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Author Topic:   Hawking's Information Paradox solution
dogrelata
Member (Idle past 5312 days)
Posts: 201
From: Scotland
Joined: 08-04-2006


Message 16 of 42 (371972)
12-24-2006 10:25 AM
Reply to: Message 7 by cavediver
11-26-2006 11:26 AM


Re: Explanation please?
cavediver writes:
As we start to consider quantum gravity, various possibilities are introduced. One of these is the idea of baby universe: branches of space-time separating off from the trunk space-time via black-holes and similar phenomena. One of Hawking's proposed solutions to the information problem used baby universes (dating back to the 80s). These are not alternate or "other" universes as such. Imagine a treee as the whole of our space-time. Take a horizontal slice through the tree at a particular height, and that gives a picture of how we consider our universe with thes ebaby universes: a central area (the x-section of the trunk) and lots of smaller distinct isolated areas (x-sections of the branches). It looks like lots of separate universes. But when you look at the whole tree, you realise that it is all one big connected space-time.
I’ll bet you guys must dread the non-scientists wandering in here with our laymen’s lack of deep underlying knowledge, but part of the fun of this place is getting the chance to ”rub shoulders’ with some very knowledgeable people
This idea of baby universes is one that I’ve often wondered about. The idea that each black hole in this universe might at some point lead to a new baby universe, and that our own universe originated from a black hole within a larger universe, which in turn may have originated similarly, etc. Okay, so there are some pretty serious problems regarding calculations of mass, etc, which requires this layman to develop his own scientific theory, i.e. it would only be possible to measure the mass of any given universe and it’s descendants, the mass of ”parent’ universes being undetectable. In the tree analogy, the ”weight’ of any branch would include all sub-branches, but not the branch or trunk from which it has sprung.
But when I use the term ”undetectable’ in the previous paragraph, there is one other thing I wonder about.
Once or twice I’ve seen an analogy used to try to describe the warping of the fabric of space-time as an object moves through it. The analogy is of a ball bearing rolling over a membrane. As it does so, it stretches and ”warps’ the membrane. Fair enough, it helps me to visualise what is happening, but I have a problem if the analogy is attempting to convey more than the 'visual' effect.
The problem is that the ”warping’ of the membrane is caused by the gravitational pull of the earth acting upon the ball bearing. For the ball bearing analogy to work, does it mean that there must be some ”external’ gravitational force acting upon the object travelling through space-time to cause the ”warping’? If so, might this gravitational force not originate from other ”branches of the tree’ that we are otherwise unable to detect because they exist outside of our universe or its sub-branches?
Okay. I’m going to go now, and will not be offended by any flak that comes my way as a result of my naivety and lack of understanding.

This message is a reply to:
 Message 7 by cavediver, posted 11-26-2006 11:26 AM cavediver has replied

Replies to this message:
 Message 17 by Son Goku, posted 12-24-2006 3:21 PM dogrelata has replied
 Message 19 by cavediver, posted 12-25-2006 8:02 PM dogrelata has replied

  
Son Goku
Inactive Member


Message 17 of 42 (372035)
12-24-2006 3:21 PM
Reply to: Message 16 by dogrelata
12-24-2006 10:25 AM


Gravity as warping.
Let's say I'm in empty space, far away from everything and I throw a ball forward at a constant speed. The ball will move in a straight line away from me. (I don't think anybody can disagree with this)
Not only is this a straight line in space but it is also a straight line in spacetime. (Why it is also a straight line in spacetime takes a while to explain, so I'll skip it for now unless you're interested.)
Now let's say I'm near the Earth. The Earth warps the nearby spacetime into a new shape. I throw the ball again, this time it falls toward Earth. It has again followed a straight line in spacetime. However because the space has a different shape, straight lines usually lead to Earth.
This is a shape called a monkey saddle, with straight lines in the space drawn in it. As you can see straight lines in a curved space can be very different from straight lines in a flat space.
Gravity is nothing more than particles following straight lines in spacetime. This is why two objects of different masses fall at the same speed, following a straight line doesn't depend on your weight.

