Evidence for Extra Dimensions?

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Ixtellor
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Evidence for Extra Dimensions?

Postby Ixtellor » Wed May 05, 2010 7:46 pm UTC

Are they just theory at this point, or is there actual empirical evidence for their existance.

Also, if your bored... likelyhood gravitons exist?
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Re: Evidence for Extra Dimensions?

Postby Minerva » Thu May 06, 2010 6:38 am UTC

We could see evidence at the LHC.

The emergence of Kaluza-Klein like particles, which seemingly violate energy/momentum conservation as they enter and exist the other dimensions - seemingly vanishing and appearing from nowhere - would be one good example.

Also, microscopic black hole formation at the LHC would be a fascinating example. Microblackhole formation at LHC is only possible if gravity becomes very strong at the TeV scale as you head down towards the Planck scale - which could only happen as a result of the presence of higher dimensions.
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Re: Evidence for Extra Dimensions?

Postby makc » Fri May 07, 2010 10:13 pm UTC

Minerva wrote:Also, microscopic black hole formation at the LHC would be a fascinating example. Microblackhole formation at LHC is only possible if gravity becomes very strong at the TeV scale as you head down towards the Planck scale - which could only happen as a result of the presence of higher dimensions.
how would you find that there is microblackhole?

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Re: Evidence for Extra Dimensions?

Postby Minerva » Sat May 08, 2010 11:22 am UTC

When it swallows up the world. :wink:
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Re: Evidence for Extra Dimensions?

Postby Assasinof6 » Sun May 09, 2010 1:46 pm UTC

by Minerva » Sat May 08, 2010 11:22 am UTC

When it swallows up the world.

I know you were joking, but just for the record...
Microblackholes are harmless..., since any microblackholes are very unstable, and wouldn't last for more than a hundredth of a second. Also, you have to be in fairly close perimeter to a black hole to actually feel its effects (within 3000 km). That's on a regular scale- microblackholes, such as the ones at the planck scale would be completely harmless- even if you were an inch away from one.

Also, since the string theory currently asks for multiple dimensions, any proof that goes towards string theory indirectly implies a presence of 7 other dimensions. Proof has been found (yay!) for string theory, and that's the fact that it can explain high temperature superconductivity.
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Re: Evidence for Extra Dimensions?

Postby gmalivuk » Sun May 09, 2010 2:31 pm UTC

Assasinof6 wrote:you have to be in fairly close perimeter to a black hole to actually feel its effects (within 3000 km). That's on a regular scale
No. Even an Earth-mass black hole will have gravity as strong as Earth's at Earth's radius, which is about 6400km. And a normal stellar-mass one would have much stronger gravity much farther away.

Proof has been found (yay!) for string theory, and that's the fact that it can explain high temperature superconductivity.
That is not proof.
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Re: Evidence for Extra Dimensions?

Postby PM 2Ring » Sun May 09, 2010 2:48 pm UTC

gmalivuk wrote:
Assasinof6 wrote:you have to be in fairly close perimeter to a black hole to actually feel its effects (within 3000 km). That's on a regular scale
No. Even an Earth-mass black hole will have gravity as strong as Earth's at Earth's radius, which is about 6400km. And a normal stellar-mass one would have much stronger gravity much farther away.

I guess it depends what he means by "feel its effects". Obviously the Moon feels some effects of the Earth's gravity, or it wouldn't be orbiting us. :) But in freefall, you don't feel the tidal distortion effects of a gravity source until you are close enough, and since that drops off according the inverse cube law, you do need to get rather close. It's primarily those tidal effects that make the spacetime curvature in the immediate vicinity of BHs (and neutron stars) significantly different to that in the vicinity of normal matter. And then there's gravitational time dilation & frame-dragging to consider, both of which are also only significant in steep gravity wells.

gmalivuk wrote:
Proof has been found (yay!) for string theory, and that's the fact that it can explain high temperature superconductivity.
That is not proof.
Agreed. But it might be evidence, not that I'm much of a string theory fan.

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Re: Evidence for Extra Dimensions?

Postby Assasinof6 » Sun May 09, 2010 3:46 pm UTC

Yes, you are both right. I apologize for hastily saying that the high temperature superconductor which can be explained by ST is proof- you are right, this is incorrect. It is more along the lines of circumstantial evidence. Anyways, the whole point of me saying that was to give a clue for evidence of extra dimensions, as indicated by the title of the forum. And no, I wasn't wrong about the fact that blackholes need to be surprisingly close to fall into its inescapable pull.
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Re: Evidence for Extra Dimensions?

Postby makc » Sun May 09, 2010 9:57 pm UTC

yeah, but... how would you detect microscopic black hole? really?

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Re: Evidence for Extra Dimensions?

Postby YoungStudent » Sun May 09, 2010 10:36 pm UTC

Energy calculations. Mathematics.
Okay, quote me - We try to explain magic, presence of spirits and supernatural with science, which only explains 'the physical world' that we observe. It's like blind earthworm declaring that there is no light.

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Re: Evidence for Extra Dimensions?

