Category Archives: Housekeeping

An Overdue Update

A number of people have asked why the blog has been quiet. To make a long story short, my two-year Harvard visit came to an end, and my grant proposals were turned down. No other options showed up except for a six-week fellowship at the Galileo Institute (thanks to the Simons Foundation), which ended last month.  So I am now employed outside of science, although I maintain a loose affiliation with Harvard as an “Associate of the Physics Department” (thanks to Professor Matt Schwartz and his theorist colleagues).

Context: U.S. government cuts to theoretical high-energy physics groups have been 25% to 50% in the last couple of years. (Despite news articles suggesting otherwise, billionaires have not made up for the cuts; and most donations have gone to string theory, not particle physics.) Spare resources are almost impossible to find. The situation is much better in certain other countries, but personal considerations keep me in this one.

News from the Large Hadron Collider (LHC) this year, meanwhile, is optimistic though not without worries. The collider itself operated well despite some hiccups, and things look very good for next year, when the increased energy and high collision rate will make the opportunities for discoveries the greatest since 2011. However, success depends upon the CMS experimenters and their CERN lab support fixing some significant technical problems afflicting the CMS detector and causing it to misbehave some fraction of the time. The ATLAS detector is working more or less fine (as is LHCb, as far as I know), but the LHC can’t run at all while any one of the experimental detectors is open for repairs. Let’s hope these problems can be solved quickly and the 2016 run won’t be much delayed.

There’s a lot more to say about other areas of the field (gravitational waves, neutrinos, etc.) but other bloggers will have to tell those tales. I’ll keep the website on-line, and will probably write some posts if something big happens. And meanwhile I am slowly writing a book about particle physics for non-experts. I might post some draft sections on this website as they are written, and I hope you’ll see the book in print sometime in the next few years.

Be Careful Waking Up a Sleeping Blog

After a very busy few months, in which a move to a new city forced me to curtail all work on this website, I’m looking to bring the blog gradually out of hibernation.  [Wordsmiths and Latinists: what is the summer equivalent?] Even so, a host of responsibilities, requirements, grant  applications, etc. will force me to ramp up the frequency of posts rather slowly.  In the meantime I will be continuing for a second year as a Visiting Scholar at the Harvard physics department, where I am doing high-energy physics research, most of it related to the Large Hadron Collider [LHC].

Although the LHC won’t start again until sometime next year (at 60% more energy per proton-proton collision than in 2012), the LHC experimenters have not been sleeping through the summer of 2014… far from it.  The rich 2011-2012 LHC data set is still being used for new particle physics measurements by ATLAS, CMS, and LHCb. These new and impressive results are mostly aimed at answering a fundamental question that faces high-energy physics today: Is the Standard Model* the full description of particle physics at the energies accessible to the LHC?  Our understanding of nature at the smallest distances, and the future direction of high-energy physics, depend crucially on the answer.  But an answer can only be obtained by searching for every imaginable chink in the Standard Model’s armor, and thus requires a great diversity of measurements. Many more years of hard and clever work lie ahead, and — at least for the time being — this blog will help you follow the story.


*The “Standard Model” is the theory — i.e., the set of mathematical equations — used to describe and predict the behavior of all the known elementary particles and forces of nature, excepting gravity. We know the Standard Model doesn’t describe everything, not only because of gravity’s absence, but because dark matter and neutrino masses aren’t included; and also the Standard Model fails to explain lots of other things, such as the overall strengths of the elementary forces, and the pattern of elementary particle types and particle masses. But its equations might be sufficient, with those caveats, to describe everything the LHC experiments can measure.  There are profound reasons that many physicists will be surprised if it does… but so far the Standard Model is working just fine, thank you.

Quantum Field Theory, String Theory, and Predictions

One of the important lessons of last Tuesday’s debate about string theory is that if I’m going to talk about theories that do or don’t predict things, I’d better be very clear about

  • what’s a theory?
  • what’s a scientific theory expected to do?
  • what’s a prediction?

On Thursday I asked my readers if they felt misled by Tuesday’s article. Most didn’t feel that way (I’m gratified), but if you’re a good scientist you focus attention on the negative feedback you receive, because that’s where you are most likely to learn something. And you also look for negative signs in the positive feedback. So thank you, especially those who were critical yet reasonable. I will respond in due course, by putting out a better, clearer article on what string theory can and cannot do, on what we know and do not know about it, a bit about its history, etc. Then I can avoid creating or contributing to confusions, such as the ones Dr. Woit expressed concerns about.

But today I want to explain why I found my conversation with Dr. Woit troubling scientifically (as opposed to pedagogically or politically). It wasn’t because I’m a string theorist — in fact, I’m not a string theorist, by anyone’s reasonable definition (except possibly Dr. Woit’s [and probably not even by his.])

