gravity – Close Read

For space, frugality is a harmful aspiration

Ref:

‘ISRO’s Chandrayaan-2 mission to cost lesser than Hollywood movie Interstellar – here’s how they make it cost-effective’, staff, Moneycontrol, February 20, 2018. ∞

‘Chandrayaan-2 mission cheaper than Hollywood film Interstellar’, Surendra Singh, Times of India, February 20, 2018. ∞

The following statements from the Moneycontrol and Times of India articles have no meaning:

The cost of ISRO’s Mars Orbiter Mission was less than the production cost of the film Gravity.
The cost of ISRO’s Chandrayaan 2 mission is expected to be less than the production cost of the film Interstellar.

It’s like saying the angular momentum of a frog is lower than the speed of light. “But of course,” you’re going to say, “we’re comparing angular momentum to speed – they have different dimensions”. Well, the production cost of a film and mission costs also have different dimensions if you cared to look beyond the ‘$’ prefix. That’s because you can’t just pick up two dollar figures, decide which one’s lower and feel good about that without any social and economic context.

For example, what explains the choice of films to compare mission costs to? Is it because Gravity and Interstellar were both set in space? Is it because both films are fairly famous? Is it also because both films were released recently? Or is it because they offered convenient numbers? It’s probably the last one because there’s no reason otherwise to have picked these two films over, say, After Earth, Elysium, The Martian, Independence Day: Resurgence or Alien: Covenant – all of which were set in space AND cost less to make than Interstellar.

So I suspect it would be equally fair to say that the cost of C’yaan 2 is more than the budget of After Earth, Elysium, The Martian, Independence Day: Resurgence or Alien: Covenant. But few are going to spin it like this because of two reasons:

The cost of anything has to be a rational, positive number, so saying cost(Y) is less than cost(X) would imply that cost(X) > cost(Y) ≥ 0; however, saying cost(Y) is greater than cost(X) doesn’t give us any real sense of what cost(Y) could be because it could approach ∞ or…
Make cost (Y) feel like it’s gigantic, often because your reader assumes cost(Y) should be compared to cost(X) simply because you’ve done so

Now, what comparing C’yaan 2’s cost to that of making Interstellar achieves very well is a sense of the magnitude of the number involved. It’s an excellent associative mnemonic that will likely ensure you don’t forget how much C’yaan 2 cost – except you’d also have to know how much Interstellar cost. Without this bit of the statement, you have one equation and two variables, a.k.a. an unsolvable problem.

Additionally, journalists don’t use such comparisons in other beats. For example, when the Union budget was announced on February 1 this year, nobody was comparing anything to the production costs of assets that had a high cultural cachet. Rs 12.5 crore was Rs 12.5 crore; it was not framed as “India spends less on annual scholarships for students with disabilities than it cost to make Kabali“.

This suggests that such comparisons are reserved by some journalists for matters of space, which in turn raises the possibility that those journalists, and their bosses, organisations and readers, are prompted to think of costs in the space sector as something that must always be brought down. This is where this belief becomes pernicious: it assumes a life of its own. It shouldn’t. Lowering costs becomes a priority only after scientists and engineers have checked tens, possibly hundreds, of other boxes. Using only dollar figures to represent this effort mischaracterises it as simply being an exercise in cost reduction.

So, (risking repetition:) comparing a mission cost to a movie budget tells us absolutely nothing of meaning or value. Thanks to how Moneycontrol’s phrased it, all I know now is that C’yaan 2 is going to cost less than $165 million to make. Why not just say that and walk away? (While one could compare $165 million to mission costs at other space agencies, ISRO chief K. Sivan has advised against it; if one wants to compare it to other PSUs in India, I would advise against it.) The need to bring Interstellar into this, of course, is because we’ve got to show up the West.

And once we’re done showing up the West, we still have to keep. Showing up. The West. Because we’re obsessed with what white people do in first-world countries. If we didn’t have them to show up, who knows, we’d have framed ISRO news differently already because we’d have been able to see $165 million for what it is: a dimensionless number beyond the ‘$’ prefix. Without any other details about C’yaan 2 itself, it’s pretty fucking meaningless.

