Schrödinger’s… keys?

If I can’t find my keys, they could be on the counter, or in the kitchen table hiding under some junk mail. Or maybe I left them hanging on the door. Until I find them, I obviously can’t say which. It’s a bit like sealing a radioactive atom in a box and leaving it isolated: until I open the box I can’t say whether it decayed. Sounds familiar?

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Quantum… jokes?

Many jokes, particularly puns and one-liners, rely on on setting up expectations, just to subvert them, on double meanings and ambiguity. Take this one:

I would tell you a chemistry joke, but I wouldn’t get any reaction.

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What the heck is a boson?

Particles are strange. In more than one way: for example they behave as if they were spinning, like a top. But they aren’t moving at all. Even if they were, trying to imagine how some of them “spin” would probably melt your brain. The property that measures this “spinning” (though nothing is moving at all here!) is, creatively, called spin.

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The mirror world of antimatter

Now and then in books, movies, or comic books, a mysterious “antimatter” pops up. Usually, what it is and what it does is so vague that it ends up being the sciency version of magic.

A creature of “antimatter” appears in an old Doctor Who episode. credit:

Antimatter is very real: we know it so well we even use it in medicine. Discovering it was one of the greatest successes of theoretical physics. At the same time, though, it put us in quite a predicament.

In the 1920s and 30s, physicists were trying to connect Special Relativity and Quantum Mechanics. The only way to make it work was to introduce a new, strange matter, just like normal matter, but opposite. Like someone’s mirror image. They look the same and move the same, if one raises its left hand, the other raises its right. In particle words, if one has positive charge, or spin up, or anything, the other has negative charge, or spin down, or anything at the opposite. It was indeed more than matter’s mirror image, it was almost its evil twin: they called it antimatter.


The name came from exactly where you think it did— from being the opposite of matter.

As all opposites, when matter and antimatter meet, they cancel out. They disappear in a snap, turning into pure energy—a process called annihilation.


Antimatter wasn’t just sleight of maths: soon scientists sighted the first antiparticles. Finding them was an unprecedented success: theory had traced the path to a then-unseen universe.

But why had it been unseen? Why does our universe consist of matter? Why is it at all? Shouldn’t it have annihilated with an equal and opposite anti-universe? Are the laws of physics different for antimatter?

The Alpha experiment at CERN tries to answer at least the last question. After managing to create and isolate atoms of anti-hydrogen—with anti-electrons, anti-protons and whatnot—scientists stimulated them with lasers. The reaction they saw from anti-hydrogen is exactly the same as the one we know from hydrogen. Antimatter seems equal in front of the law (of physics).

Probably, we’re all made of matter because there was a teeny bit more of it in the early universe. The origin of the microscopic imbalance that gave the universe to matter, however, remains one of the biggest mysteries in science.

A representation of the matter-antimatter imbalance at the Deutsches Museum in Munich (Germany). The tank of black sand represents antimatter in the early universe, the white one represents matter. They are 1 meter tall, the white one has a single grain more. credit:


Cover photo: CC0 Julia Schwab/pixabay

The Big Bell Test: do particles talk to each other behind our backs?

The quantum world is strange. So strange, in fact, that even Einstein—who, we can all agree, was a rather smart man—had issues coming to grips with some stuff in the quantum realm.

For one thing, he really fretted over particle pairs in the so-called entangled state. Without going into much detail: measuring each separately gives random answers, but compare the results and they will always be consistent with each other.

No matter how distant the two particles are, it’s as if they telepathically communicated to each other what to do. I’ll leave it to Veritasium to explain it better than I would.

Einstein didn’t want to believe this. He thought what I’m doing with my particle over here cannot affect your particle over there faster than the speed of light. Which seems very reasonable—but is also wrong. In the sixties John Stewart Bell proved mathematically that, if a theory is to reproduce the results of quantum mechanics (which are right), it has to allow for telepathic particles. This, of course, goes for Quantum Mechanics too, not just for crackpot theories.

Despite verifications that Quantum Mechanics really does what Bell said, some very smart people are still unwavering. So several universities, from Australia to Rome, from Munich to the USA, set up a massive collaborative experiment: the Big Bell Test (get the name now?). In each location, they measured pairs of particles checking Bell’s prediction that they would be “telepathic”. The more random the test, the harder it is to fake telepathy (for people and particles alike), so they measured in random ways.