I’m a quantum field theorist. Quantum field theory is the mathematical language of particle physics; quantum field theory equations are used to describe and predict the behavior of the known elementary particles and forces of nature.  Throughout my 25 year career I have mainly studied quantum field theory and some of its applications. Its applications are many. I have focused on the applications to particle physics, with some also to string theory, astronomy and cosmology, and even quantum gravity. (Other applications that I haven’t worked on include the physics of “condensed matter” — solids and liquids; magnets; electrical conductors, insulators, and superconductors; and a lot of weirder things — and phase transitions, such as the melting of a solid to a liquid, or the change of a material from magnet to a non-magnet.)

And meanwhile, while doing quantum field theory, I use every tool I can. I use fancy math. I use what I can learn from other people’s experiments, or from their big numerical simulations.  Sometimes I use string theory. Sometimes I use computers.   If loop quantum gravity were useful as a tool for quantum field theory, I’d use it. Heck, I’d use formaldehyde, bulldozers, musical instruments and/or crowds of hypnotized rats if it would help me understand quantum field theory. I’ve got a job to do, and I’m not going to stray from it just because somebody with a different job (or an axe to grind) loves or hates my tools.

The Scientific Issue

So here’s what bothers me about Dr. Woit’s argument.  First he said: “to deal with the scientific issue here and make an accurate statement, one needs to first address the following:

  1. What is a prediction?
  2. What is string theory?
  3. What are the vacuum states of string theory?

Hard to argue with that!  [He elaborated on each of these three points, but I leave it to you to go back and read the elaboration if you like.]  And then he concludes:

What is the difference between this situation and Quantum Field Theory? That’s pretty simple: no problems 2 and 3. And those problems are not problems of calculations being hard.

Woit’s implication is that we do know what field theory is and we do understand the vacua of field theory… and that while prediction in field theory is merely hard in practice, we know what we are doing… and that we understand so little about string theory that prediction in string theory is impossible in principle.  This, as a quantum field theorist, I strongly disagree with.  

If you are concerned, as you should always be in these situations, that Woit’s being misquoted or quoted out of context, you can go back and reread the comment exchange to Tuesday’s post.

What bothers me about this is that this kind of sweeping statement does a disservice to both subjects: it understates what we know about string theory and overstates what we know about quantum field theory. If only quantum field theory always made it straightforward (albeit difficult) to make predictions! My job would be a lot easier, and it might even be much easier to solve some of the deepest puzzles in nature.

Also, this blanket statement leaves it completely unclear and mysterious why string theory could be such a helpful tool for a quantum field theorist like me — which is a real loss, because the usefulness of string theory for field theory is one of the most interesting aspects of both subjects.

Our understanding of quantum field theory, while perhaps no longer in its infancy, is still clearly in adolescence, at best — and it seems likely to me that we know even less than we think. And I think that many of my readers would like to hear more about this.

What I intend to do over the coming weeks, as time and news permits, is

  1. describe to you what we do and don’t know about quantum field theory
  2. describe to you what we do and don’t know about string theory
  3. explain how, over the past 20 or so years, we have used some of the things we do know about string theory to learn some things we didn’t know (and often didn’t know we didn’t know) about quantum field theory.
  4. describe how one can use quantum field theory to learn something more about string theory

I’ll do items numbers 1 and 3 carefully.  Specifically, in number 3, I will focus on predictions made for quantum field theory using string theory [and we’ll talk very carefully, at that time, about what “prediction” means.]) Both 2 and 4 are more nebulous, and I don’t work on them directly, but I think I can do a decent job on them. I’m sure my colleagues will correct me if I get any facts wrong.

What Does “Theory” Mean to a Physicist?

First, an important, fundamental question. When I say: “quantum field theory”, or “string theory”, or “theory of relativity” — well, what is a theory?

It’s not what it means in Webster’s dictionary of the English Language.  It’s not the same as a guess or a hypothesis. It’s not the opposite of a “fact”. It’s something much more powerful than either one.  And it’s certainly not what it means in various academic departments like Literature or Art or even Sociology.

I could write a whole article on this (and someday I might) but here’s the best definition I have at the moment.  Probably there are better definitions out there.  But here’s my best shot for now: in my line of research, a theory is a set of mathematical equations, along with a set of accompanying concepts, that can be used to make predictions for how physical objects will behave, on their own and in combination — and these predictions may be relevant either in the real world or in imaginary (but reasonable, imaginable) worlds.

Wait! Why are imaginary worlds important? Why focus on anything other than the real world?  How could studying imaginary worlds be “scientific”?


