Saturday, January 28, 2017

LHC robots

Symmetry has an article about the robots of the LCH.
As you might expect, the subterranean tunnel which houses the LHC is not always the friendliest place for human visitors.

“The LHC contains 120 tons of liquid helium kept at 1.9 Kelvin,” says Ron Suykerbuyk, an LHC operator. “This cooling system is used to keep the electromagnets in super conducting state capable of carrying up to 13,000 Amps of current through its wires. Even with all the safety systems we have in place, we prefer to limit our underground access when the cryogenic systems are on”.

Unfriendly is a bit of an understatement. When the magnet quenched the resulting explosion shoved a 35 t dipole magnet into its neighbor, and the escaping liquid helium allegedly condensed the air.

Near the collision points the radiation levels are pretty doggone high. I'm not sure robots would survive in the collision halls--for that matter I don't know if they can go in. And you have to worry about little things like the fringe of the magnetic field for CMS--high enough to mean that power supplies have to be kept far away from the electronic devices they power--which costs some DC power loss.

So, meet TIM. Except the picture at the top of the article isn't of TIM ("the Train Inspection Monorail. TIM is a chain of wagons, sensors and cameras that snake along a track bolted to the LHC tunnel’s ceiling"). The video is, though.

Thursday, January 26, 2017


David Warren posted this link to a translation of a short work by a Colombian I'd never heard of before, on the subject of The Authentic Reactionary. "If the progressive casts himself into the future, and the conservative into the past, the reactionary does not measure his anxieties with the history of yesterday or with the history of tomorrow."

Wednesday, January 25, 2017

Political postings

In the run-up to the elections in 2008, I came to the conclusion that commenting on politics was bad for my soul. The temptation to despise seemed overwhelming. During the past 8 years I've more or less held to my resolution to back off. And when all's said and done, much that's said never changes any minds anyway--sometimes the values and presuppositions are too different.

Is liberty valuable, and if so what is its scope? For that matter, what is it? Not a question people like to discuss, but an illuminating one...

The tribe that believes that people are perfectible doesn't generally value liberty very highly--probably for the same sort of reasons that kings punished heretics. Monarchs owed it to their subjects to protect them from those who could mislead them into hell--or, these days, from being perfected subjects with all traces of evil ideas scrubbed away.

Naturally that protection requires more and more centralization, and more and more micromanaging, and more and more careful parsing of anything that might smack of subtle evil ideas (an analysis that apparently only certain people are capable of--and as with The Force, they must trust their feelings).

No, an essay on "why you should deliberate carefully when trying to overhaul the health care system for a nation" is not going to change any minds across that kind of divide. Nor are those impatient to undo the damage going to listen to an essay about "why there needs to be some bandaging to let things grow back."

I'm probably not going to be commenting much during this administration either.

Thursday, January 19, 2017


Pulsars are neutron stars whose EM radiation (light, radio waves, gamma rays) seem to blink or pulse. This is related to how they rotate (and their rotation can be measured to be slowing down). Because the magnetic poles don't usually line up with the axis of rotation, sometimes the pole is pointed more in our direction, sometimes less so--and it seems to pulse.

But what they radiate seems to be all over the map. Sometimes they radiate gammas but not radio, sometimes radio but not gammas, sometimes both. Why? Maybe it has to do with which way the star is pointed relative to us.

based on these observations, Geminga’s magnetic poles appear to be oriented at the top and bottom of the neutron star from our point of view, which also align with its spin poles. Because these areas are where a pulsar’s radio emission should originate, it makes sense that no radio waves are detected. The pulsar’s gamma rays, however, are created over a larger area at higher altitudes, causing them to sweep out over a larger area of the sky and making them detectable from Earth.

It makes sense. Verifying that would be kind of hard--we'd have to have a clear idea of how far from the rotational axis the magnetic poles point, and then try to correlate that with the ratio of gamma to radio. But I've no idea how to measure that angle. You could get some notion of the direction of the axis of rotation from the jets of stuff shot away from it (you'd measure the doppler shifts of each of the two lobes to try to pin down their speed and direction), but measuring the magnetic field direction sounds hard. Polarization of light would be going this way and that with the moving field, and I'm not sure you could tell that from randomness.

Tuesday, January 17, 2017


Pick one:
NASA has approved a mission to explore 16 Psyche, an iron-rich asteroid whose contents are said to be worth over 100-thousand times the value of the entire world economy.

"Psyche is almost certainly an iron-nickel alloy asteroid, possibly formed after a larger body, like a dwarf planet, had its mantle stripped away from a violent collision with another asteroid. So, Psyche is probably the exposed core of a small planet," Bercovici said.

Do you want to pull your hair out when you see "gee wow" reporting like this? "Psyche is an asteroid with a diameter in excess of 125 miles, about the same size of the state of Massachusetts, and is almost entirely composed of iron and nickel. The abundance of these metals gives the asteroid's contents an estimated worth of a staggering \$10 quintillion — that is a one, followed by 19 zeros. Comparatively speaking, the world economy is estimated to be worth just under \$74 trillion. Psyche's contents are worth approximately 130,000 times as much as every single human industry put together." Transportation costs aside, supply and demand considerations make complete nonsense of this sort of calculation. You're supposed to get excited about big numbers, even when they don't make any sense.

If Psyche is indeed the remains of a much bigger object, that's more exciting. The problem is, I don't know if explorations would tell us much about a long-gone planetary crash. So it may just be exciting in a T-Rex skeleton sort of way. (The Field Museum's Sue exhibit has a case with some extra "belly bones" and the confession that nobody knows where they fit.)

