Tag Archives: Physics

What is dark matter? A deep dive

If you’ve been following our space articles, you may have come across something called “dark matter”. It’s the most abundant type of matter in the universe — our best models have established that dark matter comprises 84.4% of the matter contained in the known universe — but we still don’t really understand just what it is. Dark matter is something that we know is out there, but we have little idea what it’s made of.

Credit: News-G.

Wait, so how do we know it’s even real?

“Regular” matter (technically called baryonic matter) is made of electrons, protons, and neutrons. Cosmologists define the three particles as baryons –technically speaking, electrons are something else, but that’s beside the point here. Baryons make up gas, gas makes up stars, stars go boom and make planets and other things — including you. Yes, you are made of star stuff — baryonic star stuff, to be precise.

All this is done thanks to the electromagnetic (EM) force that forms chemical bonds, glueing regular atoms together But Dark Matter (DM) plays a different game.

Dark matter doesn’t interact with things the way baryonic matter does. It doesn’t scatter or absorb light, but it still has a gravitational pull. So if there are beings made of dark matter living right here, right now, you probably wouldn’t even know it because the perception of touch is felt when your sensory nerves send the message to your brain, and these nerves work thanks to the EM force.

We can’t touch dark matter, and no optical instruments can detect, so how do we ‘see’ it? Indirectly, for starters. Look for gravity, if there isn’t enough visible mass to explain to explain the gravitational pull felt by a region of the universe, then there something there. Invisible does not mean non-existant. If it weren’t for its gravity effect, there would be little indication of dark matter existing.

The main observational evidence for dark matter is the orbital speeds of stars in the arms of spiral galaxies. If Kepler and Newton were correct, stars’ velocity would decrease with the orbital radius in a specific way. But this was not observed by Vera Rubin and Kent Ford, who tracked this relationship. Instead, Rubin and Ford got a velocity vs radius relation that looked like the stars had a nearly constant behavior from a certain point of the galactic orbit.

This could only be explained if there would be a lot more matter somewhere that we’re not seeing. Something was pulling at these stars gravitationally, and that something is dark matter.

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the ‘flat’ appearance of the velocity curve out to a large radius. Credits: Phil Hibbs.

Another important evidence of dark matter comes from galaxy superclusters like 1E 0657-558. Astronomers observed that within this cluster, there are two groups of galaxies placed in a peculiar position to one another. 

If you look at the Hubble Space Telescope image below (1st and 2nd), you’ll notice that there are many galaxies on the left and another group on the opposite side. When astronomers observed in X-ray, they concluded that these two clusters collided and left a gas trace of the shock. The faster cluster was like a bullet (it’s even named the Bullet Cluster) passing through the slower one at around 3000–4000 km/s nearly 100-200 million years ago (3rd pic).

Visible light image from the Hubble Space Telescope, NASA, ESA and the Magellan Telescope, University of Arizona
Visible light image from the Hubble Space Telescope, NASA, ESA and the Magellan Telescope, University of Arizona
X-ray light image from the Chandra X-ray Observatory: NASA, CXC

But one of the most convincing evidence of dark matter came with gravitational lensing.

Scientists used gravitational lensing to estimate the mass of the objects involved in the collision. They found that the galaxies which hadn’t collided agreed with the weak lensing detections. This indicates those galaxies are ahead of ‘the X-ray evidence’ (below, 1st image). Since dark matter doesn’t interact with nearly anything, in this phenomenon, we see a bunch of mass (blue) moving faster than the gas (purple), barely affecting the baryonic matter (2nd image).

Dark matter map: NASA, STScI; ESO; University Arizona
Composite image (visible, dark matter map, X-ray): NASA, ESA, ESO, University Arizona

So what is Dark Matter?

Just because we don’t know what dark matter is doesn’t mean we have no idea. In fact, researchers have a few theories and are considering several plausible candidates.

There are three ways to classify dark matter. Cold dark matter describes the formation of the large-scale structure of the universe and is the fundamental component of the matter in the universe. It’s called cold because it moves ‘slowly’ compared to the speed of light.

Weakly interacting massive particles (WIMPs) are the candidates for cold dark matter particles. They supposedly interact via weak nuclear force. The particles which belong to this group are thought to be the lightest particles of the supersymmetric theories. Neutral examples of these particles could have been produced in the early universe, and later participated in the formation of galaxy clusters.

Hot dark matter is the opposite, it moves close to the speed of light. The warm candidate particles are thought to be less interactive than neutrinos.

Another candidate particle for dark matter is the sterile neutrino — a hypothetical particle that interacts only via gravity and not via any of the other fundamental forces. These would be responsible for forming warm dark matter. They also seem to be heavier than the standard neutrino, and have a longer lifetime before they break down.

Neutrinos were thought to be the best candidates for dark matter. Neutrinos are weird particles — they barely interact with things, and even then only gravitationally (which is a weak interaction). Besides, they do not possess electrical charge, which is why they do not interact electromagnetically. However, the neutrino temperature is high and they decouple (stop interacting with other forms of matter) only at relativistic velocities. If dark matter was made of neutrinos, the universe would have looked radically different.

Massive Compact Halo Objects (MACHOs) represent a different type of candidate. They’re no WIMPs at least. They aren’t particles either, but rather brown dwarfs, planets like Jupiter, black holes in galactic haloes. The best possible MACHOs are primordial black holes( PBHs). Different from the ordinary black holes we see in the center of galaxies, PBHs are thought to have been created nearly 10 seconds after the Big Bang. No evidence for such objects has yet been discovered, but it’s still an open possibility.

Detecting dark matter

Many ideas for the detection of each plausible candidate have been developed.

Through cosmology, the main evidence comes from the Cosmic Microwave Background (CMB).  Yes, the same radiation Dr. Darcy Lewis detected (for real) in the TV miniseries WandaVision. It is the remnant electromagnetic radiation from when the universe was a 380,000-year-old baby.

The best CMB observations we have currently are from the Planck satellite 2018 survey. Different amounts of matter have distinct signals in the CMB observations, forming the temperature power spectrum.

Four Possible Models of the Universe. The yellow square marks the present in all four cases, and for all four, the Hubble constant is equal to the same value at the present time. Time is measured in the vertical direction. The first two universes on the left are ones in which the rate of expansion slows over time. The one on the left will eventually slow, come to a stop and reverse, ending up in a “big crunch,” while the one next to it will continue to expand forever, but ever-more slowly as time passes. The “coasting” universe is one that expands at a constant rate given by the Hubble constant throughout all of the cosmic time. The accelerating universe on the right will continue to expand faster and faster forever. Credits: Physics LibreTexts.

If the theory is correct, the shape of the power spectrum is different for different amounts of matter. There’s such a thing known as the critical density of the universe, which describes the density of the universe if it was coasting, expanding but not accelerating, and if it stopped its expansion. When you divide the density of the observable matter by the critical density, you get its density parameter (Ω).

The temperature power spectrum is modeled according to the different amounts of ingredients in the universe, more matter or less matter changes its shape. Planck’s observations have shown that the matter density parameter is Ω h² ~0.14, so if the shape of the graph corresponds to that value we have evidence of the amount of dark matter in the universe.

Temperature power spectrum for different matter densities. Credits: Wayne Hu.

There are also ways to detect dark matter directly, not through cosmology but through particle physics. The Large Hadron Collider (LHC) is the most powerful particle accelerator, can collide protons at extremely high (relativistic) speeds, generating a bunch of scattered particles that are then measured by the detectors.

Physicists hope to find dark matter by comparing the energy before and after the collision. Since the dark matter particles are elusive, the missing energy could explain their presence. However, no experiment has observed dark matter so far — though researchers are still looking.

Another underground experiment uses high purity sodium iodide crystals as detectors. The detectors at DAMA/LIBRA (Large sodium Iodide Bulk for RAre processes), for example, try to observe an annual variation of regular matter colliding with WIMPs due to the planet’s motion around the Sun which means we’re changing our velocity relative to the galactic dark matter halo. The problem is that DAMA’s 20 years’ worth of data didn’t have enough statistical significance. However, in an identical experiment meant to directly detect dark matter, called ANAIS (Annual modulation with NaI Scintillators), in 3 years scientists gathered more reliable data indicating this method is not conducive to finding dark matter anytime soon. 

To get a better picture of the challenge in having a conclusive result, take a look at the image below. All those lines and colorful contours represent the results of different experiments, none of them seem to agree. That’s the problem with dark matter, we still don’t have the evidence to match any theory we came up with — and we can’t really rule out any possibilities either.

WIMP discovery limit (thick dashed orange) compared with current limits
and regions of interest. Credits: J. Billard and E. Figueroa-Feliciano.

The questions of what dark matter is and how it works still have no satisfying answer. There are many detection experiments being planned and conducted in order to explain and verify different hypotheses, but nothing conclusive thus far. Let’s hope we don’t have to wait another 20 years to figure out if one experiment is right or wrong. Unfortunately, groundbreaking discoveries can take a lot of time, especially in astrophysics. While we wait, dark matter will continue to entertain our imagination.

