Far out cosmology: universe expansion not so fast? (Introduction)

by David Turell , Thursday, October 27, 2016, 22:44 (2736 days ago) @ David Turell

This article strongly disagrees:

https://blogs.scientificamerican.com/guest-blog/no-astronomers-haven-t-decided-dark-ene...

"Once you read the article, however, it’s safe to say there is no need to revise our present understanding of the universe. All the paper does is slightly reduce our certainty in what we know—and then only by discarding most of the cosmological data on which our understanding is based. It also ignores important details in the data it does consider. And even if you leave aside these issues, the headlines are wrong anyway. The study concluded that we’re now only 99.7 percent sure that the universe is accelerating, which is hardly the same as “it’s not accelerating.”

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"The recent paper that has generated headlines used a catalog of Type Ia supernovae collected by the community (including us) which has been analyzed numerous times before. But the authors used a different method of implementing the corrections—and we believe this undercuts the accuracy of their results. They assume that the mean properties of supernovae from each of the samples used to measure the expansion history are the same, even though they have been shown to be different and past analyses have accounted for these differences. However, even ignoring these differences, the authors still find that there is roughly a 99.7 percent chance that the universe is accelerating—very different from what the headlines suggest.

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"Furthermore, the overwhelming confidence astronomers have that the universe is expanding faster now than it was billions of years ago is based on much more than just supernova measurements. These include tiny fluctuations in the pattern of relic heat after the Big Bang (i.e., the cosmic microwave background) and the modern day imprint of those fluctuations in the distribution of galaxies around us (called baryon acoustic oscillations). The present study also ignores the presence of a substantial amount of matter in the Universe, confirmed numerous times and ways since the 1970’s, further reducing the study confidence. These other data show the universe to be accelerating independently from supernovae. If we combine the other observations with the supernova data, we go from 99.99 percent sure to 99.99999 percent sure. That’s pretty sure!

"We now know that dark energy, which is what we believe causes the expansion of the universe to accelerate, makes up 70 percent of the universe, with matter constituting the rest. The nature of dark energy is still one of the largest mysteries of all of astrophysics. But there has been no active debate about whether dark energy exists and none about whether the universe is accelerating since this picture was cemented a decade ago.

"There are now many new large surveys, both on the ground and in space, whose top priority over the next two decades is to figure out exactly what this dark energy could be. For now, we have to continue to improve our measurements and question our assumptions. While this recent paper does not disprove any theories, it is still good for everyone to pause for a second and remember how big the questions are that we are asking, how we reached the conclusions we have to date and how seriously we need to test each building block of our understanding."

Comment: Over-hyped science reporting has served to confuse the issue. It seems that we are really expanding faster than thought in years past.