A radar image obtained by Cassini during a near-polar flyby on February 22, 2007, showing a big island in the middle of Kraken Mare on Saturn's moon Titan. Caption and credit: NASA

Why Titan is awesome #11


Here we go again. 😄 As has been reported, NASA has been interested in sending a robotic submarine to Saturn’s moon Titan to explore the hydrocarbon lakes near its north pole. Various dates have been mentioned and in all it seems likely the mission will be able to take off around 2040. In the 22 years we have left, we’ve got to build the submarine and make sure it can run autonomously on Titan, where the sea-surface temperature is about 95 K, whose waterbodies liquid-hydrocarbon-bodies are made of methane, ethane and nitrogen, and with density variations of up to 30%.

So researchers at Washington State University (WSU) tried to recreate the conditions of benthic Titan – specifically as they would be inside Kraken and Ligeia Mare – by working with the values of four variables: pressure, temperature, density and composition. Their apparatus consisted of a small, cylindrical cartridge heater submerged inside a cell containing methane, ethane and nitrogen, with controls to measure the values of the variables as well as modify conditions if needed. The scientists took a dozen readings as they varied the concentration of methane, ethane and nitrogen, the pressure, sea temperature, the heater surface temperature and the heat flux at bubble incipience.

The experimental setup used by WSU researchers to recreate the conditions inside one of Titan's liquid-hydrocarbon lakes. Source: WSU/NASA
The experimental setup used by WSU researchers to recreate the conditions inside one of Titan’s liquid-hydrocarbon lakes. Source: WSU/NASA
The data logged by WSU researchers pertaining to the conditions inside one of Titan's liquid-hydrocarbon lakes. Source: WSU/NASA
The data logged by WSU researchers pertaining to the conditions inside one of Titan’s liquid-hydrocarbon lakes. Source: Hartwig and Leachman, 2017/WSU

Based on them, they were able to conclude:

  • The moon’s lakes don’t freeze over even though their surface temperature is proximate to the freezing temperature of methane and ethane because of the dissolved nitrogen. The gas lowers the mixture’s freezing point (by about 16 K below the triple point), thus preventing the formation of icebergs that the robotic submarine would then have had to be designed to avoid (there’s a Titanic joke in here somewhere).
  • However, more nitrogen isn’t necessarily a good thing. It dissolves better in its liquid-hydrocarbon surroundings as the pressure increases and the temperature decreases – both of which will happen at lower depths. And the more nitrogen there is, the more the liquids surrounding the submarine are going to effervesce (i.e. release gas).

What issues would this pose to the vehicle? According to a conference paper authored among others by Jason Hartwig, a member of the WSU team, and presented earlier this year,

Effervescence of nitrogen gas may cause issues in two operational scenarios for any submersible on Titan. In the quiescent case, bubbles that form may interfere with sensitive science measurements, such as composition measurements, in acoustic transmission for depth sounding, and sidescan sonar imaging. In the moving case, bubbles that form along the submarine may coalesce at the aft end of the craft and cause cavitation in the propellers, impacting propulsive performance.

  • The quantity of effervescence and the number of sites on the submarine’s surface along which bubbles formed was observed to increase the warmer the machine’s outer surface got.
The planned design of the submarine NASA plans to use to explore Titan's cold hydrocarbon lakes. Source: Hartwig and Leachman, 2017/WSU
The planned design of the submarine NASA plans to use to explore Titan’s cold hydrocarbon lakes. Source: Hartwig and Leachman, 2017/WSU

If NASA engineers get all these details right, then their submarine will work. But making sure the instruments onboard will be able to make the observations they’ll need to make and the log the data they’ll need to log presents its own challenges. When one of the members of the WSU team decided to look into the experimental cell using a borescope (which is what an endoscope is called outside a hospital) and a video recorder, this is what he got:


Oh, Titan.

(Obligatory crib: the university press release‘s headline goes ‘WSU researchers build -300ºF alien ocean to test NASA outer space submarine’. But in the diagram of the apparatus above, note that the cartridge heater standing in for the submarine is 5 cm long. So the researchers haven’t built an alien ocean; they’ve simply reconstructed a few thimblefuls.)

  1. Why Titan is awesome #1
  2. Why Titan is awesome #2
  3. Why Titan is awesome #3
  4. Why Titan is awesome #4
  5. Why Titan is awesome #5
  6. Why Titan is awesome #6
  7. Why Titan is awesome #7
  8. Why Titan is awesome #8
  9. Why Titan is awesome #9
  10. Why Titan is awesome #10

Featured image: A radar image obtained by Cassini during a near-polar flyby on February 22, 2007, showing a big island in the middle of Kraken Mare on Saturn’s moon Titan. Caption and credit: NASA.

Note: This post was republished from late February 15 to the morning of February 16 because it was published too late in the night and received little traffic.

A Falcon 9 lifting off in 2014. Credit: SpaceX

ISRO v. SpaceX doesn’t make sense

Though I’ve never met the guy, I don’t hold Pallava Bagla in very high regard because his stories – particularly of the Indian space programme – for NDTV have often reeked of simplistic concerns, pettiness and, increasingly of late, a nationalistic pride. The most recent instance all these characteristics were put on display was February 12, when NDTV published a 20-minute video of Bagla interviewing K. Sivan, ISRO’s new chairman.

The video is headlined ‘New ISRO Chief Rocket Man Sivan K, A Farmer’s Son, Takes On SpaceX’. What a great story, innit? A farmer’s son taking on SpaceX chief Elon Musk! But if you’re able to stop there and ask a few questions, you’re going to realise that the headline is a load of tosh. First off, the statement that Sivan is a “farmer’s son” is a glancing reference, if not more, to that New York Times cartoon – the implicit jingoism of which we really must get past soon. The national government has been building false narratives around supporting farmers but here we are, valorising the son of one.

