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New survey casts doubt on supernova evidence for Dark Energy



 
 
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  #1  
Old October 24th 16, 12:34 PM posted to sci.physics,sci.astro
Yousuf Khan[_2_]
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Default New survey casts doubt on supernova evidence for Dark Energy

Now, a team of scientists led by Professor Subir Sarkar of Oxford University’s Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set — a catalogue of 740 Type Ia supernovae, more than ten times the original sample size — the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.

“However, there now exists a much bigger database of supernovae on which to perform rigorous and detailed statistical analyses. We analysed the latest catalogue of 740 Type Ia supernovae — over ten times bigger than the original samples on which the discovery claim was based — and found that the evidence for accelerated expansion is, at most, what physicists call ‘3 sigma’. This is far short of the 5 sigma standard required to claim a discovery of fundamental significance.


https://astronomynow.com/2016/10/21/...rate-or-is-it/
  #2  
Old October 24th 16, 06:45 PM posted to sci.astro
dlzc
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Default New survey casts doubt on supernova evidence for Dark Energy

Dear Yousuf Khan:

On Monday, October 24, 2016 at 4:34:58 AM UTC-7, Yousuf Khan wrote:
....
“However, there now exists a much bigger database of
supernovae on which to perform rigorous and detailed
statistical analyses. We analysed the latest
catalogue of 740 Type Ia supernovae — over ten times
bigger than the original samples on which the
discovery claim was based — and found that the evidence
for accelerated expansion is, at most, what physicists
call ‘3 sigma’. This is far short of the 5 sigma
standard required to claim a discovery of fundamental
significance.


https://astronomynow.com/2016/10/21/...rate-or-is-it/


The Scientists's arxiv.org history:
https://arxiv.org/find/astro-ph/1/au.../0/1/0/all/0/1

A different, but related paper:
https://arxiv.org/abs/1610.04677

Will be nice to have a longer history available to the Universe, for sure.

David A. Smith
  #3  
Old October 28th 16, 05:54 PM posted to sci.physics,sci.astro
Steve Willner
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Posts: 1,172
Default New survey casts doubt on supernova evidence for Dark Energy

In article ,
Yousuf Khan writes:
https://astronomynow.com/2016/10/21/...rate-or-is-it/


The actual article is open access at
http://www.nature.com/articles/srep35596

The key result is shown in Figure 2 of the article. Dark energy
being zero requires low matter density and therefore a curved
universe. That seems to be ruled out by the CMB fluctuations, which
show the universe to be very nearly flat.

In Fig 2, flat would be represented by a straight line from (0,1) to
(0.8,0.2), i.e., the sum of the two Omegas is equal to 1.

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  #4  
Old October 28th 16, 07:18 PM posted to sci.physics,sci.astro
Yousuf Khan[_2_]
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Posts: 1,692
Default New survey casts doubt on supernova evidence for Dark Energy

On 10/28/2016 12:54 PM, Steve Willner wrote:
In article ,
Yousuf Khan writes:
https://astronomynow.com/2016/10/21/...rate-or-is-it/


The actual article is open access at
http://www.nature.com/articles/srep35596

The key result is shown in Figure 2 of the article. Dark energy
being zero requires low matter density and therefore a curved
universe. That seems to be ruled out by the CMB fluctuations, which
show the universe to be very nearly flat.

In Fig 2, flat would be represented by a straight line from (0,1) to
(0.8,0.2), i.e., the sum of the two Omegas is equal to 1.


So what's your interpretation of these figures?

Yousuf Khan

  #5  
Old October 28th 16, 11:08 PM posted to sci.physics,sci.astro
Steve Willner
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Posts: 1,172
Default New survey casts doubt on supernova evidence for Dark Energy

In article ,
Yousuf Khan writes:
So what's your interpretation of these figures?


I don't have anything special to say. All data so far are consistent
with "concordance cosmology." That's the reason for the name. There
are numerous observations in progress that should give better
data. We'll see whether anything unexpected turns up. At a minimum,
the uncertainties on the parameters will shrink.

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  #6  
Old November 2nd 16, 12:36 PM posted to sci.physics,sci.astro
Yousuf Khan[_2_]
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Posts: 1,692
Default New survey casts doubt on supernova evidence for Dark Energy

On 10/28/2016 6:08 PM, Steve Willner wrote:
In article ,
Yousuf Khan writes:
So what's your interpretation of these figures?


I don't have anything special to say. All data so far are consistent
with "concordance cosmology." That's the reason for the name. There
are numerous observations in progress that should give better
data. We'll see whether anything unexpected turns up. At a minimum,
the uncertainties on the parameters will shrink.


But if this new model results in Dark Energy going away, how does that
affect the "concordance"? Cosmology has all but completely accepted Dark
Energy as real, can they take another shock to the system where all of a
sudden it isn't anymore?

Yousuf Khan

  #7  
Old November 2nd 16, 03:16 PM posted to sci.astro
dlzc
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Default Supernova Data, Best Fit.

