Thu 14 Mar 2024 22:35
How many digits of Pi could you possibly need?
While nobody can deny that reciting from memory 70,030 digits of Pi is a remarkable feat, how many digits of Pi might someone possibly need for a calculation? How might one think about this question?
One approach is to consider how Pi is typically used. It's used for computing things like the circumference or area of a circle, or the volume of a sphere. A reasonable way of asking ourselves how many digits of Pi could be useful is to imagine that we were computing the volume of a very large sphere using the very smallest possible units. Then imagine that we were computing that volume to very high precision. What would be the highest precision we might want? Well, if we're using the largest possible sphere and measuring volume in the smallest possible units, it doesn't make sense to consider more digits of Pi than what you would need to compute that sphere's volume to such high precision that the error would be less than one unit of volume.
So what might be the largest sphere we might compute the volume of? And what might be the smallest units that we could use for this calculation? Well, the observable universe is a very large sphere, about 93 billion light years in diameter. Thanks to quantum physics, we know the smallest useful unit of distance is the Planck Length, making the smallest unit of volume the Planck length cubed. The Planck length is a very small number, 1.616255×10−35 m; cubing it gives 4.848765×10−105 m3.
As I was feeling a bit lazy, I asked ChatGPT to do the calculation for me. It claims that the volume of the universe, is about 8.45×10−184 Planck lengths cubed. That suggests that one can't conceivably need more than 185 digits of Pi for any expected calculation in physics. If any physicists are reading this and can think of a viable need for more digits of Pi than that, I'd be interested to hear about it.
That, of course, doesn't mean that knowing thousands of digits of Pi is somehow less of an impressive, if abstract, feat of pure memorization. Just don't expect any physicists attending a recitation to stay tuned beyond digit 185. Happy Pi day!
Tue 31 Oct 2023 09:11
Computing the Climate
I'm very glad I did. I am a computer scientist myself, whose career has been dedicated to building and running sometimes complex computer systems to support computer science teaching and research. I recognize in climate modelling a similar task at a much greater scale, working under a much more demanding "task-master": those systems need to be constantly measured against real data from our planet's diverse and highly complex geophysical processes, processes that drive its weather and climate. The amount of computing talent devoted to climate modelling is considerable, much more than I realized, and the work done so far is nothing short of remarkable. In his book, Steve outlines the history of climate modelling from very early work done on paper, to the use of the first electronic computers for weather prediction, to the highly complex and extremely compute-intensive climate models of today. Skillfully avoiding the pitfalls of not enough detail and too much, Steve effectively paints a picture of a very difficult scientific and software engineering task, and the programmers and scientists who rise to the challenge, building models that can simulate the earth's climate so accurately that viable scientific conclusions can be drawn from them with a high degree of confidence.
As a story of scientific discovery and software engineering, this tale of the building of systems that can model the earth's climate would be enough on its own to make a compelling book, and it is, but of course there is more to the story. The stakes around climate are very high today. Carbon dioxide concentrations has been increasing steadily in the earth's atmosphere for well over a century. Carbon dioxide, a pollutant that is produced by the burning of fossil fuels, is easily emitted, but once in the atmosphere, it is very difficult to remove, remaining there for centuries. As a pollutant, it raises the temperature of the planet by causing the earth's atmosphere to retain more of the sun's heat. The rising temperature is changing the climate of the planet in ways that will be soon harmful to millions, and difficult to address. Because the world's climate is changing quickly, we can't "wait and see what happens" because the evidence is ever increasing that what will happen is not going to be something we want: human suffering will be great, and parts of the world will become much less habitable. Our society needs to do something about the changing climate to ward off as much as possible the coming difficulties, but what?
Reassuringly, Steve shows in his book that we have enough information in hand to know what needs to be done. His book outlines clearly the high quality scientific and computational work behind the climate models of today, which produce results that match observed data quite closely. These all paint the same picture: through decisive societal action to reduce carbon dioxide pollution in the atmosphere, and through the active development of suitable carbon capture technologies, our planet can avoid the most seriously damaging implications of climate change. The sooner we act, the less damaging the changes, and the lower the risk of extreme consequences. Yes, it requires doing things differently as a society, which is more difficult than maintaining the status quo. But as Steve's book shows, the reasons for action are sound: the computer models are excellent, the software engineering behind them is superb, and the data supports the conclusions. Failure and catastrophe are not inevitable. Steve's book shows the remarkable work that has already been done to understand the climate. It is true that much more good work will be needed, to act on this understanding. But something can be done. Let us not delay in working together to do what we need to do.
Sun 12 Sep 2021 18:05
Why it is a good idea to get the Covid19 vaccine?
While I understand becoming short of patience with vaccine refusal, I don't think that most people who refuse COVID19 vaccination are idiots. Vaccination and viruses can be complicated to understand. There are a lot of misinformed posts and videos on the Internet. If you don't know enough about how viruses and vaccines work, both in general and for COVID19, how would you know what to believe? When my father died of COVID19 last summer, one of the ways I dealt with the loss was through understanding better how COVID19 works and what can be done to fight it. My hope here is that by explaining the benefits of vaccination in simple terms, I can maybe help others avoid COVID19. I hope you will find it helpful. If not, there are other sites that address this same question: maybe you will like those better?
