# The Naked Scientists Forum

### Author Topic: Do dimensions expand when space expands?  (Read 4865 times)

#### Jon Francis

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##### Do dimensions expand when space expands?
« on: 11/08/2010 02:26:58 »
Do the three dimensions become nine dimension when space expands?

#### flr

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##### Do dimensions expand when space expands?
« Reply #1 on: 11/08/2010 05:42:33 »

Apparently no, but I would add another question on this issue:

Does the other 8-9 small (curved) space dimensions from string theory expand as well with the expansion of our macroscopic three space dimension?

#### Murchie85

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##### Do dimensions expand when space expands?
« Reply #2 on: 11/08/2010 11:39:59 »
As far as i am aware, super string theory and super gravity theory states..

As 3/4d space time expands the other dimensions recede and curl up, but at the point of the big bang the dimensions were much bigger.
The main reason behind this hypothesis is to explain the ratio of gravity to the other 3 forces, because gravity is very weak in comparison (hence the reason you can pick a piece of metal up on the top of a mountain with a magnet, Electromagnetism in this case wins out over the gravity from the whole earth!). The point being that gravity leaks out into the other dimensions and is thus weaker than it should be if there were only 3/4 dimensions.
The theory is still in its infancy at the moment and subject to many changes but hinges on there being more dimensions, just smaller.

#### chrisdsn

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##### Do dimensions expand when space expands?
« Reply #3 on: 16/08/2010 06:36:09 »

When people talk about space expanding, they usually refer to the a foxe dimension of
space expanding (i.e. everything is getting further away from everything else, but no new dimensions are added)

#### CreativeEnergy

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##### Do dimensions expand when space expands?
« Reply #4 on: 16/08/2010 12:38:36 »
The three spatial dimensions are only directions of freedom in which one can move. They do not have a quantity and therefore cannot expand or shrink.

#### Murchie85

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##### Do dimensions expand when space expands?
« Reply #5 on: 16/08/2010 13:14:55 »
Yes CreativeEnergy, but as I have mentioned the space in which the dimensions take up change size respective to that dimension. I.e 3 dimensional space is expanding and higher dimensions are contracting at present.

#### CreativeEnergy

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##### Do dimensions expand when space expands?
« Reply #6 on: 16/08/2010 13:28:04 »
Yes CreativeEnergy, but as I have mentioned the space in which the dimensions take up change size respective to that dimension. I.e 3 dimensional space is expanding and higher dimensions are contracting at present.

Well, if you want to really get technical and talk about "branes" in ll dimensional M-Theory, then I suppose you could say that dimensions can expand. But, the questioner only asked about the three spatial dimensions, and I try to not make things more complicated than the question asked.

#### LeeE

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##### Do dimensions expand when space expands?
« Reply #7 on: 17/08/2010 19:38:48 »
As CE says, dimensions are just directions, so talking about dimensions expanding is like asking how long is North (or East, South or West, or up or down, or left or right).

#### Murchie85

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##### Do dimensions expand when space expands?
« Reply #8 on: 17/08/2010 23:47:15 »
I am afraid im going to disagree, I know dictionary wise when we talk of an expanding dimension is nonsensical but in this context when I say spacial dimensions expand what I am referring to is the amount of space taken up in that dimension. So LeeE i would not say how long is north but the space north has expanded by is another 20 meters for example I don't think im alone in that expression.
Also CE he asked if 3 dimensions become 9 if space expands, so I thought to clarify the higher dimensions (a little) instead of just saying "no" as the next question would surely be, well what are the higher dimensions for? Or what do they do?.
« Last Edit: 17/08/2010 23:50:21 by Murchie85 »

#### Raghavendra

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##### Do dimensions expand when space expands?
« Reply #9 on: 18/08/2010 12:50:34 »
How does space expands, having dark matter around us !

#### LeeE

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##### Do dimensions expand when space expands?
« Reply #10 on: 18/08/2010 16:45:23 »
Space (or space-time) and dimensions are not the same thing.  Space (or space-time) can have any number of dimensions, or perhaps it might be better to say that you can have different dimensional orders of space (or space-time).