The article was primarily based on the 2020 Review of Particle Physics from Particle Data Group’s Dark Matter category.

What is entropy, and why is it always increasing?

Life as we know it hinges on us maintaining order. Our bodies die if not kept fueled and at the proper conditions. Appliances break down when you scramble their wires. Our parents get disappointed when we don’t make the bed.

Image via Pixabay.

But regardless of how hard we work at keeping our rooms clean and tidy, the Universe seems to be against us. One value — entropy — describes disorder. And, according to physics, we can’t win against it. No matter what we do, the second law of thermodynamics says that entropy in the universe will stay constant, or increase.

“Technically, physicists define a number called the entropy to measure how scrambled-up the universe is at a given moment of time,” wrote George Musser for Scientific American.

Thus, entropy is perhaps the only truly unstoppable force in the universe, even though it isn’t a force. It started acting ever since the Big Bang. It won’t stop until the heat death of the Universe.

But far from being a malign influence, cynically plotting our demise from the shadows, entropy is simply a product of statistics. It could very well be the thing that gives meaning and direction to the concept of time.

If nothing else, it is a great reminder that in the large picture, what we call order could in fact be chaos, that our planet, our bodies, and our works are the exception, a statistical fluke against a law-abiding, empty Universe.

Sounds cool? Well it does to me, and I’m the guy with the keyboard, so today we’re going to talk about entropy.

The mess of the messy room

The most common way entropy is explained is as disorder or randomness. A clean room, for example, has less entropy than that same room after it hasn’t been tidied for two weeks. It will grow more cluttered over time, but sadly never clean itself by chance.

Cărămizi, Morman, Red, Construcţii, Stivă, Multe
Neither will this.
Image via Pixabay.

Both this example and the equation with disorder have some flaws, as we’ll see later on, but they’re descriptive enough that they’re a good starting point. To get more specific about this concep, we’ll have to look at physics and probability.


Each system has a macrostate (its shape, size, temperature, etc) and several microstates. Microstates define the arrangement of all molecules within that system and how they interact. Each arrangement (each microstate) has a chance of ‘happening’. Entropy is a way of quantifying how likely the system’s current microstate is.

A coin is a very good analogy. Its macrostate is its shape, size, color, temperature. Flip it two times, however, and you get four possible microstates — alternating heads and tails, two heads, or two tails. All are possible, but one outcome (a sequence of heads and tails) has a 1 in 2 chance of happening, while the others have a 1 in 4. Because of that, the heads-and-tails sequence is the one with the highest entropy.

This statistical understanding of the term is rooted in the physical definition of entropy, and I’m simplifying things a lot, but I feel it’s the best rough idea of how it works.

Castles grow moss and crumble, heels snap off of shoes. Ordered systems break down over time because there’s a single microstate in which they stay the same, and countless in which they change. It’s immensely more likely to happen.

Spontaneous reductions in entropy are possible, such as the formation of life or crystals. Josiah Willard Gibbs, an American engineer from the early 1900’s even found a way to calculate why (more on that later). However, overall, entropy in a system increases over time, because changes towards disorder are overwhelmingly more likely than those towards order.

From a physical point of view

We all instinctively understand that disorder is more likely than order, but why?

The meat of it is that randomness is simple and low on energy. It’s homogeneous. Nature loves that.

A glass of ice is more orderly than a glass of water. Molecules in ice are kept in a very specific arrangement, forming a lattice that we perceive as ice cubes. If you were to simulate a glass of it, you’d have to program their molecular composition, shape, size, and position relative to one another. For the glass of water, all you need to do is define the shape of the glass and how high you’re filling it because its molecules move in an undefinable manner. The ice takes more data to make it what it is, it’s more complicated, so it’s less probable.

Entropy also moves things along towards low states of energy (including potential energy) because spontaneous processes tend to work towards fixing imbalances and thus expending energy. A glass filled half with ice and half with boiling water has a higher imbalance and a lower entropy than a glass where they’re mixed — so they do.

Some probabilities are more likely than others — which is our statistical entropy — because they lead to simpler, more homogenous systems by transforming energy — our physical entropy. And in nature, quite like in finances, nothing happens unless you pay for it (with free energy).

Bringing us neatly to:

Gibbs’ Free Energy

In short, Gibbs’ free energy formula tells us if a process will happen spontaneously, or not.

The free energy of a system can be used to perform physical work (to move things). It’s enthalpy (heat) minus the product of temperature and entropy. As long as it’s negative, the system — such as a chemical reaction — can start spontaneously. This means that either a transfer of heat, which is energy, or an increase in entropy can provide power for the system. This latter one is usually seen as changes to volume, especially in endothermic (heat absorbing) reactions.

Gibbs’ formula shows us that there is energy to be had from breaking apart chemical bonds, so molecules generally try to become as small as they can. Fluids, like liquids or gas, are generally made of smaller, lighter molecules. They’re also an a higher entropy state than solids, for example, since their molecules can move freely among themselves.

The arrow of time

Since things naturally tend to gain entropy, then complex systems tend to break down into disorganized ones. It is one of few physical notions that require a very definite direction in time.

There’s technically no natural laws which say that a piece of burnt wood and a puddle of water can’t un-burn and freeze back, apart from entropy. All the energy and matter in the world was at some point concentrated in a single point during the Big Bang. It’s still here. The only difference since then is that there’s way more entropy around, and it’s always growing.

Because entropy flows a single way, it has been argued that entropy makes time-travel impossible — but only time will tell.

From what we know so far, one of two possible outcomes is for entropy to win out in the end. We call this hypothetical scenario the Big Freeze or Big Chill, or “the heat death of the Universe“. I personally like the last one because it just seems appropriately dramatic. In such a scenario, there is no more free energy in the whole universe. As such, there can be no increase in entropy. But it also means that nothing would happen, nothing would ever move.

So are we doomed? Not necessarily. We could subvert this if we learn how to create hydrogen from pure energy. Hydrogen powers stars, and those could (maybe?) be used to stave off this heat death. There’s also the other alternative, the Big Rip, but that one doesn’t sound pleasant either.

All in all, entropy is a very complex topic. It can only be defined through the system it’s being applied to, so different academic areas will somewhat focus on particular elements of this concept.

But it definitely is a fascinating subject. It’s a bit humbling to know that the same thing making your bedroom dirty is also probably going to end the universe one day.

The tale of physics’ most famous cat is one that is familiar to many, but what is the inside story of the feline so demanding it requires its own Universe, and how does it illustrate the 'weirdness' of the quantum world?

Superposition! The strange tale of Schrödinger’s cat

The tale of physics’ most famous cat is one that is familiar to many, but what is the inside story of the feline so demanding it requires its own Universe, and how does it illustrate the 'weirdness' of the quantum world?
The tale of physics’ most famous cat is one that is familiar to many, but what is the inside story of the feline so demanding it requires its own Universe, and how does it illustrate the ‘weirdness’ of the quantum world? (Robert Lea)

Of all the counter-intuitive elements of quantum physics introduced to the public since its inception in the early days of the twentieth century, it is quite possible that the idea that a system can be two (or more) contradictory things at once, could be the most challenging.

As well as defying a well-known aspect of logic — the law of non-contradiction — thus irritating logisticians, this idea of the coexistence of states, or superposition, was even a challenge to the fathers of quantum physics. Chief amongst them Erwin Schrödinger, who suggested a diabolical thought experiment that would show what he believed to the ludicrous nature of a system existing in contradictory states. 

The thought experiment would go on to become perhaps the most well-known in the history of physics, weaving its way on to witty t-shirts, hats, bags and badges, infiltrating pop-culture, TV and film. This is the strange tale of Schrödinger’s cat, and what it can teach us about quantum physics and the nature of reality itself. 

Before delving into the experiment that Schrödinger devised, it is worth examining the circumstances that led him to consider the absurd situation of a cat that is both living and dead at the same time. 

Wanted: Dead or Alive! How the cat got put in the box

In many ways, Erwin Schrödinger’s place in the history of quantum mechanics is overshadowed by his feline-based thought experiment. The Austrian physicist was responsible for laying the foundation of a theoretical understanding of quantum physics with the introduction of his eponymous wave equation in 1926. As Joy Manners describes in the book ‘Quantum Physics: An Introduction’:

“The Schrödinger equation did for quantum mechanics what Newton’s laws of motion had done for classical mechanics 250 years before.”

Joy Manners, Quantum Physics: An Introduction

What Schrödinger’s equation shows is that the state of a system — the collection of all of its measurable qualities — can be described as a wavefunction — represented by the Greek letter Psi (Ψ). This wavefunction contains all the information of a system that it is possible to hold. Each wavefunction is a solution to Schrödinger’s equation, but here’s the crazy part; two wavefunctions can be combined to form a third, and this resultant wavefunction can contain completely contradictory information.

When the wavefunctions of a system are combined it is in a ‘superposition’ state. There is also no limit no how many of these wavefunctions cam be combined to form a superposition. 

