Archive for September, 2013


This is pretty cool.

J002E3 is a object that was discovered in Earth orbit in 2002. It was initially thought to be an asteroid, but turns out that it was probably the S-IVB third stage of Apollo 12.

It was off in a heliocentric orbit for 31 years, made a brief 6-orbit visit home, and now it’s off galavanting around the sun again. May get captured temporarily again in 2040

Animated gif of the orbits

It looks like “chasing the moon” on the last orbit is what gets it kicked out of earth orbit.

Lethargic Time Flies

With Earth spinning more slowly, time isn’t flying as fast as before

CHalk this up as another example of an article title not really matching up with what the article concludes. It’s misleading — as the story eventually alludes — because we now use atomic time, so there is no slowing of time. The rate is the same. The explanations of the variability of earth rotation rates have implications on leap seconds, which we add to keep earth rotation time (terrestrial time) in synch with atomic time. We can’t adjust the earth, so we adjust the clocks.

GPS figures prominently in the discussion of technology enabled by atomic time, but there’s an omission in the discussion:

“If we relied on the Earth’s length of day, we could not have any of this,” says O’Brian, whose group at NIST develops, maintains and improves the supremely regular atomic clocks on which all other timekeeping ultimately is based.

GPS is actually synched with Naval Observatory time, and while USNO time and NIST’s time agree to great precision, to say “on which all other timekeeping ultimately is based” is a bit of hyperbole — it makes it sound as if others are adopting technology only after they develop it, and that the international time standard follows NIST, instead of the other way around. Timing labs around the world follow the international standard from BIPM, to whom we all contribute data. (Some of us contribute more than others. And some of us are closer in realizing the international standard.) /ChestThumping

“We have come full circle,” O’Brian says. The rotation of the Earth had long been the most accurate measure of time for humanity, but now such technologies as atomic clocks and GPS devices make it possible to measure tiny variations in Earth’s rotation. And the scientific reverberations are not just for space junkies. In a July paper in the journal Nature, for instance, researchers in England and France argued that sub-millisecond-scale variations in Earth’s rotation that occur on a 5.9-year cycle are probably linked to motions and interactions within the planet’s molten core where no one has ever been to take a look.

I think it’s pretty cool that our timekeeping is such that we can uncover evidence of processes that are redistributing mass inside the earth.

We Don't Talk About What We Know, We Talk About What We Don't Know

Stuart Firestein: The pursuit of ignorance

I really liked this talk. The post title is from his discussion of what scientists do at the end of the day at a conference, when they get together for a beer — they ask questions, and discuss the unknown.

Another paraphrase — Knowing a lot of stuff doesn’t make you a scientist. The purpose of knowing stuff is so you can ask questions. IOW, the whole purpose of learning a body of knowledge is to be able to define what isn’t known. Then you can go off and investigate that.

I also liked that even though he’s in a different field, the talk addressed general issues. There was nothing specific to neuroscience or the life sciences; even though he used examples from neuroscience, the concepts applied to physics (and, I imagine, chemistry). That doesn’t always happen

Messin' With Sasquatch

Sasquatch here being wall-plug (mains) electricity

The initial inquiry at work was innocent enough, I think — a colleague asked what the voltage limit of a BNC connector is. Wikipedia (linking back through a vendor’s spec sheet) says 500 V, and one also has to worry about the coaxial cable, which was the discussion until another colleague popped out of an office with “Two-and-a-half kiloVolts”. Complete with a description of the apparatus where that appeared in the experiment.

That led into a discussion of some of the crazy things we had done in the lab when we occasionally (or not so occasionally) didn’t have a strong grasp of what was going on. Two of the items that came up (and I had heard the story before, but it had been a few years) were The Cord of Death™, and Son of the Cord of Death™.

The Cord of Death™ sounds scary enough: it was a standard 3-prong power plug, i.e. with a ground pin (NEMA 5-15) … on both ends. Which is not advisable under almost any conditions. Apparently it was used to power a power strip whose power cord connection was bad and could not be fixed, but the rest of the strip was fine. And since all of the connections are in parallel, if you supply power to any outlet in it, the rest will have the juice. And in a grad school situation, I can see how such a kludge would be done instead of spending money on a new power strip.

