Experimental evidence of higher dimensions. What will they be?

[yoda9999]

Has there been any direct or indirect evidence from particle accelerators, telescopes, or observatories that the universe has more than 3 spatial dimensions? If not, what kind of evidence or data are particle physicists looking for? Are there some unexplained phenomenon that could only be attributed to the existence of higher dimensions?

I've been told that the Large Hadron Collider could yield some results about extra dimensions. If anyone wants to elaborate on that, that'll be fine. Thanks!

 

[Haelfix]

Yes several methods..

1) Indirect proof.. Usually associated with phenomology. The so called phenomological desert most places and boom lots of activity at some critical scale.

2) Direct proof. Kaluza Klein Modes, which would be very evident in a particle accelerator.

3) Even more direct proof, large extra dimensions and departure from Newtons laws at say nm scales

 

[Farsight]

I read a nice clear article a while back about the LHC possibly revealing extra dimensions, yoda. I'll try to dig it up. Meanwhile there's a lot of papers you can find via a google search.

http://www.google.co.uk/search?hl=en&q="large+hadron+collider"+dimensions&meta=

Rather too many, so maybe one of the experts here could select a few out for you.

 

[xionium]

lowered Planck energy

I've heard that if there are any extra dimensions compactified on a scale significantly larger than the Planck length, the Planck energy would be lower than its calculated value of ~10^19 GeV. Consequences of this would evident at the LHC II next year, like the production of microscopic black holes or a (hopefully remote) chance of triggering a cosmological phase transition (a.k.a. vacuum decay) and thus ending the universe as we know it. Other consequences would be departures from Newtonian gravitation and general relativity at the length scale of the not-fully-compactified dimension(s). These departures would usually involve a weakening of the expected gravitational force at the length scale involved.

 

[ptabor]

... chance of triggering a cosmological phase transition (a.k.a. vacuum decay) and thus ending the universe as we know it.

surely there are other processes in the universe whose energy output is many orders of magnitude beyond that of the LHC... wouldn't it be more probable that such reactions would trigger such a phase transition?

Of course, there is no guarantee it hasn't happened yet, and we're waiting to find out.

 

[xionium]

That is one of the primary arguments against those who claim that the LHC II will end the universe as we know it next year. It is similar to the calculations that there is a one-in-a-billion chance that a thermonuclear weapon will ignite the atmosphere, ending most life on the planet. If you detonate enough thermonuclear weapons, one of them will eventually destroy the planet. Similarly, if you achieve the Planck density enough times (assuming that we can even reach it with the LHC), one of those times it will destroy the universe. Everything has an associated risk.

 

[Norman]

It is similar to the calculations that there is a one-in-a-billion chance that a thermonuclear weapon will ignite the atmosphere, ending most life on the planet.

I don't mean to be rude but I have to call this BUNK. Can you show me this calculation? Because a report authored by Konopinski, Marvin and Teller (LA-602), which was commisioned by Oppenheimer (declassified in 1973) showed that it could never happen (with the fission weapons of the time). You can see the document http://www.fas.org/sgp/othergov/doe/lanl/docs1/00329010.pdf"

The main finding was that even if you can achieve the needed temperature (which may or may not be possible today- I do not know), compton scattering would make a chain reaction impossible. Now, I have only skimmed the document and I do not have a nuclear weapons background, so I wouldn't mind someone correcting me.

On the notion of the LHC creating a cosmological phase transistion... not being a cosmologist and all, could someone spell this out a little? Or give a credible reference for it please?

 

[xionium]

You are correct---apparently it was thought that there was a slim but finite chance that thermonuclear weapons could ignite the atmosphere until it was proven impossible. Thanks for the info. Even though it is impossible, though, the analogy for cosmological phase transitions/vacuum decays still holds. Most likely a cosmological phase transition will not occur at the LHC, even if the Planck energy is reached, but I would feel a lot better if it could be proven mathematically impossible, like the atmospheric ignition.

 

[Norman]

Do you know on what theoretical framework this notion that a cosmological phase transition is based on?

 

[xionium]

Basically, a cosmological phase transition is when the universe decays to a stabler and less energetic state, similar to the phase transitions of matter. Past cosmological phase transitions include the Planck, GUT, and electroweak transitions. These transitions involved major changes in the forces and constituents of the universe, such as the decay of the X and Y bosons of GUT theories to produce a matter-antimatter asymmetry in our universe. Scientists predict that the next cosmological phase transition would probably not occur naturally for another 10^100 to 10^1000 years. This is way beyond what big bang theorists call the "big freeze" or heat death of the universe. The universe would most likely not be able to support "life" at that time, even in its most speculative forms.

 

[Norman]

So with the LHC the worry is about the Planck transition I garner. But aren't all (maybe a better question is any) these theories of the Planck transition based on some sort of SUSY framework? Implying no SUSY = no worries. And the whole notion that IF these POSSIBLE extra dimensions exist the Planck energy MIGHT be lower than the "accepted" value seems wildly speculative.