Einstein formulated the Special Theory of Relativity to describe how an object moving near the speed of light undergoes three specific transformations:
1.Length contracts in the direction of travel.
2.Mass increases towards infinity.
3.Time slows down.
Later, he stated that gravity and acceleration were the same thing, and expanded the theory to describe a gravitational field as a mass-distortion of spacetime.
Can Relativity be expanded further?
(I don’t mean supersymmetry/super strings/M-theory)
I have a nagging suspicion that Dark Matter and Dark energy are in fact spacetime distortions which operate on principles different than GR on galactic/intergalactic scales.
I don’t trust my knowledge enough to explain why in detail, but generally physicists reject the idea that dark matter or dark energy can be explained by the rules changing at very large scales.
Einstein’s breakthrough at describing the anomaly of Mercury’s orbit…the precession of perihelion…finally had a physical/mathematical explanation which couldn’t be explained by Newtonian physics.
Things are “different” when you are within the gravity well of a massive object like the Sun.
If the rules change at the stellar scale, why not change again at the Galactic and Cosmologic scales?
Many people have tried very hard to make that work. It never does.
Furthermore, if dark matter doesn’t exist and is just a manifestation of different rules of gravity, that just adds yet another puzzle, because then we’d have to answer the question of why there isn’t any dark matter. The existence of dark matter is what we’d naively expect: Why should all matter interact with electromagnetism, after all?
Now, dark energy, there you have a point. What we know about dark energy can equally well be explained by either a slight tweak in general relativity (the precise form of the tweak is known, and was familiar even to Einstein), or by a weird substance pervading all of space with exotic properties (and the description of those properties is also known). Right now, it’s in vogue to describe it as a substance, but there isn’t really any substantial basis for that, and if you prefer to explain it in terms of the cosmological constant, you’re not wrong.
Things are different inside any gravity well. Relativity is needed to explain multitudes of things on, above, and orbiting Earth. No GPS without relativity, e.g. No Large Hadron Collider either, and the effects are shown on an extremely small scale.
The Large Hadron Collider has nothing whatsoever to do with General Relativity nor with gravity wells. It does have to do with Special Relativity, but I’m not exaggerating when I say that SR is the best-understood and best-supported theory in the history of science.
I didn’t specify either special or general relativity, so your nitpicking lens is fuzzy.
But both are applicable to the two examples I gave.
It turns out that GPS must account for both special relativity and general relativity to deliver position at 1-meter level and time at 100-nanosecond level to its users.
Of course the long-lastingness of near-light-speed particles that helps the LHC get its results depends on special relativity, specifically reference by @EnolaStraight, whose second post I was responding to, not yours. But it took about two seconds to find a cite from CERN saying that they also run experiments to test general relativity.
According to Albert Einstein’s much-tested theory of general relativity, the modern theory of gravity, antimatter and matter should fall to Earth in the same way. But do they, or are there other long-range forces beyond gravity that affect their free fall?
In a paper published today in Nature, the ALPHA collaboration at CERN’s Antimatter Factory shows that, within the precision of their experiment, atoms of antihydrogen – a positron orbiting an antiproton – fall to Earth in the same way as their matter equivalents.
The only real hole in General Relativity is the prediction by Penrose et al that once enough mass is confined in a small enough space, that the resulting gravitational collapse is limitless– that is, it ends up being a point of zero volume and infinite density. Basically we’re sure that any prediction of physics that gives the answer “infinite” just can’t be right. But short of being able to actually observe micro-black holes we don’t know how to come up with an answer.
I would add a fourth one, the relativity of simultaneity - two observers in different frames of reference cannot agree with each other whether two events occur at the same point in time or not. This is often forgotten, and it’s usually the solution to apparent paradoxes in special relativity (pole in the barn, twins etc.).
While we’re at it, you can describe relativistic momentum in terms of the mass changing with velocity… but it’s a really clunky, awkward description, and there are other, much simpler, ways of describing the results which leave the mass constant.
Right. For one thing the gravity “abberation” is not consistent across galaxies; some galaxies behave as though they are almost entirely visible matter, while most seem to be mostly invisible matter. A hypothesis of dark matter being a kind of “stuff” can explain this; it’s a much harder task for hypotheses of modifications to gravity.
(I know it sounds weird talking about the hypothesis that dark matter is “stuff”, when the word “matter” seems to entail “stuff”, but at this point the term “dark matter” is used for both the phenomenon itself and the hypothesis of it being the result of some kind of invisible mass)
Really?
I’ve only ever heard a cosmological constant as a serious contender. Do you mean since the DESI data earlier this year implied that dark energy might have changed in strength over time?
I mean in the past couple of decades, or so. Even the term “dark energy” implies that it’s some sort of substance. I think that this is because the vacuum energy hinted at by particle physics should qualitatively have the right behavior, but quantitatively, the estimates are so far off that I personally think it’s worse than having no hypothesis at all.
I haven’t seen the specific DESI results you’re referring to, but there have been papers talking about the whatever-it-is changing in strength over time ever since the phenomenon was discovered. It’s never exactly a confident result, though, and mostly just reflects the fact that a model with an added parameter (in this case, a rate of change) will always fit any given data set better than a model without that parameter.