For example, a square will have two-dimensional space but not three-dimensional space, and the size of that space may change i.e. expand or contract, so that the square may become larger or smaller.  It is the space though, that has changed, not the dimensional order of that space, and both the larger and smaller squares still occupy the same unchanged two spatial dimensions even though they are different sizes.

#### Jon Francis

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##### Do dimensions expand when space expands?
« Reply #11 on: 23/08/2010 21:53:16 »
Dimensions are the means by which two points in space are referenced to each other. When space expands, I assume it expands in all directions at the same time. The two points would independently expand so the reference needed to relate one position to the other would include the normal x,y and z plus a degree of expansion. So to relate the position of one to another would require the normal x,y and z co ordinates plus a further three measures of expansion for each point, giving nine co ordinates.

#### LeeE

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##### Do dimensions expand when space expands?
« Reply #12 on: 23/08/2010 22:34:33 »
Dimensions are the means by which two points in space are referenced to each other.

Hmm... 'fraid not.

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When space expands, I assume it expands in all directions at the same time.

You can end up misleading yourself if you make such assumptions.

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The two points would independently expand[...]

Points cannot expand.

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[...]so the reference needed to relate one position to the other would include the normal x,y and z plus a degree of expansion. So to relate the position of one to another would require the normal x,y and z co ordinates plus a further three measures of expansion for each point, giving nine co ordinates.

You wouldn't need an extra term for expansion to relate two coordinates in space-time, just as you don't need an extra term to relate your height as a new-born baby to your current height.

#### Jon Francis

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##### Do dimensions expand when space expands?
« Reply #13 on: 28/08/2010 12:17:44 »
Surely we use dimensions to describe space? We describe a cube as having three dimensions, a height, a width and a length. Using the co ordinates to define the volume or any point within on the surface or outside that cube? Time defines the position in a journey where space is moving or expanding. The cube would be in a different position in an expanding universe at each moment of time. So defining a point in space without stating the relative time would not fully define that point in space?
Surely a singularity is a point? I understand the big bang started with a singularity which expanded into the universe we know today? I imagine a point to be relative to scale. A point at a vast distance could be the size of a galaxy. While close up it could be the size of a pin head. Both could expand?
What I was referring to was the expansion of the space between the two points.
A child in the same location of space would only be viewed through three dimensions of space. Its growth would be viewed relative to you relative to time. The child grows it does not expand. It takes up more space, it does not expand the space it exist in.
The four dimensions we can visualise, three spacial and one of time. Are they the only ones that we could ever visualise? Are the other dimensions predicted by string theory spacial dimensions? I understand that the strings of energy are wrapped inside these dimensions? and they are smaller than the three spacial dimensions we are familiar with?
If you walk out through a door into another room you become aware of the space within that room only when you enter it. Could it be that we are not aware of the other dimensions because we have to travel to get to them? or could they be in view through the other dimension we see but we do not recognise them?

#### LeeE

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##### Do dimensions expand when space expands?
« Reply #14 on: 29/08/2010 01:17:36 »
Describing space(-time) is really tricky.

Dimensions are to space-time as colour is to paint, but just as the colour is not the paint, the dimensions are not the space-time.  Space-time can have any number of dimensions, just as paint can be any colour, and while the dimensions of a space-time are an important quality of that space-time, just like the colour of the paint, they aren't what makes the space-time in the first place, just as the colour does not make the paint.

So just as we might say we have a particular shade of red, or green or blue paint, we can have one, two, three etc. dimensional space (or indeed, space-time).

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Time defines the position in a journey where space is moving or expanding.

In four-dimensional space-time you need four coordinates to define the location of anything, regardless of whether it is moving or not, for even if it is not moving through space it will still be moving through time.

Now although we can say that the universe started ~4 billion years ago, giving us a fixed temporal reference point from which we could in theory make our measurements, the rate at which things travel through time varies according to the speed at which they're moving, so if it were possible for a traveller to have set off on a journey when the BB occurred, at half the speed of light, and to then land on Earth right now, they wouldn't be ~4 billion years old, even though from our point of view they started ~4 billion years ago.

