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Galaxy Clusters' Stunted Growth Confirms Dark Energy
A new study of 86 galaxy clusters in the early universe has provided independent confirmation of the existence of dark energy. In its absence, gravity's pull should have caused the number of clusters to increase by a factor of 50 over the last 5.5 billion years. What is observed is a factor of 10 increase. "Together with earlier observations... the new data strengthen the suspicion — but do not prove — that dark energy is a weird antigravity called the cosmological constant that was hypothesized and then abandoned by Albert Einstein as a 'blunder' almost a century ago. If that is true, the universe is fated to empty itself out eventually, and all but the Milky Way's closest neighbors will eventually be out of sight. ... Adam Riess of Johns Hopkins and the Space Telescope Science Institute, said: 'If this was a fox hunt and dark energy was the fox, I think they have closed off another escape route. But there is still a lot of terrain left for the fox, and we've seen little more than a glimmer of fur.'"
Galaxy Clusters' Stunted Growth Confirms Dark Energy
"Together with earlier observations... the new data strengthen the suspicion â" but do not prove â" that dark energy is a weird antigravity called the cosmological constant that was hypothesized and then abandoned by Albert Einstein as a 'blunder' almost a century ago.
Wait, what?
If that is true, the universe is fated to empty itself out eventually, and all but the Milky Way's closest neighbors will eventually be out of sight.
Not only that, but depending upon the key value of state w, the ratio between dark energy pressure and its energy density, if the value of w is less than -1 then the universe will eventually be pulled apart as the rate of expansion begins to accelerate towards infinity. First the nearest galactic clusters will fade from view, then the nearest galaxies in our cluster, then the stars in our galaxy. Finally, approximately three months before the end, the solar system itself will become gravitationaly unbound, in the last minutes stars and planets will be torn apart, and finally, an instant before the end of everything individual atoms and their subatomic pieces will be ripped into ever smaller pieces until there is nothing left (i.e. the last bits just wink out of existence). The end, if it were to occur in this way, is around 50 billion years, or approximately 3.8 times the current known age of the universe, into the future. This hypothesis is known colloquially as the Big Rip.
For those interested the full paper is here. Apart from a couple of cosmological parameters they don't really improve previous estimates. It's still nice though that all the parameters agree very well with the previous (CMB + Supernova 1a) data with a completely independent method, hence the confirmation talk. I think though if there had been disagreement our understanding of clusters would have been blamed first. So in some senses this confirmed the current cluster models more than the cosmological constant, but that's not as 'sexy'!
The summary makes it sound like they actually proved that dark matter exist, not simply added to the inference of it's existence :(
Science is not in the business of making provable claims. It's impossible to prove anything using the scientific method. Science makes falsifiable claims, and any experiment that fails to falsify them confirms the theory, but most certainly does not prove it. An experiment that "confirms" a theory is one that produces a result compatible with that theory under circumstances where a different result would have falsified it. Confirmation merely strengthens a theory, it cannot ever prove it.
"Convictions are more dangerous enemies of truth than lies."
Einstein invented his "repulsive" effect to explain why the universe was static, and neither expanding or contracting. Unfortunately for Einstein, Hubble's redshift observations a few years later indicated that the "static" property of the universe that Einstein's CC had been invented to reproduce within GR, wasn't correct.
Dark energy was invented to explain why, when we take an expanding universe model decribed with general relativity, and try to compare it with reality, the numbers still don't appear to match up with the theory.
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Einstein's Cosmological Constant was an attempt to force GR to produce a wrong answer that Einstein (at that time) happened to think was a mathematically elegant one. The system seemed to describe a universe that would have to be expanding or contracting, and Einstein said ... "Well we know that THAT has to be wrong, so to make things nice and static, I'll write in an additional term for a necessary effect that I've just made up, that would exactly cancel the large-scale effect of gravity ... "
The motivation, function, and results for the two hypothesised effects are different. Both effects are repulsive, and both of them are essentially "made up" as accounting fudges without any deeper physical or philosophical justification, to force a theory that generates one result to generate a different result that we like better, but that's about all they have in common.
They're really different animals. Dark energy isn't an effect designed to explain why the universe is static. However, if you're inventing an arbitrary effect to bring your theory into line with experiment, the awkwardness of admitting that you're basically making stuff up to force the answer you want is reduced if you can claim some "provenance" for the idea, and present your "new" effect as if it's a logical historical development of an earlier idea by a Famous Physicist. That adds an air of legitimacy.
But if we think that the DE idea is any good, then the idea that DE is a historical extension of Einstein's CC is phoney. Einstein's CC is dead and buried. The only way that DE might turn out to be able to claim descent would be if DE turns out to be a rotten idea too, in which case we could say that there's a common theme running through both bad ideas. :)
But if the Dark Energy idea is good, then it's really not "bringing back Einstein's cosmological constant in revised form".
Eric Baird