Metastable

A wide swath of fundamental physics and chemistry is defined by the pursuit of the ground state. Since we began elucidating the structure of the atom in the 1910s, much of what we know about how particles, quasiparticles and molecules behave can be described by a desire among each of these entities to lose all the energy that they can in the given circumstances and simply exist with the bare minimum. This is why the ground state is both an illuminating and fascinating object of study: the former because it is what particles are always tending towards and the latter because it is the ultimate destiny of the ergic constituents of our world, symbolising a kind of particulate amor fati. The ground state is the home to which all matter seeks to return; by studying the home and the forces that keep it, we can explain to a large extent the nature of the things that want to return there.

“The ground state is interesting because small excitations above it are what we effectively mean by (quasi)particles,” says Madhusudhan Raman, a theoretical physicist. “That is, when you find the right variables in which to study small excitations of the ground state, you have understood your physical system perturbatively.”

For example, the electrons around an atomic nucleus are forbidden from occupying the same… the same what? “Might I suggest an analogy?” Raman butts in. “Electrons are like home-owners: they may live in the same town, or even on the same street, but no two electrons live together. That is the exclusion principle.” And all the electrons in an atom are concentric vis-a-vis the atomic nucleus. By asking why they would do this when they could all simply journey around the nucleus in an orbit that affords them the lowest energy possible, we come upon the work of Wolfgang Pauli, Paul Dirac, Enrico Fermi, among others. By wondering if other particles in other systems are subjugated similarly, we come upon the work of Satyendra Nath Bose and Albert Einstein, among others.

Why, fast-forward to 2011, when the Higgs boson was discovered because the unstable amount of energy it embodied ‘decayed’ into clumps of lighter, long-lived and so more observable particles. If particles didn’t behave this way, the Large Hadron Collider would be completely useless – nor would we have had last week’s exciting blazar neutrino discovery.

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A choice example from the realm of physics is the superconductor, which – as we all know – is a material that can conduct an electric current with zero resistance. One way to explain this phenomenon is by taking recourse through BCS theory, which imagines the electrons in a superconductor to have joined up in specific circumstances to form so-called Cooper pairs, effectively getting transformed from being fermions of higher energy to bosons of lower energy. And bosons are exempt from Pauli’s exclusion principle, free to form a phase of matter called the condensate at low temperatures. This condensate sea of electrons is what conducts the electricity. “This, incidentally, is a good example of finding the right ground state,” Raman said.

Superconductors are comparable to time crystals, a hypothetical crystal whose particulate constituents would be in motion in their ground state. The principle difference between them is that time crystals exhibit the spontaneous breaking of time-translation symmetry (as explained here), whereas superconductors don’t. However, superconductors are still cooler – not least for their befuddling variety and their involvement in kooky experiments to uncover anomalous quantum effects and ‘artificial’ particles.

Unfortunately, all these materials and their properties are very difficult to engineer and then observe in action. In most cases, the observation itself consists of watching numbers on a screen or reading pre-recorded data. Compare this to how exciting it would be to observe an object oscillating between either sides of its ground state in a classical setting. Of course, this also would be hard to engineer because the object would have to act against gravity, which takes a lot of work, which in turn takes a lot of energy (think of Newton’s cradle). Perhaps it can be made to work if we went just a little smaller, unto a scale where the object is heavy enough to be affected by gravity but also light enough to be affected by one of the other fundamental forces, preferably in the form of a controllable electrochemical reaction.

This is somewhat the case with the mercury heartbeat experiment. Place a drop of mercury in a small pool of acid with an iron nail at a short distance from the drop. The acid strips off electrons from the mercury atoms it comes in contact with, ionising them and forcing them to repel each other. This causes the mercury drop to flatten out – and make contact with the iron nail. The nail has enough negative electrochemical potential, i.e. functions as an anode, to deionise the mercury atoms and cause them to pull themselves together again thanks to surface tension. As a result, the drop de-flattens into a sphere-like shape, loses contact with the iron nail and starts the cycle all over again.

Last week, scientists from China announced that they’d done something similar with liquid gallium – but with more interesting effect. They filled a petri dish with sodium hydroxide, placed 50-150 microlitres of liquid gallium at its centre and then set up a graphite fence around it. The fence would act like the nail in the mercury experiment if it was positively charged with a DC current. When the dish was tilted slightly, the gallium flowed down towards the fence and came in contact. Its surface became electrified, i.e. gallium atoms lost electrons to become ions, and the surface tension vanished. As the drop spread out over the incline for more of it to come in contact with the fence, the amount of electrification also increased, eventually causing the liquid and the fence to repel each other so much that the former moved back up the incline – cutting contact, reacting with the base to regain electrons, restoring surface tension and flowing back down the incline.