Also, referring to Sivan as a “farmer’s son” IMO reduces the man to that one factoid (particularly to serve a narrative Sivan himself may not wish to pursue), as if that’s all we’re going to choose to see about his origins, neglecting what else could have enabled him to succeed the way he has.

Second: ISRO “takes on SpaceX” is a dumb statement. ISRO is a public sector organisation; SpaceX is a private corporation. Their goals are so markedly different that I’m not entirely sure why whoever crafted the headline (not necessarily Bagla) feels ISRO might be threatened by SpaceX’s Falcon Heavy launch (on February 4); I’m less sure why Bagla himself went on to spin his story thus. Case in point: SpaceX is going bigger to be able to take humans to Mars within 10 years; ISRO’s going smaller to help Antrix capitalise on the demand for launching micro and nanosats as well as bigger to launch heavier telecom satellites. Additionally, I know for a fact that ISRO has been cognisant of modularised launch vehicles for at least three years, and this isn’t something Sivan or anyone else has suddenly stopped to consider following the Falcon Heavy launch. The idea’s been around for a bit longer.

All of this is put on show in an exchange about five minutes into the video, as Bagla goes hard at the idea of ISRO possibly lagging behind SpaceX whereas Sivan says (twice) that the PSLV and the Falcon 9 can’t be compared. Transcript:

KS: We can’t compare how much the launch vehicles cost. It depends on the environment in which the manufacturing is realised. I can assure you that our costs are very low because of the way we are manufacturing, the materials we’ve chosen to work with – this way, our costs are always low. But I don’t want to compare because this is always subjective.

PB: But at the same time, we are known for our very low cost missions. For a Falcon 9, they charge about $70 million per launch (ballpark figures) while India did a mission to Mars for roughly the same price. This included the rocket and the satellite, going all the way to Mars. Does that make us feel like we’re very, very competitive in pricing, which is why so many foreign customers are also coming to India?

(ISRO’s Mars Orbiter Mission was a technology demonstrator. The endeavour’s primary mission was to provide a proof of concept of an Indian orbiter at Mars. Second, the satellite’s size and capabilities were both limited by the PSLV’s payload capacity; to wit, MOM’s scientific payload weighed a measly 15 kg whereas the NASA MAVEN, which launched in the same window as MOM, had instruments weighing 65 kg. Third, not many scientific papers have been published on the back of MOM-specific findings. When Bagla says “India did a mission to Mars for roughly the same price” as a single Falcon 9 launch, I also invite him to consider that ISRO has access to cheaper labour than is available in the West and that the MOM launch was noncommercial whereas the Falcon 9 is a rocket developed – and priced – for commerce and profit.)

KS: Foreign customers are coming to India for two reasons. One is, as you said, we’re cost effective – mainly by way of manufacturing and selection of materials. We also make simple rockets. The second reason customers prefer us is the robustness. The reliability of our PSLV is large. When a customer comes to us, they want to make sure there’s a 100% chance their satellite reaches its orbital slot.

PB: So are we cheaper than SpaceX or not?


KS: Again, I don’t want to compare because it is not correct to compare. If the two rockets were made in the same timeframe, in the same place with equivalent amounts of effort, we can compare. But the rockets have been made in different parts of the world, according to different needs. What I can say is that we have a low-cost vehicle.

Almost exactly a year ago, I’d argued the same thing for The Wire, in an article that didn’t go down well with most readers (across the political spectrum). The thrust of it was that the PSLV had been designed from 1977 onwards to launch Indian remote-sensing satellites and that ISRO receives all its funding from the Department of Space. OTOH, SpaceX designed the Falcon 9 to fit prevailing market needs and, though the company receives a lot of money through NASA contracts, its raison d’être as a private entity is to make money by commercialising launch services. Excerpt:

Casting the GSLV, presumably the Mk-III, as a super-soldier in the space-war arena could be misguided. Unlike SpaceX or Arianespace, but much like Roscosmos, ISRO is a state-backed space agency. It has a mandate from the Department of Space to be India’s primary launch-services provider and fulfil the needs of both private entities as well as the government, but government first, at least since that is how policies are currently oriented. This means the GSLV Mk-III has been developed keeping in mind the satellites India currently needs, or at least needs to launch without ISRO having to depend on foreign rockets. …

On the other hand, Arianespace and SpaceX are both almost exclusively market-driven, SpaceX less so because it was set up with the ostensible goal of colonising Mars. Nonetheless, en route to building the Falcon Heavy, the company has built a workhorse of its own in the Falcon 9. And either way, together with Arianespace, it has carved out a sizeable chunk of the satellite-launching market. …

Thus, though Antrix is tasked with maximising profits, ISRO shouldn’t bank on the commercial satellites market because its mix of priorities is more diverse than those of SpaceX or Arianespace. In other words, the point isn’t to belittle ISRO’s launchers but to state that such comparisons might just be pointless because it is a case of apples and oranges.

Sadly for Bagla – and many others like him looking the fools for pushing such a silly idea – our own space programme assumes value only when compared to someone else’s agenda, irrespective of whether the comparison even makes sense. I also wonder if Sivan thinks such are the questions the consumers of NDTV’s journalism want answered – an idea not so farfetched if you consider that not many journalists get access to ISRO’s top brass in the first place – as well as what fraction of the Indian citizenry consumes the success of the Indian space programme simply relative to the successes of others and not as an enterprise established to serve India’s needs first.

