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Comment by mjburgess | Hacker News Reader

Einstein did not discover that the speed of light was fixed. This was a consequence of Maxwell's research on electromagnetism in the late 19th C.

It is entirely reasonable for any physicist (indeed, Maxwell himself could've done it with enough time), to work through the consequences of a non-relativistic equation for the speed of light.

This approach is routine in physics, and there's nothing in it that would appear crazy or unusual. Physicsts do not simply just pluck crazy ideas from their imagination and, from-nothing, deduce possible consequences. This is a myth, and insofar as people do that, they're cranks.

The imagination of a phyiscist is heavily guided by the totality of physics that has been developed. Einstein did not simply say, "what if the speed of light was fixed?"

He said, 'given we have good reasons to suppose it is, what are the concequences on relativity ?'

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> Einstein did not discover that the speed of light was fixed. This was a consequence of Maxwell's research

Maxwell certainly did discover that the speed of light was fixed.

But he did not discover that it was fixed for all observers. It was presumed to be fixed relative to some reference medium that permeated the universe.

https://en.wikipedia.org/wiki/Luminiferous_aether

There were 40 years of experiments after Maxwell figured out the speed of light where people tried to show how the aether worked and how the Earth moved through it, before Einstein "discovered" the idea that the speed of light was fixed relative to all observers rather than relative to the universe.

Which is deeply weird, if you live in a universe where nothing like that has ever been discovered before.

> There were 40 years of experiments after Maxwell figured out the speed of light where people tried to show how the aether worked and how the earth moved through it, before Einstein “discovered” the idea that the speed of light was fixed relative to all observers rather than relative to the universe.

Not quite, experiments already showed the speed of light was fix independent of earths motion before Einstein did anything. 1887: https://en.wikipedia.org/wiki/Michelson–Morley_experiment

Which is why his ideas caught on so quickly, they where an elegant solution for a well known experimental result.

I'd add a not quite to you as well! The Michelson Morley experiment is fabulously interesting. There's a famous quote from Michelson from 1894:

"...It seems probable that most of the grand underlying principles [of physics] have been firmly established and that further advances are to be sought chiefly in the rigorous application of these principles to all the phenomena which come under our notice. It is here that the science of measurement shows its importance — where quantitative work is more to be desired than qualitative work. An eminent physicist remarked that the future truths of physical science are to be looked for in the sixth place of decimals."

Note that quote is from 7 years after his experiment. Michelson did not believe his own result! The idea that he was discovered was correct, was so utterly weird and difficult to understand, that the possibility of it being true simply did not even occur to him, or most of anybody for that matter! He actually thought that his failure to measure the speed of light was related to instrumentation or precision, and he would repeatedly pursue various efforts to try to correct his mistake, which was not a mistake at all!

Basically he showed that (from the perspective of the time) 2+2=5. Naturally he rejected this without even really considering it, while Einstein not only accepted that it might be true, but then spent years working out an explanation for why! Had Einstein been wrong, it would have looked like the odd behavior of a man battling with his sanity, even more so given that much of his key research came while he was working as a patent inspector, no university of the time being willing to take him on as staff!

Michelson & Morley was a flawed experiment.

All you're saying is that it's Maxwell + Michelson–Morley (who discovered there was no aether) that we should thank, more than maxwell alone. That's true.

That is even moreso to my point that einstein did not just say, "what if crazy-unprecedented-idea? "

Add more names if you like, that's only further evidence of my view.

Again, he didn't _discover_ it. He just _assumed it_ and worked out the consequences if it were true, which turned out to be _very weird_. Then it was confirmed through experiment that he accurately predicted the consequences of it.

No, experiments showing a fixed speed of light came first. Ex: 1887 https://en.wikipedia.org/wiki/Michelson–Morley_experiment It’s a critical point people miss. Rather than come up with his ideas in a vacuum Albert Einstein instead was trying to explain some results which seemed really counterintuitive.

He made many other predictions which where tested afterwards. People also repeated the speed of lights tests in new ways, but the light experiments where consistent with earlier results.

Yes, I know that. What was proved by experiment later was the _consequences_ of a fixed speed of light that he worked out. (ie: time dilation, etc)

Did you heavily edit your comment?

- "Einstein did not discover that the speed of light was fixed. This was a consequence of Maxwell's research on electromagnetism in the late 19th C."

It's not enough, unless you explicitly insist that Maxwell's equations are invariant under coordinate transforms. This step is so obvious from the modern perspective that it's easy to overlook (the grandparent comment is insightful!) But pre-modern physicists thought it was the opposite which was intuitively obvious: that the constant "c" in Maxwell's equations implied the existence of a fixed frame in which solely those equations were valid. That Maxwell's equations should "obviously" transform in some different way in which c is additive, like the speed of sound.

Sure; the Lorentz coordinate transformation falls directly out of Maxwell's equations—if, only if, you add that particular coordinate-invariance condition.

> Einstein did not discover that the speed of light was fixed. This was a consequence of Maxwell's research on electromagnetism in the late 19th C.

The principle of relativity, which what OP was talking about, cannot be derived from Maxwell's equations alone.

The speed of light in maxwell's eqns is non-relativistic. That is itself basically just the insight and founding principle of special relativity. The rest is just to work out how to revise relativity to account for non-relativistic velocities -- and this is fairly trivial at the special relativity level.

More novel, from einstein, was GR but many insights here can be found "in the air" amongst professional physicists, in particular you could see GR as following from a formal elaboration of Mach's principle

(itself, in many ways, just a reply to a thought experiment Netwon had made centuries earlier)

The point is that "non-crank" physics doesnt have the crank-like "moments of genuis" that people assume. It isnt just plucking ideas from the air. Those ideas are heavily embeded in thousands of years of reflection

Had anyone presaged the special relativity energy mass equation that would result?

E = mc^2? No, that was absolutely novel.

But special relativity? Yes, Henri Poincare had already come up with a mathematically equivalent theory to special relativity. Einstein's is a much simpler theory by all means, but the original commenter talking about it like it came out of no where and people must have thought Einstein was crazy or lost his mind, that's just a gross misunderstanding of history.

If anything, Einstein's theory of special relativity gained acceptance rather quickly because it basically converged to where physics was already heading.

Special relativity was not surprising. Physics overall was converging toward it.

General relativity, on the other hand, was definitely ahead of its time.

> Physicsts do not simply just pluck crazy ideas from their imagination and, from-nothing, deduce possible consequences.

I have bad news for you.

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