# Star's rosette orbit around our supermassive black hole proves Einstein's Theory of General Relativity correct

Astronomers have observed a star tracing a rosette shape in its orbit around a supermassive black hole for the first time, an effect that provides further proof of Einstein's Theory of General Relativity. The international team of researchers known collectively as the GRAVITY collaboration painstakingly mapped the star's …

1. #### Theory?

Um, if this *proves* Einstein’s theory of General Relativity, shouldn’t we call it a law?

Or not call it a proof.

1. #### Re: Theory?

My pet peeve as well. As they say, proof is for math and booze. Evidence is the word the author is looking for.

1. #### Re: Theory?

Generally agreed, but on the other (gripping?) hand, 'evidence' hasn't been well verbed yet, as a standalone. Of course, there are perfectly viable ways to recast the sentence.

2. #### Re: Theory?

General Relativity has been demonstrated to accurately model the relationship between gravity and time so many times over the last 100+ years, that announcing in 2020 that something proves General Relativity is correct is a bit like my turning on a light switch and announcing that the bulb bursting into life proves the existence of electricity.

The first time General Relativity was used to explain Schwarzschild precession was in 1915, in respect of Mercury's orbit.

1. #### Re: Theory?

Still finding more evidences that could rule out other explanations is always useful.

1. #### Re: Theory?

Still finding more evidences that could rule out other explanations is always useful.

Up to a point. If our understanding of General Relativity was wrong, it wouldn't just be astronomy that was broken.

GPS has been around for nearly fifty years, and its clocks need to be compensated by about 38 microseconds a day because time runs a bit faster in low Earth orbit than on the Earth's surface. Without that correction, GPS position fixes would drift by about 10 km a day which would certainly cause a few problems.*

*http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

1. #### Re: Theory?

But we do have strong evidence that it is wrong, or if you prefer, incomplete, just as relativity exposed the limitations of Newton's laws of motion. The fact that we can't create a consistent view between GR and quantum mechanics should and has set alarm bells ringing. Or have you missed all the speculation regarding string theory or other hypothetical solutions?

1. #### Re: Theory?

Since the incompleteness could very well be in the quantum theory, that is not very strong evidence that GR is either wrong or incomplete. On the other hand, it is known that QM does not predict that gold preferentially absorbs blue light due to the 5d-6s transition distance and so appears yellow, thus we have the field of relativistic quantum chemistry. And then there's gravity... No, I would think relativity has demonstrated more incompleteness in QM than vice versa.

2. #### Re: Theory?

Until recently, the evidence was mainly restricted to the "weak field limit", i.e. where GR was a small correction to Newtonian gravity. This did not discriminate between Eistein's GR and some other GRs. (I guess the existence of black holes was not weak field, but also might not have discriminated). The gravitational wave results were AFAIK the first validations at strong fields.

2. #### Re: Theory?

The scientific meaning of the word "theory" differs from the generally accepted use of the word. Specifically, a scientific theory is reliable, rigorous and comprehensive (thanks Wiki!) which means it can be accepted as proven through mathematical rigour and consensus within the community. Physical proof is just another element of that rigour. The more general use of the word is analogous with the scientific use of the word "hypothesis". So Einstein's Hypothesis of General Relativity would require proving, through one of a few different ways, be it mathematical or observational, before it could be accepted (amongst the scientific community at least) as a Theory.

1. #### Re: Theory?

Still, a theory can be mathematically sound, but not represent a law Nature obeys to.

2. #### Re: Theory?

If you REALLY want to blow the minds of faux-pendants, tell them that the various subbranches of mathematical study are generally referred to as "theory". "Game Theory", "Category Theory" ...

3. #### Re: Theory?

There is no proof of a theory, or law, in science, merely evidence that fits predictions which fail to disprove the theory, which in turn bolsters it. Theories and laws are simply the best fit for the available evidence that we have at this given moment and are always open to be disproven or improved upon.

For example Newton's Law of gravitation is an approximation (i.e. limited in scope and accuracy) of Einstein's general relativity which itself is almost definitely an approximation of some yet to be discovered unified theory of everything.

1. #### Re: Theory?

"an approximation of some yet to be discovered unified theory of everything"

Not necessarily. It's perfectly possible that there are multiple "forces" (for want of a better term) acting independently even at the finest level of detail.

A theory, after all, is only a human attempt to approximate to observed fact. What actually is may never coincide perfectly with any theory we can come up with, if for not other reason that, despite the amount we've grasped so far, everything is quite probably intrinsically beyond our capacities to observe and understand. We didn't evolve to understand the universe, but merely to persist as a species.