This message is a reply to:
 Message 16 by dogrelata, posted 12-24-2006 10:25 AM dogrelata has replied

Replies to this message:
 Message 18 by dogrelata, posted 12-25-2006 5:03 PM Son Goku has not replied

  
dogrelata
Member (Idle past 5312 days)
Posts: 201
From: Scotland
Joined: 08-04-2006


Message 18 of 42 (372206)
12-25-2006 5:03 PM
Reply to: Message 17 by Son Goku
12-24-2006 3:21 PM


Re: Gravity as warping.
Son Goku writes:
Gravity is nothing more than particles following straight lines in spacetime. This is why two objects of different masses fall at the same speed, following a straight line doesn't depend on your weight.
Cheers Son.
I’m not sure if this helps me understand whether the ball bearing/membrane analogy is a good one though. In the analogy, the warping of the membrane will be mainly down to the earth’s gravitational force acting upon the bearing, causing it to warp the membrane. If you were to take the bearing to a part of the universe where the gravitational forces were much less strong, presumably the warping effect would be much less pronounced.
The question I’m trying to ask is, how certain are we that the warping we observe in the fabric of space is entirely due to the gravitational forces acting upon it by the objects travelling through it?
And whilst I’m on a roll with crazy, nave questions, I’d like to ask one more.
As far as I understand it, science believes that the rate of expansion of the universe is still accelerating and there are those who have a problem with this, as they believe it ought not to be, given their understanding of the processes involved. So the question is, if there were external gravitational forces acting upon our universe, might that be a possible cause of the continued acceleration?

This message is a reply to:
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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 19 of 42 (372211)
12-25-2006 8:02 PM
Reply to: Message 16 by dogrelata
12-24-2006 10:25 AM


Re: Explanation please?
Okay, so there are some pretty serious problems regarding calculations of mass
Very much so. Mass of a simple space-time is a difficult enough concept, without the added complications of a branching universe. You essentially measure mass across a slice of space-time; the question is what kind of slice?
You are right, the rubber sheet analogy does require the Earth's gravity to work, but it is only an analogy. In reality, mass/energy at a particular point in space-time helps define the curvature of space-time at that point. There is no action at a distance, no gravitational force.
Curvature at a point helps define the curvature at neighbouring points, and hence the effect of the mass/energy propegates out through space-time. As SG has pointed out, a particle will follow a straight line through space-time, which will appear curved to us (orbits, projectile motion) because of our reduced 3d perspective. Simple as that.
Particles that are sufficiently massive to create non-negligible curvature are a little more complicated to work with, but the same principles apply (e.g. the Earth moving on its orbit through space)
The question I’m trying to ask is, how certain are we that the warping we observe in the fabric of space is entirely due to the gravitational forces acting upon it by the objects travelling through it?
Again, gravitational forces are our naive interpretation of the warping. Spae-time is not warped by 'gravitational forces'. Mass, energy, and momentum (and most importantly space-time curvature) all generate space-time curvature. Oh, also a cosmological constant, which is important for the accelerating Universe.
At present we have no need to introduce any other concepts to explain the large-scale structure of the Universe.
Edited by cavediver, : No reason given.

This message is a reply to:
 Message 16 by dogrelata, posted 12-24-2006 10:25 AM dogrelata has replied

Replies to this message:
 Message 20 by dogrelata, posted 12-26-2006 7:51 AM cavediver has replied

  
dogrelata
Member (Idle past 5312 days)
Posts: 201
From: Scotland
Joined: 08-04-2006


Message 20 of 42 (372260)
12-26-2006 7:51 AM
Reply to: Message 19 by cavediver
12-25-2006 8:02 PM


Re: Explanation please?
cavediver writes:
Again, gravitational forces are our naive interpretation of the warping. Spae-time is not warped by 'gravitational forces'. Mass, energy, and momentum (and most importantly space-time curvature) all generate space-time curvature. Oh, also a cosmological constant, which is important for the accelerating Universe.
So are we saying that the warping of space-time is not caused solely by mass/energy? That space-time is ”naturally’ warped? Or is space-time comprised of mass/energy, which causes it to warp itself? Apologies for all the questions, but I’d always been led to believe that the warping was due to gravitational forces.
Finally, isn’t the cosmological constant still a highly contentious issue?

This message is a reply to:
 Message 19 by cavediver, posted 12-25-2006 8:02 PM cavediver has replied

Replies to this message:
 Message 21 by fallacycop, posted 12-26-2006 8:15 AM dogrelata has not replied
 Message 22 by Son Goku, posted 12-26-2006 9:21 AM dogrelata has not replied
 Message 23 by cavediver, posted 12-26-2006 12:17 PM dogrelata has not replied

  
fallacycop
Member (Idle past 5521 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 21 of 42 (372262)
12-26-2006 8:15 AM
Reply to: Message 20 by dogrelata
12-26-2006 7:51 AM


