What is graphene?

Want to win a Nobel prize while discovering a material that’s cheap, transparent, flexible but resistent, and an astonishing electric conductor? Grab a pencil and a roll of adhesive tape. I’m serious.

Pencil leads are made of graphite, a form of carbon made of layers of atoms organized in hexagonal cells, like a bee hive. Atoms on the same layer stick together tightly, but are much more loosely attached to the next layer. So, when we write, a few layers peel off the tip and go to the paper.

CC-BY-SA AlexanderAlUS via commons

The sci-fi tech that lead to the discovery of graphene
credit: WikimediaImages/pixabay

If graphite sounds like graphene, it’s because they’re pretty much the same thing. Andre Geim and Konstan Novoselov (who won the Nobel prize for their discovery) created graphene for the first time by repeatedly sticking tape to graphite and ripping it off. Every time a few layers would stick to the tape, until what was left was a single atom thick.

Because it’s so thin, graphene has only the properties of the carbon layer. Without interference from the other layers, it doesn’t behave like a pencil’s graphite anymore. Instead, it supercharges its properties.

For example, each atom is somewhat willing to part with four of its electrons. In a graphene sheet, the atom only has three neighbors to share electrons with, so one is pretty much free to leave and roam around. This makes graphene extremely conductive. If the electrons were busy sticking to other layers (as in graphite) the material would conduct less.

Being so thin, graphene is rather transparent, and very light. But it’s also spectacularly strong (more than steel), thanks to the strong bonds between its atoms.

Thanks to its fantastic properties, graphene is the protagonist of countless works in material science. Electronic devices cannot ask for better than a very conductive material, that doesn’t break and can be used for touch screens.

Making big enough sheets isn’t easy, though, so it still takes a while to have industrial-scale use of graphene.

And if you still want that Nobel prize, I’m afraid the sticky tape and pencil way is taken.

If you want more

Cover photo: Graphene, CC-BY-NC-SA Martin Griffiths/flickr

A singular post

You may have read around that a black hole “is a singularity”. But, if you are interested in artificial intelligence, you also heard about The Singularity, when robots will surpass us. So… robots in black holes? Actually, it all makes sense.

In maths, a singularity is a point that sticks out, because a function does something singular there: it becomes infinite, breaking its usual, mundane behavior. Take the function 1/x. It’s a half when x is 2, it’s a third when x is 3, it’s some number for each and every value of x you can think of. Except for 0, you cannot divide by zero.

Stars collapsing into a black hole create another singularity. According to Einstein’s General Relativity, mass bends spacetime, the more mass, the more bending. Some stars have so much mass that, when they collapse, they bend space and time beyond recognition. Matter, then, keeps falling closer and closer into a single point, infinitely small and infinitely dense. A gravitational singularity, and the star creates a black hole.

Ray Kurzweil is a famous tech author. He describes The Singularity as the moment when computers become better than humans at designing computers, which create even better computers, in a runaway effect. It resembles the gravity runaway inside black holes, and, like we cannot see a black hole’s singularity, we cannot foresee what will happen beyond The Singularity. So The Singularity is kind of like a singularity. Plus the name is cool.

So where can we see what a real-world singularity looks like? Unfortunately, nowhere.

Singularities show the limits of a physical laws. Before you reach those limits, you cross the material ones of the physical world. Before abstract laws break, something concrete will.

If you want more
  • The Stanford Encyclopedia of Philosophy has an entry explaining the meaning of these fascinating points that break physics
  • There’s a lot more to gravitational singularities: there’s a cool post about it on Universe Today
  • What sort of singularity caused that bridge to collapse? Watch this minutephysics video about that
  • PBS Infinite Series explained a bit more about singularities in math

Cover photo: CC0 Pascal Laurent/pixabay

Enceladus: a song of ice and tides

An artist impression of Cassini diving into Enceladus water plumes. credit: NASA/JPL

Cassini will terminate its 20-odd-years-long mission in September. But it’s determined to go out with a bang. In yesterday’s press conference, NASA announced that the probe, during a 2015 flyby of Saturn’s moon Enceladus, found clues that the ocean within the icy moon has almost all we think it needs to spark life.

Enceladus is a fascinating world, with an ice version of Earth’s tectonic activity. Like Earth, Enceladus has volcanoes on its surface, but they spew water, which is what Cassini investigated. Instead of magma, in fact, its surface floats on a gigantic salty ocean. This ocean, NASA announced, seems now the place to go look for life in our solar system.

An illustration of the interior of Enceladus: its icy crust, rocky core and liquid ocean in between. credit: NASA/JPL-Caltech

But that is way off the habitable zone! Shouldn’t Enceladus and all the other ocean worlds be frozen solid all the way through?

They might just escape an icy death using an unusual tool: tides. For astronomers, tides are the difference between gravitational pulls on different sides of a planet or moon. For example, one side of Enceladus is closer to Saturn than the other, so it feels a little more gravity. Since it pulls more on one side than the other, the tidal force stretches Enceladus.