"42"

1. #### Re: Theory?

"We didn't evolve to understand the universe, but merely to persist as a species."

Maybe. But then there are these things that require an observer to become real, so sometimes I doubt your statememt.

1. #### Hello Bishop Berkeley

There are no "things" that require an observer to become "real". The universe has been completely real for approximately 14 billion years, most of that time without any observers in evidence.

4. #### Re: Theory?

After more then one hundred years, and many successful experiments and evidences found, it's probably time to call it the Law of General Relativity, yes... but probably people are too used to its original name.

One of the problem is anybody accepts an apple falls (although they usually miss the other essential part - the Apple attracts the Earth too....) - Relativity describes phenomena most people aren't used to - so it looks much more like a theory than a law.

1. #### Re: Theory?

> Apple attracts the Earth too....

I know, right? In happier times I've seen almost half of it queuing outside the store for the latest iBling.

1. #### Re: Theory?

No, that Apple attracts money through the medium of fanboys which fell into the well of its reality distortion field.

Even Einstein would have found difficult to explain Apple's prices which are very relative to the real value of the item itsel, see the $999 stand and the$699 wheels.

Anyway the rosetta orbit is very much alike the trajectory of a fanboy in an Apple store in front of the latest iDevice.

2. #### Re: Theory?

Except despite our inability to falsify either General Relativity or Quantum Mechanics, there is still the issue of spooky action at a distance.

Don’t mistake our inability to falsify a theory for our acceptance that it is 100% correct.

1. #### Re: Theory?

Nope. If the gravitational wave signals profiles had been different, they could have falsified standard GR. Action at a distance vanishes with SR, and the finite speed of propagation of information. Quantum entanglement doesn't change that.

2. #### Re: Theory?

[...] the issue of spooky action at a distance [...]

This is something that makes us, and famously Einstein, uncomfortable, but it's no reason to disbelieve any theory. There's no rule that says fundamental physical laws need to make sense to us intuitively, and it turns out that they don't: that says something about the limitations of what's inside our heads, but that's all it says.

If QM predicted, for instance, problems with causality (ie time-travel, say) then this would be more of a problem. But it doesn't do that.

1. #### Re: Theory?

If you want to get really freaked out take a look at the theories that grow out of the math of a KERR OBJECT.

1. #### Re: Theory?

Yes, my abandoned PhD (stupid decision to give up, a long time ago & too late now) was on things like that: specifically whether you could get CV solutions from plausible initial conditions.

3. #### Falsify?

Don’t mistake our inability to disprove a theory for our acceptance that it is 100% correct.

FTFY.

Falsify would imply the use of deliberately made-up data to demonstrate that the theory didn't hold, and I'm sure we're perfectly capable of doing that!

1. #### Re: Falsify?

'Falsify' in the sense that is used for scientific theories means 'show experimentally (or perhaps mathematically) that a theory is false in some cases': it does not mean 'use false data'.

Thus you could say that 'the lack of an ultraviolet catastrophe experimentally falsifies classical mechanics' for instance: classical mechanics together with electromagnetism predicts an ultraviolet catastrophe, but we're still here, so something is clearly terribly wrong with the theory.

As a GR person I think that GR has been essentially mathematically falsified: it makes predictions (singularities) which are clearly physically absurd. But it has proved itself very resistant to experimental falsification, which is the more interesting case. In particular experiments to explore cases where we expect it to fail are absurdly hard to do (or even, really, imagine being able to do), and there's at least a good case that all the absurd predictions are always censored so we can't go out and look for them.

I think that scientists would tend to say 'confirm' and 'falsify' in practice, although I'm not sure. Certainly 'prove' makes me uncomfortable even though it has meanings which are reasonable, simply because I spend so much time dealing with mathematical proofs, so that sense has infested my mind, and that isn't the right sense here.

3. #### Re: Theory?

Best stick with calling it a Theory.

The rate at which the local populace break the Laws around these parts, absolute chaos would quickly follow.

5. #### Re: Theory?

This is the original meaning of the words "proof" and "prove", meaning "test".

Still used with this meaning when referring to proof-mark, proving guns, and proving ground.

If something passes a specific test or tests, it has been proven.

Proven has never meant that something is true, only that it has passed the tests.

1. #### Re: Theory?

Still used with this meaning when referring to proof-mark, proving guns, and proving ground.

