With a request to place a red hot nickel ball on a block of ice, and also to satisfy my own curiosity, I do just that
It appears to be warmer than that — it turns red-hot about a diameter in to the block of ice
Category Archives: Physics
Cool Physics at Room Temperature
Bose-Einstein condensate created at room temperature
Ayan Das and colleagues have now used a nanoscale wire to produce an excitation known as a polariton. These polaritons formed a Bose-Einstein condensate at room temperature, potentially opening up a new avenue for studying systems that otherwise require expensive cooling and trapping.
The Tell-Tale Strontium Heart
Beating heart of a quantum time machine exposed
A little vacuum system porn for you.
The lasers are fired through three of the glass shafts emanating from the cube, but must be carefully directed out of the other side to prevent them scattering within the clock, which is why there are six shafts in total.
However:
… the beating heart of a time machine! Or “clock”, as most people call them …
… or possibly “frequency standard” as I like to pedantically point out. Though this being an ion clock, it can probably run for extended periods of time, and one might actually be able to say it’s running as a clock.
I also find the description of the six arms to be curious; normally, trapping schemes send light in both directions. It’s true you don’t want the light scattered in the chamber, but the description implies there are only three, and none of the NPL write-ups I have read say anything about a novel cooling geometry requiring only three beams.
Aaand it gives the Sr transition frequency as an exact number. There should be an uncertainty, since it’s the Cs hyperfine transition which is defined.
So read it for the picture, and not so much the article.
Supersonic Ping Pong Ball
What happens when a ping pong ball moving at supersonic speed hits a paddle? Here’s a video explaining the physics of how a ping pong ball can be accelerated to supersonic speed along with some clips showing test shots.
She Wears, and Doesn't Wear, Quantum Short Shorts
We sought videos no longer than three minutes that were inspired by quantum physics. We made this challenge: Does the idea of a quantum multiverse fill your head with stories? Can you picture a quantum superposition? We don’t want you to explain quantum physics to us: instead, show us something of how it makes you think about the world.
I haven’t watched any yet, though. Caveat Emptor.
Feynman and the Shuttle
Richard Feynman and the Space Shuttle Challenger investigation
Short video and an excerpt from his report at the link.
Clear thought, clear writing. Feynman was perhaps the most efficient mechanism ever conceived for consuming complexity and pumping out simplicity.
Amen to that, though we have some good ones today, too.
Another Path to Degeneracy
One of my colleagues mentioned this in group (as in meeting, not therapy) — research that has formed a Bose-Einstein Condensate directly from laser cooling and trapping: Laser cooling to quantum degeneracy
In order to form a BEC, you have to get enough atoms together in a potential well, and with a low enough energy in order to trigger the transition that leaves the bulk of them in the ground state (that’s the condensation). Normally, atoms under such confinement will distribute themselves among the various quantized energy states, but under the proper circumstances the condensation will happen. The tipping point occurs when the phase space density — the number of atoms in a volume defined by the cube of the deBroglie wavelength (which is momentum dependent, so it’s related to the kinetic energy) is above some critical value. The trick, then, is getting enough atoms cold enough and confined such that their deBroglie waves are overlapping.
Up until now, the path to BECs have involved a stage of magnetic trapping, but since magnetic traps are shallow (energetically speaking) you laser-cooled and trapped atoms to load into the magnetic trap. The trap “walls” were then lowered, allowing the most energetic atoms to escape, much like the most energetic molecules leave a hot cup of water, so this is called evaporative cooling. It results in the average energy, and thus temperature, going down. A drawback is that you also lose atoms, but if the phase-space volume decreases faster than atoms are lost it results in the phase space density going up, and a condensate.
So why not simply laser-cool the atoms? The problem with that is that atoms absorbing the photons that are cooling them also re-emit those photons, and when the physical density is large, those emitted photons hit other atoms rather than escaping, and this limits both the density and the temperature. This interaction can’t be present where the condensate is formed.
So the researchers turned it off, in a manner of speaking. They added a second form of trap, a dipole trap, which doesn’t involve the absorption and emission of photons — the light is far from resonance, and you use the electric field gradient of the light to form the trap. In the region where this trap was present, the laser scattering was turned off by shifting the energy of the excited state, which you can do if you add an external field. This was accomplished by the addition of another laser, which gives rise to the AC Stark shift (Johannes, not Tony), or a light shift. The trapping light is no longer near resonance, so the scattering is greatly suppressed. It’s also localized, so it’s only in effect where you shine the laser.
The area where the trapping is still occurring still contains very cold atoms, so the atoms in the dipole trap can still collide and thermalize with them, but once that second trap fills sufficiently, the critical phase-space density is achieved and a BEC forms. Very neat.
The New Phonebook's Here! The New Phonebook's Here!
Oops, I mean Phys Rev A
Tests of local position invariance using continuously running atomic clocks
As the disembodied voice said, “If you build it, he will come.” Meaning, in this case, that if you have a bunch of atomic physicists who have built one type of continuously running atomic clock, which is different than other, commercially available kinds of continuously-running atomic clocks, it means there is an opportunity to do a test of one of the principles of general relativity.
There should be a version up on ArXiv soon, so I’ll post a link when I can, and after the ScienceOnline 2013 conference I intend to write up a blurb, muddling through the general relativity a bit, in the context of what we did. (and by “we” I mean the first author, Steve, who did the heavy lifting)
(Oh, and BTW, this paper’s publication was of course timed to coincide with my 5th Blogoversary, which was yesterday)
That's What it Is
Uncertain principles: Physics Is About Rules, Not Facts
The idea that air resistance forces somehow invalidate Newtonian mechanics is depressingly common, but it’s based on a common misconception of what physics is. Physics is not a collection of facts, it’s a set of rules for understanding the universe– in the specific case of Newtonian physics, rules governing the effect that forces have on the motion of objects. “All objects near the Earth’s surface fall at the same rate” is not a central idea of Newtonian physics, just one of the simplest predictions from it. The central ideas of Newtonian physics are the rules used to quantify the effect of interactions, chiefly the “second law of motion” which says that the rate of change of the momentum of an object is equal to the sum of all the forces acting on it.
And I Say it's All Right
Sun Primer: Why NASA Scientists Observe the Sun in Different Wavelengths
Specialized instruments, either in ground-based or space-based telescopes, however, can observe light far beyond the ranges visible to the naked eye. Different wavelengths convey information about different components of the sun’s surface and atmosphere, so scientists use them to paint a full picture of our constantly changing and varying star.