Evidence of 6 Dimensions or More?

shelflife writes "Nature.com is reporting that there may be evidence of 6 dimensions. Galaxies seem to behave as there were more matter in them than is actually visible. 'One explanation, they say, is that three extra dimensions, in addition to the three spatial ones to which we are accustomed, are altering the effects of gravity over very short distances of about a nanometre.'" Update by J : Like most of string theory, this is acknowledged by its authors to be "extremely speculative."

Comments

How dimensions wrap themselves up

[ReformedExCon]

The way I understood this phenomenon, as it was explained in Kaku's book, was that the extra dimensions were curled up on themselves so that they were smaller than could be detected.

The thought experiment was similar to the following. Imagine a sheet of paper with a line crossing from one edge to the opposite edge. You can see that the line exists when viewing the sheet in two dimensions. However, imagine if you rolled the sheet of paper up tightly with the line not directly aligned with the roll. Now you would have instead of a line a single dot or a series of evenly-spaced dots. The line hasn't gone anywhere, it has simply been rolled onto itself so that it seems to have become small and barely detectable.

Now extend that idea to multiple spatial dimensions beyond just two or three. Since we humans can only perceive three spatial dimensions, it is hard to imagine what multiple extra dimensions would be like. However, if we can take the extra dimensions and "roll" them into themselves, we can make a little more sense of the concept.

Re:How dimensions wrap themselves up

[m50d]

The WMAP results suggest the curvature runs the other way - the geometry of our universe is slightly hyperbolic. There's enough margin for error that a "flat" spacetime is just about possible (and preferred for simplicity) but a "positively" curved universe (i.e. 4-dimensional sphere or similar) seems pretty unlikely.

Re:So if we can't see it, it's in another dimensio

[Anonymous Coward]

It's simple: They plug what they observe into a mathematical model and see if they can come up with a model that matches observation. It's not simple blind guesswork.

Someone came up with a model called string theory that includes systems with multiple "hidden" dimensions.

The dark matter they're talking about in the article is behaving in a way predicted by one of the current string theory models, which doesn't fit the more traditional models, thus the assertion that it must be 6 dimensions at work.

Round and Round

[Quirk]

Resources

Greene's Elegant Universe

The Mechanical Universe

Last book I enjoyed, Three Roads to Quantum Gravity by L. Smolin... ya, ya, I know, nothing fits, is, isn't, yo momma... no yo momma... can, can't... I'm not touching you!

somewhere to start

[martian67]

If you need somewhere to start, and don't know any physics, try one of the free introductory physics books listed here. After that, if you want to try to bring yourself up to the level a book like the "road to reality" by Penrose is shooting for, try some of these:

• Relativity Simply Explained by Martin Gardner
• Black Holes and Time Warps: Einstein's Outrageous Legacy by Kip Thorne
• Spacetime Physics by Taylor and Wheeler (special relativity, with a little more math)
• Exploring Black Holes: Introduction to General Relativity by by Taylor and Wheeler (general relativity, with a little more math)
• QED: The Strange Theory of Light and Matter by Richard Feynman
• Three Roads to Quantum Gravity by Lee Smolin

For the actual reference

[volsung]

The actual paper this article is about is here:
Observational Evidence for Extra Dimensions from Dark Matter

(It's actually a draft of a paper submitted to Physical Review Letters, not yet approved.)

It's a nice phenomenology paper without any heavy math that puts together a bunch of theoretical ideas floating around. Even better, it has testable hypotheses! (unlike many papers these days)

1. Gravity should deviate from the inverse-square law at the nanometer scale.
2. Dark matter should be composed of a particle with mass 3e-16 GeV/c^2. (For comparison, mass of electron is 5e-4 GeV/c^2.)
3. The large extra dimensions assumptions all this is based on would require us to see all sorts of quantum gravity interactions at the LHC.

Now short-range gravity experiments are just approaching the micron scale, so we're 3 orders of magnitude away from testing hypothesis #1. I doubt anyone has an idea how to close that gap right now.

Checking hypothesis #2 would require some independent way of determining the mass of dark matter particles. I don't know what the sensitivity range of the various dark matter experiments running or planned are. Maybe they would be able to see something this light.

#3 however is going to start running in 2 years, and then we'll get some good information either way.

