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Yonatan Zunger
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Yonatan Zunger

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I don't often share press articles about our products – they rarely seem to say much of use – but this was just such a good case of a journalist Getting It Right that I had to share. Google+ is very much alive, and our recent changes are focused on making it be the best product it can be for what it's best at: helping people meet people and have great conversations about things they're passionate about. 

One particularly noteworthy thing in this article is its discussion of the "majority illusion:" people tend to assume that their friends are typical of the wider world, but almost by definition they aren't – for one thing, they all have one uncommon attribute in common, which is being your friend in the first place. And since people don't choose their friends randomly from the entire spectrum of humanity, one's friends are always a distorted sample. 

So yes, we have here a tech press article which (correctly) uses an important result in cognitive psychology to explain why lots of tech press articles are nonsense.
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Hoe does removing Ripples and sharing of Circles make Google+ a better product? :(
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+John Scalzi installs Windows 10. Its final form will soon be upon us.
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+Yonatan Zunger So glad I'm not a sysadmin any more. ;)
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The National Academy of Sciences is hosting an exhibition of art quilts inspired by the chemical elements – and it's quite a thing to see. Below is "Iridium: My Darkness To Light II," by (cell biologist) Grace Harbin Weaver, inspired by the use of Iridium electrodes implanted in the human brain to study vision and perception. You can see all of the works here:

or at the NAS itself, at 2101 Constitution Ave. NW in DC.

h/t to +Josh Witten and to +The Finch & Pea, which has more on this exhibit at .
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Superbe, Yonatan
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Prostheses from the late 19th century got remarkably sophisticated. Gillingham's work was distinguished by his focus on fitting the prosthetic carefully to the individual. The resulting devices, made of wood and leather, shifted the whole world of artificial limbs.
"James Gillingham ran an ordinary shoemaking business, the Golden Boot, in Chard, England. In 1866, he met a man who had lost an arm in a cannon mishap and had been told by doctors that there was nothing to be done about it.

Eager to put his craftsmanship to test, Gillingham offered to make the man a new arm for free."

How a humble English cobbler stunned the medical world.
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Here +Fraser Cain gives an excellent explanation of what would happen if you collided an ordinary black hole with a black hole made out of antimatter. The answer is that they wouldn't annihilate each other: you would just end up with a single, bigger black hole.

There's a lot of interesting science behind it, but the two most important things to know for this are a pair of acronyms: CPT symmetry and ADM equations. The first tells us what antimatter is; the second, what black holes look like. And importantly, we have to understand the idea that "black holes have no hair."

CPT stands for "Charge, Parity, Time Reversal." These are three separate switches you could flip on any piece of matter you encountered. If you flipped the charge, you would replace + charges with - charges, and also you would flip some of the more exotic (non-electrical) charges that other kinds of matter had. If you flipped the parity, you would exchange your left hand for your right hand; importantly, for some particles (like neutrinos) their direction of rotation about their axis is related to their direction of motion by a "right-hand rule" (point your right thumb in the direction of motion; your fingers show the direction of rotation) or a "left-hand rule." That would get flipped. And if you flipped the direction of time, you would literally play back the laws of physics backwards, having everything go the opposite way.

These seem like three rather random changes you could make to the universe, but what's important about them is that if you made all three changes – flipped all the charges in the universe, exchanged right and left, and played everything backwards – it turns out that the laws of physics would be exactly the same. That's called "CPT Symmetry," and it's very important in quantum mechanics.

But what would that look like? Imagine you started with an electron moving along its merry way, say moving from your left to your right, and you CPT'ed it. You would end up with something that had the same mass as the electron, but a positive charge (C). P doesn't do anything to electrons (or rather, what it does is subtle and complicated to explain and doesn't really add anything here), but T would mean that the positively-charged electron would be "moving backwards in time," which would look like it was moving from your right to your left. The CPT rule tells you that our same laws of physics should describe this reversed situation. What that means from the perspective of quantum field theory, whose job it is to explain all of the various particles we see in the universe, is that if there's a particle that looks like an electron – having a charge of -1, a mass of 511MeV, and so on – then the same laws of physics should also describe this "flipped electron," with a charge of +1, a mass of 511MeV, and so on.

These "flipped particles" are what we call antimatter. Basically, a good way to think about it is to ignore time reversal; a particle moving from right to left is now moving from left to right, but for our purposes it's easiest to just note that yes, it's a particle, and it moves around. (It turns out that this actually works out well at the level of the math as well) For every particle, if you flip all its charges and its handedness, there should be a second particle in the universe that has those properties.