A screenshot from the film 'The Cloverfield Paradox' (2018). Source: Netflix

All the science in ‘The Cloverfield Paradox’

I watched The Cloverfield Paradox last night, the horror film that Paramount pictures had dumped with Netflix and which was then released by Netflix on February 4. It’s a dumb production: unlike H.R. Giger’s existential, visceral horrors that I so admire, The Cloverfield Paradox is all about things going bump in the dark. But what sets these things off in the film is quite interesting: a particle accelerator. However, given how bad the film was, the screenwriter seems to have used this device simply as a plot device, nothing else.

The particle accelerator is called Shepard. We don’t know what particles it’s accelerating or up to what centre-of-mass collision energy. However, the film’s premise rests on the possibility that a particle accelerator can open up windows into other dimensions. The Cloverfield Paradox needs this because, according to its story, Earth has run out of energy sources in 2028 and countries are threatening ground invasions for the last of the oil, so scientists assemble a giant particle accelerator in space to tap into energy sources in other dimensions.

Considering 2028 is only a decade from now – when the Sun will still be shining bright as ever in the sky – and renewable sources of energy aren’t even being discussed, the movie segues from sci-fi into fantasy right there.

Anyway, the idea that a particle accelerator can open up ‘portals’ into other dimensions isn’t new nor entirely silly. Broadly, an accelerator’s purpose is founded on three concepts: the special theory of relativity (SR), particle decay and the wavefunction of quantum mechanics.

According to SR, mass and energy can transform into each other as well as that objects moving closer to the speed of light will become more massive, thus more energetic. Particle decay is what happens when a heavier subatomic particle decomposes into groups of lighter particles because it’s unstable. Put these two ideas together and you have a part of the answer: accelerators accelerate particles to extremely high velocities, the particles become more massive, ergo more energetic, and the excess energy condenses out at some point as other particles.

Next, in quantum mechanics, the wavefunction is a mathematical function: when you solve it based on what information you have available, the answer spit out by one kind of the function gives the probability that a particular particle exists at some point in the spacetime continuum. It’s called a wavefunction because the function describes a wave, and like all waves, this one also has a wavelength and an amplitude. However, the wavelength here describes the distance across which the particle will manifest. Because energy is directly proportional to frequency (E = × ν; h is Planck’s constant) and frequency is inversely proportional to the wavelength, energy is inversely proportional to wavelength. So the more the energy a particle accelerator achieves, the smaller the part of spacetime the particles will have a chance of probing.

Spoilers ahead

SR, particle decay and the properties of the wavefunction together imply that if the Shepard is able to achieve a suitably high energy of acceleration, it will be able to touch upon an exceedingly small part of spacetime. But why, as it happens in The Cloverfield Paradox, would this open a window into another universe?

Spoilers end

Instead of directly offering a peek into alternate universes, a very-high-energy particle accelerator could offer a peek into higher dimensions. According to some theories of physics, there are many higher dimensions even though humankind may have access only to four (three of space and one of time). The reason they should even exist is to be able to solve some conundrums that have evaded explanation. For example, according to Kaluza-Klein theory (one of the precursors of string theory), the force of gravity is so much weaker than the other three fundamental forces (strong nuclear, weak nuclear and electromagnetic) because it exists in five dimensions. So when you experience it in just four dimensions, its effects are subdued.

Where are these dimensions? Per string theory, for example, they are extremely compactified, i.e. accessible only over incredibly short distances, because they are thought to be curled up on themselves. According to Oskar Klein (one half of ‘Kaluza-Klein’, the other half being Theodore Kaluza), this region of space could be a circle of radius 10-32 m. That’s 0.00000000000000000000000000000001 m – over five quadrillion times smaller than a proton. According to CERN, which hosts the Large Hadron Collider (LHC), a particle accelerated to 10 TeV can probe a distance of 10-19 m. That’s still one trillion times larger than where the Kaluza-Klein fifth dimension is supposed to be curled up. The LHC has been able to accelerate particles to 8 TeV.

The likelihood of a particle accelerator tossing us into an alternate universe entirely is a different kind of problem. For one, we have no clue where the connections between alternate universes are nor how they can be accessed. In Nolan’s Interstellar (2014), a wormhole is discovered by the protagonist to exist inside a blackhole – a hypothesis we currently don’t have any way of verifying. Moreover, though the LHC is supposed to be able to create microscopic blackholes, they have a 0% chance of growing to possess the size or potential of Interstellar‘s Gargantua.

In all, The Cloverfield Paradox is a waste of time. In the 2016 film Spectral – also released by Netflix – the science is overwrought, stretched beyond its possibilities, but still stays close to the basic principles. For example, the antagonists in Spectral are creatures made entirely as Bose-Einstein condensates. How this was even achieved boggles the mind, but the creatures have the same physical properties that the condensates do. In The Cloverfield Paradox, however, the accelerator is a convenient insertion into a bland story, an abuse of the opportunities that physics of this complexity offers. The writers might as well have said all the characters blinked and found themselves in a different universe.

My photo of the Lexus LS 500h as depicted in an ad in The Hindu, dated February 2, 2018.

Veblen cars and the risk of harbouring a useless concern for the climate

Lexus has an ad on the jacket of today’s The Hindu for its new premium hybrid electric vehicle, the LS 500h. The product description states that the car “extends relentless innovation to environmentally conscious engineering with a performance-centric Multi Stage Hybrid System. Crafted with luxury in mind and engineered with the environment at heart” (emphasis added).


This is first-class poop.