It all comes out of how viruses work. Viruses are not alive themselves, but they use the bodies of living creatures (like us) to spread. They find their way into the cells of our body, then take over those cells to produce more copies of themselves. This is the only way viruses spread: they can't reproduce on their own. For COVID19, you may have heard of the "spike protein". This is the spiky part on the outside of the COVID19 virus that makes it look like a spiky ball. It's why it's called a "coronavirus", it looks a little like the spikes on a crown: "corona" is crown in Latin. This protein helps the viruses get inside the body's cells. Then, when inside, the viruses take over the cell to make and release more viruses. Those viruses invade other cells, and those start making more viruses too. Things can get out of hand very quickly, a bit like a forest fire spreading in a dry forest.
Happily, our body has a defence system against viruses (the "immune system"). When those defences recognize an invading virus, it takes as many viruses as possible out of action, keeping them from invading more cells. If the defences can keep up, the viruses won't spread spread very far, and our body will have fought off the infection. If the defences can't keep up, the infection spreads.
But our body's immune system needs to know, first, that something it sees is a virus, before it can act. Immune systems learn from exposure and time. If the body is exposed to enough viruses over time, the immune system can learn how to recognize the virus, and start fighting back. When someone gets sick from a viral infection like COVID19, they get sick because the virus is spreading faster than the immune system can fight it off. Because the immune system needs time to learn how to recognize the virus, while it is learning, the virus is spreading, faster and faster. Sadly, this can cause significant damage, depending on how far ahead the virus gets. This is what happened to my father last summer when he caught COVID19. At first, It spread much faster than his body could fight it, because his immune system had to first learn how. As COVID19 spread, it caused damage to his organ systems, including his heart. When his body's defences finally learned how to fight off COVID19, the damage it had already done to his heart was too great for him to stay alive. Sadly, he passed away shortly after.
If the body survives, its immune system can remember viruses that it has learned to recognize. When it is exposed later to the same virus, it recognizes it right away, and fights it off quickly before it can spread. This is why if you have successfully recovered from a viral disease, you are less likely to get it later. This is the basis of vaccination. Vaccination trains the body's immune system to recognize a virus quickly, so that it will be able to muster a strong defence against it right away, without giving the virus much chance to spread.
The way COVID19 vaccinations work is that they train the body's immune system to recognize the spike protein on the outside of a COVID19 virus. It doesn't inject the spike protein itself, but rather it injects something that instructs the body's cells to temporarily produce a bit of spike protein for training. Your body's defences learns from this to recognize anything with the spike protein (such as a COVID19 virus) as an invader. If later it is exposed to COVID19 virus, the body's defences will be primed and ready to get rid of it before it can spread very far.
Unfortunately, the body's defences against viruses aren't perfect. In the case of COVID19, a single exposure to the spike protein does train the body to recognize it, but not always quickly and thoroughly enough. Like us, when we're learning a new skill, our immune systems learn better with multiple lessons. That is why most COVID19 vaccinations require two shots: the immune system learns better with two lessons than one, and in some cases three (a booster) rather than two. This is also why people who have had COVID19 should still get vaccinated: a successful recovery from a COVID19 infection does provide some protection, but additional lessons for the body's defences will still help if exposed to the virus again. This is also the reason why vaccinations are not perfect. They train the body's immune system to recognize and eliminate the virus, but if the body is exposed to too much virus too quickly, the viruses can still spread faster than the immune system can eliminate it. This is why a few people who are fully vaccinated do get sick from COVID19, though not usually as seriously as people who were not vaccinated. This doesn't mean that the vaccine "doesn't work", it just means that even trained immune systems can sometimes be overwhelmed by a virus.
Because vaccinations train the immune system to recognize and fight off a virus, after a vaccination, we sometimes feel a bit sick: some of the symptoms we experience when we are sick are caused by the body's defences: e.g. fever, aches, fatigue,and feeling unwell. In the case of a vaccination, though, this is not long-term, because a vaccination, unlike a virus, does not reproduce and spread, and so its effects will wear off quickly.
Vaccinations can sometimes cause side effects that are more serious. This is why they are tested carefully before approval. In the case of the major COVID19 vaccines, there are some very rare side effects that are serious: certain COVID19 vaccines cause very rare but quite serious blood clots, and certain others cause very rare heart inflammation. These side-effects don't happen very often in people who receive the vaccine: they are much less likely than the probability of the average person being hit by lightning in their lifetime.
The fact is, the vaccine is much less dangerous than the disease. A COVID19 infection can cause very serious health effects, and many of those effects are not rare. While most people who catch COVID19 recover at home, more than one in twenty require hospitalization to stay alive. Of those, on the order of one in ten die. Moreover, many who recover from COVID19 suffer long-term health effects ranging from difficulty breathing, to fatigue, pain, and memory, concentration and sleep problems. Organ damage to the heart, lungs and brain is also possible. COVID19 is spreading around the world and most people will eventually be exposed to it. It is better to get the vaccine first, so that you are less likely to be harmed by the disease later.
