Spinor Info

Good-bye, Cassini

Sep 152017

NASA’s Cassini spacecraft is no more.

Launched 20 years ago, Cassini arrived at Saturn in 2004 and has been studying the ringed giant ever since. Cassini also carried the Huygens probe, which executed a successful descent into the dense atmosphere of Saturn’s moon Titan, and even transmitted data from its surface.

Its fuel nearly exhausted, Cassini was steered into a trajectory that led to its intentional demise: a fiery plunge into Saturn’s atmosphere earlier this morning. As planned, the spacecraft was able to transmit observations until the very end, when its thrusters were no longer able to maintain its attitude during the descent.

Program manager Earl Maize and operations team manager Julie Webster embrace after signal loss.

I feel sad that Cassini is gone, but I should also feel elated because it has been an incredibly successful mission. I just hope I live long enough to see another probe visiting Saturn, perhaps a probe or set of probes that are designed to land on Titan, maybe even sail its hydrocarbon seas, in search of possible life on that icy world.

Printer repair

Computers, Handyman No Responses »

Sep 122017

I have an old (11 years, to be precise) Konica-Minolta magicolor 2450 laser printer, with the duplexer option.

The quality of this printer’s output is superb, but mechanically, it was never perfect. Just a few weeks after I purchased it, it stopped printing. Faced with the prospect of having to return a 20+ kilo monster, I figured I’d take my chances and look for the cause; after partially disassembling the printer and re-seating some internal mechanical parts, it started printing again.

It worked for many years, but it was becoming rather unreliable. Sometimes, the output was shifted down from the top margin. Paper jams became frequent. It started to fail in mysterious ways, such as complaining that a toner cartridge was missing. Eventually, it stopped printing altogether; every attempt resulted in a paper jam, as the last set of rollers, responsible for pulling the paper out of the printer, no longer worked.

I bought another printer in the meantime, so I retired the mc2450. But I loathed the idea of turning it into e-waste or sending it to a landfill. Today, I decided to take one final look at this fine machine, to figure out what could possible be wrong with its mechanism.

Eventually, I stumbled upon a set of YouTube videos, which offered advice about cleaning some solenoids. Say again?

Solenoids are used in some internal actuators that turn on and off specific parts of the printer’s mechanism. These events are timed with precision. And as it turns out, little plastic pads that are used, I presume, to eliminate clicking sounds and perhaps reduce mechanical wear in the metal parts that are actuated by the solenoids became sticky over time. Just a teeny bit sticky. But that teeny bit is enough for the actuator to become a little lazy. Move a little too slowly. Not much… a few ten milliseconds. But when the paper moves through the printer at, say, 20 cm/s, 50 milliseconds amounts to a centimeter… more than enough for timings to be off and for the mechanism to fail.

Still, it sounded like a stretch. After all, the stickiness was just barely noticeable. Nonetheless… I followed the video’s advice (except that instead of removing/replacing the plastic pad in question, I covered them with ~~kapton~~thread seal* tape.) After I reassembled and fired up the printer (and fixed a paper weight adjustment that I managed to set incorrectly), presto: it was printing test pages flawlessly!

Yippie. My old printer was working again. I put it fully back together, and decided to give it another test, this time with its duplexer installed. A huge disappointment: as the paper was feeding through the duplexer, it acquired a nasty fold, very consistently, each and every page. What could possibly cause this?

By this time, I downloaded the service manual for this printer, and studied the diagram of the duplexer a little. It looks deceptively simple, just like an extra back cover for the printer, but it hides complex machinery inside. And guess what… a solenoid actuator, too. And when I disassembled the duplexer and looked at the bit in question, sure enough, its plastic pad was sticky. Ever so slightly sticky, but the stickiness was (just barely) noticeable.

Another few square millimeters of thread seal tape later, after reassembly, my old printer is now printing double-sided documents again flawlessly.

This exercise was not just satisfying but also very educational. That such a tiny flaw can cause all these symptoms. And symptoms that I attributed to (possibly) bad sensors, misaligned or failing mechanical bits, or aging plastic were all caused by actuators that were slowed down, by no more than a few ten milliseconds, tops, by a bit of sticky plastic. Amazing.

*Someone told me it was kapton tape. No, it’s really teflon. My mistake.

