On the basis of classical theory of gravity relying on "real" Time-Space, we can only suppose two behaviors for the Universe : or it existed eternally or it began by a singularity in a determined moment of the past.

But in fact we know that classical theories are all of them only approximately true, and we know that at scales smaller than the so-called Planck length the classical theory of gravity does not hold. So the best interpretation is to say that neither of the imagined possibilites is relevant

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But in quantum theory of gravity, there is a third option : the ambiguous time. In the "real" time, Universe has a beginning and an end in singularities. Singularities being the borders of Time-Space , the laws are anihilated on those points. But in ambiguous time, singularity and border are absent.

Some quantum theories are like that, others are not. Until we have a quantum gravity that works it is just speculation to say any more than 'time may be ambiguous'.

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Given a scientific theory is a mathematical paradigm we made to explain our observations , and it exists only in our mind, so this question that which one of the two, real time or ambiguous time is "real" doesn't matter, the question is which one can give a simpler description.

That is the *second* criteria we use to choose a theory.

The first, and most important, is that a theory generates predictions which are testable and which provide a genuine 'risk' that the theory may be disproved. Without that it is not a theory in the proper scientific sense.

If we choose between untestable theories on the basis of preference we are doing philosophy (or maybe theology), we are doing not science in my opinion. That is not a problem so long as we understand that we are doing science philosophy inspired by science rather than science itself.

If scientists were as exact in their language as they like to pretend, they would not talk of 'string theory' but of 'the string approach', and similarly all the other quantum gravity 'theories'.

River~~

Thank you River, I'v been enlightened. Next time i will try being more "scientific".

ut I'd still like very much to believe that humans posses the ability to evaluate equilibria, and then make decisions regarding action upon particular states, and that such decisions are based on notions of 'right and wrong' rather than 'hot and cold.' Is this belief an illusion? Or can maths be used to show that right = hot and wrong = cold ?

Don't worry, after quantum mechanics with it's probabilities and Heisenberg's Uncertainty Principle I think determinism in the 18th century sense is no longer held by theoreticians. Plenty of room for free choice in a world view.

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Clearly there are more dimensions than just 3 spatial ones. All due respect to Hawking and others, if the structure of these dimensions (however many) accommodates singularities, then isn't all information necessarily preserved on both sides of an event horizon

that's the tricky bit, because will we ever know if we can't ever measure it? However Hawking has proposed a radiation mechanism at the event horizon, where sometimes half of a virtual particle pair falls into the hole and the other half escapes. These pairs spontaneously form out of the vacuum due to the high energy density of the gravitational field, so the story goes. Eventually the hole should 'evaporate', sooner for smaller holes and at a rate with is quicker the smaller the hole is. So maybe the information/entropy returns to the universe later on, which seems to imply that you could deduce what the black hole ate for breakfast when it was a young lad! :-)

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and in the distance between the horizon and the singularity, why shouldn't it take something longer to traverse that distance than it takes, say, for a photon to go from the core of a star to the surface?

It certainly can. For a really big black hole, with millions of solar masses, you could tool around for days inside the event horizon before you ( inevitably ) met the singularity. Also tidal forces ( gravity gradient ) can be quite gentle for most of that time too, so you won't be ripped to pieces until you got your money's worth! Alas you won't be able to tell us how much you enjoyed it. The hole gets your money and your life. :-)

I have made this letter longer than usual because I lack the time to make it shorter.Blaise Pascal

that's the tricky bit, because will we ever know if we can't ever measure it? However Hawking has proposed a radiation mechanism at the event horizon, where sometimes half of a virtual particle pair falls into the hole and the other half escapes. These pairs spontaneously form out of the vacuum due to the high energy density of the gravitational field, so the story goes. Eventually the hole should 'evaporate', sooner for smaller holes and at a rate with is quicker the smaller the hole is. So maybe the information/entropy returns to the universe later on, which seems to imply that you could deduce what the black hole ate for breakfast when it was a young lad! :-)

From what I've heard and can understand, Hawking's solutions are brilliant. And of course it's difficult to figure out something that you can't measure directly. What I'm wondering is why anything else should fall into the singularity once it has formed. Surely matter must overshoot it, in what must be a maelstrom that makes a stellar core look like a nice place for a picnic..? Also, the entire coordinate system for n-dimensions takes up exactly zero volume. Can I say from this that 'information' can likewise exist (even if gravitationally bound, curled up in the origin)?

Nice article in the 12/05 Scientific American (cover story, actually) titled, "Echoes of Black Holes" explaining that studying sound waves in fluids can be quite like studying light waves in curved spacetime. Condensed matter resembles a continuum, and a black hole analog is a Laval nozzle, where fluid flow changes from subsonic to supersonic (forming an event horizon for sound waves). Of course, it also begs the question on regarding spacetime then as a fluid 'like the ether of pre-Einsteinian physics.' Is there any conjecture about black holes that strikes you more profoundly (as being plausible) than, say, wormholes (these weren't mentioned in the article) for example? And what do you think about the sound/light analogy?

