It has been a while since I last saw a temperature like -27.9 on our thermometer. And that’s just on our balcony!
Then again, this is Canada in January, so perhaps it’s not that unusual. Still, it is one of those days when I am really glad that I work from home.
Recently I came across a blog post that suggests (insinuates, even) that proponents of modified gravity ignore the one piece of evidence that “incontrovertibly settles” the question in favor of dark matter. Namely this plot:
From http://arxiv.org/abs/1112.1320 (Scott Dodelson)
In this plot, the red data points represent actual observation; the black curve, the standard cosmology prediction; and the various blue curves are predictions of (modified) gravity without dark matter.
Let me attempt to explain briefly what this plot represents. It’s all about how matter “clumps” in an expanding universe. Imagine a universe filled with matter that is perfectly smooth and homogeneous. As this universe expands, matter in it becomes less dense, but it will remain smooth and homogeneous. However, what if the distribution of matter is not exactly homogeneous in the beginning? Clumps that are denser than average have more mass and hence, more gravity, so these clumps are more able to resist the expansion. In contrast, areas that are underdense have less gravity and a less-than-average ability to resist the expansion; in these areas, matter becomes increasingly rare. So over time, overdense areas become denser, underdense areas become less dense; matter “clumps”.
Normally, this clumping would occur on all scales. There will be big clumps and small clumps. If the initial distribution of random clumps was “scale invariant”, then the clumping remains scale invariant forever.
That is, so long as gravity is the only force to be reckoned with. But if matter in the universe is, say, predominantly something like hydrogen gas, well, hydrogen has pressure. As the gas starts to clump, this pressure becomes significant. Clumping really means that matter is infalling; this means conversion of gravitational potential energy into kinetic energy. Pressure plays another role: it sucks away some of that kinetic energy and converts it into density and pressure waves. In other words: sound.
Yes, it is weird to talk about sound in a medium that is rarer than the best vacuum we can produce here on the Earth, and over cosmological distance scales. But it is present. And it alters the way matter clumps. Certain size scales will be favored over others; the clumping will clearly show preferred size scales. When the resulting density of matter is plotted against a measure of size scale, the plot will clearly show a strong oscillatory pattern.
Cosmologists call this “baryonic acoustic oscillations” or BAO for short: baryons because they represent “normal” matter (like hydrogen gas) and, well, I just explained why they are “acoustic oscillations”.
In the “standard model” of cosmology, baryonic “normal” matter amounts to only about 4% of all the matter-energy content of the visible universe. Of the rest, some 24% is “dark matter”, the rest is “dark energy”. Dark energy is responsible for the accelerating expansion the universe apparently experienced in the past 4-5 billion years. But it is dark matter that determines how matter in general clumped over the eons.
Unlike baryons, dark matter is assumed to be “collisionless”. This means that dark matter has effectively no pressure. There is nothing that could slow down the clumping by converting kinetic energy into sound waves. If the universe had scale invariant density perturbations in the beginning, it will be largely scale invariant even today. In the standard model of cosmology, most matter is dark matter, so the behavior of dark matter will dominate over that of ordinary matter. This is the prediction of the standard model of cosmology, and this is represented by the black curve in the plot above.
In contrast, cosmology without dark matter means that the only matter that there is is baryonic matter with pressure. Hence, oscillations are unavoidable. The resulting blue curves may differ in detail, but they will have two prevailing characteristics: they will be strongly oscillatory and they will also have the wrong slope.
That, say advocates of the standard model of cosmology, is all the proof we need: it is incontrovertible evidence that dark matter has to exist.
Except that it isn’t. And we have shown that it isn’t, years ago, in our paper http://arxiv.org/abs/0710.0364, and also http://arxiv.org/abs/0712.1796 (published in Class. Quantum Grav. 26 (2009) 085002).
First, there is the slope. The theory we were specifically studying, Moffat’s MOG, includes among other things a variable effective gravitational constant. This variability of the gravitational constant profoundly alters the inverse-square law of gravity over very long distance scales, and this changes the slope of the curve quite dramatically:
From http://arxiv.org/abs/0710.0364 (J. W. Moffat and V. T. Toth)
This is essentially the same plot as in Dodelson’s paper, only with different scales for the axes, and with more data sets shown. The main feature is that the modified gravity prediction (the red oscillating line) now has a visually very similar slope to the “standard model” prediction (dashed blue line), in sharp contrast with the “standard gravity, no dark matter” prediction (green dotted line) that is just blatantly wrong.
