[LeeE]

The problem with everything happening at once is that it's a static state, equivalent to nothing happening at all.

Along with DrBeaver, I think that regardless of how many spatial dimensions you're dealing with, you need a specific 'time' dimension for any change to occur.  Now this time dimension may or may not be the same as a spatial dimension, and only appears to be different depending on your point of view - for example, you could view a cylinder as the entire lifetime of a circle, where the spatial length of the cylinder is the temporal length, or lifetime, of the circle.  The cylinder, to us is static, but from the circle's point of view it is dynamic.  This view can be applied both up and down - the diameter of the circle could be viewed as the temporal length of a line (and in this case, the change in the nature of the line over it's temporal length is obvious - at the start of it's life it has zero length, half way through it's life it's length is the diameter of the circle and by the end of it's life, it's length has become zero again), while at the same time dynamic three-dimensional objects in our four-dimensional universe could be seen as static four-dimensional objects in a hypothetical five-dimensional universe.

Alternatively, we could view 'everything happening at once' as being like a super-position of states but even then, for this super-position of states to be resolved in to a specific single state where time and space have been resolved in to their current states, a before and after is still required.  That is to say, without a time dimension somewhere the super-position couldn't have been resolved.

Heh  [] I really don't want to go in to the possibility that we might actually still be existing in an unresolved super-position of states, and in any case, the states of space and time do seem to have been resolved.

[DoctorBeaver]

erm... yeah... what LeeE said  []

[Soul Surfer]

The two fundamental features of our (and probably any other long lived) universe are the conservation of energy and the conservation of angular momentum these laws are a fundamental part of the universe having consistent laws and being understandable. Assuming that thes laws can be extrapolated back beyond the big bang imply that our universe originated in something that was collapsing.

[LeeE]

Matter wasn't created until fairly late on in the Big-Bang and until that point it seems that there was just energy, so I don't think you can even extrapolate angular momentum back to the very start of the BB, let alone beyond it.

I don't think that the physical laws that operate in our four-dimensional space-time would work in universes with a different number of dimensions, although the laws that did operate might be related to our ones.  It might seem reasonable that all four-dimensional space-times have the same laws as ours, but I wouldn't want to put money, of which I am extremely short, on it.

[Soul Surfer]

Interesting points and I see they could be very relevant but having three spatial dimensions is important for a long lived universe.  The reason for this that long range energy fields follow an inverse square law and the only law that allows long term stable orbits to form is an inverse square law.

[LeeE]

...but having three spatial dimensions is important for a long lived universe

But isn't that just saying that a universe with a different number of spatial dimensions has to have different laws?

Also, don't just think down to < 3 spatial dimensions - you've got to think up to > 3 as well.

[Soul Surfer]

Yes but changes from the number of extended dimensions of three space and one of time in either direction result in gravitational orbits not being stable because three space dimensions result in an inverse square law in which a two body orbit can be stable against quite large disturbances. If you change the inverse square law by even a tiny bit you can produce an orbit in a two body system but the slightest disturbance will cause that orbit to become unstable and not last for a long time.
 
You can however have a many extra compacted dimensions you like

[LeeE]

I think you're still applying 4D space-time laws to non-4D space-time environments and the point is that spacetime environments with other than four dimensions would need different laws.  Saying that less than four-dimensional space cannot exist because it doesn't conform to 4D-spacetime rules is like saying apples can't exist because they're not oranges.  Saying that greater than 4D spacetime can exist only if the other dimensions are treated differently is like saying apples can only exist if you buy them at a particular store.  In either case, there needs to be a reason why different solutions, to what is really a simple hierarchic system, are treated so differently.  Claiming that only one level in the hierarchy is possible because only that level works with that level's rules doesn't really seem like a valid arguement to me.

[JP]

Doesn't the definition of spatial and temporal dimensions depend on their geometric properties?  In other words, space dimensions behave one way, and time another, and their interaction is defined in a geometric way by general relativity.  If you assume these same relations hold and change the number of dimensions, the universe as we know it isn't stable. 

