Category Archives: Physics

Can Everyone Get on With Their Normal Jobs Now?

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A question asked over at The Great Beyond

A while back I ran across a blog post about the “dangers” of Bose-Einstein Condensates — the purported great peril of a “Bosenova” explosion happening in liquid He, and wrote a post about the various misconceptions that were present. Malcolm Fairbairn and Bob McElrath wrote a response to this that is now available at arXiv. There is no explosion risk associated with superfluid Helium in the LHC cooling system
(Yeah, that will calm the conspiracy fruitcakes)

Liquid 4He has a monatomic structure with s-wave
electrons, zero nuclear spin, no hyperfine splitting, and as a consequence no
Feshbach resonance which would allow one to change its normally repulsive
interactions to be attractive. Because of this, a Bose-Nova style collapse
of 4He is impossible. Additional speculations concerning cold fusion during
these events are easily dismissed using the usual arguments about the
Coulomb barrier at low temperatures, and are not needed to explain the
Bose-Einstein condensate Bose-Nova phenomenon. We conclude that that
there is no physics whatsoever which suggests that Helium could undergo
any kind of unforeseen catastrophic explosion.

It turns out that there’s more of this fumbling and bumbling out there that I had missed. Collider Incidents at LHC Facts (Not sure why “Facts” isn’t in scare quotes) takes things to a new level. There are responses from both Eric Cornell and Carl Wieman (and another researcher) that clarify some of the technical jargon and other statements that have been so badly mangled, and the wingnut conclusion is that the scientists are just covering up!

“I can state ABSOLUTELY CATEGORICALLY that it is totally inconceivable that a black hole could be produced by these phenomena.”
Methinks Dr. Wieman doth protest TOO MUCH…
There are many physicists who can not only conceive it but believe it too. Not too mention those of us with “a terrible ignorance of physics” but an abundance of common sense.

and

What I’d really like to know, and maybe you can find out, is if the ‘Bosenova’ was such a fantastic experiment that raised so many interesting questions why they don’t fire them up all the time. Seems like they would want to keep repeating the experiment wouldn’t they? Unless, of course, they did make a stable MBH, they know it, and they’re scared. They sound scared.

Funny, but not really “ha, ha” funny.

There’s a nice takedown of this, and the original nonsense article by Alan Gillis, over at The Physics Anti-Crackpot Blog. There will be no Bose-Novae at the LHC

So this claim of Gillis & Rössler is completely and totally specious. Any responsible researcher, before making a claim that something will explode like a nuclear bomb, should look up the relevant physics, to see if his idea makes sense. In this case, Rössler or Gillis didn’t even take the first step to see how a Bose-Nova works, and if his proposal is even remotely reasonable. The two crackpots in this story reinforce each other, neither checking their facts. It’s odd here that the “journalist” originates a crackpot idea, asks it of a crackpot, and of course he agrees. Crackpots are not in the business of proving or disproving things.

Given the above article, I don’t think Alan Gillis should be allowed anywhere near the term “journalist”, but I think the term “crackpot” certainly applies. A good journalist, when hearing such a dangerous claim, should call up a few more physicists, to see if this guy is a crackpot, or whether this issue has any credibility in the scientific community. Perhaps he should also contact people who have done or mathematically explained Bose-Nova experiments (as Fairbairn and McElrath apparently did — judging by their acknowledgments they contacted one of the original Bose-Nova experimenters, Elizabeth Donley).

But as we can see above, getting in contact with people who know — really know — what they are talking about doesn’t seem to matter a whole lot. To them, you either agree with the wingnuts or you are part of a coverup, trying to deceive the public. Which is why it can be frustrating to talk science with some people.

The World Will Not End, Thanks to a Technicality

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I’m sorry, this is abuse. You want 12A, next door.

Day of reckoning for doomsday lawsuit

Basically the decision came down to an issue of jurisdiction: Wagner and a co-plantiff made their claim under the National Environmental Protection Act (NEPA). But NEPA only applies to “major federal actions,” and the judge said that the US contribution to the LHC (US$531 million or about 10% of the overall cost) was too small to constitute a major federal project.

Viva Las Vegas

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One of the questions one asks when trapping atoms in a magneto-optic trap (MOT) is “What shall we do with the atoms?” You often have an idea before you do the trapping — it’s not like we’re trophy hunters, trapping just to have something on the wall. Trapping in and of itself hasn’t been the goal for quite some time now, at least in experimental labs; one wants to do some kind of experiment with the atoms. Some of the time that can be done in the trap, but quite often it involves moving the atoms somewhere else. Sometimes you actually wanted an atomic beam of some sort, instead of a collection of atoms just sitting there, suspended in space — the trapping environment involves bright, near-resonant laser light and magnetic fields and those could be undesirable. The atom beam gets you away from this, and if you look at the beam from a perpendicular direction, the Doppler shift is very small. Perhaps you want low-speed collisions, and tuning the speed of the beam allows you to do your experiment. There are also a number of atom-optics experiments that can be done, e.g. sending the atoms through transmission gratings comprising an interferometer. The problem could also be the relatively high vapor pressure of the gas in your vapor cell giving you excessive background signals, or collisions with that background vapor could be the problem, limiting the trap lifetime. So you need to move the atoms, transporting them to a region that is better-suited for the experiment you are doing.