There are claims on the Internet that COVID19 vaccines are much more dangerous than what I've written here. Many of these claims are misunderstandings. Millions of people have received COVID19 vaccines. A few who have had health problems after receiving the vaccine have reported their health problems as a possible "side effect" of the virus. In the US, there is a vaccine reporting system called VAERS where people can report bad health events that happened to them after receiving a vaccine: this lets scientists investigate whether the vaccine might have caused the problem. If the vaccine is causing a particular health problem, that problem would happen more often to people who receive the vaccine than to those who do not. But for most of the health problems reported to VAERS, they are not happening more often to vaccinated people, they happen at roughly the same rate as they happen to anyone, and so the vaccine cannot be responsible. It appears that COVID19 vaccines cause very few serious health problems, and those are very rare. The evidence for this is that millions of people around the world have received COVID19 vaccines and almost nobody has gotten seriously sick from them. The COVID19 disease itself is much more dangerous, which is why hospitals are full of people suffering from the disease, not the vaccine.
Even so, wouldn't it be better to avoid both the vaccine and the disease? Yes, it would be, if you could be assured of never being exposed to COVID19. But that is not so easy. COVID19 spreads very easily: it spreads through tiny moisture droplets in exhaled breath that float in the air like smoke from a cigarette, so if you are indoors with someone who is exhaling COVID19 virus, and there is poor air circulation, you will inhale some. The longer you are there, the more COVID19 virus you will inhale. Not everyone who gets COVID19 feels very sick right away: some feel fine, at least for a while, and many who feel sick don't feel so sick that they stay home. They will spread the virus whereever they go, simply by exhaling. You may be in a room with an infected person who has no idea that they are spreading COVID19. This is why masks are so helpful, because the mask over the nose and mouth of an infected person reduces the amount of COVID19 viruses they breathe out, and the mask over the nose and mouth of other people in the room reduces the amount of COVID19 virus they might breathe in. It's also a reason why indoor fresh air circulation is so important, and why COVID19 is so much more of a danger indoors than outdoors. COVID19 is very contagious, especially the new "delta" variant which is the dominant variant circulating today: on average, a sick person will spread it to six or more others. It's only a little less transmissible than chickenpox, but a lot more transmissible than flu. It's quite possible that we will all be exposed to it eventually.
An even more important reason to be vaccinated is to reduce the spread of COVID19 to others. Remember that the only way for a virus to reproduce is in the body of an infected person. If most people make their bodies inhospitable to the virus by getting vaccinated, then the virus will find very few opportunities to spread. It's like fire trying to spread in a very wet forest: only the dry sticks will burn, and the fewer dry sticks there are, the less likely the fire will find more sticks to spread to, and the more likely it will burn out. So by getting vaccinated, we protect not only ourselves, but everyone around us, especially those who, for medical reasons, can't be vaccinated, or who have immune systems that don't work well. If not enough of us get vaccinated, the number of COVID19 cases will overwhelm the hospitals. Most of those who need hospital care for their COVID19 infections will die instead. Also, many people who need hospital care for other serious illnesses won't be able to get the care they need, and they will die too.
So please be brave: if you can, get vaccinated. Yes, the effects of the vaccine may be unpleasant for a few days as the body learns how to fight the virus. But the vaccine will not harm you like the disease will, and it will train the body's immune system to fight it. My father got COVID19 too early, last summer, before COVID19 vaccines were available. If they had been available then, he might still be alive today. They're available now. Please get vaccinated if you can. If enough people around the world get vaccinated against COVID19, we may eventually be able to eliminate this disease altogether, and that would be a thing worth doing.
Sun 06 Jun 2021 13:39
The Covid19 Blues
The arts find inspiration in times of trouble, none more so than the sort of music known as the blues. Blues are creative and emotional, sometimes raw, but never fake. Blues are not about superstars and megahits, blues are about the endurance and hope of ordinary people. As Covid19 drags on, endurance and hope are needed more than ever. Here are pointers to a few Covid19-inspired blues tracks that I appreciate.
Enjoy! Mon 23 Nov 2020 00:00
Thoughts on Covid19
Another reason is that Covid19 didn't just affect me professionally, it affected me personally: I lost a parent to Covid19 this summer. While I am not in any way unique in having lost someone to this disease, I was not really in a good state to blog, for quite some time.
There is still another factor, though, one that also kept me from blogging. I am no epidemiologist. Still, as a thinking person, I seek to understand what was going on, why, and what can be done about it. Seeking to understand is, for me, theraputic: it helps me deal with stress, anxiety, grief, and loss.
First, I looked for good sources of information about the pandemic itself. The Centre for Disease Control and Prevention in the US has plenty of good material about it. One thing I found particularly helpful was an analysis in mid-May about a choir practice in Washington state with 61 attendees, one that led to most becoming infected. It resulted in three hospitalizations and two deaths. The CDC report is a very helpful example of rigorous statistical data analysis set in a small, understandable real-world context. As an illustration of what the Covid19 virus is like, I find it very helpful. For instance, it suggested airborne spread before that became generally realized.
Secondly, information about previous pandemics. Again, the Centre for Disease Control and Prevention in the US has a very good past pandemics page, put together before the Covid19 pandemic started, covering the horrifying 1918 influenza pandemic that killed fifty million people around the world, and the later influenza epidemics of 1957, 1968, and 2009. Each of these provide a general helpful picture: firstly, that each pandemic has a timeframe that is typically greater than one year but less than two, that transmission reduces in the summer but increases in the fall/winter due to indoor crowding and decreased relative humidity, and that mass vaccination can be an effective way to ward off a disaster of the scale of the 1918 pandemic.