As Enceladus moves around, it gets stretched and pulled in ever-changing ways. So its crust and its interior have to rearrange themselves all the time under this force, parts move and slip on each other. The friction warms the planet up, in a process called tidal heating.

It happens to Earth as well, of course, with tidal forces from the Moon and the Sun. But our planet has an enormous amount of heat left over from its formation, enough to melt rock into magma. Tidal heating doesn’t do much here.

To keep this heat in, Enceladus’ ocean has another unusual ally: the kilometers-thick ice crust over it. Ice is a pretty good thermal insuator, and acts like a giant blanket around the ocean, keeping the freezing void out and precious heat in.

We always focus on what sort of atmosphere planets must have to harbor life, or how far they have to be from cold, dim stars. But it might turn out that a big fat ice cover and powerful tides might go quite some way.

If you want more
  • NASA, as usual, put together a great package with al lot of info on Enceladus and other ocean worlds
  • While sufficient to keep oceans all over some of Jupiter’s moons, tidal heating doesn’t seem to be enough to maintain an ocean around all of Enceladus

Cover photo: CC0 Tilgnerpictures/pixabay

Phenomenal cosmic power, itty bitty living space

Wouldn’t it be great to take the universe in the lab? Astronomy is one of the most captivating parts of physics. I mean, one can’t scoff at the idea of unveiling the mysteries of the cosmos. Unfortuntely, galaxies and black holes don’t exactly cooperate as far as experimenting goes.

A group of physicists is working on a solution.

As it turns out, bottling the immense cosmos in a handful of atoms is but one of the amazing properties of graphene. Graphene is a very thin sheet of carbon, just a single atom thick, all arranged in hexagons like cells in a beehive. Normally, then, each cell has six atoms, but scientists can add or remove one here and there, making some cells with five or seven.

CC-BY-SA AlexanderAlUS via commons

The normal structure of graphene lets a few electrons (one per atom, precisely) rather free to roam around. Cells with one atom more or less mess up this nice order. Electrons can’t just skip around carefree, instead they are attracted to five-atom cells and repelled by seven-atom ones. This creates a little bit of electric current in the material.

Big whoop.

Here comes the cool part, though: this current seems to bend exactly as how spacetime does according to General Relativity. So, appropriately placing atoms, you could simulate fantastically large cosmic phenomena in teeny tiny devices.

An example of wormhole in two-dimensional space-time. credit: telegraph.co.uk

For example, the researchers connected two sheets of graphene to simulate a wormhole—the hypothetical tunnel connecting two far-apart regions of spacetime, like in Interstellar.

The research is still just theoretical, but a tangible prototype should be just around the corner. The researchers say that it should have plenty of applications for electronic devices.

Personally, I’m also interested in holding the (ok, simulated) forces of gravity in the palm of my hand.

If you want more
  • The study isn’t published on journals yet. As far as I understand it’s about to be, in the meantime you can find the manuscript here

Cover photo: CC-BY-SA Karl Wienand, (using felixioncool, WikiImages, skeeze)

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.

Whether you find it funny or not, you can see that it’s all about the double meaning of “reaction”. And that would never work if, when understanding one meaning, you immediately forgot the other. It’s as if, as the joke unravels, “reaction” gained two incompatible meanings simultaneously.

You know what else behaves in multiple, incompatible ways at once? Good old quantum objects.

When measuring the properties of quantum systems, the results depend on context. How you measure the system matters, as does how you prepared your system for the experiment. Something similar also holds for jokes: who tells the joke, how they deliver it, and in what context can make the difference between funny and offensive. Seth Myers has a whole segment based on this.

According to a recent paper on Frontiers of physics, quantum mechanics could be the way to approach humor mathematically. However, as the scientists are quick to specify, this does not mean that humor has any sort of actual quantum behavior. Just that the same math tools could work in both cases.

In this “quantum” framework, the joke-teller sets up some superposition state of words, which now has two meanings at once (like that famous dead and alive cat). As listener gets the joke, they “measure” its funniness, which is a different property (in quantum speak, it’s a different basis), but is also in superposition. Following quantum rules, the measurement destroys the superposition, it picks one of the possible results: either the joke is funny or it’s terrible. Which is picked depends on the listener, on how it was set up, on context, etc.

It’s pretty cool, but researchers only got preliminary and “not terribly surprising” results (their words) from experiments, so it’s not quite clear whether this method can actually work. Still, comedy has used science for years: in movies, TV and comics (just to name a few). Now it could be payback time!

If you want more
  • If you feel you need more details on this whole measuring quantum properties thing, I recommend one of many introductory books, or this nice video

Cover photo: CC0 Sandrine Rongère/pixabay

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.

