D-Brane Fun!

image Turns out that it still a lot of fun to lecture about string theory and D-branes! (The latter are an important type of extended object, generalizing membranes, that have been very useful in theoretical physics for the last 20 years. — My goodness, it has been 20 years since Joe Polchinski first demonstrated their importance for string duality!) The students at the Latin American String School here in Mexico City seem to be very engaged and enjoying themselves. Although I was having fun I was also not without a presentation error or two brought on by […] Click to continue reading this post

Thomas and Fermi

thomas-fermiThe other day the Thomas-Fermi model (and its enhancements by Dirac and others) wandered across my desk (and one of my virtual blackboards as you can see in the picture) for a while. Putting aside why it showed up (perhaps I will say later on, but I cannot now), it was fun to delve for a while into some of these early attempts in quantum mechanics to try to understand approximation methods for treating fairly complicated quantum systems (like atoms of various sizes). The basic model showed up in 1927, just a year after Schrodinger’s […] Click to continue reading this post

Goodbye Nambu

nambu-gotoOne of the towering giants of the field, Yoichiro Nambu, passed away a short while ago, at age 94. He made a remarkably wide range of major (foundational) contributions to various fields, from condensed matter through particle physics, to string theory. His 2008 Nobel Prize was for work that was a gateway for other Nobel Prize-winning work, for example 2012’s Higgs particle work. He was an inspiration to us all. Here’s an excellent 1995 Scientific American piece (updated a bit in 2008) about him, which nicely characterises some of his style and contributions, with comments from several notable physicists. Here is a University of Chicago obituary, a Physics World one, one by Hirosi Ooguri, and one from the New York Times. There are several others worth reading too.

Since everyone is talking more about his wonderful work on symmetry-breaking (and rightly so), I’ve put up (on the board above) instead the Nambu-Goto action governing the motion of a relativistic string (written with a slight abuse of notation). This action, and its generalisations, is a cornerstone of string theory, and you’ll find it in pretty much every text on the subject. Enjoy.

Thank you, Professor Nambu.

-cvj Click to continue reading this post

Earth Not Swallowed!

So, here we are. Still in existence. Hurrah!

cern_LHC_tunnelThe Large Hadron Collider (image right is courtesy of CERN) started a new phase of experimental work today, colliding particles at double the energy it was working at a few years back when the Higgs was discovered. By time I was making breakfast and checking email, their live blog, etc., this morning, it was clear that (contrary to fears expressed by some) the LHC had not created a black hole that swallowed the earth, nor had it created some sort of strange chunk of new vacuum that condensed that of the entire universe into a new phase. (Or if it did either of those things, the effects are hardly noticeable!!)

As I keep emphasising (actually I’ll be talking about this to a puppet character on a TV show tomorrow too – details later) the LHC (or any of the particle collision experiments we’ve ever done) is not doing anything that Nature does not do routinely right here at earth (and most times way more violently and […] Click to continue reading this post

‘t Hooft on Scale Invariance…

Worth a read: This is ‘t Hooft’s summary (link is a pdf) of a very interesting idea/suggestion about scale invariance and its possible role in finding an answer to a number of puzzles in physics. (It is quite short, but think I’ll need to read it several times and mull over it a lot.) It won the top Gravity Research foundation essay prize this year, and there were several other interesting essays in the final list too. See here.

-cvj Click to continue reading this post

Excellent Witten Interview!

ooguri_witten_kavli_ipmuI just learned of an excellent interview with Edward Witten, one or our field’s grandmasters, or rather: the grandmasters’ grandmaster. I strongly recommend reading it. (This is for technically equipped people working in the field, most likely – I believe that it is not intended for the general public, although you are welcome to read it too!)

There’s a lot of discussion (of among other things like his current work) of that golden period during the 1990s that I had the privilege to work in during my postdoc years (some of them under the guidance of Witten) that remain one of […] Click to continue reading this post

Sometimes there is Smoke without Fire

…Or at least, not always the fire you’re looking for. So, as suspected for several months now, the signal seen by BICEP2 experiment and dubbed “a smoking gun” type of direct evidence for cosmic inflation (for which we have lots of strongly suggestive indirect evidence, by the way) is likely an artefact of the effects of galactic dust. I spoke about this in a post a while back, so I won’t repeat myself here. What everyone has been waiting for has been the results of a joint analysis between the BICEP2 people and the ESA’s Planck mission. The Planck satellite, you may recall from reading here or elsewhere, is also designed toPlanck_view_of_BICEP2_field_node_full_image_2 carefully study the polarisation of the cosmic microwave background (the earliest light to shine in the universe), and so can (through thorough analysis of the effects of dust that it has measured independently) help rule in or out whether there is a signal. Planck studies essentially the whole sky, not just the patch that BICEP2 was carefully looking at, and one of […] Click to continue reading this post

The Visitors

jim_gates_talk_usc_26_jan_2015_smallYesterday I sneaked on to campus for a few hours. I’m on family leave (as I mentioned earlier) and so I’ve not been going to campus unless I more or less have to. Yesterday was one of those days that I decided was a visit day and so visit I did. I went to say hi to a visitor to the Mathematics Department, Sylvester James Gates Jr., an old friend who I’ve known for many years. He was giving the CAMS (Center for Applied Mathematical Sciences) distinguished lecture with the title “How Attempting To Answer A Physics Question Led Me to Graph Theory, Error-Correcting Codes, Coxeter Algebras, and Algebraic Geometry”. You can see him in action in the picture above.

I was able to visit with Jim for a while (lunch with him and CAMS director Susan Friedlander), and then hear the talk, which was very interesting. I wish he’d had time to say more on all the connections he mentioned in the title, but what he did explain sounded rather interesting. It is all about the long unsolved problem of finding certain kinds of (unconstrained, off-shell) representations of extended supersymmetry. (Supersymmetry is, you may know, a symmetry that […] Click to continue reading this post

Time to Plan…

Happy New Year! So, it is the second of January. You’ve spent all of the day yesterday recovering from the euphoria (and perhaps revelry) of New Year’s Eve, and so today it is time for the traditional next thing on the new calendar: Planning what you’ll do next New Year’s Eve, of course!

acp_stillBefore doing that however, if you are a research physicist, I’d like to invite you to consider doing something else: Plan your Summer research travel. What I am really trying to do is to make you aware that the end of this month is the deadline for applying to attend the Aspen Center for Physics during some period inside the Summer operating dates Memorial Day (in May) to around Labor Day (September). Now, a lot of people (too many, in my and the opinion of others who care about the ACP) just assume that the place is not for them, for a number of reasons that are really not good ones. So let me address one or two quickly right now.

First, it is not an old boy’s country club. It is for everyone, working in all* fields of physics. Don’t apply and you have zero chance of getting in. Apply and there is […] Click to continue reading this post

Black Hole Slides!


Since people were asking for copies of my slides from my colloquium chalkboard-style talk on black holes and the things I call “holographic heat engines” last month at Harvey Mudd College, I decided to export them as a movie. You can find it on YouTube. Link below. It was a 50 minute talk, but all the builds are compressed down to a 6 minute file! I try to keep the bulk of the narrative in my head and speak it with the slides as visual aids (instead of writing everything on the slides as is often the practice) and so I do not know […] Click to continue reading this post