APOD: Orbiting a Black Hole (2013 Jul 01)

[Chris Peterson]

That which you said does not move and does not fall into a black hole, which is understandable. IF it does not move, how could it fall. But what is it that does not move?

Basically, I'd say that spacetime is a mathematical construct that models what we observe. It doesn't move because the mathematics we use to manipulate it don't correspond to any concept like motion. Spacetime is the coordinate system of the Universe. Mass distorts the system locally, but there's nothing to move.

[Boomer12k]

"Space does not fall into a black hole, space is not moving. Just what the heck is "space", really??

What is "really", really?

That which you said does not move and does not fall into a black hole, which is understandable. IF it does not move, how could it fall. But what is it that does not move?"
---------as per the above conversation.....

It neither falls....nor moves.....it Stretches...bends, warps, and dimples.....it is LIKE...Similar too....but not exactly the same as.....a boat being put on water.....the water bends, warps, around the shape of the boat...it pushes on the boat, but also pushes back on itself...causing other currents and phenomena...similar as an analogy...but not the same...and yet this "thing" is a nothingness as we perceive it...even a "dimensional nothingness" can still have "properties"....and thus you get an effect...."Gravity is the effect of Mass on Spacetime".....someone once said...

:---[===] *

[Beyond]

That which you said does not move and does not fall into a black hole, which is understandable. IF it does not move, how could it fall. But what is it that does not move?

Basically, I'd say that spacetime is a mathematical construct that models what we observe. It doesn't move because the mathematics we use to manipulate it don't correspond to any concept like motion. Spacetime is the coordinate system of the Universe. Mass distorts the system locally, but there's nothing to move.

So the term 'spacetime' is like a static overlay, that man uses to try and understand how the things in space, affect space itself? Sort of like taking a series of 'screenshots' and studying them individually to understand what processes are going on and how they operate? I seem to be looking for a definition (or explanation) of what space is, minus the things that are in it. The term vacuum, or perfect vacuum is lacking for me. When you've caused a perfect vacuum in a bell jar, for example, what is really left in the bell jar, that you've taken everything out of?

[Beyond]

...this "thing" is a nothingness as we perceive it...

Yeah, that's the problem. Even with telescopic and microscopic help, man is still about as blind as a bat with broken radar. Well... maybe in the future sometime, man will be able to see things that are now nothings. Thanks Boomer 12k and Chris.

[geckzilla]

Maybe the black hole is confounding you. Take away the black hole and you only take away the black hole. Space is still there just as it was before black hole formed, as it was while the black hole occupied it, and light can travel through it no problem now without the black hole.

[Beyond]

Maybe the black hole is confounding you. Take away the black hole and you only take away the black hole. Space is still there just as it was before black hole formed, as it was while the black hole occupied it, and light can travel through it no problem now without the black hole.

If you mean 'me' being confounded, no, it's not. A black hole is just one of the many things in the nothing that we perceive.

[geckzilla]

How silly of me to suggest that the infallible Beyond could possibly be confused.

[Beyond]

How silly of me to suggest that the infallible Beyond could possibly be confused.

ha,ha, i 'fallible' all over da place. But in this case the black hole had nothing to do with what i was asking. It was something that Chris said about the space around the black hole that triggered my asking.

[deathfleer]

I would rather call it a black core because of the something massive lies in the centre most galaxy, otherwise we would keep going to perceive that it is a hole in the nothingness of space!!!!

[Willy]

Here is the link to a slower paced version of the video I made a few months ago, using Dr.Nemiroff's simuation.

Click to play embedded YouTube video.

Thanks a lot for this version, at its' slower speed it's a lot easier to digest for someone like me, a not-so-initiated amateur.

[Markus Schwarz]

Just what the heck is "space", really??

This discussion goes back to the days of Newton an Leipniz. Newton argued for an absolute space, while Leipniz insisted the only thing you can measure are the positions of objects relative to each other. My quick answer is that you cannot measure space (or time for that matter) but only distances in space and the passage of time.

This was a major source of confusion for gravitational waves. A gravitational wave is a "wiggle in spacetime". But to truly detect a gravitational wave you need to measure the proper distances between particles, not "the space at which the particle sits". Similar, the spacetime around a static black hole is not sucked into it. But particles moving in this spacetime are sucked in.

The flowing water represents the pull the black hole exerts on a particle. But unlike the water, the spacetime is not moving. This is were the analogy to a waterfall breaks down.

[Beyond]

Just what the heck is "space", really??

This discussion goes back to the days of Newton an Leipniz. Newton argued for an absolute space, while Leipniz insisted the only thing you can measure are the positions of objects relative to each other. My quick answer is that you cannot measure space (or time for that matter) but only distances in space and the passage of time.

This was a major source of confusion for gravitational waves. A gravitational wave is a "wiggle in spacetime". But to truly detect a gravitational wave you need to measure the proper distances between particles, not "the space at which the particle sits". Similar, the spacetime around a static black hole is not sucked into it. But particles moving in this spacetime are sucked in.