Re:So if we can't see it, it's in another dimensio

[taniwha]

no what they have is a bunch of conjectures that they think explain what's happening elsewhere in the universe better that the others we have at the moment (aka string theories) problems are that they posit extra dimensions (mostly more than 6) - so how to prove ones conjecture? - start hypothesis: "existence of tiny extra dimensions will also cause macroscopic (ie galaxy sized) things that can't normally be explained or microscopic (ie nanometer sized at the size of the dimension) things that can't normally be explained" - at this point one goes off and looking for proofs of your hypothesis ...

That IS the scientific method - you start with a 'conjecture' which IS a made up explanation and look for ways to prove or disprove it. If you think it's done by fairies at the bottom of the garden you race down there and start looking under leaves. "God did it"? start looking for gods to photograph and measure. Extra dimensions? start looking for evidence of them

explaination

[Shinaku]

I watched a stream yesterday which explained how dimensions can be interweaved into our own, and how the laws of gravity and Quantum physics can be combined with string theory,

http://www.pbs.org/wgbh/nova/elegant/

Everyone abuses Occam's razor

[PsiPsiStar]

I'm starting to think that Occam's razor is abused more often than it is used correctly.

Parent asserted;
Occam's Razor, which is a basic tenent of modern scientific thought says that the simplest explanation is the best.

This is an abuse of the version of Occham's Razor used in modern scientific thought, though an oft repeated misinterpretation.

A better way of phrasing the desire for elegance in modern science is; "Given two identically predictive models, choose the one which requires the fewest assumptions." Reducing the number of assumptions is not always the same as 'simplifying' the problem.

Also, remember that the purpose of science is to generate predictive value. If one of those models is more complex but also more predictive, then it is ALWAYS the better model, no matter how complex.

The original version of Occam's Razor, as correctly expressed in the Wiki article, is "Entities should not be multiplied beyond necessity" where 'necessity' equates to generating the maximum level of predictive value.

Check out the following link, which gives a better summation of the role of Occham's razor in science than the wiki article does.

http://www.physics.adelaide.edu.au/~dkoks/Faq/Gene ral/occam.html

Sheldon Glashow doesn't believe in strings

[50000BTU_barbecue]

Read the interview here.

Something less speculative that may be at work ...

[bluevector]

Plasma physics:

it may dominate the large scale structure and behavior of the universe (star formation, galaxy formation, intergalactic structures . . .); though most scientists are either unaware that this is so, or are not ready to admit it.

Check out the following:

Plasma Cosmology .net

Plasma Universe

Guided Tour of the Plasma Universe

Electric Currents and Transmission Lines in Space

Immense Flows of Charged Particles Discovered Between the Stars

Interesting quote from Hubble regarding redshift:

Edwin Hubble. "Humason assembled spectra of the nebulae and I attempted to estimate distances." So wrote Hubble of his colleague Milton Humason in 1935 by which time spectra had been obtained for over 150 nebulae. Hubble was a stern warner of using the Doppler effect for galaxies and argued against the recessional velocity interpretation of redshift, convincing Robert Millikan, 1923 recipient of the Nobel Prize for Physics and director of physics at the California Insitute of Technology, that the redshift interpretation as an expanison of the universe was probably wrong, the year before both of their deaths in 1953.

Hubble ended his book Observational Approach to Cosmology with the statement:..."if the recession factor is dropped, if redshifts are not primarily velocity-shifts, the pic[t]ure is simple and plausible. There is no evidence of expansion and no restriction of time-scale, no trace of spatial curvature, and no limitation of spatial dimensions. Moreover, there is no problem of internebular material. The observable region is thoroughly homogeneous; it is too small a sample to indicate the nature of the universe at large. The univers[e] might even be an expanding model, provide[d] the rate of expansion, which pure theory does not specify, i[s] inappreciable. For that matter, the universe might even be contracting."

Taken from:

http://public.lanl.gov/alp/plasma/people/contribut ors.html

Thuderbolts.info

Thunderbolts' Picture of the Day

Picture of the Day Archive

A few very interesting selections from the archive:

The Picture that Won't Go Away

Quasars in Infrared are Still Nearby

Predictions on "Deep Impact"

Electric Stars

Of Pith Balls and Plasma

Space Shuttle Struck by Megalightning?

The website of Halton Arp

The Observational Impetus For Le Sage Gravity