist, which some people do, then what was discovered is that the ether is utterly unlike any normal material substance in which waves are observed; no matter how fast or in what direction you are moving relative to me, both of us are at rest relative to the ether.) So one must not be too quick to assume that a lack of discovery is actually a step backwards; it may actually be a huge step forward.

Epicycles or a Revolution?

There were various attempts to make sense of Michelson and Morley’s experiment.   Some interpretations involved  tweaks of the notion of the ether.  Tweaks of this type, in which some original idea (here, the ether) is retained, but adjusted somehow to explain the data, are often referred to as “epicycles” by scientists.   (This is analogous to the way an epicycle was used by Ptolemy to explain the complex motions of the planets in the sky, in order to retain an earth-centered universe; the sun-centered solar system requires no such epicycles.) A tweak of this sort could have been the right direction to explain Michelson and Morley’s data, but as it turned out, it was not. Instead, the non-detection of the ether wind required something more dramatic — for it turned out that waves of light, though at first glance very similar to other types of waves, were in fact extraordinarily different. There simply was no ether wind for Michelson and Morley to detect.

If the LHC discovers nothing beyond the Standard Model, we will face what I see as a similar mystery.  As I explained here, the Standard Model, with no other particles added to it, is a consistent but extraordinarily “unnatural” (i.e. extremely non-generic) example of a quantum field theory.  This is a big deal. Just as nineteenth-century physicists deeply understood both the theory of waves and many specific examples of waves in nature  and had excellent reasons to expect a detectable ether, twenty-first century physicists understand quantum field theory and naturalness both from the theoretical point of view and from many examples in nature, and have very good reasons to expect particle physics to be described by a natural theory.  (Our examples come both from condensed matter physics [e.g. metals, magnets, fluids, etc.] and from particle physics [e.g. the physics of hadrons].) Extremely unnatural systems — that is, physical systems described by quantum field theories that are highly non-generic — simply have not previously turned up in nature… which is just as we would expect from our theoretical understanding.

[Experts: As I emphasized in my Santa Barbara talk last week, appealing to anthropic arguments about the hierarchy between gravity and the other forces does not allow you to escape from the naturalness problem.]

So what might it mean if an unnatural quantum field theory describes all of the measurements at the LHC? It may mean that our understanding of particle physics requires an epicyclic change — a tweak.  The implications of a tweak would potentially be minor. A tweak might only require us to keep doing what we’re doing, exploring in the same direction but a little further, working a little harder — i.e. to keep colliding protons together, but go up in collision energy a bit more, from the LHC to the 100 TeV collider. For instance, perhaps the Standard Model is supplemented by additional particles that, rather than having masses that put them within reach of the LHC, as would inevitably be the case in a natural extension of the Standard Model (here’s an example), are just a little bit heavier than expected. In this case the world would be somewhat unnatural, but not too much, perhaps through some relatively minor accident of nature; and a 100 TeV collider would have enough energy per collision to discover and reveal the nature of these particles.

Or perhaps a tweak is entirely the wrong idea, and instead our understanding is fundamentally amiss. Perhaps another Einstein will be needed to radically reshape the way we think about what we know.  A dramatic rethink is both more exciting and more disturbing. It was an intellectual challenge for 19th century physicists to imagine, from the result of the Michelson-Morley experiment, that key clues to its explanation would be found in seeking violations of Newton’s equations for how energy and momentum depend on velocity. (The first experiments on this issue were carried out in 1901, but definitive experiments took another 15 years.) It was an even greater challenge to envision that the already-known unexplained shift in the orbit of Mercury would also be related to the Michelson-Morley (non)-discovery, as Einstein, in trying to adjust Newton’s gravity to make it consistent with the theory of special relativity, showed in 1913.

My point is that the experiments that were needed to properly interpret Michelson-Morley’s result

  • did not involve trying to detect motion through the ether,
  • did not involve building even more powerful and accurate interferometers,
  • and were not immediately obvious to the practitioners in 1888.

This should give us pause. We might, if we continue as we are, be heading in the wrong direction.

Difficult as it is to do, we have to take seriously the possibility that if (and remember this is still a very big “if”) the LHC finds only what is predicted by the Standard Model, the reason may involve a significant reorganization of our knowledge, perhaps even as great as relativity’s re-making of our concepts of space and time. Were that the case, it is possible that higher-energy colliders would tell us nothing, and give us no clues at all. An exploratory 100 TeV collider is not guaranteed to reveal secrets of nature, any more than a better version of Michelson-Morley’s interferometer would have been guaranteed to do so. It may be that a completely different direction of exploration, including directions that currently would seem silly or pointless, will be necessary.

