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DaCaptain
2017-Jan-21, 07:13 PM
Does this make sense? If the gravity of a black hole is so strong that light can't escape, does that mean gravity is "faster" than light?

a1call
2017-Jan-21, 07:22 PM
It's comparing apples to oranges.
If a beam of light consists of enough energy mass to collapse on itself then they would be on equal footing.

cjameshuff
2017-Jan-21, 08:05 PM
Does this make sense? If the gravity of a black hole is so strong that light can't escape, does that mean gravity is "faster" than light?

Gravity is an effect of the curvature of spacetime by mass and energy. The curvature is already there when the black hole forms and it becomes impossible for anything to escape, so speed isn't an issue. The mass curves spacetime as it falls in and forms/is added to the black hole, it doesn't constantly send out something to keep it curved.

Ara Pacis
2017-Jan-22, 06:35 AM
Gravity is an effect of the curvature of spacetime by mass and energy. The curvature is already there when the black hole forms and it becomes impossible for anything to escape, so speed isn't an issue. The mass curves spacetime as it falls in and forms/is added to the black hole, it doesn't constantly send out something to keep it curved.

I'll ask the obvious follow-up question. Do gravitons count, if they exist?

DaCaptain
2017-Jan-22, 11:32 AM
Here's an interesting article I found on gravitons (http://astronomy-links.net/GravitonComponents.html).

Shaula
2017-Jan-22, 12:03 PM
Here's an interesting article I found on gravitons (http://astronomy-links.net/GravitonComponents.html).
Sorry - but it is pretty much complete gibberish.

Shaula
2017-Jan-22, 12:05 PM
I'll ask the obvious follow-up question. Do gravitons count, if they exist?
Gravitons are one way of modelling the quantised interactions with the more fundamental quantum field. As they are excitations in the field and they are only present for interactions the picture of a body continually beaming out gravitons is a sub-optimal way of visualising what is going on.

cjameshuff
2017-Jan-22, 03:14 PM
I'll ask the obvious follow-up question. Do gravitons count, if they exist?

A massive body is no more a big source of graviton emissions than a charged body is a brightly shining photon emitter. As Shaula said, they are a way of modeling an interaction with a quantum field, not "real particles".

Canis Lupus
2017-Jan-22, 06:57 PM
... is a sub-optimal way of visualising what is going on.

Must try and sneak this phrase into conversation a little. Hopefully the listener will be amused.


... pretty much complete gibberish.

No doubt I will have plenty of opportunity for this one also.

DaCaptain
2017-Jan-25, 05:39 PM
Sorry - but it is pretty much complete gibberish.

That's why I like this blog. Members cut the crap from the internet fog of disinformation.

Geo Kaplan
2017-Jan-25, 05:50 PM
That's why I like this blog. Members cut the crap from the internet fog of disinformation.

Throwing yin and yang into the mix with a random photo of a building housing a synchrotron light source smacks of desperation. That article is such poor gibberish that other gibberish is embarrassed to be seen with it in public.

Shaula
2017-Jan-25, 06:09 PM
That's why I like this blog. Members cut the crap from the internet fog of disinformation.
I'm glad you feel that way! It is hard to know whether to cut to the chase and say "that blog is gibberish" or try to be more circumspect. On one hand the fact that you are looking for more information and new things to understand is great and I wouldn't want to put you off through my bluntness. But on the other hand it is really easy to find superficially science based pages out there that are in fact not much more than fairy stories.

DaCaptain
2017-Jan-25, 06:34 PM
I'm glad you feel that way! It is hard to know whether to cut to the chase and say "that blog is gibberish" or try to be more circumspect. On one hand the fact that you are looking for more information and new things to understand is great and I wouldn't want to put you off through my bluntness. But on the other hand it is really easy to find superficially science based pages out there that are in fact not much more than fairy stories.

So at the top of the questions and answer page there's a huge list of resources under the topic "** FAQs ** Resources On The Web". I take it when I do my research I should stick to resources listed here rather than a generic Google search. Seems like everything here should be properly vetted.