Yet, infinite though a wavefunction can be, eternal it is not. The act of taking a measurement on the system in question seems to cause the wavefunction to collapse — something there is as yet no physical or mathematical description for. There are, however, interpretations of what happens, which go to the very heart of reality.

Before tackling these interpretations, first, we should get to our cat in the box before he gets too impatient. 

A most diabolical device 

It was in 1935, whilst living in Oxford fleeing the rise of the Nazis, that Schrödinger first published an article that expressed his concern with the idea of measurement, wave function collapse, and contradictory states in quantum mechanics. Little would he know, it would lead to him becoming history’s most infamous theoretical-cat-assassin. 

A common illustration of the Schrodinger’s Cat thought experiment (Dhatfield / CCbySA 3.0)

Below Schrödinger describes the terrible predicament that his unfortunate moggy finds himself in. 

“A cat is placed in a steel chamber with the following hellish contraption… In a Gieger counter a tiny amount of a radioactive substance, so that maybe within an hour one of the atoms decays, but equally probable is that no atom decays…”

So, there is a 1/2 chance that an atom of the substances decays and causes the Gieger to tick over the hour duration of the experiment. 

“If one decays the counter triggers a little hammer which breaks a container of cyanide.” 

So, if the atom decays over the hour, the cat is killed. If it doesn’t, the cat survives. Treating the box and the cat as a quantum system how would we describe its wavefunction (Ψ)?

The wavefunction of the system now exists in a superposition of the individual wavefunction that describes the cat as being alive, and the one that declares it dead. According to the rules of quantum physics, the cat is currently both dead and alive.

Our unfortunate feline isn’t doomed to live out its existence as some bizarre quantum zombie, though. A quick peek inside the box constitutes a measurement of the system. Thus, by opening the box we collapse the wavefunction and determine the fate of Schrödinger’s cat. It really is curiosity that kills the cat, in this case.

Let’s end our analogy on a happy note. We open our box and fortunately the substance has not undergone decay. The cyanide bottle remains intact. Our moggy survives, unscathed if irritated. The wavefunction collapsed leaving the blue sub-wavefunction intact, but what actually just happened here? How was the cat’s fate determined? 

The short answer is, we don’t know, but we have some interpretations. Next, we compare the two most prominent. 

Way more than nine lives. The many-worlds interpretation 

What we have discussed thus far consists of a very rough description of the Copenhagen interpretation of quantum mechanics. The reason it’s common sense to present this first is that it is generally the interpretation that is most widely accepted and taught.

As you’ve seen, the Copenhagen interpretation describes a system with no established values until a measurement occurs or is taken and a value — in our case ‘alive’ — emerges. If this sounds deeply unsatisfactory, well, it is. One of the questions it leaves open is ‘why does the wavefunction collapse?’

In 1957, an American physicist Hugh Everett III, asked a different question: ‘What if the wavefunction doesn’t collapse at all? What if it grows?’ From this emerged Everett’s ‘relative state formulation’, better known to fans of science fiction, comic books and fantasy as the ‘Many Worlds Hypothesis/interpretation’.

Below we see what happens to the wavefunction in the Copenhagen interpretation. The box is opened and the wavefunction collapses. 

So what happens in the ‘many worlds’ interpretation? Rather than collapsing, as the box is opened the wavefunction expands. The cat does not cease to be in a superposition, but that superposition now includes the researchers and the very universe they inhabit. We become part of the system.

In the many-worlds interpretation, the researchers do not open the box to discover if the cat is dead or alive, they open the box to see if they are in the universe where the cat survived or the universe in which it was dispatched. They and their world have become part of the wavefunction. An entirely new universe in superposition with the old. The only difference. 

One less cat.

Schrodinger’s Kittens: Some words of caution

Again, as with the Copenhagen interpretation, there is no real experimental evidence of many worlds concept. In many ways, any interpretation of quantum mechanics is really more a realm of philosophy than science. Also, when considering ‘many worlds’ it’s worth noting that this is a different concept than the idea of a ‘multiverse’ of different universes created at the beginning of time. 

Further to this, there are some real problems with considering the ‘cat in a box’ as a quantum system. Researchers are constantly finding quantum effects in larger and larger systems, the current record seems to be 2,000 atoms placed in a superposition. To put that into perspective; a humble cat treat contains around 10²² atoms!

Many physicists have suggested reasons why larger systems fail to display quantum effects, with Roger Penrose suggesting that any system that has enough mass to affect space-time via Einstein’s theory of general relativity can’t be isolated. Via the influence of gravity, it is constantly having ‘measurements’ taken. This would definitely apply to even the most minuscule moggy. 

It is worth noting here that the general description of the thought experiment and the opening of the box has led some to speculate that it is the addition of a ‘consciousness’ that actually causes the wavefunction collapse. 

This is an idea that has sold a million or so books on ‘quantum woo’ and it arises from the unfortunate nomenclature of quantum physics. The use of the words ‘measure’ and ‘observe’ imply the intervention of a conscious observer. The truth is that any interaction with another system is enough to collapse a quantum wavefunction, as they tend to exist in incredibly delicate, easily disturbed states. 

Sources and further reading

Schrödinger. E,

Griffiths. D. J, ‘Introduction to Quantum Mechanics,’ [2017], Cambridge University Press.

Broadhurst. D, Capper. D, Dubin. D, et al, ‘Quantum Physics: An Introduction,’ [2008], Open University Press.

Nomura. Y, Poirer. B, Terning. J, ‘Quantum Physics, Mini Black Holes, and the Multiverse,’

Orzel. C, ‘How to Teach Quantum Physics to your Dog,’ [2009], Simon & Schuster. 

Nobel Physics Prize goes to cosmology and exoplanet pioneers

The Nobel Physics Prize 2019 has been jointly awarded to James Peebles, Michel Mayor and Didier Queloz. Peebles received half of the prize “for theoretical discoveries in physical cosmology”, while the other half was jointly awarded to Mayor and Queloz “for the discovery of an exoplanet orbiting a solar-type star.”

It was a fitting award in the field of cosmology, which has undergone a dramatic transformation in recent decades.

“This year’s Laureates have transformed our ideas about the cosmos,” the Assembly wrote in a release accompanying the Prize’s announcement. “While James Peebles’ theoretical discoveries contributed to our understanding of how the universe evolved after the Big Bang, Michel Mayor and Didier Queloz explored our cosmic neighbourhoods on the hunt for unknown planets. Their discoveries have forever changed our conceptions of the world.”

James Peebles is widely regarded as one of the world’s leading theoretical cosmologists, being a major figure in the field ever since the 1970s. He made numerous contributions to the Big Bang model, particularly explaining what happened in the universe in the instances after the Big Bang took place. Along with several cosmologists, he successfully predicted the existence of the cosmic microwave background radiation. He was working in the field of physical cosmology long before it was regarded as a “serious” branch of physics and did much to change this unwarranted perception. Peebles also contributed to the establishment of the dark matter concept, and also worked on dark energy.

Meanwhile, Mayor and Queloz were the first to discover an exoplanet around a main-sequence star, in a solar system fairly similar to our own. In 1995 Queloz was a Ph.D. student at the University of Geneva, and Mayor was his advisor. Together, they used Doppler spectroscopy (an indirect velocity measurement using the Doppler shift) to discover 51 Pegasi b, an exoplanet which lies around 50 light-years away from Earth. 51 Pegasi b is the prototype for a class of planets called “hot Jupiters” — planets which look like Jupiter, but orbit much closer to their star and are very hot. The star marked a breakthrough in astronomical research and is still actively studied today (in 2017, traces of water were detected in its atmosphere). The exoplanet’s discovery was announced on October 6, 1995, in the journal Nature.

“I couldn’t breathe,” said Queloz upon receiving the news.

Today, the field of cosmology is well established, and we have discovered thousands of exoplanets — but these three were true trailblazers for their respective fields. It’s a remarkable testament to how far we’ve come and how influential their work was.

Herein also lies one of the beauties and the curses of the Nobel Prize: because it’s often awarded decades after the discovery was made, it serves as a lifetime achievement award, but it often feels non-contemporary.

Previously, a trio won the Nobel Peace Prize for medicine for uncovering how cells sense and adapt to oxygen levels. The remaining 2019 Nobel Prizes are yet to be awarded.

Decade-old debate put to rest with new measurement of proton diameter

We now have an accurate measurement of how large protons are.

Image via Pixabay.

Back in 2010, a team of physicists set their field (figuratively) on fire. They measured the radius of a proton and found it to be 4% smaller than expected. Physicists are very passionate about this kind of stuff and it sparked a huge debate. Now, researchers from York University have put the debate to rest by taking a precise measurement of the size of the proton.

How big is something very small?

“The level of precision required to determine the proton size made this the most difficult measurement our laboratory has ever attempted,” said Distinguished Research Professor Eric Hessels, Department of Physics & Astronomy, who led the study.

