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Astrophysics/M-theory

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Hi,
 I have a question about M-theory and the other dimensions it implies must be there.If by some chance you feel it is not something you have expertise in specifically, no problem. I just then ask for your best hypothesis or guess at an answer since even that would be more knowledgeable than mine.I know that at this point it is only theoretical but for sake of argument and for this question lets take M-theory and assume its a fact. With that said, I understand that it states that there are the 3 dimensions we live in, plus time and then 7 other dimensions we are unable to perceive for a total of 11.Understood completely.
My question is that the way that these 7 dimensions are usually described is as tiny little strings that are everywhere, on your body, in the air, everywhere. However that's basically as far as they go. Maybe that is because it is hard to describe something that is really just hypothetical, or maybe for a scientist, that is enough of an explanation. However for me it isn't. I guess because I am a layman and because I am so accustomed to thinking of things as we know them, in 3-D I have an extremely hard time understanding and picturing what those dimensions are actually like. Ok, lets say that the other 7-D are tiny string like dimensions that surround us. If we were somehow able to enter those, what would/could they be like(Hypothetical of course)?If its impossible to really know, I get that. If that's the case really I am just asking for your educated opinion.Something to help make it easier to imagine.
I've wondered this for a long time.
Thank You

Answer
Hello Jason,

You ask a very intriguing question. But first, I must address your basic assumption - that M-theory is correct. A very good book on string theory and its inability to prove anything is "Not even Wrong" by Peter Woit. In it, he argues that any scientific theory should be testable and predict certain results, which string theory can't. It can't be proven right or wrong. It's simply a way of trying to make sense of the universe, but is not a testable scientific theory. See http://www.math.columbia.edu/~woit/. So unless a theory is tested by the scientific method (i.e., predicts certain outcomes and reproduces predicted results), it must be taken with a grain of salt. That said, I'll accept your assumption (as long as we agree it's just an assumption) and move on.

Let's not think of the other 7 dimensions as tiny strings. We normally think of strings as one-dimensional objects (they have only length). When we pluck a string, it can vibrate in two dimensions (in a plane). If we pluck it again (sideways motion), it can vibrate in a circular or elliptical motion - in 3 dimensions. Since the string has a period of vibration (it takes time to make a full vibration cycle), we have to know the exact time in order to locate any particular point on the vibrating string - the 4th dimension. Or we can simply stop and start the string vibration at certain times (again, adding in the 4th dimension). M-theory simply states that the tiny "strings" which comprise all matter are vibrating in 7 more (mathematical) dimensions.

Can we visualize those additional dimensions? Not really, but we can come up with analogies to illustrate how additional dimensions (unknown to  us 4-dimensional beings) might be possible.

Imagine a thin garden hose. You're standing far away, and to you, the hose looks like a line. One-dimensional. On the other hand, a flat (2-dimensional) ant on the hose notices that it can move along two dimensions - along the hose and around the hose. In this way, the 2nd dimension of the garden hose is "curled up" and hidden except at small (ant) levels. If we got closer, we'd actually see that the hose is 3-dimensional.

Now suppose we came along and lifted the ant up and moved him to another garden hose. He'd have no concept of a third dimension (he's a flat 2-dimensional ant). He would think that he was magically transferred through "another unseen dimension" to the new garden hose.

Perhaps a better explanation was given by Nova - http://www.pbs.org/wgbh/nova/physics/imagining-other-dimensions.html.

But you asked for my opinion. Although I don't think we're close to proving M-theory, I certainly think that additional dimensions are possible in our universe (and others). I think of dimensions as a means of locating an object or event in the universe. We need to specify certain "coordinates" to locate an event. If I said to meet me at the top of the Empire State Building, you'd know the latitude and longitude of the building (2-dimensions), and you'd know the floor (top floor) - the third dimension. But you would not know WHEN to meet - unless I specified the time (4th dimension).

One way to visualize that there could be higher dimensions is this: Suppose I gave you the time to meet me at the top of the Empire State Building, and that I was going to display a hologram of me (I wouldn't actually be there). Well, holograms are produced with lasers, and these operate at a particular frequency of light. My laser has a wavelength of 632.8 nm. So when you got to the top of the Empire State Building (at the time I set), you'd see a red glowing hologram of me. So far so good. But now suppose I changed the wavelength of my laser to infrared. My hologram would suddenly disappear. It would still be there, but you couldn't see it. Unless you got another device to "see" infrared (the other dimension). In this example, I'd have to specify the location of the building, the floor, the time of the event, and the frequency of light (the latter could be considered the fifth dimension).

Hope that helps. Interesting thought exercise. Mathematically true. Physically true? No one knows (yet).

Prof. James Gort  

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James Gort

Expertise

Questions on observational astronomy, optics, and astrophysics. Specializing in the evolution of stars, variable stars, supernovae, neuton stars/pulsars, black holes, quasars, and cosmology.

Experience

I was a professional astronomer (University of Texas, McDonald Observatory), lecturer at the Adler Planetarium, professor of astrophysics, and amateur astronomer for 42 years. I have made numerous telescopes, and I am currently building one of the largest private observatories in Canada.

Publications
StarDate, University of Texas, numerous Journal Publications

Education/Credentials
B.A. Physics and Astronomy M.Sc. Physics Ph.D. Astrophysics

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