Re: Explanation please?
So are we saying that the warping of space-time is not caused solely by mass/energy? That space-time is ”naturally’ warped? Or is space-time comprised of mass/energy, which causes it to warp itself? Apologies for all the questions, but I’d always been led to believe that the warping was due to gravitational forces.
It would be more accurate to say that the gravitational forces are due to the warping of space-time, and that the warping is due to , not only matter/energy, but also to momentum, pressure, torsion, or even by space itself. Anything that has those properties will warp space. (Even the very energy of the space warp will feed back into itself creating more warp, which makes for highly non-trivial non-linear equations)
Finally, isn’t the cosmological constant still a highly contentious issue
The need for a cosmological constant is becoming more and more accepted those days. What creates the cosmological constant, though, is still a matter of intense debate and research.
Edited by fallacycop, : fix quote box

This message is a reply to:
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Son Goku
Inactive Member


Message 22 of 42 (372271)
12-26-2006 9:21 AM
Reply to: Message 20 by dogrelata
12-26-2006 7:51 AM


Re: Explanation please?
So are we saying that the warping of space-time is not caused solely by mass/energy? That space-time is ”naturally’ warped? Or is space-time comprised of mass/energy, which causes it to warp itself? Apologies for all the questions, but I’d always been led to believe that the warping was due to gravitational forces.
Finally, isn’t the cosmological constant still a highly contentious issue?
The warping of spacetime is caused by mass/energy density, energy/momentum flux, pressure and viscosity of a given piece of matter or a field of force(e.g. eletromagnetism).
However a better word than caused is related, for every distribution of matter and force there is a corresponding spatio-temporal shape. When you have one, you have to have the other.
Gravitational Forces are a result of the warping and the warping is required by the existence of a given distribution of matter & force.

This message is a reply to:
 Message 20 by dogrelata, posted 12-26-2006 7:51 AM dogrelata has not replied

  
cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 23 of 42 (372290)
12-26-2006 12:17 PM
Reply to: Message 20 by dogrelata
12-26-2006 7:51 AM


Re: Explanation please?
That space-time is ”naturally’ warped?
Yes, it can be. As I said, space-time curvature generates space-time curvature - not in an out-of-control positive feedback cycle, but in a self-supporting type of notion.
Quick analogy off the top of my head: imagine a long strip of paper (space-time) How can we add some humps to the paper? Easy, stick some blocks (matter) under the strip to prop up bits of it. What if we have no blocks? Well how about putting a few knots in the paper itself. That will introduce similar (if somewhat contorted) humps, without the need of adding anything else.
There are an infinite variety of vacuum solutions of General Relativity: space-times that contain no matter, no extra energy, nothing except the space-time itself. They are far from trivial, like our paper above with its knots.
The classic Schwarzschild solution, our most simple black hole, is one such solution. Despite everything you may think you know about black holes, this one has no matter whatsoever. Yet there it is with its event horizon and singularity, but with all of its 'gravitational field' generated purely from the space-time itself. It even has a mass if you try to measure it using any of the usual methods, again generated purely from the curved space-time.
Finally, isn’t the cosmological constant still a highly contentious issue?
We have long (~100 years) assumed it to be zero for no good reason other than to fit with observation. Now observation dictates it has a small value, and suddenly we are interested in the reason. Nothing has changed, we have just had a prod to our laziness. The problem is the GR leaves the CC as a free parameter. The theory does not dictate the value. This is a huge clue to the idea that GR is not a final theory but an emergent theory (perhaps not as huge a clue as its non-quantum nature)
But GR itself is untouched by the discovery of a non-zero CC, or the existence of 'dark energy' (you listening, RAZD? ) The great thing about the observed CC is that it is pushing us into considering a deeper theory sooner than we had anticipated.
Edited by cavediver, : No reason given.

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Fabric
Member (Idle past 5672 days)
Posts: 41
From: London, England
Joined: 02-27-2005


Message 24 of 42 (372436)
12-27-2006 12:38 PM


theories on the cosmological constant
What are the leading theories on what cause's this cosmological constant, i read that it
was the energy of empty space, something to do with the quantum world...
thanks
Kev

Replies to this message:
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cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 25 of 42 (372948)
12-30-2006 7:46 AM
Reply to: Message 24 by Fabric
12-27-2006 12:38 PM


Re: theories on the cosmological constant
A true CC is constant in time and space. It would arise from some deeper theory about which we know little - perhaps some aspect of M-theory or something not even yet considered.
A pseudo-CC would be a dynamic field - essentially a new particle - that varies very slowly across space and time. It would take its place in family of fields (particles) of which we are aware, and again would arise from some deeper theory, as do all of the fields: space-time, strong, electroweak, matter, etc.
The observed very small CC could be the remainder of the above two working aainst each other, similar to the idea that observed matter is the slight left-over discrepancy of the original matter/anti-matter annihilations.

