[Semaphore (OP)]

I siad when and not if because I'm sure someone would have got there, but when? And what else might have got delayed too?

And a related question: do we need another genius to make the next great step?

[zx16]

The concept of "relativity" goes back at least as far as Galileo, in the 17th century.  He compared the relative movements of a observer on a ship, to an observer on land, and noted that there would be no difference in their respective observations. This is a kind of intuitive thought that must have struck everyone throughout history.

Einstein's contribution, was to put the intuitive thought into precise mathematical equations. By publishing his "Special Theory of Relativity", and then the "General Theory" in 1915.  But if he hadn't done it, someone else would have, without doubt.  The whole thing was "in the air" at that time.

So, in answer to your first question, I think "Relativity" would, even without Einstein, have emerged no later than 1920, at tops.

About your second question, do we need a need a new genius, this is very interesting. Has the time for individual geniuses passed?
 
I mean, was there an individual who "discovered" the Higg's Boson?  (if there really is such a thing, which I doubt).  Nowadays, isn't actual scientific discovery more about teamwork, with the strongest personality in the team managing to get the Nobel Prize.  Or is that too cynical?

[evan_au]

Einstein's contribution

Einstein's other major contribution was identifying the speed of light as an upper speed limit.
The hints here were the null result of the Michelson Morley experiment, and aligning that with Maxwell's equations of electromagnetism.

do we need another genius to make the next great step?

Hawking created some pretty fundamental bridges between the high-gravity regime of general relativity, and quantum theory.
He is apparently collaborating now on integrating that with string theory.
Whether it leads anywhere will probably require another 20 years - and a black hole upon which to experiment.

[zx16]

It's interesting to note that Einstein won his Nobel Prize, in 1921 -  not for "Relativity" - but for his paper in 1905, on the "Photo-Electric" effect. Boosted by his paper on "Brownian Motion", in the same year, which deservedly got him big kudos.   Note that both these papers were based on solid physical evidence.

But his "Relativity" stuff never fully convinced anyone, because it is (to misquote Einstein in another but intimately related context), "spooky".

As for Hawking, he also is a practitioner in "spookiness".

What he needs is, as you rightly imply, an actual "Black Hole" to experiment on, so we can all see whether what he claims is true, or more likely a mathematical phantasm!

[geordief]

I heard that Maxwell would possibly have worked it out if he had lived longer.

[zx16]

That's right. I think Einstein was inspired by Maxwell.  Didn't Einstein say that he'd never heard of the Michelson-Morley experiment when he began developing his early ideas?

[Semaphore (OP)]

Thanks for the input. There some interesting views too on this thread:

https://www.quora.com/If-Albert-Einstein-had-never-existed-at-all-in-the-world-would-relativity-theory-have-been-found-and-proposed-by-others-by-now

I think some new genius is overdue now. We've not got very far recently in terms of a 'Theory of Everything', many alternative theories are not testable, and we can't resolve the problem with 'dark energy', which is a plug to make the data fit the theory. We keep smashing things together harder and that's helping but not much.

[zx16]

You might be right , that a new "genius" is due.  But if such a lone person appeared, could such he/she get accepted by the scientific community?

The modern scientific community is a massive assemblage of thousands, or rather hundreds of thousands, of scientists.  They've published huge numbers of papers supporting the current scientific view that "Dark Energy" is real.  They have reputations at stake.  No-one wants the embarrassment of being proved wrong.

So, what would the community make of a single "genius" who tried to publish, in a scientific journal, a paper which conclusively proved that "Dark Energy" doesn't really exist?

Well, the paper would have to be "peer-reviewed".  The reviewing would be done by people with a vested interest in maintaining the idea that "Dark Energy" does exist. So they'd likely reject the paper, and it wouldn't get into the journal.

This modern "peer-reviewing" would've severely obstructed new ideas, if it'd been applied in the past.

For example, suppose Newton's draft "Principia", or Darwin's "On The Origin of Species", had been "peer-reviewed".  By acknowledged experts in Physics and Biology. In the 17th and 19th centuries respectively.

Would the books have got published?