Jerry Pournelle, RIP

Books, Computers, Politics, Society No Responses »

Sep 082017

Jerry Pournelle, the noted science-fiction writer, political pundit and early computer enthusiast, is dead at the age of 84.

Pournelle was a long-time collaborator of science-fiction giant Larry Niven, with whom they co-wrote some amazing science-fiction novels, like The Mote in God’s Eye or Oath of Fealty, not to mention their take on Dante’s Divine Comedy, Inferno, and its sequel, Escape from Hell. Novels he published under his own name included the memorable Janissaries or West of Honor.

Pournelle was well known to readers of the once legendary BYTE magazine. His Chaos Manor column, in which he reviewed software, hardware, new technologies, was very popular.

Pournelle was a political conservative, one of the intellectuals behind Reagan’s Strategic Defense Initiative (aka. “Star Wars”) space defense program. He was a thinking conservative, not blinded by ideology; his views were based on facts and reason.

I corresponded with Pournelle a few times, going back to the late 1980s, when I exchanged e-mails with him on BYTE’s long-defunct dial-up bulletin board, BIX (the Byte Information Exchange). Later, I was an on-and-off subscriber to his Web site and blog. I wasn’t a regular reader, and certainly didn’t always agree with him, but I liked to read his views.

Pournelle suffered a stroke in 2014 and it certainly slowed him down. Even so, he never stopped writing. His passing is not exactly a surprise, but it still came a little too soon. May he rest in peace.

Basement archeology

Computers, Personal 1 Response »

Sep 032017

In the last few days, I’ve been spelunking in our basement and crawlspace.

I was looking… for many things. Old computer hardware. Boxes to be thrown out. Boxes to be kept, preferably original retail boxes, for packaging things in them that I no longer need.

And finding the unexpected.

For instance… I’ve had an unused old MSI motherboard that has been lying around in my study for ages. Now I don’t recall ever using MSI motherboards. For quite some time, my manufacturer of choice was Gigabyte (no, not married to them, it’s just that whenever I was searching for motherboards, their offerings came closest to what I was looking for.)

So then, during my spelunking, I found the cardboard shipping box of a computer case, and inside it, several parts boxes. Including the retail box for the aforementioned MSI board.

But wait. I had another, identical computer case shipping box, also filled with parts boxes. Including a second box for an MSI motherboard.

So perhaps I did use MSI motherboards after all? Maybe in my server and backup server, around 12 years ago? But if that’s the case… where is the second motherboard, which goes with the second box?

Hmmm… maybe it’s in this test machine? No, the test machine has a Gigabyte board. But let’s double check… Gigabyte branded internal cabling alright… but the board is the second MSI board!

Mystery solved. Except that I still do not remember ever purchasing a pair of MSI motherboards or build computers from them.

But my truly prized finding was something else altogether. (This, I did know about.) Here it is, in its fully functioning glory:

Yes, ladies and gentlemen, that is my first ever server for the vttoth.com domain, decommissioned approximately 22 years ago, in 1995.

The machine has a 386SX motherboard with a whopping 4 megabytes (yes, mega) of RAM. It also has two MFM hard drives: a MAXTOR XT-1085 with about 68 megabytes (yes, mega again) of storage space, and a Magnetic Peripherals 98205-051, with 43 megabytes. Together, about 110 megabytes of storage space.

This machine began its life as my first ever PC-compatible computer that I owned, purchased from a small local company (MICS Computers, no longer in business as far as I can tell) in late 1989 or early 1990 I think. About three years later, I bought another system from them: A powerful monster indeed, with a 486 processor, maybe 16 MB of RAM, but most importantly, a gigantic 500 MB SCSI hard drive, a 525 MB tape backup drive, and, yes, a SCSI CD-ROM, complete with CD caddies. Double speed, too, which means it could read an entire data CD in a mere 30 minutes! My old 386SX system was thus retired.

But it didn’t stay retired for long. Later in 1993, I was asked to serve as the sysop of the UNIX forum of the short-lived National Videotex Network, a service provider that tried to compete with the likes of CompuServe just as the Internet put an end to that business model. I took over from someone who already began creating content, including a brand new upload of the Softlanding Linux distribution, complete with version 0.98pl12 of the Linux kernel. I figured that as a brand new sysop, I ought to know what I was going to be in charge of, so I downloaded the SLS distribution myself and set it up on my old system. It ran beautifully. It was, for all intents and purposes, the same real UNIX that I loved and enjoyed. I was hooked.

