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ToSeek
2005-Mar-11, 05:14 PM
Evidence of dark energy missed 30 years ago (http://www.newscientist.com/article.ns?id=dn7109)


The discovery in the 1990s that there could be some kind of mysterious dark energy that is accelerating the expansion of the universe came from studies of supernovae billions of light years away. Now, it turns out that the evidence for dark energy was there in our cosmic backyard all along, and that astronomers could have discovered it nearly 30 years ago.

Grey
2005-Mar-11, 10:35 PM
These deviations are called "peculiar velocities", but Sandage pointed out that galaxies in our vicinity - those lying just beyond our "Local Group" of the Milky Way and its immediate neighbours - showed abnormally low peculiar velocities.

So could astronomers have used the observations to propose dark energy in the 1970s? Governato is not sure how far they could have got without today's computer power. Also, "even if someone had written a paper claiming dark energy back in the 1970s, I don't think anyone would have believed them," he says.
I'm inclined to agree. At that point, it would have been a relatively minor anomaly, and I'm sure that there would be other possible explanations if that data were the only indication of dark energy. No surprise that it took evidence that couldn't be ignored.

dgruss23
2005-Mar-12, 01:55 PM
I think Peacock's statement in the article is the most important one:


"You have to find a signature that cannot be confused with anything else. This is not it."

This is very important to understand relevant to scientific reasoning. Some tests may be consistent with a hypothesis or theory without ruling out other explanations. And this statement by Governato is an overstatement:


"This proves that the galaxies are islands in a sea of dark energy," says Governato.

Computer simulations are now "proof"? I thought observations did that! What Governato has shown is that his computer simulations - which incorporate dark energy - are consistent with the observed low velocity dispersion of local galaxy groups (~25-75 km s-1). That does not rule out other explanations.

This illustrates a point I made in the global warming discussions. Here:


I never said I dispute the results of the lilac study. In fact at one point I specifically said I have no doubts that the researchers are capable of accurately determining that lilac’s are blooming 4 days earlier than in 1965. What I dispute is their over-reaching claim that the 4 day earlier blooming can be attributed to AAGW.

This is a good lesson for all those that are trusting the GW scenario based upon “concensus” of experts. Should the empirical research results of climate experts published in the journals be trusted? Yes - no matter where people stand on a theoretical issue, methodological flaws will be identified and pointed out – eventually if not prior to publication.

But trusting concensus on observational results is far different from trusting interpretations (inferences). Being a trained empirical researcher does not automatically vaccinate one from making inferential errors. The lilac’s results illustrate that.

The researchers in question associated the earlier blooming of lilacs with CO2 forced GW (AAGW). It is well established in the surface temperature record that the period from 1940-1970 was a cooling period. Since they used 1965 as a comparison with the recent blooming dates – and since the 1970-present temperature records indicate a warming, it is not surprising that lilacs are blooming earlier now than in 1965.

What these researchers can conclude is that lilac blooming appears to respond to changing surface temperatures. But their results provide absolutely no evidence about the cause of the warming. To claim it is AAGW is an inferential error.

It is also known that the 1940-1970 cooling period corresponds with decreased solar activity and that the warming since then corresponds with increased solar activity. If it turns out the warming since 1970 is greater than solar activity can account for, you still must account for non-CO2 anthropogenic sources of warming such as the Urban heat island and recent finding on the warming effects of jet contrails. If you can establish the amounts of those warming sources then you can say how much of what is left could be caused by CO2 – and according to the papers I’ve read it won’t be much.

In other words – eventually – the lilac study researchers might be able to say: “After accounting for solar and other influences, there is a (insert decimal or hundredths place value) deg C warming that could be influencing a portion of the observed 4-day earlier blooming of lilacs.”


I've bolded the important part, but Governato has provided another example.

dgruss23
2005-Mar-12, 02:01 PM
Here (http://xxx.lanl.gov/abs/astro-ph/0412583) is the research article on astro-ph.

Grey
2005-Mar-12, 04:25 PM
Computer simulations are now "proof"? I thought observations did that! What Governato has shown is that his computer simulations - which incorporate dark energy - are consistent with the observed low velocity dispersion of local galaxy groups (~25-75 km s-1). That does not rule out other explanations.
I'd absolutely agree. Although I would consider this an interesting piece of supportive evidence for dark energy. That is, it's something that the model seems to get right, even though it's fairly far outside the original observational reasons for proposing dark matter. That's typically a good sign for a theory, even though, as you point out, it's a long way from ruling out other models.