Obviously, as a Veblen good (priced at Rs 1.77 crore), the LS 500h is pandering to the self-indulgence of India’s upper class. The car allows the highfalutin to be able to claim that they’re riding around in a vehicle that’s environmentally friendly. It’s not. The LS 500h measures, in metres, 5.2 × 1.9 × 1.4 (l, b, h). That’s a lot for a carrying capacity of five persons. So the car’s design is quite effectively symptomatic of a belief that pro-environmental engineering is only about rethinking or retooling the car’s central source of power as opposed to redesigning it to take up less space on the roads as well.

As we all know, the public transport system in urban India is far from ideal. Buses are ill-maintained and don’t ply well-optimised routes. Auto-rickshaw fares are regulated but rarely, if ever, enforced. Trains always run at full capacity, are subject to frequent breakdowns and the associated infrastructure (e.g. stations) are unclean and, in many cases, unsafe. Overall, they are always in high demand and the commute experience they provide is often stressful. So those who can afford private transportation exercise the option (esp. in the form of two-wheelers). Ultimately, given that most parts of India’s tier I and II cities are unplanned formations, roads are often overcrowded, jammed and/or unnavigable (apart from being damaged themselves).

So improving this situation needs policymakers and citizens alike to assume an interdisciplinary approach, particularly since transport emissions also have to be mitigated to meet both climatic and health targets. In this multivariate context, one of the variables to be optimised for, among accessibility, affordability, etc., is space. Specifically, it becomes desirable for more people to occupy less space while commuting so that time spent traveling and fuel use efficiency are reduced and increased, resp.

For five people to occupy a ground area of 10 sq. metres in the LS 500h is bordering on the unconscionable in the specific context of Lexus claiming that the car was “engineered with the environment at heart”. Let’s be honest: this is a fancy car that’s like any other fancy car but with some fancy machines (in the form of two engines – electric and V6 – plus a Li-ion battery). It aspires to mitigate its own emissions but does nothing else that’s environmentally friendly; this is cutting-edge innovation as Lexus might like to claim but limited to the subset of thermodynamic consequences of using a car.

Whether this singular contribution will make a difference is also doubtful. For the upper class to be able to claim they’re being ‘green’ requires them to implement those claims at scale – particularly since possessing the car itself would require capital accumulation to the tune of a few tens of crores. Such wealth can be better redistributed to help those who can’t yet afford to live green but aspire to; in the long-term, sustainable living has the potential to be cheaper, but in the short-term, it is bound to be quite costly. Without redistribution, affirmative pro-climate action through the production and utilisation of Veblen goods will remain an oxymoron.

Featured image: My photo of the Lexus LS 500h as depicted in an ad in The Hindu, dated February 2, 2018.

Credit: Free-Photos/pixabay

On cancers, false balance and the judiciary

Climate change has for long been my go-to example to illustrate how absolute objectivity can sometimes be detrimental to the reliability of a news report. Stating that A said “Climate change is real” and that B replied “No, it isn’t” isn’t helping anyone even though it has voices from both sides of the issue. Now, I have a new example: cancer due to radiation from cellphone towers. (And yes, there seems to be a pattern here: false balance becomes a bigger problem when a popular opinion is on the verge of becoming unpopular thanks new scientific discoveries.)

This post was prompted by a New York Times article published January 5, 2018. Excerpt:

From 1991 to 2015, the cancer death rate dropped about 1.5 percent a year, resulting in a total decrease of 26 percent — 2,378,600 fewer deaths than would have occurred had the rate remained at its peak. The American Cancer Society predicts that in 2018, there will be 1,735,350 new cases of cancer and 609,640 deaths. The latest report on cancer statistics appears in CA: A Cancer Journal for Clinicians. The most common cancers — in men, tumours of the prostate; in women, breast — are not the most common causes of cancer death. Although prostate cancer accounts for 19 percent of cancers in men and breast cancer for 30 percent of cancers in women, the most common cause of cancer death in both sexes is lung cancer, which accounts for one-quarter of cancer deaths in both sexes.

This is a trend I’d alluded to in an earlier post: that age-adjusted cancer death rates in the US, among both men and women, have been on a steady downward decline since at least 1990 whereas, in the same period, the number of cellphone towers has been on the rise. More generally, scientific studies continue to fail to find a link between radio-frequency emissions originating from smartphones and cancers of the human body. Source: this study and this second study.

The simplest explanation remains that these emissions are non-ionising – i.e. when they pass through matter, they can excite electrons to higher energy levels but they can’t remove them entirely. In other words, they can cause temporary disturbances in matter but they can’t change its chemical composition. Some have also argued that cellphone radiation can heat up tissues in the body enough to damage them. This is ridiculous: apart from the fact that the human body is a champion at regulating internal heat, imagine what’s happening the next time you get a fever or if you go to Delhi in May.

Those who continue to believe cellphone towers can damage our genes do so for a variety of reasons – including poor outreach and awareness efforts (although I’m told TRAI has done a lot of work on this front) and, more troublingly, the judiciary. By not ensuring that the evidence presented before them is held to higher scientific standards, Indian courts have on many occasions admitted strange arguments and thus pronounced counterproductive verdicts.

For example, in April 2017, the Supreme Court (of India) directed a BSNL cellphone tower in Gwalior be taken down after one petitioner claimed radiation from the structure had given him Hodgkin’s lymphoma. If the court was trying to err on the side of caution: what about the thousands of people now left with poorer connectivity in the area (and who are not blaming their ailments on cellphone tower radiation)?

This isn’t confined to India. In early 2017, Joel Moskowitz, a professor at the Berkeley School of Public Health, filed a suit asking for the state of California to release a clutch of documents describing cellphone safety measures. Moskowitz believes that cellphone radiation causes cancer, and that Big Telecom has allegedly been colluding with Big Government to keep this secret away from the public.

In December 2017, a state judge ruled in Moskowitz’s favour and directed the California Department of Public Health (CDPH) to release a “Guidance on How to Reduce Exposure to Radiofrequency Energy from Cell Phones” – a completely unnecessary set of precautions that, by the virtue of its existence, reinforces a gratuitous panic. By all means, let those who believe in this drivel consume this drivel, but it shouldn’t have been at the expense of making a mockery of the court nor should it have been effected by pressing the CDPH’s reputation to endorse the persistence of pseudoscience. What a waste of time and money when we have bigger and more legitimate problems on our hands.

… which brings us to climate change and the perniciousness of false balance. On December 20, 2017, Times of India published an article titled ‘Can mobile phones REALLY increase the risk of brain cancer? Or is it too far-fetched?’. It quotes studies saying ‘yes’ as well as those saying ‘no’ but it doesn’t contain any attributions, citations or hyperlinks. Sample this:

Lab studies where animals are exposed to radio frequency waves suggest that as the waves are not that strong and cannot break the DNA, they cannot cause cancer. But some other studies claim that that they can damage the cells up to some level and this can support a tumour to grow.

It also contains ill-conceived language, for example by asking how radio-frequency waves become harmful before it goes on to ‘discuss’ whether they are harmful at all, or by saying the waves are “absorbed” in the human body. But most of all, it’s the intent to remain equivocal – instead of assuming a rational position based on the information and/or knowledge available on the subject – that’s really frustrating. This is no different from what the Californian judge did or what the SC of India did: not consider evidence of better quality while trying to please everyone.

Featured image credit: Free-Photos/pixabay.

The journey of a crow and the story of a black hole

The Washington Post has a review, and introduction therewith, of a curious new book called Ka, authored by John Crowley (acclaimed author of Great Work of Time). It is narrated from the POV of a crow named Dar Oakley, who journeys repeatedly into the realm of the dead with a human companion. A para from the WaPo piece caught my attention for its allusion to an unsolved problem in physics:

In many cultures, crows have long been regarded as “death-birds.” Eaters of carrion and corpses, they are sometimes even said to convey the soul into the afterlife. Crowley’s title itself alludes to this notion: Dar Oakley croaks out “ka,” which isn’t just a variant spelling of “caw,” but also the ancient Egyptian word for the spiritual self that survives the decay of the body. Yet what actually remains of us after our bones have been picked clean? Might our spirits then dwell in some Happy Valley or will we suffer in eternal torment? Could death itself be simply an adventure-rich dream from which we never awake? Who knows? The narrator, who might be a writer, says of his dead and much-missed wife Debra that “the ultimate continuation of her is me.” What, however, becomes of Debra when he too is dead?

What indeed. The question is left unanswered so the reader can confront the unanswerability supposedly implicit in this riddle. But while this scheme may be acceptable in a book-length “exploration of the bond between the living and the dead”, physicists don’t have much of a choice. They really want to know, would love to know, how a very similar situation plays out in the quantum realm.

It’s called the black hole information paradox. A black hole is a single point in space around which spacetime is folded into a sphere. This means that if you get trapped in this region of spacetime, you’re locked in. You can’t leave the sphere. The surface of this sphere is called the event horizon: it’s the shortest distance from the black hole from which you can pull away.

Now, there’s no way to tell two black holes apart if their mass, angular momentum and electric charge are the same. This is called the no-hair conjecture. This means that whatever a black hole swallows – whether it be physical matter or information as a sequence of 0s and 1s encoded as an electromagnetic signal – doesn’t retain its original shape or patterns. They become lost, observable only in changes to the black hole’s mass, angular momentum and/or electric charge.

In 1974, Stephen Hawking, Alexei Starobinsky and Yakov Zel’dovich found that, thanks to quantum mechanical effects near an event horizon, the black hole within could be emitting radiation out into space. So assuming a black hole contains a finite amount of energy and has stopped eating material/info from the outside, it will evaporate slowly over time and vanish. This is where the information paradox kicks in.

You’re obviously thinking the info the black hole once swallowed was all converted into energy and emitted as Hawking radiation. This is actually where the problem begins. Quantum mechanics may be whimsically counterintuitive about what it allows nature to do at its smallest scale. But it does have some rules of its own that it always follows. One of them is that information is always conserved, that when information passes into a black hole, it can’t be converted into the same energy mulch that everything else is converted to.

We don’t know what happens to the ‘spirit’ of Debra when Dar Oakley passes away. And we don’t know what happens to the information inside a black hole when the latter evaporates.

Black holes are unique objects of study for classical and non-classical physicists alike because they combine the consequences of both general relativity and quantum mechanics. Those pursuing a unified theory, broadly called quantum gravity, hope that data about black holes will help them find a way to reconcile the laws of nature at the biggest and smallest scales. Resolving the black hole information paradox is one such path.

For example, string theory, which is a technical framework that gives physicists and mathematicians the tools to solve problems in quantum gravity, proposes a way out in the name of the holographic principle. It states (in highly simplified terms) that the information trapped by a black hole is actually trapped along the event horizon and doesn’t fall inside it. Over time, fluctuations on the horizon release the information out. However, neither the complete shape and consequences of this theory nor some contradictory predictions are fully understood.

Even whether humans will be able to resolve this paradox in their lifetime at all remains to be seen – but it’s important to hope that such a thing is possible and that the story of a black hole’s life can be told from start to finish someday. Crowley also tries to answer Dar Oakley’s question about Debra’s fate thus (according to the WaPo review):

“Maybe not, said the Skeleton. But look at it this way. When you return home, you’ll tell the story of how you sought it and failed, and that story will be told and told again. And when you’re dead yourself, the story will go on being told, and in that telling you’ll speak and act and be alive again.”