Please don’t celebrate frugality. It’s an unbecoming tag for any space programme. ISRO may have been successful in keeping costs down but, in the long run, the numbers will definitely go up. Frugality is a harmful aspiration vis-à-vis a sector banking on reliability and redundancy. And for fuck’s sake, never compare: the act of it creates just the wrong ideas about what space agencies are doing, what they’re supposed to be doing and how they’re doing it. For example, consider Sivan’s answer when asked by a Times of India reporter as to how ISRO kept its costs down:

Simplifying the system, miniaturising the complex big system, strict quality control and maximising output from a product, make the missions of Indian space agency cost-effective. We keep strict vigil on each and every stage of development of a spacecraft or a rocket and, therefore, we are able to avoid wastage of products, which helps us minimise the mission cost.

If I didn’t know Sivan was saying this, I’d have thought it was techno-managerial babble from Dilbert (maybe with the exception of QC). More importantly, Sivan doesn’t say here what ISRO is doing differently from other space agencies (such as, say, accessing cheaper labour), which is what would matter when you’re rearing to go “neener neener” at NASA/ESA, but sticks to talking about what everyone already does. Do you think NASA and ESA waste products? Do they not remain vigilant during each and every stage of development? Do they not have robust QC standards and enforcement regimes?

Notice here that Sivan isn’t saying “we’re doing it cheaper than others”, only that doing these things keeps the space agency “cost-effective”. Cost-effective is not the same as frugal.

Featured image: The Moon impact probe that went up on the PSLV C11 mission along with Chandrayaan 1. Credit: ISRO.

Why do we need dark matter?

The first thing that goes wrong whenever a new discovery is reported, an old one is invalidated, or some vaguely important scientific result is announced has often to do with misrepresentation in the mainstream media. Right now, we’re in the aftermath of one such event: the October 30 announcement of results from a very sensitive dark matter detector. The detector, called the Large Underground Xenon Experiment (LUX), is installed in the Black Hills of South Dakota and operated by the Sanford Underground Research Facility.

Often the case is that what gets scientists excited may not get the layman excited, too, unless the media wants it to. So also with the announcement of results from LUX:

The detector hasn’t found dark matter
It hasn’t found a particular particle that some scientists thought could be dark matter in a particular energy range
It hasn’t ruled out that some other particles could be dark matter.

Unfortunately, as Matt Strassler noted, the BBC gave its report on the announcement a very misleading headline. We’re nowhere near figuring out what dark matter is as much as we’re figuring out what dark matter isn’t. Both these aspects are important because once we know dark matter isn’t something, we can fix our theories and start looking for something else. As for what dark matter is… here goes.

What is dark matter?

Dark matter is a kind of matter that is thought to occupy a little more than 80 per cent of this universe.

Why is it called ‘dark matter’?

This kind of matter’s name has to do with a property that scientists believe it should have: it does not absorb or emit light, remaining (optically) dark to our search for it.

What is dark matter made of?

We don’t know. Scientists think it could be composed of strange particles. Some other scientists think it could be composed of known particles that are for some reason behaving differently. At the moment, the leading candidate is a particle called the WIMP (weakly interacting massive particle), just like particles called electrons are an indicator of there being an electric field or particles called Higgs bosons are an indicator of there being a Higgs field. A WIMP gets its name because it doesn’t interact with other matter particles except through the gravitational force.

We don’t know how heavy or light WIMPs are or even what each WIMP’s mass could be. So, using different detectors, scientists are combing through different mass-ranges. And by ‘combing’, what they’re doing is using extremely sensitive instruments hidden thousands of feet under rocky terrain (or obiting the planet in a satellite) in an environment so clean that even undesired particles cannot interact with the detector (to some extent). In this state, the detector remains on ‘full alert’ to note the faintest interactions its components have with certain particles in the atmosphere – such as WIMPs.

The LUX detector team, in its October 30 announcement, ruled out that WIMPs existed in the ~10 GeV/c² mass range (because of a silence of its components trying to pick up some particles in that range). This is important because results from some other detectors around the world suggested that a WIMP could be found in this range.

Can we trust LUX’s result?

Pretty much but not entirely – like the case with most measurements in particle physics experiments. Physicists announcing these results are only saying they aren’t likely to be any other entities masquerading as what they’re looking for. It’s a chance, and never really 100 per cent. But you’ve got to draw the line at some point. Even if there’s always going to be a 0.000…01 per cent chance of something happening, the quantity of observations and the quality of the detector should give you an idea about when to move on.