In spatial terms it's even more tricky because we don't have the spatial equivalent of the start of time that we have with the temporal dimension and this is largely because geometrical points cannot expand, at least in the sense that we're familiar with things expanding.

The problem here is that a geometrical point has zero size and no matter how you try to multiply it, it'll always have zero size.  Now if the BB did indeed start from a geometrical point then the term 'expansion' is simply inadequate to describe what happened; rather than something very small getting bigger, something that appears to have had no dimensions or size, or had a dimensional order of zero, was raised to a higher dimensional order, and in fact, as far as we can tell, to four dimensions, which gave it a non-zero size and which allowed it to start expanding.

The cleverest bit of all though, is that the original geometrical point, having no size, was by definition uniform i.e. it was the same everywhere, so when it was raised to a higher dimensional order there could have been nothing to cause any non-uniformity between any two points in the resulting four-dimensional universe.  The consequence of this would be that every point in the universe must be considered to be the same as any other point in the universe.

On the other hand though, if the singularity from which the BB originated had non-zero size, then it must have had at least one dimension, which implies that at least one dimension had to exist before the singularity could exist within it.  A non-zero sized singularity too, already having a non-zero size, can quite happily expand, for simple expansion doesn't require an increase in its dimensional order.

#### yor_on

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##### Do dimensions expand when space expands?
« Reply #15 on: 06/09/2010 14:29:40 »
Why would they become 9 Jon?

We live in a measurable universe, within reason naturally and according to the dictates relativity makes upon it (As I think Murchie pointed out.) We talk about SpaceTime expanding, to explain the Recession of Galaxies we measure through their red-shift. It's still a theory though, not an absolute truth. the dimensions we know of are four, length, width, height (depth) and time.

Mathematicians create models to explain certain behaviors they observe in nature, and in that discipline their restrictions are only those of their mathematical proofs and how those explain nature. But a gifted mathematician can as easily create a logical construct, valid and proof-able where all parallel lines in the universe at some point will converge into each other becoming one, And actually did so in the 19 century, if I remember right, presenting perfectly valid proofs mathematically.

So we create more 'dimensions'. We talk about everything from one, up to an infinity of dimensions, like nature being some mathematical puzzle tugged together. But you need to remember that we can only proof 4 of them experimentally, for 'real', and that those are seamlessly knit together. The mathematical theory that works will be the one closest to our experiments, ideally able to predict new experiments outcome, as well as old unexplained, and preferably also suggesting how they should be set up before anyone thought of them. And If that math seems to work better than the math we used before, we expects it to be closer to how 'reality' works. String theory f.e is still a mathematical theory without grounding in any experiments even though it makes predictions for what might happen inside the event horizon of a black hole.

So for that case is any theory laboring with more than those four dimensions, as far as I know. And when Scientists write about 'two-dimensional latices', as the atoms in a graphene layer they actually play with words, those atoms and that layer is still three-dimensional, and what they really mean is that the atoms in it acts as if restricted in only two dimensions. But it gives laymen the impression that there really exist two dimensional latices consisting of f.e length and width only. But a real two dimensional system would have to disappear from certain angels, and I do mean disappear for real. Consider a piece of matter without width, it still have a length and a depth (height) but with no width, how would you see it?

That we have the concept of several singular dimensions is because they are very useful in mathematical theory, and also opens for a lot of interesting math, like string theory. But as far as I know we have no experiments proving either two dimensional objects or five dimensional.
==

And there is always the possibility of the Universe working in a manner not expected by us. We use f.e 'Ockham's Razor' to choose between competing theories, the idea that the simplest of two competing theories is the preferred, if both gives as good explanations. It seems very reasonable for us to do so, and we expect the universe to agree with that, but we can't guarantee it. And would that theory, or archetype as it more rightly seems to be, then show itself wrong? Well, then we would go through a heck of a lot more trouble before deciding which theory might be the correct one of those competing.
« Last Edit: 06/09/2010 15:01:33 by yor_on »

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##### Do dimensions expand when space expands?
« Reply #15 on: 06/09/2010 14:29:40 »