Lookin’ For Some Hot Stuff

Hot, hot, hot, hot stuff
hot, hot, hot
hot, hot, hot, hot stuff
hot, hot, hot

– from “Hot Stuff”, by Donna Summer (1979). I refer to not only the physics but the c. 100 oF temperatures we’ve been having here every day recently.

On my way back from the conference, I spotted this book (below left) last Saturday in Foyles (the booksellers) in London1. Quark Gluon Plasma book It is a collection of reprints of a lot of the papers forming the foundations of the physics of the quark-gluon plasma (QGP) idea, going back the early to mid 1970s with such papers as Collins and Perry (Gosh, I had no idea Malcolm was one of the early workers on this idea. He’s much more thought of as associated with black holes, gravity, strings and so forth, ideas which – ironically – have recently turned out to be relevant to the discussions of the physics too. See my recent post, and there are also various popular articles to be found2).

Putting aside the usual ridiculous price that Springer Elsevier charges for books, I found myself in two minds about this book, in view of the surprises being uncovered about the properties of this remarkable state of matter at the RHIC experiment. Is this collection of early papers a useful working tool, or is it now just of historical interest, since many of the basic expectations about the properties of the plasma seem now to be incorrect?

rhic collision of gold ionsWell, after a bit of thought, I decided that the latter view would be way too hasty. First and foremost, on a general level, even if some of the computations in some papers were done in the “wrong” light (it’s a strongly coupled liquid that flows, not a weakly coupled gas of quarks and gluons), much of their content will still be useful in many ways – good and correct calculations last for all time, it is the sense of the words decorating them that may crumble over time. More specifically, one can worry about whether there were assumptions (and approximations based on those) that went into the computations that will render entire works invalid. I’m sure that will be true in some cases, but not all, and even in those cases where this is true, there is still (I find) value in reflecting upon such results too. (Image above right: Snapshot of the particles ejected after one of the RHIC heavy ion collisions.)

[Update: In the comments, Stefan also points out that there are lots of later works in the collection that are of considerable value and remain (to date) the state of the art: For example, papers about the phenomenolgy and analysis of heavy ion collision experiments that are used to deduce the properties of the QGP, whether it be liquid or gas.]

Finally, more reasons to not be hasty center around the fact that the explorations (and surprises) really have only just begun. The strongly coupled liquid phase of the quark-gluon plasma might not persist forever – at much higher temperatures the originally anticipated gas phase (with all the expected properties) could well appear, and then there’d be direct relevance for all those earlier papers. Also, there’s the experimental window afforded by the CERN’s Large Hadron Collider (LHC) yet to come (see the ALICE experiment) – it is to be hoped that we’ll get confirmation of what has been learned at RHIC, and then more information about what lies beyond.

I love the way science works. You never know for sure what ideas will be useful, and in quite what way, until you’ve consulted with Nature.


(And now I’ve got that song stuck in my head, I’m off to buy the album.)


  1. …After having a nice lunch there with regular commenter Candace and her partner Paul. Good to meet face to face with some of the readers of the blog from time to time. [return]
  2. There’s also an article by Tim Folger in February’s Discover magazine (2007) on the issue. (I borrowed the above RHIC collision image from it.) Overall it is a nice layperson’s guide, with interviews and so forth, but beware (for example) of the statements about how close to QCD (the standard theory of nuclear) the string theory computations currently can get. There’s still a lot to learn and a lot to do, and we’re still surprised about how well some of the things are working, and it is not yet understood why. This has to change before we can be quite so bold about what we’re doing. See my earlier blog post for more discussion and thoughts. [return]


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