Postby dainbramage » Mon May 10, 2010 6:41 am UTC

Also small black holes tend to explode violently

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Re: Evidence for Extra Dimensions?

Postby SummerGlauFan » Mon May 10, 2010 7:00 am UTC

They also emit certain types of radiation.

Basically, just like regular black holes, you won't actually see them, but will see their effects.
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Re: Evidence for Extra Dimensions?

Postby Josephine » Mon May 10, 2010 7:15 am UTC

I was going to write a post about how saying that a black hole is only visible from its effects doesn't mean much as we observe everything that way. Then I realized we detect black holes by gravitational effects, not hawking radiation.
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Re: Evidence for Extra Dimensions?

Postby SummerGlauFan » Mon May 10, 2010 7:20 am UTC

nbonaparte wrote:I was going to write a post about how saying that a black hole is only visible from its effects doesn't mean much as we observe everything that way. Then I realized we detect black holes by gravitational effects, not hawking radiation.


Yeah. :) By no means was I saying that we can only detect them by their radiation, I was just adding it to the list of things other people wrote about how to detect them.
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Re: Evidence for Extra Dimensions?

Postby makc » Mon May 10, 2010 9:47 am UTC

Then I realized we detect black holes by gravitational effects
what gravitation effects? lensing of single photon with 10^-123 probability?

p.s. thanks mods for removing my post. now YoungStudent's reply looks so much more meaningful.

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Re: Evidence for Extra Dimensions?

Postby Josephine » Mon May 10, 2010 10:08 am UTC

makc wrote:
Then I realized we detect black holes by gravitational effects
what gravitation effects? lensing of single photon with 10^-123 probability?

p.s. thanks mods for removing my post. now YoungStudent's reply looks so much more meaningful.

gas orbiting a black hole is rather hot. not gravitational lensing, it's even more indirect than that.
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Re: Evidence for Extra Dimensions?

Postby makc » Mon May 10, 2010 10:46 am UTC

we're talking microscopic black holes, remember?

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Re: Evidence for Extra Dimensions?

Postby Josephine » Mon May 10, 2010 10:55 am UTC

true. I imagine the hawking radiation would give it away under those conditions.
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Re: Evidence for Extra Dimensions?

Postby Minerva » Mon May 10, 2010 11:28 am UTC

Basically, the micro black hole will evaporate relatively rapidly, and it will create a shower of different particles and photons and stuff as it decays, which will be detected inside a detector like ATLAS or CMS and the event and the properties of the original particle reconstructed, much like the analysis of other unstable massive particles within the detector.

Anyway... I'm interested in learning more about the claim that string theory explains high temperature superconductivity. More resources or links for me to read, please. :)
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Re: Evidence for Extra Dimensions?

Postby gmalivuk » Mon May 10, 2010 1:22 pm UTC

Minerva wrote:Basically, the micro black hole will evaporate relatively rapidly

That's putting it very, very mildly. A Planck mass black hole will evaporate in 10-40 seconds or so, and even a metric ton will go in 84 nanoseconds.
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Re: Evidence for Extra Dimensions?

Postby PM 2Ring » Mon May 10, 2010 1:30 pm UTC

gmalivuk wrote:
Minerva wrote:Basically, the micro black hole will evaporate relatively rapidly

That's putting it very, very mildly. A Planck mass black hole will evaporate in 10-40 seconds or so, and even a metric ton will go in 84 nanoseconds.

Of course, the LHC can't produce BHs under standard theory, only non-standard variants (including brane theories where gravity leaks from our universe via compact dimensions), so if they are produced, their lifetimes may be a little longer & their temperatures may be a little cooler. But not by very much. :)

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Re: Evidence for Extra Dimensions?

Postby Assasinof6 » Mon May 10, 2010 8:46 pm UTC

Minerva wrote:
Anyway... I'm interested in learning more about the claim that string theory explains high temperature superconductivity. More resources or links for me to read, please.


Sure thing. http://www.lmgtfy.com/?q=high+temperature+superconductivity+explained+by+string+theory
once you're at the page, click on any one of the links you see on that page.
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Re: Evidence for Extra Dimensions?

Postby JWalker » Tue May 11, 2010 1:41 am UTC

String theory does not explain high temperature superconductivity, a mathematical tool developed for use in string theory has been applied to help explain a certain aspect of high temperature superconductivity. Nothing to do with string theory really.

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Re: Evidence for Extra Dimensions?

Postby BlackSails » Tue May 11, 2010 1:48 am UTC

Speaking of superconductors, is the resistivity really 0, or is it only 0 to some order in perturbation theory? Its hard to imagine that it is actually exactly 0, since there are going to be all sorts of fluctuations in the electric field and stuff.

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Re: Evidence for Extra Dimensions?

Postby PM 2Ring » Tue May 11, 2010 12:24 pm UTC

BlackSails wrote:Speaking of superconductors, is the resistivity really 0, or is it only 0 to some order in perturbation theory? Its hard to imagine that it is actually exactly 0, since there are going to be all sorts of fluctuations in the electric field and stuff.

Really. Or so close to zero that it doesn't matter. :)
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Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years. Theoretical estimates for the lifetime of a persistent current can exceed the estimated lifetime of the universe, depending on the wire geometry and the temperature.