From what I've heard and can understand, Hawking's solutions are brilliant. And of course it's difficult to figure out something that you can't measure directly. What I'm wondering is why anything else should fall into the singularity once it has formed. Surely matter must overshoot it, in what must be a maelstrom that makes a stellar core look like a nice place for a picnic..? Also, the entire coordinate system for n-dimensions takes up exactly zero volume. Can I say from this that 'information' can likewise exist (even if gravitationally bound, curled up in the origin)?

For a ( non-rotating ) black hole, I think the problems are several:
- the theory, as is, predicts infinite densities etc at a single point, ie. the singularity.
- with an event horizon, how can you know or measure either way.
- even if singularities do exist, what does that actually mean outside of the mathematics. I think it was Penrose that showed that a singularity without an enclosing event horizon would cause violation of physics laws everywhere else, causality included.
- once you pass the event horizon, all world lines ( light included ) end in the singularity.

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Nice article in the 12/05 Scientific American (cover story, actually) titled, "Echoes of Black Holes" explaining that studying sound waves in fluids can be quite like studying light waves in curved spacetime. Condensed matter resembles a continuum, and a black hole analog is a Laval nozzle, where fluid flow changes from subsonic to supersonic (forming an event horizon for sound waves). Of course, it also begs the question on regarding spacetime then as a fluid 'like the ether of pre-Einsteinian physics.' Is there any conjecture about black holes that strikes you more profoundly (as being plausible) than, say, wormholes (these weren't mentioned in the article) for example?

If there is rotation ( more likely in fact ) then the singularity forms a ring like a donut, where the axis of rotation of the hole goes through the ( empty ) centre of the donut. It is hypothecated that with suitable planning one could actually pass through that ring and come out, well, somewhere else. Fortunately this is precisely the type of spacetime anomaly that a 3D Homer would eagerly volunteer for. :-)

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And what do you think about the sound/light analogy?

Well I think spacetime will have to be modelled as being discrete to reconcile all this stuff. That is, there needs to be minimum length intervals in space and minimum ticks in time. That way you can't stack any amount of mass onto a point and thus create singularities. The Hawking radiation can originate very close to but not at the event horizon, and get around the frequency shift problem. In fact the horizon becomes a shell with thickness. More generally since the reciprocal of something non-zero is non-infinite, then suitably arranged you can have little quanta of energy, angular momentum etc come out naturally alongside things like a universal maximum speed. On the downside quantization of lengths implies preferred directions, as you lose rotational symmetry if you to have jump some minimum distance. So you'd have to reconcile that idea at small scales with why we don't see preferred directions at large scales. This suggests a different sort of mathematics maybe, or a definition of length which is scale dependent ( most surely non-Euclidean, but no one worries about that anymore ).
Aside #1: Bear in mind that there are two quite different types of objects that are fully specified by mass, charge and angular momentum - black holes and fundamental particles. I feel there is a deep connection here for some young bright spark to illuminate!
Aside #2: Ever wonder how those jets are formed with quasars? You know - the bloody great, bloody fast, bloody energetic outflows from ( presumably ) the polar regions of supermassive objects with accretion disks. If you quantize space, so matter can't stack up indefinitely on a point, then it must 'push out' along the axis - so the stuff spiralling in must choof out ( North and South to conserve linear momentum )! As the outgoing matter along the jets may have little or no angular momentum - being close to the axis and unable to orbit faster than light - then what of that? The angular momentum of the ingoing matter is transferred to ( or stored in ) the twisting of spacetime at the axis. After all if one can speak of energy and momentum transmission by gravitational waves propagating linearly through spacetime, why not rotation?
Ahhhh..... but this is conjecture .... now quick, hide ... I hear the footsteps of an angry mob of theorists with pitchforks, firebrands and the hounds :-)

(edit) I refer to the toroidal sort of donut ( like a bicycle tyre ) not the filled in solid type ( like a round bun ).

I have made this letter longer than usual because I lack the time to make it shorter.Blaise Pascal

## RE: RE: On the basis

)

Thank you River, I'v been enlightened. Next time i will try being more "scientific".