It is an abusive relationship. The liquid gallium is forced to oscillate between being a droplet at the centre of the dish and being a pancake in contact with the fence, whereas all it would like to do is not have the incline and just lounge on its basic bed. Sadly, it is not going to have its paradise anytime soon because the Chinese team found that the gallium’s ‘heartbeat’ movement up and down the incline could be controlled by the amount of DC current supplied – whereas the mercury’s ‘heartbeat’ throb couldn’t be controlled by the iron nail. In their paper, the Chinese group writes,

A comparatively special feature of the gallium-based liquid oscillator is that the electrochemistry allows the beating to be activated or deactivated just using an applied DC voltage. … Without the applied voltage, the drop docks with the inner side of the electrode due to the electrode inclination. The voltage causes the drop to self-actuate and a stable periodic motion is obtained soon afterward. … The oscillations stop after the voltage is removed. The motion can end abruptly; although in some cases, slower irregular beats persist for a few more cycles after the voltage is removed, indicating stored charges on the drop. Despite some background mechanical vibrations in the apparatus, the liquid metal itself shows a behaviour that is self-correcting and self-regulating, governed by a well-defined characteristic frequency… This indicates that the phenomena occur at a steady-state frequency that is relatively robust against mechanical perturbations.

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Numerous reports (listed below) have appeared on the web discussing the potential of this gallium pulse to power robot muscles of the future – which is to reduce the quasi-sublime beauty of what is happening here to the pithiness of a battery, and move on. But don’t move on just yet.

The transmission of forces and the progression of a phenomenon happens faster in the quantum realm than in the classical one. Moreover, the phenomena also seem ‘cleaner’ in that there is no arbitrary, anthropogenic intervention apart from the preservation of certain state variables. For example, maintaining a cryogenic temperature is necessary for a superconductor to come to life – but the performance of superconductivity does not demand continuous human intervention in the form of, say, an iron nail or an electrified graphite fence.

Of course, superconductors are a cherry-picked example, possibly even a flawed one because the line between human intervention and the need to preserve a functionally conducive environment vanishes completely in many other examples. One is the discovery last year of Majorana modes in a topological superconductor: the material in question does not exist in nature, is almost impossible to create by accident and can only be built by an intelligent species. Given this, did the scientists discover the Majorana modes or did they invent them?

Classical examples, on the other hand, don’t present such conundra, at least not as often as their quantum counterparts do. It is easier when gravity lords over the other fundamental forces to tell apart natural occurrences from synthesised ones – just as easily as one can differentiate between greatness and transcendentalism. To illustrate how, consider two objects that behave strangely at or near their ground states: the Cooper pairs condensate and the liquid gallium/sodium hydroxide/graphite ensemble. The condensate has zero viscosity and can keep flowing forever. There is here a deeper alteration of the substance’s nature, so much so that the essence of the sum is not the essence of its parts. But this is not so with liquid gallium, which in comparison is dramatic prose but prosaic nonetheless.

The implicit inferiority of the gallium and mercury examples is further borne out by the introduction of an incline and a nail. The petri dish had to be inclined at some angle to kickstart the experiment, the nail had to positioned at a short distance from the droplet to jumpstart the throbbing. Such considerations are arbitrary – and they’re arbitrary because their precision is inconsequential. Perhaps the petri dish could be tilted at 45º if enough current is supplied to the graphite corral. Perhaps the iron nail could be placed 10 cm away from the mercury if there is enough mercury and enough electrolyte. However, a superconductor just won’t superconduct above its critical temperature, no matter how many electrons are available or what the shape of the material is.

There is a fragility that makes mathematical order easier to summon, and behold, out of the chaos of reality, a sort of principled existence that draws sharper lines between ground states and excited states in a way that gravity never aspires to in its stabler demesne. This is certainly one reason why we choose to be interested in quantum mechanics even as we keep our didactic metaphors in the classical domain. The quantum offers the asymptotically perfect realisation of natural beauty and the classical offers a crude grammar to translate between physics and aesthetics. The ground state, of course, is the pursuit that unites them both.

The Wire
July 21, 2018

(I can speak only for myself here) I certainly seem to be needing a monthly reminder that to focus on pure science as a journalist is not in any way an abdication of one’s responsibilities as a citizen of India. The more forceful the reminder – i.e. the stronger the argument made – the longer it lingers in memory, in my consciousness, but these days its lifespan seems limited to 30 days at best.

Why is this reminder necessary? As people involved with an industry founded on the pursuit of truth, it’s important to know that what we’re doing (individually) is relevant and in the public interest. This compulsion frequently, and easily, supersedes personal interest.

This morning, I wanted to write about dynamic equilibrium in a droplet of liquid gallium trapped on a positively charged graphite ring. I thought it was cool – but there was the overwhelming sense that I could be spending my time and words better. And if you read the newspaper every day, you know better is applied science, science policy, administration, women in STEM, higher ed, public/private GERD, research misconduct, faculty hiring, IoEs, etc.

It’s very difficult to hold in your mind the importance of being interested in and even focusing on fundamental research when there is very little, if any, public dialogue or even public interest in/on it.