Some particles behave the same way no matter how you rotate them, they have spin 0. Some others look different if you rotate them, but will come back full circle after… well… a full circle turn: they have spin 1, like a spinning top. Some others come back the same after just half a turn (so not at all like a spin): they have spin 2. And so on.

The sphere on the left doesn’t change, no matter how much you turn it, like a spin 0 particle. The middle one is the same if you give it a full turn, like spin 1. The one on the right comes back after just half a turn, like it had spin2

Some particles have an additional coat of weird: they come back only after two full turns, they have spin 1/2. All the electrons, all protons and neutrons in all the atoms, indeed indeed all the quarks anywhere in the universe have spin 1/2.

These particles are called fermions, because Enrico Fermi was one of the people who described how they behave. Quantum mechanics dictates that no two fermions can be in the same exact same quantum state. This rule is called the exclusion principle, it’s what keeps atoms from melting into chaos. Ultimately, the exclusion principle is the thread suspending our universe’s order over an abyss of indistinguishable particles.

You could call this a fermion-based source of boson radiation. Credit: pexels/pixabay

Particles of integer spin (0, 1, …) don’t have to deal with this nuisance. They can traverse the quantum world oblivious of what their siblings do. All photons (spin 1) coming out of an ideal laser at the same time would be in the exact same quantum state.

Photons don’t usually come out of a laser exactly at the same time, and they are not exactly at the same place. But in principle they could be in the exact same place. Electrons couldn’t CC-BY-SA Andrea Pacelli/flickr

They are called bosons in honor of the work of Satyendra Nath Bose, who worked on describing them. Their job is hitting particles, to make them “feel” some fundamental interaction. Photons carry electromagnetic interactions, the Higgs boson carries the Higgs mechanism, which gives particles their mass, as Dr. Don Lincoln from Fermilab explains more in detail (though the video is a little dated).

If, instead of interacting with one of these so-called “fields”, particles interact with each other, they exchange short-lived “virtual” bosons, but that’s another story. So, if you’re wondering, you are 0% bosons.

If you want more
  • The great Veritasium made a nice video with an explanation of how spin actually works

Cover photo: CC0 Pexels/Pixabay

Circles, social circles and Pi Day

March 14 (or 3/14) is Pi Day. During this somewhat whimsical holiday, science nerds around the globe eat pies and perform needlessly complicated operations to celebrate the fact that the ratio between a circle’s circumference and diameter is 3.14152653… It may be a little confusing from the outside, but that’s sort of the point.

There are several reason behind Pi day, I think: Pi is a good symbol for science, it’s a fantastically inclusive one, and it’s the perfect thing to turn into a nerdy holiday.

Let’s start from its symbolic value. Pi is very recognizable, because most people have run into it at some point in their education. That holds also for a lot of important physical and mathematical constants. Physical constants, however, are not really absolutely constant (their value depending units of measure), plus they are often unsavorily large or very small.

Mathematical constants, instead, are just numbers, like 0 and 1. So why not celebrate excellent numbers like those? Well, Pi has more depth. Nobody knows all of Pi because it’s an infinite, ever-changing sequence of digits. Irrational numbers like Pi (or the golden ratio, e, square root of 2) are elusive and fascinating, but none makes as good a holiday as Pi.

Few (if any) of them can be as easily turned into a date. Then, none is as well-known as Pi. This number is freakin’ everywhere: from school geometry to quantum mechanics, from pendulums to number theory and probability.

Its ubiquity is a testament of how circles enter everywhere in science: whether something involves actual circles (or spheres) or trigonometry (which is just badly disguised circles), Pi is bound to pop up. Any oscillation, from a pendulum to the waves in the sea, to the wave function of quantum mechanics, calls for some trigonometry, and its Pi. Actually it shows up so much in quantum mechanics that scientists found ways to avoid having to write it.

In statistics and mathematics, Pi often comes out through calculations that involve the famous Gaussian probability distribution. This amazing function describes an unbelievable number of phenomena, from the result of rolling many many dice to the distribution of people’s height.

Students organized by height in an old experiment: they follow the characteristic bell shape of a Gaussian distribution.

The Gaussian is circles’ ninja way to come back in the picture (because of details in the math: won’t bore you with that). And one can tell they came through, you guessed it, from Pi.

So mathematician, physicists, engineers and all scientists alike are familiar with this fantastic number and use it practically every day. At the same time, Pi appears almost only in scientific contexts. As a symbol, it includes every branch of science, nothing more and nothing less.

This is also why it’s a great nerdy holiday. One of my favorite definition (-ish) of nerd comes from John Green:

What is nerdier, then, than celebrate the fact that a date looks like the ratio of a circle’s circumference to its radius? In other words, it’s not really about Pi: it’s about meeting and eating pies and finding creative new ways to calculate the ineffable number.

As Christmas is actually a day about love and family, Pi day is actually about community, nerd identity, and being unironically enthusiastic about science and math. There aren’t many such days, let’s cherish this one.

Cover photo: CC-BY Bill Ward/flickr