Rick16 said:
TL;DR: What happened to unified field theory?
Are there currently professional physicists who work on Einstein’s quest to unify the gravitational field and the electromagnetic field (as classical fields), or has this idea been completely abandoned? Is it simply a hopeless endeavour?
There are maybe a dozen or two preprints filed in the
General Relativity and Cosmology category of arXiv on this subject every year (I review the new preprints in that category daily, but don't keep a rigorous count of these kinds of papers, so my estimate is pretty rough but still reality based). See
this Physics Stack Exchange Q and A providing the equation of a simplified model of this kind, and a
preprint of a conference paper from 2009 on the subject.
I don't know how many, if any, of these papers are published in peer reviewed journals. But these preprints are generally written by professional theoretical physicists, not by crackpot lay people.
It isn't a very popular area of research (there are probably something on the order of 4,000-8,000 General Relativity-Cosmology preprints posted every year of all kinds) because we know for a fact that classical electromagnetism is a less accurate description of reality than its quantum mechanical counterpart called "
quantum electrodynamics" or QED for short. So, writing a paper about unifying general relativity and classical electromagnetism isn't an attempt to understand the final and true laws of nature.
Instead, writing a paper about this topic is an intellectual exercise undertaken in the hope that solving the probably easier problem of integrating general relativity with classical electromagnetism could provide an intermediate step to integrating general relativity with the Standard Model of Particle Physics (which is quantum mechanical, rather than classical).
Toy model GR-Maxwell's equations unifications are also considered as approximations of reality to simplify consideration of physical scenarios (often involving black holes) where the math of the Standard Model (which is inherently incompatible with the math of classical general relativity at a fundamental level) is impossible to calculate with. And, even used as a simplified approximation, these papers are often very difficult reading. See, e.g.,
this published paper.
Einstein, of course, was himself trying to formulate a "theory of everything" (TOE) in the era when the strong force, the weak force, and QED were not yet well developed. No serious professionally trained physicist is trying to call a unification of classical general relativity with classical electromagnetism in Maxwell's equations a theory of everything anymore.
This is also probably a good time to mention some of the main research programs very similar in intent to what Einstein was trying to do that are alive and well.
One is an effort to model the Standard Model of Particle Physics (a quantum theory) in the classical space-time of General Relativity, eschewing any effort to develop a theory of quantum gravity.
There are many preprints and published papers that explore the possibility of finding a way to do quantum physics (either in general, or in the specific case of the Standard Model of Particle Physics) in the curved space-time of classical General Relativity, as opposed to the "flat" space-time of the Standard Model. The Standard Model incorporates special relativity but not general relativity, and the "flat" space-time in which it operates is called
Minkowski space-time.
The most well-known fruit of this research program is Stephen Hawking's 1974 introduction of the concept known as
Hawking radiation, which flows from treating ordinary matter in a quantum mechanical way, while treating general relativity in a classical way.
Another example, which is far less notable, is a fairly recent preprint (which, to be clear, is a quite speculative preprint that I'm citing only to give you a flavor of the kind of papers being written these days and not to argue for this theory) that argues that the apparent neutrino mass in the Standard Model could actually be an effect of massless neutrinos operating in the curved space-time of General Relativity, creating an effect that is absent in the Standard Model in Minkowski space-time. That preprint is: Golam Mortuza Hossain, Pushpit Kumar, "Neutrino Oscillations without Mass: A Re-analysis of KamLAND Data following the Dirac Equation in Curved Spacetime"
arXiv:2609.39638 (September 30, 2026).
The other research program is an effort to unify the (quantum) Standard Model of Particle Physics with gravity by developing a viable quantum gravity theory to replace classical general relativity.
This second research program is the more popular one (with many subbranches of different approaches to coming up with a quantum gravity theory) and had looked very promising in the 1970s and 1980s.
But various mathematical roadblocks to making this approach work (especially the problem that the most obvious path to doing so is "not renormalizable" which basically means that it has mathematical properties that make it impossible to calculate with) slowed progress on this front to a snail's pace since then.
This is where most physicists think the truth probably actually lies, but so far, they can't make it work.