One problem with this current pandemic is that, unlike the pandemics of 1957, 68, and 2009, the virus is not influenza, but a coronavirus. There are four coronaviruses that have been circulating widely for years (229E, NL63, OC43, and HKU1), but they typically don't cause serious illness. Two others (SARS-CoV and MERS-CoV) emerged in the early 21st century, both quite dangerous and certainly serious enough to warrant vaccination were they to spread widely, but due to a great deal of diligence and effort, and not a little good fortune, both of these were kept from spreading through the world population. The current Covid19 pandemic, caused by yet another coronavirus, SARS-CoV2, is the first coronavirus both serious enough and widespread enough to warrant a vaccine. Unlike for influenza, a coronavirus vaccine has never been produced before, so it has taken longer than it would if this pandemic had been influenza. Only now, as we approach the one year mark of the virus' first emergence, are we seeing some likely vaccine candidates. It will still take some time to produce and distribute suitable vaccines.
In the meantime, while efforts continue to design, test, produce and distribute a suitable vaccine, the challenge is to keep Covid19 from spreading far and fast. While at first it was believed that Covid19 spreads primarily through surface contact, there is increasing evidence for areosol spread (fine droplets in the air). So methods are needed to hinder the passing of the virus from one person to another. There are two main approaches: keeping people further apart, and putting physical barriers (e.g. masks) and processes (e.g. handwashing) in place so that the virus can't easily pass from one person to another.
The best way to hinder the transmission of Covid19 is to find out who may be contagious (through testing and contact-tracing), and keep them away from everyone else (quarantine) until they are no longer contagious. One challenge is that it can sometimes be very hard to detect when someone has Covid19 and is spreading the virus. There is a wide variation in how Covid19 affects people who have it. For many, it can take days for symptoms to emerge (presymptomatic), and for some, Covid19 can be mostly or completely asymptomatic, yet asymptomatic and presymptomatic Covid19 patients can spread the disease. If those who may have Covid19 can be identified (through testing and thorough contact tracing), then those individuals alone can be quarantined until they are no longer contagious. If they cannot be identified, then the only way to hinder the spread of the disease is to assume that almost anyone might have Covid19. This requires such things as requiring everyone to wear masks, and, despite severe social and economic cost, lockdowns, which are a sort of semi-quarantine for everyone. As I write this, Covid19 has been spreading quite quickly in my city, Toronto, despite a mask mandate, and so Toronto is going into lockdown.
How will it all end? In the struggle between pessimism and hope, I choose hope. I hope that I will not lose any more family members to this disease. I hope that effective vaccines will soon be available in the necessary quantities. I hope that the measures taken to hinder the spread will be effective. I think it is reasonable to expect that we will see the widespread distribution of effective vaccines in 2021, and this pandemic will be over sometime next year. Will everything be the same? No, I think not. Some businesses (tourism and travel, for example) will have a massive economic hole to climb out of, and some companies will not survive, but people will travel again. Working from home, and technology in support of it, will be more widely accepted. Cheek-to-jowl "open-concept" offices, handshaking, and other close-quarters working practices will be less readily accepted. There will be a greater consciousness of viral hygiene, and a greater acceptance of masks. But life will go on. Covid19 will no longer command the attention it is getting now. Other things will seem important again. And there will be many worthwhile things to blog about.
Mon 26 Aug 2019 06:51
Why we thought for a while Pluto was a planet, but it never was.
More than a decade after Pluto's demotion from the rank of planet, some still do not accept it. I can sympathize. Like many of us, I grew up memorizing in school the nine planets of the Solar system, the last of which was Pluto: icy, distant and mysterious. I remember as a child poring over a diagram of the solar system, marvelling at the concentric elipses of the planetary orbits, and wondering why Pluto's orbit was so odd. For odd it was: all the other planets orbited the sun in more or less concentric elipses, but Pluto was eccentric: its orbit was at an unusual angle, and it even briefly came closer to the sun than Neptune. None of the other plants had orbits like this: why Pluto? But I didn't question that it was a planet. It had been recognized as a planet since Clyde Tombaugh discovered it before my parents were born. For me, Pluto was weird, but it was still "planet", the astronomical equivalent of a sort of odd uncle who behaved strangely and kept to himself, but still family.
But the idea of Pluto as a planet started to become problematic in the early 1990s. In 1992, Jewitt and Luu discovered another object beyond Neptune: Albion, much smaller than Pluto, and also with an odd orbit. Because it was a small object, it was pretty clearly not a planet, so Pluto's status was not yet in question, but it was only the first of many. By 2000, more than seventy such objects had been discovered. Most of these were very small, but some were not so small. And the discoveries continued. In 2003, with the discovery of the Eris, a trans-Neptunian body more massive than Pluto itself, the problem became acute. No longer was Pluto the odd uncle of the planets: now there were on the order of 100 odd uncles and aunts, and at least one of them, Eris, aptly named after the greek goddess of discord, had a better claim to planethood than Pluto itself. Something had to be done. This bunch of odd objects, odd in the same way as Pluto, were either all planets, or they were none of them planets. There was no reasonable distinction that could be made that would keep Pluto a planet but deny planethood to Eris and many of her siblings. To do so would be arbitrary: we would be saying that Pluto was a planet simply because we discovered it first and it took us a long time to discover the others. What to do?
