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spacecowboy342

Is the universe inside a black hole?

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I was watching an old you tube video by Lawrence Krauss and at the end there was a question and answer section where the question was posed about whether if the universe had come about due to quantum fluctuation if it would ever be possible to witness such an event happen again.Dr. Krauss responded that it might be possible to create such an event in the Hadron supercollider but in such a case though from inside the tiny pocket universe it would appear to be expanding from our side it would appear to be collapsing into a black hole. He didn't go into the reasons for this, but I am wondering if this is true if from outside our universe the same would be true and we would appear to be collapsing into a black hole, and if the acceleration of this collapse could in some way explain the acceleration of expansion of our universe?

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He didn't go into the reasons for this, but I am wondering if this is true if from outside our universe the same would be true and we would appear to be collapsing into a black hole, and if the acceleration of this collapse could in some way explain the acceleration of expansion of our universe?

I don't think so. I think if we were inside a black hole we would see a preferred direction towards a point (namely, the direction towards the centre of the black hole) in the Hubble flow, rather than the observer preferred direction of away from us (which presumably means away from every point, since there is no reason why our position is ``speciall'') indicative of an expanding Universe.

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This is a great exercise in human fantasy. Once you accept the theory of blackholes as true, you can then also accept that our universe began from a singularity. Literally, the entire mass in our universe came from nothing. If you believe that then worm holes and multiple dimensions are also possible.

I do not believe that a singularity can ever exist. It comes from the human brain as an answer to a flawed math equation. It is a fantasy idea that will never be proven, but must be real for science fiction to kick in.

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I don't think so. I think if we were inside a black hole we would see a preferred direction towards a point (namely, the direction towards the centre of the black hole) in the Hubble flow, rather than the observer preferred direction of away from us (which presumably means away from every point, since there is no reason why our position is ``speciall'') indicative of an expanding Universe.

Yeah I guess I'm not getting what he meant when he said inside the pocket universe it would appear to be expanding while from the outside it would appear to be collapsing into a black hole

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Posted (edited)

This is a great exercise in human fantasy. Once you accept the theory of blackholes as true, you can then also accept that our universe began from a singularity. Literally, the entire mass in our universe came from nothing. If you believe that then worm holes and multiple dimensions are also possible.

I do not believe that a singularity can ever exist. It comes from the human brain as an answer to a flawed math equation. It is a fantasy idea that will never be proven, but must be real for science fiction to kick in.

I have heard others voice similar opinions and at least one physicist say that singularity just means we don't really know what is going on inside a black hole. It is hard for me to conceive of a mass collapsing to 0 volume and my mind tries to explain this by imagining space kind of turning inside out, so to speak resulting in explosive expansion, but I don't have a clue if this is in any way valid Edited by spacecowboy342

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I don't think so. I think if we were inside a black hole we would see a preferred direction towards a point (namely, the direction towards the centre of the black hole) in the Hubble flow, rather than the observer preferred direction of away from us (which presumably means away from every point, since there is no reason why our position is ``speciall'') indicative of an expanding Universe.

Would this not entirely depend on the curvature of space within the speculated black hole, sepulchrave?

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My understanding is that if one were to create a new Big Bang with an inflationary episode and all that in a collider or some other way, that we wouldn't even notice -- it would all happen in a new and different set of dimensions.

We all have trouble with the notion of a singularity, but because we cannot understand how something is possible don't mean it ain't. Nature does what it does without checking whether we will be able to understand it or not.

Still, it may well be that things happen at or near plank space to prevent things from going further -- especially if space/time is quantized at around that level.

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Would this not entirely depend on the curvature of space within the speculated black hole, sepulchrave?

It would definitely depend on the curvature, but I think that as long as space is topologically simple (without loops or knots, etc.) we should be able to see distant galaxies moving towards some region of space.

I don't think there is a way of smoothly curving space so that the singularity would appear to be at some point in the far distance regardless of which direction we look, unless space is spherical and we are in the ``privileged'' position of being directly opposite the singularity (as in, the singularity is the ``north pole'' and we are on the ``south pole'').

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Posted (edited)

It would definitely depend on the curvature, but I think that as long as space is topologically simple (without loops or knots, etc.) we should be able to see distant galaxies moving towards some region of space.