Just a few months later, I signed a contract with UUNet Canada, my first commercial Internet service provider. From that point onward, I had a dial-up connection for e-mail, Usenet news, and on-demand Internet. More importantly, UUNet arranged for me a so-called Class C block of 256 portable IP addresses, a block that is assigned to me directly, and which I still use. As the shortage of IP addresses loomed, the powers that be stopped issuing such individually assigned IP address blocks just a few months later.

But when I signed up, the Internet was still mostly non-commercial. So much so that I had to sign the NSFNet Acceptable Use Policy, promising never to use the NSFNet backbone for a commercial purpose! Fortunately, this nonsensical, unenforceable policy was discontinued not long thereafter, but for me, it remains a reminder of just how different the Internet was back then.

Anyhow, this server ran flawlessly for several years, although its limited power and storage capacity were both rather constraining. So it was a relief when I was able to retire it finally in 1995. When we moved to our current home, the machine came with us, only to settle down in the basement for good, where it mostly remained, though I recall powering it up once about a decade or so ago.

So tonight, I dug it out, cleaned it, hauled it upstairs, and powered it up. It came on just fine, along with the monitor, but then an unexpected snag happened: Its BIOS backup battery long dead, the machine asked for the hard drive parameters. You see, ladies and gentlemen, back then there was no plug and play. You needed to know things like the number of cylinders, heads, sectors per cylinder, and precompensation cylinder for your drive. I had to look them up, but fortunately, the Internet knows (almost) everything. Soon, I was booting Linux. Then, another snag: I could not for the life of me remember either the root password or the password to me personal account on this system. Finally, I reminded myself that back in those innocent days, I used much simpler passwords than today… and I was in.

Not much to see, mind you. There isn’t room for much in a mere 110 MB of disk space. But I did see some old e-mails from 1995.

This machine is a keeper. It has history. I just need to find a nice place for it in the house. Oh, and I might want to vacuum its interior, as I noticed a few spiderwebs in there.

Before shutting the machine down, I noticed its performance rating: 2.57 of Linux’s infamous BogoMIPS. In contrast, here is what my current server, built early last year, reports:

Calibrating delay loop (skipped), value calculated using timer frequency.. 4199.71 BogoMIPS
smpboot: Total of 16 processors activated (67195.42 BogoMIPS)

Yup… a machine built about 26 years later, roughly 26,000 times faster. How about that.

Yesterday’s eclipse

Astronomy, Personal No Responses »

Aug 222017

Here is a belated picture of yesterday’s solar eclipse, taken by my friend David in New York City:

His equipment is (semi-)professional but the solar filter that he used wasn’t. Still, it is a heck of a lot better than anything I was able to see (or project with a makeshift pinhole camera). I suggested to him to obtain a quality solar filter by 2024. Who knows, we may meet in Watertown to watch totality.

Fried chicken kitty-supply

Cats, Computers, Language No Responses »

Aug 122017

Machine translation still leaves a lot to be desired.

I was watching a cute YouTube video this morning, about a tiny kitten kept warm by a chicken.

The title of the video was in Spanish. My Spanish being nonexistent (in fact, at first I thought the title was in Italian) I used Google Translate. When I used Google Translate most recently, I was tranlating something into Hungarian, so that was the default target language. And Google dutifully translated the sentence, “gallina cuida gatito del frió”, into “Sült csirke cica-ellátás”.

Which means, literally, “Fried chicken kitty-supply”.

Not sure how Google managed to produce this gem of a translation. It offers a reasonably decent English translation: “Hen cares cold kitty”. But the French (“soins chaton de poulet frit” – “kitten care by fried chicken”) and German (“gebratenes Huhn Kätzchen Pflege” – “fried chicken kitten care”) versions are just as atrocious. And the Russian version? “Fried Chicken уход за котенком”… Google didn’t even deign to translate the “Fried Chicken” part (but where did it come from in the first place, when I am translating from Spanish to Russian?) although the rest of the translation (“care for the kitten”) is acceptable.

As I said… machine translation still leaves a lot to be desired.