Current in a superconductor is carried by Cooper Pairs, pairs of electrons with correlated momenta. They act as a quantum unit, even though they are separated from each other by many intervening atoms in the crystal lattice. The total spin of a pair of electrons is integral, so it behaves like a boson, not a fermion. In particular, Cooper Pairs do not obey Pauli exclusion but instead follow Bose-Einstein statistics, producing a kind of condensed state, similar to the correlation that happens to photons in a laser beam.

I said above that the current is carried by Cooper Pairs, but the Cooper Pair formation occurs through the interaction between electrons & phonons, quantized crystal vibrations. This page has good definitions of common terms used in superconductivity & some neat animations.

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Re: Evidence for Extra Dimensions?

Postby Josephine » Tue May 11, 2010 10:21 pm UTC

Wait, so does that mean that a room-temperature superconductor would work as a battery (among other things)?
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Re: Evidence for Extra Dimensions?

Postby Soralin » Tue May 11, 2010 10:52 pm UTC

nbonaparte wrote:Wait, so does that mean that a room-temperature superconductor would work as a battery (among other things)?

Yes, and in fact, current superconductors have already been used for that purpose, see: http://en.wikipedia.org/wiki/SMES

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Re: Evidence for Extra Dimensions?

Postby Josephine » Tue May 11, 2010 10:57 pm UTC

Well, I know how energy on Triton would be stored...
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Re: Evidence for Extra Dimensions?

Postby attempt » Wed May 12, 2010 3:09 am UTC

PM 2Ring wrote:Of course, the LHC can't produce BHs under standard theory, only non-standard variants (including brane theories where gravity leaks from our universe via compact dimensions), so if they are produced, their lifetimes may be a little longer & their temperatures may be a little cooler. But not by very much. :)

I started to probe through wiki for brane theory gravity leaks. Unfortunatly I wound up visiting short string theory pages. Although M-Theory (http://en.wikipedia.org/wiki/M-theory ) seems an interesting with its 11 dimensions. Time to start reading about 5d-10d first. :P

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Re: Evidence for Extra Dimensions?

Postby Minerva » Fri May 14, 2010 12:29 pm UTC

But that's part of what makes microscopic black hole formation in colliders fascinating; if it ever actually happened, then those theoretical cosmologies would not just be fascinating hypotheses, they would basically be fact.
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Re: Evidence for Extra Dimensions?

Postby massivefoot » Wed May 26, 2010 4:19 pm UTC

There seems to be a lot of confusion regarding how string-theory relates to high-temperature superconductivity, and I think I can clear some of it up.

Assasinof6 wrote:Proof has been found (yay!) for string theory, and that's the fact that it can explain high temperature superconductivity.


JWalker wrote:String theory does not explain high temperature superconductivity, a mathematical tool developed for use in string theory has been applied to help explain a certain aspect of high temperature superconductivity. Nothing to do with string theory really.


The actual status is somewhere in between these two statements. Firstly, assuming that string theory represents an accurate "theory of everything" does not explain high-T superconductivity. Even if it did this would not be proof that string theory was a correct fundamental theory, just one experimental test that it passed.

The model we are interested in for a high-temperature superconductor is still a quantum field theory with electrons as the basic matter. There's a non-dynamical background electromagnetic field. Since this is non-dynamical, the U(1) symmetry associated to it is a global, rather than gauge, symmetry. However, we expect that the theory is strongly coupled, and this means we can no longer use the particle approximation of the field theory (which we could at low T to explain everything in terms of Cooper pairs.)

Now this is the point at which string theory comes in: there's a conjecture called the Holographic Correspondence (or sometimes the AdS/CFT correspondence) that states that string theory in (d+1) dimensions is dual to a scale-invariant quantum field theory in d dimensions. There's something of a 'dictionary' of correspondences between quantities in the two theories. The most compelling argument in favour of this duality comes from looking at strings and D-branes in AdS space.

So we've gone from one theory where it's hard to do calculations (a strongly coupled QFT) to another where it's hard to do calculations (a string theory of quantum gravity.) But, certain limits of the boundary QFT correspond to certain limits of the string theory. In particular, strongly coupled QFT with a global symmetry corresponds to classical gravity with gauge fields. So we have Einstein-Maxwell theory, which we can do calculations in.

Now there's some caveats here. I don't know the details of the superconductivity work, but I suspect they're using massless electrons (to make the field theory conformal) and the field in question might be U(N) in the large N limit. This is a model for how high-T superconductivity might arise, rather than a concrete theory of how it does arise in the real world. A similar calculation has been done for QCD in the large colour limit, and it shows confinement, which is promising.

So this certainly isn't evidence that string theory provides a fundamental model of the world, but it's a lot more than just "a mathematical tool developed for use in string theory" - string theory itself plays a big part in the argument.

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Re: Evidence for Extra Dimensions?

Postby Klotz » Sat Jun 05, 2010 8:30 pm UTC

If an extra dimension exists, it must have a size of less than 44 microns.

http://www.npl.washington.edu/eotwash/p ... 021101.pdf


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