See subject. Assume his mind is in mid-season form, as P.G. Wodehouse puts it.
I think black holes would bother him, particularly now that they seem to be pretty much confirmed as factual things. And some of the physics and implications regarding them that have been developed since his death.
At first glance Einstein would be most displeased by the continuing preeminence
of Quantum Mechanics, which he vehemently objected to because of its reliance
on Probability (“God does not play dice with the Universe”).
Perhaps he might now be won over by the supporting evidence developed since
his death, and since his “midseason form” lasted a good 13+ years he might as
a convert be able to make significant contributions to it.
Himself, for being a zombie.
What physics is most:
[ul]
[li]impressive - GR, that he was right, and still being validated today, nearly 100 years later, with no change to the theory.[/li][li]shocking - Continued success of QM to explain everything, except GR.[/li][li]incomprehensible - String theory[/li][/ul]
Since hypothetical questions raise opinions more than facts, let’s move this one from GQ to IMHO.
samclem, moderator
Einstein would be particularly bemused by “dark energy”, considering that he postulated a similar effect to keep the Universe static despite finding the idea inelegant. Once Hubble discovered that the Universe was expanding it, Einstein couldn’t drop the idea fast enough.
Einstein made clear he did not believe in a personal god…he subscribed to Spinoza’s philosphy that god is within nature…i never understood why Spinoza and Einstein referred to nature as a non personal god, that one may communicate with…its just nature, to me. Referring to nature as god is handy when ppl lived in times when you were ostracized (if not killed) for denying a personal god.
Countless ppl have mistakenly quoted this statement by Einstein, as proof he belived in god.
Another big mistake by Albert…he assumed that a quanta of light behaved the same as a gas of quanta
I have read enough by (Ideas and Opinions, a collection of his and bon mots) and
about Einstein to know of his skeptical views on mainstream religion. One of his
biographers referred to those views as “virtual atheism.” I do not understand his
preference for retention of God either, but bear in mind that all-out atheism does
not seem to have appeared in force among scientists until 1-2 generations after
Einstein, with Paul Dirac (fl. ca. 1925 & ff) being the earliest I am aware of
(Darwin was ambivalent, Dirac was not).
I don’t know about the light-gas quanta matter, but quanticization of light was accurate,
and it was what he was awarded his Nobel Prize for.
Even when he made a mistake Einstein raised issues not considered before and requiring attention.
See the Cosmological Constant and EPR on that note. An analogue of the CC (Dark Energy) has appeared
in the last 10-15 years which appears to be accelerating universal expnasion; EPR posed problems about
locality, revived by J. S. Bell in the 1960s.
Frankly, I think he’d be disappointed by how little progress has been made over the past 50 years, compared to the preceding 50 years.
I don’t think any physics today would be incomprehensible to Einstein. Disclaimer: I only say that because I find general relativity and quantum field theory equally inaccessible.
I guess he’d have to bite the bullet about quantum mechanics being here to stay.
That said, if he got up to speed on the Standard Model, and was ‘still in his prime’ he might well make some breakthroughs.
I agree with Alessan that he’d be disappointed in the last 50 years or so of physics, or at least the theoretical side of it. We’ve got lots of amazing experimental/observational stuff - the cosmological and astronomical observations that provide the placeholders ‘dark matter’ and ‘dark energy’, and tons of data from particle physics. But theoretically we’re still chipping away trying to unify two grand theories from completely different mindspaces.
Could he hack the math quickly enough to be able to contribute appreciably?
First off he would be astonished by Bell’s theorem and Alain Aspect’s experimental verification of “spooky action action at a distance”. That would, I think, put an end to his rejection of QM. Second, I think he would find string theory incomprehensible. I think he would be happy with the standard model of particle physics and welcome the Higg’s field (and accompanying boson).
It would be astonishing if he did not find the string model incomprehensible, since that would represent an increase of undefined magnitude in the number of people who comprehend it.
Heh, that’s funny Chronos. 
It was my understanding that Einstein’s objections (or distaste rather) of QM was very early and he later came to accept it. I googled for this but didnt find anything easily to support it. I did find however that the whole ‘god does not play dice’ thing to be a very over simplified misquote, as usual.