What do "most physicists" work on?

It always amazes me how skewed the image of physics research in the popular press is. To begin with, the amount of coverage is totally unrepresentative for the actual amount of research on a given topic. Controversial and outright fantastic topics are typically hotly discussed, so is everything that captures the public imagination. On the other hand, down-to-earth research like soft condensed matter or statistical mechanics rarely makes headlines.

The field I work in myself, quantum gravity, is among the over-represented fields. If you believe what you read, the quest for quantum gravity has become the "holy grail" of theoretical physicists all over the planet, and we're all working on it because the end of science is near and there's nothing else left to do.

Since coverage by the media is driven by popularity and not by relevance, one can expect such a skewed representation. It probably isn't much different in other areas of our lives. (Who actually wears those wacky clothes that fashion designers celebrate?) What bothers me much more than the skewed selection of topics is how their relevance is misrepresented even in these articles. I must have read hundreds of times that "many physicists" believe this or that, while in reality most physicists couldn't care less and probably have no opinion whatsoever.

Here are some examples:

"According to the current thinking of many physicists, we are living in one of a vast number of universes. We are living in an accidental universe. We are living in a universe uncalculable by science."

Alan Lightman, The Accidental Universe.

"The team’s verdict, published in July 2012, shocked the physics community."

Zeeya Merali, in a recent nature issue, Astrophysics: Fire in the hole!. We note in the passing that the article doesn't have much, if anything, to do with astrophysics.

"Most physicists believe that space is not smooth, but it is rather composed of incredibly small subunits, much like a painting made of dots. This micro-landscape is believed to host numerous black holes..."

Mihai Andrei, in an article titled Finding black holes at a quantum scale about a deeply flawed paper by Jacob Bekenstein. (Which, depressingly, got published in PRD.)

But why limit ourselves to physicists, let's be bold:

"Many scientists claim that mega-millions of other universes, each with its own laws of physics, lie out there, beyond our visual horizon. They are collectively known as the multiverse."

George F. R. Ellis, Scientific American, Does the Multiverse Really Exist? "They" presumably refers to the "other universes," and not to the "many scientists".

So then let's try to quantify "most physicists" by estimating an upper bound on the fraction of physicists who are working on these topics, a sub-area of quantum gravity. The topics under question here tend to appear on the arXiv under hep-th cross-linked to gr-qc or the other way round. That there is no subject category for "quantum gravity" should already tell you that there aren't all that "many" people working on it. First let us have a look at the arXiv submission rates

The left graph shows the total number of submissions, the right shows the percentage. Blue, which presently accounts for about 10%, is high energy physics and collects hep-th+hep-ph+hep-lat+hep-ex. Note that for historical reasons hep is likely to be over-represented in the arXiv statistics relative to the actual distribution of researchers. In hep, pretty much every paper goes on the arxiv, but the same is not true in other areas (at least not yet). Also, hep tends to be a very productive and communicative field, so looking at the number of arXiv submissions rather than researchers is probably an over-estimate. Be that as it may, the topics we are looking for almost certainly occupy less than 10% of researchers.

More data that tells you that the vast number of physicists aren't working on anything related to quantum gravity can be obtained from the number of members in sections of the German Physical Society. The section on Particle Physics (which includes beyond the standard model physics and quantum gravity) has about 2,500 members. The section on Quantum Optics and Photonics has more than 3,000 members, Physics of Semi-conductors 3,800, Low Temperature Physics 1,450, Atomic Physics together with Hadronic and Nuclear Physics come to about 3,000, Material Physics together with Chemical and Polymer Physics and Thin Films another 3,500. Not all sections have membership numbers online, so this doesn't cover the full spectrum. But this already tells you that "most physicists" don't even do high energy physics, certainly not quantum gravity, and have no business with multiverses, firewalls, or "micro-landscapes of black holes".

But we can try to get a better estimate by seeing how many papers are cross-linked from hep-th to gr-qc, assuming that the opposite cross-linking is similarly frequent. For this, we look at the submission statistics of gr-qc for the first four months of the year 2013. It lists the submissions as well as the cross-lists. Click on any of the months, select "show all" and count the number of times "cross-list from hep-th" appears on the page. The numbers I get for January to April are: 70,71,52 and 67. If you look at the titles, you'll note that the papers you find this way fit well to the topics we're looking for.

Comparing these numbers with the total arxiv submissions per month (about 7500), we can estimate that it's about 1%. Multiply by two to account for gr-qc cross-linked to hep-th.

Now this is a rather crude estimate and I have mentioned several reasons why it's inaccurate: 1) Some fields of research are not as well represented on the arXiv as is hep-th. This means 2% is still an over-estimate. 2) Some fields might be more productive in paper output than others. If hep-th is on the more productive side, this means the 2% is even more of an over-estimate. 3) Not every paper in the area we're looking for might be hep-th cross-linked to gr-qc or vice-versa. This leads to an under-estimate. 4) On the other hand, not every paper cross-listed as such is about quantum gravity or related topics. 5) There are probably more people following the literature than actively working on it, which also leads to an under-estimate.

However, even if you'd add up all these errors, you would still be left to conclude that the above quoted uses of "most physicists" or "physics community" are extremely inaccurate and misleading.