If you broach it, there will be zero immediate validation. It will always be contested, by the people and many scientists alike. A debate like this may be good in the bigger scheme of things – but in the absence of any sort of go-to resource to top up your conviction with on this line of argument, support for non-applied science remains islanded, devoid of opportunities for consensus. In other words, there is NIL institutional motivation to writing about non-applied scientific research.

I’ve personally grown tired of resorting to complex arguments about research always paying off in the long run to convince people that it’s important. History and economics together make nuanced suggestions about the “right” course of action but their careful study is like the climate, whereas I’m talking about the weather here.

One kind of argument that works with Left liberals who say “we have finite resources and we should put them to best possible use” is to offend their intellectual desire to negate the Modi govt’s policies. So I reply: “we have finite resources because the govt isn’t investing enough, and you choosing to ‘spend it wisely’ is no different from buckling under pressure, preparing to legitimise govt underspending by letting it affect your actions”.

Obviously this isn’t an objectively good argument because it only works when the govt and one particular political class is vehemently at odds. Instead, what we need is an ‘all-weather’ argument that works irrespective of one’s moralities. In my (new) case, that argument is “BECAUSE IT’S FUCKING COOL!”

It’s clearly not the best argument, it’s not even independent of my morals, etc., but it’s the argument that I need to just work. And by all means it should because what’s life without “wow”? I also realise my privilege here in that I’m a full-time science journalist with incredible freedom about what I write on. But somehow this acknowledgment feels similar to expecting one to thank nutjobs for not lynching you to death.

Then again, I’m also uncomfortable with being given a responsibility to make people go “wow” all the time. I would edit the mandate to say – as @anilananth said – “You’re on science’s side”, and add “while ‘wow’ is good, it’s the road to ‘wow’ that’s really cool.”

I hope you’ll quickly see a meta-problem here. If you ask any journalist as to why covering politics is important, the minimum viable answer is “Because.” Ask them why writing about ‘heartbeats’ in gallium is important, and it’s not just “Because.” It’s always something longer, and deliverable in full only to someone who already professes interest and has time. So in other words, I need a reason to write about non-applied science whose labour cost-of-rationalisation is comparable to that for politics or business journalism.

On Twitter today, @thattai published a short thread about how framing the ‘debate’ about cellphone radiation harming biological tissue between ionising and non-ionising radiation is not a good idea because even non-ionising radiation (called so for its inability to strip electrons from atoms) can precipitate biochemical effects by interacting with energy reservoirs in the body.

Although he tried to be extra-careful and repeated that he’s said in his thread that studies thus far have been inconclusive, his last tweet advised people against sleeping with their phones close to their heads. At this point, @avinashtn intervened with interesting consequence. @avinashtn said that until scientists were able to come to a definitive (in a relative sense of the term) conclusion, guiding lay people towards a certain course of action was very risky – especially, in his view, if the course would cause them to fear cellphone radiation.

This is obviously a legitimate concern and a major part of the modern scientific zeitgeist: even when scientists have been able to reach consensus over the safety of X or Y product, people have feared that product because they have effectively been taught to do so. Examples include GMO, vaccines and bisphenol. The opposite is also true, such as with (some instances of) climate change communication, fats and – what has been my go-to case study thus far – cellphone radiation. That bad news spreads faster on the social media doesn’t help.

However, in a time when entire sections of scientific inquiry are under scrutiny for their empirical methods and conclusions, scepticism threatens to transform into its more villainous avatar: cynicism. While constantly questioning whether X or Y is no longer safe or unsafe is what will enable us to keep up with the times, we will allow doubts to consume us instead of the firmer footing of belief (and faith) if scepticism becomes cynicism.

In other words, by advocating wariness – as @thattai wishes to do with cellphone radiation – or non-wariness – as @avinashtn wishes to do – we seem to be at a crossroads that will determine the level of public trust in science, particularly in the time of the replication crisis but also (rather more importantly) lesser research funding, weaker public institutions and diminishing instruments to ensure public accountability.

Extrapolating further, it will be interesting to explore how the rise of nationalism around the world has transformed the place of doubt in our daily lives. And even further: to ask what history can teach us about the place of inconclusiveness in society such that we can moderate its place in the public psyche and increase trust in science.

For now, I stand against being wary of cellphone radiation, but I hope a broader view of science and scepticism over space and time can provide a more substantial – and unavoidably nuanced – answer about what would be the better position to take.

Featured image: Straphangers on a train looking intently into their phones. Credit: Hugh Han/Unsplash.

There was an announcement from CERN on June 20 that I’d wanted to cover, missed it and which – to my zero surprise – no one else covered either. For the first time, two Asian schools have won CERN’s annual Beamline for Schools competition. The winning students will visit the French mega-lab later this year to conduct physics experiments at the lab’s facilities and present their results.

