One of the reasons we started this website was to raise awareness about the open problems and promising research lines in theoretical physics, particularly in the study of gravitation. However, when we look at what professional researchers in academia are actually doing when they claim to be researching theoretical gravitation, these are the kinds of paper titles we typically encounter on the ArXiv and published in well-known journals:
Spontaneous Scalarization of Black Holes in Gauss-Bonnet Teleparallel Gravity
The phase transition of Rastall AdS black hole with cloud of strings and quintessence
Observable Primordial Gravitational Waves from Non-minimally Coupled R^2 Palatini Modified Gravity
Circularly symmetric thin-shell wormholes in F(R) gravity with (2+1)-dimensions
But there are no wormholes, AdS black holes, strings, primordial gravitational waves or quintessence fields, as far as observations show. F(R), Palatini or teleparallel gravity are not better than General Relativity to describe any natural phenomena we know about in a consistent way. We don’t know which fields are there inside black holes, if any. And we certainly don’t live in 2+1 dimensions or another weird combination of them, with no evidence pointing towards hidden extra ones. Physics is the branch of science concerned with nature, and I can’t see any nature in these papers, only mathematics. What does this all have to do with the observable universe?
You might be wondering why theoretical gravitation research usually looks like this. It is because today’s academic system is driven by citations, and to be cited, one must publish. With the ever-growing number of graduates and PhDs who need publications to advance their academic careers, combined with intense competition, many researchers are pushed toward working on topics that everyone knows do not make progress in gravitational physics, but only “safely” extend some particular lines of research. They are the only way to stand out and secure a position.
And one could say that perhaps this is mathematical physics, which is important for physics, because it was often the case in the past, that new mathematics were required for the new physical theories that were being developed. But this is labelled as normal physics in theoretical gravitation. It is expected for you to work in areas like this if you want to do gravity from the theoretical side, and the topics cited in these papers are popular ones in academia today.
It is easy to get caught in this trap while studying a bachelor or master in physics, since your professor, who you admire because he knows much more than you do about gravitation, is researching these topics. So, you assume he should know better than you what to research, and if you want to join his department, this is what you will be pushed to do.
If you don’t want to participate in this madness, you can compromise and plan to do mainstream physics while doing what you really like and value on the side. But in the end, you won’t have time for it. Some quit and do research independently, others interested in truly understanding the theories become philosophers or historians of physics (for which I have a lot of respect since sometimes they understand physics better than the researchers themselves), and very few do honest new work.
And I know what you’re thinking. Then tell us how research in gravity should be! As we already explained in our previous post about the crisis in theoretical physics, one needs to look back and understand what has worked in the past to make progress in theoretical physics. There are clearly two main ways: solving incompatibilities (mathematical or physical) between theories or in the theories themselves, and solving disagreements with observations. And regarding gravity, we know about both cases! General Relativity is inconsistent with what Einstein considered that a full theory of gravity should satisfy (the General Principle of Relativity and Mach’s principle), it is incompatible with quantum mechanics (this is a correct motivation, although it can derive into nonsense proposals), and it is in disagreement with observations such as dark matter and dark energy, and perhaps also singularities (either the big bang or black holes, although one should focus on the testable theories, which is not the case for the inside of black holes). And one cannot simply hypothesize again and again every possible mathematical trick that could solve them. Research must be motivated by physical ideas and observations, not by pure mathematics.
Here in Independent Physics, apart from explaining aspects of gravity that you won’t find in other places, we explore modified gravity related to the problem of dark matter, and inconsistencies of Newtonian and Einsteinian gravity regarding their foundations, such as Mach’s principle.
And although we have been promoting MOND in this channel, we also believe that some theories related to MOND also fall into the trap of being more mathematical than physical, such as TeVeS or MOG, because of how artificial they become when introducing several fields and free parameters without a physical justification. Join us in our journey searching for the origin of MOND (which is motivated by observations) here, in Independent Physics.