Featured image credit: Free-Photos/pixabay.

Why a pump to move molten metal is awesome

The conversion of one form of energy into another is more efficient at higher temperatures.1 For example, one of the most widely used components of any system that involves the transfer of heat from one part of the system to another is a device called a heat exchanger. When it’s transferring heat from one fluid to another, for example, the heat exchanger must facilitate the efficient movement of heat between the two media without allowing them to mix.

There are many designs of heat exchangers for a variety of applications but the basic principle is the same. However, they’re all limited by the explicit condition that entropy – “the measure of disorder” – is higher at lower temperatures. In other words, the lower the temperature difference within the exchanger, the less efficiently the transfer will happen. This is why it’s desirable to have a medium that can carry a lot of heat per unit volume.

But this is not always possible for two reasons. First: there must exist a pump that can move such a hot medium from one point to another in the system. This pump must be made of materials that can withstand high temperatures during operation as well as not react with the medium at those temperatures. Second: one of the more efficient media that can carry a lot of heat is liquid metals. But they’re difficult to pump because of their corrosive nature and high density. Both reasons together, this is why medium temperatures have been limited to around 1,000º C.

Now, an invention by engineers from the US has proposed a solution. They’ve constructed a pump using ceramics. This is really interesting because ceramics have a good reputation for being able to withstand extreme heat (they were part of the US Space Shuttle’s heat shield exposed during atmospheric reentry) but an equally bad reputation for being very brittle.2 So this means that a ceramic composition of the pump material accords it a natural ability to withstand heat.

In other words, the bigger problem the engineers would’ve solved for would be to keep it from breaking during operation.

DOI: 10.1038/nature24054
DOI: 10.1038/nature24054

Their system consists of a motor (not visible in the image above but positioned to the right of the shaft, made of an insulating material), the gearbox, a piping network and a reservoir of liquid tin. When the motor is turned on, the pump receives liquid tin from the bottom of the reservoir. Two interlocking gears inside the pump (shown left bottom) rotate. As the tin flows between the blades, it is compressed into the space between them, creating a pressure difference that sucks in more tin from the reservoir. After the tin moves through the blades, it is let out into another pipe that takes it back to the reservoir.

The gearbox. Source: https://www.youtube.com/watch?v=Y_6K-Xo4nH8
The gearbox. Source: https://www.youtube.com/watch?v=Y_6K-Xo4nH8

The blades are made of Shapal, an aluminium nitride ceramic made by the Tokuyama Corporation in Japan with the unique property of being machinable. The pump seals and piping network are made of graphite. High-temperature pumps usually have pipes made of polymers. Graphite and such polymers are similar in that they’re both very difficult to corrode. But graphite has an upper hand in this context because it can also withstand higher temperatures before it loses its consistency.

Using this setup, the engineers were able to operate the pump continuously for 72 hours at an average temperature of 1,200º C. For the first 60 hours of operation, the flow rate varied between 28 and 108 grams per second (at an rpm in the lower hundreds). According to the engineers’ paper, this corresponds to an energy transfer of 5-20 kW for a vat of liquid tin heated from 300º C to 1,200º C. They extrapolate these numbers to suggest that if the gear diameter and thickness were enlarged from 3.8 cm to 17.1 cm and 1.3 cm to 5.85 cm (resp.) and operated at 1,800 rpm, the resulting heat transfer rate would be 100 MW – a jump of 5,000x from 20 kW and close to the requirements of a utility-scale power plant.

And all of this would be on a tabletop setup. This is the kind of difference having a medium with a high energy density makes.

The engineers say that their choice of temperature at which to run the pump – about 1,200ºC – was limited by whatever heaters they had available in their lab. So future versions of this pump could run for cheaper and at higher temperatures by using, say, molten silicon and higher grade ceramics than Shapal. Such improvements could have an outsize effect in our world because of the energy capacity and transfer improvements they stand to bring to renewable energy storage.

1. I can attest from personal experience that learning the principles of thermodynamics is easier through application than theory – an idea that my college professors utterly failed to grasp.

2. The ceramics used to pave the floor of your house and the ceramics used to pad the underbelly of the Space Shuttle are very different. For one, the latter had a foamy internal structure and wasn’t brittle. They were designed and manufactured this way because the ceramics of the Space Shuttle wouldn’t just have to withstand high heat – they would also have to be able to withstand the sudden temperature change as the shuttle dived from the -270º C of space into the 1,500º C of hypersonic shock.

Featured image credit: Erdenebayar/pixabay.

A problem worth its weight in salt

Pictures of Jupiter’s moon Europa taken by the Galileo space probe between 1995 and 2003 support the possibility that Europa’s surface has plate tectonics. In fact, scientists think it could be one of only two bodies in the Solar System – the other being Earth – to display this feature. But it must be noted that Europa’s tectonics is nothing like Earth’s if only because the materials undergoing this process are very different – compare the composition of Earth’s crust and Europa’s ice shell. There are also no arc volcanoes or continents on Europa.1 But this doesn’t mean there aren’t any similarities either. For example, scientists have acknowledged that shifting ice plates on the moon’s surface, with some diving over others and pushing them down, could be a way for minerals on the top to plunge further interior. Because Europa has been suspected of harbouring a subsurface ocean of liquid water, a mineral cycle could be boosting the chances of finding life there. Plate tectonics played a similar role in making Earth habitable.