Happily, there was a precedent: this sort of thing had come up before. In 1801, Giuseppe Piazza discovered Ceres, a body orbiting between Mars and Jupiter. This was a big deal. Only twenty years before, a new planet had been discovered for the first time in recorded history: Uranus, found by accident by William Herschel in 1781. Now, twenty years later, Piazza had found a second. And this one was not out beyond Saturn, it was nearer than Jupiter. But Piazza's share of the limelight was soon to lessen. his planet had a rival: a year later, Heinrich Wilhelm Olbers discovered Pallas, another body between Jupiter and Mars. Two years later, in 1804, Karl Harding discovered another: Juno. Not to be outdone, Olbers in 1807 discovered yet another, Vesta. By the middle of the 19th century, fifteen bodies orbiting between Mars and Jupiter were known, and while none of them were anywhere as large as Ceres, one of them, Vesta, had nearly a third of Ceres' mass. Were there really many small planets between Mars and Jupiter, or were these something else? When in 1846 the planet Neptune was discovered beyond Uranus, it became clear that some decision about these bodies between Mars and Jupiter needed to be made. A consensus emerged: Ceres and other such objects were not planets. They were called "asteroids", a name coined in 1802 by William Herschel. It was a good call: there are now well over 100,000 known asteroids, far too many for schoolchildren to memorize.
With Pluto, a similar situation was now occurring. While we weren't yet at 100,000 Pluto-like bodies, we knew about quite a few more than fifteen. And Pluto, unlike Ceres, wasn't even the most massive: Eris was, and quite possibly, bigger ones would be found. There was no denying the facts. Pluto, like Ceres, could not be a planet. It must be something else.
Of course this was quite controversial. People had been calling Pluto a planet for the better part of a century. Generations of schoolchildren had memorized it as part of the list of planets. But the choice was clear: either the schoolchildren would have to start memorizing longer lists, much much longer ones, or Pluto would have to be demoted. Well, not demoted, exactly, but newly recognized for what it really was all along: something different. In the sumer of 2006, the International Astronomical Union (IAU) declared that Pluto isn't a planet, it is a dwarf planet. While this designation is a little confusing (if a dwarf planet isn't a planet, why is it called a dwarf planet?), one thing was now clear: Pluto is not the same sort of thing as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; it, and Eris, and probably a couple of other larger trans-Neptunian bodies discovered since the 1990s, are something different. But guess what: Ceres, too, fits IAU's definition of dwarf planet, the only asteroid that does. Two centuries after its discovery, Ceres, first-born of the non-planets and largest of the asteroids, was deemed a dwarf planet, and Piazza, its discoverer, though not the second person in recorded history to discover a new planet, was recognized as the very first to discover a dwarf one.
Tue 26 Feb 2019 06:27I spent all of 2018 intending to blog, and not doing it. Sadly, this is an all too human situation. We intend to do things, when we can, when time permits, but we can't; time doesn't permit. Or at least this is one of those stories we tell ourselves. The truth is a little simpler: throughout 2018, my intention to blog was not strong enough for me to re-prioritize things in my day so that I would do it.
I had plenty to say. I continue to have plenty to say. I had plenty of important things to do, and that also continues to be true. Despite my other responsibilities, I am making time now, and I will continue to make time, every so often, to say things in this blog. I am being intentional about it.
To be intentional about something means to be deliberately purposeful: to make one's actions a directly chosen consequence of one's thoughtful decisions. For most people, myself included, life is full of input, distractions, demands, requests. It is easy to fill time without much effort. But if I am not intentional, it will be filled with reaction, not action: things that circumstances and prior commitments have chosen for me, not things I have chosen for myself.
Reaction is fine, even good and necessary. Many people, myself included, build up throughout their lives various important responsibilities: responsibilities to family, work, friends, communities. Responsibilities carry with them a commitment to react to the needs of others. This is well and good. But it is not enough, at least not for me. I realize that to be authentic, I have to consider carefully what is important to me, decide what to do about it, and then act on it. This is intentionality. I've decided to be intentional about blogging. Look for more blog entries in the coming weeks.
Tue 12 Dec 2017 13:07
A Way to Visualize Relative Masses of Things in the Solar System
Every so often we hear things in the news about the solar system: a mission
to a planet or asteroid, talk of manned missions to mars, arguments about
whether Pluto is a planet or not. We tend to have pretty sketchy ideas of
what most bodies in the solar system are like compared to Earth. The fact
is that they're more wildly different in size and mass than we might think.
Let's look at mass. Imagine you decide to row across San Francisco bay in a 12-foot aluminum rowboat. You pack a couple of suitcases, your 15 inch Macbook Pro (can't go without connectivity) and your ipad mini, you get in your rowboat and start rowing. As you row, you get hungry, so you pull out a Snickers bar. Now imagine that the USS Nimitz, a massive nuclear-powered aircraft carrier, passes by. There you are, in a rowboat with your two suitcases, your Macbook Pro, your iPad, and your Snickers bar, alongside a huge supercarrier.
