Physics
drorzel | August 14, 2013We're getting toward the end of the cold-atom technologies in my original list, but that doesn't mean we're scraping the bottom of the barrel. On the contrary, the remaining tools are among the most important for producing and studying truly ultra-cold atoms.
Wait, isn't what we've been talking about cold enough? There is, as always, more art than science in the naming of categories of things. "Cold" and "ultra-cold" get thrown around a lot in this business, and the dividing line isn't quite clear. Very roughly speaking, most people these days seem to use "cold" for the microkelving scale…
drorzel | August 13, 2013Today's dip into the cold-atom toolbox is to explain the real workhorse of cold-atom physics, the magneto-optical trap. This is the technology that really makes laser cooling useful, by letting you collect massive numbers of atoms at very low temperatures and moderate density.
Wait a minute, I thought we already had that, with optical molasses? Doesn't that make atoms really cold and stick them in space? Molasses does half the job, making the atoms really cold, but it doesn't actually confine them. The photon scattering that gives you the cooling force and Doppler cooling limit produces a "…
catdynamics | August 12, 2013Is the general audience "black board" talk at KITP today, giving an overview of the quantitative approches to morphogenesis program currently unverway.
Symmetry breaking and mechanics.
The Kavli Institute for Theoretical Physics runs parallel programs and currently there is a biophysics program New Quantitative Approaches to Morphogenesis concurrent with the astrophysics program on A Universe of Black Holes
During each multi-week program there is a black board lunch talk, for all members of KITP, giving an overview of the theme of the program or some key aspect of it. The talk is intended to…
drorzel | August 12, 2013Via a retweeted link from Thony C. on Twitter, I ran across a blog post declaring science a "bourgeois pastime." The argument, attributed to a book by Dierdre McCloskey is that rather than being at the root of economic progress, scientific advances are a by-product of economic advances. As society got more wealthy, it was able to direct more resources to science, which made great advances possible.
And, you know, if you're looking to make a bold and contrarian argument, you can certainly do that. Unfortunately, the bit quoted from McCloskey as an illustration of the power of the argument is:…
catdynamics | August 9, 2013Lawrence Krauss just wrote an interesting letter: "Higgs Seesaw Mechanism as a Source for Dark Energy" - Krauss & Dent, PRL 2013
in it he argues for a see-saw mechanism in the Higgs sector which gives a natural scale for dark energy which is small, as observed.
The key point is that the energy scale is suppressed by
λ ~ (mH/mX)2)
where mH is the Higgs scale and X is some unification scale with mX >> mH
as a bonus you may expect a new long range weak force to go with the new physics.
Potentially interesting speculation.
Many moons ago, I wrote almost massless world on this here very…
catdynamics | August 9, 2013Final day of the "A Universe of Black Holes" workshop with a session: "Modeling Black Hole Accretion and Outflows" - all MHD sims today...
Chris Reynolds (Univ. of Maryland) starts with - The temporal variability of model accretion disks
Had to miss this. Go check it online, Chis gives fab talks.
Julian Krolik (JHU) "The Bardeen-Petterson effect in magneto-hydrodynamics"
Krolik demonstrated large Reynolds stress...
cf " Alignment of supermassive black hole binary orbits and spins" - Miller & Krolik 2013
Jim Stone (Princeton) "New magneto-hydrodynamic simulations of radiation pressure…
esiegel | August 8, 2013"What was most significant about the lunar voyage was not that men set foot on the Moon, but that they set eye on the Earth." -Norman Cousins
What would life on Earth be like without the Moon?
Our nearest neighboring body in the cosmos has a profound effect on us. It's helped not only shape our evolution, biologically, but has shaped the entire evolution of our planet. Created some 4.5 billion years ago -- when our planet and Solar System were still in their infancy -- when a roughly Mars-sized planetoid crashed into a young proto-Earth, the Moon has been our companion-in-orbit ever since.…
catdynamics | August 8, 2013The workshop on Massive Black Holes at the Kavli Institute for Theoretical Physics continues with today's session on "Co-evolution of black holes and their host galaxies".
I continue a semi-liveblog of the proceedings.
As before, talks are online here - podcast, audio and video options; pdfs of talk slides added as speakers get them in.
First up is Yohan Dubois (IAP / Oxford Univ.) - on "AGN feedback in adaptive mesh refinement cosmological simulations" - high res AMR simulations of massive gas rich halos at z ~ 5-6
make some assumptions about SMBH formation and accretion efficiency on small…
drorzel | August 8, 2013This topic is an addition to the original list in the introductory post for the series, because I had thought I could deal with it in one of the other entries. Really, though, it deserves its own installment because of its important role in the history of laser cooling. Laser cooling would not be as important as it is now were it not for the fact that cooling below the "Doppler limit" in optical molasses is not only possible, but easy to arrange. That's thanks to the "Sisyphus cooling" mechanism, the explanation of which was the main reason Claude Cohen-Tannoudji got his share of the 1997…
catdynamics | August 7, 2013We are back to "Massive Black Holes"
Happy Birthday Alberto!
Alberto Sesana (AEI) leads off with "Probing massive black holes with space-based interferometry and pulsar timing"
starts with overview of gravitational radiation - characteristic frequencies, amplitudes, timescales
Baby Black Holes - up for adoption, get collectible adoption certificates with a picture of your very own baby black hole, or one much like it
- this is eLISA's plan for fundraising...