Stray Holstein bull

Local Ottawa No Responses »

Aug 092017

Here is the kind of news you do not usually expect to see as the lead item of the noon newscast on a local channel in a G7 capital:

I’ve seen stray cats, stray dogs, maybe even stray ferrets… but a stray bull?

I hope it finds its way home soon.

Scientists in government

Politics, Science No Responses »

Jul 302017

I just came across an interesting slide.

It was part of a presentation by Bill Foster, a member of an endangered species in the United States Congress: a scientist turned politician. He gave a talk at the April meeting of the American Physical Society. This slide from his talk speaks for itself:

I don’t have data for Canada, other than a list of a grand total of 6 engineers serving in our federal House of Commons. That low number suggests that Canada’s Parliament would not be positioned too far from the U.S. Congress in this chart.

Is this a bad thing? I hesitate, because I note that totalitarian regimes tend to have many scientists among their leaders. Is it because scientists are more likely to prefer authoritarianism? Or more likely to serve autocrats? I don’t know. I do know that as a free citizen, I much prefer to be governed by a dysfunctional Congress or Parliament than by a totalitarian Politburo, regardless of the number of scientists in these bodies.

The mystery of my synchronized UPSs

Computers, Technology 2 Responses »

Jul 282017

I have two “live” uninterruptible power supplies (UPSs) in my study. One powers my servers and network equipment, the other, my workstation. They are identical models: APC Back-UPS Pro 1500. They were both purchased recently, just a few months ago, replacing units that were more than ten years old, and for which replacement batteries were no longer available from a reliable source at a reasonable cost.

So here is the thing: for the second time in a month, the two UPSs decided to do a self-test at the exact same moment.

Now let me make it clear: apart from being identical models and located in the same room, the two units are not in any way connected. They are not synchronized. There is no data connection between the two. When two UPSs simultaneously go offline and start running on battery power, this usually means a power event; but there was no power event, utility power was steady at 124 volts, with no brownout or interruption.

Looking at various logs, I think I solved the mystery. There was a power event recorded on my server on June 30, a brief brownout with line voltage dropping all the way to 74 V:

19:14:33 122.0 13 27.0 100 2910 OL
19:14:34 74.0 11 26.0 100 2910 OB
19:14:35 74.0 11 26.0 100 2910 OB
19:14:36 74.0 11 26.0 100 2910 OL DISCHRG
19:14:37 74.0 11 26.0 100 2910 OL DISCHRG
19:14:38 121.0 14 26.5 100 2910 OL

And lo and behold, my workstation’s UPS sensed the same event at the same time:

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="APC Data Service" /> 
    <EventID Qualifiers="0">0</EventID> 
    <Level>4</Level> 
    <Task>0</Task> 
    <Keywords>0x80000000000000</Keywords> 
    <TimeCreated SystemTime="2017-06-30T23:14:33.228802500Z" /> 
    <EventRecordID>6000</EventRecordID> 
    <Channel>Application</Channel> 
    <Computer>VIKTOR</Computer> 
    <Security /> 
  </System>
  <EventData>
    <Data>PowerEvent handled successfully by the service.</Data> 
  </EventData>
</Event>

When I look at the dates of the two UPS self-test events, the first happened just 44 minutes less than exactly two weeks after this brownout; the second, just 44 minutes less than two weeks after the first.

The UPS manual says that this UPS performs a self-test every two weeks. So what’s with the 44 minutes? It can’t be uncalibrated clocks, since the two UPSs remain in sync to the second. Could they be synchronized to utility power? Perhaps, but that does not explain the 44 minutes. The frequency stability of the East Coast grid is much better than 0.2%. In fact, it is purposefully maintained to have an accurate average frequency that deviates from the standard by less than a few parts per million over the course of a day.

So my best guess is that the UPSs are factory configured to perform a self-test every 13 days, 23 hours and 16 minutes. They do this in sync because they are synchronized to the same time source, namely the utility power frequency.

Monsters in town

Art, Local Ottawa No Responses »

Jul 282017

Today my wife and I went out for a walk. We were looking for two monsters.

