What’s the matter?

Mysterious and invisible dark matter is still mysterious, but possibly a little less invisible after hints of its existence were announced at CERN yesterday, in a cautious but read-between-the-lines-nudge-nudge-wink-wink presentation.

The Alpha Magnetic Spectrometer (AMS) experiment, led by Professor Samuel Ting – who won the Nobel Prize in Physics in 1976 for his part in the discovery of the J/ψ meson and hence the charm quark – confirmed that there are more positrons in space than you’d expect, and this could be due to dark matter. Of course, it could also be due to something else, but Professor Ting sounds like he’s betting on dark matter.

Graph showing the fraction of positrons compared to electrons in cosmic rays, plotted against their energy. The AMS results (red dots) are compared to those of previous experiments, notably PAMELA and FERMI, which also saw an excess of positrons but had much higher uncertainty. The levelling off occurs at an energy of about 350 GeV – after that, who knows? (Image AMS-02 collaboration)

What AMS did was look at cosmic rays, which are charged particles that zip through outer space, and which would likely kill us all if we weren’t protected by Earth’s atmosphere and magnetic field.

Based on the International Space Station, AMS uses magnets and other clever devices to measure the electric charge, energy and momentum of the cosmic ray particles and so work out what they are.

In particular, it looked at the ratio of electrons to anti-electrons, known as positrons (because they have positive charge). The universe is full of electrons, but positrons are generally only produced when other particles interact. This means that there should be fewer positrons at higher energies, as there are fewer parent particles at higher energies to create them.

But AMS found that although there is a dip at an energy of around 10 GeV, after that the proportion of positrons increases. So something is creating more positrons at higher energies.

This could be dark matter, which many people believe to be WIMPs, short for weakly interacting massive particles. These particles would interact via the weak nuclear force, as do electrons and positrons. So if a WIMP and an anti-WIMP happen to collide (or possibly if WIMPs are there own anti-particles), they would produce an electron-positron pair.

The numbers of positrons produced would then be expected to rise until you reach the energy corresponding to the mass of the WIMPs (E=mc²), after which they’d suddenly drop off. This would be a good sign that what we’re looking at is indeed due to dark matter.

If not, it could be something else in the universe, like a pulsar. However, the signal that AMS found appears to be coming from all directions, so that seems  unlikely. But then it’s still possible that it’s being produced by something else that astrophysicists don’t know about. Which would also be cool.

The previous ‘smoking gun’ of dark matter, the so-called Bullet Cluster. Two galaxies collided, separating the ordinary matter (pink), distorted into bullet shapes by the crash, from the dark matter (blue), which passed right through. The caption is my little joke about dark matter occupying the universe… (Image from NASA)

So what are we seeing? Well, at the moment we’re just seeing the number of positrons rise with higher energy, but levelling off at around 350 GeV. Beyond that, the AMS team haven’t detected enough positrons to say. There were only 72 found at 350 GeV, and the fewer there are the greater the statistical uncertainty. Professor Ting’s demeanour hinted that he has an idea about what might be found at the higher energies, but he refused to be drawn.

This is admirable restraint, which actually shouldn’t be that surprising coming from a guy who won a Nobel Prize for experimental physics. But these days there’s often a tendency to call a press conference as soon as there’s even a hint of an exciting discovery, which then evaporates as more data comes in. Remember those faster-than-light neutrinos?

So it makes sense that Professor Ting is being cautious by refusing to release “preliminary results”, and saying he’ll only make an announcement when they’re statistically confident they have something. Plus as he pointed out, doing experiments in space is very difficult, so it takes time to get it right. And since he’s been working on this for 18 years, he’s prepared to wait a little longer.

As for what any WIMPs actually are, that’s up to the theoretical physicists to work out. And it has to be compatible with what’s being found – or rather, not being found – at the Large Hadron Collider at CERN.

But whatever is the origin of the signal seen by AMS, it’s likely to be something new to physics, which is exciting. And considering the last big announcement from CERN was that the Higgs boson is probably really the Higgs boson, we could do with some new physics.

We just have to wait until Professor Ting is ready to tell us.

Why toast lands buttered side down

In one of the very first posts on this blog, we tackled the question of how cats always land on their feet. Now, two years later, it’s time to tackle another species with a similar skill: namely toast.

A demonstration of the typical behaviour of falling toast. It’s physics, not bad luck, that causes it to land butter-side down.

As with the cats, the answer turns out to be physics – and not, as you may have expected, Murphy’s Law, which is more of an engineering principle.

You see, Murphy’s Law is frequently taken as a pessimistic prediction that things will always go wrong. This is clearly not true: the principle says “anything that can go wrong will go wrong”, but usually there are many, many things that can go wrong, and they can’t all happen at once.