The exact size of the proton is an important unsolved problem in fundamental physics today, one which the present study addresses. The team reports that protons measure 0.833 femtometers in diameter (a femtometer is one-trillionth of a millimeter). This measurement is roughly 5% percent smaller than the previously-accepted radius value.

“After eight years of working on this experiment, we are pleased to record such a high-precision measurement that helps to solve the elusive proton-radius puzzle,” said Hessels.

The exact measurement of the proton’s radius would have significant consequences for the understanding of the laws of physics, such as the theory of quantum electrodynamics, which describes how light and matter interact. Hessels says that the study didn’t exist in a vacuum — three previous studies were pivotal in attempting to resolve the discrepancy between electron-based and muon-based determinations of the proton size.

The 2010 study was the first to use muonic hydrogen to determine the proton size (whereas previous experiments used regular hydrogen). Hydrogen atoms are made up of one proton and one electron In the 2010 experiment, the team replaced the electron with a muon, a related (but heavier) particle.

While a 2017 study using simple hydrogen agreed with the 2010 muon-based result, a 2018 experiment, also using hydrogen, supported the pre-2010 value. Hessels and his team spent the last eight years trying to get to the bottom of the issue and understand why researchers were getting different results when measuring with muons rather than electrons.

The team carried out a high-precision measurement using a technique they developed for this purpose, the frequency-offset separated oscillatory fields technique (FOSOF). In essence, they used a fast beam of hydrogen atoms created by shooting protons through hydrogen molecules. Their result agrees with the value found in the 2010 study.

The paper “A measurement of the atomic hydrogen Lamb shift and the proton charge radius” has been published in the journal Science.

We’re 50 km closer to quantum internet

A team of researchers based in Innsbruck reports sending light entangled with quantum information over a 50-kilometer-long stretch of optic fiber.

Image credits Joshua Kimsey.

The study comes as a collaboration between members at the Department of Experimental Physics at the University of Innsbruck and at the Institute of Quantum Optics and Quantum Information of the Austrian Academy of Sciences. They report setting the longest record for the transfer of quantum entanglement between matter and light.

Such results pave the way for long-range quantum communication, which would enable transfer between different cities, for example. Effectively, the early stages of quantum bit Internet.

Lasers and crystals

“[50 km] is two orders of magnitude further than was previously possible and is a practical distance to start building inter-city quantum networks,” says Ben Lanyon, the Ph.D. and experimental physicist at the Austrian Academy of Sciences who led the research.

One of the most appealing prospects of a quantum internet is that it should be completely tap-proof. Information in such a network is encrypted and unbreakable, and any interference with the signal readily apparent.

However, quantum information cannot be copied, so it wouldn’t work through your router.

Such information needs to be carried by entangled particles. So the team took a calcium ion, secured it in an ion trap, and blasted it with lasers. This step both ‘wrote’ the information into the ion as a quantum state and made it emit a photon (to ‘glow’, basically). Then, this photon needed to be amplified to be sent down the optic fiber.

“The photon emitted by the calcium ion has a wavelength of 854 nanometers and is quickly absorbed by the optical fiber,” says Lanyon.

The researchers sent the photon through a crystal illuminated by a strong laser to boost it up to a wavelength of 1550 nanometers. The calcium atom and light particle were still entangled even after the conversion and a 50-kilometer journey through the optic cable.

In the future, the team wants to double the distance such a particle can travel to 100 km of optic fiber, potentially enabling connections between cities. Only a handful of trapped ion-systems would be required to maintain a quantum internet link between Innsbruck and Vienna (387km/240mi), for example.

The paper “Light-matter entanglement over 50 km of optical fibre” has been published in the journal npj Quantum Information.

We can now film chemical reactions on an atomic level as they unfold

Researchers manage to film a chemical process unfolding on the atomic scale for the first time in history.

The paper, lead-authored by Junfei Xing at The University of Tokyo, Department of Chemistry, shows that there are distinct stages in the process of chemical synthesis. Their work could help guide new strategies and methods for chemical synthesis with greater control and precision than ever before. Prime applications are in materials science and drug development, according to the authors.

Smile for the camera

“Since 2007, physicists have realized a dream over 200 years old—the ability to see an individual atom,” said Project Professor Eiichi Nakamura, the paper’s corresponding author.

“But it didn’t end there. Our research group has reached beyond this dream to create videos of molecules to see chemical reactions in unprecedented detail.”

Nakamura’s team specializes in the field of material synthesis, with an emphasis on the control of the processes that are used in this field. However, they’ve always been hampered by the lack of any tool to observe these processes as they unfold.

The different stages of complex chemical reactions are difficult to study as they involve multiple intermediate steps, making them very hard to model. In theory, we could just look at these steps unfolding. In practice, however, it was impossible to isolate the products at each stage and to see how these changed over time.

“Conventional analytical methods such as spectroscopy and crystallography give us useful information about the outcomes of processes, but only hints about what takes place during them,” explained Koji Harano, project associate professor in the Nakamura group and co-author of the study.

“For example, we are interested in metal-organic framework (MOF) crystals. Most studies look at the growth of these but miss the early stage of nucleation, as it is difficult to observe.”

Nakamura and the team spent over 10 years working on a solution — and finally they developed one they call molecular electron microscopy. This meant, overcoming the engineering challenge of combining a very powerful electron microscope with a fast and sensitive imaging sensor (used to record video), while at the same time finding a way to pick and hold molecules of interest in front of the lens.

For the latter, the team employed a specially-designed carbon nanotube which was held in place at the focal point of the electron microscope. This would snag up passing molecules and hold them in place, but not interfere with them chemically. The reaction could thus unfold on the tip of the nanotube, where the team could record it. Harano admits that “what surprised us very much in the beginning was that our plan actually worked.”

“It was a complex challenge, but we first visualized these molecular videos in 2013,” he adds. “Between then and now, we worked to turn the concept into a useful tool.”

“Our first success was to visualize and describe a cube-shaped molecule, which is a crucial intermediate form that occurs during MOF synthesis. It took a year to convince our reviewers what we found is real.”

The team says their work is the first step towards gaining control over chemical synthesis in a precise and controlled manner — a term they call “rational synthesis.” If we know what goes on along every step of a chemical reaction, we can better control the outcome.

In time, the team hopes their work will lead to things like synthetic minerals for construction, or even new drugs.

The paper “Atomistic structures and dynamics of prenucleation clusters in MOF-2 and MOF-5 syntheses” has been published in the journal Nature.

New study reveals why dandelions are among the best fliers — they take to the air in a unique way

There’s something poetic about blowing dandelions to the wind, but there’s also a lot of science to it. A new study has shown that dandelion seeds fly in a way that’s never been seen before in nature, and that could inspire a new generation of airborne sensors.

Note the peculiar structure.

Blowing dandelions might have a romantic appeal, but for these plants, taking to the air is of utmost importance. Using their parachute-shaped bundle of bristles, their seeds can spread over more than a kilometre, sustained by nothing but wind power. This is essential for the plant to be able to spread out over large areas, which also helps explain why the plant is so common in many parts of the world. But a team of researchers working in Edinburgh, Scotland, realized that we don’t really know how dandelions are able to fly such a long distance.

“Dandelions (Taraxacum officinale agg.) are highly successful perennial herbs that can be found in temperate zones all over the world,” researchers write. “Dandelions, as with many other members of the Asteraceae family, disperse their bristly seeds using the wind and convective updrafts.”

Their long fights are a bit surprising because the parachute-like structure the flowers exhibit is, for the most part, empty — it’s filled with air, which at a first glance seems woefully unfit for taking flight. Essentially, instead of looking like an umbrella or a parachute, it looks more like the skeleton-like frame of a parachute — and having a porous parachute doesn’t seem to make much sense.

An image of a micro CT scan of a dandelion seed, artificially coloured grey. Image credits: Madeleine Seale, Alice Macente.

Dandelions use a bundle of bristly filaments, called a pappus, to help keep their seeds aloft for dispersal. After the pappus takes to the air, it also prolongs the descent of the seed, enabling it to be carried much farther away. This is not uncommon in the plant world, as many other species employ a similar strategy — but they have a wing-like membrane instead of the spiky pappus.

So Naomi Nakayama, Ignazio Maria Viola, and colleagues set out to study exactly what happens to the dandelion flight. They constructed a vertical wind tunnel to visualize the flow around freely flying and fixed dandelion seeds, employing long-exposure photography and high-speed imaging to monitor any effects. They illuminated the seeds with a laser to make the entire system easier to visualize.

Researchers found that air does indeed flow through the bristles of the pappus, but the amount of air is very closely controlled by the spacing between the bristles, and this is very important. This particular structure formes a stable, doughnut-shaped air bubble, floating around each pappus. They call this air bubble a vortex ring.

According to co-author Cathal Cummins, an applied mathematician at the University of Edinburgh, the pressure differences between the air moving through the spokes and the air moving around the seed creates the vortex ring. The vortex ring is detached from the seed body, and the dandelion’s pappus porosity is fine-tuned to stabilize this vortex.