The schools were R.N. Podar School, Mumbai, and the International School of Manila, Philippines. The Indian group’s experiment – called ‘Cryptic Ontics’ – involves the following, according to a CERN statement:

The “Cryptic Ontics” team consists of 9 boys and 9 girls. A core team of 9 students will visit CERN to study the deflection of protons and electrons in a magnetic field. By studying the interaction between charged particles and a magnetic field in the lab, the team hopes to learn about the anomalies in the Earth’s magnetic field as a function of the variance of the cosmic ray detection rate.

I don’t entirely understand this but hopefully I can find out soon. The Filipino effort is equally interesting: the students from Manila want to find out how radiation other than X-rays could be used to study cancers in the human body, for starters by irradiating pions into artificial tissue.

It’s really heartening that such things are happening and equally disheartening that they don’t receive mainstream press coverage. It’s not that the media won’t cover what school students are doing – journalists have highlighted ridiculous claims by young hacks in the past (see here and here, e.g.) – but that it has displayed an unusual knack for staying away from the legitimate, and legitimately good, stuff.

It isn’t tempting to write about Elon Musk in that it is easy but in that it is an event that few thought we could witness live: a successful businessman letting his inner recklessness show. Yes, I’m accusing Musk of something as simple as lacking composure – but sadly for him, even though all he’s done is open a window into his mind, its occupants are unsavoury. It is tempting to write about Musk because we can for once stop speculating about how it is that Silicon Valley entrepreneurs cut from the same cloth as Musk and Peter Thiel think, and take a break from amassing piles of secondhand, implicative evidence. Now we have proof – and an opportunity to characterise the psyche of this odiously powerful class of world society.

For the uninitiated: Vern Unsworth was one of the expert divers who helped rescue the young Thai football team and its coach from the cave they had been trapped in. In an interview published over the weekend, he called Musk’s offer to help with a small submarine a “PR stunt”. Musk responded on Twitter with an ad hominem, calling Unsworth a “pedo”, short for pedophile, and following it up with “Bet ya a signed dollar it’s true”. These tweets were deleted shortly after.

From all that he has said and done over the last few months, it’s evident that Musk thinks he should be celebrated more than he is and criticised less. But like a big baby, every time Musk does say such things, he’s taken less and less seriously – or more by those looking for a spectacle. When someone doesn’t agree, Musk lashes out in abusive ways. His disgusting potshot at Unsworth is just the latest example, and isn’t out of line with previous salvos. Before this, Musk wanted to revolutionise journalism by floating a platform where people could ‘rate’ journalists, editors and their work – after multiple news reports found evidence of mismanagement at Tesla Motors.

Dan Fagin, who was briefly my science writing teacher at New York University, called journalism “the history of now”. It is the stories of ‘now’ that we want to write and preserve, and good journalism will remember that Musk accused Unsworth of being a child sex criminal to his 22 million Twitter followers. If journalists turned a blind eye just because Musk deleted his tweets, would Pravda – the rating platform Musk wants – forgive us? Of course not. (Would Musk then accuse Pravda of having been hijacked? It’s not impossible.)

As Zeynep Tufekci noted in the Times, many Silicon Valley intellectuals unfortunately believe that because they have made a billion dollars solving a very specific technological problem, they are to be treated as authorities in completely unrelated fields. This isn’t an illness found only in the American west coast; such things happen when people become institutions. Musk has Twitter. Narendra Modi has his own podcast and makes speeches at rallies. Men mansplain because of the patriarchy. Physicists hold forth on how to reform adoption of GMO technology as well as higher education in India because they’re Nobel laureates. Those who haven’t studied evolutionary biology think the subject is in the grip of broken theories.

There’s a second way to reverse extrapolate the rich white entrepreneur’s conviction that “I’m an authority”, which is to the belief that all problems are engineering problems. This is why SpaceX and Tesla are awesome if only at the outset while Hyperloop and the Boring Company set off alarm bells. Musk believes everyone wants to own a car because they’re afraid they might bump into serial killers on the bus. Fiverr thinks it’s okay to exploit freelance labour by glamourising penury. Cities around the world have had to legislate against Airbnb so homeowners don’t evict long-term residents in favour of short-term ones willing to pay higher. Amazon thinks space is a better investment than working conditions at its warehouses. Google wants to build a “horizontal” building, whatever that is, in the age of increasing population density away from coasts. Juicero and Teforia built juicers and teapots connected to the internet priced Rs 27,000 apiece. Facebook thinks it’s okay to dillydally between identifying as a platform and as a publisher. And we are all too familiar with Über’s actions worldwide.

Silicon Valley, its incentives, its inflated estimates and its upper-class jurisdiction have all together amplified the words of its businesspeople beyond their due, creating what are effectively headstrong analysts who believe all the world’s a San Francisco and everyone who deploys non-San-Franciscan solutions is not as smart.

