Physics
drorzel | August 27, 2013Element: Francium (Fr)
Atomic Number: 87
Mass: Numerous isotopes ranging in mass from 199 amu to 232 amu, none of them stable. The only ones laser cooled are the five between 208 amu and 212 amu, plus the one at 221 amu.
Laser cooling wavelength: 718 nm
Doppler cooling limit: 182 μK.
Chemical classification: Alkali metal, column I in the periodic table. The heaviest known alkali, it's presumably metallic in appearance, if you could ever get enough of it together to look at.
Other properties of interest: Francium has no stable isotopes, and the longest lifetime of any of its isotopes is around…
catdynamics | August 26, 2013The Kavli Institute for Theoretical Physics is currently holding a "Rapid Response Workshop" on Black Holes: Complementarity, Fuzz, or Fire?, August 19-30.
Organizers: Raphael Bousso (UCB), Samir Mathur (OSU), Rob Myers (PI), Joe Polchinski (KITP), Lenny Susskind (Stanford)
The lunch talk today is Lenny Susskind "Inside Black Holes"
That talk will be available on video, audio and podcast feeds soon
The general session talks from the Fuzz, or Fire are available as they become available at the link above.
drorzel | August 26, 2013In one of those Information Supercollider moments, two very different articles crossed in my social media feeds, and suddenly seemed to be related. The first was this New York Post piece by a college essay consultant:
Finally, after 15 or so years of parents managing every variable, there comes the time when a student is expected to do something all by herself: fill out the actual application. Write an essay in her own voice.
By this point, our coddled child has no faith in her own words at all. Her own ideas and feelings, like a language she has not practiced, have fallen away.
Her parents…
drorzel | August 26, 2013Element: Strontium (Sr)
Atomic Number: 38
Mass: Four stable isotopes, ranging from 84 to 88 amu
Laser cooling wavelength: Two different transitions are used in the laser cooling of strontium: a blue line at 461 nm that's an ordinary sort of transition, and an exceptionally narrow "intercombination" line at 689 nm.
Doppler cooling limit: 770 μK for the blue transition, below a microkelvin for the red. The Doppler limit for the red line turns out not to be all that relevant, as other factors significantly alter the cooling process.
Chemical classification: Alkaline earth, column II of the…
esiegel | August 23, 2013“People say sometimes that Beauty is superficial. That may be so. But at least it is not so superficial as Thought is. To me, Beauty is the wonder of wonders. It is only shallow people who do not judge by appearances. The true mystery of the world is the visible, not the invisible.” -Oscar Wilde
Beyond the planet Earth, beyond all the stars in the night sky, and beyond the Milky Way galaxy, there's literally an entire Universe out there.
Image credit: R. Jay GaBany, of http://cosmotography.com/.
The farther away we're able to look, the more galaxies we're able to see. As far as our…
drorzel | August 22, 2013When I wrote up the giant interferometer experiment at Stanford, I noted that they've managed to create a situation where the wavefunction of the atoms passing through their interferometer contains two peaks separated by almost a centimeter and a half. This isn't two clouds of atoms each definitely in a particular position, mind, this is a wavefunction representing a bunch of atoms that are each partly in two places at the same time , separated by 1.4 centimeters.
I emailed Mark a link to the post, and in his reply he said that they've increased that to about 4cm (which is just a matter of…
drorzel | August 22, 2013Element: Xenon (Xe)
Atomic Number: 54
Mass: nine "stable" isotopes, masses from 124 to 136 amu. Xenon-136 is technically radioactive, but with a half-life of a hundred billion billion years, so, you know, it's pretty much stable.
Laser cooling wavelength: 882 nm
Doppler cooling limit: 120 μK
Chemical classification: Noble gas, part of column VIII of the periodic table. Doesn't react with anything, so poses much less danger to scientists than any of the alkalis, though it has, at times, been used as an anesthetic, and Will Happer's group at Princeton has a funny story about a student's…
drorzel | August 21, 2013After a couple of very productive days where I closed my Twitter tab because it was too freakin' annoying to read, I checked in briefly Wednesday morning, and found Rhett Allain and Frank Noschese discussing this Veritasium bullet-in-block experiment:
Tom at Swans On Tea offers some analysis, and Rhett offers a video response doing out some of the math:
I basically agree with their explanations, and that should have been that, except that in his discussion Rhett mentioned that the bullet probably doesn't go as far into the spinning block, which prompted Frank to ask whether you could…
drorzel | August 21, 2013Element: Helium (He)
Atomic Number: 2
Mass: two stable isotopes, 3 and 4 amu.
Laser cooling wavelength: 1083 nm
Doppler cooling limit: 38 μK
(It should be noted, though, that despite the low temperature, laser-cooled helium has a relatively high velocity-- that Doppler limit corresponds to an average velocity that's just about the same as for sodium at 240 μK. This is because temperature is a measure of kinetic energy, and helium is much, much lighter than any of the other laser-cooled elements.)
