well, IANAP, but...
in response to number 1:
string theory has helped unite general relativity and QM in a pretty good way; the big problem is, GR requires a very uniform and smooth surface to space-time, and QM dictates that in fact space-time is very rough and choppy (read: 'quantum foam') at scales smaller than the Planck length.
string theory refutes this by showing that the Planck length is in fact the smallest possible scale possible, and thus such possible uncertainty undulations are ignored, and space has an overall smoothness good enough for GR to be applied.
secondly, given the non-zero length of strings, the infinities disappear since zero does not come into play. thirdly, string theory not only predicts a zero-mass particle with a spin of two (a graviton), it requires it
regarding number 3, that's a bit hard to say.
red-shifted photons (eg cosmic background photons whose wavelengths are being 'stretched out' by Hubble expansion) are treated thermodynamically as a kind of 'photon gas'.
the thing is, its not as if a red-shifted photon starts out as a regular photon, then midway through its journey to an earth telescope, it somehow 'stretches', throwing away energy somewhere. the red shift occurs at the moment the photon is emitted. its hard to say where the energy goes, but its also hard to assume that it is somehow 'absorbed' by the vacuum, because that would be a circular process;
1. a photon is red-shifted due to cosmic expansion
2. said photon thus gives energy to the vacumm
3. said more energetic vacuum causes more expansion.
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give a man religion and he'll starve to death while praying for a fish
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