For an electron, this "flipped particle" is called a positron; for other matter particles, their name comes from giving them the prefix "anti." So just as three quarks (two ups and a down) make up a proton, three antiquarks (two anti-ups and an anti-down) make up an antiproton, and the antiproton has a charge of -1 and the same mass as a proton. Photons are their own antiparticles: they have no charge and come in all handednesses. So there's no "antiphoton," nor is there an "antigraviton." 

So that's CPT, and it's all about very small things. ADM (named after its inventors, Arnowitt, Deser, and Misner) is a set of equations for describing behaviors in general relativity, our best theory of gravity.

The ADM equations are actually a very general tool, but what's important about them for our purpose is that they tell us that whenever you have an object that's bounded in space (i.e., that doesn't either stretch off to infinity in some direction, or distort spacetime so badly that even infinitely far away they have an effect), you can meaningfully talk about the "total energy" or "total mass" in that object. Basically, if there's any meaningful sense in which you can "get far away" from an object – so that you're basically in empty, flat space with some object far away – then you can talk about measuring the properties of that object in some way.

This is true of black holes, just like it is of basically every other configuration of matter, and so we can talk about a black hole's "ADM mass," its total mass measured using this method. Through a very similar argument, we can see that it's not just mass you can measure this way: you can also measure the total momentum of the black hole (if it's moving), its angular momentum (if it's spinning), its electrical charge (if it has any), and in fact the exact same set of charges that we talked about when we talked about CPT.

(That's actually not a coincidence: these charges aren't picked at random. Probably the most important theorem in mathematical physics is what's called Noether's Theorem, which says that there is a conserved quantity associated with a system if and only if there's a symmetry of the system, and those are related in a particular way. For example, if the system would be the same if you shifted its position by any amount, the associated conserved quantity is momentum. Shifting things forward and backwards in time leads to energy conservation; rotating them, angular momentum. The symmetries associated with electric charge and the like are more complicated, but they're fundamental to how physics works. The ADM "total energy" calculation basically works because you can zoom out until you're far enough away from the system that it's basically empty space with something in the middle, then use that symmetry and pull out the value of the conserved quantity using Noether's technique. Applying that to each symmetry in turn, you can measure total energy, momentum, and so on.)

And now another interesting fact kicks in: "Black holes have no hair." This is a fact about general relativity which takes some serious proving, but what it means is that the only properties which black holes have that are measurable from the outside are exactly these global conserved charges. In particular, black holes have a shape completely determined by these charges (a perfect sphere unless they have angular momentum, in which case they distort in a particular way from rotation); they don't have filaments, curves, hairballs, or anything else like that. 

So now, let's combine these ideas. Say you had two black holes: one matter and one antimatter. The matter one has some mass, some charge, some angular momentum, and so on, and so does the antimatter one. But as we know from understanding what antimatter is, the anti-black hole still has positive mass; it just got built up out of antiparticles, so maybe it has an opposite charge.

When the two black holes merge, the only thing that matters (by the no-hair theorem) is those total amounts, and they simply add up. So you end up with one bigger black hole.

In fact, what that means is that there's no such thing as an "anti-black hole" at all: no matter what went in to forming the black hole, at the end all that matters is the total mass, charge, and so on. You could have gotten a charge from anything – positrons or ordinary protons – and it would come out the same.

Here's another way to think about it. Imagine that we weren't just colliding black holes, we were also manufacturing them. One of them we're going to build by crushing a big lump of matter; the other, by crushing a big lump of antimatter. Now, we know from the above that if we first build them, and then collide them, we end up with a single black hole. But what would happen if we first collided them and then built them? Would it matter (so to speak) if the black hole formed just before or just after the collision?

The answer is no. When matter and antimatter react, they get converted into energy, but all of those charges are conserved. (Remember that matter is energy, so the mass of the particles gets turned into energy as well) For example, an electron and a positron can react to turn into two photons, but the total charge stays the same (-1 from the electron, +1 from the positron, 0 for the two photons), and so does the energy: 511MeV worth for each particle, plus whatever kinetic energy they had, turns into the energy of the emitted photons. (You may have noticed, if you know some physics notation, that I actually gave the mass of the electron in units of energy; that’s very common in physics, since you go back and forth between the two all the time anyway) 

So if the matter bundle and the antimatter bundle collided before forming into a black hole, they’d react dramatically, explode and so on, and produce a total energy which is exactly equal to the energy (and mass!) that went into them, with a total charge which is exactly equal to the charge that went into them, and so on. And if that were to form a black hole, it would form the exact same black hole that would have formed if they had made two black holes and then merged!