Dear Jeff-Relf.Me:

On Wednesday, November 2, 2016 at 5:31:44 AM UTC-7, Jeff-Relf.Me wrote:
....
You still have to explain why the expansion doesn't
slow down due to the gravity of everything it contains.


That part is easy. Gravity does not reduce the amount of space in spacetime, so only entropy can produce more space, more intermediate states. Expansion is easy ("just" the one-way arrow of time), acceleration is slightly less easy, contraction (say towards a "Big Crunch") essentially requires reversing entropy.

I'd like to see addressed (someday) what causes acceleration, in terms of the contents of the Universe, something that might be controllable, adjustable. Because if the Big Bang event is the only way contents can enter, and cooling is how new force-systems come into play, what causes acceleration of expansion?

Saying Dark Energy, something that is uniformly distributed across the Universe at each epoch, and yet varies with time (at least between the Big Bang Event and now), isn't a model I can wrap my head around, yet. Sounds more like a boundary condition, yet we have only two boundaries... the Big Bang event and "the laws of physics".

David A. Smith
  #8  
Old November 2nd 16, 03:25 PM posted to sci.physics,sci.astro,comp.os.linux.advocacy
Jeff-Relf.Me
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Default Supernova Data, Best Fit.

PRE Style='Font-Family: OCR A, monospace !important;'
Quoting
<A hRef='http://www.ibtimes.co.uk/relax-expansion-universe-still-accelerating-1589265'
target=_blankRelax, the expansion of the universe is still accelerating/A>
November 1, 2016: <<

A universe that just expands at a constant rate is
actually just as strange as one that accelerates.

You still have to explain why the expansion doesn't
slow down due to the gravity of everything it contains.

So even if the non-acceleration claim made in this
paper is true, the explanation still requires new
physics, and the search for the "dark energy"
that explains it is just as important. >>

Supernova Data, Best Fit:
img Src="https://d.ibtimes.co.uk/en/full/1563353/universe-expansion.jpg" Alt="Supernova Data, Best Fit."
  #9  
Old November 2nd 16, 07:13 PM posted to sci.physics,sci.astro
Steve Willner
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Posts: 1,172
Default New survey casts doubt on supernova evidence for Dark Energy

In article ,
Yousuf Khan writes:
But if this new model ...


The paper we are discussing is not a "new model." What makes you
think that? It's a new analysis of existing data. As with any
analysis, it has its own strengths and weaknesses.

... results in Dark Energy going away,


Why should it do that? The new analysis is entirely consistent with
Dark Energy. All the analysis says is that if you look at the SN
data alone and don't consider any other data, Dark Energy is not
absolutely required (though its existence is statistically favored).

how does that affect the "concordance"? Cosmology has all but
completely accepted Dark Energy as real, can they take another
shock to the system where all of a sudden it isn't anymore?


The reason Dark Energy is widely accepted is because it fits all
existing data, and so far no model without Dark Energy does.

If someone does come up with a model that fits the data without Dark
Energy, that model will be evaluated on its merits: how well does it
fit the data, and how many free parameters does it have?

I might point out, though, that a cosmological constant is an
inherent part of the Friedmann equations. Its value might be zero
(as was widely assumed before the evidence came in), but there's no
reason I can see for favoring zero over any other value. Indeed
quantum mechanics suggests the cosmological constant ought to be
enormous. From that point of view, the problem is explaining why
Dark Energy is so small.

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Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
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  #10  
Old November 3rd 16, 02:41 PM posted to sci.physics,sci.astro
Yousuf Khan[_2_]
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Posts: 1,692
Default New survey casts doubt on supernova evidence for Dark Energy

On 11/2/2016 2:13 PM, Steve Willner wrote:
how does that affect the "concordance"? Cosmology has all but
completely accepted Dark Energy as real, can they take another
shock to the system where all of a sudden it isn't anymore?


The reason Dark Energy is widely accepted is because it fits all
existing data, and so far no model without Dark Energy does.

If someone does come up with a model that fits the data without Dark
Energy, that model will be evaluated on its merits: how well does it
fit the data, and how many free parameters does it have?


Well, before there was Dark Energy, there was a model that fit the data
too. That was the hot Dark Matter model, where the place of Dark Energy
was filled by neutrinos.

I might point out, though, that a cosmological constant is an
inherent part of the Friedmann equations. Its value might be zero
(as was widely assumed before the evidence came in), but there's no
reason I can see for favoring zero over any other value. Indeed
quantum mechanics suggests the cosmological constant ought to be
enormous. From that point of view, the problem is explaining why
Dark Energy is so small.


Well, that Dark Energy size vs. Vacuum Energy disconnect has been around
ever since the DE was first discovered. If the entire amount Vacuum
Energy were available as Dark Energy, then likely the universe would've
blown up milliseconds after the Big Bang, with an even Bigger Bang.

In fact, I wonder if something like that didn't actually happen? If that
entire Inflation after the Big Bang wasn't as a result of the universe
getting rid of a little extra vacuum energy?

Yousuf Khan
 




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