A more charitable interpretation – which was supposedly one of the original meanings when the law was named for USAF Captain Ed Murphy, who built rocket sleds in the 1950s – is that if there’s a known flaw you should try and rectify it, rather than just leave it and hope that it won’t happen.

To give an example, consider the Death Star. It was built with the engineering fault of an exhaust vent that, if you hit it just right, would cause the whole thing to explode. But Grand Moff Tarkin apparently just assumed that the Rebels would never be good enough shots to hit it (perhaps he was used to the lousy accuracy of Imperial Stormtroopers, not to mention targeting computers). If he had have known of Murphy’s Law, he might have decided to put a cover over it instead.

But enough sci-fi nonsense: back to toast. As I mentioned, this is actually straightforward physics, first documented by Robert Matthews of Aston University, an achievement for which he won an IgNobel Prize (Matthews RAJ 1995, “Tumbling toast, Murphy’s Law and the fundamental constants”, European Journal of Physics, vol. 16, no. 4, p. 172, doi:10.1088/0143-0807/16/4/005).

Toast usually falls by tipping over the edge of something, like a plate or the edge of a table. When it does, it teeters first, rotating about the edge of the plate/table, before dropping down. It continues to rotate while in the air, and under typical conditions does a half-turn and lands upside-down.

Diagram of the dynamics of falling toast, taken from “The Anthropomurphic Principle”, by Roland Krenn

I say ‘typical conditions’ because the amount it rotates depends on a number of factors, like the height of the table, the amount the toast is overhanging the edge when it’s released, how fast it’s moving horizontally, the friction between the toast and the table, and the size of the toast.

It’s fairly straightforward to model a simplified scenario where the toast doesn’t slip against the edge of the table (see Roland Krenn 2005, “The Anthropomurphic Principle”, Karl Franzens Universität Graz). In the no-slipping case, the toast doesn’t fall until it’s aligned vertically (θ = 90° in the diagram above).

Using those calculations, you can show that you’d need to drop the toast from a height of about 3 metres for it to do a full rotation and land right-side up again. Needless to say, this rarely happens.

When you add in the slipping it gets more complicated, and you need sophisticated computer modelling to do the calculations. Fortunately, people have done just that (Bacon ME, Heald G & James M 2001, “A closer look at tumbling toast”, American Journal of Physics, vol. 69, no. 1, pp. 38-43, DOI: 10.1119/1.1289213, PDF 475 KB).

They found that slipping causes the toast to rotate faster, but for small amounts of overhang – which is realistic for natural toast dropping – it will still land upside-down.

So, going back to Murphy’s Law, how can we save our toast from dirty butter? Well, the experts have a number of suggestions:

1. carry the plate above your head at about 3 metres high
2. equivalently, only use toast about 2.5 cm wide (maybe that French mini-toast)
3. when the toast starts to fall, pull the plate away quickly so it doesn’t rotate.

Considering that last point, I have an alternative idea: if you are able to pull the plate away, you should also be able to push it back under the plate. Why let it fall at all?

Murphy would be proud.

Negative absolute temperature will burn your brain cells

The new year in science is so far shaping up to be a confusing one, with the first surprising physics result being the reaching of temperatures below absolute zero.

If that sounds bizarre to you, well it does to me too; but it’s thermodynamics and I’ve always found that difficult. But having calmed down and taken a bit of time to read and think about it, I think I can write something sensible.

What’s happened is that a team of German physicists have manipulated ultracold potassium atoms using lasers and magnetic fields to achieve a state that technically has negative temperature (Braun S, Ronzheimer JP, Schreiber M, Hodgman SS, Rom T, Bloch I & Schneider U 2013, “Negative absolute temperature for motional degrees of freedom”, Science, vol. 339 no. 6115 pp. 52-55, doi: 10.1126/science.1227831).

This works because temperature isn’t exactly what you think it is. We normally think of it as representing the average kinetic energy of the atoms or molecules in a sample, i.e. how rapidly they’re all jiggling around. So absolute zero corresponds to when they’ve stopped moving altogether, which is why it’s an absolute.

Well that’s almost right. The technical definition relates temperature to the distribution of energy in the system, and the rate that the entropy changes when the energy changes.

Entropy is an expression of the disorder in a system. You may remember it from the Second Law of Thermodynamics. That’s the one that says that the entropy in a closed system can never decrease: everything tends to move towards a more disordered state.

This is the reason that a cup that falls off a table won’t spontaneously put itself together again and jump back up. For one thing, it would need to convert heat energy – the random jiggling of atoms – into uniform motion of the whole cup. And of course the random jiggling is more disordered, i.e. has more entropy.