Ed - ok it is real it is an etsy thing and they are ***adorable***
quick pitch for eLISA/NGO
Ed: New improved eLISA web page - see…
drorzel | August 7, 2013I spent an hour or so on Skype with a former student on Tuesday, talking about how physics is done in the CMS collaboration at the Large Hadron Collider. It's always fascinating to get a look at a completely different way of doing science-- as I said when I explained my questions, the longest author list in my publication history doesn't break double digits. (I thought there was a conference proceedings with my name on it that got up to 11 authors, but the longest list ADS shows is only eight). It was a really interesting conversation, as was my other Skype interview with a CMS physicist.…
catdynamics | August 6, 2013the Massive Black Holes workshop at KITP continues, with another Black Hole Pairs session
Mike Eracleous kicks off: Observational Searches for Close Supermassive Binary Black Holes
emission line signatures of close (~ sub-parsec) supermassive binary black holes
cf "A Large Systematic Search for Recoiling and Close Supermassive Binary Black Holes"
and "Emission Lines as a Tool in Search for Supermassive Black Hole Binaries and Recoiling Black Holes"
look for single line emitters, broad emission line displaced from narrow emission lines - displacement is ~ 1,000 km/sec
orbital periods of…
catdynamics | August 6, 2013"Massive black hole pairs" is the topic of today's session at the BHOLES13 workshop at KITP
Talks are online here - note that slides of talks show up later as speakers get their act together and send in slides
Monica Colpi (Milan) starts the session with Formantion of Binary Black Holes in Galactic Nuclei
starts off with good summary of "last parsec" problem and why it is a bit of a red herring
followed by discussion of role of gas at late stage of mergers and summary of sims
new trendy things to do is to look at star formation in situ in outer accretion disks - something must happen, but it…
drorzel | August 6, 2013Last time in our trip through the cold-atom toolbox, we talked about light shifts, where the interaction with a laser changes the internal energy states of an atom in a way that can produce forces on those atoms. This allows the creation of "dipole traps" where cold atoms are held in the focus of a laser beam, but that's only the simplest thing you can use light shifts for. One of the essential tools of modern atomic physics is the "optical lattice," which uses patterns of light to make patterns of atoms.
OK, what do you mean "patterns of light"? Well, remember, light has both wave and…
catdynamics | August 5, 2013and we are back from lunch
J. Johnson (LANL) talking about supermassive stars as seeds for supermassive black holes - going to be getting more technical
supermassive star has a gas mass ~ 105 solar masses (as oppesed to few hundredish solar masses for standard Pop III stars that could provide low mass seeds)
form later than Pop III - maybe ~ 4-500 Myr after Big Bang
something like that may be needed for observed high luminosity quasars at redshift > 6.
radiative feedback, still not doing it right
but are we they doing it well enough...?
argues supermasive star formation common at z ~ 8-12…
drorzel | August 5, 2013One of my colleagues at Union is doing a physics education research project with a summer student, and is using an online survey to collect data. Obviously, the more people respond to the survey, the more scientific it becomes (subject to the limitations imposed by relying on self-selected Internet samples, of course), so I offered to plug it here. Here's the blurb and link:
I'm doing a summer research project at Union College with a student, and I need as many people as possible to fill out a survey that we created. If you complete the survey by 11:59pm (EST) on Sunday, August 11, 2013, you…
catdynamics | August 5, 2013Visiting lovely KITP for the A Universe of Black Holes programme, and specifically the associated "Massive Black Holes: Birth, Growth and Impact" workshop.
As usual the talks will (eventually) be posted on line, both slides and web, but in the mean time I will be semi-transcribing my semi-coherent stream-of-consciousness thoughts on the issues.
And we are off, with new KITP Director Lars Bildsten welcoming the hordes.
As is typical, about half the attendees are noobs and have not visited KITP before.
Are they in for a treat.
Marta Volonteri (IAP), one of the workshop organizers, leads off…
drorzel | August 5, 2013SteelyPalooza came off very well, despite high disaster potential. We were, after all, inviting a dozen five-year-olds plus assorted siblings to our house, on a day when Kate and The Pip were out of commission due to coxsackie virus. Everything went smoothly, though: the kids loved the bouncy-bounce, SteelyKid's playset and playhouse, and the six-person tent we set up out back. They're getting close to an age where they can entertain themselves, so I was even able to enjoy snatches of adult conversation during brief lulls in my hosting duties.
This was, however, thoroughly exhausting, so…
esiegel | August 2, 2013“Faultily faultless, icily regular, splendidly null, dead perfection; no more” -Lord Alfred Tennyson
Ahh, the Standard Model of elementary particles and their interactions. It's right up there with General Relativity -- our theory of gravitation in the Universe -- as the most successful physical theory of all-time.
Image credit: DoE, NSF, LBNL, and CPEP, via http://www.cpepphysics.org/.
While General Relativity describes the relationship between matter-and-energy and spacetime, the Standard Model describes all the known particles in the Universe and how they interact with one another. This…
drorzel | August 2, 2013The Pip is home with coxsackie virus today, and we're having a big party for SteelyKid tomorrow (her fifth birthday is next week), so I'm too busy to do more cold-atom blogging today. So instead, we'll consider one of the great linguistic conundra of modern physics:
The document preparation system LaTeX is pronounced:
This is a purely classical poll, so you can choose one and only one answer, not a quantum superposition of several. And if you choose wrong, everybody will point and laugh. No pressure, though...