What is the coldest temperature in the Universe?

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Offline DrQuincy

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What is the coldest temperature in the Universe?
« on: 08/05/2008 08:29:08 »
Tim Bennett asked the Naked Scientists:
What is the coldest temperature in the universe? I know radiated heat can travel through space (i.e. a vacuum) but does this heat reach every part of the universe?

Is there a minimum temperature any given point in the universe will be?


What do you think?

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Offline syhprum

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What is the coldest temperature in the Universe?
« Reply #1 on: 08/05/2008 09:46:30 »
The lowest naturally occurring temperature in the universe is that of the CMBR i.e 2.73K but in the laboratory temperatures in the order of micro Kelvins can be produced.
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Offline na na

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« Reply #2 on: 08/05/2008 12:40:00 »
I would have to assume that if there is no "maximum" temp, there is no "minimum" temp.

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Offline techmind

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What is the coldest temperature in the Universe?
« Reply #3 on: 08/05/2008 13:45:40 »
I would have to assume that if there is no "maximum" temp, there is no "minimum" temp.

No, the minimum possible temperature anywhere in our universe is "absolute zero", 0 Kelvin (-273.15 Celcius).

This can be inferred from many physical measurements, not least Charles' Law http://en.wikipedia.org/wiki/Charles%27s_law
which relates the volume of a fixed quantity of gas to its temperature. From measurements at easily-available temperatures (eg 0C and 100C) the graph can be extrapolated backwards, and reaches zero volume at -273 Celcius.
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Offline Pumblechook

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lyner

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What is the coldest temperature in the Universe?
« Reply #5 on: 08/05/2008 15:11:44 »
You can have unlimited energy in a box (subject only to practicalities) but you can't have less than none. Temperature is the average energy per molecule - so 0K is the minimum. Don't be misled by the scale, which has equal steps for equal steps in energy but doesn't represent equal steps in difficulty of attaining that temperature.
The minimum temperature in the Universe cannot be zero kelvin any more than the speed of a particle with mass can be c. To get to each of these values  would require infinite energy so, no go.

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Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #6 on: 08/05/2008 15:57:53 »
The coldest temperatures in the universe are to be found in super-massive black holes - the temperature drops in proportion to the mass of the BH. 
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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lyner

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What is the coldest temperature in the Universe?
« Reply #7 on: 08/05/2008 16:19:50 »
That's interesting. This is an idea which must be very  theoretical. It would imply that the average KE of the particles is nearly zero. The density, being so high, would mean that the total KE inside would also be very high.
This sounds a bit like the fact that the highest temperature in the regions surrounding sun is actually the corona and not the surface. It's a matter of how temperature is defined, I think.

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Offline LeeE

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« Reply #8 on: 08/05/2008 16:53:31 »
It is theoretical insofar as we haven't actually seen it, but it's implied by the  observation that a BH acts like a black-body radiator.

In the sun's corona, the temperature is a measure of the kinetic energy of the individual atoms, and in fact, a similar state exists within our own atmosphere.  While the kinetic energy of the individual atoms in the corona is higher than those on the suface of the sun, there are a lot less of them and subjectively, it would feel colder (were it not for the fact that you'd be right beside the sun).  The same thing occurs on the Earth where the temperature of the upper atmosphere is higher than it is at the surface, but because the upper atmosphere is so rarified it is subjectively colder.

With a BH though, it's temperature isn't a measure of the kinetic energy of the individual particles within it, because it is effectively just one single particle, but of how it radiates energy.  So yup, how you define temperature is relevent.

...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline Bored chemist

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« Reply #9 on: 08/05/2008 19:21:44 »
With the "right" deffinition of temperature the 2 energy levels of a laser during a population inversion represent a negative thermodynamic temperature. When the laser "fires" it returns to normal temperatures by going infinitely negative then falling back from an infinitely positive temperature.
This sort of result is only useful for annoying people trying to teach physics, as in 
"Please Sir, If the Boltzman distribution can be used to calculate temperature, surely the temperature in a laser can go negative and you just said temperatures can't do that.".
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lyner

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What is the coldest temperature in the Universe?
« Reply #10 on: 08/05/2008 23:37:01 »
You've met that smartarse, too!

