How many dimensions are there ?

Mathematicians love to come up with weird stuff...like quantum mechanics needing a whole bunch of other dimensions. Some say 10, some say 11. Which is correct ??

Originally posted by woadman
Mathematicians love to come up with weird stuff...like quantum mechanics needing a whole bunch of other dimensions. Some say 10, some say 11. Which is correct ??

Eleven if you count time as an dimension. (I might be wrong here.)

I have asked questions like "How many time dimensions are there?" and get many negative responses. "One, of course, dumbnut" is only one of them.

But why wouldn't it be possible that there are more than one time dimension?

If we call space dimensions and time dimensions for dimension families, then we know of two. Another question I have that noone has ever manage to answer: "How many dimension families are there?"

I like that concept of dimensional families..it makes a lot of sense. My point was mathematics is simply a tool...and its results are open to interpretation. But quantum mechanics is mainstream science, even "forcing" the math to accept string theory , etc.

Originally posted by woadman
Mathematicians love to come up with weird stuff...like quantum mechanics needing a whole bunch of other dimensions. Some say 10, some say 11. Which is correct ??

Quantum mechanics (as it is formulated today) uses four dimensions: three spatial ones and one for time. There is also a relativistic formulation of quantum mechanics, which also uses four dimensions, but formulated in such a way that time and space are no longer independent.

There was a great internet film out there which explained it all.
Basically folding a piece of paper.

1. A single dot.
2. a line (2D or connecting 2 dots)
3. 3D (or looping 2D)
4. time
5. splitting into multiple universes
6. 4D (or connecting two 3D's)
7. Mulitple starting points
8. 5D (or connecting all the 4D's from all various starting points)
9, 10, 11...

There were 11 in the video (which I watched years ago), but I can't imagine what the other points were. Something about looping such and what-not.

Here's the video (I think):
YouTube

Originally posted by shavixmir
There was a great internet film out there which explained it all.
Basically folding a piece of paper.

1. A single dot.
2. a line (2D or connecting 2 dots)
3. 3D (or looping 2D)
4. time
5. splitting into multiple universes
6. 4D (or connecting two 3D's)
7. Mulitple starting points
8. 5D (or connecting all the 4D's from all various starting points ...[text shortened]... ng such and what-not.

Here's the video (I think):
http://www.youtube.com/watch?v=p4Gotl9vRGs

A dot would be zero-dimensional, a line one-dimensional, and a surface two-dimensional. Mathematically, there is no restriction and one can formulate any number of dimensions including an infinite number and a fractional (or fractal) number.

Originally posted by woadman
Mathematicians love to come up with weird stuff...like quantum mechanics needing a whole bunch of other dimensions. Some say 10, some say 11. Which is correct ??

Nobody knows yet. It depends on whether string theory is correct, and if so, which version. Since nobody has been able to find any hard proof for or against string theory, we aren't sure how many of which dimensions the universe really has. All we know is that "normal" physics only needs three space and one time, and all the rest are only used by the "weird" bits of quantumwhateverdynamics.

Originally posted by FabianFnas
Eleven if you count time as an dimension. (I might be wrong here.)

I have asked questions like "How many time dimensions are there?" and get many negative responses. "One, of course, dumbnut" is only one of them.

But why wouldn't it be possible that there are more than one time dimension?

If we call space dimensions and time dimensions for dimens ...[text shortened]... r question I have that noone has ever manage to answer: "How many dimension families are there?"

I think people have looked at more than one time-like dimension. From the article in New Scientist (or somewhere like it I can't remember) there's causality problems. Most theories with more than four dimensions only have one time-like dimension. Why there should be a time-like dimension and why only one is anyone's guess. I don't think it's obvious that there should only be one so I don't think the "one of course dumbnut" response is particularly clever - you may have been asking the right question.

If you regard space like dimensions as one family and time like dimensions as one family, then with supersymmetric extensions 4 or 8 I suppose. That depends on whether supersymmetry is a symmetry of nature and on whether it's a natural move to regard dimensions as coming in families. This is physics beyond the standard model and we're a bit short of empirical data.

Originally posted by DeepThought
I think people have looked at more than one time-like dimension. From the article in New Scientist (or somewhere like it I can't remember) there's causality problems. Most theories with more than four dimensions only have one time-like dimension. Why there should be a time-like dimension and why only one is anyone's guess. I don't think it's obvious ...[text shortened]... in families. This is physics beyond the standard model and we're a bit short of empirical data.

Okay, thanks for not calling me dumbnut. So you inspire me to hypothesize a bit further.

In low velocities and weak gravitational fields, two time dimensions are nearly parallel. Meaning we cannot differ one from the other. So it seems that there is only one. In fact in zero velocity and zero gravitational field they are actually perfectly aligned.

But near black holes, there are two time dimensional dimensions, in extremum they are ortogonal. Therefore you can explain time dilation. At the Big Bang event they were also ortogonal. Therefore one time started then and there, but the other in fact was there even before BB. Like the f(t) = 1/t.

It would be better to present this idea on the April 1st so we can laugh together. If someone sees something worth working with, then be my guest.

Originally posted by woadman
Mathematicians love to come up with weird stuff...like quantum mechanics needing a whole bunch of other dimensions. Some say 10, some say 11. Which is correct ??

Blame physicists. Mathematicians have little to do with it. Which is correct? Quite possibly neither.

Originally posted by FabianFnas
In low velocities and weak gravitational fields, two time dimensions are nearly parallel.

Unless I am mistaken, dimensions are orthogonal by definition. Or at least, if they are not, then it is always possible to find orthogonal dimensions to use rather than non-orthogonal ones.

Originally posted by twhitehead
Unless I am mistaken, dimensions are orthogonal by definition. Or at least, if they are not, then it is always possible to find orthogonal dimensions to use rather than non-orthogonal ones.

In Physics, dimensions are related to a reference frame. The axis of a reference frame (or in a more properer language: the basis vectors ) need not to be orthogonal they only need to describe all the degrees of freedom of a given system.

Most of the time an orthogonal frame of reference is a good choice to use but there are also plenty of times where you should use non-orthogonal frames basis vectors in order to more properly describe and solve a given physical system.

Originally posted by twhitehead
Unless I am mistaken, dimensions are orthogonal by definition. Or at least, if they are not, then it is always possible to find orthogonal dimensions to use rather than non-orthogonal ones.

Do they need to be 90 degrees between them to be ortogonal?
Cannot dimensions be nearly parallel and yet be ortogonal?

Originally posted by FabianFnas
Do they need to be 90 degrees between them to be ortogonal?
Cannot dimensions be nearly parallel and yet be ortogonal?

It is not so much a question of angle, but rather a question of relationship. Can an object move in one direction without moving in the other?

Originally posted by adam warlock
In Physics, dimensions are related to a reference frame. The axis of a reference frame (or in a more properer language: the basis vectors ) need not to be orthogonal they only need to describe all the degrees of freedom of a given system.

Most of the time an orthogonal frame of reference is a good choice to use but there are also plenty of times wher ...[text shortened]... gonal frames basis vectors in order to more properly describe and solve a given physical system.

For spacial dimensions, one can have different axis constituting different reference frames and for most purposes the choice of direction seems arbitrary. Is this possible with time? ie can you have a reference frame in which a dimension is not along the traditional time axis, but rather is a combination of time and space?

If one uses polar co-ordinates for space, are they considered orthogonal?