At least, that’s how it works at positive temperatures. Adding more energy increases the jiggling and increases the disorder. And until they receive more energy, most of the atoms can be found in the low energy, low entropy states.

Graph showing how entropy varies when there are both minimum and maximum energies. The temperature is actually the inverse of the slope of the curve, so it’s -0 at minimum energy and +0 at maximum energy. In the middle, where the entropy curve flattens out, it switches from positive to negative infinity (Image by Braun et al, Science)

But in this latest experiment they turned that around. First of all, they cooled the atoms down to a few billionths of a Kelvin. The atoms would normally repel each other, but they used lasers to trap them in a lattice arrangement.

Then they flipped it over. They changed the force between the atoms to an attractive one, and used the lasers to try to push them apart.

The result is that all the atoms were suddenly in a maximum energy state, but a very ordered one because they were all in this lattice arrangement. Any lower energy states were more disordered.

This reversed the relationship between energy and entropy, and so corresponds to a negative temperature.

Not only that, but because the Second Law of Thermodynamics means systems want to increase their entropy, it also means that the atoms want to lose their energy and move to a lower energy state.

So if you put a negative temperature system in contact with one with positive temperature, energy will tend to flow from the negative to the positive temperature. This has led some people to claim that negative temperatures are hotter than any positive temperature. Even though they’re a few billionths of a Kelvin below zero.

The way to understand this is that the temperature scale also doesn’t work the way you think it does. Normal number systems go from negative infinity, through zero and up to positive infinity. Like this:

−∞ … 0 … +∞

But with temperature, it works more like this:

+0 K … +∞ K, −∞ K … -0 K

So absolute zero is still a limit, it’s just a limit at either end. And the infinities meet in the middle.

I’ll let you go away and think about that, but leave you with one very cool (sorry) consequence.

Pressure and temperature are proportional to each other, so a negative temperature should also have negative pressure. And negative pressure is the very strange property exhibited by dark energy, which causes the accelerating expansion of the universe. It’s possible that by studying these weird, idiosyncratic atomic systems, we may get a better idea of how the cosmos works.

So it’s strange stuff, but worth understanding. If you still don’t get it and would like to read more, with clever analogies, see What the Dalai Lama can teach us about temperatures below absolute zero (Empirical Zeal), or Leprechauns and laser beams (Coffeeshop Physics).

Electromagnetic shielding foiled again

The ineffectiveness of tinfoil hats against government mind control rays received a bit of media and internet attention this year, despite the fact the study in question is 7 years old and that mind control doesn’t appear to exist.

In 2005, four electrical engineers at MIT tested the shielding of three different helmets made of ‘tinfoil’ – actually aluminium foil – over radio frequencies from 10 kHz to 3 GHz (Rahimi A, Recht B, Taylor J & Vawter N 2005, “On the effectiveness of aluminium foil helmets: an empirical study”, published online 17 Feb 2005).

The principle is based on the Faraday cage, invented by English physicist Michael Faraday in 1836. This is a box made of conducting material: when an electric field is applied to the outside, the charges in the conductor realign and cancel out the electric field inside. For a more detailed explanation, see The Feynman lectures on physics vol. 2, 1964, section 5.10.

My homemade Faraday cage. When an external electric field is applied (traditionally represented by arrows running from positive to negative), the charges in the conductor move accordingly. Negative charges are attracted towards the external positive charges, and positive to the external negative. This redistribution of charges sets up its own electric field, which is equal and opposite to that from outside. The two fields cancel each other out, so inside the cage there is no field (Photo own work)

Faraday cages work really well at low frequencies, and they’re the reason you’re not affected if you’re in an airplane that’s struck by lightning: the metal fuselage shields you from the high voltages outside.

At higher frequencies, you need to make sure you’re using a good conductor (refer to this table of electrical conductivity, by TIBTECH).

You also need to make sure that any holes in the enclosure are small enough so that the electromagnetic waves don’t fit through. The basic rule is that the holes need to be less than about half a wavelength (with the wavelength equal to the speed of light divided by the frequency).

A microwave oven is a good example. Microwaves have a frequency of about 2.45 GHz, i.e. a wavelength of 12 cm. So the holes in the metal mesh in the oven door are too small for the microwaves to fit through, but big enough for you to see in (light is also electromagnetic radiation, but with wavelength between 390 and 750 nm). For more technical details, see ‘Practical electromagnetic shielding’, by Learn EMC.