Well, the mass of the sun compared to the earth is like that aircraft carrier compared to you and your boat. The mass of Mars is like your two suitcases. The mass of the moon is like your 15 inch Macbook Pro, and the mass of Pluto is like your iPad mini. As for the Snickers bar, it's like Ceres, the largest of the asteroids.
Now let's suppose the massive wake of the aircraft carrier tips over your rowboat and leaves you in the water. Along comes a rich tech founder in his 70 foot yacht, and fishes you out. That yacht is like Jupiter, the largest planet.
So forget any mental images you might have of planets being something like the Sun, only a bit smaller and cooler. The sizes of things in the solar system are really quite different, and there is nothing, absolutely nothing, in the solar system that is anything quite like the Sun.
Thu 09 Mar 2017 12:58
A closer look at topuniversities.com's 2017 rankings for Computer Science.
The QS World University Rankings for 2017 are out, including the subject rankings. For the subject "Computer Science & Information Systems", the University of Toronto does very well, placing tenth.
A closer look at the top ten shows some expected leaders (MIT, Stanford, CMU, UC Berkeley) but some less expected ones, such as Oxford and Cambridge. These are superb Universities with good Computer Science programs, but are their CS programs really among the ten best in the world?
A closer look at how the score is computed sheds some light on this question. The Overall Score is a combination of Academic Reputation, Citations per Paper, Employer Reputation, and H-index Citations. Academic Reputation and Employer Reputation are, in essence, the opinions of professors and employers respectively. While (hopefully) they are reasonably well founded opinions, this is a subjective, not an objective, metric. On the other hand, Citations per Paper and H-index Citations are objective. So I looked at Citations per Paper and H-index Citations for the top forty schools on the 2017 QS Computer Science & Information Systems ranking.
By Citations per Paper, top five of those forty are:
No MIT? This seems off. So lets look at the top five by H-Index Citations:
That looks more reasonable. So let's look at the top twenty by H-Index Citations:
That's a list that makes more sense to me. While it puts my department 14th instead of 10th, I think I have more confidence in the objectivity of this ordering than I do in the QS Overall Score ordering.
Wed 26 Oct 2016 10:41On October 16th, 2016, Kelly Gotlieb, founder of the Department of Computer Science at the University of Toronto, passed away in his 96th year. I had the privilege of knowing him. Kelly was a terrific person: brilliant, kind, and humble. He was always willing to make time for people. He was a great thinker: his insights, particularly in the area of computing and society, were highly influential. I never fully realized how influential he was until we, here at the department of Computer Science, created a blog, http://socialissues.cs.toronto.edu, in honour of the 40th anniversary of Social Issues in Computing, the seminal textbook he and Allan Borodin wrote in 1973 in the area of computers and society. I served as editor of the blog, and solicited contributions from the top thinkers in the field. So many of them responded, explaining to me how influential his ideas had been to them, and the blog was filled with insightful articles building in various ways upon the foundation that he and Allan had laid so many years before. I interviewed Kelly for the blog, and he was terrific: even in his nineties, he was full of insights. His mind active and enthusiastic, he was making cogent observations on the latest technologies, ranging from self-driving cars to automated medical diagnosis and treatment.
To me, Kelly epitomized the truth about effective teaching that is all too often missed: teaching is not just about information, teaching is about inspiration. Kelly was a truly inspiring teacher and thinker. He was completely authentic in everything he did, he was full of enthusiasm, and that enthusiasm was infectious. Conversations with Kelly so often left me energized and inspired, thinking along new directions of thought that something he said had triggered, or leaping past obstacles that had previously seems insurmountable. That is true teaching. Information without inspiration is simply fodder for forgetfulness, but teaching that inspires leads to new insights, integration of ideas, genuine understanding, and a better, clearer and sharper window on the world. Kelly inspired so many people for so many years. We are truly blessed that he was among us. He will be remembered.
Tue 23 Apr 2013 12:56
Handling Unsolicited Commercial Email
My email address is all over the web: at the time of writing this, a search on google for my email address produces about 15,800 results. So anyone who wants to find my email address can do so easily. Many people or companies who want to sell me something send me email out of the blue. I get a great deal of such unsolicited commercial email, too much to read or pay adequate attention to. I simply delete them. Unfortunately, many sources of such email persist. So for some time now, I've elicited the help of technology. I process my incoming email using procmail, a powerful piece of software that lets me script what happens to my email. When I receive unsolicited commercial email, if it is from a vendor or organization I don't have a relationship with, I will often add a procmail rule to discard, unseen, all future email messages from that vendor. I've got about 400 organizations (mostly vendors) in my discard list so far, and the list slowly grows. Am I still getting unsolicited commercial email from these sources? I am, but I am not seeing it. It's the same effect, really, as manual deletion (i.e. the message is deleted, unread), but it's easier for me, because I am not interrupted. But of course I think it would be better still if the email were not sent at all.
If you are a vendor with whom I do not have a pre-existing relationship, and you want to send me email introducing your products, please don't. I do not accept cold salescalls either. Instead, advertise effectively on the web, so that if I am looking for a product like yours, I can find you. If you must contact me directly, send me something by postal mail, where, unlike email, the communication does not have an interruptive aspect.