These companies have all demonstrated an infuriating misunderstanding of what makes modern society liveable and which of its foundations shouldn’t be tampered with. Or, more plausibly, they understand perfectly well but know they can get away with it. It is precisely this mindset that we all hoped Musk would never don, and anointed him our counter-idol and potential counter-institution. For those of us who can afford to spare some more optimism, it might just be reasonable to cultivate a new hope: that Musk’s actions are a reflection of his being torn between retaining the ego necessary to believe everything is fixable, the discretion necessary to ensure even your detractors take you seriously and the humility necessary to keep from taking yourself too seriously. But it increasingly looks as if Musk only wants to preserve the ego.

Remember how with Donald Trump, and with the Modi government in fact, there came a time when we really had to stop believing that the former knew what he was doing and that the later did not. We’re inching closer to that time with Elon Musk as well – when it would be in the best interests of everyone to cease hoping that he is going to fix anything but nuts and bolts. The only thing stopping us at the moment is an acknowledgment of our inner demons, the misguided belief that perhaps we want another person to fail because we’re envious and/or resentful. I’m sure Musk will put those thoughts to the test soon and, hoping against hope, we will have our answer then.

The Wire
July 15, 2018

I’m not fully convinced as to why everyone is currently bashing the Jio Institute up. When the ‘Institutions of Eminence’ scheme’s rules were announced in August 2017 and greenfield institutions were welcomed to apply, everyone was either perfectly okay with the idea or didn’t bother. But now everyone has a problem with it because Jio Institute chose to apply and was selected as one of those greenfield institutions.

This somehow reeks of Vijay Mallya all over again: to focus on one scapegoat – vulnerable as they are by virtue of being in the news and exposing the government to public pressure – instead of paying equal attention to the numerous other private institutes that have wrecked the higher education system through capitation fees. If ‘greenfield institutions’ is a legitimate category and if the government relaxed the rules a bit to let the Reliance-sponsored Jio Institute apply, I don’t see a problem as long as the rules haven’t prevented others from applying.

I get that some will say Mukesh Ambani himself wouldn’t have been able to apply if he wasn’t so pally with the PM and that it’s all crony capitalism on show. I’m more pissed off that only six non-greenfield institutions could be selected from a pool of 114 applicants – that’s a proper fuck-up right there. But most of all, I’m still interested in the fact that there’s still time: the MHRD hasn’t dished the tags out yet; it’s only mailed letters of intent out that transform to MoUs that provide the tag after a three-year follow-up.

When the ‘Institutions of Eminence’ rules were first put down, we didn’t give a damn, which I’m going take as an admission that it’s okay for greenfield institutions to exist and apply. If we really give a damn about this particular idea, then the fact that the MoUs are three years away should make us sit up, take notice and fight. We. Have. Time.

We shouldn’t be getting carried away just because it’s Reliance. The fouls haven’t yet been committed and I think if we don’t give Jio Institute a chance (and open ourselves up to just a little bit of disappointment, I’m aware), it’s just… stupid. It’s acrimony for acrimony’s sake.

There’s a video from Postcard News doing the rounds, showing a lady demonstrating the ability of a cow-urine-based substance to purportedly detoxify the human body. It does a fabulous job of making a mockery of itself given that it is only a few minutes long – and I’ve reached the point where I know I can draw a line and say debunking this is, at long last, beneath me.

What truly irked me about the video is its viewership: I’m not sure if Postcard News cares about whether the video is being shared by people poking fun at it but it’s bound to be pleased that, on Facebook, the clip’s been watched over 83,000 times in the last 80 hours, with lots of engagement. Throw in on-site views and WhatsApp and I can easily imagine 200,000 views in the same period. Thus far, these figures have been impossible to achieve with legitimate videos showing bona fide science at work, at least without a little paid push. (I’m not counting videos celebrating ISRO.)

I think this viewer behaviour confirms something I’ve been suspecting for about a year now: that people on the political left are more adhesive and those on the right are more cohesive vis-a-vis their reactions to ideas from across the aisle. To use the USGS’s language of hydrology:

Right → “Water is attracted to water”
Left → “Water is attracted to other substances”

Of course, such characterisation seems morally desirable, at least as the left would look upon the right and see protectionism and xenophobia, and the right will look upon the left and see exclusion and degeneracy. However, the same self-conception has put science journalism in an uncomfortable place: appropriated by a faction whose appreciation is passive at best and disappropriated by a faction that promises to celebrate it in exchange for some amount of debasement.

For example, I would contrast Postcard’s video about cow-urine-based detox with one on black holes from The Wire‘s stable, and the latter will brook no discussion – even one motivated by antipathy – in left or right circles, nor will the general populace of the left actively defend further its message. However, have a person on-screen prescribe cow piss for, you know, holistic wellbeing and you’ve got people on the right standing up for what they think is right and pushing it in the left’s face, and people on the left circlejerking off to how dumb they think others are.