Incidentally, the microwave oven’s shielding is meant to block radiation from the inside, not the outside as in a basic Faraday cage. For this purpose the principle is pretty much the same, except that the enclosure needs to be grounded. Without the ability to bring in more charge from the ground, the conductor is basically transparent to any charges inside (thanks to Gauss’s law).

It is fairly easy to build your own Faraday cage using aluminium foil and test it by placing a mobile phone inside. We did this on air, risking violation of the rule of not using a mobile phone in the radio studio. Fortunately, the shielding worked and the phone didn’t ring when we called it.

Aluminium works well because it’s a fairly good conductor, not far behind gold (which itself ranks below silver and copper). But you really need to make sure you crimp all the seams, as these are the main weak points. Even though they’re not very wide, they can easily be long enough to let in the electromagnetic waves (in Australia, 3G mobile networks use 0.85-2.1 GHz, with 4G or LTE on 1.8 GHz, or a wavelength of 17 cm).

This is the big problem with the foil hats. Because they have to fit a head in, they’re never totally enclosed. So right away, basic electromagnetic theory tells us they won’t work as Faraday cages.

However, although they won’t totally block all radiation, we should at least see some attenuation of the signal. Which is what the MIT researchers looked for, and indeed what they found.

There was a 10 decibel (dB) reduction in signal strength at most frequencies, with the greatest attenuation being 20 dB at 1.5 GHz.

But the biggest surprise was amplification of the signal at 2.6 GHz and 1.2 GHz! Those frequencies saw increases of 30 dB and 20 dB respectively.

Now, I don’t have specific data on the dimensions of the hats involved, but considering those frequencies correspond to wavelengths of 11 cm and 25 cm, I suspect they’ve hit on resonant frequencies of the cavities they’ve created. Effectively, the radiation is bouncing around inside, echoing and building up in strength.

The engineers go on to point out that frequencies in the range of 1.2-1.4 GHz are reserved by the Federal Communications Commission, nominally for GPS and other satellite use. And in the US, 2.6 GHz is used by mobile phone companies, i.e. multi-national corporations.

This leads to the ‘conclusion’ that perhaps the very idea of foil hats was seeded by the government and their corporate cohorts as a bluff to get people to wear them and so amplify the mind control rays. Which is really doubling-down on the conspiracy theory.

So if you’re paranoid, this may be enough to amplify your paranoia.

For the rest of us, what it does show is that although electromagnetic shielding is quite possible, it requires a bit more care and crimping than you might have thought.

(This story aired on 20 December 2012 – you can listen to the podcast.)

Massive, supermassive and superdupermassive black holes

There’s a monster lurking in the middle of our galaxy. You might not be able to see it, but we know it’s there. Its diameter is 10 times that of the Sun, but its mass is 4 million times. It’s what we call a supermassive black hole.

OK, it’s 27,000 light years away, so it’s probably not going to get you, but still: a supermassive black hole. Let that sink in, so to speak.

‘Normal’ black holes sound pretty massive themselves. If a star is bigger than about 3 times the mass of the Sun, then eventually it reaches a point where it can no longer hold up under its own weight, and it collapses into an object with gravity so strong that even light cannot escape. These are called stellar black holes.

The biggest stellar black hole so far confirmed is about 16 solar masses, but there are indications they can get up to around 33 solar masses.

However, the black holes believed to be at the centres of most galaxies are much, much bigger: more than 100,000 times the mass of the Sun. Hence the label supermassive black holes.

Our galaxy’s supermassive black hole is hidden behind opaque dusk in the Milky Way, in the constellation Sagittarius. It can’t be seen in visible light, but it can be seen in the radio or X-ray spectrum, as seen here in the inset photo taken by NASA’s Chandra X-ray Observatory. Click to see a bigger image (Photo sources Moondigger and NASA/CXC/MIT/F. Baganoff, R. Shcherbakov et al., via Wikimedia Commons)

So if there’s something that big in our galaxy, then why can’t we see it? Well, between it and us there’s an awful lot of stuff.

You’ve probably seen the Milky Way in the sky, a cloudy band visible at night when you’re well away from the city. That’s the main plane of our galaxy. If you could stand outside and away from it, you’d see that it’s a spiral galaxy, i.e. a sort of disc shape made of four swirling arms, with a pronounced bulge in the centre.

From the inside, you just see a cloudy band stretching across the sky, with a lot of opaque dust and gas blocking out the good bits like the dense middle. But it’s there alright, in or near the constellation Sagittarius (see the picture above).

Even though we can’t see it directly – at least not with visible light – we can detect it with radio waves. And in the radio spectrum we see a very, very powerful radio source called Sagittarius A*. The radio waves are believed to be electromagnetic radiation given off from the accretion disk of the black hole: that’s where things spin around it really, really fast before they fall in. And when charged particles spin around fast like that they give off electromagnetic radiation (which actually means they lose energy and so fall in even faster. Not a good idea perhaps, but you can’t fight physics).

