Technologies made possible by general relativity

I’m not a physicist, but I’m doing a lot of reading lately on Einstein.

As I understand it, the concensus is that special relativity would have been formulated within a few years of the 1905 paper, but general relativity was much more advanced, and quite possibly might have not been discovered yet.

Assuming this is true (corrections welcome if it isn’t), what technologies would not have been possible until the formulation of general relativity? E.g., I assume nuclear energy was dependent on GR.

Global Positioning systems are at least they have to correct for it so, if we did not know about relativity, we couldn’t get the signals to be received the way they need to be in order by calculate a position. Long-term space probe tracking - same deal.

Nope. Nuclear energy is dependant on Special Relativity (the famous equation E = mc[sup]2[/sup] is from SR), and probably quantum mechanics (though probably not so much, that: You’d need QM to calculate some things a priori, but you could also probably get most of that from experiments, without understanding why). But GR, which deals with gravity, is completely irrelevant for nuclear reactions.

Among current technologies, GPS is the only one I can think of. Even there, though, we could probably have figured out how to correct for the effects, without necessarily knowing the causes. Most likely, with the launch of the GPS satellites, we would have figured out GR, if we didn’t have it already. As it is, they’re currently the best experimental test we have for many of the features of GR.

Then there are several technologies which we may eventually develop (or rather, will, if our civilization lasts long enough) utilizing black holes. Those, of course, would be heavily dependant on GR. But we’re not there yet, and probably won’t be for a long time.

That’s Special Relativity, not General.

I don’t understand this sentence. SR “would have been formulated” and GR “might have not been discovered yet” under what circumstances? And “yet” is a reference to what point in time?

-FrL-

Not really. As Chronos notes, you could fudge it; the impact is minor and could be easily emprically determined. Ditto for tracking interplanetary space probes, and in fact adjustments for the effects of relativity are so minor compared to error that they’re often not computed at all. I’m not sure you’d even need to worry about the effects of GR for excursions to nearby stars.

I can’t think of anything else that really is signicantly impacted by GR. We use technologies that involve gravity all the time, but not at the gradients at which GR is manifested. Save for time machines, warp drives, polarized gravity fields generated by fields of charged quantum black holes in an active magnetic field, and other totally speculative sci-fi stuff like that, I don’t see that there’s any obvious technical application for GR. But it’s still fun stuff, and knowing about it lets us understand all manner of other phenomena in the Universe.

I believe he’s referring to the time dialation effects that come from being inside a gravitational (noninertial) field. The effects are small but measurable at microsecond precision.

Einstein didn’t develop Special Relativity in a vacuum; the general concepts had been floating around for at least a couple of decades. The case for General Relativity is even more shaky, as Einstein’s theory was heavily dependant on the work done by Daivd Hilbert and students who in all fairness should probably be co-credited. It’s likely that someone would have put together the ideas at some point, as the critical mass of information and ideas was coming together. I wrote more extensively on the topic [post=7946575]here[/post].

Stranger

It’s both.

Special relativity is needed to correct for the satellites’ speed in orbit relative to the earth; general relativity is needed to correct for the gravitational effects.

The profundity of my lack of understanding is even this deep: That I can’t understand how what you wrote here is a way to answer the question I asked.

To explain my post further, and hopefully to shed light on what I’m missing:

The sentence I quoted from the OP is in terms of “would have” and “might have.” Sentences with such a “might have” phrase generally mean something like “under non-actual circumstance C, X might have done Y.” But I do not know what C is being alluded to in the OP. For this reason, I do not understand the meaning of the sentence I quoted from the OP.

-FrL-

Any idea what the errors for these two corrections are?

I think C is “had Einstein never existed.” As in, even without Einstein, Special Relativity would likely have been formulated by someone else.

See post #6. Actually, doing a crude back-of-envelop calculation gives me corrections on the order of 10[sup]-5[/sup] seconds/day; like I said, small but measureable, especially when measuring errors are within a small fraction of an arcsecond from orbit to surface.

Stranger

Got it! It all begins to come together for me now… :slight_smile:

-FrL-

Aren’t astronomers using gravitational lensing so image distant objects? I seem to recall reading something about that not long ago.

It is used, along with other methods, to estimate masses and distances of extrasolar bodies that are either very nonluminous or comparatively small (large planets, MACHOs, black holes). I guess that qualifies, though it certainly isn’t anything that, at least currently, has much impact on daily life; it’s basically of interest to astronomers, astrophysicists and cosmologists, and science geeks who crack open Cosmos every so often to look at the totally cool pictures of conceptual interstellar spacecraft. :wink:

Stranger

I’d dispute the claim for GR. Yes, there was plenty of work being done on Riemannian geometry, but how much of it was done by physicists, in the context of gravity? Many others could have and probably did describe the behavior of objects in a curved space-time, but without Einstein, would anyone have realized that the presence of mass would cause a curvature of space-time, and that this distortion by mass could account for gravity? For that matter, would anyone have even realized that curved spacetimes actually describe our Universe at all, and aren’t just a clever mathematical construct? So far as I know (though I could be mistaken: History of science isn’t my forte), Einstein was the only one doing work in that direction.

This is in contrast to special relativity, whose physical consequences were already being measured and studied, and in a practical, not just abstract mathematical, way. The seeds of SR were already sown in Maxwell’s equations, for anyone who knew to notice them, and even without Einstein, the Michelson-Morley experiment would have forced it to everyone’s attention.

In grad school, I read some fascinating papers by Helmholtz investigating the possibility of curved spacetime from the physicist’s perspective. He concluded that a variably curved spacetime was ruled out by existing physical observations; if spacetime was variably curved, he proved, we would see objects appear to accelerate without being subject to forces (from our Euclidean perspective), and since we observe no such thing, spacetime must be of constant curvature. His math was all perfectly correct–he was millimeters from uncovering general relativity, but his assumptions blinded him, and there weren’t any known issues with Newtonian gravity to inspire him to look harder. Had there been, there’s little doubt he would have worked it out decades before Einstein showed up … But who knows how often geniuses of that caliber turn up in the world?

precession of Mercury.

like I said.

>he was millimeters from uncovering general relativity, but his assumptions blinded him

See, that’s the thing. What you gotta love about Einstein is what he was able to recognize about assumptions. Did anybody else even recognize as assumptions the assumptions Einstein let go?