Ariane

## RE: ut I'd still like very

)

Don't worry, after quantum mechanics with it's probabilities and Heisenberg's Uncertainty Principle I think determinism in the 18th century sense is no longer held by theoreticians. Plenty of room for free choice in a world view.

that's the tricky bit, because will we ever know if we can't ever measure it? However Hawking has proposed a radiation mechanism at the event horizon, where sometimes half of a virtual particle pair falls into the hole and the other half escapes. These pairs spontaneously form out of the vacuum due to the high energy density of the gravitational field, so the story goes. Eventually the hole should 'evaporate', sooner for smaller holes and at a rate with is quicker the smaller the hole is. So maybe the information/entropy returns to the universe later on, which seems to imply that you could deduce what the black hole ate for breakfast when it was a young lad! :-)

It certainly can. For a really big black hole, with millions of solar masses, you could tool around for days inside the event horizon before you ( inevitably ) met the singularity. Also tidal forces ( gravity gradient ) can be quite gentle for most of that time too, so you won't be ripped to pieces until you got your money's worth! Alas you won't be able to tell us how much you enjoyed it. The hole gets your money and your life. :-)

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## RE: that's the tricky bit,

)

From what I've heard and can understand, Hawking's solutions are brilliant. And of course it's difficult to figure out something that you can't measure directly. What I'm wondering is why anything else should fall into the singularity once it has formed. Surely matter must overshoot it, in what must be a maelstrom that makes a stellar core look like a nice place for a picnic..? Also, the entire coordinate system for n-dimensions takes up exactly zero volume. Can I say from this that 'information' can likewise exist (even if gravitationally bound, curled up in the origin)?

Nice article in the 12/05 Scientific American (cover story, actually) titled, "Echoes of Black Holes" explaining that studying sound waves in fluids can be quite like studying light waves in curved spacetime. Condensed matter resembles a continuum, and a black hole analog is a Laval nozzle, where fluid flow changes from subsonic to supersonic (forming an event horizon for sound waves). Of course, it also begs the question on regarding spacetime then as a fluid 'like the ether of pre-Einsteinian physics.' Is there any conjecture about black holes that strikes you more profoundly (as being plausible) than, say, wormholes (these weren't mentioned in the article) for example? And what do you think about the sound/light analogy?

## RE: From what I've heard

)

For a ( non-rotating ) black hole, I think the problems are several:

- the theory, as is, predicts infinite densities etc at a single point, ie. the singularity.

- with an event horizon, how can you know or measure either way.

- even if singularities do exist, what does that actually mean outside of the mathematics. I think it was Penrose that showed that a singularity without an enclosing event horizon would cause violation of physics laws everywhere else, causality included.

- once you pass the event horizon, all world lines ( light included ) end in the singularity.

If there is rotation ( more likely in fact ) then the singularity forms a ring like a donut, where the axis of rotation of the hole goes through the ( empty ) centre of the donut. It is hypothecated that with suitable planning one could actually pass through that ring and come out, well, somewhere else. Fortunately this is precisely the type of spacetime anomaly that a 3D Homer would eagerly volunteer for. :-)

Well I think spacetime will have to be modelled as being discrete to reconcile all this stuff. That is, there needs to be minimum length intervals in space and minimum ticks in time. That way you can't stack any amount of mass onto a point and thus create singularities. The Hawking radiation can originate very close to but not at the event horizon, and get around the frequency shift problem. In fact the horizon becomes a shell with thickness. More generally since the reciprocal of something non-zero is non-infinite, then suitably arranged you can have little quanta of energy, angular momentum etc come out naturally alongside things like a universal maximum speed. On the downside quantization of lengths implies preferred directions, as you lose rotational symmetry if you to have jump some minimum distance. So you'd have to reconcile that idea at small scales with why we don't see preferred directions at large scales. This suggests a different sort of mathematics maybe, or a definition of length which is scale dependent ( most surely non-Euclidean, but no one worries about that anymore ).

Aside #1: Bear in mind that there are two quite different types of objects that are fully specified by mass, charge and angular momentum - black holes and fundamental particles. I feel there is a deep connection here for some young bright spark to illuminate!

Aside #2: Ever wonder how those jets are formed with quasars? You know - the bloody great, bloody fast, bloody energetic outflows from ( presumably ) the polar regions of supermassive objects with accretion disks. If you quantize space, so matter can't stack up indefinitely on a point, then it must 'push out' along the axis - so the stuff spiralling in must choof out ( North and South to conserve linear momentum )! As the outgoing matter along the jets may have little or no angular momentum - being close to the axis and unable to orbit faster than light - then what of that? The angular momentum of the ingoing matter is transferred to ( or stored in ) the twisting of spacetime at the axis. After all if one can speak of energy and momentum transmission by gravitational waves propagating linearly through spacetime, why not rotation?

Ahhhh..... but this is conjecture .... now quick, hide ... I hear the footsteps of an angry mob of theorists with pitchforks, firebrands and the hounds :-)

(edit) I refer to the toroidal sort of donut ( like a bicycle tyre ) not the filled in solid type ( like a round bun ).

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal