An easy, direct link, for example:
Careful observation of the orbit of Mercury —> Special Relativity —> General Relativity —> GPS satellites able to keep exact time —> the map app on your mobile phone.
Careful observation of the orbit of Mercury —> Special Relativity —> General Relativity —> GPS satellites able to keep exact time —> the map app on your mobile phone.
That it was able to explain Mercury's orbit was a nice bit of empirical confirmation after the theory was developed. Having such evidence probably helped get the theory accepted faster; but probably wasn't necessary. Almost by definition, a theory that is ultimately useful can be confirmed without need of astronomy. If the theory is useful to do X, then we can try doing X as an experiment and see if it works how the theory predicts.
As a secondary point, we could probably get GPS to work even without relativity. The core idea makes just as much sense under any theory of a finite speed of light. When we actually launched a GPS constellation and try it, the engineers would notice that the clocks were drifting for some unknown reason. Some ad-hoc corrections later and the engineers could account for the drift based on empirical evidence, likely with regular re synchronization and recalibration of the fudge factors.
What special relativity did was solve the purely theoretical contradictions between Newtonian mechanics and Maxwell's electrodynamics (hence the title of Einstein's paper "On the electrodynamics of moving bodies"), reinterpreting Lorentz' math for the description of movement through the ether as transformations of spacetime itself and doing away with the ether.
There is a myth of Einstein that just isn't credible, which is that Einstein, while working as a patent clerk just came up with Special Relativity out of the blue without anyone's input, without the benefit of history.
But Special Relativity was in the air. Henri Poincare was already writing about relativity, and so were others in years previous to Einstien's publication. If Einstein hadn't published when he did, someone else would have within a few years at best.
Einstein was amazing, also, just a man, but definitely was not the myth taught to us in elementary school, like Abe Lincoln carrying an ax, these are childish and frankly false ideas. Einstein stood on the shoulders of giants, and there was massive amounts of empirical evidence for Special Relativity going back thousands of years, really, billions.[1]
[1] https://en.wikipedia.org/wiki/History_of_special_relativity
Heroes, such as Einstein, are good in that they motivate certain people, me included, to go into natural sciences, but once you start grasping more of historical context of scientific breakthroughs you begin to wonder why some scientists were elevated to that rank in general public's mind.
I would say that this is some kind of PR type selection. It's natural that general public is aware of science communicators (amongs other things) like Carl Sagan, Jacob Bronowski or Neil deGrasse Tyson, but it is interesting that they wouldn't know as much about Lorenz, Poincare or Riemann, even though they have played significant roles in Special and General Relativity developments.
There seems to be a preference for scientists that deal with more concrete problems, easier to understand in a very generic way (Cosmology seems to be a good pick).
Also particular personal struggle like in Hawking's case or personality (Feynman comes to mind).
So it is easier to talk about black holes and expanding universe (Hawking, Einstein) than abstract mathematics with none/loose/difficult to grasp connection to reality (Poincare, Riemann). Outside CS it might even be rare for people to know about Von Neumann.
I wonder from current generation of scientists who will be remembered and what would be a reason behind it.
There seems to be a requirement for some form of mystic atmosphere around a person in order to be talked about.
I don't know how it was in Riemann's, Einstein's or Feynman's times, but today, most of the actual original research in sciences and math (and CS) is done not by the big prof but by the lower tiers, all the way down to PhD students. Those are doing the footwork, write the papers, work long hours with ridiculous pay. Sure you need some visionary at the top, but the actual results are not produced by those.
Everybody is well aware that Elon Musk didn't personally build the first Tesla or the first SpaceX rocket. But big theorems or theories are still named after by the big prof instead of the person who actually did the work.
For general relativity, yes.
> My understanding was that experimental impetus for relativity was the Michelson–Morley experiment
This was one of the results that pointed the way to special relativity. It had nothing to do with general relativity.
> General relativity was then developed on a purely theoretical basis.
No, it wasn't. There was a huge body of experimental evidence already about gravity. It was true that all of that evidence, except for the anomalous precession of Mercury's perihelion, could be explained by Newtonian gravity; but general relativity, as a proposed new theory of gravity, had to also account for all of that experimental evidence. In other words, in the appropriate limiting case (weak fields and low speeds compared to the speed of light), general relativity had to reproduce all of the correct predictions of Newtonian gravity. That was a huge, and very important, experimental constraint.
> Almost by definition, a theory that is ultimately useful can be confirmed without need of astronomy.