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Offline Kryptid

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What is the coldest temperature in the Universe?
« Reply #11 on: 08/05/2008 23:45:15 »
There is a theoretical upper limit to temperature called the Planck Temperature, whose value is ≈ 1.417 x 1032 Kelvins. Above this temperature, the particles that make up this superhot substance would collapse into black holes.

http://en.wikipedia.org/wiki/Planck_temperature
http://www.straightdope.com/classics/a3_347.html
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Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #12 on: 09/05/2008 00:56:04 »
I've got to confess that I've been more pre-occupied with looking at the apparent lower limits of resolution in the universe but the planck temp implies an upper limit too.  Hmm...

Even so, I'm not sure that 'collapse' is the right term to use here - perhaps it's better to think in terms of energy density.

...or perhaps not.  Dunno.

I find it very interesting that while BH's appear to have vanishingly small temperatures, as far as their black-body radiation is concerned, high enough temps can lead to a similar state, in terms of energy density.

So what would happen if you were able to heat a BH to the plank temp?  The attempt should just make it more massive, and therefore cooler.  Heh:) - Negative Energy becomes a requirement, looks at it's watch and decides that, once again, it's time to raise it's incomprehensible head above the parapet to check that nobody has spotted it yet:)
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline science_guy

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« Reply #13 on: 09/05/2008 02:51:02 »
Quote
The minimum temperature in the Universe cannot be zero kelvin any more than the speed of a particle with mass can be c. To get to each of these values  would require infinite energy so, no go.

0 kelvin, would usually mean NO energy, infinite energy is as far away as you can get from that goal.
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Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #14 on: 09/05/2008 08:15:39 »
Just a little observation from someone who knows nothing about anything.

If nothing can escape from a blackhole then surely heat can't either. Doesn't that imply that the measurable temperature be absolute zero?

And as a supplementary - can absolute zero ever be measured? Wouldn't using something to make the measurements cause an increase in temperature?
« Last Edit: 09/05/2008 08:17:55 by DoctorBeaver »
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Offline DoctorBeaver

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« Reply #15 on: 09/05/2008 08:18:50 »
Negative Energy becomes a requirement, looks at it's watch and decides that, once again, it's time to raise it's incomprehensible head above the parapet to check that nobody has spotted it yet:)


 [:D]
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Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #16 on: 09/05/2008 16:22:19 »
I think that the temperature really only applies to the event horizon.

What I am curious about is that if gravitons are to exist, how do they escape a BH?
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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lyner

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What is the coldest temperature in the Universe?
« Reply #17 on: 09/05/2008 21:00:04 »
Quote
The minimum temperature in the Universe cannot be zero kelvin any more than the speed of a particle with mass can be c. To get to each of these values  would require infinite energy so, no go.

0 kelvin, would usually mean NO energy, infinite energy is as far away as you can get from that goal.
What I meant is that, to get a refrigerator to cool a region to 0K, you would need infinite energy - nearer and nearer but never there. Very much like c.

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Offline DoctorBeaver

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« Reply #18 on: 09/05/2008 21:37:27 »

What I am curious about is that if gravitons are to exist, how do they escape a BH?


They jump the fence on a motorbike a la Steve McQueen!

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Offline LeeE

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« Reply #19 on: 09/05/2008 21:39:46 »
Heh - funny sometimes how the most obvious answers can elude you:)

...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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« Reply #20 on: 09/05/2008 22:56:18 »
If I've got this right, gravitons are not theorised as particles that attract matter. What they do is warp spacetime. As such, they would not need to escape from the BH. Spacetime would be warped from within the BH and its warping would extend beyond the event horizon.