As well as alcohol strength - originally 100% proof alcohol was concentrated enough that black powder would still ignite if soaked in the stuff. This equates to around 60% by volume, which coincidentally (or not) is the same alcohol concentration required in hand sanitiser to kill a certain bug that seems to be in the news a lot these days.

Oh for the days when you could still measure stuff by blowing things up...

1. #### Re: Theory?

"Oh for the days when you could still measure stuff by blowing things up..."

I present to you: the type Ia supernova. Used for measuring distances (as long as we've got the reason behind the boom! correct).

2. #### Re: Theory?

> originally 100% proof alcohol was concentrated enough that black powder would still ignite if soaked in the stuff

It's not "% proof", just proof or degrees/° proof, 100% alcohol is 175°, that's 75° over proof.

> Oh for the days

It's still not difficult to make your own black powder, 'though you can't walk into a chemists' shop like I did as a kid and walk out with three twists of paper containing charcoal, potassium nitrate and flowers of sulphur.

1. #### Re: Theory?

Potassium nitrate I can collect from the celler walls, charcoal I've got in bags for the bbq. So it's only sulfur that I'd really struggle with. That said, I won't be able to get much more than 10 grams of potassium nitrate off the walls I reckon, there's only a couple of walls it really collects on.

1. #### Re: Theory?

For potassium nitrate you just go to the nearest farm shop and buy a bag of artificial fertilizer. Ammonium nitrate (same source) works even a bit better.

6. #### Re: Theory?

Um, if this *proves* Einstein’s theory of General Relativity, shouldn’t we call it a law?

There's the little matter of dark energy and the perceived accelerating expansion of the universe. If this phenomenon really is occurring, then the theory of General Relativity is not necessarily wrong, but in scientific terms 'incomplete', so calling it a 'law' would not be appropriate.

1. #### Re: Theory?

There's the little matter of dark energy and the perceived accelerating expansion of the universe. If this phenomenon really is occurring, then the theory of General Relativity is not necessarily wrong, but in scientific terms 'incomplete', so calling it a 'law' would not be appropriate.

While people often say this it's not actually true. GR, in its original form, contained a thing called the cosmological constant, Λ (capital-λ). Einstein wanted to use this to let GR support a static universe, as people thought the universe was static at the time he came up with GR: it doesn't work for that, as it's fairly easy to show that such a universe is unstable. And he famously missed a huge trick, which would have been to say that, if GR is correct, the universe must either be expanding or collapsing, with or without Λ. And of course, Hubble &co discovered observationally that it is expanding.

So, since Λ wasn't useful for its original purpose, and since its original purpose turned out to be wrong anyway, people just quietly assumed that Λ was zero. Sometimes it was mentioned in passing (certainly it was when I learned GR in the 1980s), but the later development of the theory would simply omit it. But there was never any good reason to set it to zero: Λ is essentially a constant of integration in the theory, and as such you need to find a way of setting it, which in the case of GR is going to be to go out and look at how the universe behaves. And in the 1990s we finally did that properly, and it turns out that the universe doesn't behave the way GR with Λ = 0 predicts. But as best we can tell it does behave the way that GR with a small positive value of Λ predicts.

So from a GR perspective, 'dark energy' seems to be compatible with Λ being non-zero after all: Λ doesn't give us a static universe, but it does give us a universe which is expansion and whose expansion, at late stages, will accelerate as the positive value of Λ drives it apart.

I say 'seems to be compatible with' because it's possible that the accelerating expansion of the universe requires some more complex thing than Λ to describe it properly. If that turns out to be true then GR is indeed wrong at large scales, beause Λ is really the only parameter you can tweak. As far as I know this doesn't seem to be true: so far a non-zero Λ explains what we see.

7. #### Re: Theory?

In the original sense of 'prove' meaning 'test' or 'try'. Compare French 'prover', Italian 'provare', presumably all from the Latin.

8. #### Re: Theory?

The difference between Newton's Law of Gravity and Einstein's Theory of General Relativity is time. Not space-time, chronological time. Newton wrote the Principia when well proven (I.e. tested) theories were called Laws. By Einstein's time well proven theories were still called Theories.

BTW, Newton's Law of Gravity specified that the Apple attracted the Earth as well as the Earth attracting the Apple. The difference with Einstein's Theory of General Relativity is that Einstein said it was not an attraction but rather a warping of space-time. In either case gathering of fanbois outside Apple stores does cause other people to move towards them.

2. #### Spirograph

Who remembers playing with a Spirograph?