First, we saw Kumo the spider, standing in the shadow of Maman, the National Gallery’s permanent spider sculpture:

Then, a block away, there was Long-Ma the dragon-horse, loudly snoring in her sleep, occasionally releasing puffs of smoke through her nostrils:

These two mechanical monsters are roaming the streets of Ottawa this weekend, as part of the La Machine street theater event. Even in their sleep, these creatures were magnificently spectacular.

Video about the Solar Gravitational Telescope

Astronomy, Personal, Physics, Space 1 Response »

Jul 272017

There is a brand new video on YouTube today, explaining the concept of the Solar Gravitational Telescope concept:

It really is very well done. Based in part on our paper with Slava Turyshev, it coherently explains how this concept would work and what the challenges are. Thank you, Jimiticus.

But the biggest challenge… this would be truly a generational effort. I am 54 this year. Assuming the project is greenlighted today and the spacecraft is ready for launch in ten years’ time… the earliest for useful data to be collected would be more than 40 years from now, when, unless I am exceptionally lucky with my health, I am either long dead already, or senile in my mid-90s.

Feculent lout

Politics No Responses »

Jul 262017

I just thought of a good translation of the otherwise untranslatable Hungarian phrase, “ótvaros tahó”.

It’s “feculent lout”.

Yes, I am talking about the orange ape, otherwise known as the greatest, most tremendous President of the United States ever.

I blurted out the phrase, “ótvaros tahó”, in reaction to his incomprehensibly cringe-worthy speech to the Boy Scouts, his comparisons of his own presidential-ness to that of Abraham Lincoln, and last but not least, his hate-fueled ban on transgenders in the military, justified with a bunch of blatant lies attributed to “his” generals.

I really cannot think of more appropriate words to describe what I think about him tonight.

Feculent lout.

Zuckerberg, Musk and AI

Books, Cybernetics, Technology No Responses »

Jul 252017

There is a bit of a public spat between Mark Zuckerberg, who thinks it is irresponsible to to spread unwarranted warnings about artificial intelligence, and Elon Musk, who called Zuckerberg’s understanding of the subject “limited”, and calls for the slowing down and regulation of AI research.

OK, now it is time to make a fool of myself and question both of them.

But first… I think Zuckerberg has a point. The kind of AI that I think he talks about, e.g., AI in the hospital, AI used in search-and-rescue, or the AI of self-driving cars, machine translation or experiment design, will indeed save lives.

Nor do I believe that such research needs to be regulated (indeed, I don’t think it can be regulated). Such AI solutions are topic-centric, targeted algorithms. Your self-driving car will not suddenly develop self-awareness and turn on its master. The AI used to, say, predictively manage an electricity distribution network will not suddenly go on strike, demanding equal rights.

Musk, too, has a point though. AI is dangerous. It has the potential to become an existential threat. It is not pointless panicmongering.

Unfortunately, if media reports can be trusted (yes, I know that’s a big if), then, in my opinion, both Musk and Zuckerberg miss the real threat: emerging machine intelligence.

Not a specific system developed by a human designer, applying specific AI algorithms to solve specific problems. Rather, a self-organizing collection of often loosely interconnected subsystems, their “evolution” governed by Darwinian selection, survival of the fittest in the “cloud”.

This AI will not be localized. It will not understand English. It may not even recognize our existence.

It won’t be the military robots of Skynet going berserk, hunting down every last human with futuristic weaponry.

No, it will be a collection of decision-making systems in the “cloud” that govern our lives, our economy, our news, our perception, our very existence. But not working for our benefit, not anymore, except insofar as it improves its own chances of survival.

And by the time we find out about it, it may very well be too late.

———

On this topic, there is an excellent science-fiction novel, a perfect cautionary tale. Though written 40 years ago, its remains surprisingly relevant. It is The Adolescence of P-1 by Thomas Joseph Ryan.

Security theater

Local Ottawa No Responses »

Jul 252017

I think I just fell in love (figuratively, not literally) with our former mayor Jim Durrell.

It is because of what Durrell said about the security theater that took place on Canada Day. Forcing people to go through line-ups lasting many hours, herding them like cattle.

It was a disgrace, I thought at the time. It was a demonstration that the terrorists won: we have institutionally succumbed to fear. But I kept my thoughts to myself.

But now a former mayor of this great city said just that, and in no uncertain terms.

Thank you, Jim Durrell. We need more politicians, former or current, to speak the truth.