The Son of the Cord of Death™ was a power cord, with the ground pin snipped off, and a BNC connector on the far end. I’m sure there are several applications for a connection where you want and AC signal at 60 Hz and around 120V, so why not skip the middle-man and avoid a power supply that’s just going to give you what the mains is supplying (oh, safety. Well, there is that, I suppose…)

All reminiscent of connecting two forks or metal rods onto a power cord to cook a hot dog or make a pickle glow.

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I didn’t have any contributions quite so reckless. I blew several things up in the lab in grad school — I don’t think any of our laser diodes died of old age — but I stayed away from deliberately messing with wall socket electricity as much as possible.

Sane Clown Posse Time

Vertiasium and Minute Physics team up to explain magnets.

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I was worried for a minute they were going to leave it at “magnets behave that way because electrons behave like tiny magnets” which only moves the goalposts, but there’s a nice reality check there, and it’s good even though they don’t delve too much into the quantum — they gloss over that it’s related to spin, and also lean a little on the Bohr description of the orbital motion. (IOW, it’s not that the orbital motion cancels, per se, it’s that there are no classical trajectories to begin with.

I saw this at It’s Okay to be Smart, and in a followup I think that Joe is right when he claims that when Feynman says (in the last video in the link) he can’t explain magnets, he’s not actually saying he can’t explain what the videos covered — he actually does (briefly) mention the answer. He’s explaining why “why” questions are difficult in physics — we always hit that point (mentioned in the video above) where you have to say “No-one knows. That’s just the way the universe works”.

Floating Some Ideas

What It’s Like To Spend 55 Days in Space

Moreover, it’s not clear that private space initiatives are the answer to the problem. “Space exploration is not an immediate payback, fiscally or otherwise,” Ivins says. “It is a generational kind of investment. And the only group that can afford to make that kind of an investment is a government.”

This is not exclusive to NASA, it’s true of research in general.

Plus, for the benefit of geeks across the universe, Ivins explains why the Borg cube from Star Trek can maneuver just as well as any starfighter that Hollywood has ever dreamed up. “In space, they’re one and the same,” says Ivins.

This is probably the one bit of science that space-based science fiction gets pretty consistently wrong — that maneuvering a craft in space would be anything like a plane or even a submarine. Most of the time the engine exhaust only points to the rear, and the engines are firing even when traveling at constant speed. Which is wrong even before you get to the fancy maneuvering.

I Thought Crossing the Streams Was Bad, Ray

1842: Jean-Daniel Colladon guides light with water

The great thing about [total internal reflection] is that it can be done with other transparent, optically dense materials — such as a curved stream of water!

Knock Me Down With a Feather*

*Knocking me down with a feather is not intended to diagnose, treat, cure or prevent disease.

Copper Bracelets, Magnetic Wrist Straps Fail to Help Rheumatoid Arthritis

I had noted a long time ago that based on the proposed mechanism, there was no basis to expect magnetic bracelets to work. No real surprise that they don’t.

The research published in PLOS ONE, show that both the standard magnetic wrist strap and the copper bracelet provided no meaningful therapeutic effects beyond those of a placebo, which was not magnetic and did not contain copper.

I like that they point this out about the placebos.

Getting to the Next Level Down?

A Jewel at the Heart of Quantum Physics

I have no way to evaluate this. This could be overselling a new idea or they could be onto something. If there’s a geometric way of expressing scattering probabilities, great. I suppose it’s possible to view Feynman diagrams as expansion terms of some function, so if they’ve found a way to figure out the underlying function, that’s wonderful. Amplituhedron seems a tad cute, but then I’m in a sub-field where someone made up Bosenova, so atomic physics doesn’t exactly have the high moral ground here.

One thing that gives me pause is any claim that they have discovered any “true” nature of anything. Like all of physics, we are talking about models. Physics describes how nature behaves, not what it really is.

Almost No Loopholes

Nanotechnology students build low cost Atomic Force Microscope using LEGO

This is pretty cool, but I won’t quote anything because the site has that annoying feature that adds “read more” with a link every time you copy/paste, so go read it.

The short version is that 3D-printed parts are allowed, which makes it slightly less impressive than if it were all LEGO.

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