This is not to say that a 100 TeV collider isn’t needed!  It might be that all we need is a tweak of our current understanding, and then such a machine is exactly what we need, and will be the only way to resolve the current mysteries.  Or it might be that the 100 TeV machine is just what we need to learn something revolutionary.  But we also need to be looking for other lines of investigation, perhaps ones that today would sound unrelated to particle physics, or even unrelated to any known fundamental question about nature.

Let me provide one example from recent history — one which did not lead to a discovery, but still illustrates that this is not all about 19th century history.

An Example

One of the great contributions to science of Nima Arkani-Hamed, Savas Dimopoulos and Gia Dvali was to observe (in a 1998 paper I’ll refer to as ADD, after the authors’ initials) that no one had ever excluded the possibility that we, and all the particles from which we’re made, can move around freely in three spatial dimensions, but are stuck (as it were) as though to the corner edge of a thin rod — a rod as much as one millimeter wide, into which only gravitational fields (but not, for example, electric fields or magnetic fields) may penetrate.  Moreover, they emphasized that the presence of these extra dimensions might explain why gravity is so much weaker than the other known forces.

Fig. 1: ADD's paper pointed out that no experiment as of 1998 could yet rule out the possibility that our familiar three dimensional world is a corner of a five-dimensional world, where the two extra dimensions are finite but perhaps as large as a millimeter.

Fig. 1: ADD’s paper pointed out that no experiment as of 1998 could yet rule out the possibility that our familiar three-dimensional world is a corner of a five-dimensional world, where the two extra dimensions are finite but perhaps as large as a millimeter.

Given the incredible number of experiments over the past two centuries that have probed distances vastly smaller than a millimeter, the claim that there could exist millimeter-sized unknown dimensions was amazing, and came as a tremendous shock — certainly to me. At first, I simply didn’t believe that the ADD paper could be right.  But it was.

One of the most important immediate effects of the ADD paper was to generate a strong motivation for a new class of experiments that could be done, rather inexpensively, on the top of a table. If the world were as they imagined it might be, then Newton’s (and Einstein’s) law for gravity, which states that the force between two stationary objects depends on the distance r between them as 1/r², would increase faster than this at distances shorter than the width of the rod in Figure 1.  This is illustrated in Figure 2.

Fig. 2: If the world were as sketched in Figure 1, then Newton/Einstein's law of gravity would be violated at distances shorter than the width of the rod in Figure 1.  The blue line shows Newton/Einstein's prediction; the red line shows what a universe like that in Figure 1 would predict instead.  Experiments done in the last few years agree with the blue curve down to a small fraction of a millimeter.

Fig. 2: If the world were as sketched in Figure 1, then Newton/Einstein’s law of gravity would be violated at distances shorter than the width of the rod in Figure 1. The blue line shows Newton/Einstein’s prediction; the red line shows what a universe like that in Figure 1 would predict instead. Experiments done in the last few years agree with the blue curve down to a small fraction of a millimeter.

These experiments are not easy — gravity is very, very weak compared to electrical forces, and lots of electrical effects can show up at very short distances and have to be cleverly avoided. But some of the best experimentalists in the world figured out how to do it (see here and here). After the experiments were done, Newton/Einstein’s law was verified down to a few hundredths of a millimeter.  If we live on the corner of a rod, as in Figure 1, it’s much, much smaller than a millimeter in width.

But it could have been true. And if it had, it might not have been discovered by a huge particle accelerator. It might have been discovered in these small inexpensive experiments that could have been performed years earlier. The experiments weren’t carried out earlier mainly because no one had pointed out quite how important they could be.

Ok Fine; What Other Experiments Should We Do?

So what are the non-obvious experiments we should be doing now or in the near future?  Well, if I had a really good suggestion for a new class of experiments, I would tell you — or rather, I would write about it in a scientific paper. (Actually, I do know of an important class of measurements, and I have written a scientific paper about them; but these are measurements to be done at the LHC, and don’t involve a entirely new experiment.)  Although I’m thinking about these things, I do not yet have any good ideas.  Until I do, or someone else does, this is all just talk — and talk does not impress physicists.

Indeed, you might object that my remarks in this post have been almost without content, and possibly without merit.  I agree with that objection.

Still, I have some reasons for making these points. In part, I want to highlight, for a wide audience, the possible historic importance of what might now be happening in particle physics. And I especially want to draw the attention of young people. There have been experts in my field who have written that non-discoveries at the LHC constitute a “nightmare scenario” for particle physics… that there might be nothing for particle physicists to do for a long time. But I want to point out that on the contrary, not only may it not be a nightmare, it might actually represent an extraordinary opportunity. Not discovering the ether opened people’s minds, and eventually opened the door for Einstein to walk through. And if the LHC shows us that particle physics is not described by a natural quantum field theory, it may, similarly, open the door for a young person to show us that our understanding of quantum field theory and naturalness, while as intelligent and sensible and precise as the 19th century understanding of waves, does not apply unaltered to particle physics, and must be significantly revised.