The dandelion seed and the vortex that it generates. Cummins et al / Nature.

The porous dandelion pappus consistently contains 90 to 110 filaments — no more and no fewer. If the number of filaments strays outside this range, the air bubble doesn’t form and the dandelion’s flight properties are negated. But if it stays within that range, the pappus delivers more than four times more drag per unit area compared to a conventional, wing-like membrane. The authors argue that this makes the plumed design far more efficient than a wing-like membrane for the dispersal of lightweight seed. It’s also a type of flight that’s never been observed before.

“The discovery of the separated vortex ring provides evidence of the existence of a new class of fluid behavior around fluid-immersed bodies that may underlie locomotion, weight reduction and particle retention in biological and manmade structures,” the paper states.

This is very significant, for more than just dandelions. This type of structure could be replicated in the design of small-scale drones that require very little or no power consumption at all. These drones could function as remote sensing or pollution sensors.

The study has been published in Nature.

Mathematicians solve old mystery about spaghetti breaking

Here’s an experiment: grab a dry spaghetti noodle on both ends. Bend it more and more, until it breaks. Intuitively, you’d think it breaks into two pieces, but that’s almost never the case — it typically breaks into 3 or 4 different pieces. Try again and again, as many times as you want, you’ll likely never end up with two pieces.

Experiments (above) and simulations (below) show how dry spaghetti can be broken into two or more fragments, by twisting and bending.

The Spaghetti Conundrum

If that confuses you, don’t worry — you’re in good company. This spaghetti conundrum has flummoxed scientists for decades. Even the renowned and ever-curious physicist Richard Feynman was fascinated by this. By his own account, he spent the better part of an afternoon breaking spaghetti in halves and wondering why they don’t snap in two. He couldn’t come up with a satisfying explanation, and the mystery remained unsolved until 2005 when physicists from France came up with a working theory.

They found that when a spaghetti — and for that matter, any long rod — is bent at the ends, it will break near the center, where it is most curved. But as it breaks, triggers a “snap-back” effect, producing a bending wave, or vibration, which further breaks the rod. The theory was demonstrated, and as a reward for their trouble, the French physicists received an Ig Nobel Prize, a parody of the Nobel Prize, which celebrates unusual or trivial findings.

But even after this, a question remained: is it never possible to break a spaghetti in two? The answer is ‘yes’, with a twist — as in if you twist them, you can break them in only two. In a paper published this week in the Proceedings of the National Academy of Sciences, researchers report that if you also twist the spaghetti, this dampens the shock wave and reduces the chance of breaking into several pieces. Essentially, if a stick is twisted past a critical degree, then slowly bent in half, it will break in two.

However, researchers say, this could have far-reaching implications, going way beyond culinary curiosities. The findings could be used to control fractures and increase toughness in rod-like materials such as multifiber structures, engineered nanotubes, or even microtubules in cells.

“It will be interesting to see whether and how twist could similarly be used to control the fracture dynamics of two-dimensional and three-dimensional materials,” says co-author Jörn Dunkel, associate professor of physical applied mathematics at MIT. “In any case, this has been a fun interdisciplinary project started and carried out by two brilliant and persistent students — who probably don’t want to see, break, or eat spaghetti for a while.”

The spaghetti can be broken in two by adding a 270 degree twist, due to the snap-back and twist-back effects working together.

Pasta maths

The two students Dunkel is referring to are Ronald Heisser, now a graduate student at Cornell University, and Vishal Patil, a mathematics graduate student in Dunkel’s group at MIT. Their co-authors are Norbert Stoop, instructor of mathematics at MIT, and Emmanuel Villermaux of Université Aix Marseille. They designed a device that can controllably bend and twist spaghetti ends, focusing on two types of spaghetti: Barilla No. 5 and Barilla No. 7, which have slightly different diameters.

“They did some manual tests, tried various things, and came up with an idea that when he twisted the spaghetti really hard and brought the ends together, it seemed to work and it broke into two pieces,” Dunkel says. “But you have to twist really strongly. And Ronald wanted to investigate more deeply.”

Meanwhile, Patil developed a mathematical model to explain this behavior, building on the previous work done by French scientists Basile Audoly and Sebastien Neukirch, who first studied this behavior. Putting all the hard work together, they finally solved this unusual puzzle — but there is one caveat.

Their study works on the assumption of cylindrical shapes — in other words, it only works for “classic” pasta. Other types of pasta, like fussili or linguini will have a different behavior because they also have a different geometry.

The study has been published in PNAS.

egg spinning

Why a spinning hard-boiled egg always faces up

Sometimes, it takes a lot of time and dedication before a clever mind comes along and solves a long-standing mystery. Take the mind-boggling conundrum of the spinning hard-boiled egg that always stands upright as it continues to whirl around.

egg spinning

Credit: Giphy.

Physicists have come to learn that the spinning egg mainly rises due to the force of friction between the egg and the table. However, these explanations often employ complex equations and don’t capture the full picture. It was only recently that Rod Cross, a physicist at the University of Sydney, finally came up with a more elegant explanation.

Cross’ expertize is in plasma physics, but the retired Australian physicist is a sort of a local celebrity for his entertaining studies in Sports Mechanics, an interest that has led him to become a consultant to the police in murder investigations. On his website, you can find all sorts of video and explanations on everything from the physics of billiards and tennis balls to silly putty.

spinning egg

Credit: Ross Cross.

In a recent paper published in the European Journal of PhysicsCross showcased the findings of his experiments with a solid aluminum spheroid. The experiments showed that a spinning hard-boiled egg rotates, or precesses, about two different axes. One is the vertical axis, which is obvious as the egg spins. The other is the horizontal axis around which the egg rotates as it stands up on its end due to the horizontal friction force. When the egg starts rolling, the friction force drops to zero, stopping the egg’s motion.

“If an egg is on its fat end when it falls, it slides forward. On its pointy end, the egg rolls right over then slides. The egg has more potential energy when the fat end is at the top, so there is more kinetic energy when it falls. If the fat end remains at the bottom after falling, then the thin end can rotate all the way up to the top with enough energy left over to swing it past the top,” Cross wrote on his website. 

“Spun slowly clockwise, the egg precesses in a counter-clockwise direction,  rocking from one end to the other, in the same way that people move heavy furniture.”

Cross’ experiments also confirmed that the faster an egg spins, the more upright it stands. And if the egg isn’t spun with enough force, it won’t rise at all because friction causes the egg to roll instead of sliding and standing up. These characteristics are reminiscent of spinning coins and the inversion of a tippe top.

Rod Cross. Credit: Rod Cross.

Rod Cross. Credit: Rod Cross.

“Spinning eggs have been studied for more than 100 years, but there has not previously been a simple explanation for the rise, either of spinning eggs or the tippe top,” Cross told Phys.org. “The essential physics cannot be conveyed to an undergraduate student or to a physics teacher by explaining that an egg rises because the equations predict that it will rise.

“Part of the problem is that there have not been enough experimental measurements to pin down the separate roles of sliding and rolling friction in causing the egg (or tippe top) to rise and then causing it to stop rising if it is not spun fast enough.”

Scientists design $100 muon detector

With the price you’d pay for a big night out with your friends, you could build your very own muon detector.

Physicists at MIT have designed a pocket-sized cosmic ray muon detector to track these ghostly particles. Courtesy of the researchers.

Our planet is constantly showered with a cocktail of high-energy cosmic rays. Thankfully, we have the atmosphere to protect us, and the cosmic rays don’t really penetrate to the planetary surface; after colliding with the Earth’s atmosphere, they disintegrate into muons — elementary particles similar to the electron, but with a larger mass.

The problem is that muons disintegrate extremely fast. They can be found in every layer of the Earth’s atmosphere, circulating in the air around us, but they’re hard to study because their entire lifespan stretches to approximately 2.2 microseconds.

Now, physicists working in MIT’s Laboratory for Nuclear Science have designed a small, pocket-sized muon detector. Using only common, relatively cheap electrical parts, MIT researchers have built a detector that lights up and counts each time a muon passes through. It only costs $100 to build, if you have the necessary facilities.

Spencer Axani, the man behind the project, set up an outreach program called CosmicWatch with a website that lists where to buy all the parts and how to assemble them into a functioning device. The team estimates that it would take a high school student with average skills about 4 hours to build it, and then just one hour to build it a second time.

The more of these are built, the more useful the measurements get, Axani explains.

“If you make 100,000 of these, it starts becoming a very large detector,” Axani told Symmetry Magazine. “Instrumenting airplanes and ships would let you start measuring cosmic ray rates around the world.”

You might not get much of a thrill from the detector, but for a physics demonstration, or for unleashing your inner scientist, it’s a unique project which allows you to do some top notch science from the comfort of your bedroom. You might also get some secondary applications, such as checking the altitude you’re at — through muon detection.

“You get funny looks when you take particle detectors into the subway, but we did that in Boston,” Axani says. “Since the muon rate will decrease the further down you go, we put the detectors in a subway station to measure how far underground we were.”