An analogy would be water going down a plughole. Nothing comes from the plughole into the water, but the water for quite a large area around is affected by the the hole "sucking" water into itself1.

1 I know that's not really what happens, but give me a break!
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Offline shmengie

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What is the coldest temperature in the Universe?
« Reply #21 on: 10/05/2008 04:02:34 »
The condensate is cool! no, really, I mean it!

newbielink:http://www.google.com/search?q=bose+einstein+condensate&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a [nonactive]
BTW:  I'm new to this forum, hope ya'll enjoy my warped sense of humor, if it ever appears.
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Offline LeeE

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« Reply #22 on: 10/05/2008 19:03:43 »
I think the important thing about BHs is that whatever is inside the BH, that causes the distortion in spacetime, manages to exert it's influence outside the BH, which is something that nothing else that we are aware of is able to do.

The graviton only really makes sense to me if it distorts spacetime around itself, locally.  That way you can imagine gravitons being emitted by matter, propagating over time and following an inverse square law, falling off in intensity with distance.  But then we're back to how do they escape a BH?

Alternatively, a graviton could exist in a different number or set of dimensions, one or more of which could intersect the set of dimensions that make up our spacetime.  For example, a two-dimensional plane can intersect a three dimensional volume and fully occupy two of the dimensions but none of the third.

As such, you could speculate that a hypothetical two or fewer dimensional object may not be subject to laws that govern the behaviour of three-dimensional objects, or may only be subject to a subset of those laws.

Depending on how you mess with different dimensions, you could come up with different models for gravitons, from a stream of discrete particles, which when taken together produce a field, to the field being the expression of the entire life time of a single particle, with it's time-line dimension being mapped to our spatial dimensions.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline LeeE

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« Reply #23 on: 10/05/2008 19:15:03 »
Yeah - that BEC is fascinating stuff, but not quite as cold as the temps theorised for supermassive BHs.  There's an interesting experiment described in the 'Unusual characteristics' section in the wikipedia article:)

http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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« Reply #24 on: 11/05/2008 00:17:22 »
LeeE - have you come across the Randall-Sundrum warped extra dimensional theories of gravity? Or localisation?

Either of those could possibly explain how gravity "escapes" from a BH.
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Offline LeeE

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« Reply #25 on: 11/05/2008 12:22:03 »
No, I hadn't - thanks for that:)

...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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« Reply #26 on: 12/05/2008 08:35:32 »
Having reconsidered, I'm not sure localisation can provide a mechanism for it. But I think SR1 & SR2 can.

Thinking about it, wouldn't a theory involving Planck scale (or even larger) rolled-up dimensions provide a means for gravity to escape?

Also, something is tickling the back of my little beaver brain concerning quantum entanglement of gravitons. If 1 of an entangled pair of gravitons were inside the BH and the other outside...  [???]
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Offline LeeE

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« Reply #27 on: 12/05/2008 22:09:48 »
The idea of 'rolled up' dimensions seems odd to me - I can't see how the 'shape' of a dimension is going to be directly perceptable from within it.  That doesn't mean that the contents of a dimension need to be infinite though, and because it'll only be the presence of something within the dimension that has any effect, the dimension could be considered to be finite.  Hmm...  you'd also need another dimension to do the rolling in.

Quantum Entanglement of gravitons is an interesting idea.  Unlike everything else we're aware of (hmm... just remembered that BH's can have a charge - anyone know if a BH's charge acts as though it's from a single particle?), it would seem that gravitons must be preserved in a BH, otherwise there would be no gravity, so entanglement across the event horizon seems possible.  But I think the question, instead of being 'How does a graviton escape from a BH? then becomes 'How does a graviton survive in a BH?  I think that essentially, they are the same question - if something can maintain it's integrity within a BH, then escaping from probably isn't impossible either.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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« Reply #28 on: 12/05/2008 23:32:42 »
An extra dimension can be curled up from every point in a 3D universe. It would exist outside of those dimensions, not within them.