I’m happy to note that The Wire has made space for a science section but beyond my colleagues and writers themselves, it certainly feels like a passive installation – the hosting of a science section for a science section’s sake. If it was not, I should be seeing higher engagement from one side of the spectrum; I’m not, whether I’m going by offline engagement or online. While this bodes quite well for being able to have a bipartisan audience that can be engaged if journalists and editors are persistent as well as didactic enough, it doesn’t bode well at all for the leftist’s oft-righteous claim to be on the side of reason.

From my POV at least, it seems like most pro-left people I engage with have taken for granted some second-hand assurance that they’re on the side of reason without knowing what a significant chunk of the architecture of reason actually looks like.

There was no post on July 11 because whatever I wrote on that day was for the article below. I couldn’t share it on that day itself because the embargo for the scientific papers it was based on lifted at 8.30 pm on July 12.

I. Prologue

Before Earth was born, a supermassive black hole far, far away shot a catastrophic jet of radiation into space. It was so powerful that one piece of that radiation was able to travel for 4.6 billion years through the universe and reach Earth, where it terminated in a quiet ping inside a detector buried under Earth’s south pole last September. Just like that, a potentially major finding was on humanity’s cards.

Meanwhile on Earth, scientists working at the same detector, called IceCube, reported a curious finding in 2013. They had identified 28 high-energy variants of particles called neutrinos between 2010 and 2012 coming from a source outside the Solar System. They were of such high energy that they couldn’t have come from the only two extraterrestrial objects we knew were capable of emitting them: the Sun and a supernova known as 1987A, about 168,000 lightyears away.

The higher the neutrino’s energy is, the higher the energy of the natural phenomenon that produced it. At very high energies (upwards of ~10,000 GeV/c², where 1 GeV/c² is about the mass of a proton at rest), we’re looking at natural and colossal particle accelerators whose energy efficiency makes the Large Hadron Collider look like a spinning keychain. What do these behemoths look like and how do they work?

Neutrinos are commonly called “ghostly” but “snooty” might be more apt. They are particles that flood space but very rarely interact with normal matter, as if they refuse to acknowledge matter’s proletarian presence. There are 100 billion neutrinos passing through your body every second and one of them will interact with you in your lifetime, two if you’re lucky.

They are emitted by many high-energy events. A nuclear reactor generates trillions of neutrinos per second, and the Sun trillions upon trillions. They are also born when cosmic rays from outer space collide with Earth’s upper atmosphere, showering neutrinos towards the ground.

We already know of some candidates capable of emitting very-high-energy neutrinos; black holes and supernovae are two of them. However, although “IceCube has been detecting neutrinos of astrophysical origins for the last six or seven years, none of those events have been associated with any known source,” Debanjan Bose, a physicist at IIT Kharagpur, told The Wire. “Follow-up observations for those events by other telescopes found nothing either.”

We’re also yet to unravel the precise mechanism of their production. In 2013, when IceCube didn’t have the wherewithal to say whether the 28 neutrinos were from a common source or where they where coming from, it did know these neutrinos were much more powerful than those from the Sun or 1987A.

A part of the answer lay in that quiet September ping, which scientists have announced today with great fanfare.

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II. Two sides of a mystery coin

According to announcements on July 12, the black hole that produced the ancient flare is possibly a blazar. A giant galaxy with an active supermassive black hole at its heart – guzzling interstellar gas and belching heat and light – can sometimes focus these emissions in a beam in Earth’s general direction. These systems are called blazars.

“As sources of high-energy neutrinos and cosmic rays, blazars have always been among the most promising candidates from the theoretical side,” Chad Finley, a physicist at Stockholm University, told The Wire. “However, recently it had started to seem that we should be seeing evidence of neutrinos from blazars by now, if they were the main sources.” That evidence, at least the promise of it, is finally here.

The neutrino detected in September has an estimated energy of 290,000 GeV.

A blazar is defined by the laser-like beam of high-energy radiation that it sometimes shoots out along its poles, travelling at near lightspeed towards Earth. The supermassive black hole at the centre of a blazar is thought to be the source of these beams, called relativistic jets. When a blazar emits a relativistic jet, it is said to be flaring. Scientists don’t fully understand how these jets are emitted, although they are thought to arise from super-hot matter falling into the black hole.

The blazar currently in the limelight, designated TXS 0506+056, is located 4.6 billion lightyears away from Earth. The discovery is exciting for multiple reasons. One is that this blazar produced relativistic jets so powerful that the neutrinos in them had enough energy to travel 40,000 billion billion km and reach Earth to give the precocious field of neutrino astronomy its first pièce de résistance.

Yet another is that this blazar may have been one of the sources of those 28 high-energy neutrinos spotted at IceCube before 2012. However, Finley clarified, “We don’t yet know what fraction of the total high energy neutrino flux” at IceCube or at other detectors “might be due to blazars”. This is an important unanswered question at the moment, he added.