“At sea level, you might see one count every two seconds […] but on a plane at cruising altitude, that rate increases by about a factor of 50 — a dramatic change,” Axani says. “From the measured rate you can back-calculate what the actual altitude of the plane was.”

Recently, a different team of researchers also identified a potential cavity beneath the Great Pyramid in Egypt using similar muon measurements.

Hiker with luggage.

Why wheelie suitcases wobble out of control and what you can do to stop them

Researchers from the MSC laboratory at Université de Paris have cracked the decades-old problem which plagues travelers everywhere — why won’t our wheelie suitcase just stay put and not wobble?

Hiker with luggage.

Image credits Pixabay.

If you’ve ever had to pull a roller luggage for any meaningful length you know how wobble-prone these things are. For us muggles, the bag’s fishtailing only amounts to a nuisance and a secret sense of shame at not being able to control the things, but for physicists, it’s an actually intriguing problem — much like it is with shoelaces.

To get to the bottom of things, a team of researchers from Université de Paris took a model suitcase to the treadmill and observed its motions. Now, they report that the luggage’s side-to-side motions at any point in time are directly related to its forward motion, its tilt, and the distance between its center of weight and the line of travel.  In essence, because the two wheels are fixed together on a single rod and can’t move independently, they create a link between the bag’s forward movement and its rotational motion — in short, the wheeled bag as we know it today is almost designed to wobble.

Inherently unstable

Let’s imagine you’re pulling one such suitcase straight ahead, then something happens (such as a change of direction or a bump in the pavement) which causes the right wheel to lift. The now-tilted suitcase will turn right initially, but when the wheel falls down to the ground and the left one goes airborne your suitcase (which is now tilted and orientated slightly rightwards) banks left.

It’s this process, repeating again and again, that makes your suitcase wobble more intensely instead of steadying down. It’s kind of like resonance, only much more annoying — or, as study coauthor Sylvain Courrech du Pont, a physicist at Paris Diderot University puts it, “a bit funny and counterintuitive.”

If your first instinct is to slow your pace and give the wheelie some time to settle down then you’re doing it wrong, it seems. Du Pont says that the wobbling should actually decrease as the suitcase rolls faster. Lowering the angle of the suitcase (bending down and lowering the handle closer to the ground) also helps, and can even stop the rocking altogether.

The stakes, as they say, are higher than the frustration the wheelies inflict on tourists every day. Understanding how the bags behave in motion can help us design more stable two-wheeled carriers like car-pulled trailers

“The suitcase is a fun way to tackle the problem but the study would be the same for any trolley with two wheels or blades,” Courrech du Pont said.

“In the near future, maybe we will have a car without a driver. It would be a good thing if the car knows how to stop this kind of motion.”

How to Repair Wobbly Suitcases

You’ll find suitcases with built-in wheels, giving you the option to pull or push your luggage. While it’s such a convenient feature, the wheels of your luggage undergo wear and tear, eventually needing repair. You can fix the wheels yourself or take your luggage to a repair shop.

Here’s how to repair wobbly suitcases:

  • Buy replacement wheels for your wheelie suitcases. Most suitcase manufacturers sell the spare wheels or buy them from a suitcase store that’s selling your brand. Make sure to check the replacement wheels, so they’re all identical to your old ones to ensure stability.
  • Open your luggage and unzip the liner. This is done to expose the nut bolts that hold the screws in place.
  • Using a wrench, grip the nut bolt from the inside and remove all the screws around the luggage wheel using a screwdriver by turning them counter-clockwise.
  • Find the small clip, and push it out to remove the bolt inside the wheel. Next, remove the damaged wheel and discard it. Once broken, luggage wheels cannot be repaired.
  • Insert the replacement wheel and place a washer on both sides of the wheel.
  • Secure the wheel by attaching the clip to the axle slot.
  • Properly position the luggage wheel to its original position, tucking in any material.
  • Screw the wheel in place to secure it. Test your suitcase to ensure that the wheels are not wobbly or crooked.

If your suitcase is old and needs replacement, you might want to consider buying and using one of the best rolling backpacks, which makes carrying your things more convenient and flexible. A durable rolling backpack prevents travel problems, like ripped fabric and broken zippers. An ideal rolling backpack is made from durable fabric, with high-quality zippers, reinforced stitching, and an additional layer of protective lining.

The full paper “The rolling suitcase instability: a coupling between translation and rotation” has been published in the journal Proceedings of the Royal Society A.

Why clouds don’t fall


Our day to day life puts us face to face with many very interesting natural phenomena, but the average person doesn’t try to understand them; if asked about some of the simplest things, most people would just laugh at such silly questions. However, some questions seem simple and dismissable until you consider them — after, those same smiles slowly inch away people realize the question is way more interesting than it seems.

For example, take a few moments and think about why clouds don’t fall. Seems to be quite an idiotic question, but it’s actually not. For example, let’s take a look at the clouds themselves. Clouds are made of droplets of water or frozen crystals, which are heavier than the air around them — so why don’t they fall?

If we want to solve this puzzle, we need to know some things. First of all, clouds are made of really small drops of water. These small drops have a harder time at falling than their heavier counterparts. As they fall, their motion generates friction with the air around them. Since they have smaller mass but not that less surface area, they have a harder time pushing down through the air than their heavier counterparts — think of them like tiny ice parachutes. Just like parachutes, they fall slowly but they still fall. Meaning there’s something else that has to be considered.that something else is wind. We think of

That something else is wind. We think of wind as going parallel with the ground, from one side of the globe to another. But wind can also blow in perpendicular to the ground, straight up, for example, in what is called an updraft. This type of wind that stops small drops from falling down.

But going a bit further from our question, one would assume that it’s possible for the drops to get bigger until the wind is not strong enough to keep them from falling. But even then, it wouldn’t be correct to say that the whole cloud falls at once, just as a big chunk of cheese would. The biggest drops fall first, followed by progressively smaller ones until there isn’t enough water left to form more drops. We know this as rain.

A model of a single-molecule car that can advance across a copper surface when electronically excited by an scanning tunneling microscope tip.

World’s tiniest race will pit nanocars against each other in Toulouse this April

This April, Toulouse, France will be host to the world’s first international molecule-car race. The vehicles will be made up of only a few atoms and rely on tiny electrical pulses to power them through the 36-hour race.

A model of a single-molecule car that can advance across a copper surface when electronically excited by an scanning tunneling microscope tip.

A model of a single-molecule car that can advance across a copper surface when electronically excited by a scanning tunneling microscope tip.
Image courtesy of Ben Feringa.

Races did wonders for the automotive industry. Vying for renown and that one second better lap time, engineers and drivers have pushed the limits of their cars farther and farther. Seeing the boon competition proved to be for the development of science and technology in pursuit of better performance, the French National Center for Scientific Research (Centre national de la recherche scientifique / CNRS) is taking racing to a whole new level — the molecular level.

From April 28th to the 29th, six international teams will compete in Toulouse, France, in a 36-hour long nanocar race. The vehicles will only be comprised of a few atoms and powered by light electrical impulses while they navigate a 100-nanometer racecourse made up of gold atoms.

The fast (relative to size) and sciency

The event is, first of all, an engineering and scientific challenge. The organizers hope to promote research into the creation, control, and observation of nanomachines through the competition. Such devices show great promise for future applications, where their small size and nimbleness would allow them to work individually or in groups for a huge range of industries — from building regular-sized machines or atom-by-atom recycling to medical applications, nanomachines could prove invaluable in the future. It’s such a hot topic in science that last year’s Nobel Prize for chemistry was awarded for discovering how to make more advanced parts for these machines.

But right now, nanomachines are kind of crude. Like really tiny Model T’s. To nudge researchers into improving this class of devices, the CNRS began the NanoCarsRace experiment back in 2013. It’s the brainchild of the center’s senior researcher Christian Joachim, who’s now director of the race, and Université Toulouse III – Paul Sabatier Professor of Chemistry Gwénaël Rapenne, both of whom have spent the last four years making sure everything is ready and equitable for the big event.

Some challenges they’ve faced were selecting the racecourse — which must accommodate all types of molecule-cars — and finding a way for participants to actually see their machines in action. Since witnessing a race so small unfurl could prove beyond the limitations of the human eye, the vehicles will compete under the four tips of a unique tunneling microscope housed at the CNRS’s Centre d’élaboration de matériaux et d’études structurales (CEMES) in Toulouse. It’s currently the only microscope in the world allowing four different experimenters to work on the same surface.

Scanning Tunneling Microscope explained.

Image credits CNRS Universite Paris-Sud / Physics Reimagined, via YouTube.

Scanning Tunneling Microscope in action.

Image credits CNRS Universite Paris-Sud / Physics Reimagined, via YouTube.

