In many experimental sciences, a lot of research projects now require an effort that a few authors cannot handle. There are some discussions if this means that instead of being creative, people are merely scaling up, which is probably true in some cases, but often strong empirical results that enable "real-world" progress require such efforts. But that's not Math. I work (partly) in a field of theoretical CS which is Math-heavy and attracts mathematicians and there I also feel the indirect effects of Covid-19. As a junior in the field, I need to rely on the feedback of more senior people, and these people move fastest on the whiteboard/with pen and paper, in physical meetings. The good thing about these collaborations is that we juniors can provide fresh ideas and the seniors can shoot down the bad ones quickly (before a long, formal review process) and make sure the good ones are executed with the necessary rigor.

(Note: I find the comment of "your" reviewer strange as well.)

Many current problems are simply too complex to be solved by a single person, often because it requires expertise from very different fields. High energy physics, biology and neuroscience come to mind. There is not a single person who understands all aspects of CERN. Likewise there isn’t a single person who understands how to 1. Build a large scale Electron microscope to acquire high res images of an entire brain 2. Analyze hundreds of terabytes of data to make these images usable and 3. Analyze the results which would require highly specific domain knowledge of neural circuits or other biological features of the system you are looking at. My experience is opposite to yours. You are lost as a lone researcher in many fields and the best papers these days are written by enormous collaborations.

The topic is math, not building megamachines.

I've been following the progress in number theory proofs for the past few years, and email and forums have worked fine.

The parent explicitly talks about science in general. There is a tendency of some (often of those outside of science) that feel like science is getting worse over time and nothing of value is found anymore. The parent seems to echo this sentiment and gives very shallow anecdotes to make his point. Still it is the top comment as of writing. It’s just plain wrong in my opinion.

I didn't argue that science is getting worse in general and that nothing valuable is being done now, and that's not what I believe. I could see how someone could infer the former from the number of authors per paper increasing and me thinking that papers with many authors tend to be worse. My experience, at I said, could be field specific. (I work in fluid dynamics.) My view is more that science has never been particularly well done as a whole, though some recent things like the reproducibility crisis in social science and verification and validation in engineering have been promising.

That some projects require a large amount of expertise that no single person is likely to have is true. But there are disadvantages to having more authors as well, e.g., "design by committee" immediately comes to mind. And I don't think a majority of current projects require expertise that no individual could have to an extent that would explain why collaboration is expected in science. Ultimately I think a mix of the two would be ideal for science in general, with a larger contribution from individuals than is seen at present.

Also: If my example is a shallow anecdote than your CERN example is as well. I don't have hard data on any of this and you didn't mention any either. I'd be happy to look at any hard data that exists, but I don't know if there is any.

Unless you were planning on going to Subway anyway:

https://www.independent.co.uk/news/science/that-figures-prof...

Others have mentioned the size of projects, which might be true.

Another factor is the incentive structure. There's immense pressure to obtain grants (due to indirect fund income) and focus on h factors increases this as well. The best case strategy given both of those incentives is to have large groups of people who each submit as many grants and papers as possible, and put each other on each submission. That way, even with a high grant failure rate each will bring some money in, and self-citations to a paper will be multiplied by the number of authors.