Originally posted by jaywill So is this generally accepted? That is traveling in a "straight path" to the ends of the universe should lead us back to the same point we left ?
I want to know if that is the consensus.
How about the belief proposed that the whole universe is rotating ? Do you think that may be true that the whole universe is spinning?
Everything else seems to be moving or spinning.
Everything that is spinning is spinning relative to something else.
What would you relate the whole universe to?
If there only was one thing in the whole universe - how would we detect it to rotate?
Originally posted by FabianFnas Everything that is spinning is spinning relative to something else.
What would you relate the whole universe to?
If there only was one thing in the whole universe - how would we detect it to rotate?
Can a singularity spin?
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Everything that is spinning is spinning relative to something else.
What would you relate the whole universe to?
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Good question. I don't know. But I thought about it
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If there only was one thing in the whole universe - how would we detect it to rotate?
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I don't know. I just read that there was a theory of a rotating entire universe.
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Can a singularity spin?
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I still am not that clear on what a singularity is. But I think it is not suppose to have mass. This side of the big bang I have not heard of the universe discribed as a singularity.
One possible exception may be that those who propose 11 or so additional dimensions (some beyond time and space) I may have heard talk about the universe being some kind of singularity in a much larger system.
Originally posted by jaywill Tell me what you know.
I don't think I know so much. The questions was just a fodder for thoughts.
(1) If someone says that the universe really is rotating, then I have to counterask: Relative to what? I don't know.
(2) If there was only one planet in the whole universe, how would we know if it is rotating or not? Perhaps by the centrifugal force? It would measure different at the equator and the poles. But what would it rotate in relation with? I don't know.
(3) If we define a singularity as something (with mass or without) with no extension in any dimension, a point with no dimensions, then can it really rotate? I don't know.
Now when you talk about traveling along world lines, does this have to do with Newton's idea that moving things should not stop moving unless some force forms resistence to their velocity?
I am trying to grasp if your leading up to an idea that everything is traveling (hence velocity).
Yes, that is what I'm trying to say. Everything in flat spacetime would travel through it on a straight line with 4-velocity unless impeded by a force, which would curve its world line. Gravitation manifests itself as curvature of spacetime itself.
A straight line .... whose slope ... ?
Inverse of its velocity ?
I have seen the flexible graph picture for many years. It helps a tiny bit. But I guess I don't know enough about velocity or the mathematics it takes to demonstrate these concepts.
Don't be discouraged. I'm here and there trying to pick up more understanding. Maybe you could help by talking just a wee bit more about the inverse of velocity.
I should say the slope is the inverse of its three-velocity, rather than its four-velocity spacetime counterpart.
Can you say a little bit about how [b]time figures into this "falling" object on this curves spacetime grid.
Okay, I get a glimmer of the curvature of space. How does time factor into gravity. Just a few words. I can understand that you can't in a forum post really make it totally clear to a novice.[/b]
Space and time are intrinsically connected. One can not curve space without modifying the time dimension as well.
To make the case for curvature of the time dimension, consider gravitational time dilation. Just as the three-dimensional force of gravity can be attributed to the curvature of space, the dilation of time in a gravity well can make the case for the curvature of time.
I was wondering that myself--not exactly a singularity, but on one of those science programs, a scientist from CalTech or MIT or one o' them hi-falutin' places, said that there is NOTHING in the universe that does not spin. She mentioned that most spin in one direction (which I think makes Uranus, or one of the moons out there an oddity since it spins "backwards" to most other objects), but that blanket statement "Everything spins"---that stuck with me, as do any absolute statements. In my humble experiences, more often than not, "Always" and "Never" don't occur in factual sentences.
gravitational force
05 Jan '10 14:39
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