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Byron Jennings | TRIUMF | Canada

View Blog | Read Bio

The Trouble with Particle Physics*

Ya got trouble, my friend, right here,
I say, trouble right here in River City.[1]

What is the current trouble with particle physics? That’s an easy one: a paucity of new experimental results that challenge the status quo. In contrast, in the past twenty years, cosmology has surged ahead, fueled by the new results from COBE, WMAP, Hubble, and other novel devices. Yet that field may now also be reaching the point of diminishing returns. Without new experimental results any field stagnates. But before addressing this in more detail let’s look at some other suggested problems with particle physics.

One of the criticisms of particle physics is the large size of the collaborations. Well that is just the nature of beast. To probe short distances we need large machines. They are expensive and require large collaborations to build, operate and maintain. Being a successful member of a large collaboration requires, in part, a different skill set from that for tabletop science.  It relies much more on social skills and no one is required to be a jack-of-all-trades as different members of the collaboration can specialize in different areas. While the skills required may be different they are still as useful to society. The World Wide Web grew out the need for particle physics to collaborate widely. While particle physics still has the largest collaborations, other fields are also moving in that direction. The collaborations need to build and launch satellite observatories are also large. Even nuclear physics is moving towards large, long time span facilities. While still not in the same league as the ATLAS detector at the LHC, the TIGRESS detector at ISAC (TRIUMF) took seven years to build.

Other problems were suggested in Lee Smolin’s book The Trouble with Physics. (It should have been called The Trouble with Particle Physics since it only dealt with that rather small – important but small – part of the totality of physics.) One of his points was that there is too much herd mentality in the field with too many people working on, for example, string theory. To some extent this is a valid objection. Science works best when a variety of different approaches are explored.  However, science is self-correcting and trying to impose diversity from the outside is doomed to failure.  When there are too many people in one area they sooner or later realize this and some move on. People moving on is the only sure sign that there are too many people in a field. Indeed, this is starting to happen in string theory and will probably turn into a stampede when (hopefully not if) the LHC finds surprising new results. He also suggested that particle physics needs more theorists thinking deep thoughts. In my humble opinion, that is the last thing we need – more navel-gazing theoretical particle physicists and this from a long time navel-gazing theorist. What we need are more experimental results so the theorists have something more interesting to gaze at.

Why the shortage data? Two reasons: The first is not really a shortage of data but a shortage of challenging data. The standard model of particle physics is just too damn (am I allowed to say that?) successful. The detectors at the Large Hadron Collider (LHC) are starting to churn out data but to date nothing earth shaking. Essentially all tests of the standard model have failed to find anything new, at least at a convincing level. The one possible exception to this is neutrino physics with the underground detector systems. Whether this is an exception depends on how you define the standard model. Independent of that, the neutrino mass and mixing measurements have added excitement to the field with a number of new results, for example the neutrino mixing angle, θ13, from T2K and Double Chooz.

The second reason is the size and time scale of particle-physics projects. For example the LHC has taken more than 15 years from conception until it will produce it first interesting results. T2K has taken a shorter time but it is still many years. The long time scales mean that the exciting new results tend to happen infrequently and the large size also precludes doing things in parallel. This is worrying as it makes independent replication difficult. We have only one large hadron collider. A second was planned but cancelled due to the cost.

A new accelerator, the International Linear Collider (ILC), has been planned and worked on for some time. In 2000, I was assured that by 2006 the construction would have started. The bestlaid schemes o’ mice an’ men. Gang aft agley[2].  It has not happened. When it will happen is anyone’s guess. Funding a large accelerator project in the current financial situation is going to be tricky.

So LHC, we are relying on you – no pressure or anything. If the LHC finds the Higgs and nothing unexpected, particle physics will be in tough shape; the dark comedy referred to in the footnote. We have the standard model, which is widely believed to be incomplete, and without unexpected results we have no clue how to go beyond that model – maybe the universe really is fined tuned to many decimal places. Theorists are doing their creative best, but are spinning their wheels. What we need is data to reign in their imaginations.

Not finding the Higgs would be better (except for the public relations disaster) but even then we would need further experimental indications for what went wrong in order to progress. The best result would be herds of unexpected new particles; barring that, finding particles moving faster than the speed of light would do just fine. Then the trouble with particle physics would be over.

Additional posts in this series will appear most Friday afternoons at 3:30 pm Vancouver time. To receive a reminder follow me on Twitter: @musquod

* Not be confused with Hitchcock’s 1955 black comedy: The Trouble with Harry. However, depending on how it turns out, it may indeed be a black comedy.

[1] From the 1963 movie The Music Man.

[2] To a Mouse by Robert Burns