I believe that lot of extensions of GR (string theory, for example) include extra dimensions by assuming they don't have the properties of spatial/time dimensions.

[LeeE]

I think it depends on who you ask  []

This comes back to saying that we appear to be able to move freely through the spatial dimensions but not through the temporal dimension.  However, it's not as simple as that.  While it seems that we cannot move freely back and forth along the temporal dimension this must be qualified - that is to say we cannot move backwards in time while our personal time-frame continues moving forward, which is what most people think of when talking about going back in time.  In absolute terms, what you did last week is still happening last week, and if you were to go back to last week you wouldn't be aware of the fact unless your personal time-frame continued going forward while you were going backwards i.e. you'd actually end up being a week older than you were a week ago.

Yes, the time dimension appears to be different, from our point of view, to the spatial dimensions but saying exactly how and why is very difficult to put your finger on, although I personally think that phenomenon like time dilation give an insight to how the spatial and temporal dimensions are essentially equivalent and their appearance and behaviour depends upon your point of view (not only from what you're doing but also from how many dimensions you're observing from).  It's a bit like not being able to see the forest because of the trees - we can only see it from inside, whereas we really need to see it from outside to definitively answer this.

Purely personally, I don't like solutions where anything other than three spatial dimensions has to be treated differently without a clear reason for doing so, even when those solutions provide some good answers.  Sure, those solutions are worth studying and refining, and we learn and gain new insights from them, but they hardly seem to be unified if they add new abstracts - new clauses that cannot be expressed in related lower order solutions.

[Soul Surfer]

The simple point is that less than three dimensions and there isn't room for anything to develop.  Two dimensions gives a simple inverse law of power fall of with distance.  Three dimensions of space gives an inverse square law of power fall off and four dimensions of space an inverse cube law.

[DoctorBeaver]

The simple point is that less than three dimensions and there isn't room for anything to develop.  Two dimensions gives a simple inverse law of power fall of with distance.  Three dimensions of space gives an inverse square law of power fall off and four dimensions of space an inverse cube law.

Isn't that only true if the dimensions are the same size?

[Soul Surfer]

Same size?  please explain what you mean.  dimensions can either be large and extended to infinity (or the size of the universe) or curled up incredibly tiny and cyclic I am not sure that a halfway position makes any sense.

[DoctorBeaver]

There are theories of warped extra dimensions that allow them to be up to 0.1mm in diameter. That is something that is to be tested with the LHC.

If 1 dimension is that size and the others are compactified to, say, the Planck scale, there would not be a consistent dilution of gravity through all dimensions. It would dilute more in the large dimension.

[LeeE]

SoulSurfer - you still seem to be doggedly applying 4D laws to non-4D situations, and what is more, some of these 4D laws don't always hold to be true in our 4D space-time.  For example, the angles of a triangle always add up to 180, yeah?  Well this only works in flat space-time - plot a triangle in the curved space-time near a black-hole, equivalent to plotting it on a sphere, and the sum of the angles will always be greater than 180.  There is no flat space-time in our universe and any laws that depend on it being so will always be very slightly wrong.

[neilep (OP)]

INTERLUDE ANNOUNCEMENT

Thanks for the fascinating posts all !

END OF INTERLUDE

[DoctorBeaver]

INTERLUDE ANNOUNCEMENT

Thanks for the fascinating posts all !

END OF INTERLUDE

OI... I didn't have time to get an ice-cream!  [!]

[neilep (OP)]

INTERLUDE ANNOUNCEMENT

Thanks for the fascinating posts all !

END OF INTERLUDE

OI... I didn't have time to get an ice-cream!  [!]

Sorry for the short interlude !

I didn't want to upset the flow of the thread...here..have this on me !

 [ Invalid Attachment ]

[DoctorBeaver]

Have it on you? You think I'm depraved?

[neilep (OP)]

Have it on you? You think I'm depraved?

LOL..I kind of walked into that one....would I be more attractive ....if it ....was hummus  ?