So we can see the radio waves, but how do we know Sagittarius A* is a black hole? Well, we can also detect 28 other stars orbiting it. One of them, called simply S2, orbits every 15.2 years and gets as close as 122 times the distance from the Earth to the Sun.

From the speed and distance of S2, we can calculate that the object in question has a mass of about 4.1 million times the mass of the Sun. That much mass in that small a volume has to be a black hole.

Its dimensions are given by something called the Schwarzschild Radius, which tells us that the black hole’s event horizon – the point at which light is no longer able to escape - is at about 13.3 million kilometres. That’s only about 10 times the diameter of the Sun, or 9% of the distance from the Sun to the Earth.

And yet it has a mass 4 million times that of the Sun. For comparison, the Sun is 333,000 times the mass of the Earth. The difference between the black hole and the Earth is the same as that between you and a grain of pollen.

Even so, there are bigger black holes out there. Much, much bigger (you can see where this is going).

Recently, one with a mass of 17 billion suns was discovered in a galaxy only 250 million light years away (van den Bosch RCE, Gebhardt K, Gültekin K, van de Ven G, van der Wel A, Walsh JL 2012, “An over-massive black hole in the compact lenticular galaxy NGC1277″, Nature, vol. 491, no. 7426, pp. 729-731, doi:10.1038/nature11592, arXiv:1211.6429v1 [astro-ph.CO]).

I call it a superdupermassive black hole, although the authors called it ‘over-massive’.

This term is actually appropriate, because it’s much larger compared to its host galaxy than previously discovered black holes. Although small in comparison, our galaxy is in more typical proportion, with the central black hole being 0.1% the mass of all other stars. But the black hole in NGC1277 is 14% of its galaxy’s stellar mass.

The animation embedded below shows how the black hole was identified, using measurements of stars in the galaxy to calculate their orbits and hence the mass at their centre. The photo in the background was taken by the Hubble Space Telescope (NASA/ESA/Fabian/Remco C. E. van den Bosch MPIA).

But even though it’s so big, this superdupermassive black hole isn’t a unique freak. The researchers have also found five other galaxies with similar extreme proportions. Instead, it suggests we may need to rethink our theories of how galaxies form. After all, we’ve been using our own galaxy as a typical example, but there seems to be a much bigger and more complex variety.

What we can say for certain is that it shows what huge objects are out there in the universe. Much too huge for our puny human adjectives.

I spoke to Professor Rachel Webster from the University of Melbourne about this discovery, on our show that aired on 13 December 2013. You can listen to the podcast.

A transcript follows after the break…

How to make a self-filling water bottle

Generating water out of the air is tricky, but it can be done thanks to the Namib Desert Beetle, which figured out the trick long ago, and a bit of biomimicry.

Biomimicry is the use of inspiration from nature to create new technologies. A good example is Velcro, which is based on burrs from plants and their habit of sticking to socks. In this case though, the kudos for cleverness really does belong to the beetle in question.

Namib Desert Beetle, Stenocara dentata, with its black wing casings covered with water-attracting bumps. Click to see the bumps up close (Photo by Hans Hillewaert, via Wikimedia Commons)

This beetle belongs to the genus Stenocara and it lives in the Namib Desert, on the coast of Namibia in south west Africa. The desert is very dry, receiving less than 10 millimetres of rain per year, but about six times per month there are morning fogs that sweep across the sand. And it’s from the fog that Stenocara gets its water (Parker AR & Lawrence CR 2001, “Water capture by a desert beetle”, Nature, vol. 414, no. 6859, pp. 33-34, doi:10.1038/35102108).

It’s a member of the family Tenebrionidae, or the darkling beetles, so-called because they have black wing casings. In the Stenocara these wing casings (which are actually the forewings, or elytra) are fused together, and the whole thing is covered with little bumps about half a millimetre in diameter.

The trick is that these bumps are hydrophilic, meaning that water sticks to them, much like it clings to and spreads out on smooth glass. But the areas in between the bumps are waxy and hydrophobic, i.e., they repel water.

What happens is that in the morning the beetle stands on its long, spindly legs facing into the breeze, with its body angled at about 45 degrees. As the fog flows past, tiny droplets accumulate on the hydrophilic bumps. When they get to about 5 millimetres in diameter, they become too big to stick to the bumps and they detach and roll down the hydrophobic grooves to the beetle’s mouth.