I don't think there is a way of smoothly curving space so that the singularity would appear to be at some point in the far distance regardless of which direction we look, unless space is spherical and we are in the ``privileged'' position of being directly opposite the singularity (as in, the singularity is the ``north pole'' and we are on the ``south pole'').

But this also depends on observing from a static frame of reference, but in a "black hole universe" (say, something shaped like a trumpet) this would not be the case. We would be accelerating towards the singularity at a rate different to other objects at varying distances from that singularity. This could give the impression of those objects moving away from us in all directions, especially if rotation around/across the 'surface' of the trumpet-shaped universe was involved.

Edited by Leonardo

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But this also depends on observing from a static frame of reference, but in a "black hole universe" (say, something shaped like a trumpet) this would not be the case. We would be accelerating towards the singularity at a rate different to other objects at varying distances from that singularity. This could give the impression of those objects moving away from us in all directions, especially if rotation around/across the 'surface' of the trumpet-shaped universe was involved.

In that situation, I don't see why we wouldn't be able to tell which direction was ``into'' the trumpet and which direction was ``out of'' the trumpet.

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In that situation, I don't see why we wouldn't be able to tell which direction was ``into'' the trumpet and which direction was ``out of'' the trumpet.

How would we be able to tell the difference?

From our perspective (a false perspective, but the only one we could measure from) we would appear to have a stationary frame of reference and all other objects would appear to be moving away from us. There would be no observable 'universal direction of motion' and so we would observe exactly what we currently observe.

Edited by Leonardo

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A problem I see is, black holes rotate. If our universe were inside a black hole, wouldn't our universe be rotating, too? Then we'd be living in a universe similar to a Godel rotating universe, which would contain closed timelike curves. For instance, looking at right angles to the rotation, we would see ourselves in our past. We would also be confused as to whether an event happened before or after an other event.

I also think we would see a preferred direction to in the universe, the direction of rotation. I'm not an expert on this, I'm just saying.

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A problem I see is, black holes rotate. If our universe were inside a black hole, wouldn't our universe be rotating, too? Then we'd be living in a universe similar to a Godel rotating universe, which would contain closed timelike curves. For instance, looking at right angles to the rotation, we would see ourselves in our past. We would also be confused as to whether an event happened before or after an other event.

I also think we would see a preferred direction to in the universe, the direction of rotation. I'm not an expert on this, I'm just saying.

How does one "look at right angles to the rotation", when light's motion is with the rotation - not perpendicular to it?

And my understanding (admittedly very incomplete) of Godel's solution is the topography it would represent would be more akin to a 'spinning top' than a 'rotating trumpet' - as it does not involve a singularity.

Edited by Leonardo

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How does one "look at right angles to the rotation", when light's motion is with the rotation - not perpendicular to it?

I think it's because light emitted counter-rotationally is looped around by the rotation of the space it is traveling in and returns to its source.

According to Hawking and Ellis, another remarkable feature of this spacetime is the fact that, if we suppress the inessential y coordinate, light emitted from an event on the world line of a given dust particle spirals outwards, forms a circular cusp, then spirals inward and reconverges at a subsequent event on the world line of the original dust particle. This means that observers looking orthogonally (at right angels) to the da10249f7319c312363a643e1d304b73.png direction can see only finitely far out, and also see themselves at an earlier time.

http://en.wikipedia.org/wiki/G%C3%B6del_metric

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I read that, but have a problem with this...

According to Hawking and Ellis, another remarkable feature of this spacetime is the fact that, if we suppress the inessential y coordinate, light emitted from an event on the world line of a given dust particle spirals outwards, forms a circular cusp, then spirals inward and reconverges at a subsequent event on the world line of the original dust particle.

If this behaviour is only observed through suppressing the y coordinate, then surely that suggests the y coordinate is not "inessential", but is essential to suppress this behaviour?

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If this behaviour is only observed through suppressing the y coordinate, then surely that suggests the y coordinate is not "inessential", but is essential to suppress this behaviour?

Yeah, I think it's a complex subject. Here's a long, detailed page entitled "Visualization of the Godel Universe" by...