Not if the differences between its predictions and the predictions of the previous theory (in this case Newtonian gravity) are only measurable in astronomical observations at the time the new theory is proposed. That was true of general relativity in 1915 and for at least a couple of decades afterwards. The differences between GR and Newtonian gravity for earthbound experiments were simply too small for the technology of the time to measure. So astronomical observations were the only way to test GR when it was proposed.
> we could probably get GPS to work even without relativity
Technology can of course be developed on a purely empirical basis, if you're prepared to make a lot of mistakes along the way that you wouldn't make without a good theoretical foundation. If it hadn't been for the knowledge of relativity on the part of the scientists involved, the GPS satellites probably would have been launched without any capability for adjusting their clock rates. Which would have meant that, once clock rate drift due to relativistic effects was seen, there would have been no way to adjust for it. So those satellites would have become expensive but useless toys, and a new constellation of satellites would have had to be built and launched.
Yes. I assumed that reproducing Newtonian gravity in the classical limit would be considered theoretical, as we had a solid theoretical understanding of Newtonian physics. Implicit in that would be a bunch of empirical evidence; but Einstein wouldn't need to explicitly think about the details of what evidence supported Newtonian mechanics (beyond the general understanding that it was all in the classical limit).
> Not if the differences between its predictions and the predictions of the previous theory (in this case Newtonian gravity) are only measurable in astronomical observations at the time the new theory is proposed.
Such a theory is not "useful", for many definitions of useful. Astronomical observations allowed us to verify Relativity earlier than we otherwise would be able to; but eventually technology advanced to the point where we could conduct satellite based experiments to directly confirm it. The theory was not practically useful until we had this technology.
> Technology can of course be developed on a purely empirical basis, if you're prepared to make a lot of mistakes along the way that you wouldn't make without a good theoretical foundation. If it hadn't been for the knowledge of relativity on the part of the scientists involved, the GPS satellites probably would have been launched without any capability for adjusting their clock rates.
Its not like we launched the entire GPS constellation then just hoped it would work. Before launching the GPS constellation, we launched the experimental Timation satellites to act as a proof of concept. Difficulties with maintaining accurate clocks in orbit would have been noticed then (if not sooner).
GR itself is a classical (i.e., non-quantum) theory. The Newtonian limit of GR is not usually considered a "classical" limit, just a weak field, slow motion limit.
> would be considered theoretical
Ok, then we just have different definitions of "theoretical". To me, having to account for a mass of experimental data is an experimental constraint. It might be easier for a theory to meet it if the theory can be shown to reduce in an appropriate limit to a previous theory that accounts for all that data.
By contrast, for researchers investigating possible quantum theories of gravity, any quantum constraints on their theories can only be theoretical, since we have no experimental data at all on quantum aspects of gravity. But to me, the fact that a quantum theory of gravity has to account for all of the classical experimental data on gravity is an experimental constraint (which any such theory would presumably meet by reducing to GR in the classical limit).
> Such a theory is not "useful", for many definitions of useful.
No theory is useful for all definitions of useful.
> Before launching the GPS constellation, we launched the experimental Timation satellites to act as a proof of concept.
As I understand it, the Timation satellites did not keep independent time using clocks aboard the satellites. They just re-broadcast time signals from the ground. One of the major difficulties with getting GPS operational was the additional complexity involved in having independent clocks on the satellites that would keep their own time, with only periodic updates from the ground. And one of the major issues with that was that many non-scientists involved in the GPS project did not understand relativity and did not believe that the "natural" clock rates of the clocks on the satellites would be different from those of ground clocks, so some kind of adjustment would have to be made. And there was no data from previous projects to convince them since the relative clock rates of previous satellites vs. ground clocks had not been measured. If the non-scientists in the GPS project had not given in to the scientists who wanted to include the capability for adjusting the clock frequency in the initial set of GPS satellites, those satellites would indeed have been useless.
I mean the original context is societal contribution, so getting something import understood faster I think counts, no?
I wished everyone would read "Law, Legislation & Liberty" by Hayek, where he criticizes people who think systems, like economy, work like an organization. That is, that one can through rational planning and arrangement achieve some goal. That is NOT how markets, economy, society etc. works. That is of course an attack on the utilitarian principles.
Only uneducated minds could fall into the trap of thinking in exploitative utilitarian ways about everything, including themselves by self-abusive through productivity obsession. This discussion could not be more US American.