Of course the LHC is still a young machine, and it may still permit additional major discoveries, rendering everything I’ve said here moot. But young people entering the field, or soon to enter it, should not assume that the experts necessarily understand where the field’s future lies. Like FitzGerald and Lorentz, even the most brilliant and creative among us might be suffering from our own hard-won and well-established assumptions, and we might soon need the vision of a brilliant young genius — perhaps a theorist with a clever set of equations, or perhaps an experimentalist with a clever new question and a clever measurement to answer it — to set us straight, and put us onto the right path.

Galileo’s Winter

While the eastern half of the United States is having a cold winter so far, the same has not been true in Italy. The days I spent teaching in Florence (Firenze), at the Galileo Galilei Institute (GGI), were somewhat warmer than is apparently the usual, with even low temperatures far above freezing almost every night. A couple of people there said to me that they “hadn’t seen any winter yet”. So I was amused to read, on U.S. news websites, yet more reports of Americans uselessly debating the climate change issue — as though either the recent cold in the eastern U.S. or the recent warmth in Europe can tell us anything relevant to that discussion. (Here’s why it can’t.) It does seem to be widely forgotten in the United States that our country occupies only about 2% percent of the area of the Earth.

Of course the warmer Italian weather made my visit more pleasant, especially since the GGI is 20 minutes up a long hill — the Arcetri hill, of particular significance in scientific history. [I am grateful to the GGI, and the scientist- organizers of the school at which I taught, especially Stefania de Curtis, for making my visit to Arcetri and its sites possible.] The University of Florence used to be located there, and there are a number of astronomical observatories on the hill. And for particle physics, there is significance too. The building where I was teaching, and that hosts the GGI, used to be the department of Physics and Astronomy of the university. There, in 1925, Enrico Fermi, one of the greatest physicists of the 20th century, had his first professorial position. And while serving in that position, he figured out the statistical and thermodynamic properties of a gas made from particles that, in his honor, we now call “fermions”.  [His paper was recently translated into English by A. Zannoni.]

All particles in our world — elementary particles such as electrons and photons, and more complex objects such as atoms — are either fermions or bosons; the classic example of a fermion is an electron. The essential property of fermions is that two identical fermions cannot do precisely the same thing at the same time. For electrons in atoms, this is known as the Pauli exclusion principle (due to Wolfgang Pauli in 1925, based on 1924 research by Edmund Stoner): no two electrons can occupy the same quantum state. All of atomic physics and chemistry, and the very stability of large chunks of matter made from atoms, are dependent upon this principle. The properties of fermions also are crucial to the stability and structure of atomic nuclei, the existence of neutron stars, the electrical properties of metals and insulators, and the properties of many materials at cold temperatures.

Plaque commemorating Fermi's work on what we now call `fermions'. [Credit: M. Strassler]

Plaque commemorating Fermi’s work on what we now call `fermions’. [Credit: M. Strassler]

Inside the building is a plaque commemorating Fermi’s great achievement. But Fermi did not remain long in Florence, or even in Italy. A mere 15 years later, in the midst of the Fascist crisis and war in Europe, and having won a Nobel Prize for his work on radioactive atoms, Fermi had taken a position in the United States. There he directly oversaw the design, building and operation of humanity’s first nuclear reactor, in a secret underground laboratory at the University of Chicago, paving the way for the nuclear age.

But the main reason the Arcetri hill is famous for science is, ironically, because of a place of religion.

Both of Galileo’s daughters had taken the veil, and in 1631 the aging scientist was prompted to rent a villa on a small farm, within sight and a short walk of their nunnery.  Unfortunately, what must have seemed like an idyllic place to grow old and do science soon turned into a nightmare. After years of coexistence with and even support from within the Catholic Church, he had pushed too hard; his publication in 1632 of a comparison of the old Ptolemaic view of the universe, with the Earth at the center, with the newer Copernican view (to which he had greatly contributed, through his astronomical discoveries, in the 1610s), engendered a powerful backlash from some who viewed it as heretical. He was forced to spend 1633 defending himself in Rome and then living in exile in Sienna. When he was allowed to return to Arcetri in 1634, he was under house arrest and not allowed to have any scientific visitors. Shortly after his return, his 33-year-old daughter, with whom he was very close, died of a sudden and severe illness. His vision failed him, due to unknown diseases, and he was blind by 1638. Unable to go to Florence, his home town, scarcely three miles away, and rarely able to meet visitors, he spent the rest of his time in Arcetri isolated and increasingly ill, finally dying there in 1642.