In a single day, the beetle can collect 12% of its weight in water. So it’s not surprising that people have been trying to make similar materials artificially, usually by depositing drops of hydrophilic substance on a hydrophobic substrate.

One company, called NBD Nano, is trying to commercialise it and create efficient, artificial fog harvesters. Of course, this isn’t the first technology that’s been tried for this purpose.

Dehumidifiers are a familiar example, taking water out of the air by cooling it and causing condensation. But of course that requires quite a bit of energy to run – although in 2011 an Australian inventor won the James Dyson Award for a device that cools the air using underground coils, so you only need enough energy to pump the air down a pipe.

Another low energy technique is that used in the Atacama Desert in Chile, and is basically just a piece of mesh strung between two poles, with a trough under it. They get a fog too, and as it flows through the mesh, drops of water condense and run down into the trough.

But NBD Nano claim that the beetle’s skin is several times more efficient than the Chilean method. So far they claim a square metre of beetle-inspired material, at 21 °C and 75% relative humidity, can produce 3 litres of water per hour.

Energy is still used to blow air across the collector, but so far they’ve gotten away with using solar panels and a rechargeable battery. So using this as a covering for a greenhouse would be a very simple way to generate enough water for the plants at fairly low cost.

Of course, you don’t need a fan to blow the air if there’s a foggy breeze, like in Chile or Namibia. But it’s also unnecessary if the collector itself is moving, like on a car or a boat, or even a marathon runner.

This is where the idea for a ‘self-filling water bottle’ comes in: imagine running along, carrying a bottle with a panel of this material, and your motion is what allows it to generate water.

That’s a long way off, but it’s a good reminder that the air carries a lot of water that’s just waiting to be harvested. All we need to do is copy the Namib Desert Beetle, and we can do it too.

(This story aired on 6 December 2012 – you can listen to the podcast.)

So you think you can make a super-alloy

You might think that science lacks the raw power of interpretive dance, but worry no more. Dance Your PhD is a yearly competition where scientists get to try a style of communication that’s a bit more active than peer-reviewed journals.

This year’s winner is Peter Liddicoat from the University of Sydney, who explained his PhD thesis on the nanostructure of aluminium alloys by using a circus strongman, a unicyclist, jugglers and clowns.

Now known as Dr Liddicoat, Peter won $1000 and a trip to Belgium for a screening of his dance at TEDxBrussels.

Of course, $1000 doesn’t go very far in scientific research, but Dr Liddicoat and his colleagues are using the publicity to help with their crowd-funding campaign to build an atom microscope for biology. You can find out more about that at www.indiegogo.com/atom-microscope

On our show that aired on 22 November 2012, Beth spoke to Dr Liddicoat about his research and his dance – you can listen to that interview on our podcast.

Vertical stripes make you look fat

If science teaches us anything, it’s that you should look at the evidence and not just believe what you’re told. Even when it’s common-sense wisdom like ‘horizontal stripes make you look fat.’ Really, the opposite is true, and it’s due to an optical illusion described in 1867 by Hermann von Helmholtz.

Ah, the 19th century, when a scientist could still be an expert in everything. Helmholtz was like that. Born in 1821, his first major work, when he was 26 years old, was to identify conservation of energy in the context of muscle movement.

Helmholtz was far from the first to ‘discover’ the principle of conservation of energy. But his work was significant because it went against what most German natural philosophers believed at the time, which was that there’s some sort of vital force needed to move muscles. Helmholtz realised that the energy in muscles, which he called a ‘force’, was no different to that found in mechanics, heat, light, electricity and magnetism.

He went on to measure the speed at which nerve signals travel (he got between 24 and 38 metres per second), he invented an acoustic resonator that could mimic vowel sounds by combining multiple frequencies, he studied electric oscillations, and the Helmholtz coil with its uniform magnetic field is named after him.

In optics, he became famous for inventing an opthalmoscope, which was used to examine the inside of the human eye. But in his book on optics, published in 1867, he also mentioned some optical illusions.

The one that is named after him is the Helmoltz illusion, in which a square filled with horizontal lines appears taller than one filled with vertical lines. This is a particular version of what’s also known as the Oppel Kundt illusion, in which a space that’s filled looks bigger than one that’s empty.

Two optical illusions: on the left, the Helmholtz illusion, where the square of horizontal lines appears to be taller and narrower than the identical square of vertical lines. On the right, the Oppel–Kundt illusion: point B appears closer to A than to C, indicating that the filled region B–C appears larger than the unfilled A–B (Image from Thompson and Mikellidou, i-Perception)

In his book, Helmholtz wrote about the practical consequences of these illusions:

“There are numerous illustrations of the same effect in everyday life. An empty room looks smaller than one that is furnished; and a wall covered with a paper pattern looks larger than one painted uniformly in one colour. Ladies’ frocks with cross stripes on them make the figure look taller.”
- Helmholtz 1867, Handbuch der physiologischen Optik, vol. 3 (translation by J P C Southall 1925)

This is the exact opposite of modern fashion advice. So which is right?