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Calypso
Junior Member (Idle past 5156 days)
Posts: 28
Joined: 06-05-2006


Message 26 of 42 (382068)
02-03-2007 1:23 AM
Reply to: Message 13 by cavediver
12-10-2006 7:07 AM


Re: Explanation please?
If the teacup was melt was there any way of knowing precisely it had been a teacup?
Theoretically yes, practically no. But if Hawking had been right, then it would have also have been "theoretically no", which has profound implications for physics.
There is no way for you to know you silly little 4 dimensional beast. But unlike you god can travel through time (among other dimensions) and can see the teacup before it was destroyed so no information was lost to god. 10 dimensional beings have their privileges.
Have you seen this? Imagining the Tenth Dimension - A Book by Rob Bryanton

This message is a reply to:
 Message 13 by cavediver, posted 12-10-2006 7:07 AM cavediver has replied

Replies to this message:
 Message 27 by cavediver, posted 02-03-2007 4:33 AM Calypso has replied

  
cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 27 of 42 (382076)
02-03-2007 4:33 AM
Reply to: Message 26 by Calypso
02-03-2007 1:23 AM


Re: Explanation please?
But unlike you god can travel through time (among other dimensions) and can see the teacup before it was destroyed so no information was lost to god. 10 dimensional beings have their privileges.
Any being that "travels" along the dimensions of our existence (time and/or space) does not merit the term "god". 10 dimensional beings are as far below god as we are.
Yes. Up to 4d, it has some good bits and bad bits. After that, the scientific term is "pure bollocks".

This message is a reply to:
 Message 26 by Calypso, posted 02-03-2007 1:23 AM Calypso has replied

Replies to this message:
 Message 28 by Calypso, posted 02-03-2007 1:15 PM cavediver has replied
 Message 30 by Hyroglyphx, posted 02-03-2007 10:30 PM cavediver has replied

  
Calypso
Junior Member (Idle past 5156 days)
Posts: 28
Joined: 06-05-2006


Message 28 of 42 (382140)
02-03-2007 1:15 PM
Reply to: Message 27 by cavediver
02-03-2007 4:33 AM


Re: Explanation please?
Sounds a bit close minded cavediver. I like to think that it's possible, but not proven, and probably not likely to be proven anytime soon by the human race. "Pure bollocks" would be more appropriate for something completely disproven or out of the realm of possibility. This at least makes mathematical sense. But then the latest video game is all mathematically based as well but has no basis in reality so who knows.

This message is a reply to:
 Message 27 by cavediver, posted 02-03-2007 4:33 AM cavediver has replied

Replies to this message:
 Message 29 by cavediver, posted 02-03-2007 1:27 PM Calypso has not replied

  
cavediver
Member (Idle past 3644 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 29 of 42 (382145)
02-03-2007 1:27 PM
Reply to: Message 28 by Calypso
02-03-2007 1:15 PM


Re: Explanation please?
"Pure bollocks" would be more appropriate for something completely disproven or out of the realm of possibility.
In this case it is more simple - it's just wrong As in, when we talk about extra dimensions in physics (string theory, M-theory, SuperGravity, etc) it has very little if anything to do with the concepts shown in that video. Where the ideas in that video come from (for d>4) I have no idea, but it's not part of extra-dimensional physics as we practise it. My first work was in 26 dimensions. I wonder how he'd explain those extra 16
Fundemental physics is weird and exciting enough - it doesn't need "bollocks" like this!
Edited by cavediver, : Corrected imbecilic use of language

This message is a reply to:
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Hyroglyphx
Inactive Member


Message 30 of 42 (382256)
02-03-2007 10:30 PM
Reply to: Message 27 by cavediver
02-03-2007 4:33 AM


Re: Explanation please?
Up to 4d, it has some good bits and bad bits. After that, the scientific term is "pure bollocks".
I thought someone like yourself would appreciate String Theory. Or are you just critiquing the website that was clearly geared for laymen?

"A man can no more diminish God's glory by refusing to worship Him than a lunatic can put out the sun by scribbling the word, 'darkness' on the walls of his cell." -C.S. Lewis

This message is a reply to:
 Message 27 by cavediver, posted 02-03-2007 4:33 AM cavediver has replied

Replies to this message:
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