The teams have also been hard at work, facing several challenges. Beyond the difficulty of monitoring and putting together working devices only atoms in size, they also had to meet several design criteria such as limitations on molecular structures and form of propulsion. At the scale they’re working on, the distinction between physics and chemistry starts to blur. Atoms aren’t the things axles or rivets are made of — they’re the actual axles and rivets. So the researchers-turned-race-enthusiasts will likely be treading on novel ground for both of these fields of science, advancing our knowledge of the very-very-small.

Out of the initial nine teams which applied for the race before the deadline in May 2016, six were selected for the race. Four of them will go under the microscope on April 28th. The race is about scientific pursuit, but it’s also an undeniably cool event — so CNRS will be broadcasting it live on the YouTube Nanocar Race channel.

[panel style=”panel-info” title=”The rules of the race” footer=””]The race course will consist of a 20 nm stretch followed by one 45° turn, a 30 nm stretch followed by one 45° turn, and a final 20 nm dash — for a total of 100 nm.
Maximum duration of 36h.
The teams are allowed one change of their race cars in case of accidents.
Pushing another racecar a la Mario Kart is forbidden.
Each team is allotted one sector of the gold course.
A maximum of 6 hours are allowed before the race so each team can clean its portion of the course.
No tip changes will be allowed during the race.[/panel]


NASA wants to create the coolest spot in the universe

Sometimes, NASA are just the ultimate hipsters: they want to make the coolest spot ever and it’s going to be “totally out there” — on the International Space Station.

We’ve been cool before, but never in outer space

Artist’s concept of an atom chip for use by NASA’s Cold Atom Laboratory (CAL) aboard the International Space Station. CAL will use lasers to cool atoms to ultracold temperatures.
Credits: NASA

The quest for achieving ever-colder temperatures has been a significant theme for physicists in the past decades. The quest has proven fruitful, yielding breakthroughs in superfluidity and superconductivity, as well as in quantum physics. Now, NASA wants to take this one step further, and bring a Cold Atom Laboratory (CAL) into outer space.

“Studying these hyper-cold atoms could reshape our understanding of matter and the fundamental nature of gravity,” said CAL Project Scientist Robert Thompson of JPL. “The experiments we’ll do with the Cold Atom Lab will give us insight into gravity and dark energy — some of the most pervasive forces in the universe.”

Basically, astronomers will take an ice chest-sized box and bring it aboard the International Space Station. There, they will cool matter to an extremely low temperature, almost reaching the absolute 0, the minimum temperature at which anything can exist in the universe. More specifically, they will lower matter to a billionth of a degree above the Absolute 0, more than 100 million times colder than the depths of space. At this temperature, matter creates what is called a Bose-Einstein condensate. In this form of matter, familiar physics fades away, and quantum phenomena start to take over, even at a macroscopic scale. Matter almost stop behaving as particles and starts behaving more like waves. In other words, you could observe “waves of atoms”, moving synchronized with each other just like water drops in an ocean wave.

Velocity-distribution data (3 views) for a gas of rubidium atoms, confirming the discovery of a new phase of matter, the Bose–Einstein condensate. Left: just before the appearance of a Bose–Einstein condensate. Center: just after the appearance of the condensate. Right: after further evaporation, leaving a sample of nearly pure condensate. Image via Wiki Commons.

This is where this approach kicks in: bose-Einstein condensates have been created on Earth before several times, but due to Earth’s gravitational pull, they always fall down and therefore physicists only have fractions of a second to observe them. In space, the matter will be in “free fall” which will allow NASA to observe it for up to 10 seconds at a time. With further technological advance, that time is expected to be extended up to two minutes.

To coldly go where no one has gone before

This experiment could also help us broaden our horizon, in an astrophysical kind of way. As Kamal Oudrhiri of JPL, the CAL deputy project manager explains, the universe is roughly 27 percent dark matter, 68 percent dark energy and about 5 percent ordinary matter. We’ve seen quite a bit of the 5% matter… but that’s still just 5%.

“This means that even with all of our current technologies, we are still blind to 95 percent of the universe,” Oudrhiri said. “Like a new lens in Galileo’s first telescope, the ultra-sensitive cold atoms in the Cold Atom Lab have the potential to unlock many mysteries beyond the frontiers of known physics.”

But it’s not all theoretical science. The results of these experiments could send big ripples through the scientific world, and help us better understand strange mishaps at the cutting edge of technology — which is usually what happens when quantum mechanics starts to kick in. Among others, bose-Einstein condensates could help us develop better sensors, quantum computers and atomic clocks used in spacecraft navigation.

Another interesting facet of the extremely cold matter is that it’s a “superfluid” — a fluid with no viscosity. As explained above, atoms move in sync with each other and there’s basically no friction inside the fluid. Instead, it all moves in unison as if it were a solid.

“If you had superfluid water and spun it around in a glass, it would spin forever,” said Anita Sengupta of JPL, Cold Atom Lab project manager. “There’s no viscosity to slow it down and dissipate the kinetic energy. If we can better understand the physics of superfluids, we can possibly learn to use those for more efficient transfer of energy.”

The mission is currently in its last batch of tests. If everything goes according to plan, then we’ll pretty soon be hearing about ultra-cold matter on the ISS.

“The tests we do over the next months on the ground are critical to ensure we can operate and tune it remotely while it’s in space, and ultimately learn from this rich atomic physics system for years to come,” said Dave Aveline, the test-bed lead at JPL.


Czech researchers turn graphene sheets into the first stable non-metallic magnets

Researchers have created the first stable non-metal magnet ever by treating graphene layers with non-metallic elements.

Image credits Wikimedia / AlexanderAlUS.

A team from the Regional Center of Advanced Technologies and Materials at the Palacky University, Olomouc, Czech Republic, announced that they have created the first non-metal magnet that can maintain its properties at room temperature. The process requires no metals — the team created their magnet by treating graphene layers with non-metallic elements such as fluorine, hydrogen, or oxygen.

“For several years, we have suspected that the path to magnetic carbon could involve graphene — a single two-dimensional layer of carbon atoms,” lead researcher Radek Zbořil, director of the RCATM, in a press release.

“[Through the process] we were able to create a new source of magnetic moments that communicate with each other even at room temperature. This discovery is seen as a huge advancement in the capabilities of organic magnets.”

They’ve also developed the theoretical framework to explain why their unique chemical treatment creates magnets without any metal.

“In metallic systems, magnetic phenomena result from the behavior of electrons in the atomic structure of metals,” explained co-author Michal Otyepka.

“In the organic magnets [i.e. the graphene ones] that we have developed, the magnetic features emerge from the behavior of non-metallic chemical radicals that carry free electrons.”

Graphene is already getting a lot of attention for its unique electrical and physical properties as well as electrical conductivity. Adding magnetism to the list of it can do opens up a whole new range of possibilities for a material that is in essence sheet carbon you can cook make from soy.

“Such magnetic graphene-based materials have potential applications in the fields of spintronics and electronics, but also in medicine for targeted drug delivery and for separating molecules using external magnetic fields,” the team adds.

The full paper “Room temperature organic magnets derived from sp3 functionalized graphene” has been published in the journal Nature.


Light-bending material could bridge quantum and classical physics

Scientists may have found a substance that allows them to finally link the opposing models of quantum and classical physics. In time, this finding could allow them to understand why the classical model breaks down at an quantum level, why quantum physics doesn’t seem to work at visible scales, and how the two can be reconciled.


Image credits SB Archer / Flickr

We know these two models of understanding the physical world — the quantum for really small bits and the classical for larger bits — don’t mix well together. Usually when one is in charge, the other is completely absent. Most of the rules of classical physics break down at the quantum level — gravity, for example, doesn’t seem to be doing much on the atomic level even as it’s literally holding the universe together overall. There’s nothing in the rules of classical physics that can explain quantum entanglement, either.

Scientists know that there must be something tying the two models together, but we’ve yet to find even a clue of what that is. Now, thanks to a newly developed material, scientists have a chance to see quantum mechanics in action on a scale visible to the naked eye — offering hope of finding a bridge between the two models.

“We found a particular material that is straddling these two regimes,” says team leader N. Peter Armitage, from Johns Hopkins University.

“Usually we think of quantum mechanics as a theory of small things, but in this system quantum mechanics is appearing on macroscopic length scales. The experiments are made possible by unique instrumentation developed in my laboratory.”

The material Armitage developed is a topological insulator, a class of material first theoretically predicted in the 1980s, and first produced in 2007. Topological insulators are conductive on their outer layer while being insulators on the internal one. This causes the electrons flowing along the material to do some pretty weird stuff. For example, Armitage and his team found that a beam of terahertz radiation (sometimes called THz or T-rays – an invisible spectrum of light) passing through their bismuth-selenium topological insulators can be made to rotate slightly — an effect only observed at the atomic scale up to now.

This rotation could be predicted with the same mathematical systems that govern quantum theory — making this the first time researchers have witnessed quantum mechanics occurring on the macro scale. It could form the basis on which the quantum and classical models can be linked, the ‘theory of everything’ that scientists have been trying to find for decades.

