Sylvan Wizard

There are 11 dimensions according to string theory and M-theory. It turns out 11 dimensions is a requirement. The math actually predicts 11 dimensions. The theories don't work with any other number of dimensions. There has to be 10 spatial dimentions and one of time. If you want to know what's real to separate the cranks, I'd suggest reading Elegant Universe by Brian Green.

acronos

In terms of mental constructs, I can easily envision more dimensions. I come up with something very similar to what godless wonder did. However, I also suspect a reason that we can't experience the extra dimensions. That is because they don't influence our world on a scale we can see. There is no motion along that axis.

I disagree with what phil said about points and plane's don't exist in our universe. If you are saying there are no physical objects in our universe that are a plane(infinite dimensions), you are probably correct. However, there are probably no physical objects in our universe that are a volume(infinite dimensions) either. There are plenty of flat objects without infinite dimensions and we can define any slice of 3d space as a plane of infinite dimensions, or at least as large as the universe is.

If we as a human were incapable of any motion whatsoever (a brain in a vat), we would be a point to our perspective whether we fit in one dimension or twelve. If we were only capable of perceiving and moving on a plane (2 dimensions) we would probably believe there were only 2 dimensions even if our mind physically required 3 or 12 dimensions to exist. If a sphere were to pass through our 2 dimensional world, we would have evidence of 3 dimensions. However, if there were no spheres or anything passing through, how would we know there was more than 2 dimensions. It is our ability to perceive and move in 3 dimensions that creates our experience that the universe is 3 dimensional whether it really is or not. Maybe matter only exists in 3 dimensions but energy requires 11 or 12. Since our experience of energy is only through matter, it would make sense that we only thought there were 3 dimensions. It is only at the atomic scale where matter breaks down that we begin to suspect there might be more than 3. However, I am only making a case that is possible that there are more dimensions, not that there are.

crocodile deathroll

If the human brain does not physically occupy any of these higher dimensions then that may be a perfectly plausible explanation why that human mind cannot imagine them even if they do exist.

Theli

I don't know if this example is really accurate, I mean it obviously takes place in a world that has a time dimension. If the world didn't have a time dimension you could not display the cube, it would just either exist or not exist.
I think we have a rather obtuse definition of existence that require an object to have both 3D geometry and a place in time.
If a fourth geometric dimension were discovered, it would certainly put things into perspective.
But I agree with your conclution nontheless, no twodimensional object could exist within our spacetime.

phil

Actually I meant the opposite! (funny how people percieve things, huh?) Consider a finite plane; it is 10 units by 10 units, however, its depth is infintesimal. Can this plane exist? No. Why not? Well, can a physical object exist that has legth and width, but no depth? No matter how flat something is, it still has some depth to it in order for it to exist.

That is the point I was trying to make. Every dimension needs the other. You can't have physical existence without all of them.

As far as the necessecity of time, what about this: Could anything have existence as we know it with out time? For something to exist it must have both dimension and duration.

Here's a thought I had about time a week ago. I think you'll find it interesting.

Time is the fourth spatial dimension! Bear with me here, I'll try to explain it in a reasonable amount of space.

Has anyone here ever made a flipbook? When I was little, my and friends and I would take a stack of post-it notes and draw little stick figures on them. Then when we'd flip through the stack the stick figures would move and embark on an amazing 2D adventure, jumping over clifs and swining on ropes until they got sqaushed by running into a rock or something.

Little did we know what exactly we were doing! We were creating a 2D word that had legth and width, but no depth (for all practical purposes). However, what did we do when we wanted our stick figures to experience time, we added anothere dimension, depth! Depth became time for our 2D world!

That is the exciting part, what ever dimensional world you have time is always the next spatial dimension! For a 0D world time would be the first dimension, and in 'reality' would look like a line. A 1D world would have time as the second dimension, and 'reality' would be a plane etc.

I hope this makes sense. Tell me what you think.

-phil

wordsmyth

I'm new around this particular forum, so perhaps this observation is a bit silly, but...

Saying that time is the "4th spatial dimension" seems innacurate because time isn't even remotely similar to the other 3 spatial dimensions.

Isn't it more appropriate to say there are 3 spatial dimensions and 1 temporal dimension?

Xeno

Of course.

Proof:

http://mathworld.wolfram.com/KleinBottle.html

acronos

Phil,
I also think of time as a spatial dimension, but with some exclusive characteristics. I think of the universe as something similar to the 2d surface of a sphere. The sphere itself is 3d just as the universe is 4d. The last dimension we cannot move in just as an ant could not control his movements beyond the 2d on the surface of the sphere. The sphere is expanding and it is this expansion that gives the universe many of it's properties. Time to me is just the expansion of the sphere. I think of our universe like a 3d point sound wave. It starts at a point and propagates out in all 3d directions at the same time. The wave cycles up and down as it propagates. My current model of the universe does exactly the same thing as this sound wave but in 4 dimensions, and we are only able to walk along the surface in the 3 dimensions that make up the surface of this 4 dimensional "sphere." I also suspect many of the properties of energy and matter derive directly from this expanding wave of "time" that is really just the surface of this 4d "sphere." I personally think a dimension is a dimension and as such don't find it fruitful to say this is one type of dimension and this is another. All dimensions are dimensions and have the properties that make it a dimension, however not all dimensions have the same properties outside of those that make it a dimension. So, I think we agree.

Probably many of the physicists here have a much better understanding that I do. My current model makes sense to me with what I know right now.

As to our discussions of planes. A plane could cut straight through the atoms that make up an object. The electrons would be coming in and out of the plane and the proton would be cut in two. My perception of what you are saying is that a plane cannot be built of matter, which I agree with. However, that to me does not say a plane cannot exist nor that a plane could not include matter. It would just include a 2d slice of matter.