Enter Peter Thompson and Kyriaki Mikellidou from the University of York. Dr Thompson first presented some work on this topic at a conference in 2008, and last year the pair published a complete paper (Thompson P & Mikellidou K 2011, “Applying the Helmholtz illusion to fashion: horizontal stripes won’t make you look fatter”, i-Perception, vol. 2, no. 1, pp. 69–76, DOI: 10.1068/i0405).

To begin with, they tested the basic Helmholtz illusion by flashing up on a screen images of rectangles of horizontal and vertical lines, and testing whether volunteers thought they were the same height and width. The results varied with the thickness of the lines, but a pattern of vertical lines had to be 4.1-10.1% taller than an equivalent pattern of horizontal lines to be perceived as being the same height.

Similarly, a pattern of horizontal lines had to be 1.3-6.5% wider to appear the same as a vertical pattern. Or to put it another way, in squares of the same size, horizontal patterns looked taller and vertical patterns looked wider. It seems Helmholtz was right.

Naturally, this doesn’t necessarily generalise to human figures or 3-dimensional shapes. So next they tried it on both a cartoon figure of a woman and on pictures of cylinders, and got similar results.

Finally, they used 3-D images of mannequins with vertical or horizontal stripes on their torsos. And again, they found that the mannequin in horizontal stripes had to be 10.7% wider to be seen as the same as the one wearing vertical stripes – consistent with what Helmholtz said.

An example of the mannequins used in the experiment, where both have the same outline but the one with vertical stripes appears broader. This is a stereoscopic image, so try crossing your eyes to make it look 3-D! (Image from Thompson and Mikellidou, i-Perception)

Thompson and Mikellidou claim that another way to observe this effect yourself is by stacking coins: people asked to stack coins to a height equal to their diameter will typically fall short by about 30% – try it and see!

So considering that this optical illusion has been known for so long, why has fashion gotten it wrong? Is it one of those ideas that sounds like it makes sense, so we think it must be true?

If so, then this demonstrates that common sense isn’t always sensible, and you should question everything. And the scientific method, employing careful experiments, is the best way to find the answers.

Record highs

As well as being a demonstration of nationalism and the fact that money can buy gold, the London Olympics gave us the usual advances in human performance. But is there a limit to how fast, high and strong we can get? Sounds like a question for science.

It’s a tricky one though: you’d expect there to be restrictions from physiology or mechanics, but we don’t necessarily understand those well enough to draw a line. Plus there’s always the chance of some innovation in technology or technique that pushes those limits further – for example, the Fosbury flop in the high jump.

But the other way to tackle the problem is to look at the statistics and see whether records are approaching a limit, which is just what Spanish physicist Filippo Radicchi from the Universitat Rovira i Virgili has done (Radicchi F 2012, “Universality, limits and predictability of gold-medal performances at the Olympic Games”, PLoS ONE, vol. 7, no. 7, e40335, doi:10.1371/journal.pone.0040335).

The probability of reaching particular milestones – measured in seconds – in five different athletic events increases every year (image F Radicchi, PLoS ONE)

Radicchi looked at medal-winning performances from previous Olympics and showed that they followed a normal distribution relative to each other, which implies that they can be considered to be exponentially approaching a future limit or asymptote. Looking at the rate they’re approaching this limit also enables a prediction for each future Olympic Games.

As an example, we’ll look at the big one, the men’s 100 metre sprint. Radicchi’s calculations, published on 12 July 2012, predicted a time of 9.63±0.13 seconds for the London Olympics. On 5 August 2012, Usain Bolt won the gold medal in this event with a winning time of… 9.63 seconds.

Unfortunately, Radicchi says that some of the early data for these shorter events is unreliable, so calculating the ultimate limit is a bit tricky. The unadulterated calculations give an estimate of 8.28 seconds. But discarding some of the dodgier figures – blame them on less sophisticated timing techniques – a more conservative figure is 8.80 seconds.

Compare that with Usain Bolt’s own 2009 world record time of 9.58 seconds. Even with the conservative estimate, the limit is still a while off.