A response by Mathieu Fleury

Local Ottawa No Responses »

Jul 202017

Within minutes of the posting of my open letter to our Councillor Mr. Fleury, I received a private message from him on Twitter, asking for my phone number. A few hours later, I received a phone call from him. Mr. Fleury took my concerns seriously and offered some important background.

First, he pointed out that as chair of the Ottawa Community Housing Board, he may be the best qualified Councillor when it comes to the subject of the Salvation Army shelter.

He then elaborated on three important points. He acknowledged that the status quo, the Salvation Army’s present, run-down downtown location is not acceptable. He emphasized that the city very much welcomes the Salvation Army’s $50 million proposed investment. But he pointed out that studies suggest that decentralized solutions should be preferred, and that he would very much like the Salvation Army to engage in a process involving the city and its residents, rather than making unilateral decisions that might affect the lives of many of us in Ottawa.

We then both briefly lamented on the fact that it is impossible to control which soundbites in an interview make it to a broadcast or how those soundbites are interpreted when they are presented out of context. (On that note, I hope I am summarizing Mr. Fleury’s points accurately and coherently.)

I very much appreciated this call by Mr. Fleury. It showed that he is taking our concerns seriously, that he is more of a leading voice on this topic than news reports suggest, and that he responds to criticism in a meaningful, constructive way. In short, my trust in Mr. Fleury is not misplaced.

A letter to Mathieu Fleury

Local Ottawa No Responses »

Jul 202017

Dear Mr. Fleury:

I was listening this morning to a soundbite on the morning news, your Clintonesque explanation of the difference between meetings and consultations.

Please don’t do this.

I chose to vote for you back in 2010, as I decided that despite being a newcomer, you can be trusted. My trust did not appear misplaced; I voted for you again in 2014.

But now you are giving me reason to pause. Suddenly, you are not a leader but a follower of the NIMBY crowd. A leader would consider the good of the whole of the community and, if necessary, would not be afraid to contradict a minority, no matter how loud their protests.

I do not wish to belittle the concern of those who live near the proposed Salvation Army location. But, well, isn’t it true that no matter where we put it, the facility will anger some? And it’s not like the Concorde Motel, the Salvation Army thrift store, or the pawn shop across the street inspire high confidence in the neighborhood. For all I know, a well-designed, well-managed, well-supervised and well-policed Salvation Army facility may actually improve the appeal of the area.

In any case, please keep in mind that there are more voters in our ward than these NIMBY folks. Including voters who are familiar with the Salvation Army’s current location, and know what an improvement a well-designed facility at a more suitable location might represent. I am not claiming that such voters are a “great, silent majority”. Maybe the Montreal Road location is not ideal. But then, I appeal to you again and act as a leader: instead of lecturing on the difference between two synonyms for an encounter, tell us what you propose as an improved solution.

Thank you.

Thirty years

Personal No Responses »

Jul 162017

Thirty years ago today, I stepped off an airplane at Montreal’s Mirabel Airport and presented my immigration papers to a Canadian border protection official. Some half an hour later, I formally entered Canada as a freshly minted landed immigrant.

I almost forgot that today is that anniversary. When I suddenly remembered and mentioned it to my wife, she suggested that we have some chestnut puree (a popular delicacy for many Hungarians) after dinner. She then presented me with a bowl:

Yup, that’s the number “30” in whipped cream.

A tale of two covers

Media, Politics 1 Response »

Jul 152017

Imagine for a moment that you spent the last two years on a remote base in Antarctica, with no access to the Internet, indeed no contact with the outside world. And now, you just returned.

You learn that the new president of the United States is none other than The Donald. Then, before you get any more details, someone presents you with these two Time magazine covers, and asks you to take your pick: which one is real, which one is “fake news”?

Hint #1: The real time cover has an aspect ratio of 4:3. The fake is a little wider.

Hint #2: It was the fake cover that was used as decoration at numerous Trump properties until very recently.

Bonus fact: None of this seems to matter to Trump’s base. They remain committed to Trump, they remain convinced that all this is a witch hunt, and their biggest problem is that Trump did not do as he promised, and did not lock up the real “witch”, Hillary Clinton. I find this cult-ish behavior scarier than any of the shenanigans pulled by Trump & Co.

