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Previous Next Up Topic Cosmology / Alternative Cosmology / Space/Time rubber sheet problem (4529 hits)
By Eduffy80911 Date 2011-06-23 15:43
m'kay, so while watching another trippy science show, it occurred to me for some reason, that the rubber sheet analogy for space/time has a serious flaw. In the analogy,
matter is like bowling balls on a rubber sheet and the effect of gravity is when things roll into the dimples created by them.

Problem - for this analogy to work, there has to be a "down", otherwise, no dimple. What's causing the matter to act on the sheet in one direction rather than another, or no direction at all?

Unless you add something outside of space/time, acting on our rubber sheet as well as the matter upon it, the analogy doesn't work.

...I did like the bit about dark-flow possibly confirming a multi-verse theory, that I added my own bit to, making the multi-verse a kind of developing organism in it's very early stages, but that's another story.
By Jade Annand Date 2011-06-25 05:42
I've often wondered about that analogy myself. Back when imagining the universe as a hypersphere occupied quite a bit of my imagination, I wondered such things. Sure, you could say "well, it's pulling everything to a center", but that still does not quite describe what the "pull" is.

I've seen some field the thought that the hypersphere is expanding and gravity is the dimples from the inertia of the mass. Depending on such ideas as drag, elasticity of space, etc., the hypersphere would either have to be at a constant 'velocity' or accelerating.

The universe is too old for that, though, I would say.

I wonder how different gravity is going to turn out to be from the rest of the forces.
By Eduffy80911 Date 2011-07-18 06:02
I wonder if maybe gravity appears so much weaker than the other forces because it's really a net result of more than one force. Doesn't really help the mystery any, since the other force(s) would be ones that no one has a clue about either.
By bangstrom Date 2011-07-23 07:40
Understanding gravity as curved spacetime requires an ability to visualize space in four dimensions. This is may be humanly impossible so the next best thing to do is find a three dimensional model that can serve as an analogy for 4-D space and this is where the rubber sheet analogy comes in. The “flaw” in this analogy is that it is lacking a fourth spatial dimension but, What else can you do? If you combine the rubber sheet analogy with the old balloon analogy for an expanding universe, our rubber sheet is a small part of a greater rubber surface that is expanding. DOWN in this analogy is towards the center of the balloon and, since the balloon is expanding outward in time, the direction DOWN is towards the past. It is hard to imagine how either space or time can be considered as curved so I prefer to think of gravity as 'shorter space and slower time'. In the rubber sheet analogy DOWN is the direction where clocks run slower and lengths are shorter. As you go down in a depression on the rubber surface (a gravity well) time runs slower and lengths grow shorter at the bottom. Objects that are free to move in a spacetime gradient will move from areas of high energy where spacetime is less curved (time runs fast and lengths are long) to areas of low energy where spacetime is more highly curved (time runs slower and lengths are shorter). So any direction towards greater spacetime curvature (slower time and shorter space) is DOWN in the rubber sheet analogy and that is gravity. There is no need for an 'outside of spacetime' attractor. Gravity is a spacetime gradient.
By Eduffy80911 Date 2011-09-04 00:55
i think a less mystic way of saying "time runs slower" is just that things move slower. Time is relative motion. i suppose if everything moves proportionally slower "time runs slower". But it still has to be in relation to something else. You can't freeze or stop time because the only way to accomplish that is to remove every speck of energy. No energy, no stuff. No stuff, no relative motion. Time hasn't stopped, it just isn't there.

But back to the gravity thing. I heard a version of the 4th dimension that envisions it as a ridiculously small revolutionary orbit of every individual particle on a sub-sub atomic scale. I suppose gravity could be the cumulative by product of all that revolutionary motion. What's it all orbiting? Maybe pockets of what I've referred to as "the nothing" for lack of another term. Don't know what it is, but the existence of something other than matter and energy, with opposing properties, helps clear a few things up, even if all you know about it is that it's there.
By bangstrom Date 2011-09-04 05:05
I heard a version of the 4th dimension that envisions it as a ridiculously small revolutionary orbit of every individual particle on a sub-sub atomic scale.

This sounds like the Kaluza-Klein theory to give it a name.
Previous Next Up Topic Cosmology / Alternative Cosmology / Space/Time rubber sheet problem (4529 hits)

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