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Author Topic:   Dark energy without dark energy
fallacycop
Member (Idle past 5521 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 1 of 10 (459645)
03-09-2008 8:36 AM


I've recently read this paper where the author describes a cosmological model without dark energy. They claim to solve the Dark Energy mistery without any new physics beyond standars GR (An ultraconservatist model). If true, that would be very exciting news. It would also be slightly embarassing to the comunity that it took so long to find a solution like that.
I'm wondering what main stream cosmologists think of this model.
Dark energy without dark energy

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Message 2 of 10 (459654)
03-09-2008 9:45 AM


Thread moved here from the Proposed New Topics forum.

  
Percy
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Message 3 of 10 (459657)
03-09-2008 9:54 AM
Reply to: Message 1 by fallacycop
03-09-2008 8:36 AM


New scientist just had an article on this last week: Dark energy may just be a cosmic illusion
Subscription required to read the whole article.
As near as I can make out from the article, cosmologists seem to agree with David Wiltshire, the author of the paper you cited, that we need more accurate models that take into account the lumpiness of the distribution of matter in the universe, but aren't convinced his model yet succeeds in doing this, and also aren't ready to abandon the obvious implications of general relativity that the universe must be expanding.
--Percy

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Chiroptera
Inactive Member


Message 4 of 10 (459662)
03-09-2008 10:53 AM
Reply to: Message 1 by fallacycop
03-09-2008 8:36 AM


It would also be slightly embarassing to the comunity that it took so long to find a solution like that.
I'm not sure why this would be a cause for embarrassment. I'm not qualified to really judge the paper, but the proposal here seems to be a new way of thinking about the issues. Meanwhile, the idea of "dark energy" was a pretty obvious solution -- in fact, Einstein himself proposed a cosmological constant to make his theory consistent with what he thought was the observational evidence, so there is precedent for "dark energy." I don't think that going for an obvious solution as opposed to a new way of thinking is a cause for embarrassment.
A historical analogy is the anomalies of the orbit of Mercury. Regular Newtonian physics couldn't account for the actual observed orbit of Mercury. The obvious solution was to try to "fix" Newton's laws to account for this. One solution was to replace Newton's inverse square law of gravity with one where the gravitational force was proportional to ralmost-but-not-quite -2. As it turns out, the correct explanation for Mercury's orbit was use the totally new theory of General Relativity. But I don't think astronomers should have felt embarrassed that they took so long to come up with such a radical new solution -- "fixing" Newton's laws seems, to me anyway, a much more obvious first step.

...Onward to Victory is the last great illusion the Republican Party has left to sell in this country, even to its own followers. They can't sell fiscal responsibility, they can't sell "values," they can't sell competence, they can't sell small government, they can't even sell the economy. -- Matt Taibbi

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RAZD
Member (Idle past 1405 days)
Posts: 20714
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Message 5 of 10 (459672)
03-09-2008 12:12 PM
Reply to: Message 1 by fallacycop
03-09-2008 8:36 AM


Interesting ...
Thanks

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fallacycop
Member (Idle past 5521 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 6 of 10 (459703)
03-09-2008 1:56 PM
Reply to: Message 4 by Chiroptera
03-09-2008 10:53 AM


That's why I qualified it with the word "slightly".
The Embarrassment would be in the fact that they splashed the news 10 years ago with the discovery of that very misterious dark energy, and now it may turn out to be just an elaborate illusion.

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fallacycop
Member (Idle past 5521 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 7 of 10 (459847)
03-10-2008 9:02 AM


Bump.
cavediver?
Son Goku?
I would love to know what you guys think of this bumpy universe model.

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Son Goku
Inactive Member


Message 8 of 10 (459938)
03-11-2008 8:28 AM
Reply to: Message 7 by fallacycop
03-10-2008 9:02 AM


Wiltshire's paper
First of all, I recommend never reading New Scientist if you want a decent idea of what is going on in mathematics and physics. They seem to have a habit of randomly jumping on a recent paper that proposes a radical new idea and then going “OMG!!!11eleventy-one!!!, time travel to ancient Rome possible?” In this sense they often distort what paper is actually saying and make it sound like theoretical physics is full of bonkers ideas. (As an example they have mentioned the possibility of time travel several times in the last few years and yet have never had a decent article mentioning quantum field theory.)
As for Wiltshire’s paper, the idea is certainly not new. In fact it originated with Kolb et al in 2005. This is Wiltshire’s second major paper on the idea. As an idea it is very clever. His basic proposal is that GR with visible matter already matches observations; there is no need for dark energy. In his previous paper people had a few problems related to acausal effects. However his new paper seems to get good numbers out and an excellent match to some observations. It would be interesting to see a paper comparing to WMAP’s five year observations rather than the three-year ones here in the paper.
This line of investigation is very new and so far there are only a few papers. Even Wiltshire’s paper above have no citations beyond a single trivial one mentioning the papers existence, so it’s best to give this idea some time. Here are a few results that you should know about this model:
1. It still needs dark matter; it only gets rid of dark energy.
2. There still aren’t predictions for certain important cosmological observables.
3. The results aren’t near strong enough to rule out the dark energy interpretation of standard cosmology.
4. The five-year WMAP produced results that match the standard model of cosmology very strongly, something this idea hasn’t been pitched against yet.
However really the idea needs more time for it to be given a fair analysis.
Edited by Son Goku, : Title and clarity.

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2ice_baked_taters
Member (Idle past 5851 days)
Posts: 566
From: Boulder Junction WI.
Joined: 02-16-2006


Message 9 of 10 (461015)
03-21-2008 6:18 AM
Reply to: Message 8 by Son Goku
03-11-2008 8:28 AM


Re: Wiltshire's paper
1. It still needs dark matter; it only gets rid of dark energy.
There cannot be both dark matter and dark energy. Nothing is composed of it's capacity to do work. Are you saying capacity to do work can exist without matter?
When I am confused I ask.
Edited by 2ice_baked_taters, : No reason given.

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Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 10 of 10 (461017)
03-21-2008 7:16 AM
Reply to: Message 9 by 2ice_baked_taters
03-21-2008 6:18 AM


Re: Wiltshire's paper
2ice_baked_taters writes:
There cannot be both dark matter and dark energy.
The phenomena behind the hypotheses of dark matter and dark energy are not related to one another. You would be making as much sense if you said, "There cannot be both shadows and gasoline."
When I am confused I ask.
You might consider adding the preliminary step of looking things up at someplace like Wikipedia.
--Percy

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