Yet despite this, or perhaps because of it, Galileo’s science did not come to a halt. (This was also partly because of the his support from the Grand Duke of Tuscany, who interceded on his behalf to allow him some scientific assistance after he went blind.) At Arcetri, Galileo discovered the moon did not always present exactly the same face toward the Earth; it appears, to us on Earth, to wobble slightly. The explanation for this so-called “lunar libration” awaited Issac Newton’s laws of motion and of gravity, just 50 years away. And he finished formulating laws of motion (which would also later be explained by Newton), showing that (on Earth) objects tossed into the air follow a trajectory that mathematicians call a parabola, until affected by what we now call “air resistance”, and showing that uniform motion cannot be detected — the first Principle of Relativity, authored 270 years before Einstein presented his revision of Galileo’s ideas.

Vaulted ceiling in the main entry hall of Galileo's rented villa in Arcetri. (No, the light fixture is not original.) [Credit: M. Strassler]

Vaulted ceiling in the main entry hall of Galileo’s rented villa in Arcetri. (No, the light fixture is not original.) [Credit: M. Strassler]

To step into Galileo’s villa, as I did a few days ago, is therefore to step into a place of intense personal tragedy and one of great scientific achievement. One can easily imagine him writing by the window, or walking in the garden, or discussing the laws of motion with his assistants, in such a setting. It is also to be reminded that Galileo was not a poor man, thanks to his inventions and to his scientific appointments. The ceilings of the main rooms on the lower floor of the villa are high and vaulted, with attractively carved supports. There is a substantial “loggia” on the upper floor — a balcony, with pillars supporting a wooden roof, that (facing south-east, south and west) would have been ideal, while Galileo could still see, for observing the Moon and planets.

While Galileo’s luck ran badly in his later years, he had an extraordinary string of luck, as a younger scientist, at the beginning of the 1600s. First, in 1604, there was a supernova, as bright as the planet Jupiter, that appeared in the sky as a very bright new star. (Humans haven’t seen a correspondingly close and bright supernova since then, not even supernova 1987a.  There is one you can see with a small telescope right now though.) Observing that the glowing object showed no signs of parallax (see here for a description of how parallax can be used to determine the distance to an object), Galileo concluded that it must be further away than the Moon — and thus served as additional evidence that the heavens are not unchanging. Of course, what was seen was actually an exploding star, one that was nearly a trillion times further from the Earth than is the Moon — but this Galileo could not know.

Next, just a few years later, came the invention of the telescope. Hearing of this device, Galileo quickly built his own and figured out how to improve it. In the following years, armed with telescopes that could provide just 20-times magnification (typical binoculars you can buy can provide 10-times, and with much better optical quality than Galileo’s assistants could manufacture) came his great string of astronomical discoveries and co-discoveries:

  • the craters on the Moon (proving the Moon has mountains and valleys like the Earth),
  • the moons of Jupiter (proving that not everything orbits the Earth),
  • the phases of Venus and its changing apparent size as Venus moves about the sky (proving that Venus orbits the Sun),
  • the rings of Saturn (demonstrating Saturn is not merely a simple sphere),
  • sunspots (proving the sun is imperfect, changeable, and rotating),
  • and the vast number of stars in the Milky Way that aren’t visible to the naked eye.

One often hears 1905 referred to as Einstein’s miracle year, when he explained Brownian motion and calculated the size of atoms, introduced the notion of quanta of light to explain the photoelectric effect, and wrote his first two papers on special relativity. Well, one could say that Galileo had a miracle decade, most of it concentrated in 1610-1612— playing the decisive role in destroying the previously dominant Ptolemaic view of the universe, in which the Sun, Moon, planets and stars orbit in a complex system of circles-within-circles around a stationary Earth.

We live in an era where so much more is known about the basic workings of the universe, and where a simple idea or invention is rarely enough to lead to a great change in our understanding of our world and of ourselves. And so I found myself, standing in Galileo’s courtyard, feeling a moment of nostalgia for that simpler time of the 17th century, cruel and dangerous as it was… a time when a brilliant scientist could stand on the balcony of his own home, looking through a telescope he’d designed himself, and change the world-view of a civilization.

Looking across the enclosed courtyard of the villa, at the second-floor loggia, suitable for telescopic observing.  It is not hard to imagine Galileo standing there and peering into the sky.  [Credit: M. Strassler]

Looking across the enclosed courtyard of the villa, at the second-floor loggia. It is not difficult to imagine Galileo standing there and peering into his telescope. [Credit: M. Strassler]

Moon and Jupiter Galileo-Style, ***This Evening***

If you have a clear sky, don’t forget to look overhead tonight!  And go get your binoculars or small telescope…

After an overnight flight and a train that brought me to Florence (Firenze), Italy, where I’ll be teaching this week, I decided to fight off sleep by taking a walk down into the city and wandering around for a while.  It was a beautiful evening, with deep blue twilight.  And it wasn’t long before the planet Jupiter, and then the full Moon, rose above the buildings and high into the sky.  I caught a photo of them, between the Duomo (cathedral) and its campanile (bell tower).  Jupiter is the little white dot directly above the moon, at the top of the second set of windows on the campanile.

