
Detailed analysis of a star’s orbit near supermassive black hole - furcyd
http://newsroom.ucla.edu/releases/einstein-general-relativity-theory-questioned-ghez
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idlewords
This is a weird title given the content of the article, which is that
researchers observing a supermassive black hole got a result completely
consistent with general relativity.

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btilly
The title was the best clickbait that they could get, based on an offhand
comment that the theory has to break down inside the black hole.

But if the title was, "General Relativity succeeds again", who would have read
the article?

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hetman
It's unfortunate some people think having their article read is a priority.
Perhaps we need a browser plugin where people can rank the accuracy of titles
from various outlets so the user can decide if an article is likely to waste
their time.

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ngold
That's a good idea, it's basically why everyone checks the comment section
first.

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agiri
Not questioned, the best approximation we have for now. As for all theories
attempting to describe empirical truth.

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ddingus
That's science. Hate this headline. Basically, every theory is "standing for
now."

We get understanding, that leads to questions, which leads to greater
understanding...

A predictive theory, finally found to not be predictive, is still valid for
all it can predict. Our understanding improves in some way, or technology
does, and we advance all of those things, being able to predict to greater
detail and depth.

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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?

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btilly
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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luc4sdreyer
The title is pretty misleading. Yes, it's technically correct, but it implies
they found something else that might question it.

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dang
Ok, we've swapped it out for the subtitle.

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RandomTisk
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?

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wwarner
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 the very center at the
singularity. 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.

~~~
AgentME
> 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.

I can see how this could maybe be true for a black hole that never has
anything fall into it after yourself, but for regular black holes that have
things falling in regularly I think the situation would be pretty different.
As you get closer to the event horizon, the rest of the universe appears to
speed up. This means that as you get closer, the rate of objects / energy
coming into the black hole past you and sometimes colliding into you will
increase. You can imagine that at some point near the event horizon, every
second, 100 years will pass for the rest of the universe, and 100 years worth
of debris and light will enter into the black hole, some of it colliding with
you. As soon as you reach the event horizon, an infinite amount of time's
worth of debris and light will enter into the black hole, some of it colliding
with you. From inside the black hole, it must look like everything that has
ever fallen into the black hole in the history of the universe has fallen into
it at the same instant. (And then I'm not entirely sure how black hole
evaporation fits into this. I'd expect the perspective of someone going into a
black hole must look like you immediately collide with everything that ever
has and ever will fall into the black hole, and then instantly everything is
obliterated into Hawking radiation.)

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wwarner
I'm just a reader, but Kip Thorne doesn't agree with your picture. In his
book, he claims you wouldn't notice passing through the event horizon, except
for extreme tidal forces that would tear you apart. The time freezing and red
shifting reverse so that looking away from the center, distant objects move
faster and are bluer.

His book for the layman is Black Holes and Time Warps.

~~~
shagie
The tidal forces depend on the size of the black hole.

[http://www.hawking.org.uk/into-a-black-
hole.html](http://www.hawking.org.uk/into-a-black-hole.html)

> ... If you fall towards a black hole feet first, gravity will pull harder on
> your feet than your head, because they are nearer the black hole. The result
> is, you will be stretched out longwise, and squashed in sideways.. If the
> black hole has a mass of a few times our sun, you would be torn apart, and
> made into spaghetti, before you reached the horizon. However, if you fell
> into a much larger black hole, with a mass of a million times the sun, you
> would reach the horizon without difficulty. So, if you want to explore the
> inside of a black hole, choose a big one. There is a black hole of about a
> million solar masses, at the center of our Milky way galaxy.