Shaula
2017-Jan-25, 06:54 PM
So at the top of the questions and answer page there's a huge list of resources under the topic "** FAQs ** Resources On The Web". I take it when I do my research I should stick to resources listed here rather than a generic Google search. Seems like everything here should be properly vetted.
Given that there are links in there to places like the Electric Universe sites, Iron Sun pages and Richard Hoagland's sites I'd feel very nervous about recommending that list.

I'd carry on doing your research via searches, but just be careful to check and corroborate what you find. Either ask here or look for sites affiliated with research bodies (although that is not a hard and fast rule). It is tough - the web has given amazing reach to science outreach pages. But it has also given a huge amount of drivel its day in the sun.

cosmonut
2017-Jan-26, 12:41 AM
Why is it that light cannot escape a black hole's event horizon, but gravity is able to punch right through it? If gravity propagates at the speed of light, shouldn't it also bend back in on itself? The answer to this thought experiment seems to point to light and gravity being fundamentally different in some way. It actually lies at the heart of some of the most vexing questions in modern physics. There is much work to do before we can unify EM and gravitation in one theory.

Reality Check
2017-Jan-26, 01:56 AM
The reason that light cannot escape from inside an event horizon is that that every possible trajectory includes the singularity in the future and never the outside of the event horizon.
The reason is that gravity "punches through" an event horizon is because it is already on both sides of the horizon. Gravity is caused by the curvature of spacetime. That curvature is what creates the event horizon.

cosmonut
2017-Jan-26, 03:03 AM
Yes, the question was posed as a thought experiment to which I already gave the answer.

I guess I'm looking beyond the basic physics of it and reconsidering some assumptions about gravity propagating at the speed of light (something that's taught in physics textbooks). Maybe it's incorrect to even say that gravity has a speed.

So to answer the OP's question, I would say that yes, gravity is indeed "faster" than light - at least in certain inertial frames of reference within curved spacetime.

DaCaptain
2017-Jan-26, 04:02 AM
The reason that light cannot escape from inside an event horizon is that that every possible trajectory includes the singularity in the future and never the outside of the event horizon.

I don't follow how every possible trajectory includes the singularity in the future? Can you explain this better? (preferably in newbie language) Thanks

Shaula
2017-Jan-26, 06:33 AM
I don't follow how every possible trajectory includes the singularity in the future? Can you explain this better? (preferably in newbie language) Thanks
Essentially it means that spacetime is so curved that no matter which free-fall path you take from a point inside the event horizon it always ends up taking you to the centre. Throw your rock ahead? Eventually it reaches the centre. Throw your rock right? Same thing. If you then try to work out what route you would have to take to get to a point outside the event horizon you'd find that there simply wasn't one.

Grey
2017-Jan-26, 02:18 PM
Yes, the question was posed as a thought experiment to which I already gave the answer.

I guess I'm looking beyond the basic physics of it and reconsidering some assumptions about gravity propagating at the speed of light (something that's taught in physics textbooks). Maybe it's incorrect to even say that gravity has a speed.

So to answer the OP's question, I would say that yes, gravity is indeed "faster" than light - at least in certain inertial frames of reference within curved spacetime.This is incorrect, as others have pointed out. Here (http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html)'s a pretty straightforward explanation; we can go into more detail if needed.

cosmonut
2017-Jan-26, 08:28 PM
Which part is incorrect? That link doesn't add anything new. Just confuses things by introducing gravitons and virtual particles. Here's a better explanation with some background history:
https://briankoberlein.com/2015/08/21/how-does-gravity-escape-a-black-hole/
This seems to confirm that gravity does indeed appear to act instantaneously. I would still answer OP's question in the positive, gravity is "faster" than light (note the quotation marks), simply because light must literally follow gravity (i.e. follow the curvature of spacetime).

Swift
2017-Jan-26, 10:20 PM
I guess I'm looking beyond the basic physics of it and reconsidering some assumptions about gravity propagating at the speed of light (something that's taught in physics textbooks). Maybe it's incorrect to even say that gravity has a speed.

cosmonut

First, welcome to CQ.