Chemical classification: Noble gas, part of column VIII of the periodic table. Doesn't react with…
drorzel | August 21, 2013I'm writing a bit for the book-in-progress about neutrinos-- prompted by a forthcoming book by Ray Jaywardhana that I was sent for review-- and in looking for material, I ran across a great quote from Arthur Stanley Eddington, the British astronomer and science popularizer best known for his eclipse observations that confirmed the bending of light by gravity. Eddington was no fan of neutrinos, but in a set of lectures about philosophy of science, later published as a book, he wrote that he wouldn't bet against them:
My old-fashioned kind of disbelief in neutrinos is scarcely enough. Dare I…
esiegel | August 20, 2013"[S]cience is not a consumption good to be expanded in good times and restricted in bad times. The doing of science as well as the supporting of science is an expression of faith in the future. It would have been possible to have told Newton and Faraday, Maxwell and Einstein, Bohr and Heisenberg that, given the poverty and squalor around them, their research were luxuries which could not be afforded. To have done so would be to destroy the economic c progress that came out of their science and which was the main factor in relieving that poverty and squalor. We seem to be on the verge of…
drorzel | August 20, 2013A little over a year ago, I visited Mark Kasevich's labs at Stanford, and wrote up a paper proposing to use a 10-m atom interferometer to test general relativity. Now, that sounds crazy, but I saw the actual tower when I visited, so it wasn't complete nonsense. And this week, they have a new paper with experimental results, that's free to read via this Physics Focus article. Which might seem to make me blogging it redundant, but I think it's cool enough that I can't resist.
OK, dude, "Multiaxis Inertial Sensing with Long-Time Point Source Atom Interferometry" is not the sexiest title in the…
drorzel | August 20, 2013Element: Rubidium (Rb)
Atomic Number: 37
Mass: two "stable" isotopes, 85 and 87 amu (rubidium-87 is technically radioactive, but it's half-life is 48 billion years, so it might as well be stable for atomic physics purposes.
Laser cooling wavelength: 780 nm
Doppler cooling limit: 140 μK
Chemical classification: Alkali metal, column I of the periodic table. Like the majority of elements, it’s a greyish metal at room temperature. Like the other alkalis, it’s highly reactive, and bursts into flame on contact with water, even more so than sodium (in general, the alkalis get more violently reactive…
drorzel | August 19, 2013Element: Sodium (Na)
Atomic Number: 11
Mass: one stable isotope, 23 amu
Laser cooling wavelength: 589 nm
Doppler cooling limit: 240 μK
Chemical classification: Alkali metal, column I of the periodic table. Like the majority of elements, it's a greyish metal at room temperature. Like the other alkalis, it's highly reactive, and bursts into flame on contact with water. For this reason, all physicists working with sodium have True Lab Stories about accidentally blowing stuff up with it.
Other properties of interest: Scattering length of around 80 a0; Feshbach resonance at around 900 G.
History:…
drorzel | August 19, 2013At the tail end of the cold-atom toolbox series, I joked about doing a "trading card" version shortening the posts to a more web-friendly length. In idly thinking about this, though, it occurred to me that if one were going to have cold-atom trading cards, it might make more sense to have them for the atoms, rather than the techniques. And having just devoted many thousands of words to technique, I don't really feel like trying to cut those down more, but atoms...
The "featured image" up top is a slide from my laser cooling lectures for our first-year seminar class. Elements outlined in red…
esiegel | August 16, 2013"On a cosmic scale, our life is insignificant, yet this brief period when we appear in the world is the time in which all meaningful questions arise." -Paul Ricoeur
Ask anyone who's looked up at a dark sky on a clear, moonless night, and you'll immediately hear tales about how incomprehensibly vast the Universe is.
Image credit: Randy Halverson, flickr user dakotalapse, from http://dakotalapse.com/.
But what you're looking at isn't much of the Universe at all. In fact, practically every point of light you see, including the vast swath of stars too dim to individually resolve, comes from…
drorzel | August 16, 2013This is probably the last trip into the cold atom toolbox, unless I think of something else while I'm writing it. But don't make the mistake of assuming it's an afterthought-- far from it. In some ways, today's topic is the most important, because it covers the ways that we study the atoms once we have them trapped and cooled.
What do you mean? They're atoms, not Higgs bosons of something. You just... stick in a thermometer, or weigh them, or something... OK, actually, I have no idea. They're atoms, yes, but at ultra-low temperatures and in very small numbers. You can't bring them into…
drorzel | August 15, 2013Writing up the evaporative cooling post on cold atom techniques, I used the standard analogy that people in the field use for describing the process: cooling an atomic vapor to BEC is like the cooling of a cup of coffee, where the hottest component particles manage to escape the system of interest, and what's left behind is colder. The departing atoms or coffee molecules carry off more than the average energy per particle, leaving a lower average energy (and thus a lower temperature) for the remainder.
A question that sometimes comes up when I talk about this is how you can possibly use this…
drorzel | August 15, 2013In our last installment of the cold-atom toolbox series, we talked about why you need magnetic traps to get to really ultra-cold samples-- because the light scattering involved in laser cooling limits you to a temperature that's too high for making Bose-Einstein condensation (BEC). This time out, we'll talk about how you actually get to those ultra-cold temperatures.
What do you mean? I assumed it was just part of the trapping process? No, because the forces involved in magnetic trapping are like those involved in optical dipole traps. In physics jargon, they're "conservative" forces, which…
esiegel | August 14, 2013"It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge." -Enrico Fermi
As you probably know, the Large Hadron Collider -- site of discovery of the last fundamental particle in the Standard Model, the Higgs Boson -- is the most energetic particle accelerator in the history of humankind. When the upgrades it's currently undergoing are complete, it will reach collision energies of 14 TeV.
Image credit: CERN / LHC, add-on created by http://www.panglosstech.com/.
The way this happens is that protons are circulated in a giant ring, underground, that'…