What's your dissertation about?

[Profpointy]

Why don't you do one on Dark Matter? They still don't know what that is. If you could work that out you might win a Nobel and be invited onto In Our Time to explain it to Melvin Bragg. You might even get on the Joe Rogan podcast.

Actually that's a better choice as there is some hope of chipping away at various options and ruling out some of them. Trying to get a workable quantum gravity theory has eluded the greatest of physicists, so implausible even even for a fantasy PhD choice of subject