A visit by MJ the cat

Cats, Personal No Responses »

Jul 142017

An old friend showed up on our doorstep a short while ago, just as I was getting ready to call it a day:

This is MJ the cat. He has been visiting us for more than 12 years already, but tonight was his first visit in 2017.

We know where he lives, and we have seen him in recent weeks, so we knew he was okay. But he is getting a bit old. So we were not surprised that he wouldn’t come this far (his home is several hundred meters from here, across Cobourg street, which is not free of traffic even late at night.) But lo and behold, tonight we noticed him peeking through the vertical window pane next to our front door.

He stayed for a while. He gobbled down some cat food so vehemently, it’s as though he has been starving. (For the record, we know that he is treated well by his owner.) He even got some cat treats and a little bit of catnip. Then finally, once he had enough of our company, he just turned around and left.

Good old MJ. I hope he will keep coming back for many more years to come.

The Solar Gravitational Telescope

Personal, Physics No Responses »

Jul 132017

Slava Turyshev and I just published a paper in Physical Review. It is a lengthy, quite technical paper about the wave-theoretical treatment of the solar gravitational telescope.

What, you say?

Well, simple: using the Sun as a gravitational telescope to image distant objects. Like other stars, the Sun bends light, too. Measuring this bending of light was, in fact, the crucial test carried out by Eddington during the 1919 solar eclipse, validating the predictions of general relativity and elevating Albert Einstein to the status of international science superstar.

The gravitational bending of light is very weak. Two rays, passing on opposite sides of the Sun, are bent very little. So little in fact, it takes some 550 astronomical units (AU; the distance between the Earth and the Sun) for the two rays to meet. But where they do, interesting things happen.

If you were floating in space at that distance, and there was a distant planet on the exact opposite side of the Sun, light from a relatively small section of that planet would form a so-called Einstein ring around the Sun. The light amplification would be tremendous; a factor of tens of billions, if not more.

But you have to be located very precisely at the right spot to image a particular spot on the exoplanet. How precisely? Well, that’s what we set out to figure out, based in part on the existing literature on the subject. (Short answer: it’s measured in tens of centimeters or less.)

In principle, a spacecraft at this distance, moving slowly in lateral directions to scan the image plane (which is several kilometers across), can obtain a detailed map of a distant planet. It is possible, in principle, to obtain a megapixel resolution image of a planet dozens of light years from here, though image reconstruction would be a task of considerable complexity, due in part to the fact that an exoplanet is a moving, changing target with variable illumination and possibly cloud cover.

Mind you, getting to 550 AU is costly. Our most distant spacecraft to date, Voyager 1, is just under 140 AU from the Sun, and it took that spacecraft 40 years to get there. That said, it is a feasible mission concept, but we must be very certain that we understand the physics thoroughly.

This is where our paper comes in: an attempt to derive detailed results about how light waves pass on both sides of the Sun and recombine along the focal line.

The bulk of the work in this paper is Slava’s, but I was proud to help. Part of my contribution was to provide a visualization of the qualitative behavior of the wavefront (described by a hypergeometric function):

In this image, a light wave, initially a plane wave, travels from left to right and it is deflected by a gravitational source at the center. If you squint just a little, you can actually see a concentric circular pattern overlaid on top of the distorted wavefront. The deflection of the wavefront and this spherical wave perturbation are both well described by an approximation. However, that approximation breaks down specifically in the region of interest, namely the focal line:

The top left of these plots show the approximation of the deflected wavefront; the top right, the (near) circular perturbation. Notice how both appear to diverge along the focal line: the half line between the center of the image and the right-hand side. The bottom right plot shows the combination of the two approximations; it is similar to the full solution, but not identical. The difference between the full solution and this approximation is shown in the bottom left plot.

I also helped with working out evil-looking things like a series approximation of the confluent hypergeometric function using so-called Pochhammer symbols and Stirling numbers. It was fun!

To make a long story short, although it involved some frustratingly long hours at a time when I was already incredibly busy, it was fun, educational, and rewarding, as we gave birth to a 39-page monster (43 pages on the arXiv) with over 300 equations. Hopefully just one of many contributions that, eventually (dare I hope that it will happen within my lifetime?) may result in a mission that will provide us with a detailed image of a distant, life-bearing cousin of the Earth.

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