Thu 29 Nov 2012 00:00
A closer look at the University of Toronto's international ranking in Computer Science.
International rankings of universities seem to be all the rage these days. The interest seems to be fed by three rankings of particular prominence that have emerged in the past decade. These are Shanghai Jiao Tong University's Academic Ranking of World Universities (sometimes known as AWRU, or simply as the "Shanghai Ranking"), Quacquarelli Symonds' QS World University Rankings, and the Times Higher Education World University Rankings. Part of the attractiveness of these rankings is that they can become a way of "keeping score", of seeing how one institution does in comparison to others.
My employer, the University of Toronto, does quite well in these rankings, particularly my department, Computer Science. The subject area of Computer Science is not ranked separately in the Times Higher Education World University Rankings (it's bundled together with Engineering), but in the other two, Toronto has consistently ranked in the top ten in the world each year in Computer Science, with only one exception.
This exception is recent, however, and worth a closer look. In the QS World University Rankings for Computer Science and Information Systems, Toronto dropped from 10th in 2011 to 15th in 2012. This big drop immediately raises all sorts of questions: has the quality of Toronto's Computer Science programme suddenly plummetted? Has the quality of Computer Science programmes at other universities suddenly soared? Or has the QS World University Rankings changed its methodology?
To answer this question, let's look at how other universities have changed from 2011 to 2012 on this ranking. Many (MIT, Stanford, Berkeley, Harvard, Oxford, Cornell, and others) stayed where they were. Others dropped precipitously: Cambridge University dropped from 3rd to 7th, UCLA from 8th to 12th, and Caltech plummetted from 7th to 27th. Some other universities went up: Carnegie Mellon University (CMU) went from 9th to 3rd, ETH Zurich from 11th to 8th, the National University of Singapore (NUS) from 12th to 9th, and the Hong Kong University of Science and Technology (HKUST) soared from 26th to 13th. Surely these curious and significant changes reflect a methodology change? But what?
The QS university rankings website, in the Methodology section, Academic subsection, reveals something of interest:
NEW FOR 2012 - Direct Subject Responses Until 2010, the survey could only infer specific opinion on subject strength by aggregating the broad faculty area opinions of academics from a specific discipline. From the 2011 survey additional questions have been asked to gather specific opinion in the respondent's own narrow field of expertise. These responses are given a greater emphasis from 2012.To understand this change, it needs to be recognized that the QS rankings rely highly on the opinions of academics. A large number of academics around the world are surveyed: the QS rankings website indicates that in 2012, 46079 academic responses were received, of which 7.5% addressed Computer Science." The seemingly modest change made in 2012, to weigh more heavily the opinions of academics in a field about their own field, given its impact on the 2012 results for Computer Science, leads one to wonder about the regional distribution of academics in Computer Science in comparison to academics in other disciplines. One significant factor may be China.
In 1999, courses in the fundamentals of computer science became required in most Chinese universities, and by the end of 2007, China had nearly a million undergraduates studying Computer Science. While QS rankings does not indicate regional distribution by discipline for the academics whose opinions it consults, the surge in the number of Chinese computer scientists worldwide in the past decade almost certainly must have an effect on the regional distribution of academics in Computer Science as compared to other disciplines. As such, is it any surprise to see world universities prominent in China that possess strong Computer Science programmes (such as HKUST and NUS) climb significantly in the rankings, and others less prominent in China plummet? But if a world ranking of universities is so affected by regional shifts in those whose opinion is being solicited, how reliable is it as an objective gage of the real quality of a given university?
Perhaps a more reliable gage of quality can be found in the Shanghai ranking, which is not opinion-based, but relies on concrete indicators and metrics. On the Shanghai ranking, the University of Toronto consistently ranks 10th in the world in Computer Science in 2010, 2011, and 2012. But what does this mean, concretely?
To answer these questions, we need to grapple with an important fact: in Computer Science, the US dominates. As a nation, the US has been enormously supportive of Computer Science ever since the field first existed, and as a result, it has become pre-eminent in computing. Nine of the top ten schools in the Shanghai ranking, and twenty of the top twenty-five, are in the US. For the University of Toronto to be one of the handful of universities outside the US to break into the top twenty-five, and the only one to break into the top ten, is a significant accomplishment. A chart is illustrative:
Of course, the University of Toronto is in Canada, so a comparison to other schools in Canada is also illustrative. For Computer Science, on the Shanghai ranking, there seems to be no close Canadian rival. In 2012, UBC comes closest, being a only a few points short of breaking into the top 25, but all other Canadian schools rank well back:
Even compared to other disciplines that have Shanghai rankings (only science, social science, and related disciplines seem to be ranked), Toronto's pre-eminence in Computer Science in Canada is striking:
From a score-keeping perspective, I think we can conclude that the University of Toronto is doing very well in Computer Science with respect to other universities in Canada, and it is one of the few non-US schools that can keep up with the US in this field.
But all this needs to be put into perspective. After all, rankings are not a full picture, they're aggregations of metrics of varying value, they represent a formulaic approach to something (university education) that cannot always be so conveniently summarized, and they reflect methodologies chosen by the producers of the rankings, methodologies that may not always best reflect objective quality. Of course, if the University of Toronto were to climb to fifth, I'd be pleased, and if it were to drop to fifteenth, I'd be disappointed: surely the score-keeper in me can be allowed this much. But in the overall scheme of things, what matters most for Computer Science at Toronto is not our score on a ranking system, but the objective quality of our programme, the learning outcomes of our students, and the impact of our research, and these things, not our score on rankings, must always remain our top priorities.