MoonJupiterOverDuomo

The Moon and Jupiter (tiny dot well above the Moon) shine between the Duomo of Florence (left) and its Campanile. Photo credit: Matt Strassler

I then pulled out my binoculars, which aren’t quite as powerful as Galileo’s telescope was 400 years ago, but are still enough to reveal what Galileo discovered.  Just as Galileo (and his competitor Thomas Herriot) did in 1609, I could see all sorts of structure to the Moon’s surface, including what we now know are basalt plains, and hints of impact craters.  [Admittedly, impact craters and mountains are actually easiest to see when the Moon isn't full, because then the shadows that mountains cast are longer.]

And looking at Jupiter, which is relatively close to Earth right now, I could easily see that it was a disk, not a dot like a star, and that there are three dim dots, sitting in a line that passes through the planet.  These are three of Jupiter’s four large moons: Callisto, Ganymede, Europa and Io.  [The fourth one might well be visible if you're lucky and have good eyes and good timing.]  If you watch them day by day, they will change position, a fact that Galileo used to guess they were moons orbiting Jupiter.

So if you have good weather, tonight’s a great opportunity for some simple but very satisfying astronomy.  Don’t miss the naked-eye view that’s on offer right now or in a few hours, depending on where you reside.  And if you’ve got binoculars handy, you can relive Galileo’s remarkable discoveries about the Moon and Jupiter, and contemplate how the first telescopes forever changed the way humans envisioned their cosmos.

Wednesday: Sean Carroll & I Interviewed Again by Alan Boyle

Today, Wednesday December 4th, at 8 pm Eastern/5 pm Pacific time, Sean Carroll and I will be interviewed again by Alan Boyle on “Virtually Speaking Science”.   The link where you can listen in (in real time or at your leisure) is

http://www.blogtalkradio.com/virtually-speaking-science/2013/12/05/alan-boyle-matt-strassler-sean-carroll

What is “Virtually Speaking Science“?  It is an online radio program that presents, according to its website:

  • Informal conversations hosted by science writers Alan Boyle, Tom Levenson and Jennifer Ouellette, who explore the explore the often-volatile landscape of science, politics and policy, the history and economics of science, science deniers and its relationship to democracy, and the role of women in the sciences.

Sean Carroll is a Caltech physicist, astrophysicist, writer and speaker, blogger at Preposterous Universe, who recently completed an excellent and now prize-winning popular book (which I highly recommend) on the Higgs particle, entitled “The Particle at the End of the Universe“.  Our interviewer Alan Boyle is a noted science writer, author of the book “The Case for Pluto“, winner of many awards, and currently NBC News Digital’s science editor [at the blog  "Cosmic Log"].

Sean and I were interviewed in February by Alan on this program; here’s the link.  I was interviewed on Virtually Speaking Science once before, by Tom Levenson, about the Large Hadron Collider (here’s the link).  Also, my public talk “The Quest for the Higgs Particle” is posted in their website (here’s the link to the audio and to the slides).

The Twists and Turns of Hi(gg)story

In sports, as in science, there are two very different types of heroes.  There are the giants who lead the their teams and their sport, winning championships and accolades, for years, and whose fame lives on for decades: the Michael Jordans, the Peles, the Lou Gherigs, the Joe Montanas. And then there are the unlikely heroes, the ones who just happen to have a really good day at a really opportune time; the substitute player who comes on the field for an injured teammate and scores the winning goal in a championship; the fellow who never hits a home run except on the day it counts; the mediocre receiver who turns a short pass into a long touchdown during the Super Bowl.  We celebrate both types, in awe of the great ones, and in amused pleasure at the inspiring stories of the unlikely ones.

In science we have giants like Newton, Darwin, Boyle, Galileo… The last few decades of particle physics brought us a few, such as Richard Feynman and Ken Wilson, and others we’ll meet today.  Many of these giants received Nobel Prizes.   But then we have the gentlemen behind what is commonly known as the Higgs particle — the little ripple in the Higgs field, a special field whose presence and properties assure that many of the elementary particles of nature have mass, and without which ordinary matter, and we ourselves, could not exist.  Following discovery of this particle last year, and confirmation that it is indeed a Higgs particle, two of them, Francois Englert and Peter Higgs, have been awarded the 2013 Nobel Prize in physics.  Had he lived to see the day, Robert Brout would have been the third.

