# The Naked Scientists Forum

### Author Topic: What's the definition of a Dimension?  (Read 3940 times)

#### Rincewind

• Jr. Member
• Posts: 42
##### What's the definition of a Dimension?
« on: 22/01/2006 21:59:55 »
I know what the four macro ones we see are, I just don't know exactly what a dimension is.

Could we treat electrical charge as a dimension, say, or magnetic charge?

#### Solvay_1927

• Sr. Member
• Posts: 383
##### Re: What's the definition of a Dimension?
« Reply #1 on: 22/01/2006 23:08:57 »
Interesting question, Andrew, never really thought about it.  I'd be interested in what answers you get from the proper physicists on this site.

I suppose a dimension is just an abstract way of measuring something - or, rather, of measuring the difference in something (e.g. of measuring the displacement of two events in space or time).

Depending on the context, I can't imagine there's any reason why you couldn't use electrical charge, for example, as a dimension. But the usefulness and meaningfulness of doing so would depend on what other quantities you're measuring in the other dimensions.

When they say that time and space can be combined into a 4-dimensional "space time" (in relativity - or 11-dimensional in string theory?), what I think they mean is that you need to take all 4 of these dimensions into account in order to give a complete description of a series of events.

For example, imagine you're taking a penalty.  If you want to know if you've scored a goal, you'd need to know not only where the ball went in the x direction (i.e. did it even cross the goal line?), but also the y-direction (was it between the posts?) and the z-direction (was it below the cross-bar?).

(It seems Chris Waddle never really "got" the concept of a z-dimension...[:o)])

So to give a complete description, you need to measure all 3 dimensions simultaneously.

But then if you kick the ball at relativistic speeds, you find that these 3 dimensions aren't enough to give you a complete description.
At a high enough speed, you might find that the distance from the penalty spot to the goal line is measurably different to what it was when the ball was at rest, and the width and height of the goal might be different too (if the ball is climbing/bending as it travels).  So you still don't know if you've scored unless you also take the time dimension into account too.

(OK, so maybe this analogy doesn't work - I'm just making this up as I'm typing.  But I don't think it's bad for an off-the-cuff explanation! )

I don't see any reason why you couldn't come up with a theory that uses, say, 3 space, 1 time, and 1 electric charge dimension - if you think that electric charge is also needed (as an independent dimension) to give a complete description of events.

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: What's the definition of a Dimension?
« Reply #2 on: 23/01/2006 00:00:24 »
Mathematically a dimension can be anything that we chose it to be it is usually used to describe an independant variable in a calculation and has no real relationship to the physical dimensions that we know.

When we get to describing processes that have some physical reality it could imply another level of copmositeness for particles but that this compoositnes is best describe in terms of fields than particles.

witin many theories of everyting the values of critical physical constants may be variable accoding to the nature of the universe.  The am is to describe why the have the rather peculiar values that allow atoms stars and life to form.  there are some aspects of this that suggest that the laws may have evolved physically to enable the universe to grow large last a long time and therefore develop complexity.

Learn, create, test and tell
evolution rules in all things
God says so!

#### Rincewind

• Jr. Member
• Posts: 42
##### Re: What's the definition of a Dimension?
« Reply #3 on: 23/01/2006 01:00:27 »
Ah, I'm glad you're here SoulSurfer, because the question came from you making me think about angular momentum.

Stop me if I get too mad...

I'll keep it short:  Could a photon be thought of as a particle, or a pair of particles, spinning round each other and kept apart by angular momentum?  Spinning on the plane of electricity/magnetism.

I'm not sure if that would have further ramifications but it would be a way to explain wave/particle duality wouldn't it?

(Yeah!  Someone should have told Chris Waddle about that z dimension.  I can't even remember what world cup it was in but I haven't forgiven him yet:))

My physics knowledge, now that I come to excersize it after all this time, is pretty damn shakey.  I'm gonna go and look up in exactly what ways light behaves as a wave and a particle - all I can remember is the diffraction grating proving it's a wave.

What's a field again?  Again, I know what one is, more or less, but I need a precise definition.  I mean, could the intensity of any field at a given point be thought of as a displacement on a dimension?  Would there be any point?  I let myself get carried away I'm afraid:(

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: What's the definition of a Dimension?
« Reply #4 on: 23/01/2006 19:55:34 »
I have myself wondered what tiny particles that interected only by gravity and possibly formed in pairs orbiting each other according to similar quantum rules to my semi classical desctription of the hydrogen atom might be like  (see elsewhere on these pages).  I have called them ground state black holes.

However this has nothing to do with electromagnetic waves and photons which are quite easy to understand.  A changing electrical field creates a magnetic field and a changing magnetic field creates an electrical one so the propagation of energy is by the electrical field turning into a magnetic one and the magnetic one then coming back to an electrical one like two players throwing the ball (the energy)to each other.

Learn, create, test and tell
evolution rules in all things
God says so!
« Last Edit: 23/01/2006 19:59:12 by Soul Surfer »

#### Rincewind

• Jr. Member
• Posts: 42
##### Re: What's the definition of a Dimension?
« Reply #5 on: 23/01/2006 20:44:16 »
Is there a deeper explanation than that?

First of all forget I said 'particle'.  I don't mean particle, I just mean a displacement from the zero value (where the plane of electromagnetism intersects with space).  If electromagnetism were a plane, and the electromagnetic charge were attracted to zero, that would explain why, as electric charge changes, a magnetic charge is induced.  Why the wave propogates.  It's spinning round the origin.

All the energy is, is the movement, ay?  the change.

On a side note (because you seem to know your stuff), A physics teacher years ago told me that electric current is actually the exchange of electrons and positrons, not just the flow of electrons as it is usually described - he said that was a simplification for the purposes of teaching.  Is that true?

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: What's the definition of a Dimension?
« Reply #6 on: 23/01/2006 23:55:16 »
Why do you need anything more than the simple truth?   Electromagnetic theory has been fully explaned to fantastially high precision for well over a hundred years  almost all technology depends on this!

There are some elements of validity in your descriptions but there are just as many errors.

Your teacher was talking tripe.  Or probably more truthfully he had not grasped properly somehing he at learned in training and was trying to show off his greater knowledge and getting it very wrong.  This is just like lots of schoolteachers seem to be doing these days.  There are very few real physics teachers left and this vital subject is being very badly taught.

I am seriously worried about the great many bad concepts that arte flying around

Learn, create, test and tell
evolution rules in all things
God says so!

#### Rincewind

• Jr. Member
• Posts: 42
##### Re: What's the definition of a Dimension?
« Reply #7 on: 28/01/2006 09:46:16 »
The faster a charged particle moves through space, the greater the magnetic field associated with it.

Somewhat like, the faster a massive particle moves through space, the greater the gravitational field associated with it.

#### The Naked Scientists Forum

##### Re: What's the definition of a Dimension?
« Reply #7 on: 28/01/2006 09:46:16 »