This is a fundamental idea that shows up over and over in science: conserved quantities are really conserved, no matter what, but everything else tends to get mushed up fairly easily. As we saw above, black holes “have no hair:” the only properties they have are conserved charges. Both matter and antimatter obey this rule, and the two differ in properties like their handedness and their charges, so that when they react, while they may turn into energy (rather explosively), that energy (and thus mass) is exactly the same amount that went in.

And that’s why there’s no such thing as an “anti-black hole.”
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+Bill C. Riemers +Zack Weinberg It is a theorem of classical GR. It's not true in the quantum theory, which has to do with information preservation in Hawking radiation. (Something which even Hawking [finally] conceded a few years ago)

In this particular case, no-hair applies whenever you're ignoring Hawking radiation, so an anti-BH and a BH are identical. When you look at the full quantum theory, what you're really seeing is that a bunch of particles collided to form the BH, and all the information of how it was formed will ultimately come out in the Hawking radiation. 
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Note to self: Remember this answer for future use. 

(See also:
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Ketamine is used also in wildlife parks as anaesthetic for big animals.
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Apparently, obscenities in the US have a marked regional distribution. Looking at these maps makes me want to do correlations between them, as well as to give a sort of obscene weather forecast.

(It occurs to me that I probably shouldn't continue typing what I was typing, because since so much of my work right now deals with hate and harassment online, my mental bar for what a normal amount of obscenity is to hear in an ordinary work conversation is probably a wee bit skewed right now.)
Lots of interesting regional trends in these maps. (Warning: contains strong language, which is the point.)
Swearing varies a lot from place to place, even within the same country, in the same language. But how do we know who swears what, where, in the big picture? We turn to data – damn big data. With g...
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Thanks for the reminder that I currently reside in the Bible belt. Damn
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There is a flaw in this sculpture. Namely, that it doesn't have any way to climb in to the compartment and sit in it, because that would be awesome.
The Train to Heaven ... "The Train to Heaven is a monument depicting an old, real steam locomotive standing upright and pointing towards the sky, located at Strzegomski Square in Wroclaw, Poland. The 65-years-old engine was procured from a museum and erected here in 2010 by artist Andrzej Jarodzki. The sculpture was commissioned by the city of Wroclaw and Wroclaw’s developer company Archicom to commemorate its 20 years of commercial activity in the city. The steam engine is 30 meters long and weighs 80 tons. The monument is said to be the largest urban sculpture in Poland.

Andrzej Jarodzki, an artist from Wroclaw, came up with the idea a long time ago while playing with his son’s toy engine. At one point he set the toy upright and that’s where the idea came from. However, Jarodzki was unable to realize it until he was approached by Archicom. Only five years old, the Train to Heaven is already Wroclaw’s most famous attraction. ,,,"

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You don't need a bus, just follow the politicians.
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A fundamental principle of good engineering is that you design the whole system to function well, not just the part you're concentrating on. Most systems include humans as components -- as operators, maintainers, passengers, or even obstacles. And when you fail to take that seriously into account in your design, you make a fundamental design error which can have lethal consequences.

It appears that the cause of the SpaceShipTwo crash was precisely of this sort: the designers never considered the possibility that a particular switch might be flipped at an incorrect time. In this case, it was flipped only a few seconds too soon, at a speed of Mach 0.8 instead of Mach 1.4. (This under rocket power, where acceleration is fast) That caused the tail system to unlock too soon, be ripped free by acceleration, and destroy the spacecraft, killing the co-pilot and severely injuring the pilot.

Scaled Composites' design philosophy of "relying on human skill instead of computers" here reeks of test pilots' overconfidence: the pilots are so good that they would never make a mistake. But at these speeds, under these g-forces, under these stresses, and tested repeatedly, it's never hard for an error to happen.

There are a few design principles which apply here.

(1) It should not be easy to do something catastrophic. There are only a few circumstances under which it is safe for the feathers to unlock, for example, and those are easy to detect based on the flight profile; at any other time, the system should refuse to unlock them unless the operator gives a confirmatory "yes, I really mean that" signal.

(2) Mechanical tasks that can lead to disaster are a bad idea. Humans have limited bandwidth to process things: while our brain's vision center is enormously powerful, our conscious mind's ability to think through things works at language speed, a few ideas per second. Here, time was wasted with a human having to perform a basically mechanical task of unlocking a switch at a particular, precise time. This requires the human to pay attention, time something accurately, and flip a switch, at a time that they should be simply watching out for emergencies. Since the time of unlock is already known long before takeoff, a better design would be for the unlock to happen automatically at the right time -- unless the risks from having an automatic unlocker (perhaps due to a reliability issue, or having a complex part prone to failure) exceed the benefits of removing it.