The experiment is definitely “a piece of the puzzle” but according to Armitage, there’s still a lot of work to be done before this link is fully understood. He hopes that one day we’ll have a completed picture of physics, and new materials like the team’s topological insulator might be the way we get there.

The full paper “Quantized Faraday and Kerr rotation and axion electrodynamics of a 3D topological insulator” has been published in the journal Science.

In 1975, a physicist co-authored a paper with his cat. He did it for a very good reason

F.D.C. Willard, also known as Chester, is a cat who co-authored a high-quality physics paper in 1975 in a reputed journal. His owner had a very good (and practical) reason for including Chester as one of the authors.

Chester was a siamese cat like this one.

Jack H. Hetherington was a professor of physics at Michigan State University in 1975. His research yielded some valuable results in the field of low-temperature physics so he sent a paper for publication in the Physical Review Letters – one of the leading journals in physics. So he sent it for peer reviewal, and it was received warmly, but one reviewer signaled a problem. Hetherington had used the pronoun “we” throughout the paper when in fact, he was the sole author. You see where this is going?

Keep in mind, this was happening in 1975 before the internet was a thing, and even before computers. In fact, the entire paper was typewritten, and for all you kids out there — that took a LOT of time. So Hetherington had two possibilities: either rewrite the entire thing or find another author. The first option just wouldn’t do, it was too much wasted time. But adding another author was also problematic as Hetherington himself admitted: it would reduce his prestige and even his financial remuneration. There was also the problem of time: the results were really promising, and for every day he waited, Hetherington risked someone else finding the same results and pitching a paper in front of him. So after “an evening’s thought,” he found the solution: just add Chester as an author.

Now obviously, ‘Chester’ is not something you can put on a scientific paper, so he invented a name: F.D.C. Willard. The “F.D.C.” stood for “Felix Domesticus, Chester” and Willard was the name of Chester’s father. So “selling” F.D.C. Willard as one of his colleagues from the university, Hetherington re-sent the paper, where it was promptly accepted and published, going on to be quoted more than 50 times to this day. Job well done, Chester!

Of course, people eventually found out about it but Hetherington says he has no regrets. As quoted in a piece on Today I Found Out, Hetherington said, “Everyone laughed and soon the cat was out of the bag.”

“Why would I do such an irreverent thing? … If it eventually proved to be correct, people would remember the paper more if the anomalous authorship were known. In any case I went ahead and did it and have generally not been sorry.”

In the end, everyone (except for the journal’s editors) laughed about the idea and went with it. After all, the paper was good, and Hetherington’s motivation was understood by the community. He even took the joke further and issued reprints signed by both authors — a regular signature under his name, and a pawprint beneath Willard/Chester’s name. He even started describing his cat as the university’s “Rodentia Predation Consultant.”

Someone from the University reportedly even invited Willard/Chester to join the University full time, probably as a publicity stunt (or who knows, maybe for his research inclination). The letter hilariously read:

“Let me admit that if you had not written I should never have had the temerity to think of approaching a physicist so distinguished a physicist as F. D. C. Willard with a view to interesting him in joining a university department like ours, which after all, was not even rated among the best 30. Surely Willard can aspire to a connection with a more distinguished department.”

But it ended on a more optimistic note:

“Can you imagine the universal jubilation if in fact Willard could be persuaded to join us, even if only as a Visiting Distinguished Professor?”

As for Willard, his comment on the matter was never obtained, though hopefully he got some privileges after his success as a publisher. He even went on to publish another scientific paper, this time in French. It didn’t receive the recognition the first one did, but it did ensure that Willard was the only cat to ever publish scientific papers in two different languages.

You can read the first paper here and the good thing is that the American Physical Society declared in 2014 that all cat-authored papers would now be available as open-access documents. They did that on April 1st.


Squished-booms: looking at the behavior of underwater explosions

Some things go boom, others don’t. The first category is definitely more fun.

Other things go boom in unusual places — these are arguably the best.
Image via Youtube / Slow Mo Guys.

A material explodes when it increases in volume rapidly and releases a lot of energy. The most usual energy storage used to create explosives is of the chemical kind, but explosives can be created using atomic, electrical, or mechanical sources. The characteristic boom or bang of an explosion is how your ears pick up on the “changing volume” part of the explosion, the shockwave. This is the force that lends explosions their destructive nature. The biggest part of an explosive’s energy is expended as light, heat, and work.

Not all explosions are made the same. The medium in which detonation takes place has a huge influence on the way the explosion and its shockwaves behave. And, while surface explosions are pretty ubiquitous in movies, underwater explosions aren’t — which is a shame, because they’re really pretty.

So let’s watch some

First thing first: explosions are inherently hard to enjoy properly — they’re ephemeral, gone in a flash of the eye.

That is, unless you film it thousands of times faster than the eye can see, which is exactly what the Slow Mo Guys did. They took a firecracker, set it alight, then submerged it in a fish tank to blow up — all under the watchful lens of a 120.000 fps high-speed camera. The resulting reel slows the detonations down enough for us to observe some basic principles of underwater explosions. I’ve taken the explosions and turned them into gifs below, but the whole video is pretty good and you should watch it.

Here are the firecrackers exploding.

Image via Youtube / Slow Mo Guys.

Underwater detonations spread out in the begging, creating a hollow sphere inside the liquid. This soon collapses in on itself, as water rushes to fill the gap.

Image via Youtube / Slow Mo Guys.

This happens for two reasons. One, water is much denser than air, so it’s a lot harder to push around. Then there’s the fact that water, unlike air, can’t be compressed. This is the same property that underpins hydraulic systems (incompressibility) and because of it, the firecracker has to act on the fluid as a whole. In essence, this means that it has to perform work on a much denser, much larger medium. This property is also used by SWAT teams and military personnel to breach doors in the form of water impulse charges — water here is used to direct the force of the blast evenly onto a surface.

A firecracker set off in normal conditions can propel gas and fragments a few meters away, but underwater the explosion has enough energy to expand only a few centimeters across.

In this gif, the detonation took place closer to the water’s surface and you can actually see the liquid pouring in on the collapsing bubble.

Image credits Youtube / Slow Mo Lab.

Apart from this shot, the video itself doesn’t add that much from the one above (the guy shooting it does have a necktie though). You can see it here.

The shockwaves

The gases released during detonation are then squashed by the liquid’s weight. This compression-explosion interplay can become quite lively, as the water compresses the gas as far as it can, then gets pushed back, and repeat. The collapse of the hollow bubble generates the first shock wave. Secondary shock waves are created as gas and water wrestle.

TheBackyardScientist can help explain with his liquid nitrogen bomb. He only shot with a 240 fps camera, so you can’t actually see the liquid being pushed during the explosion — but you can see the awesome gas-water play after it.

Here are some highlights.

Wub dub dub dub.
Image via Youtube / TheBackyardScientist.

Wub dub dub dub, the sequel.
Image via Youtube / TheBackyardScientist.

TBS conveniently placed some balloons around the point of detonation, to pick up on the shockwaves’ motions. As you can see, there’s a lot of motion going on throughout the fluid as the gas gets compressed then expands.

The surface

So this one will feature a nuke ’cause its the last part — why not go big?


As you can see, the highest point the water is thrown upwards lies directly above the point of detonation — the center point of the shockwave. If you pause the video or look at the thumbnail image you’ll see that the shape of the column of water being pushed upwards follows an exponential curve — not the round shape we saw in the bubbles.


The 2016 Nobel Prize in physics awarded to trio of topological experts

This year’s Nobel Prize in physics goes to David Thouless from the University of Washington, Duncan Haldane from Princeton University, and to Michael Kosterlitz from Brown University for their work in mathematical topology — “opening the door on an unknown world where matter can assume strange states”.

Topology describes shapes and structures by breaking them down into their fundamental characteristics, such as number of holes or faces. Topologically speaking, a bucket, a doughnut, and a bagel are the same because they have one hole — but they’re distinct from a pretzel, which has two. The trio used topology to analyze the properties of exotic states of matter, such as superconductors or superfluids. Their work could underlie future advances in material science and electronics, such as quantum computers.

Thirty years ago, it was widely believed that superconductivity (zero electrical resistance) couldn’t occur in thinly layered mediums. Thouless and Kosterlitz showed otherwise using topological means. They showed that thin conductive layers could form in materials by taking the form of discrete topological steps, where going up one step is like changing from a bagel to a pretzel.

Using similar concepts, Haldane explained the magnetic properties of several materials — the work “seemed very abstract” in the beginning, said Haldane, but as time went by more and more properties could be explained by topology.

“It turned out that many materials people had been looking at for years had these properties,” said Haldane, “they just hadn’t been seen.”

The work the trio did is pertinent to several different materials, but it’s still too early to understand the full implications of topology. “What these discoveries show,” said Haldane, “is that we have a long way to go to discover what’s possible.”

Haldane “was very surprised and very gratified” when he was informed about the decision. Much of this work took place in the late 70s and the 80s, but Haldane said “it’s only now that lots of tremendous discoveries based on this work are now happening.”