What is the reason that there are so many questions at this stack (physics) comparing to the others?

Question

As far as I know on this physics stack are far more questions posted than other stacks. But why is that. I can't imagine that a study of biology, chemistry or history etc. would comprise less detailed information or question. Is that because in physics is so much unclear comparing to other studies or is it very difficult to understand is well, or are there just more students doing physics or is it just more interesting?

Answer 1

Looking at the sciences only,¹ the total numbers can be found here (sorted by total number of questions). I've made an abridged table here:

Site          Quest.
--------------------
Math         573,000
Stats         74,000
Physics       72,000
MathOverflow  69,000
Chemistry     14,000
Biology       11,000

All of these sites are more than 3 years old (with MO, Math, Stats & Physics all being more than 5), so I don't think time is a factor here.^{see below} What probably is a factor is the number of users:

Site          Users 
--------------------
Math         241,000
Stats         78,000
Physics       81,000
MathOverflow  53,000
Chemistry     16,000
Biology       14,000

There are 5 times as many users on Physics as Chemistry & Biology, which seems to correlate to the 5 times as many questions found here than there.

Why there are 5 times as many users here, I'm not sure. But, I suspect it boils down to several factors: site policy, popularity (both academic & general interest), and difficulty of subject among them.

Response to criticism:

It was presented in the comments that age should be a factor in the number of questions. On a naive level, it makes sense: if you've been around longer, you're likely to accrue more questions. And this is sorta backed by data:²

All data taken from the SE team, but I'm putting a cap at 1e5 (which ignores a few sites, including Math.SE & SO).

But look at ~40500 (which corresponds to about 5 years, 8 months ago). That's quite the spread of question totals on a single date! Look at the table below, these are the sites that are 5 years, 8 months old.

  Site         Q       U
--------------------------
Web Apps      19k     69k
Arqade        65k     82k
Webmasters    23k     45k
Cookign       14k     29k
GameDev       31k     61k
Photography   16k     31k
Stats         76k     79k
Math         576k    242k
DIY           22k     31k
GIS           65k     49k
TeX          108k     79k
AskUbuntu    219k    328k

Which is just fairly inconsistent with the naive hypothesis that age should be important. Going back to the graph, there are some younger sites that have more questions than older sites, including Russian SO (81k questions in 1 year)!

So while it's reasonably true on a very naive level, I don't see how someone can claim it as an important factor, as was done in the comments.

<sup>1. The technology sites dominate, with Stack Overflow having over 11 million questions at the time of writing; Ask Ubuntu & SuperUser have more than 200,000 questions as well. All three of those sites have more than 300,000 users as well.
2. A log-linear version of the plot can be found here; this shows the roughly linear fit (meaning power-law relation, roughly n=-71 at R-sq=0.47).</sup>