My articles Why The Higgs Particle Matters and The Higgs FAQ 2.0; the particles of nature and what they would be like if the Higgs field were turned off; link to video of my public talk entitled The Quest for the Higgs Boson; post about why Higgs et al. didn’t win the 2012 Nobel prize, and about how physicists became convinced since then that the newly discovered particle is really a Higgs particle;

The paper written by Brout and Englert; the two papers written by Higgs; the paper written by Gerald Guralnik, Tom Kibble and Carl Hagen; these tiny little documents, a grand total of five and one half printed pages — these were game-winning singles in the bottom of the 9th, soft goals scored with a minute to play, Hail-Mary passes by backup quarterbacks — crucial turning-point papers written by people you would not necessarily have expected to find at the center of things.  Brout, Englert, Higgs, Guralnik, Kibble and Hagen are (or rather, in Brout’s case, sadly, were) very fine scientists, intelligent and creative and clever, and their papers, written in 1964 when they were young men, are imperfect but pretty gems.  They were lucky: very smart but not extraordinary physicists who just happened to write the right paper at the right time. In each case, they did so

History in general, and history of science in particular, is always vastly more complex than the simple stories we tell ourselves and our descendants.  Making history understandable in a few pages always requires erasing complexities and subtleties that are crucial for making sense of the past.  Today, all across the press, there are articles explaining incorrectly what Higgs and the others did and why they did it and what it meant at the time and what it means now.  I am afraid I have a few over-simplified articles of my own. But today I’d like to give you a little sense of the complexities, to the extent that I, who wasn’t even alive at the time, can understand them.  And also, I want to convey a few important lessons that I think the Hi(gg)story can teach both experts and non-experts.  Here are a couple to think about as you read:

1. It is important for theoretical physicists, and others who make mathematical equations that might describe the world, to study and learn from imaginary worlds, especially simple ones.  That is because

  • 1a. one can often infer general lessons more easily from simple worlds than from the (often more complicated) real one, and
  • 1b. sometimes an aspect of an imaginary world will turn out to be more real than you expected!

2. One must not assume that research motivated by a particular goal depends upon the achievement of that goal; even if the original goal proves illusory, the results of the research may prove useful or even essential in a completely different arena.

My summary today is based on a reading of the papers themselves, on comments by John Iliopoulos, and on a conversation with Englert, and on reading and hearing Higgs’ own description of the episode.

The story is incompletely but perhaps usefully illustrated in the figure below, which shows a cartoon of how four important scientific stories of the late 1950s and early 1960s came together. They are:

  1. How do superconductors (materials that carry electricity without generating heat) really work?
  2. How does the proton get its mass, and why are pions (the lightest hadrons) so much lighter than protons?
  3. Why do hadrons behave the way they do; specifically, as suggested by J.J. Sakurai (who died rather young, and after whom a famous prize is named), why are there photon-like hadrons, called rho mesons, that have mass?
  4. How does the weak nuclear force work?  Specifically, as suggested by Schwinger and developed further by his student Glashow, might it involve photon-like particles (now called W and Z) with mass?

These four questions converged on a question of principle: “how can mass be given to particles?”, and the first, third and fourth were all related to the specific question of “how can mass be given to photon-like particles?’’  This is where the story really begins.  [Almost everyone in the story is a giant with a Nobel Prize, indicated with a parenthetic (NPyear).]

My best attempt at a cartoon history...

My best attempt at a cartoon history…

In 1962, Philip Anderson (NP1977), an expert on (among other things) superconductors, responded to suggestions and questions of Julian Schwinger (NP1965) on the topic of photon-like particles with mass, pointing out that a photon actually gets a mass inside a superconductor, due to what we today would identify as a sort of “Higgs-type’’ field made from pairs of electrons.  And he speculated, without showing it mathematically, that very similar ideas could apply to empty space, where Einstein’s relativity principles hold true, and that this could allow elementary photon-like particles in empty space to have mass, if in fact there were a kind of Higgs-type field in empty space.

In all its essential elements, he had the right idea.  But since he didn’t put math behind his speculation, not everyone believed him.  In fact, in 1964 Walter Gilbert (NP1980 for chemistry, due to work relevant in molecular biology — how’s that for a twist?) even gave a proof that Anderson’s idea couldn’t work in empty space!

But Higgs immediately responded, arguing that Gilbert’s proof had an important loophole, and that photon-like particles could indeed get a mass in empty space.

Meanwhile, about a month earlier than Higgs, and not specifically responding to Anderson and Gilbert, Brout and Englert wrote a paper showing how to get mass for photon-like particles in empty space. They showed this in several types of imaginary worlds, using techniques that were different from Higgs’ and were correct though perhaps not entirely complete.