Second, if you are not aware, the Answers in Q&A must be completely mainstream answers. Q&A is not for any sort of speculative answers. Speculating in Q&A can get you in trouble.

If you have not done so, I'd suggest reviewing our rules; there is a link in my signature.

DaCaptain
2017-Jan-27, 03:53 AM
The reason is that gravity "punches through" an event horizon is because it is already on both sides of the horizon. Gravity is caused by the curvature of spacetime. That curvature is what creates the event horizon.

Isn't gravity the attraction of two masses, no matter how large or small. I can't imagine there's an event horizon around every grain of sand in the desert. Yet gravity has a hold of each grain of sand on earth. I'm thinking that you could measure the gravitational pull of a black hole with or without the curvature of spacetime.

Hornblower
2017-Jan-27, 04:20 AM
Isn't gravity the attraction of two masses, no matter how large or small. I can't imagine there's an event horizon around every grain of sand in the desert. Yet gravity has a hold of each grain of sand on earth. I'm thinking that you could measure the gravitational pull of a black hole with or without the curvature of spacetime.

Has anybody ever suggested that there might be event horizons around grains of sand?

To get back to the question of what is going on when we do have a black hole with an event horizon, I would prefer not to think of gravity as having a speed. What we call gravitation is a consequence of the curvature of spacetime around massive objects, and according to general relativity that curvature does not depend on anything radiating out of whatever is inside the event horizon in the case of a black hole. It is motion-induced changes in this curved spacetime that propagate at the speed of light.

Jeff Root
2017-Jan-27, 05:21 AM
Isn't gravity the attraction of two masses, no matter how large or small.
Essentially, yes.



I can't imagine there's an event horizon around every grain of sand in
the desert.
There isn't. An event horizon is a feature of an object with extremely
intense gravity, not of every object that has gravity.



I'm thinking that you could measure the gravitational pull of a black
hole with or without the curvature of spacetime.
A black hole is where the curvature of spacetime is equal to or
greater than a certain amount. If there is no curvature, then there
is no gravitational pull and no black hole.

-- Jeff, in Minneapolis

DaCaptain
2017-Jan-27, 01:10 PM
LOL, Lesson learned . . . . think before you type.

DaCaptain
2017-Feb-01, 04:05 PM
So, if light can't escape a black holes gravitational pull, can gravity increase lights wavelength?

Grey
2017-Feb-01, 04:30 PM
So, if light can't escape a black holes gravitational pull, can gravity increase lights wavelength?Absolutely. That's exactly what gravitational redshift is.

DaCaptain
2017-Feb-01, 04:49 PM
Absolutely. That's exactly what gravitational redshift is.

That leads to the question/concussion, is that the reason we're seeing red shift through out the universe? Which is part of the reasoning behind the universe is expanding theory aka the big bang?

Jeff Root
2017-Feb-01, 06:01 PM
A very tiny part of the cosmological redshift is due to gravitational
redshift. Something like one or two percent, I think, although it may
depend radically on how far back you look. As the Universe expands,
it becomes less dense overall, so -- ignoring local variations due to
local concentrations of matter -- light travels from an earlier region
of higher density to a later region of lower density.

-- Jeff, in Minneapolis

DaCaptain
2017-Feb-05, 09:52 AM
So, if light can't escape a black holes gravitational pull, can gravity increase lights wavelength?

If gamma rays can escape from black holes while light can't, does that mean gamma rays are potentially faster than light?

slang
2017-Feb-05, 10:20 AM
If gamma rays can escape from black holes while light can't, does that mean gamma rays are potentially faster than light?

A gamma ray is light. Gamma rays can not escape from the event horizon of a black hole. But in some events there is stuff happening around the black hole, but outside the event horizon. Events that do all kinds of stuff, some of it may result in gamma rays we can detect. Very violent things in the case of a black hole merger, or very energetic things in the case of jets coming from around a supermassive black hole.