The biggest giveaway is that the moon’s surface is not littered with craters the way other Jupiter moons are. This meant that cratered patches of the ice shell were disappearing into somewhere and replaced with ‘cleaner’ patches. There are also kilometre-long ridges on the shell suggesting that something had moved along that distance, and they ended abruptly in some places. In 2014, a pair of geologists from Johns Hopkins and the University of Idaho used software like Photoshop to cut up Galileo’s maps of Europa and stitch them back together such that the ridges lined up. They found that there were some areas with a “big gap”. One way to explain it was that the patch there had dived beneath a neighbouring one – a simple version of plate tectonics. But tantalising as the possibility is, more evidence is needed before we can be sure.

If we’re hoping to find the first alien life inside a Jovian moon, we’ll need good models that can help us predict how life might’ve evolved there. A new paper from researchers at Brown University tries to help by trying to figure out why the plates might be shifting (To say something could be happening, it helps to have a simple way it could be happening and with the available resources). On Earth, interactions between the crust and the mantle are motivated among other factors by differences in temperature. The crust is cooler than the magma it ‘slides’ over, which means it’s denser, which assists its subduction when it happens. Such differences aren’t mirrored on Europa, where scientists think there’s a thin, cold ice shell on top and a relatively warmer one below. When a patch of ice from the top slides down, it becomes warmer because the upper layer provides insulation, which prevents the sliding layer from sliding further down because the density has been evened out.

Instead, the Brown University fellows think the density differences could arise thanks to salt content (which, by the way, could also be useful when reading their press release. It says, “A Brown University study provides new evidence that the icy shell of Jupiter’s moon Europa may have plate tectonics similar to those on Earth.” You know it’s not similar, especially if left unqualified like that.) Salt is denser than water, so ice that has more salt is more dense. A 2003 study also suggested that warmer ice will have lesser salt because eutectic mixtures could be dissolving and draining it out. So using a computer model and making supposedly reasonable assumptions about the shell’s temperature, porosity and salinity ranges, the Brown team calculated that ice slabs made up of 5% salt and saltier than their surroundings by 2.5% would be able to subduct. However, if the distribution of salt was uniform on Europa’s surface (varying by less than 1% from slab to slab, e.g.), then a subducting slab would have to have at least 22% salt → very high.

I said “supposedly reasonable assumptions” because we don’t exactly know how salinity and porosity vary around and through Europa. In their simulations, the researchers assumed that the ice has a porosity of 10% (i.e. 10% of the material is filled with pores), which is considered to be on the higher side of things. But the study remains interesting because it’s able to establish the big role salts can play in how the ice moves around. This is also significant because Galileo found the Europan magnetic field to be stronger than it ought to, suggesting the subsurface ocean had a lot of salt. So it’s plausible that the cryomagma2 on which Europa’s upper shell moves could be derived from the waters below.

The researchers also claim that if the subducting slab doesn’t lose all its salt in about one million years, it will remain dense enough to go all the way down to the ocean, where it could be received as a courier carrying materials from the surface that help life take root.3 But of you think this might be too out there, look at it in terms of the planned ESA Jupiter Icy Moons Explorer (JUICE) and NASA Clipper missions for the mid-2020s. Both Cassini and Galileo data have shown that there’s a lot going on with the icy moons of the gas giants Jupiter and Saturn, with observations of phenomena like vapour plumes pointing to heightened chances for the formation and sustenance of alien life. If JUICE and Clipper have to teach us something useful about these moons, then they’ll have to go in prepared to study the right things, the things that matter. The Brown University paper has shown that salt is definitely one of them. It was accepted for publication in the Journal of Geophysical Research: Planets on December 4, 2017. Full text here.

Featured image: An artist’s impression of water vapour plumes erupting from Europa’s south pole, with Jupiter in the background. Credit: NASA-ESA.

1Venus has two continent-like areas , Ishtar and Aphrodite terra, and also displays tectonic activity in the form of mountains and volcanoes, e.g. But it does not have plate tectonics because its crust heals faster than it is damaged during tectonic activity.

2One of the more well known cryovolcanoes in the Solar System is Doom Mons on where else but Titan.

3 On Earth, tectonic plates that are pushed downward also take a bunch of carbon along, keeping the surface from accumulating the element in amounts that could be deleterious to life.

Why Titan is awesome #10


How much I’ve missed writing these posts since Cassini passed away. Unsurprisingly, it’s after the probe’s demise that we’ve really begun to realise how much of Cassini’s images and data we were consuming on a daily basis, all of which is gone. There’s no more the steady stream of visuals of Saturn’s rings, bands, storms and panoply of moons – in fact all of which have been replaced by Jupiter’s rings, bands, storms and panoply of moons thanks to Juno. Nonetheless, one entire area of the Solar System has been darkened in my imagination. Until the next full mission to the Saturnian system (although nothing of the kind is in the works), we’ll have to make do with what Cassini data trickles down through NASA’s and ESA’s data-processing sieves.

One such is a new study about the temperature of the air high above Titan’s poles. Before Cassini’s death-dive into Saturn, the probe spent some time studying the moon’s polar atmosphere. Researchers from the University of Bristol who obtained this data noticed something odd: the part of the atmosphere over Titan’s poles began to develop a warm spot over late 2009 but that by 2012, it had become a ‘cold spot’. By 2015, the temperature at about 550 km above had dropped to 120 K (that’s a little below the temperature at which supercooled water turns into a glass).

On Earth, a warm spot forms over the poles because of two principle reasons: how Earth’s wind circulates around the planet and because of the presence of carbon dioxide. During winter, air over the corresponding hemispheric pole sinks down, becomes compressed and heats up. Moreover, the carbon dioxide present in the air also emits the heat it has trapped in its chemical bonds.

