Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Vincent Risi on 26/03/2011 18:30:03
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Vincent Risi asked the Naked Scientists:
We live in what we perceive as 3 dimensional space. The fact that we also experience time change we often call this the 4th dimension. We can also perceive the effects of gravity and it affects our normal 3 dimensional space as well as time. As time is a special dimension can we not consider that gravity is also a special dimension?
What do you think?
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Wish I knew exactly what constitutes a definition of a dimension?
Something measurable? Then 'Gravity' may, or may not be measurable, depending on definitions. Something that permeates everything and everywhere? If so I would say that 'gravity' will do. It's a weird weird thing :)
If you want to define it as a 'force' then it can't be a 'dimension'.
But as long as we see no evidence for a 'force'?
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String theory for example discuss very small 'dimensions' 'curled up', inside those we have? But so small that we can't notice them. So, what the he* is the correct definition of a 'dimension'??
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I understand that many theories of quantum gravity involve the addition of dimensions.
Some string theory explain the weakness of gravity by allowing it to permeate additional dimensions that other forces cannot.
General relativity, probably you know, understand that gravity is curvature of space-time.
But none of these suggest that gravity "IS" a dimension. It doesn't appear on the face of it to make much sense to say that there is a "direction/dimension" in which all the "entities/points" of low gravity are at one end, and all those with high gravity are at the other?
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How about time dilation then?
And Lorentz contraction?
Seems to me that you can define a dimension about any which way you like, as long as you get some disciples adhering to your definition?
And?
Just saying :)
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Slightly provocative, but OK, I'll bite.
Unless a definition is clear its not going to be useful to communicate meaning.
There's a reasonably well understood meaning for the word dimension, if that's not what Vincent is talking about I'd love to hear more precisely what is meant. I think it is though - stop me if i'm wrong vincent.
What about time dilation and length contraction? I have to assume your point is that the "dimensions" of time and length are stretched or squashed due to these effects? Not sure how that suggests that gravity is a dimension though, the dimensions are still time and length.
Or is there something more subtle going down... ...love to learn.
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Wish I knew?:)
In mathematics and physics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify each point within it. Thus a line has a dimension of one because only one coordinate is needed to specify a point on it. Alternatively the magnitude of something in a particular direction (especially length or width or height)
According to the first Gravity is not a 'dimension'. According to the second? Maybe it could be? I'm not particularly enchanted by dimensions myself. It's about your outlook. Define it as 'dimensions' are what create 'SpaceTime' and it will feel as if they need to be there 'first'. Define it as if a 'field' creates 'dimensions' and all dimensions you see becomes your construct of defining yourself inside a space.
A space in this manner do not need any 'dimensions' at all as I see it. We need 'dimensions' for our definitions though :). But looking at it the other way 'dimensions' no longer need to be defined as above. They are in practicality of course, but they are also constructs describing 'somewhere' where we are in relation to each other.
that makes it possible to question the idea of 'dimensions' as something 'put together' to me. Never liked the idea of SpaceTime as your 'Lego' with 'dimensions' being attachable modules. Then again, this is my guess about what 'dimensions' should be seen as.
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I guess we have to be pragmatic. If there is a benefit to seeing gravity or gravitational field strength as a dimension or even a bit like a dimension then I'd be the first to buy in.
There's no doubt you can draw a graph with one axis being gravitational field strength, when is that useful? What might lead us to consider it is "real" or a simpler/better way of modelling reality? Perhaps dimensions that are not real are equally valid, perhaps, as you seem to suggest, less valid.
Are these some of the detailed questions that underly the main thread "is gravity a dimension".