M Buser, E Kajari and W P Schleich1

wolfgang.schleich@uni-ulm.de

Institut für Quantenphysik and Center for Integrated Quantum Science and Technology (IQST), Universität Ulm, Albert-Einstein-Allee 11, D-89069 Ulm, Germany

1 Author to whom any correspondence should be addressed.

I guess if we have any questions we can send an e-mail there. ;) if anyone wants to really study the subject.

http://iopscience.io.../013063/article

Edited by StarMountainKid

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I was always lead to believe that there were many 'Blackholes' within the known Universe & not the Universe inside a Blackhole?

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A problem I see is, black holes rotate. If our universe were inside a black hole, wouldn't our universe be rotating, too? Then we'd be living in a universe similar to a Godel rotating universe, which would contain closed timelike curves. For instance, looking at right angles to the rotation, we would see ourselves in our past. We would also be confused as to whether an event happened before or after an other event.

I also think we would see a preferred direction to in the universe, the direction of rotation. I'm not an expert on this, I'm just saying.

How would we be able to tell it was rotating if we were rotating with it. What would it be rotating in relation to?

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How would we be able to tell it was rotating if we were rotating with it. What would it be rotating in relation to?

The answer is probably in my link above somewhere or somewhere else. I think we would know by the way light would behave in a rotating universe. See this image from the link:

post-50472-0-91069000-1381359914_thumb.j

It seems to me the rotation would drag space with its rotation, and a light beam would be curved around to follow that rotating space and end up at its origin, according to the diagram. So one would see one's self in the past emitting the light beam.

Edited by StarMountainKid

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The answer is probably in my link above somewhere or somewhere else. I think we would know by the way light would behave in a rotating universe. See this image from the link:

post-50472-0-91069000-1381359914_thumb.j

Yeah, I checked the link and it seems light would bend so you could tell rotation. But now I'm wondering if rotation could be so slow as to be imperceptible? I know black holes rotate fast and collapse fast, but I'm thinking in terms of time dilation. I know the point is probably moot as sepulchrave's post seemed to rule the idea out, but I was thinking in terms of a super massive black hole collapsing from all directions and here inside time running in the opposite direction slowly and so appear to be expanding. Not sure if that makes any sense but my mind works in funny ways sometimes

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How would we be able to tell the difference?

From our perspective (a false perspective, but the only one we could measure from) we would appear to have a stationary frame of reference and all other objects would appear to be moving away from us. There would be no observable 'universal direction of motion' and so we would observe exactly what we currently observe.

I still don't see why.

In my opinion, in a ``trumpet'' Universe, presumably the black hole is up in the tube of the trumpet... if we look out into space, then in one direction (Universal ``up'') we should see galaxies moving away from us at a faster speed than the average for how far away those galaxies are, since they are in a region of greater space-time curvature than we are (i.e. they are closer to the Universal singularity). If we look in the exact opposite direction (Universal ``down'') we should see galaxies moving away from us at slower speed than the average for how far away those galaxies are, since they are in a region of lesser space-time curvature than we are.

If we look in any other direction (Universal ``north'', ``south'', ``east'', or ``west'') the galaxies should have zero average speed relative to us, since they are in a region with the exact same space-time curvature as us.

A problem I see is, black holes rotate. If our universe were inside a black hole, wouldn't our universe be rotating, too?

As far as I can see, you understanding of Godel's metric is accurate. However black holes don't have to rotate.

They usually do, because they are formed from collapsed stars, and most stars rotate.

But there is nothing that makes it necessary for a black hole to rotate.

If this behaviour is only observed through suppressing the y coordinate, then surely that suggests the y coordinate is not "inessential", but is essential to suppress this behaviour?

The real answer is probably in the paper that StarMountainKid linked to. I haven't studied it yet, but my understanding of the situation is this: The metric presented in the wikipedia article is symmetric under translations in y - that is; no other coordinates depend on y (unlike t, x, and z) and the dy portion does not depend on itself (it has no scaling coefficient).

Because of that, we can easily consider cases where y = 0, and ignore it.

Since the closed-time-like curve behaviour arises by suppressing the y-coordinate, then I am not sure if this means that all possible trajectories are closed-time-like curves, but it definitely means that at least one trajectory is.

The y-coordinate is definitely ``inessential'', because it is the co-dependence between the other coordinates that make the closed-time-like curve behaviour possible.