Where are the other detectors looking for dark matter?

Some are in orbit, some are underground. Check out FermiLAT, Alpha Magnetic Spectrometer,Payload for Antimatter Exploration and Light-nuclei Astrophysics, XENON100, CDMS, Large Hadron Collider, CoGeNT, etc.

So how was BBC wrong with its headline?

We’re not nearing the final phase of the search for dark matter. We’re only starting to consider the possibility that WIMPs might not be the dark matter particle candidates we should be looking for. Time to look at other candidates like axions. Of course, it wasn’t just BBC. CBS and Popular Science got it wrong, too, together with a sprinkling of other news websites.

Why do we need dark matter?

We haven’t been able to directly detect it, we think it has certain (unverified) properties to explain why it evades detection, we don’t know what it’s made of, and we don’t really know where to look if we think we know what it’s made of. Why then do we still cling to the idea of there being dark matter in the universe, that too in amounts overwhelming ‘normal’ matter by almost five times?

Answer: Because it’s the simplest explanation we can come up with to explain certain anomalous phenomena that existing theories of physics can’t.

Phenomenon #1

When the universe was created in a Big Bang, matter was released into it and sound waves propagated through it as ripples. The early universe was very, very hot, and electrons hadn’t yet condensed and become bound with the matter. They freely scattered radiation, whose intensity was also affected by the sound waves around it.

About 380,000 years after the Bang, the universe cooled and electrons became bound to matter. After this event, some radiation pervading throughout the universe was left behind like residue, observable to this day. When scientists used their knowledge of these events and their properties to work backwards to the time of the Bang, they found that the amount of matter that should’ve carried all that sound didn’t match up with what we could account for today.

They attributed the rest to what they called dark matter.

Phenomenon #2

Another way this mass deficiency manifests is in the observation of gravitational lensing. When light from a distant object passes near a massive object, such as a galaxy or a cluster of galaxies, their gravitational pull bends the light around them. When this bent beam reaches an observer on Earth, the image it carries will appear larger because it will have undergone angular magnification. If these clusters didn’t contain dark matter, physicists would observer much weaker lensing than they actually do.

Phenomenon #3

That’s not all. The stars in a galaxy rotate around the galactic centre, where most of its mass is located. According to theory, the velocity of the stars in a galaxy should drop off the farther they get from the centre. However, observations have revealed that, instead of dropping off, the velocity is actually almost constant even as one gets farther from the centre. So, something is also pulling the outermost stars inward, holding them together and keeping them from flying outward and away from the galaxy. This inward force astrophysicists think could be the gravitational force due to dark matter.

So… what next?

LUX was a very high sensitivity dark matter detector, the most sensitive in existence actually. However, its sensitivity is attuned to look for low-mass WIMPs, and its first results rule out anything in the 5-20 GeV/c² range. WIMPs of a higher mass are still a possibility, and, who knows, might be found at detectors that work with the CERN collider.

Moreover, agreement between various detectors about the mass of WIMPs has also been iffy. For example, detectors like CDMS and CoGeNT have hinted that a ~10 GeV/c² WIMP should exist. LUX has only now ruled this out; the XENON100 detector, on the other hand, has been around since 2008 and has been unable to find WIMPs in this mass-range altogether, and it’s more sensitive than CDMS or CoGeNT.

What’s next is some waiting and letting the LUX carry on with its surveys. In fact, the LUX has its peak sensitivity at 33 GeV/c². Maybe there’s something there. Another thing to keep in mind is that we’ve only just started looking for dark matter particles. Remember how long it took us to figure out ‘normal’ matter particles? Perhaps future higher sensitive detectors (like XENON1T and LUX-ZEPLIN) have something for us.

(This post first appeared at The Copernican on November 3, 2013.)

Which way does antimatter swing?

In our universe, matter is king: it makes up everything. Its constituents are incredibly tiny particles – smaller than even the protons and neutrons they constitute – and they work together with nature’s forces to make up… everything.

There was also another form of particle once, called antimatter. It is extinct today, but when the universe was born 13.82 billion years ago, there were equal amounts of both kinds.

Nobody really knows where all the antimatter disappeared to or how, but they are looking. Some others, however, are asking another question: did antimatter, while it lasted, fall downward or upward in response to gravity?