The shape may or may not be perceptible from within. The way gravity spreads out could give a clue. It would spread differently in a simple, curled up dimension than in a Calabi-Yau manifold.

Gravitons surviving within a BH has implications for the entropy of the BH. Maybe they do have hair after all!  [:D]
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Offline LeeE

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« Reply #29 on: 13/05/2008 14:38:36 »
There could be inumerable additional dimensions but I think that the important factor is whether they interact with our ones or not, and to have an effect upon our dimensions they must have some degree of existance within them.

Yes, I think that the way that gravity spreads does give a clue - it has a very simple shape and I think that is suggestive, but the trouble is that I think it's more suggestive of less complex, rather than more complex dimensions, or alternatively, an exchange of existing dimensions.  For example, in relativity we see that time trades off against speed so that the sum of the squares remains a constant, and when one factor is 1, the other is 0, so it's conceivable that when the value of a dimension drops to zero it could be indistinguishable from any other dimension.  Or it could be said to have ceased to have any existance altogether:)  But from our point of view, that dimension must still be accounted for.

I think the issue of BH entropy is still very much up in the (h)air;)
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline syhprum

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« Reply #30 on: 13/05/2008 16:12:49 »
I entered Randall-Sundrum into Google and although I have a vague idea what most physics are about it might as well have been written in Chinese for all I could understand.
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Offline DoctorBeaver

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« Reply #31 on: 13/05/2008 22:40:19 »
There could be inumerable additional dimensions but I think that the important factor is whether they interact with our ones or not, and to have an effect upon our dimensions they must have some degree of existance within them.


The dimensions themselves would not have to interact directly with our known dimensions to have an effect on them. According to RS, gravity could be diluted by extra dimensions, which would explain its weakness relative to the other forces.

Localisation, also, would have that effect. If our known dimensions are confined to a 3D brane and gravitons originate on another brane (the G-brane) and are free to move in the bulk, but their probability wave peaks close to the G-brane and falls away sharply, the further from the G-brane you get, the less likely you would be to find one. So by the time you get to our brane their probability wave, and hence their effect, is much less than in the localilty of the G-brane.

In either case, although the extra dimensions are not interacting directly with our 3 perceivable dimensions, their existence, and their size & shape, can possibly be inferred indirectly.

It is possible that the new LHC at CERN will detect the K-K partners of gravitons, and that would indicate that extra dimensions exist. The race would then be on to interpret the data and expand on current theories of extra dimensions.
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Offline DoctorBeaver

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« Reply #32 on: 13/05/2008 22:54:48 »
I entered Randall-Sundrum into Google and although I have a vague idea what most physics are about it might as well have been written in Chinese for all I could understand.

I know what you mean. It took me quite a while, a lot of mental contortions, a fair bit of brain-ache and 2 re-reads of Lisa Randall's book to get some kind of comprehension of what it's all about.
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Offline DoctorBeaver

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« Reply #33 on: 13/05/2008 23:03:53 »
syhprum - have you read this forum conversation? http://www.physicsforums.com/showthread.php?t=119294
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Offline LeeE

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« Reply #34 on: 14/05/2008 18:23:40 »
I can't get around the idea that for one thing to affect another, there must be something in common between the two.  No matter how close something may come, unless something is shared or transferred, it's still a 'miss'.

There's no way I'd claim to clearly understand all the RS stuff, but as I interpret it, you could imagine it by dropping a few dimensions and thinking of a cube where the volume of the cube is the 5D bulk and two opposing faces are the 4-branes - hmm... perhaps a better representation might be an open convex lens shape - yeah - that's better - just two faces to deal with :)

Anyway, in this representation, we'd think of the two faces and the volume as separate entities, which strictly speaking, they are.  However, as they're also parts of a single entity, it's easy to imagine how changes in one part may affect the other parts, especially if the changes occur in the volume.  For example, making a scratch on one surface wouldn't change the other surface but if a crack was made through the volume it would affect both surfaces.  In this respect, the surfaces respond to the volume, so the 4-branes responding to events in the bulk makes sense if they're all parts of a single super-space.