As an extreme example, there is translational symmetry within all coordinates in the Minkowski metric, but there are no closed-time-like curves.

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I still don't see why.

In my opinion, in a ``trumpet'' Universe, presumably the black hole is up in the tube of the trumpet... if we look out into space, then in one direction (Universal ``up'') we should see galaxies moving away from us at a faster speed than the average for how far away those galaxies are, since they are in a region of greater space-time curvature than we are (i.e. they are closer to the Universal singularity). If we look in the exact opposite direction (Universal ``down'') we should see galaxies moving away from us at slower speed than the average for how far away those galaxies are, since they are in a region of lesser space-time curvature than we are.

In the black hole universe, everything is accelerating at different rates according to it's distance from the black hole. This behaviour also applies to light (and everything else on the EM spectrum) which we use to measure velocity/speed. The apparent conformity in the speed across directions, of objects at a distance could be due to the relativistic effects of this acceleration (which also applies to us.)

We could only observe things which had not yet reached speeds to put them outside our light cone. This applies to objects we are accelerating away from as equally as it applies to objects accelerating away from us.

If we look in any other direction (Universal ``north'', ``south'', ``east'', or ``west'') the galaxies should have zero average speed relative to us, since they are in a region with the exact same space-time curvature as us.

Not if there is also motion around an axis of rotation of the trumpet-shaped universe. In assuming a rotating black hole universe, the application of a coriolis effect could prevent the direct observation of a true (universal) north-south-east-west as you suggest.

Edited by Leonardo

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In the black hole universe, everything is accelerating at different rates according to it's distance from the black hole. This behaviour also applies to light (and everything else on the EM spectrum) which we use to measure velocity/speed. The apparent conformity in the speed across directions, of objects at a distance could be due to the relativistic effects of this acceleration (which also applies to us.)

I doubt it. We would have to be in a very peculiar space-time geometry for it to work out like that.

The gravitational field from a singularity is still ~r-2, remember. (Unless you are proposing that the singularity has a truly enormous angular momentum or unbalanced electrical charge.)

Many of the galaxies accelerating away from us are not at relativistic speeds (compared to us, anyway), so classical mechanics is still a decent approximation.

If we have two objects that are the same distance from an observer, and all three bodies are along a radial line from the singularity, the two objects will appear to have very different accelerations relative to the observer.

If the observer is a distance R from the singularity, and both objects are a distance r from the observer, than the observed acceleration of the object closest to the singularity will be:

a1 ~ (R - r)-2 - R-2

while the acceleration of the object furthest from the singularity will be:

a2 ~ R-2 - (R + r)-2

The two accelerations will never be equal in magnitude and opposite in direction.

Not if there is also motion around an axis of rotation of the trumpet-shaped universe. In assuming a rotating black hole universe, the application of a coriolis effect could prevent the direct observation of a true (universal) north-south-east-west as you suggest.

Firstly, the coriolis effect doesn't look the same in the clockwise and counterclockwise directions.

Secondly, the coriolis effect only occurs when a rotating observer is looking at non-rotating motion. If the whole universe is rotating, every galaxy should be rotating with it. Objects the same distance from the galactic centre, i.e. those visible to us in the north-south-east-west directions, would all be rotating at the same rate.

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I doubt it. We would have to be in a very peculiar space-time geometry for it to work out like that.

The gravitational field from a singularity is still ~r-2, remember. (Unless you are proposing that the singularity has a truly enormous angular momentum or unbalanced electrical charge.)

Many of the galaxies accelerating away from us are not at relativistic speeds (compared to us, anyway), so classical mechanics is still a decent approximation.

If we have two objects that are the same distance from an observer, and all three bodies are along a radial line from the singularity, the two objects will appear to have very different accelerations relative to the observer.

I'm not sure I am explaining myself properly, but I am suggesting our observations do not take place along 'radial lines' (as in spokes on a wheel - which is what I think you are implying?), but along spiralling paths.

And I am suggesting that, due to the nature of the universe, space is stretched more in one direction (towards the black hole) than the other (which accounts for the r2, unless I am mistaken - and I readily admit I may be).

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If I could ask a question, some of your discussion has been concerning the possible shape of the universe. Has it not been determined experimentally that space is flat? How would this affect possible shapes?

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