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."

Well i thought it was at least 11

[Tomah4wk]

An old professor of mine who was a string theory expert (i very much am not) once told me most of the maths he does deals with 11 dimensions.

Re:String Theory is a joke

[TopSpin]

This is why string theory is a joke. Whenever they run into a problem, they throw in more dimensions or some other kludge, like gravitons leaking out of the universe.

The meme "string theory" means something because a few brilliant people continue to believe the math involved is actually applicable to modeling reality. It may yet be dismissed as luminiferous aether. In the meantime it serves as a possibility that can be studied. Does this status justify ridicule? Certainly not from me.

Whatever happened to Occam's Razor?

[TheNarrator]

Occam's Razor [wikipedia.org], which is a basic tenent of modern scientific thought says that the simplest explanation is the best. It seems that these dark matter explanations get more and more complex. When a theory is very complex it becomes suspect. For instance, when the Earth was though to be the center of the universe, Mars moving backwards in the sky caused much grief to astronomers. They invented all kinds of head spinning mathematics to describe the motion of mars and the other planets. Of course when the Sun was put in the center of the solar system and the laws of gravity were unearthed everything turned out to be far simpler than the theorists, working with broken premises had made it out to be. In the same way, something smells funny with String theory, and multi-dimensional explanations for dark matter, etc. Isn't science about experimentation and testing hypothesises in a laboratory instead of endless mathematical tricks to get theories to fit observations?

Re:Whatever happened to Occam's Razor?

[random name 6721]

No, its not getting more complex. In fact, having more dimensions explaines the stuff _nicely_, that means without too many additional assumptions. No need for an arbitrary particle which, by chance, excatly behaves like dark matter on large distances, but is not observable otherwise. The problem only is, that the simple ideas of the string theory (which is usually the physical theory behind the multiple dimensional universe explainations) is mathematically difficult, and complex, and hence, all articles etc. which try to explain it, or parts of it, are ususally somewhat mind boggling. Its somewhat like taking Maxwells equations (which are beautufully simple) and start to explain why the sun looks red while rising - Ugh! Let some years pass, and as understanding of String theory and implications gets better, it will look simplier...

Re:Not an expert

[SEE]

The alternative to complicating the universe with dark mattter, dark energy, and multiple dimensions is replacing General Relativity with a more complicated theory. Which we know needs to be done on the quantum scale at least, but which hasn't been successfully done yet.

So, right now, we have GR. Which needs undiscovered "dark" matter to explain why galaxies are rotating faster than expected. And extra dimensions to solve the problem of different-sized galaxies. And "dark" energy to explain why these galaxies are separating from each other than they should given our estimates of their mass.

The most serious alternative to that is Modified Newtonian Dynamics (MOND) [wikipedia.org], which assumes that at very low accelerations (lower than any body in the Solar System experiences, because of solar gravitational acceleration), F=ma is wrong. This explains away dark mattter easily, and there's even been a suggestion [eprints.org] that the TeVeS version of MOND can explain away dark energy, too.

Now, if somebody can come up with a successful model of quantum gravity that also reduces to MOND on a galactic scale . . . well, he'll get a Nobel, and probably replace "Einstein" as a synonym for "genius".

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

[Anonymous Coward]

I can't wait to see you build a house someday:

An engineer will present you with carefully drawn blue prints. You will say that it is just a peice of paper with lines on it and so is no better than your plan, which is to build your house from legos.

Re:One can dream

[stevelinton]

So string theory suggests 11 dimensions 7 of which are really tiny. Think of a hosepipe: seen from a distance it looks 1-dimensional, and if you imagine creatures living in the rubber of the hose which were (say) a mile long and wrapped all around the pipe for that mile, they would see their world as 1-dimensional. If they somehow managed to examine themsselves in microscopic detail, though, they would find this second dimension just an inch or so around, which was vital to the way their internal organs worked. The suggestion is that the universe is like this. We see 4 dimensions, but if we want to understand really small things, we have to look at the other 7 dimensions as well. Many different kinds of particle are really the same kind of string, wrapped around the "small" dimensions in different ways, or vibrating in different ways.

So, now, more recently, people have proposed that the vast difference in strengths between electroweak forces and gravity can be explained by some of these small dimensions being rather less small that we thought. How small depends on how many of them there are. If it was one or two, they would have to be millimetres in size and we would have detected them by now. If it was three, they would be about a nanometer and we wouldn't have. Experimentalists are working on this.

Meanwhile, astronomers have noticed some anomalies between the prevailing theories of galaxy formation, and the observations. These theories say, very roughly that galaxies form as clumps of dark matter which gravitationally attract and hold normal matter, which may then condense to form stars and such. Different assumptions about the properties of the dark matter lead to different distributions of stars, which can be observed. When they are observed, it seems that the dark matter in small galaxies behaves a bit differently from that in large ones. This would be explained if there was a weak short-range force (in addition to the ones we know about) between the dark matter particles. People have theorised about such a force.

Which, finally brings us to the subject of today's article. The authors point our that if, the "large" dimensions theory is right, with three large dimensions, then gravity would feel stronger at distances of less than a nanometer or so. This could provide exactly the weak short-range force needed to get the dark matter to behave right. If this is true, it will have consequences that might be measures quite soon.

Re:One can dream

[Haydn Fenton]

It's not stretching it to call time a dimension, time is space, space is time, hence the term "spacetime". I won't bother explaining that to you here because it'll take me a lot of typing, and I doubt you'll bother reading it anyway judging from your post. Try reading Einsteins general theory of relativity and the experiments he did. Better yet, find a website\book which explains it in more detail and you'll be hard pushed to find a reason to deny that time is a dimension. Clearly its "not the same kind of thing", anyone with half a brain cell can see that. By the same token, the up-down dimension is not the same kind of thing as the left-right dimension.

11 Dimensions is hard to grasp for anyone, including the people that come up with these things (heck, Einstein didn't believe in some of the things he found, until he had to face the facts that his theories predicted things which wasn't possible before, and couldn't be disproved otherwise). As everyone is quantum physics says, nobody understands it, they just get used to it. I myself don't really believe there's 11 dimensions, but until it's proved either way, I'm going to accept it because the maths behind it all fits so perfectly well and has been right so many times, and to such a huge degree that it'd be grossly narrow-minded and possibly even stupid not to.