Most of all, we now know of a source of high-energy neutrinos outside the Milky Way galaxy that can be studied by neutrinos. According to Finley, who is a member of the IceCube research collaboration and was involved in processing the new finding, “This has been the goal of neutrino astronomy for decades.”

However, Roger Romani, a physicist at the Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, struck a more cautious note: “I’d rate it as interesting enough to deserve some careful thought and study of the implications, but not secure enough to bet one’s career on.”

The first step towards producing neutrinos is to accelerate protons to a high speed, giving them more and more energy. Supermassive black holes can do this when they consume matter, belching radiation that energises the matter around it.

The energised protons then decay to neutral and charged pions. Each neutral pion further decays to photons (electromagnetic radiation) that ‘conventional’ telescopes can detect. Each charged pion decays to a muon and a muon neutrino. The muon finally decays into a muon neutrino, an electron and an electron neutrino. So for each proton, there are three neutrinos: two muon neutrinos and one electron neutrino. The more powerful the process that accelerated the protons, the more energetic the neutrinos will be.

Axiomatically, that the blazar TXS 0506+056 emitted neutrinos is a sign that it accelerated protons. An important implication of this “is that at least some blazar jets accelerate protons or other baryons,” Romani said. “This is a big deal.” Bose agreed, and called this implication what made him go “wow” about the discovery.

Energetic protons and atomic nuclei are the primary components of cosmic rays – radiation streaming in from outside the Solar System and, since their discovery over a century ago, of unknown origin. As with high-energy neutrinos, TXS 0506+056 might be able to resolve this conundrum as well.

“Most studies of light from blazars find that they are adequately explained by jets whose particles are primarily electrons and positrons,” Romani explained – and this explanation provides a sense of the amount of energy in the jets. However, protons are over 1,800-times heavier than electrons, which means the jets will have to be that much more energetic to accelerate them. He believes most blazars still emit jets dominated by electrons and positrons and that among a few others, “a proton component” is present in some flares. But “until we gather more such neutrinos from several sources, it’s very difficult to say how widespread the phenomenon is.”

For now, we think we know where some cosmic rays come from, and “we can study this blazar in detail,” Bose said, alluding to TXS 0506+056 as a natural laboratory of “physics under extreme conditions”.

§

III. The multi-messenger way ahead

Being able to study an object using the neutrinos it emits is a privilege. If a body emits charged particles like protons or electrons, their trajectories through space become warped by numerous magnetic fields in their path. Neutrinos, on the other hand, don’t interact with electric or magnetic fields, not even with gravity, enabling them to shoot out in straight lines and travel unhindered for billions of years, especially if they’re high-energy neutrinos. If a neutrino streaks through IceCube in a particular direction, physicists simply have to look back along the same line to find the direction of its source.

This is why, as Bose says, “neutrinos are the only tool to probe our universe beyond a certain energy.” Bose worked with the IceCube detector from 2009 until last year. And thanks to their abundance and longevity, they could help us understand how our universe was when it was very young and why it is the way it is today.

Astrophysicists were alerted to the existence of the blazar source when, on September 22, 2017, they received an alert from an automated program running inside IceCube data looking for the signatures of high-energy neutrinos. The strength of the signal corresponding to this neutrino was too weak to count as evidence.

Fortunately, there was a way out. On the day the program alerted physicists to the presence of a high-energy neutrino in IceCube’s midst, astronomers using various ground- and sky-based telescopes had observed a gamma-ray emission from the same patch of the sky. The odds of a coincidence were small enough to suggest that the physicists and the astronomers were looking at a common source of the gamma rays as well as the high-energy neutrinos. Blazars are expected to release energetic gamma rays as well.

This corroboration, Finley said, gave physicists the confidence they needed to go back through archival data and search for signs of its activity in the past.

And there it was: between 2012 and 2015, they found stronger signs of high-energy neutrinos impinging within the IceCube detector. The data was good enough to breach the statistical significance required to claim evidence (not discovery), and they have claimed it. To paraphrase Finley, it was a sign that “there was something here rather than nothing”.

This phrasing is closer to how Romani put it:  “As with any discovery hinged on a single event” – the one in September 2017 – “or even the mild excess” – between 2012 and 2015 – “one should be somewhat cautious. There have been statistical claims of neutrino-blazar associations before that have fallen by the wayside. This result looks better, but it is not of overwhelming significance.”

Finley agreed. “There are large uncertainties given the data we have so far,” he said, “which means it will be possible to extrapolate in many different directions.”

A question automatically arises: why wasn’t the 2012-2015 data flagged earlier?

Even though neutrinos almost never acknowledge the presence of matter, detectors like IceCube designed to log their interactions have recorded over “half a million” events. “A very tiny fraction of these come from space,” Finley continued, “and the rest are created in the atmosphere when cosmic rays arrive at Earth. Only a few neutrinos per year are so high energy that they stand out from this background on their own.”