God?

1. #### Re: Spirograph

No, s/he just plays dice. (and the occasional very good hand of poker)

1. #### Spanish Train & Other Stories

And far away in some recess

The Lord and the Devil are now playing chess

The Devil still cheats and wins more souls

And as for the Lord, well, he's just doing his best

2. #### Re: Spirograph

Most gods roll dice, but Fate plays chess, and you don't find out until too late that he's been using two queens all along.

But then there's The Lady, and she has Rincewind.

3. #### Re: Spirograph

God does not play dice with the universe; He plays an ineffable game of His own devising, which might be compared, from the perspective of any of the other players (i.e. everybody), to being involved in an obscure and complex variant of poker in a pitch-dark room, with blank cards, for infinite stakes, with a Dealer who won't tell you the rules, and who smiles all the time.

3. #### Is it just me?

Or does everyone else go off vainly hunting for a footnote every time they see mention of Sagittarius A* ?

(* - not a footnote marker)

2. #### Re: hunting for a footnote

For myself, I just wonder why it's the complex conjugate of Sagittarius A.

And no doubt there are theorists working on quantum black holes who attempt to describe Sagittarius A^{\dagger}.

3. #### Re: Is it just me?

I don't understand the use of the marker either. It's not a star, it's a black hole.

1. #### Re: Is it just me?

The * really is just a marker saying that 'we've already used the name 'Sagittarius A', but we need to add another name for something closely related to it'. Sagittarius A is a hairy radio source, while Sagittarius A* is the presumed SMBH which is probaby driving the emissions from Sag A.

4. #### Re: Is it just me?

https://xkcd.com/859/

5. #### Re: Is it just me?

It's a pointer.

1. #### Re: Is it just me?

Relative or absolute?

African or European?

Coat. The spherical one since the weather looks like being very low pressure today. Baaaa!

4. #### A rosette round a black hole

Whats not to like?

5. #### really fast

"The small orbit and fast motion means that S2 completes an orbit once every 16 years."

Ouch, so the star around the black hole has more or less periods of rotations the same as normally planets around stars ???

If there are any planet around S2, anyone in there should really feel some acceleration !

1. #### Re: really fast

If I recall correctly what I've read, the environment at the center of the galaxy is so full of dangerous radiation that life has virtually no chance of existing on any planet in there, unless there is a really thick atmosphere.

Even then, the concentration of stars (and some large ones) means lots of gamma rays, and those guys don't care about atmosphere.

So no, I don't think that there's anything feeling the acceleration. However, I imagine how mind-blowing it is to think of so much mass gaining so much acceleration. If I could understand the equation for inertia and comprehend the result, my head would probably explode.

1. #### Re: really fast

My head gasket blew at the mention of 20 billions kilometres being described as "close".

2. #### Re: really fast

If there are any planet around S2, anyone in there should really feel some acceleration !

Where gravity is concerned, you don't experience / feel acceleration, as it is your mass that is being accelerated. You only experience acceleration when you are not the thing being accelerated but are stapped to something else that is.

</Pedant Mode>

6. #### Wow

3 percent of the speed of light! Holy shit. That must look awesome from up close*

If we ever want unlimited free energy, we really need to harness gravity - it just doesn't seem to run out, certainly not on the scale that we can use it.

Our current technology is still -->

*Say, 6 trillion miles, with suitable radiation shields

1. #### Re: Wow

If we ever want unlimited free energy, we really need to harness gravity

No, it doesn't work like that. The only way to harness gravity is things like Hydroelectric where gravity is used to get the potential energy out.

Getting energy directly from gravity is the same as getting energy from a stationary permanent magnet; perpetual motion and the universe does not allow that.

However (in physics there's always a "however") should we ever work out how to do anti-gravity then all bets are off.

1. #### Re: Wow

Tidal lagoon hydro-electricity is using gravity. When you hold back the tide, the moon experiences that little bit more drag, and orbits a tiny fraction more slowly and further out.

1. #### Re: Wow

When you hold back the tide, the moon experiences that little bit more drag, and orbits a tiny fraction more slowly and further out.

Which also relates to why the length of an Earth day is slowly increasing as the Earth's rate of rotation is slowed down (albeit imperceptably slowly.) At some point in the future the Earth will be tidally locked to the Moon in the same way that the Moon is tidally locked to the Earth today, and an all-night party will inevitably incur liver damage...

2. #### Re: Wow

Tidal lagoon hydro-electricity is using gravity.

