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Detailed analysis of a star’s orbit near supermassive black hole

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Re: Detailed analysis of a star’s orbit near supermassive black hole

#11

Post by contravariant »

wwarner wrote: post #7
RandomTisk wrote: post #4

Does this mean it's at least possible that space and time aren't linked in the way we think? That General Relativity only makes it appear so?

No the finding is that they tested GR near a boundary, where you might expect find issues, and found that it held up. The title and the comment Ghez makes about the interior of a black hole are a bit misleading. As far as interiors of black holes, I can only guess that she's pointing out (a) that we can't directly observe anything past the event horizon and (b) GR doesn't really make claims about what's going on in t…

In the classical black hole model anything that crosses the event horizon only has a limited time before they hit the singularity. Even for particularly big black holes this wouldn't take all that long.

I find it a bit tricky to say if you wouldn't encounter all the stuff that fell in before you though. I've always had trouble reconciling the fact that you won't see stuff enter the event horizon until you're close to it and the fact that black holes can spring into existence. I'm still not all that sure a true black hole isn't merely an approximation that breaks down as you get close.

Re: Detailed analysis of a star’s orbit near supermassive black hole

#12

Post by leereeves »

wwarner wrote: post #7
RandomTisk wrote: post #4

Does this mean it's at least possible that space and time aren't linked in the way we think? That General Relativity only makes it appear so?

No the finding is that they tested GR near a boundary, where you might expect find issues, and found that it held up. The title and the comment Ghez makes about the interior of a black hole are a bit misleading. As far as interiors of black holes, I can only guess that she's pointing out (a) that we can't directly observe anything past the event horizon and (b) GR doesn't really make claims about what's going on in t…

The interior of black holes is one of the situations in which we need a theory that incorporates both gravity and quantum mechanics.

We actually do have a couple such theories and can't verify them because the situations where they differ from GR are unobservable. It's a shame (but not surprising) this research didn't find any observable differences from GR.

Re: Detailed analysis of a star’s orbit near supermassive black hole

#13

Post by mehrdadn »

wwarner wrote: post #7
RandomTisk wrote: post #4

Does this mean it's at least possible that space and time aren't linked in the way we think? That General Relativity only makes it appear so?

No the finding is that they tested GR near a boundary, where you might expect find issues, and found that it held up. The title and the comment Ghez makes about the interior of a black hole are a bit misleading. As far as interiors of black holes, I can only guess that she's pointing out (a) that we can't directly observe anything past the event horizon and (b) GR doesn't really make claims about what's going on in t…

> From what I've read, it's thought that inside the event horizon, black holes are almost totally empty until you get to the singularity (or torus if it's spinning) at the center.

What does that actually mean? i.e. How would a black hole that's mostly empty inside differ from one that isn't?

Re: Detailed analysis of a star’s orbit near supermassive black hole

#14

Post by mehrdadn »

leereeves wrote: post #12
wwarner wrote: post #7

Earlier quoted context omitted.

No the finding is that they tested GR near a boundary, where you might expect find issues, and found that it held up. The title and the comment Ghez makes about the interior of a black hole are a bit misleading. As far as interiors of black holes, I can only guess that she's pointing out (a) that we can't directly observe anything past the event horizon and (b) GR doesn't really make claims about what's going on in t…

The interior of black holes is one of the situations in which we need a theory that incorporates both gravity and quantum mechanics. We actually do have a couple such theories and can't verify them because the situations where they differ from GR are unobservable. It's a shame (but not surprising) this research didn't find any observable differences from GR.

Are the really theories if they're known to be unfalsifiable? Or do you mean they might differ in situations we don't know about?

Re: Detailed analysis of a star’s orbit near supermassive black hole

#15

Post by JumpCrisscross »

mehrdadn wrote: post #14
leereeves wrote: post #12

Earlier quoted context omitted.

The interior of black holes is one of the situations in which we need a theory that incorporates both gravity and quantum mechanics. We actually do have a couple such theories and can't verify them because the situations where they differ from GR are unobservable. It's a shame (but not surprising) this research didn't find any observable differences from GR.

Are the really theories if they're known to be unfalsifiable? Or do you mean they might differ in situations we don't know about?

> Are the really theories if they're known to be unfalsifiable?

They're not unfalsifiable. (Not all of them.) Gravity is weak. Quantum mechanics are small. Measuring such small weak things is not presently possible.

Re: Detailed analysis of a star’s orbit near supermassive black hole

#17

Post by TheOtherHobbes »

mehrdadn wrote: post #13
wwarner wrote: post #7

Earlier quoted context omitted.

No the finding is that they tested GR near a boundary, where you might expect find issues, and found that it held up. The title and the comment Ghez makes about the interior of a black hole are a bit misleading. As far as interiors of black holes, I can only guess that she's pointing out (a) that we can't directly observe anything past the event horizon and (b) GR doesn't really make claims about what's going on in t…

> From what I've read, it's thought that inside the event horizon, black holes are almost totally empty until you get to the singularity (or torus if it's spinning) at the center. What does that actually mean ? i.e. How would a black hole that's mostly empty inside differ from one that isn't?

It's not even obvious what "center" means in this context. Or for that matter "travel" and "get to."

Re: Detailed analysis of a star’s orbit near supermassive black hole

#18

Post by ijidak »

I have a question relating to black holes. The equivalence principle in General Relativity says there is no way to devise an experiment to determine if I am in a craft accelerating due to thrust from "engines" of some g or in that same craft on the ground being accelerated by the same g due to gravity.

But wouldn't this break down inside of a black hole?

Imagine I fire a beam of light directly at a black hole. It would never been seen to come out on the other side, because it would become trapped in that black hole.

But if I fired that same beam of light normal to the path of my craft accelerating at the same g as that black hole, wouldn't the light be able to pass right through it?

So doesn't that break the equivalence principle?

Re: Detailed analysis of a star’s orbit near supermassive black hole

#20

Post by btilly »

ijidak wrote: post #18

I have a question relating to black holes. The equivalence principle in General Relativity says there is no way to devise an experiment to determine if I am in a craft accelerating due to thrust from "engines" of some g or in that same craft on the ground being accelerated by the same g due to gravity. But wouldn't this break down inside of a black hole? Imagine I fire a beam of light directly at a black hole. It wou…

The equivalence is "local only". Meaning that if you take a small volume of space, and measure first order effects, it is equivalent. But over larger volumes of space, there can be second order differences. An example of that is "curvature".

Once you get to experiments involving the geometry of a black hole, you're a long ways away from the local equivalence, and it is no surprise that you can tell that something massive is nearby.

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