The September 2017 alert was one such case, and it was made possible by physicists knowing where to look. “Otherwise it, is hard to identify the rare neutrinos from space within this large background of neutrinos from our atmosphere.”

That the blazar was tracked down with both neutrino and electromagnetic data has focused attention on a big takeaway from this affair: blazars are now the subject of multi-messenger astronomy. In this form of astronomy, astrophysicists study cosmic objects in more than one channel simultaneously. The two channels here are radiation and neutrinos. This can yield more information about a cosmic object than just one channel would – as we all found out with the discovery of the neutron-star merger.

“It has long been hoped that neutrinos could join the panoply of astrophysical messengers,” Romani said, “and the hard work by IceCube and the other neutrino teams place us at the threshold of this era.” Bose in turn called it “a tremendous boost for astroparticle physics”.

After the September 2017 alert was shared among a wider circle of observers, multiple telescopes on ground and in space sprung into action and began observing this patch, quickly establishing that the blazar was the most probable source as well as further characterising it. These included the Fermi Large Area and AGILE telescopes (both in low-Earth orbit), MAGIC (Canary Islands), HESS (Namibia), HAWC (Mexico), Subaru (Hawaii) and VERITAS (Arizona), among others.

“Five-ten years from now we may look back and say ‘they really caught the first wisps of the cosmic neutrino sources’ or we may look back and say ‘Too bad, another statistical fluke’,” Romani said. “But I hope for the former, particularly since with several more years’ observation, we could collect enough signal to probe how these blazar jets might get” protons and atomic nuclei “into the act.”

The studies (this and this) were published in the journal Science on July 12, 2018.

The Wire
July 12, 2018

The most curious thing about moving to Delhi – little anxiety, lots of a seemingly deep-rooted melancholy that I will no longer have a scientist roommate. It was one of the most fun things about my time living in Chennai, and unexpectedly so.

My roommate there was a physicist. He’s mentioned what exactly he does a few times, only keywords have stuck with me: string theory, gauge theories, supersymmetry; his PhD thesis is something about black hole event horizons and information tunnelling. More importantly, on days we were both home, he would make coffee and I’d help him drink it, and we’d chat in the living room about physics, science education and whatever else caught our fancy that day.

He was a good roommate but it seems the thing I’ll miss most about him, more than his being a roommate itself, is him. He was (and is) a kooky fellow, an opinionated physicist – rare as they are! – given to baroque pronouncements and verbose guilt about having too good a time on this planet, a penchant for losing at Monopoly and, of course, following the completion of every scientific paper with lots of whiskey.

My first day there, we bonded over inspecting a bug stuck in resin leaking from the washing machine. I once asked him why exactly QCD is so messed up, he fished out his iPad and smart-pen, launched into a well-ordered, articulate lecture, annotating his words with equations as he was speaking. He was adept at killing winged cockroaches but not so much at getting the salt right when he made fried fish.

He embodied the rejection of chaos with an eccentricity I’ve seen no one else muster. It is for roommates like him that everyone hopes. Goodbye, Mr Soufflé.

The Higgs boson has finally been observed decaying into the particles it most often decays to – six years after it was discovered. The reason for this delay was noise.

The Higgs boson is a scalar boson: it has spin 0. To preserve the value of this spin quantum number, it decays into pairs of a fermion and an anti-fermion. Fermions have spin +1/2 and anti-fermions have spin -1/2; their combined spin is 0. Moreover, the Higgs boson is likelier to decay into a heavier fermion than a lighter fermion because the boson couples stronger with the former.

The heaviest fermion is the top quark, but it is too heavy itself for the Higgs to decay into. The next is the bottom quark – and theoretical calculations suggest the Higgs should decay into a bottom quark and anti-quark 60% of the time. The third is the tau particle, which weighs almost half as much as the bottom quark and to which the boson decays only 6% of the time.

Now, the problem is that hadron colliders – Large or not – also produce an abundance of bottom quarks through other mechanisms. The rules of quantum chromodynamics (QCD: the study of quarks and gluons) enable three in particular – flavour excitation, gluon-gluon fusion and gluon splitting – that produce lots of bottom quarks.

As a result, physicists couldn’t tell if bottom quarks detected during a collision at the LHC were from Higgs boson decays or due to QCD processes… until now. The physicists were able to isolate the bottom quarks produced by decaying Higgs bosons (from the data) as well as, according to an official blog post, compare the values of “other kinematic variables that show distinct differences between the signal and the various backgrounds”.

By combining calculations across all the data collected by the machine in 2015, 2016 and 2017, the results had a significance of 4.9σ – just shy of the 5σ threshold to claim a discovery. The significance does breach the threshold when other data filters are applied but more data-taking and analysis will be necessary before the official declaration comes through.

You learn something everyday.

Featured image: Event display for the H→bb decay analysis with the ATLAS detector. Credit: ATLAS Collaboration/CERN.