Also, I can't help but think of the way that the probability decreases with distance from the strong brane as a gradient, and then we're back to what causes the gradient, swapping gravity for the probability curve:)  Heh:) - perhaps there's a gradient because the the two 4-branes are different sizes, hmm... I wonder if the strong brane could be reduced to a point... <starts thinking about cone shaped universes/>

Like I said though, with only a partial understanding of RS space I could quite easily be missing something important.

It'll be _very_ interesting to see what comes out of the LHC.  Whatever the results, it should clear some things up, one way of another.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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« Reply #35 on: 14/05/2008 22:00:49 »
Quote
I can't help but think of the way that the probability decreases with distance from the strong brane as a gradient, and then we're back to what causes the gradient,

The whole basis of RS is that the extra dimension is warped.

Our brane (RS refer to this as the Weakbrane as it works at the weak scale energy) and the Gravitybrane (at the Planck scale energy) warp the bulk dimension (5th dimension) separating them. This warping causes the strength of gravity to vary at different points within that dimension.

Quote
I can't get around the idea that for one thing to affect another, there must be something in common between the two.

The "something in common" is the graviton.

Your analogy of the lens is fine up to a point. As I mentioned, the 5th dimension is warped, and that cannot be represented by the lens.
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Offline LeeE

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« Reply #36 on: 15/05/2008 17:24:12 »
I guess that, in a way, we only get the reciprocal effect of the graviton, so although it can be vanishingly small it'll have non-zero presence in our brane - that seems fair enough.  I guess too, that the surfaces could dictate the volume, i.e. branes dictate the bulk, and if they're intrinsically different from each other, there'll need to be an intrinsic gradient of some sort between them, in the bulk.

Interesting:)
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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What is the coldest temperature in the Universe?
« Reply #37 on: 16/05/2008 06:47:52 »
i.e. branes dictate the bulk, and if they're intrinsically different from each other, there'll need to be an intrinsic gradient of some sort between them, in the bulk.

Interesting:)


I'm not sure you can say that branes dictate the bulk. However, their energy dictates the warping of the bulk.

There wouldn't be a gradient in the bulk. The warping of the bulk is the gradient.
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Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #38 on: 16/05/2008 14:56:19 »
Actually, I think we're in agreement over the principles but perhaps not the choice of words to describe it:)

If the statement: 'the energy of the branes dictates warping of the bulk' is true, is it correct to say that the energy is a property of the branes, or should it be said that the branes are a property of the energy?

And perhaps I should have said gradient _of_ the bulk instead of _in_ the bulk.

Heh:)  I do think we're actually saying the same thing.

Something that occured to me last night, while I walking somewhere, is that if one of the branes was contracted to a point, it's shape would be a simple 5D cone and the change in the 4D cross-section might do nicely for the warp.  A truncated cone would work too, without the need to contract to zero and if you need a non-linear warp you could use hyperboloids.

...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline DoctorBeaver

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What is the coldest temperature in the Universe?
« Reply #39 on: 18/05/2008 09:58:08 »

Something that occured to me last night, while I walking somewhere, is that if one of the branes was contracted to a point, it's shape would be a simple 5D cone and the change in the 4D cross-section might do nicely for the warp.  A truncated cone would work too, without the need to contract to zero and if you need a non-linear warp you could use hyperboloids.


I believe that's what RS means. As the dimension becomes smaller, gravity becomes stronger; and the larger it gets, the weaker gravity becomes. That means that the strength of gravity in our perceivable universe is merely a function of the separation between the branes. Were that separation any different, then the force of gravity here would also be different.

It has interesting ramifications for unification of forces.
« Last Edit: 18/05/2008 10:01:42 by DoctorBeaver »
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Offline LeeE

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What is the coldest temperature in the Universe?
« Reply #40 on: 18/05/2008 14:18:34 »
Yup, it's an interesting model.

...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!