Joel Fajans, a professor at the University of California, Berkeley, is one of the physicists doing the asking. “It is the general consensus that the interaction of matter with antimatter is the same as gravitational interaction of matter,” he told this correspondent.

But he wants to be sure, because what he finds could revolutionize the world of physics. Over the years, studying particles and their antimatter counterparts has revealed most of what we know today about the universe. In the future, physicists will explore their minuscule world, called the quantum world, further to see if answers to some unsolved problems are found. If, somewhere, an anomaly is spotted, it could pave the way for new explanations to take over.

“Much of our basic understanding of the evolution of the early universe might change. Concepts like dark energy and dark matter might have be to revised,” Fajans said.

Along with his colleague Jonathan Wurtele, Fajans will work with the ALPHA experiment at CERN to run an elegant experiment that could directly reveal gravity’s effect on antimatter. ALPHA stands for Anti-hydrogen Laser Physics Apparatus.

We know gravity acts on a ball by watching it fall when dropped. On Earth, the ball will fall toward the source of the gravitational pull, a direction called ‘down’. Fajans and Wurtele will study if down is in the same place for antimatter as for matter.

An instrument at CERN called the anti-proton decelerator (AD) synthesizes the antimatter counterpart of protons for study in the lab at a low energy. Fajans and co. will then use the ALPHA experiment’s setup to guide them into the presence of anti-electrons derived from another source using carefully directed magnetic fields.

When an anti-proton and an anti-electron come close enough, their charges will trap each other to form an anti-hydrogen atom.

Because antimatter and matter annihilate each other in a flash of energy, they couldn’t be let near each other during the experiment. Instead, the team used strong magnetic fields to form a force-field around the antimatter, “bottling” it in space.

Once this was done, the experiment was ready to go. Like fingers holding a ball unclench, the magnetic fields were turned off – but not instantaneously. They were allowed to go from ‘on’ to ‘off’ over 30 milliseconds. In this period, the magnetic force wears off and lets gravitational force take its place.

And in this state, Fajans and his team studied which way the little things moved: up or down.

The results

The first set of results from the experiment have allowed no firm conclusions to be drawn. Why? Fajans answered, “Relatively speaking, gravity has little effect on the energetic anti-atoms. They are already moving so fast that they are barely affected by the gravitational forces.” According to Wurtele, about 411 out 434 anti-atoms in the trap were so energetic that the way they escaped from the trap couldn’t be attributed to gravity’s pull or push on them.

Among them, they observed roughly equal numbers of anti-atoms to falling out at the bottom of the trap as at the top (and sides, for that matter.)

They shared this data with their ALPHA colleagues and two people from the University of California, lecturer Andrew Charman and postdoc Andre Zhmoginov. They ran statistical tests to separate results due to gravity from results due to the magnetic field. Again, much statistical uncertainty remained.

The team has no reason to give up, though. For now, they know that gravity would have to be 100 times stronger than it is for them to see any of its effects on anti-hydrogen atoms. They have a lower limit.

Moreover, the ALPHA experiment is also undergoing upgrades to become ALPHA-2. With this avatar, Fajans’s team also hopes to incorporate laser-cooling, a method of further slowing the anti-atoms, so that the effects of gravity are enhanced. Michael Doser, however, is cautious.

The future

As a physicist working with antimatter at CERN, Doser says, “I would be surprised if laser cooling of antihydrogen atoms, something that hasn’t been attempted to date, would turn out to be straightforward.” The challenge lies in bringing the systematics down to the point at which one can trust that any observation would be due to gravity, rather than due to the magnetic trap or the detectors being used.

Fajans and co. also plan to turn off the magnets more slowly in the future to enhance the effects of gravity on the anti-atom trajectories. “We hope to be able to definitively answer the question of whether or not antimatter falls down or up with these improvements,” Fajans concluded.

Like its larger sibling, the Large Hadron Collider, the AD is also undergoing maintenance and repair in 2013, so until the next batch of anti-protons are available in mid-2014, Fajans and Wurtele will be running tests at their university, checking if their experiment can be improved in any way.

They will also be taking heart from there being two other experiments at CERN that can verify their results if they come up with something anomalous, two experiments working with antimatter and gravity. They are the Anti-matter Experiment: Gravity, Interferometry, Spectrocopy (AEGIS), for which Doser is the spokesperson, and the Gravitational Behaviour of Anti-hydrogen at Rest (GBAR).