Thu 15 Dec 2011 15:14
Dealing with unsolicited salescalls (cold calls).
For many years, I've been plagued by unsolicited salescalls. It's not very hard to find my phone number, and various people (mostly in the IT realm) call me up out of the blue hoping to sell me something. The interruption is unwelcome, even if the product isn't.
For some years now, my policy is to explain to the caller that I don't accept unsolicited salescalls, sincerely apologize, and end the call. Occasionally, I am then asked how I am to be contacted. I explain that I prefer to do the contacting myself: when I have a need, I am not too shy to contact likely vendors and make inquiries about their products.
Occasionally I run into someone who is offended by my unwillingness to take their unsolicited salescall. I do feel more than a little sympathy for the salesperson when this happens: I imagine they may think I objected to something they did, or to their manner. The fact is, I handle all unsolicited salescalls this way. As for whether it is intrinsicly offensive to reject unsolicited salescalls out of hand, I don't think it is. Indeed, it is natural for a salesperson to want their salescall, even if unsolicited, to be better accepted. But it is unreasonable for any salesperson to expect that unsolicited sales inquiries to strangers will always be welcome. But I do apologize, each time, and in general, when I so quickly end telephone conversations with salespersons who call me out of the blue.
Dear reader, if you are a salesperson, and you are tempted to contact me to sell me something, please do not call. Instead, just advertise generally (and if you must, send me some mail in the post). Trust me to find you when the need arises. I frequently do.
Mon 30 May 2011 21:26
Einstein's special relativity isn't as complicated as many people seem to think.
I run into people who think that special relativity is some sort of mysterious thing that only Einstein and physicists can understand. But it's not. It's a bit weird, but it's no weirder than the earth being a globe.
Originally people thought that light moved like any other moving object. Einstein thought about this and wondered: what would happen if you followed some light and sped up until you travelled at the same speed as it. Then light would look to you like it was stopped. But stopped light (light "standing still") didn't (and still doesn't) make sense. So Einstein thought: what if light travels at the same speed no matter how fast you're going? What would this mean?
Well, what does it mean to travel "at the same speed"? It means light covers the same amount of distance in a given amount of time. Or, put another way, light takes the same amount of time to cover a given distance. So if the distance is short, light takes less time to go the distance. If the distance is longer, light takes proportionally more time to cover it.
So Einstein thought: OK, if light travels at the same speed for everyone no matter how fast they're going, what would that mean for someone going very fast? Imagine they're going nearly the speed of light, and are being chased by a beam of light. Clearly the light isn't going to get closer to that person as quickly as it would get closer to someone who was standing still. Ordinarily, you would think that light was moving "slower" for the person who is moving away from it. But if light moves at the same speed for everyone, than something else must be going "slower" for that person. The only possibility is time.
Put it this way: light covers a certain distance in a second. To someone watching, the pursuing light isn't making up the distance quite so fast between it and the moving person, because the person is moving away so fast. But for the moving person, light is moving as fast as it always does, it is the second that takes longer.
This sounds a little bit crazy since we aren't used to thinking of time moving faster for some people and slower for others. But it does. The reason we don't notice is that the speed of light is very fast and we can't easily go at speeds close to it.
It's the same sort of thing as the world being round (i.e. a globe). It looks flat to us, but only because it is so big that we can't see enough of it at once to see it curve. Go high enough and we can see the curve of the earth's surface easily enough.
Similarly with special relativity. Time moves slower for those who move fast. It's not obvious to us because we usually don't move very fast, so at the speeds we move, the time differences are too small to notice. But in 1971, Joseph Hafele and Richard Keating took some very accurate (cesium atomic) clocks abord commercial airliners and flew around the world. They compared their clocks to the very accurate clocks in the US naval observatory: the clocks were indeed different, and showed the results that Einstein had predicted.
What this this mean? Well, if you can wrap your head around the concept of the world being a globe, you can wrap your head around the concept of time moving more slowly for those who move fast. And that's it, right?
Well, not really. There's also general relativity (and it affects Hafele and Keating's results too). But that's a bit more complicated, and I'm not going to get into it now.
Fri 04 Sep 2009 14:57
Assessing H1N1 risk
What sort of risk does H1N1
(Swine Flu) present this flu season? To assess this, it might be
helpful to estimate some H1N1 risks and then compare it to risks with
which we are more familiar.
So let's look at some numbers. The worldwide case fatality rate of H1N1 (the number of people who have died of H1N1, divided by the number of people who have gotten H1N1) has been estimated to be 0.45%. Unlike seasonal flu, roughly 80% of those who have died of H1N1 are less than 65 years old (typically 90% of seasonal flu fatalities are 65 years old or over). If we assume a 15% probability of getting H1N1 this flu season, the likelihood of someone under the age of 65 dying of H1N1 this season is thus 0.15 x 0.0045 x 0.80, i.e 0.054% or 1 in 1852. This is a little less than the one-year general odds of death due to external causes in the US, approximately 1 in 1681.