Maybe the composition and structure can tell us about how planetary cores form--though the details of the composition will surely have been different from Earth's. Unfortunately the probe is supposed to launch in 2023 and arrive in 2030. A bit of a wait.

Paris streets

I saw a report today from the Mirror saying that French told not to fear wolves roaming Paris streets as 'they only eat four-legged animals'.

That sort of encouragement doesn't comfort. Even if Parisians were OK with wolves that only ate pets, wolves still threaten everybody.

But who else is on the streets? I don't think wolves stand a chance. People can be very thorough when dealing with threats.

Thursday, January 12, 2017

Merging black holes

We all remember the LIGO discovery: a pair of black holes merging to produce a beautiful gravity wave signal. It was followed shortly thereafter by a smaller pair producing not-so-nice a signal, but good enough.

LIGO didn't take data very long, but got 2 signals in only a few months. (They're starting up again.)

From that rate, Ioka et al estimated how many mergers there have been in our galaxy so far (mostly much smaller ones, and obviously we weren't looking at the time--weren't here for most of that time). (Basically they figure that if LIGO detected really big ones at the range they did, it would have missed the many more smaller ones in the same volume, because it wasn't sensitive enough.)

When two orbiting bodies like that merge, the result has fantastic angular momentum. If you spin a bicycle wheel and grab it, you know that it "doesn't like" being stopped. Imagine if the bicycle wheel were made of lead, and spinning that fast. You might break your hand trying to stop it. Now spin it up faster, and faster. There's a lot of energy in that thing now. There's unimaginably more in the black hole you get from merging two others.

The first direct detections of gravitational waves (GWs) from black hole (BH) mergers, GW150914, GW151226 and LVT151012, give a robust lower limit ∼70000 on the number of merged, highly-spinning BHs in our Galaxy. The total spin energy is comparable to all the kinetic energy of supernovae that ever happened in our Galaxy.

They go on to estimate what kind of activity you can get from interstellar gas falling into these things, which is of interest to people trying to study cosmic rays (like IceCube).

Let me emphasize that most of these black holes aren't very big--only a few solar masses. Still, 70,000 merged black holes in our galaxy--wow.

Of course there are some assumptions that go into that--like assuming that the rate of black hole merger is essentially constant in time. I'm not sure that's realistic. And they may have the distribution of the rate of production of different size black holes wrong. But nobody found any showstopper problems with it at the meeting today.

Tuesday, January 10, 2017


I've never been confident in the claim that the appendix is a useless vestigial organ. Everything else is doing something, sometimes many somethings at once. Why waste energy growing something useless? Maybe it is a bacteria reservoir?
They discovered that the appendix has evolved independently in several mammal lineages, over 30 separate times, and almost never disappears from a lineage once it has appeared. This suggests that the appendix likely serves an adaptive purpose.

Saturday, January 07, 2017

Dust never sleeps

Or, when it does, the ultraviolet wakes it up.

On the Moon, and presumably any airless body, UV-stimulated emission and re-capture of electrons in the cavities left between dust grains can charge the dust, and the negatively charged particles can be levitated by electrostatic repulsion.

We have recorded micron-sized insulating dust particles jumping to several centimeters high with an initial speed of ~0.6 m/s under ultraviolet illumination or exposure to plasmas, resulting in an equivalent height of ~0.11 m on the lunar surface that is comparable to the height of the so-called lunar horizon glow.

Since there's no reason it should jump straight up, a particle will fall down again some distance from its original location. So dust will spread.

This is only significant in airless regions, so don't blame the state of the bookcase on UV light.

Friday, January 06, 2017

Mark your calendars

Molnar et al are predicting that a binary star system will merge and explode in 2022. If true, Cygnus will look a little funny for a couple of years.

The eclipses of one star by the other are coming faster and faster, and if V1309 is anything to go by the pair should spiral in and merge in a moderately dramatic way in about 5 years.

If this event is anything like the 2008 explosion, it’ll take about six months to rise to its full brightness — 10,000 times greater than the brightness of the original. When it comes to space phenomena, it can sometimes be hard to tell what big numbers are actually as impressive as they sound and which are not actually big at all relative to, you know, the scale of the universe. This is the former. It will mean a noticeable change in the brightness of the night sky.

And if it takes 6 months to grow, the weather shouldn't get in the way, as it tends to with things like solar eclipses and comets and auroras.

Tuesday, January 03, 2017

Pithy wisdom and slogans

Back in 2013 I wrote about proverbs that "I don't hear these much, though perhaps I don't travel in the right circles, and I suspect we suffer for it." Since then I've been looking for places where old proverbs, or what used-to-be familiar scripture would fit in.

I'm surprised that I didn't hear anyone cite "Better the devil you know than the devil you don't" about the last presidential election. It was certainly one of the major themes.

You hear plenty of slogans and phrases encapsulating some political or social ideas, but that's not quite the same thing. The slogans anticipate, while the proverbs react to, classes of situations. For example "The people united will never be defeated" is an aspirational slogan (and piano composition): history is chock-a-block with counterexamples and compromises that only vaguely resemble victory. "He who slaughters a beast does not hesitate about skinning it," on the other hand, warns the wishful thinkers in every age. We hear "Liberty, Equality, Fraternity," or "no justice, no peace"--both aspirational (since the latter implies that there will be peace once there is justice). But "A camel never sees its own hump." You know people like that.

I like this one. Albanian: "Fire, water and government know nothing of mercy." And this "A benevolent man should allow a few faults in himself to keep his friends in countenance."