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Gravity
Jul 12, 2012 12:56:30 GMT 1
Post by Progenitor A on Jul 12, 2012 12:56:30 GMT 1
We all know Newton was wrong and that Eistein is right
Dense bodies are not attracted to one another -they distort space time and have no option but to follow that distortion that we call curvature (there is nowhere else to go)
So the big mystery of gravity has been solved hasn't it?
Ther is no great unexplained mystery as to why bodies attract one another - they quite simply do not , but follow the space-time curvature of their own making
But what determines in which direction they follow this space-time curvature?
Why is it always toward the steepest curvature and not away from that curvature (anyone that cites gravity at the reason will go to the corner of the classroom)
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Gravity
Jul 12, 2012 19:36:12 GMT 1
Post by mak2 on Jul 12, 2012 19:36:12 GMT 1
The theory says that bodies follow a geodesic path in space-time. I don't think this necessarily means that they always go towards the steepest curvature. They take the shortest route, when the time dimension is included.
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Post by Progenitor A on Jul 14, 2012 7:35:12 GMT 1
They take the shortest route, when the time dimension is included. Ok - why the shortest route - what compels them to do that?
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Gravity
Jul 14, 2012 18:28:45 GMT 1
Post by mak2 on Jul 14, 2012 18:28:45 GMT 1
I guess you could say that Einstein's field equations compel them.
As Newton observed, in flat space-time, a body will travel in a straight line ( unless acted on by a force ). A straight line is the shortest path between 2 points.
By extension, in curved space-time, a body will follow a geodesic because it is the shortest path between points.
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Post by striker16 on Jul 15, 2012 9:06:00 GMT 1
So the big mystery of gravity has been solved hasn't it? No, of course not. Until we have a theory uniting quantum mechanics and classical mechanics we do not actually know what gravity is but what we can do is to measure its effects on bodies moving through its influence. Measuring something isn't necessarily the same as understanding it. For example, we can measure the effects of consciousness but there is no consensus as to what consciousness really is. They try to re-create conditions that are similar to those that existed at the birth of the universe but how do they really know they've got it right? They can only really guess about what conditions were like 4 1/2 billion years ago. If they are wrong, this particle could be something that is simply a result of the experiment, not something that was created after the BB.
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Gravity
Sept 15, 2012 12:32:30 GMT 1
Post by speakertoanimals on Sept 15, 2012 12:32:30 GMT 1
The actual question here is why momentum is conserved -- why a body moving in a straight line in flat space will continue to do so if undisturbed. Why motion persists.
Mathematically, the reason for conservation of momentum (or conservation of energy/momentum in relativistic Minkowski space) is because the laws of physics don't depend on position. The conservation of angular momentum similary arise because the laws of physics don't depend on direction. As Emmy Noether showed, a symmetry of the laws (ANY laws, not just one particular bit of physics), leads to a conserved quantity -- like momentum or angular momentum.
As regards WHY gravity attracts -- it only does so for ordinary matter, and some theories have different types of matter which produce gravitational repulsion.
Anthropic answer -- if we had a universe where the stuff in it repelled rather than attracted, we wouldn't have stuff like stars and planets, hence no us.
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