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Originally Posted by Bjoern
I've already told you several times now that in the mainstream, it has been clear for decades that on smaller scales, there is contraction, not expansion. So what has the mainstream overlooked?
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Sure, everybody knows clouds of gas contract to form stars, and galaxies collide, etc, but where is this local-contraction in the mainstream expansion model? I've already pointed you to one mainstream source that includes only one distance-scale, and no energy input from local contraction. "It" has been clear for decades, but "it" is missing from the mainstream model.
Quote:
Originally Posted by Bjoern
True for a circular orbiting system (for elliptical orbits, I think one could say that the system expands and contracts periodically). But consider an even simpler gravitational system: one body flying away from another. That system expands, and nevertheless its total energy stays the same. Hence you can't conclude that in general, expansion always implies gaining energy.
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As you suggest, kinetic-plus-potential energy is constant; this is true for elliptical orbits and unbound bodies. My point is that the kinetic-plus-potential energy changes at the rate at which radiation carries off energy.
Consider the rings around Saturn and an accretion disk around a black hole. The rings of Saturn are quasi-stable, because they have no way to lose energy. The gas around a BH, however, reaches "billions-and-billions" of degrees, and because it is hot, it radiates away energy. Hence, the material around BHs spirals inwards (contracts) because--and only because--it is radiating away energy.
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Originally Posted by Bjoern
Again: I wouldn't say that this is "generally" the case. Citing some examples does not prove that this happens generally.
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Right. I can give a few examples of animals that have sex. This does not prove that animals in general reproduce by having sex. But it is still true. And it is still true that in general, gravitational systems do not contract, except in proportion to the amount of energy they radiate away.
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Originally Posted by Bjoern
And yet again, radiating away GPE in the form of electromagnetic radiation happens only in some cases. You have not established that this is a general phenomenon. For example, in the case of the famous double pulsars, energy is emitted in the for of gravitational waves - not electromagnetic radiation...
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Ok.
But it is still true that in general, gravitational systems do not contract, except in proportion to the amount of energy they radiate away...whatever form that radiation may take.
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Originally Posted by Bjoern
For a comparison, (the units used) obviously does not matter. But it would be far more intuitive expressed in that way.
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Since we see stars radiating so-much energy per second, I feel this is the most intuitive way to express it. Evidently, you feel different.
Quote:
Originally Posted by Bjoern
But both of your calculations, for the expansion as well as for the contraction rate, were based on some simplifying (in some cases rather crude) assumptions. Hence the results are only (crude) approximations...Doing a more accurate calculation could show that the opposite is true!
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Finally! Something we agree on
You are absolutely right: my estimates could be wrong.
But is it really my job to show it?