But weeding out every possible link between seemingly “random” data is really hard, so the scientists decided to turn to the public. 100,000+ people played an online game: their independent, unpredictable decisions there created the random measurements.

How did it end? Early to say, but the preliminary results are that… Well… Sorry, Albert: it happens to the best of us.


John Bell says: deal with it. (CC-BY-SA, modifications by me, click for original)

If you want more
  • I merrily glossed over a ton of stuff this time. In my defense, there are literally entire books on this. Personally, I like this one.
  • If you don’t have time for a whole book, the people at the Big Bell Test put together a playlist, with explanations from the very best educational youtubers.


Cover photo: CC0 Michael Schwarzenberger/pixabay

Theoretical donuts and quantum computers: the Nobel prize 2016

So it wasn’t gravitational waves after all: the Nobel prize for physics went to David Thouless, Duncan Haldane and Michael Kosterlitz. That’s the easy part. The motivation needs a little unpacking:

For theoretical discoveries of topological phase transitions and topological phases of matter.

We all know and love a few phases of matter: solid, liquid and gas (maybe plasma if you want to get kinky). Phase transitions happen when, changing temperature or other conditions, matter goes from one form to the other, like melting ice. But there are more phases and more transitions transitions, some involving electrical and magnetic properties of materials.

Thouless, Haldane and Kosterlitz

David Thouless, Duncan Haldane and Michael Kosterlitz

That’s what the newly-minted Nobel laureates where after. They studied the sudden changes in electrical conductance—the efficiency in carrying electric currents—that some cold materials (I mean -270-odd Celsius) undergo when the temperature changes slightly. This effect is impossible to deal with using quantum mechanics, because it has to do with collective behavior of electrons rather than single ones.

Instead, Thouless, Haldane and Kosterlitz used topology. Topology is the branch of math that deals with properties that stay the same when stretching, twisting and bending stuff, but not puncturing, ripping or gluing it. Topologically speaking, a donut is the same as a pipe—we can turn one into the other—but is different from a ball, because we’d have to sew its hole shut.

Topological features like the number of holes must come in integer numbers: there’s no such thing as a half-hole! So they change in jumps, like that weird conductance. So the scientists theorized that topological transformtions (though not really holes appearing), were behind it.


Steppy changes in topology cause sudden changes in conductance. There are no actual holes involved in the process, though! Holes appearing are just one example of topological changes. Credit: Johan Jarnestad/The Royal Swedish Academy of Sciences

The unusual part of the award is that the discoveries haven’t been applied quite yet: they are purely theoretical. However, they opened the floodgates for the research on materials that exploit these properties. For one, topological materials are an avenue towards the dream of building a quantum computer. During the press conference, Haldane explained that topology could protect the fragile signals in quantum computers from disruption due to impurities in the material itself.

Cover photo: CC0 Thomas Kelley via

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Cats and not


AnThere’s a sealed box, inside the box is a cute cat and a device that can kill it as soon as a radioactive atom decays. Were we to open the box, would the cat be alive? And how is it doing while the box is still closed?

In extreme synthesis, this is the idea of the famous “Schrödinger’s cat” experiment (thought experiment! no actual cats actually harmed! what kind of sicko would do that?!), named after German physicist Erwin Schrödinger, one of the fathers of quantum mechanics.

As you may have heard, as long as we don’t open the box, quantum mechanics allows the cat to be both dead and alive at the same time.

The reason behind this weirdness is one of the founding principles of quantum mechanics: the superposition principle. Simply put, in the microscopic world of quanta, some properties can have several values simultaneously. For example, an electron can be in two places at once, until we go measure it. Then it “picks” a position to be found at. Until then, it really is in several places at the same time.

The superposition principle is a real thing. For real. They did experiments. Quantum theory, then, describes a world fundamentally different than the macroscopic, classical one we know and love.

Our rules don’t work for microscopic particles, and quantum rules don’t work for, like, cats.

Using the rules of one world in the other we get in trouble: a cat cannot be both dead and alive, but an atom can be both decayed and not.

That’s exactly what Schrödinger was trying to do putting a quantum thing (the atom) together with a classical one (the cat).

Precisely those different rules are where the wonderful and magical weirdnes of quantum mechanics comes from.


Cover photo: Cat CCTV, CC-BY-SA Takashi Hososhima, via Flickr. Some rights reserved.