Archive for the ‘cosmology’ Category

Zheng & Bunn paper accepted

Monday, September 6th, 2010

A while back, I mentioned a paper by Haoxuan (Jeff) Zheng and me assessing whether some observations of anomalous patterns in the microwave background could be seen as evidence in favor of certain exotic cosmological models.  The paper has now been accepted and will appear in Physical Review D in the coming months.

The referee for the paper had a number of quite apt criticisms of the original version we submitted.  We addressed those criticisms, with the result that the final version of the paper is, I think, considerably better than the original.  It’s nice when refereeing works out this way.

Congratulations to Jeff on an excellent piece of work!

Paper submitted

Thursday, August 5th, 2010

I love the feeling right after submitting a paper for publication.  One just went off yesterday. Since my sabbatical is winding down, and I’m now acting department chair, I’m glad to have gotten this finished before the semester starts.

This one’s pretty specialized, likely to be of interest only to people who analyze microwave background polarization maps.  Here’s the abstract, in case you care:

 Separation of the B component of a cosmic microwave background (CMB) polarization map from the much larger E component is an essential step in CMB polarimetry. For a map with incomplete sky coverage, this separation is necessarily hampered by the presence of “ambiguous” modes which could be either E or B modes. I present an efficient pixel-space algorithm for removing the ambiguous modes and separating the map into “pure” E and B components. The method, which works for arbitrary geometries, does not involve generating a complete basis of such modes and scales the cube of the number of pixels on the boundary of the map.

Scientific American on energy & cosmology

Monday, June 28th, 2010

Tamara Davis’s cover article (paywall) in the latest issue of Scientific American is about the old puzzle of whether it makes sense to talk about energy conservation in the expanding Universe.  It has the good taste to refer to my work with David Hogg on the nature of the redshift, which is at the heart of this question.   In fact, one of the figures in the article is essentially a slick, nice-looking version of something from our paper:

scientificamerican0710-38-i6.jpg

I think the article’s very good.  I think it gets the science right and emphasizes pretty much the right things.

What Arnold Schwarzenegger and the microwave background have in common

Monday, November 2nd, 2009

Governor Schwarzenegger sent a letter to the California assembly along with his veto of a recent bill.  The first letters of each line of the message spell out a certain vulgar phrase.  The Governor’s office says it’s a coincidence, but apparently lots of people don’t believe them.

This has a lot in common with the subject of a colloquium I gave here at the Université Paris last week.  (If you really want to, you can see the slides for this talk.)  My talk was about several unexpected patterns that have been observed in maps of the microwave background: there are a number of things that should, according to the standard theory, be random but that look non-random.  There’s a lot of controversy over whether these patterns are significant.  The problem is that after you’ve noticed a pattern, it’s very hard to quantify just how unlikely that pattern is, and hence whether it demands an explanation.

Human beings are really good at pattern-finding.  Maybe what we’re seeing is a chance fluctuation, and we’re just fooling ourselves into thinking it’s a pattern with an underlying cause.

The probability of this particular phrase being spelled out in this particular way in Schwarzenegger’s letter are something like one in a trillion.  But if you want to decide whether you think an explanation is required (i.e., that someone did it on purpose), that one-in-a-trillion number isn’t the right one to use: you should  try to figure the probability of something like this happening, rather than the probability of this particular thing happening.

Suppose that you read in the paper that Mary Jones won the lottery.  You’re not likely to be astonished by that fact, even though the probability of this particular person winning the lottery is very small. The reason is simple: the probability of someone winning the lottery is quite large.

So in the cases of both the microwave background and the vulgar acrostic, we should ask how unlikely is it that some similarly unusual pattern would show up.  The problem is that it’s very hard to phrase that question precisely enough that it has a meaningful answer.

So what should we do?  In Schwarzenegger’s case, we should get whatever juvenile amusement we can out of the situation, then decide that it just doesn’t matter and move on.  In the case of the microwave background, things are a bit different: if these patterns are real, then they may be telling us something scientifically very important.  So we should try to figure out new data sets that will shed light on the question.  Unfortunately, that’s hard to do.

Planck launch pictures

Friday, October 16th, 2009

Ken Ganga, a member of the Planck satellite collaboration, has some nice pictures of the launch on his blog.  (Not exactly breaking news, but I just found out about these pictures.)  There’s also a story about a potentially fatal problem with the satellite that was caught just barely before launch.

By the way, in addition to his Planck blog, Ken has a personal blog, mostly about funny things he’s found while living as an American expatriate in Paris.

Bragging

Thursday, September 10th, 2009

My colleague Jerry Gilfoyle and I were just awarded an NSF grant to buy a new computing cluster.  In the past, my students and I have mostly worked on problems that could be attacked with ordinary desktop computers.  This grant means that we’ll be able to go after more computationally intensive problems.  It also means I’ll have to learn about supercomputing techniques.  Fortunately, Jerry’s very experienced at this.

This has been a good funding year for me: I submitted three NSF proposals, and all three were funded. That’s at least partly due to the federal stimulus bill: only one of the three is officially stimulus money, but no doubt all the stimulus money washing around freed up more non-stimulus money for other grants.

Correction: Actually, two out of the three, including the computing cluster, are stimulus funds.  I’m nothing if not shovel-ready.

Self-promotion

Thursday, July 2nd, 2009

 Our local public radio station aired a short interview with me about an NSF grant I was awarded recently.

I don’t know whether the interviewer is aware of what I wrote about a previous piece he did; I hope not.  Needless to say, I like the piece about me better.

Planck is on its way

Friday, May 15th, 2009

Successful launch yesterday.

Andrew Hearin ’03

Tuesday, May 5th, 2009

Like most academics, I obsessively keep track of who’s citing my work.  As a result, this paper caught my eye today.  (If that link doesn’t work, try this one.)  The lead author is a UR alumnus and winner of both of the physics departments main awards in his senior year.  During my first year here, I taught him in an independent study course on relativity.  He went off to graduate school in mathematics, but he later saw the light and came back to physics.

I haven’t read the paper in detail yet, but from the abstract it looks like a very nice piece of work (in addition to having the good taste to cite me). Congratulations, Andrew!

Redshifts

Tuesday, April 14th, 2009

My paper with Hogg on the interpretation of the cosmological redshift has been officially accepted by the American Journal of Physics.  Here’s the final version.  It’s changed in a bunch of small ways from the previous versions, but the basic argument is still the same.