Universe not expanding as quickly as believed

[Jim Leff]

Any comments on this? Doesn't seem to have been covered here previously

http://www.sciencerecorder.com/news/cos ... s-thought/

[alter-ego]

Any comments on this? Doesn't seem to have been covered here previously

http://www.sciencerecorder.com/news/cos ... s-thought/

I have a few comments:
1) I haven't researched the sources and details of this claim and I've always thought that the community had some doubt that supernovae might have some uncertainty in their luminosities mostly because of local environment (e.g. absorption) differences, but not so much from as-yet-undiscovered significant variations from a standard candle.
2) Not putting all the expansion eggs in the supernovae basket has been an ongoing parallel effort to build confidence in the acceleration claim. There are many independent observations that support both expansion rate and acceleration.
http://en.wikipedia.org/wiki/Dark_energ ... background describes several Dark Energy supporting observations. I'm particularly drawn to the BAO validation of rate and acceleration. It is quite convincing in its own right.

Peaks have been found in the correlation function (the probability that two galaxies will be a certain distance apart) at 100h^{-1} Mpc,[9] indicating that this is the size of the sound horizon today, and by comparing this to the sound horizon at the time of decoupling (using the CMB), we can confirm that the expansion of the universe is accelerating.[15]

Outside of statistical error bars, I believe there's still a discrepancy between the WMAP and Hubble in determining the Hubble Constant. However, the importance of this difference is not the magnitude difference in expansion as the error is a few percent at most I think. The importance of the difference is understanding why the two methods don't statistically converge to the same answer. So even though there'll likely be tweaks to expansion and acceleration rates as observation techniques and diagnostics improve, I'm dubious that there'll be any surprises leading to significant changes in the collective observational results and conclusions so far. I'm always interested in seeing how these "recent discoveries" turn out.

[geckzilla]

I saw this article tossed around a few times earlier. As always, the ones which claim there is a chance that we have something hugely wrong are hugely popular. Also as always, I'll let the scientists hash it out for me, if there is actually anything to hash out. Maybe Brian Koberlein will do a blog post on it. He often has something to say about these sorts of things. I'll link it here if that happens.

[Ann]

My impression, as I read the summary of the article, is that the Type Ia supernovas are more unreliable as standard candles than astronomers used to think. That in itself doesn't necessariliy imply that the universe is expanding more slowly than expected.

Ann

[Jim Leff]

Thanks, all. I have a chemist friend who I keep forwarding articles to, asking if they're real or hyped. They're almost never not hype! Guess it's the same for astro-physics articles....

[bystander]

Accelerating Universe? Not So Fast
University of Arizona | Steward Observatory | 2015 Apr 10

[attachment=0]M82_uvot_after_SN_large_labeled.jpg[/attachment]

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A UA-led team of astronomers found that the type of supernovae commonly used to measure distances in the universe fall into distinct populations not recognized before. The findings have implications for our understanding of how fast the universe has been expanding since the Big Bang.

Certain types of supernovae, or exploding stars, are more diverse than previously thought, a University of Arizona-led team of astronomers has discovered. The results, reported in two papers published in the Astrophysical Journal, have implications for big cosmological questions, such as how fast the universe has been expanding since the Big Bang.

Most importantly, the findings hint at the possibility that the acceleration of the expansion of the universe might not be quite as fast as textbooks say.

The team, led by UA astronomer Peter A. Milne, discovered that type Ia supernovae, which have been considered so uniform that cosmologists have used them as cosmic "beacons" to plumb the depths of the universe, actually fall into different populations. The findings are analogous to sampling a selection of 100-watt light bulbs at the hardware store and discovering that they vary in brightness. ...

The Changing Fractions of Type Ia Supernova NUV-Optical Subclasses with Redshift - Peter A. Milne et al

• Astrophysical Journal 803(1) 20 (2015 Apr 10) DOI: 10.1088/0004-637X/803/1/20
  arXiv.org > astro-ph > arXiv:1408.1706 > 07 Aug 2014

The article states two papers in ApJ. This is the only one I found.

http://asterisk.apod.com/viewtopic.php?t=34594

[geckzilla]

Thanks, all. I have a chemist friend who I keep forwarding articles to, asking if they're real or hyped. They're almost never not hype! Guess it's the same for astro-physics articles....

You could go through almost any article and cross out any words like "surprising" and "baffled" and it would come much closer to the truth. The variations in Type Ia supernovas has been mulled over for quite some time now. It's a clickbait world out there.

[kellogg]

Yipes.

That's going to cause some upsets. If I recall correctly, the guy who did the initial Supernova 1A work got the Nobel Prize for it.
It will be extremely embarassing if it proves incorrect.

Now, I have to wonder about the mechanism for variability.
The Type 1A supernova is thought to be caused when a binary star system, one star leeches off just enough mass and that
triggers the explosion. We're going to have to revise the models for how it explodes if we're seeing variabilty.

On the other hand, it's always kind of neat when we learn there's more going on in the universe than what we thought.

Scott Kellogg

[kellogg]

I think I need to read up on Type 1A Supernovae.

Anybody got a good source?

Thanks,

Scott Kellogg
PS. How do you get to upload an avatar on here? I can't even find an option to do it.

[Chris Peterson]

I think I need to read up on Type 1A Supernovae.

Anybody got a good source?

I'd suggest the Wikipedia article, and then follow any references from there to primary sources as you feel useful. Wikipedia should almost always be the first place you go for science information.

PS. How do you get to upload an avatar on here? I can't even find an option to do it.

Go to you User Control Panel up top. Profile tab, Edit avatar.

[Jim Leff]

Wikipedia should almost always be the first place you go for science information.

Wow, how tides have turned....

[Chris Peterson]

Wikipedia should almost always be the first place you go for science information.

Wow, how tides have turned....

Have they? Studies for the last ten years have shown that almost all Wikipedia articles are as accurate as reviewed papers and edited sources like Encyclopedia Britannica. This is especially true for science articles. About the only area where you're likely to have accuracy issues is hotly debated social topics, and occasionally current biographies. Of course, you won't find those things in more traditional sources at all.

Google the subject and you'll find lots of information. This is a nice summary from a reliable source. Sounds a bit odd, but the Wikipedia article on the subject is also excellent, and will point you to many primary sources.

[geckzilla]

https://medium.com/starts-with-a-bang/a ... 8b0a776704

[Markus Schwarz]

Thanks, all. I have a chemist friend who I keep forwarding articles to, asking if they're real or hyped. They're almost never not hype! Guess it's the same for astro-physics articles....

You could go through almost any article and cross out any words like "surprising" and "baffled" and it would come much closer to the truth. The variations in Type Ia supernovas has been mulled over for quite some time now. It's a clickbait world out there.

I second that!

The way science is supposed to work, is that scientists discovering something new first think about it critically by themselves, then publish and discuss with their peers. In most cases, a mistake will be found. Some result stand the test of time and made it into review articles and eventually textbooks. Press releases are issued only after a result is confirmed.

Nowadays, the trend is to release a press release as soon as you have your first result. This decreases the signal to noise ratio. But to be fair, most scientific articles on which these press releases are based on are more careful in what they say and claim. I don't know who is responsible for a press release. Do the scientists whose result is covered have something to say?