How many dimesions are there in the universe/space?

Jay-qu · 05-18-2006

3 spacial and we consider time to be one so there is 4, thats all we can really see and test, but new theories like super string theory require there to be more than this. Different versions of these theories bring up a different number of dimensions some have 10 and others have even more.

adam_rockstar · 05-18-2006

so there can be more... in the crazy universe we live in, but it just depends on what theories you're comparing it to and the technology and knowledge we have available to us... right?

Tormod · 05-18-2006

Quote:

Originally Posted by adam_rockstar

so there can be more... in the crazy universe we live in, but it just depends on what theories you're comparing it to and the technology and knowledge we have available to us... right?

The theories do not create dimensions, they predict them. Whether they actually exist or not in a physical sense is something else entirely.

GAHD · 05-18-2006

Point to Tormod.

For the record I do *not* agree with time being considered a dimension any more so than considering gravity one.

Bo · 05-18-2006

It all depends on what you mean by dimension. In principle the most consistent defintion for dimension is 'degree of freedom' So the number of dimensions of my problem is the number of things I can change. In this case a simple freely moving particle should not be considered to move in 3 dimensions (+time), but in 6 (+time). The reason is that the particle not only has a positionvector (3 dimensions), but also a velocity vector (also 3). If I want to I can add all kinds of other dimensions (e.g. a variable mass to effectively make gravity a dimension as GAHD wants it)
With this definition of dimension the number of dimensions is unspecified. It just depends on what degrees of freedom you take into acount.

If you talk however about spatial dimensions; our common sense tells us there are 3 of them (left/righ, up/down, forward/backward). (and indeed string theory predicts more). However relativity tells us that space and time are actually the same kind of things and space and time degrees of freedom get mixed depending on 'how you look at them'. Therefore it makes sense to talk not about spatial dimensions, but about the total of spacetime dimensions. (3+1 in our world)

Bo

Farsight · 05-18-2006

How many dimensions are there in the Universe?

Hard to say for sure. But IMHO more than three. You can tell because of gravity. It's a "force", but there's no maelstrom of whizzo magic messenger particles zigging between you and the ground making you fall down. Or making the moon go round in circles around the earth. What gravity is, is a distortion of the three regular dimensions, in some other dimension that you don't otherwise notice. The analogy is a bowling ball weighing down a rubber sheet. If you flick a marble at it, it rolls around the depression, in an orbit like the moon's orbit round the earth. The thing is, you're part of the rubber sheet along with all your rulers and light beams, which is why you don't notice the distortion directly.

http://en.wikipedia.org/wiki/Curved_spacetime

There are of course, other forces.

ronthepon · 05-18-2006

What Bo said struck my thinking.

Hey, dimension could be well defined as degree of freedom!

Then we get many different types of dimension systems, though.

Take: Observer frame D.S.
D1- left-right
D2- front-back
D3- up-down

Take: World space D.S., cartesian style
D1- +ve x axis, -ve x axis
D2- +ve y axis, -ve y axis
D3- +ve z axis, -ve z axis

Take: World space D.S., Polar style
D1- Dist from origin
D2, D3, D4: Angles with axes

Finally if we get some sort of a degree of freedom in time, +ve time, -ve time etc.

How's that for a flash insight?

Bo · 05-18-2006

Quote:

Originally Posted by Popular

How many dimensions are there in the Universe?
What gravity is, is a distortion of the three regular dimensions, in some other dimension that you don't otherwise notice. The analogy is a bowling ball weighing down a rubber sheet.

You do something very dangerous here; namely taking an analogy literally. The bowling ball picture is something we can understand and therefore it is insightfull; However you should keep in mind that it is not what realy happens. space gets curved; but not 'in a certain direction' as is the case with the bowling ball. Curved space realy means that straight lines are not straight anymore (as compared to the 'flat' space case); that a unit length is not the same everywhere; that the angles of a triangle don't add up to 180 degrees; etc.

Bo