  • By studying imaginary particles and forces, we gain insight into the real world: which properties of our universe are true of all possible universes? which properties are common but not ubiquitous? which ones are special and unique to our own?
  • Sometimes the math that describes a specially chosen combination of particles and forces turns out to be much simpler than the mathematics that describes the particles and forces in our own universe. In an imaginary world described by these equations, it may be possible to solve problems that are too hard to solve in the real world.  And even though the lessons learned don’t apply directly to our world, they may still yield fundamental insights into how the real world works.
  • The future may surprise us. Things that are imaginary today might actually turn up, in future, in the real world. For instance: the top quark that we find in nature was imaginary for over 20 years; the Higgs particle was imaginary for almost 50; supersymmetry is still imaginary, and no one knows if it will remain so.]
  • Note Added: commenter Kent reminded me of another excellent reason, and an example of it: “Sometimes it is not possible to understand the real world until we have first understood an idealization of it. There are many examples … [including] the discovery of the laws of motion by Galileo and Newton. For hundreds of years, people followed Aristotle in believing that a moving object would return to its “natural state” of being at rest unless a force acted on it. Galileo and Newton’s breakthrough was their ability to imagine a world without friction or air resistance. Only after they understood this imaginary world could they properly understand the real one and learn that the natural state of an object is to continue moving in the same way UNLESS a force acts on it.

Notice that this strategy is not unique to physics! Biologists who want to understand humans also study flies, mice, yeast, rabbits, monkeys, etc.. From this type of research — often much easier, cheaper and safer than direct research on humans — they can perhaps learn what is common to the biology of all primates, or of all mammals, or of all animals, and/or of all life on Earth, and perhaps also ascertain what it is that makes humans unique. Many experts on Earth’s geology and climate are fascinated by Mars, Venus, and the rocky moons of Saturn and Jupiter, whose similarities to and differences from Earth give us a perspective on what makes the Earth special, and what makes it typical. Kierkegaard, the philosopher, famously uses the technique of “what-if” stories — a story retold with slight differences and a quite different outcome — to try to tease apart the meaning of religious faith within the Abraham-and-Isaac story, in his famous work “Fear and Trembling”.

The Lesson: If you want to understand a particular case, study the general case, and other similar-but-yet-different particular cases, in order to gain the insights that the particular case, on its own, cannot easily give you.  Meanwhile, what you learn along the way may have wider implications that you did not anticipate.  In short, putting one’s imagination to work, in order to learn about the real, is a powerful, tried and true approach to theoretical physics.

Continued here

A New Academic Year

Welcome September!  I’m going to be quite busy for a bit, partly because I have two big science projects that need to get finished, partly because I’m settling in at my new location this week — which always takes longer than one hopes and expects. But I’ve got a few things in the pipeline for the blog, so there will be posts to follow soon.

If you were away last week, you missed the first two sections of a collection of articles that I’m writing on “naturalness”, a concept that’s central to the lines of reasoning often taken by particle physicists and their colleagues, both nowadays and over the past few decades. These articles came out last week, one on Tuesday (explaining what “natural” means in this context, and giving a first glimpse into what particle physicists mean by saying the Standard Model is “unnatural”) and one on Friday of last week, where I explained something about the quantum fluctuations of the fields of nature and how they can have lots of energy — energy which,

I said something (not very much, really) about the first problem on Friday, and it’s not my main focus right now. My plan this week is to start explaining the details of the second problem.

So stay tuned…

A Busy August

The rate of my blog posts has fallen off again, but for good reason… change is in the air.  I decided this past year to leave Rutgers University, after a six-year stint as a professor at their “New” High Energy Theory Center, or NHETC.  [No one ever deletes “new” from a name, cf. Pont Neuf. Corollary: avoid putting “new” in an institution’s title.]  Starting in September, I’ll be a Visiting Scholar at Harvard University. For scale, the distance from Rutgers to Harvard is about the distance from London to Paris.

Needless to say, there are some logistical issues involved in this change! So this is a busy August. In fact this is my third shortened summer in a row. (The previous one was curtailed by a certain dramatic discovery…) So that has reduced my blogging time considerably.

Next week is equally busy — but it will generate some blog posts instead of completely inhibiting them. I’ll be attending and speaking at a workshop on Large Hadron Collider physics.  You can expect relevant blog posts in the next few days.

A Short Break

Personal and professional activities require me to take a short break from posting.  But I hope, whether you’re a novice with no knowledge of physics, or you’re a current, former, or soon-to-be scientist or engineer, or you’re somewhere between, that you can find plenty of articles of interest to you on this site.  A couple of reminders and pointers:

* If you haven’t yet seen my one-hour talk for a general audience, “The Quest for the Higgs Boson”, intended to explain accurately what the Higgs field and particle are all about, while avoiding the most common misleading short-cuts, it’s available now, along with a 20-minute question and answer session.