A second paper by Higgs, written before he was aware of Brout and Englert’s work, gave a simple example, again in an imaginary world, that made all of this much easier to understand… though his example wasn’t perhaps entirely convincing, because he didn’t show much detail.  His paper was followed by important theoretical clarifications from Guralnik, Hagen and Kibble that assured that the Brout-Englert and Higgs papers were actually right.  The combination of these papers settled the issue, from our modern perspective.

And in the middle of this, as an afterthought added to his second paper only after it was rejected by a journal, Higgs was the first person to mention something that was, for him and the others, almost beside the point — that in the Anderson-Brout-Englert-Higgs-Guralnik-Hagen-Kibble story for how photon-like particles get a mass, there will also  generally be a spin-zero particle with a mass: a ripple in the Higgs-type field, which today we call a Higgs-type particle.  Not that he said very much!   He noted that spin-one (i.e. photon-like) and spin-zero particles would come in unusual combinations.  (You have to be an expert to even figure out why that counts as predicting a Higgs-type particle!)  Also he wrote the equation that describes how and why the Higgs-type particle arises, and noted how to calculate the particle’s mass from other quantities.  But that was it.  There was nothing about how the particle would behave, or how to discover it in the imaginary worlds that he was considering;  direct application to experiment, even in an imaginary world, wasn’t his priority in these papers.

Equation (2b) is the first time the Higgs particle explicitly appears in its modern form

In his second paper, Higgs considers a simple imaginary world with just a photon-like particle and a Higgs-type field.  Equation 2b is the first place the Higgs-type particle explicitly appears in the context of giving photon-like particles a mass (equation 2c).  From Physical Review Letters, Volume 13, page 508

About the “Higgs-type” particle, Anderson says nothing; Brout and Englert say nothing; Guralnik et al. say something very brief that’s irrelevant in any imaginable real-world application.  Why the silence?  Perhaps because it was too obvious to be worth mentioning?  When what you’re doing is pointing out something really “important’’ — that photon-like particles can have a mass after all — the spin-zero particle’s existence is so obvious but so irrelevant to your goal that it hardly deserves comment.  And that’s indeed why Higgs added it only as an afterthought, to make the paper a bit less abstract and a bit easier for  a journal to publish.  None of them could have imagined the hoopla and public excitement that, five decades later, would surround the attempt to discover a particle of this type, whose specific form in the real world none of them wrote down.

In the minds of these authors, any near-term application of their ideas would probably be to hadrons, perhaps specifically Sakurai’s theory of hadrons, which in 1960 predicted the “rho mesons”, which are photon-like hadrons with mass, and had been discovered in 1961.  Anderson, Brout-Englert and Higgs specifically mention hadrons at certain moments. But none of them actually considered the real hadrons of nature, as they were just trying to make points of principle; and in any case, the ideas that they developed did not apply to hadrons at all.  (Well, actually, that’s not quite true, but the connection is too roundabout to discuss here.)  Sakurai’s ideas had an element of truth, but fundamentally led to a dead end.  The rho mesons get their mass in another way.

Meanwhile, none of these people wrote down anything resembling the Higgs field which we know today — the one that is crucial for our very existence — so they certainly didn’t directly predict the Higgs particle that was discovered in 2012.   It was Steven Weinberg (NP1979) in 1967, and Abdus Salam (NP1979) in 1968, who did that.  (And it was Weinberg who stuck Higgs’ name on the field and particle, so that everyone else was forgotten.) These giants combined

  • the ideas of Higgs and the others about how to give mass to photon-like particles using a Higgs-type field, with its Higgs-type particle as a consequence…
  • …with the 1960 work of Sheldon Glashow (NP1979), Schwinger’s student, who like Schwinger proposed the weak nuclear force was due to photon-like particles with mass,…
  • …and with the 1960-1961 work of Murray Gell-Man (NP1969) and Maurice Levy and of Yoichiro Nambu (NP2008) and Giovanni Jona-Lasinio, who showed how proton-like or electron-like particles could get mass from what we’d now call Higgs-type fields.

This combination gave the first modern quantum field theory of particle physics: a set of equations that describe the weak nuclear and electromagnetic forces, and show how the Higgs field can give the W and Z particles and the electron their masses. It is the primitive core of what today we call the Standard Model of particle physics.  Not that anyone took this theory seriously, even Weinberg.  Most people thought quantum field theories of this type were mathematically inconsistent — until in 1971 Gerard ‘t Hooft (NP1999) proved they were consistent after all.