The flowing water represents the pull the black hole exerts on a particle. But unlike the water, the spacetime is not moving. This is were the analogy to a waterfall breaks down.

In the analogy of a waterfall, wouldn't the ground the water flows over represent the spacetime that is not moving?

[Markus Schwarz]

In the analogy of a waterfall, wouldn't the ground the water flows over represent the spacetime that is not moving?

The ground is not the reason why the swimmer is pulled over the edge, but the flowing water. The flowing water represents the gravitational pull caused by the curved spacetime.

It was already a big problem for Newton that gravity pulls objects but not push them. In every day live (or classical mechanics, to be exact) objects move because some other object pushes them. Even if you pull your coffee cup towards you, you do so by reaching around it and, thus, pushing it. I guess that's what makes it so hard to come up with good analogies for gravity.

[Beyond]

So the gravity of the black hole pulls on matter that flows along spacetime that doesn't move... just as gravity on earth pulls the water along an unmoving ground, to it's lowest point.
In the case of spacetime, the lowest point anything can go, is the black hole. In the case of water, it's the deepest depression that it can flow into.
So as usual, it's the gravity of the situation.
To me, gravity seems to be that which was blown up in the Big Bang, trying to bring itself together. On a more practical level, it keeps us from flying off a spinning planet.
And where did 'the swimmer' come from?

[Chris Peterson]

So the gravity of the black hole pulls on matter that flows along spacetime that doesn't move... just as gravity on earth pulls the water along an unmoving ground, to it's lowest point.

I agree with both you and Markus: as you said, in the waterfall analogy, spacetime is represented by the ground. But as Markus points out, the ground isn't enough to explain it, either. The real problem with the analogy is that you're trying to explain gravity using an analogy that itself depends on gravity. It becomes a circular argument, and quickly confusing. The analogy would work a little better if you got rid of the water and just had the person and the slope; the problem is, the water itself doesn't seem to represent anything in the real world.

[geckzilla]

Click to play embedded YouTube video.

[Beyond]

WOW! That coin thingy is neat! It's better than the marble ones.

[Chris Peterson]

WOW! That coin thingy is neat! It's better than the marble ones.

Although they still depends upon "real" gravity to make them work, I do think those coin drains and dimpled rubber sheet models are much better analogies than the waterfall. They do a better job teaching the important concept of distorted space and geodesics (although most people using them don't do so properly).

[Beyond]

(although most people using them don't do so properly).

Is there really much of anything that people do 'properly'

[stephen63]

WOW! That coin thingy is neat! It's better than the marble ones.

Although they still depends upon "real" gravity to make them work, I do think those coin drains and dimpled rubber sheet models are much better analogies than the waterfall. They do a better job teaching the important concept of distorted space and geodesics (although most people using them don't do so properly).

I looked for a three-dimensional representation and found this site. About halfway down the page is a 3d view. My head started to hurt when I attempted to comprehend the article. I'm sure Chris can expound on it!
Edit:

A manifold is a portion of 3 (or more) dimensional space. It may be Euclidean, or it may be scrunched or expanded (what scientists generally call ‘curved’, but this term often confuses non-scientists because we can easily think of curves in 2D, but when transposed into 3D, scrunching/expanding is a more intuitive description of what really happens).

http://networkologies.wordpress.com/200 ... d-riemann/

[Beyond]

ha-ha-ha, i fell asleep twice while going through it. One small section i just read right through fast, because i wasn't familiar at all to what the names referred to.

[Ron-Astro Pharmacist]

Thanks for the comments. It seems so inviting to think that a black hole could be the generation of a new universe if both space and matter are being drawn into one. Also seems like it opens the door to consider that the new universe would continually fed and not a one-time event such as the big band. A continuously expanding universe; where have I heard that one before

[Beyond]

Thanks for the comments. It seems so inviting to think that a black hole could be the generation of a new universe if both space and matter are being drawn into one. Also seems like it opens the door to consider that the new universe would continually fed and not a one-time event such as the big band. A continuously expanding universe; where have I heard that one before

From what i gather about the conversations thus far... space doesn't move and doesn't enter a black hole. It's some of the matter that moves in space, that is not converted to energy at the event horizon, that is blown away, that eventually falls in, like in geckzilla's video.

[Chris Peterson]

From what i gather about the conversations thus far... space doesn't move and doesn't enter a black hole. It's some of the matter that moves in space, that is not converted to energy at the event horizon, that is blown away, that eventually falls in, like in geckzilla's video.

Matter doesn't get converted to energy at the event horizon at all. The only matter that gets converted to energy around a black hole does so because it collides with other matter... no different than the process that can (and does) happen around any body with sufficient gravity to sustain orbiting material. In that respect, a black hole is no different from a star, protostar, neutron star, etc.

[Beyond]

So what is it that gets blown away as jets?