Together, they carry the potential benefit of an independent cross-check between techniques and results. “This is less important in case no difference to the behaviour of normal matter is found,” Doser said, “but would be crucial in the contrary case. With three experiments chasing this up, the coming years look to be interesting!”

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This post, as written by me, originally appeared in The Copernican science blog at The Hindu on May 1, 2013.

A different kind of experiment at CERN

This article, as written by me, appeared in The Hindu on January 24, 2012.

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At the Large Hadron Collider (LHC) at CERN, near Geneva, Switzerland, experiments are conducted by many scientists who don’t quite know what they will see, but know how to conduct the experiments that will yield answers to their questions. They accelerate beams of particles called protons to smash into each other, and study the fallout.

There are some other scientists at CERN who know approximately what they will see in experiments, but don’t know how to do the experiment itself. These scientists work with beams of antiparticles. According to the Standard Model, the dominant theoretical framework in particle physics, every particle has a corresponding particle with the same mass and opposite charge, called an anti-particle.

In fact, at the little-known AEgIS experiment, physicists will attempt to produce an entire beam composed of not just anti-particles but anti-atoms by mid-2014.

AEgIS is one of six antimatter experiments at CERN that create antiparticles and anti-atoms in the lab and then study their properties using special techniques. The hope, as Dr. Jeffrey Hangst, the spokesperson for the ALPHA experiment, stated in an email, is “to find out the truth: Do matter and antimatter obey the same laws of physics?”

Spectroscopic and gravitational techniques will be used to make these measurements. They will improve upon, “precision measurements of antiprotons and anti-electrons” that “have been carried out in the past without seeing any difference between the particles and their antiparticles at very high sensitivity,” as Dr. Michael Doser, AEgIS spokesperson, told this Correspondent via email.

The ALPHA and ATRAP experiments will achieve this by trapping anti-atoms and studying them, while the ASACUSA and AEgIS will form an atomic beam of anti-atoms. All of them, anyway, will continue testing and upgrading through 2013.

Working principle

Precisely, AEgIS will attempt to measure the interaction between gravity and antimatter by shooting an anti-hydrogen beam horizontally through a vacuum tube and then measuring how it much sags due to the gravitational pull of the Earth to a precision of 1 per cent.

The experiment is not so simple because preparing anti-hydrogen atoms is difficult. As Dr. Doser explained, “The experiments concentrate on anti-hydrogen because that should be the most sensitive system, as it is not much affected by magnetic or electric fields, contrary to charged anti-particles.”

First, antiprotons are derived from the Antiproton Decelerator (AD), a particle storage ring which “manufactures” the antiparticles at a low energy. At another location, a nanoporous plate is bombarded with anti-electrons, resulting in a highly unstable mixture of both electrons and anti-electrons called positronium (Ps).

The Ps is then excited to a specific energy state by exposure to a 205-nanometre laser and then an even higher energy state called a Rydberg level using a 1,670-nanometre laser. Last, the excited Ps traverses a special chamber called a recombination trap, when it mixes with antiprotons that are controlled by precisely tuned magnetic fields. With some probability, an antiproton will “trap” an anti-electron to form an anti-hydrogen atom.

Applications

Before a beam of such anti-hydrogen atoms is generated, however, there are problems to be solved. They involve large electric and magnetic fields to control the speed of and collimate the beams, respectively, and powerful cryogenic systems and ultra-cold vacuums. Thus, Dr. Doser and his colleagues will spend many months making careful changes to the apparatus to ensure these requirements work in tandem by 2014.

While antiparticles were first discovered in 1959, “until recently, it was impossible to measure anything about anti-hydrogen,” Dr. Hangst wrote. Thus, the ALPHA and AEgIS experiments at CERN provide a seminal setting for exploring the world of antimatter.

Anti-particles have been used effectively in many diagnostic devices such as PET scanners. Consequently, improvements in our understanding of them feed immediately into medicine. To name an application: Antiprotons hold out the potential of treating tumors more effectively.

In fact, the feasibility of this application is being investigated by the ACE experiment at CERN.

In the words of Dr. Doser: “Without the motivation of attempting this experiment, the experts in the corresponding fields would most likely never have collaborated and might well never have been pushed to solve the related interdisciplinary problems.”