The Cosmic Cocktail: Three Parts Dark Matter

Cosmic Cocktail: Three Parts Dark Matter [ 2014 ]Quite a few books have seemed good at the beginning but at the end, they just haven’t pass my (not very high) threshold of recommending.  But I can recommend this one as long as one can get past the author’s ego 🙂

After reading this book, one’d be very up-to-date about the current status of the Dark Matter searches as well as Dark Energy and other astrophysical / cosmological matters.  Though the book seems to have been written in an effort to educate the general public, the author has delved a bit deeper into the matters of Dark Matter and also Dark Energy (to slightly less extent).   I’ve found the Chapters 7 & 8 the most informative for me.  When I have been listening to seminars about Dark Matter searches, I’ve sometimes found them quite confusing as the experiment results are often contradictory to each other.  The comparison plots with so many experimental results all in one (in various colors) are very difficult to digest.  But this book is effectively like nice colleagues giving us lectures summarizing the search results of the Top quark (in ~1995’s) or the Higgs boson (in recent years).   I’ve also learnt some tidbits here or there in the last chapter (Chap. 9), not to mention the “dark star” which I probably have never really/seriously heard of and might explain the origin of those supermassive black hole with millions or billions of Solar masses.

Excluding the pages of Notes/Index, this book is only a bit more than 200 pages, certainly easier to read than Roger Penrose’s >1000-page “The Road to Reality”.  I don’t remember that I’ve heard of the author’s name before reading this book.  Apparently, she’s a professor & theoretical astrophysicist in the U. of Michigan and she’s introduced her contributions quite fully throughout this book.  From my judgment, her most significant contribution was probably her calculations with 2 other collaborators for the rates of WIMP scattering off various target materials, which has led to the start of the Dark Matter direct searches (p.131-134).  I’ve learnt that for spin-independent WIMP-nucleus interactions, the rate is amplified by A2 where A is the atomic mass or even A4 for nuclei lighter than the WIMP (p. 134-5).  But for spin-dependent scattering, there is no such factor and “a WIMP interacts only with the total spin of the nucleus” (1st sentence of the 2nd paragraph on p.135).

Dark Matter searches have been going on for years and the author has thoughtfully and interestingly divided a dark matter project into 5 stages (p. 141).  To me, dark matter project is like a conglomeration of physicists from the fields of astronomy, particle physics and condensed matter physics.  I’ve always only had a vague impression of what they’ve been doing and often assumed that they were doing the impossible.  This book has modified my impression quite substantially and though I may not be as optimistic as the author, I won’t be surprised that they might have a breakthrough in a few years.  But Dark Energy is a more difficult matter.  I remember Frank Wilczek has said that it’s the problem for the next generation in a colloquium in our Lab. a few years ago.  And of course, this kind of Standard Model of Cosmology (with Dark Matter and Dark Energy) assuming General Relativity’s validity to infinity can be totally wrong and we may need another revolution before we make real progress.

A few noteworthy points in Chap. 8: Dark Matter experiments of DAMA, Cogent and CRESST seemed to favor the evidence of WIMP whereas CDMS, XENON and LUX, up to early 2014 (I guess), seemed to have shown null results.  DAMA (famous for its annual modulation as predicted by the author and her collaborators) apparently has refused to share their data with outsiders, which makes the community skeptical (last paragraph on.151).  The indirect search in the South Pole or the space have generally found no evidence of WIMP so far.  10 GeV WIMP has been mentioned quite a bit in this book but the fact that LHC and other accelerator experiments have never seen such a not-so-heavy particle makes me personally very skeptical of its existence.

I like reading about personal things mixed with scientific discussion.  Eg. I still remember what Peter Woit has told me about Schrodinger’s personalities in his book of “Not Even Wrong”.  In this book, the personal stories in the middle of all the researches are often interesting.  Eg. two of the four co-authors of their paper (on decaying vacuum energy) has included her former fiancé and her then-fiancé (lines 5-6 of p.203) !!   She was originally an experimental particle physics graduate student in Columbia U.  She told us that her first task was to check 1000 phototubes, having to remove input cables and then replace them.  This has immediately reminded me of my friend who came to Fermilab as a gradudate student of the same Columbia U.  His advisor (our senior colleague in Dzero) told him to check hundreds (?) of our Fermilab-designed IC chips — though boring, it’s somewhat easier than the author’s task as my friend has just needed to put each chip into a socket and check whether a LED lit up.  My friend somehow felt frustrated and gave up on physics research totally soon afterwards.  But this author didn’t !  Now, I feel that it’s like an apprentice test that one has to pass before you can be a particle physics graduate student in Columbia U. … Hahaha … The advantage or luck of the author over my friend was that she knew how to drive.  When she drove to U. of Chicago to look for acting classes (!) — lines 2-3 of p.4, she has somehow ended up signing up for a cosmology class which has changed her life.  Subsequently, she left Columbia U. for U. of Chicago to work with David Schramm in theoretical astrophysics.

Nevertheless, her skills of intertwining physics with personal stories may not have achieved the optimum.  It’s obvious that she’s mentioned her contributions whenever there was a chance, and at times, you cannot but feel that she’s just wanted to brag even though the stories might not really add anything to the book.  Like on p.52 (4th line  from the bottom), when the COBE result was announced (and she’s not a member of the COBE collaboration), she wrote “At the University of Michigan, I convened a meeting of the faculty to tell them about this important result”.  If I were the editor, I’d have crossed out this sentence.  Because it doesn’t even add any glory to herself, almost like I told people that I drove to work or ate lunch that day.  Another example is on p.172-3 when she received an honorary doctorate from Stockholm University in 2012.  But there is no joke to laugh at or anything, except probably to have the chance to praise herself as “one of the world’s best known astroparticle physicists” used in the nomination.  Near the end, though not much to add to the scientific content, the author seemed to feel compelled to tell us and very proud of what she said in the annual World Science Festival when 3 women represented “dark matter” and 3 men represented “dark energy” : “Dark matter is attractive while dark energy is repulsive.” (on p.213).  I guess there are physics point of view and also that of sexism.

The least appealing chapter to me is Chap. 6 when the author discusses the Higgs discovery and I guess she probably has grabbed quite a bit from the websites and/or literature of CERN and the LHC experiments.  It’s one of the very few places that I’ve felt more familiar on certain subjects than she is.

p.85 (lines 22-23): “2009” in the sentence “The Tevatron was the premier high-energy physics laboratory until it was shut down in 2009 …” should really be 2011 as Tevatron was shut down on Sept. 30, 2011.  p.92 (8th line from the bottom): “… a radius of 3 kilometers (5 miles) …” has the obvious mistake that 3 km is not 5 miles.  p.124 (lines 16-17): “… the least powerful of the four fundamental forces, the weak force” and similarly on p.130 (4th line): “weak interactions, the least powerful of the four forces” are erroneous as in general the gravitational force should be the least powerful !


About kinyip

An experimental particle physicist ...
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