In 2012, astronomers using Cassini data had found that Titan also exhibits a wind circulation process that is moon-wide. It can be understood as Titan having two atmospheres, or layers, one on top of the other. In the lower atmosphere, there are three Hadley cells; each cell represents a distinct air circulation system wherein air rises up for 10 km or so from near the equator, moves up/down towards subtropical regions, sinks back down and returns to the equator along the surface. In the second, upper atmosphere, air moves between the two poles directly in a unified, global Hadley cell.

Titan_south polar vortex

Now, remember that Titan’s distance from the Sun means that one Titan-year is 29.5 Earth-years, that each Titanic season lasts over seven Earth-years and that seasonal shifts are much slower on the moon as a result. However, in 2012, scientists studying Cassini data found that the rate at which the air over one of Titan’s poles was sinking into the pole – like the air does on Earth – was happening really quickly: according to Nick Teanby, a researcher at the University of Bristol and also the lead author of the latest study, the rate of subsidence increased from 0.5 mm/s in January 2010 to 1.5 mm/s in June 2010. In other words, it was a shift that, unlike the moon’s seasons, happened rapidly (in just 12 Titanic days).

The same study concluded that Titan’s atmosphere was thicker than previously thought because trace gases like ethane, hydrogen cyanide, acetylene and cyanoacetylene were found to be produced at an altitude of over 500 km over the poles thanks to photochemical reactions induced by ultraviolet radiation and high-energy electrons streaming in from the Sun. These gases would then subside into the lower atmosphere over the polar region – which brings us to the latest study. It says that, unlike what carbon dioxide warming Earth’s atmosphere, the (once) trace gases actually cool the atmosphere, resulting in the dreadfully cold spot over Titan’s poles. They also participate in the upper Hadley cell circulation.

This is similar to a unique phenomenon observed over Saturn’s south pole in 2005.

Changes in trace gas abundances over Titan's south pole. Credit: ESA
Changes in trace gas abundances over Titan’s south pole. Credit: ESA

What a beauty you are, Titan. And I miss you, Cassini, more than I miss many other things in life.

I couldn’t find a link to the paper of the latest study; here’s the press release. Update: link to paper.

Links to previous editions:

  1. Why Titan is awesome #1
  2. Why Titan is awesome #2
  3. Why Titan is awesome #3
  4. Why Titan is awesome #4
  5. Why Titan is awesome #5
  6. Why Titan is awesome #6
  7. Why Titan is awesome #7
  8. Why Titan is awesome #8
  9. Why Titan is awesome #9

Featured image: Cassini’s last shot of Titan, taken with the probe’s narrow-angle camera on September 13, 2017. Credit: NASA.

What it takes to wash a strainer: soap, water and some wave optics

When I stay over at a friend’s place whenever I come to Delhi, I try to help around the house. But more often than not, I just do the dishes – often a lot of dishes. One item I’ve always had trouble cleaning is the strainer, whether a small tea strainer or a large but fine sieve, because I can never tell if the multicoloured sheen I’m seeing on the wires is a patch of oil, liquid soap or something else. The fundamental problem is that these items are susceptible to the quirks of the wave of nature of light, as a result of which their surfaces display an effect called goniochromism, also known as iridescence.

At first (and over 12 years after high school), I suspected the wires on the sieve were acting as a diffraction grating. This is a structure that has a series of fine and closely spaced ridges on the surface. When a wave of light strikes this surface, the ridges scatter different parts of the wave in different directions. When these waves interact with each other on the other side, they interfere with each other constructively or destructively. A constructive interference produces a brighter band of colour; a destructive interference produces a darker band. How the wave becomes scattered is a function of its frequency: the lower the frequency (or redder the colour), the more the wave is bent around a grating.

As a result, white and continuous light appears to breakdown into its constituent colours when passed through a diffraction grating. But it must be noted that a useful diffraction grating used in a visible-light experiment has something like 4,000-6,000 ridges every centimetre. The width of each ridge has to be of comparable size to the wavelength of visible light because only then can it scatter that portion of light. On the other hand, the sieve I was holding appeared to have only 6-8 ridges every centimetre, so the structure itself couldn’t have been what was effecting the sheen.

Goniochromism, or iridescence, is caused when two transparent or semi-transparent films – like liquid soap atop water – reflect the incident light multiple times. In fact, this is one type of iridescence, called thin-film interference. Here, imagine a thin layer of soap on the surface of a thin layer of water, itself sitting on the surface of a vessel you’re cleaning. (With a strainer, the water-soap liquid forms meniscuses between the wires.) When white light strikes the soap layer, some of it is reflected our and some is transmitted. The transmitted portion than strikes the surface of the water layer: some of it is sent through while the rest is reflected back out.

When the light reflected by each of the two layers interact, their respective waves can interfere either constructively or destructively. Depending on the angle at which you’re viewing the vessel, bright and dark bands of light will be visible. Additionally, the thickness of the soap film also decides which frequencies are intensified and which become subdued in this process. The total effect is for you to see rainbow-esque pattern of undulating brightness on the vessel.

So herein lies the rub. Either effect, although the second more than the first, produces what effectively looks like an oily sheen on the strainer in my hand no matter how many times I scrub it with soap and run it under the water. And ultimately, I end up doing a very thorough job of it if there was no oil on the strainer to begin with – or a very bad one if there was oil on it but I’ve let it be assuming it’s soap residue. It’s a toss-up… so I think I’ll just follow my friend C.S.R.S’s words: “Just rub it a few times and leave it.”

Featured image credit: Lumix/pixabay.