In the same way as hydroelectric does. It uses gravity as a tool to get at the potential energy it is not directly tapping gravity which is what the OP was suggesting.

Gravity is a function of mass, it cannot be "consumed". As long as the mass is constant the gravitational attraction is constant so it cannot be an energy source.

2. #### Re: Wow

What do you think hydro-electric is?

1. #### Re: Wow

Hydro-electric is a steam engine powered by the Sun. Sun warms ocean, creates water vapour which then descends as rain and is used to exert pressure on the blades of a turbine. Gravity is just part of the means of transmission.

1. #### Re: Wow

Nicely put, an excellent analogy - wish I thought of it first.

1. #### Re: Wow

With the exception of nuclear fission/fusion, all power generation is powered by the sun. It's just a matter of when the sun's energy went in; might be yesterday or it might be real time, or it might be a few million years ago.

Of which - has anyone done the sums yet to see how much wind and solar generators affect the climate/weather? They're both trapping thermal energy and outputing it as thermal energy somewhere else... but I don't know how many gigawatts you have to pull from the environment before it's noticeable.

1. #### Re: Wow

Well, if you consider that the heavy elements could only have been produced by supernovae explosions, then even the fissionable elements came from the energy of some star, albeit not the sun and the energy went in billions of years ago.

2. #### Re: Wow

With the exception of nuclear fission/fusion, all power generation is powered by the sun. It's just a matter of when the sun's energy went in; might be yesterday or it might be real time, or it might be a few million years ago.

I have said this to people on many occasions. But I've just realised that it's wrong! Tidal energy is not powered by the Sun, it's powered by the Earth-Moon system: even without the Sun it would work. You could argue that the Earth-Moon system only exists because of the Sun, or that without the Sun the oceans would freeze, but that's not really the point.

So that's something I've never thought of until just now!

Note that this is only for tidal power: conventional hydroelectric power does of course get its energy from the Sun since the Sun evaporates the water so it can fall high up as rain.

[...] has anyone done the sums yet to see how much wind and solar generators affect the climate/weather?

I think studies have been done, certainly for wind. There are effects, and the effects are measurable, but they're small, and they're certainly small compared with the effects of the alternative of dumping CO2 into the atmosphere. This should not be surprising since human power usage is very small compared with the amount of power arriving on Earth from the Sun.

1. #### Re: Wow

If there was no Sun, then the water would be frozen and you couldn't have tidal power at all.

1. #### Re: Wow

Yes, as I said 'the oceans would freeze'. The point is that tidal power is not extracting energy from the Sun, even indirectly: it's extracting energy from the Earth-Moon system. The Sun is there just to keep the oceans liquid.

And of course this is no problem in fact, as you can just run the system on helium: there's plenty of it out there and it is conveniently liquid at the kind of temperatures you'd be dealing with once the Sun has gone out and the Earth's core has cooled far enough. Before things get cold enough to use helium you can use hydrogen, although there will be an inconvenient gap of some billions of years between the hydrogen freezing and the helium condensing I think. Probably we should just hibernate for that.

Alternatively you can just wrap a big insulating blanket around the Earth and use the heat you generate from tidal power to keep the oceans liquid. This might be the best solution in fact.

1. #### Re: Wow

A fair point, especially the use of other materials.

3. #### Re: Wow

As others have said you can't really do that. What you can do (and I'm sure science fiction books have been written about this) is have a tame black hole and then throw stuff into it, basically controlling its accretion disk. Accretion disks generate deeply amazing amounts of power.

7. #### Proven genius

I'm sure that Einstein himself would insist on his work still being called a theory, not a law, for all the reasons so clearly and concisely outlined above. That said, I wonder how many other theories have had so many data collected which all say if not, "he was right", then very loudly say "he was not wrong". Given the difference between what is known now and what was known when he formulated his theories, the fact that "proves Relativity" type headlines (however imprecise/inaccurate) continue to be written is an impressive legacy and a testament to his genius.

1. #### Re: Proven genius

"Relativity Proven!!!" type headlines are also much catchier than simple "Yet another case of things working like we thought they would" ones.

1. #### Re: Proven genius

Does this strip prove your theory?

SMBC

8. #### Trantor

TO think that Asimov placed the capital of the Galaxy at its centre. Not a very friendly place,we now know!

1. #### Re: Trantor

They probably used blacks holes as corner pockets for inter-galactic billiards contests.

They also make great trash compactors.

9. #### missed point

SHINEY !!! I want one ! when is Apple going to release one?

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