The table below shows a similar story in a number of other major events:

Event	Predicted limit	Current world record	Gold medal 2012 London Olympics
Men’s 100 m (sec)	8.28	9.58	9.63
Men’s 110 m hurdles (sec)	11.76	12.87	12.92
Men’s 400 m (sec)	41.62	43.18	43.94
Men’s marathon (hr:min:sec)	1:36:11	2:03:38	2:08:01
Men’s pole vault (metres)	6.87	6.14	5.97
Women’s 100 m (sec)	9.72	10.49	10.75
Women’s long jump (metres)	8.12	7.52	7.12

At each successive Olympics the advances are expected to be smaller and smaller, meaning breaking records will get less and less likely. Eventually, we’ll reach the limit of not only human ability, but reasonable comparison between events, when you take into account things like weather conditions or even the accuracy of the length of the track.

But at least Radicchi’s predictions suggest we haven’t quite reached those limits. So if you’re an athlete with world record aspirations, don’t give up just yet.

Hooray for Higgs!

It’s a big night and you can read the news pretty much everywhere on the web, but I have to get in on the action: it looks like the Higgs boson has been discovered at the Large Hadron Collider.

The Large Hadron Collider, or LHC, is of course an enormous piece of physics equipment located in Switzerland at the European Organisation for Nuclear Research, or CERN (originally the Conseil Européen pour la Recherche Nucléaire, thanks to those wacky French-Swiss). Two experimental teams, known as ATLAS and CMS, have used the LHC to search for Higgs bosons in the debris from the high-energy particle collisions it generates.

Both experiments appear to have found something that looks a lot like a Higgs boson, with a mass of between 125 and 126 GeV (ATLAS got 126.5 GeV, CMS got 125.3 GeV, so that’s pretty close).

Is this the end of physics? That’s a big call, and one that sensibly no one’s willing to make. But there’s certainly a bit of “where do we go from here?”

Before this, the last major discovery of a fundamental particle was the top quark in 1995, and that time there was a much bigger concern that if we didn’t find it then much of what we knew about particle physics must be wrong. But the Higgs boson leaves many unanswered questions, and many of us were hoping that they’d find something more, well, unexpected.

Of course, there’s still unexplained physics staring us in the face, like dark matter, dark energy, inflation and that little thing called gravity. And the Higgs signal isn’t quite as predicted, which could either mean new physics or we just need more data. But for the moment, the Standard Model holds strong, and we should celebrate by boozing on for the boson.

Come back soon for a more considered discussion of what this discovery does and doesn’t mean, and until then maybe check out the unofficially combined ATLAS and CMS results on the viXra blog. And a brief explanation of terminology below:

• Higgs boson – a quantum excitation of the Higgs field.
• Higgs field – a kind of energy field that fills all of space and gives mass to everything that interacts with it. Unfortunately at this stage those masses are purely arbitrary – it would be nice if we had a theory that told us what they should be.
• Mass – you already know what this is, but it’s worth pointing out that most of the mass we can see (i.e., not dark matter) is actually due to potential energy from the forces that bind quarks into protons and neutrons, via E = mc². The Higgs field is responsible for the masses of electrons and unbound quarks, which are much smaller.
• GeV – also known as giga electron volts, is 1 billion electron volts. And an electron volt is the energy a single electron gains by being accelerated through one volt of an electrical circuit. This energy can be related back to mass via the aforementioned E = mc² (the correct nomenclature for mass is actually eV/c², but no one’s really fussy about it).
• Hadron – a particle made out of quarks. Protons and neutrons are the best known hadrons, and protons are the things that the Large Hadron Collider accelerates and collides. They’re quite large relative to their constituent quarks, but I think the LHC gets its name from the fact that it itself is rather large (27 km around).
• Boson – to put it simply, bosons (with an s that sounds like a z, not to be confused with bosuns) are particles that transmit forces between fermions, which are the particles of matter. And to put it complicatedly, bosons obey Bose-Einstein statistics and fermions obey Fermi-Dirac statistics.
• Standard Model – a theory put together in the 1970s that describes all observed interactions of fundamental particles. It includes the matter particles, or fermions, namely 6 types of quarks and 6 types of leptons (which include electrons and neutrinos), and the bosons for the forces that act between them, namely the photon (the quantum of the electromagnetic force), the W and Z bosons (of the weak nuclear force, which causes radioactive decay) and gluons (the strong magnetic force, which binds quarks into hadrons and is so strong you can’t pull them out and get a quark on its own). It also includes the Higgs boson (see above). It doesn’t include gravity, because that’s the weakest of the four fundamental forces and cannot so far be detected in particle accelerators.
• Dark matter, dark energy and inflation – these are cosmic entities whose effects can only be seen via gravity on a galactic or universal scale, and which we’ve discussed before. They are also not described in the Standard Model, but they seem to be real. So there, Horatio.