* If you want a slightly more technical and written discussion of the Higgs field and particle, complete with animated images, and suitable for people who may once have had a semester or two of university physics and math, try this series of articles first, and then go to this series.

* If you’d like to better understand the language of “matter”, “mass”, and “energy” that is everywhere in popular explanations of science, but eternally confusing because of how different authors choose to talk about these subjects, you might find some useful tips in these articles: #1, #2, #3, #4.

* If you need a reminder about what “ordinary matter” (i.e. things like pickles, people and planets) is made of, try this series, which goes all the way from molecules down to quarks.

* If you’re curious about what “particle/anti-particle annihilation” does and doesn’t mean, try this article.

* And here are the types of particles and forces of nature that we know about, and (for the moderately advanced reader) here’s how they’d be rearranged if the Higgs field were turned off.

Hopefully there’s something on that list that interests you, and many links within those articles to other things that may even interest you more.  Have fun exploring!  And stay tuned; I’ll be writing more in the near future…

Seeking Reader Input

So I think the time is approaching for a serious overhaul of this website.  First, there’s that new particle, which very much resembles a Higgs particle, though we’re not sure if it is of the simplest type; clearly many of the older pages on the website have to change to reflect this new information.  Second, the website has grown organically and now resembles an out-of-control thicket; it is difficult to navigate and to manage.  Moving pages around on a website, with all of their cross-links, is a major challenge and not necessarily advisable; one option is to provide a map or guide of some sort, with advice about which pages are devoid of technicalities, which are a bit more advanced and suitable for anyone with freshman physics background, and which ones are rather technical.  And after July’s big success at the Large Hadron Collider, August seems like the best month to get some of this work done.

But well before I start, it’s time for me to get advice from you.  The current purpose of the website is to help you answer your questions about particle physics and related subjects, including wider questions about how science is done. I am curious to know: what are the things about the website that make it difficult for you to find what you are looking for, and what are the things that you feel might help the most?  Please, in answering, consider letting me know what your level of background knowledge is, and perhaps some insight into your goals.  This information will help me understand your suggestions in proper context.

During the overhaul period I suspect blog posts will be somewhat reduced in quantity, but I’ll keep you posted on especially important issues.   And I’ll be producing my “How the Higgs Field Works” series, as well as tying off some loose ends on a couple of other incomplete series.

A Birthday of Particular Significance

Today is the anniversary of this website, born June 29, 2011. And it’s just in time for what could be the biggest news in particle physics in many years.  If we’re lucky, on July 4th the teams that run the ATLAS and CMS experiments at the Large Hadron Collider [LHC] will reveal strong evidence for a Higgs particle of some type [for more info and background click here]. Or, if we’re equally lucky, they’ll reveal strong evidence ruling out the simplest type of Higgs. Only if the results are ambiguous will we have to wait yet again for another six months of data.

Why does this website exist?  For one thing, I thought perhaps I could help address the desire of many in the public to understand more about particle physics and about the process of doing science.  Also, I was concerned that if the Higgs did not show up in 2012, there was a big risk of public and media misinterpretation of the scientific situation, which I hoped I could help counter.  And with the recession taking down my long-standing LHC research plans, I was looking for some non-scientific way to be useful.

The year has been a mixed bag.  The site’s been quoted several times in the media, and science journalists have told me they’ve found it useful.  On the other hand, the site’s readership, which leapt to about 2000 hits a day early on, has stayed fixed at that level for more than eight months. Then there are the controversies. I don’t think one can run a useful modern website without a blog that reports the news in the field, and to properly address important issues with real integrity requires one to take unpopular stands on controversial issues. Unlike some of the other more populist bloggers out there, who seem to thrive on this kind of thing, I hate it. And finally, communicating particle physics is fun and rewarding, but also problematic.  Much of my readership has also read Brian Greene, Lisa Randall, Lenny Susskind, and the like… and will (or should!) soon be reading Sean Carroll’s upcoming book on the LHC and the Higgs… and all of us well-meaning physicists are explaining the same things in slightly different ways.  I’m worrying we’re creating, collectively, a lot of confusion.

For now, the website will continue as is, through the LHC Higgs presentations and into the follow-up period in early July. If strong evidence for the Higgs emerges, the immediate dangers that helped motivate the site’s existence will recede for a few years; there will be general agreement, as there should be, that the LHC has been a resounding success and has a bright scientific future ahead of it. In that case I’ll take a break from reporting all but the most important news (I recommend Resonaances and Cosmic Variance as news sources) and instead will focus on giving the website a needed reorganization; right now it’s very hard to navigate. As for whether the site has a future, and what form that future might take, that will take some thought.

So, a quiet Happy Birthday to this website Of Particular Significance. And then let’s look forward to the news that really matters — the news from Nature — and get the cases of champagne ready, in case the time has finally come to pop the corks.