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Originally Posted by mutineer
We may judge (on the basis of observation) that our cubic parsec expands by 10% linear in a given number of years, and so (being three dimensional) becomes about one and a third cubic parsecs.
In a following period of the same duration, given that the propensity to expand is a constant, it expands by a further 10%. However, there is now more of the original chunk of raw space to expand. The overall linear expansion is 21% and the volume has grown by more than three-quarters.
Point is, we have the effect of compound interest. A constant rate of return on your investment results in an acceleration of your wealth. And a constant propensity of space to expand results in a continually increasing value for the Hubble variable.
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From my reading of recent books and journal articles, this is exactly correct; that is, this is our best description of what is happening based on observations.
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Originally Posted by Cyrek
I cannot give these 1a supernovas much credibility...
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Then you'll be pleased to know that Ryan Scranton
et al. have reportedly found independent and more direct evidence of the existence of dark energy.
When CMB photons pass by a concentration of mass (such as a galaxy) and fall into its gravitational well, they gain energy. But then they lose the same amount as they climb out of the well.... or at least they would if all they encountered was normal matter. But if the well is also permeated with dark energy, as all of space is expected to be (according to theory), the well would appear shallower as a photon passes through it (or should I say, it would get more of a dark energy "boost" upon exit, since there would be
more dark energy as the photon began to climb out of the well - 50,000 years after it entered the galaxy's gravitational influence.
So the CMB photon exits with a slight energy gain. This would make the cosmic microwave background slightly hotter where there are more galaxies. Scranton
et al. identified just such a positive correlation between the CMB temperature map and the distribution of about 25 million galaxies. Assuming the universe is flat (as is generally thought), dark energy seems to be the only explanation for the correlation.
[I'm not sure if this finding continues to hold, as it was reported nearly a year ago in
Nature on July 31, 2003. I also (vaguely) recall a similar finding that reached a different conclusion calling into question the entire CMB interpretation (?), but IIRC, fault was quickly found with that conclusion. ALSO, please note, Mr. Uniform Expansion
that the temperature variation in the CMB is really, really small, and only within the last decade or so have we been able to design instruments capable of noticing any variation at all. Hence, (if this finding withstands scrutiny), the effect of expansion on the scale of galaxies is
just barely detectable.]