When I was at TRIUMF, the problem was the background and trap lifetime. We were trapping radioactive atoms, and the idea was that when an atom decayed, the beta would go one way and the atom would recoil, and each could be detected. But a vapor-cell MOT captures only the small percentage of atoms stupid enough moving slowly enough to get trapped, leaving the majority of the zipping around in the cell or sticking to the walls (or worse, attaching themselves to detectors). Not only did this mean they would be swamping the signal from the trapped atoms, the signals would be coming from different directions and originating from different points.

About the time we started fretting about this problem (you have to trap them first before you worry about the next step, and nobody had trapped these isotopes before) we got a visit from Zheng-Tian Lu, then at JILA/NIST, and he had come up with an ingenious method of generating a low-velocity atomic beam and shared the details with us (the paper was in the pipeline but had not yet been published at the time)

A typical vapor-cell MOT uses three beams along the cartesian axes, and it’s possible to do this by retroreflecting each of these beams — the vapor is dilute, so with decent mirrors there isn’t a large drop in intensity (any imbalances will push the trap slightly off-center as the effect of the magnetic field compensates). You get the proper polarization of the beams by placing a quarter-wave plate in front of the retroreflection mirror (this changes the circular light to linear and then back to circular of opposite helicity; if you started with linear it would circularize it and change it back to linear, perpendicular to the original. Ah the fun you can have with waveplates)

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Does the Moon Orbit the Earth, or the Sun?

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The Moon that went up a Hill but came down a planet over at Bad Astronomy

[Y]ou have to look at something called the Hill sphere. Basically, it’s the volume of space around an object where the gravity of that object dominates over the gravity of a more massive but distant object around which the first object orbits.
OK, in English — and more pertinent to this issue — it’s the volume of space around the Earth where the Earth’s gravity is more important than the Sun’s. If something is orbiting the Earth inside Earth’s Hill’s sphere, it’ll be a satellite of the Earth and not the Sun.

I Don't See Tina Turner Anywhere

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Oh, wait, that was Thunderdome.

The Baikonur Cosmodrome at The Big Picture

When NASA’s last scheduled Space Shuttle mission lands in June of 2010, the United States will not have the capability to get astronauts into space again until the scheduled launch of the new Orion spacecraft in 2015. Over those five years, the U.S. manned space program will be relying heavily on Russia and its Baikonur Cosmodrome facility in Kazakhstan. Baikonur is an entire Kazakh city, rented and administered by Russia. The Cosmodrome was founded in 1955, making it one of the oldest space launch facilites still in operation. Here are collected some photographs of manned and unmanned launches from Baikonur over the past several years. (26 photos total)

Did Jules Verne Write This?

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Journey to the Center of the Neutron

A neutron contains three quarks, and nuclear physicists don’t completely understand how these move within the particle. Last year, an analysis revealed a negative charge at the center of the neutron, and now an article in the Rapid Communications section of the September Physical Review C attributes this negative core to very fast moving “down” quarks. The results elaborate on an emerging three-dimensional view of these fundamental particles and their proton cousins.

Ballistic and Nonballistic Trajectory: Career Path

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I’ve been adopted by three high school groups (so far). Last time I did this, there was a list of questions, so I got a head start on answering the ones I thought might be asked. The answers seem to have tunneled into the ether, however, but since questions about career path are likely to come up (and I haven’t done a post on that), here I go.

I’m not tempted to say “I didn’t take the typical career path” because I don’t think there is any such thing. Some might propose that the typical path is grad school to postdoc to university teaching and research position, but since only about a third of doctorates work in academia, and there are positions other than the university research professor (teaching-only positions, liberal-arts or community colleges) that’s not really “typical,” though it may be perceived to be.

I went to Hartwick College, a small liberal-arts school in the middle of nowhere Oneonta, NY, which was about two hours away from home (less now, since they put in a highway while I was there). I ended up there because the financial aid offered by my main choice, Cornell, was a tad less than I needed: they offered zero. (I was put on a waiting list and the money ran out before the candidates did). Between student loans, work-study, scholarships and grants, Hartwick was possible. I had AP credits for physics and calculus and overloaded my schedule one term to graduate early. (3.5 years)
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