Category: Science

How Deep Does Veritasium’s Bullet Go?

Screen shot from the video of the block being shot into the air.

After 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… Continue reading How Deep Does Veritasium’s Bullet Go?

Laser-Cooled Atoms: Helium

L to R, an image from Up (taken from this blog post), the helium trap at the University of Amsterdam, and an electron shell diagram of He from Wikimedia.

Element: 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… Continue reading Laser-Cooled Atoms: Helium

Eddington, Neutrinos, and the Changing of Meaning by Context

I’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… Continue reading Eddington, Neutrinos, and the Changing of Meaning by Context

Point Sources and Towers: “Multiaxis Inertial Sensing with Long-Time Point Source Atom Interferometry”

Schematic of the interferometer measurement, Fig. 1 from the paper discussed in the text.

A 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… Continue reading Point Sources and Towers: “Multiaxis Inertial Sensing with Long-Time Point Source Atom Interferometry”

Laser-Cooled Atoms: Rubidium

L to R: Rubidium metal, the first Rb BEC, and an electron shell diagram of Rb. Images from wikimedia and NIST.

Element: 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… Continue reading Laser-Cooled Atoms: Rubidium

Laser-Cooled Atoms: Sodium

L to R, sodim metal, sodium optical molasses, and an electron shell diagram of sodium. Images from Wikimedia/ NIST.

Element: 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… Continue reading Laser-Cooled Atoms: Sodium

Know Your Laser-Cooled Atoms

A somewhat outdated slide highlighting elements that have been laser cooled.

At 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… Continue reading Know Your Laser-Cooled Atoms

Tools of the Cold-Atom Trade: Atom Detection and Imaging

Sample images with and without atoms, and the subtracted image used to study BEC. From an old talk.

This 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… Continue reading Tools of the Cold-Atom Trade: Atom Detection and Imaging

Bose Condensation of Coffee?

Coffee and a notebook, from a fun Physics Stack Exchange discussion.

Writing 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… Continue reading Bose Condensation of Coffee?

Tools of the Cold-Atom Trade: Evaporative Cooling

The signature image of a cloud of rubidium atoms crossing the BEC transition, from the Nobel Prize site.

In 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… Continue reading Tools of the Cold-Atom Trade: Evaporative Cooling