The Hi(gg)story is populated with giants.  I’m afraid my attempt to tell the story has giant holes to match.  But as far as the Higgs particle that was discovered last year at the Large Hadron Collider, the unlikely heroes of the story are the relatively ordinary scientists who slipped in between the giants and actually scored the goals.

Some Pre-Nobel Prizes

This year’s Nobel Prize, presumably to be given for the prediction of the particle known today as the “Higgs boson”, will be awarded next week.  But in the meantime, the American Physical Society has made a large number of awards.  A few of them are to people whose work I know about, so I thought I’d tell you just a little about them.

The J. J. Sakurai prize went to Professors Zvi Bern, Lance Dixon and David Kosower, for the work that I have already described on this website here and here.  Dixon, a wide-ranging expert in particle physics, quantum field theory and string theory, was a young professor at the Stanford Linear Accelerator Center when I was a Stanford graduate student.  He taught an excellent course on string theory, and provided a lot of scientific advice and insight outside the classroom.  Bern and Kosower were young scientists using string theory to learn about how to do computations in quantum field theory, and their surprising results formed the starting point for my Ph. D. thesis (which has their names in its title.)   The range of their work is hard to describe in a paragraph, but let’s just say that no one is surprised that they were awarded a prize of this magnitude.

The Dannie Heineman Prize for Mathematical Physics was awarded to my former colleague Greg Moore, a professor at Rutgers University.  “For eminent contributions to mathematical physics with a wide influence in many fields, ranging from string theory to supersymmetric gauge theory, conformal field theory, condensed matter physics and four-manifold theory.”  Allow me to translate:

  • string theory: you’ve heard about it, probably
  • supersymmetric gauge theory: quantum field theories with supersymmetry, which I’ll be writing about soon
  • conformal field theory: basically, quantum field theories that are scale invariant
  • condensed matter physics: the study of solids and liquids and their mechanical and electrical properties, and lots of other things too, in which quantum field theory is sometimes a useful tool
  • four-manifold theory: the mathematics of spaces which have four-spatial dimensions, or three-spatial dimensions and one-time dimension.  These spaces are very interesting to mathematicians, and also, they’re interesting because we live in one.

This is not the complete range of Moore’s work by any means.  Unfortunately this website doesn’t yet have pages that can put his work in proper context, but perhaps I’ll return to it later.  But again, no surprise here to see Moore’s name on this award.

The Tom W. Bonner Prize in Nuclear Physics was awarded to experimental physicist William A. Zajc, currently chairman of the Columbia University physics department.  Zajc has been heavily involved in one of the most surprising discoveries of the past fifteen years: that a hot dense fireball of quarks, anti-quarks and gluons (produced in the collision of two relatively large atomic nuclei) behaves in a very unexpected way, more like a very low viscosity liquid rather like than a gas.  I’ve known him partly because of his interest in the attempts to apply string theory to certain quantum field theories that are perhaps relevant in the modeling of this novel physical system… something I’ll also probably be writing about in the relatively near future.

And the W.K.H. Panofsky Prize in Experimental Particle Physics went to Kam-Biu Luk (Berkeley) and Yifang Wang (Director of China’s Institute of High Energy Physics): For their leadership of the Daya Bay experiment, which produced the first definitive measurement of the theta-13 angle of the neutrino mixing matrix.  For the same experiment, the Henry Primakoff Award for Early-Career Particle Physics went to Daniel A. Dwyer of Lawrence Berkeley Laboratory.  I wrote about the Daya Bay measurement here; their result is one of the major measurements in particle physics in the past few years.

I wish I knew more about the other recipients outside my areas of expertise, but other bloggers will have to cover those stories.

Anyway, no surprises, but some very deserving scientists.  Let’s see if next Tuesday brings the same result.

Strings: History, Development, Impact

Done: All three parts of my lecture for a general audience on String Theory are up now…

Beyond the Hype: The Weird World of String Theory (Science on Tap, Seattle, WA, September 25, 2006). Though a few years old, this talk is still very topical; it covers the history, development, context and impact of string theory from its earliest beginnings to the (then) present.

Be forewarned: although the audio is pretty good, this was an amateur video taken by one of the organizers of the talk, and because the place was small and totally packed with people, it’s not great quality… but good enough to follow, I think, so I’ve posted it.

  1. Part 1 (10 mins.): String theory’s beginnings in hadron physics and the early attempts to use it as a theory of quantum gravity.
  2. Part 2 (10 mins.): String theory was shown to be a mathematically consistent candidate for a theory of all of quantum gravity and particle physics, and became a really popular idea.
  3. Part 3 (9 mins.): How string theory evolved through the major technical and conceptual advances of the 1990s.

By the way, if you’re interested in other talks I’ve given for a general audience, you can check out my video clips, which include a recent hour-long talk on the Quest for the Higgs Boson.