What's important to learn from this accident is that this error isn't specific to that one mechanism: this is an approach which needs to be taken across the entire design of the system. Every single potential or scheduled human action needs to be reviewed in this way.

An excellent perspective on this comes from James Mahaffey's book Atomic Accidents, a catalogue of things that have gone horribly wrong. In the analysis, you see repeatedly that once designs progressed beyond the initial experimental "you're doing WHAT?!" stage, almost all accidents come from humans pushing the wrong button at the wrong time. 

Generally, good practice looks like:

(A) Have clear status indicators so that a human can tell, at a glance, the current status of the system, and if anything is in an anomalous state.

(B) Have "deep status" indicators that let a human understand the full state of some part of the system, so that if something is registering an anomaly, they can figure out what it is.

(C) Have a system of manual controls for the components. Then look at the flows of operation, and when there is a sequence which can be automated, build an automation system on top of those manual controls. (So that if automation fails or is incorrect for any reason, you can switch back to manual behavior) 

(D) The system's general behavior should be "run yourself on an autonomous schedule. When it looks like the situation may be going beyond the system's abilities to deal with on its own -- e.g., an anomaly whose mitigation isn't something that's been automated -- alert a human."

The job of humans is then to sit there and pay attention, both for any time when the system calls for help, and for any sign that the system may need to call for help and not realize it.

This wasn't about a lack of a backup system: this was about a fundamentally improper view of humans as a component of a crtiical system.
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+Yonatan Zunger , let's see if Mr. Branson is open to such practical advice.
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It is possible that this design for a system to safely blow up buildings containing chemical or biological weapons, without spreading said weapons into the air, had its design secretly influenced by an eight-year-old. It is possible because, if I were eight and trying to come up with the coolest possible way to make something catch on fire, it would probably involve dropping a giant container full of burning bouncy balls.

I have no idea whether or not this idea would work, but it would be tremendous fun to watch.
Wherein the US government develops a warhead full of rubberized rocket-fuel superballs designed to careen through secure facilities, breaking down doors, superheating the air, and generally making a giant mess of things.
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For those who have never seen one, a trebuchet is a piece of medieval artillery that works by dropping a counterweight. This turns a long throwing arm (the throwing arm being longer than the counterweight arm, so it moves farther and thus faster) which in turn pulls a long rope (giving it even more length) at the end of which is a sling carrying a projectile. They were quite effective, and remained useful even after the invention of cannons. 

Also, they can be photographed with strobes. The counterweight is the squarish object at the bottom; you can see a long lever arm spinning at the top, a rope, a reddish sling, and some kind of yellow object being hurled at its intended victim.

h/t +Autumn Ginkgo Leaves™
The non-conventional photo class did a demo on strobes today.  What a great time to study historic weapon trebuchets.
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+Scott Montague You seem to suck at reading.
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  • Stanford University
    Ph. D., Physics, 2003
  • University of Colorado, Boulder
    B. A., Mathematics, Physics, 1997
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Chief Architect, Google+
Lots of people ask me what my job title means. I'm the senior engineer on the Google+ team, and my primary responsibility is to oversee and guide the technical design of Google+ and all of the things related to it. In practice, I'm also involved in lots of non-technical issues as well: my job is to make Google as fun, exciting, social, and pleasant a place to be as it can possibly be.

(I've been at Google since 2003, but you probably haven't seen me before this, because I worked deep in the back end: planet-scale storage, very large-scale search, ranking, and so on. Lots of teams whose unofficial motto is "if we told you, we'd have to kill you" -- as opposed to Google+, where we get to go out and talk and interact with our users.)

For those who just came here, welcome to the Google+ Project. It's something that we're all very passionate about, and which (as its name indicates) is going to continue to develop and improve at what we hope is an amazing rate. I'm avidly interested in hearing user feedback, and while I can't guarantee that I'll have time to respond to all of it, it will most certainly be listened to.

And the obligatory (very important!) disclaimer: I'm not on this system as an official representative. While I'm listening to user feedback and interacting about the system, I'm also here for perfectly ordinary social networking purposes. If I am saying something official on behalf of Google, I will make that explicitly clear; anything else that I say here is not the position of Google, or of anyone other than myself.

In fact, most of what I post about has nothing to do with CS at all. If you want a taste of it, take a look at my blog.
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