But what about the oscillations themselves? To understand what is happening there, it is first necessary to think about how the actual data points shown in these plots came into existence. These data points are the result of large-scale galaxy surveys that yielded a three-dimensional data set (sky position being two coordinates, while the measured redshift serving as a stand-in for the third dimension, namely distance) for millions of distant galaxies. These galaxies, then, were organized in pairs and the statistical distribution of galaxy-to-galaxy distances was computed. These numbers were then effectively binned using a statistical technique called a window function. The finite number of galaxies and therefore, the finite size of the bins necessarily introduces an uncertainty, a “smoothing effect”, if you wish, that tends to wipe out oscillations to some extent. But to what extent? Why, that is easy to estimate: all one needs to do is to apply the same window function technique to simulated data that was created using the gravity theory in question:
From http://arxiv.org/abs/0710.0364 (J. W. Moffat and V. T. Toth)
This is a striking result. The acoustic oscillations are pretty much wiped out completely except at the lowest of frequencies; and at those frequencies, the modified gravity prediction (red line) may actually fit the data (at least the particular data set shown in this plot) better than the smooth “standard model” prediction!
To borrow a word from the blog post that inspired mine, this is incontrovertible. You cannot make the effects of the window function go away. You can choose a smaller bin size but only at the cost of increasing the overall statistical uncertainty. You can collect more data of course, but the logarithmic nature of this plot’s horizontal axis obscures the fact that you need orders of magnitude (literally!) more data to achieve the required resolution where the acoustic oscillations would be either unambiguously seen or could be unambiguously excluded.
Which leads me to resort to Mark Twain’s all too frequently misquoted words: “The report of [modified gravity’s] death was an exaggeration.”
To all my family and friends, to all good people everywhere… happy 2013!
For me, 2012 was… interesting. Business-wise, it was not a good year (indeed, another year like 2011 and 2012 and I will be seriously worried). In other respects, however, it was a fruitful one. Our Pioneer results are now published, indeed we earned a place on the cover of Physical Review Letters, and also on the cover of IEEE Spectrum. I had several other papers accepted in respectable journals. I was also making some slow progress with my attempts to derive a weak-field formulation of Moffat’s gravity theory that would allow us to study extended distributions of matter, both continua and N-body systems.
My wife and I celebrated our 20th wedding anniversary in September, and we survived a minor health crisis with no lasting ill effects. Our closest family members are also all in good health, so who are we to complain? The world, meanwhile, didn’t end despite a certain Mayan calendar’s dreaded predictions, the Eurozone is still there, the economy is limping ahead (at least here in North America), so for now, all is well. Now about that fiscal cliff…
Anyhow, I’m looking forward to 2013. I have some interesting contract work. I’ll be going to Texas to talk at a conference early in the coming year. And, I hope, I’ll be able to continue my work on modified gravity and achieve some useful results.
And last but not least… in a few months, I will be half a century old. A strange milestone, as I am still wondering what I’ll be when I grow up.
And from the crew of Apollo 8, we close with good night, good luck, a Merry Christmas and God bless all of you – all of you on the good Earth.
– Frank Borman from Apollo 8, December 24, 1968
My other extracurricular activity today involved a shovel.
That is because we ended up with quite a few inches of wet, heavy snow, courtesy of this year’s first major winter storm. And I like to shovel the snow off my balcony, rather than let it rot the deck and leak in through our balcony door.
At least I didn’t have to go anywhere. Those who did had a hard time on the roads. A poor double-decker actually ended up in the ditch this morning.
But hey, we’re all still alive! Contrary to certain Mayan prophecies, the world did not come to an end. The daily struggle of our existence continues.
I use a simple WordPress plugin, called “Simple Facebook Connect”, to automatically post my blog posts to Facebook. The plugin also provides a Like button for my posts. Recently, I noticed that a number of my posts acquired a fair number of Likes from apparent strangers.
Today, it became clear to me that the plugin is cheating. After exchanging a series of comments on Facebook in response to one of my blog posts, I noticed that every time a comment was added, the number of Likes went up by one. So no, I am not nearly as popular as I previously thought.
Oh well. Blogs are meant to be written, not read.
Spotted today at a Loblaws store:
One of my favorite photographs ever, in fact one that I even use on my Facebook timeline page as a background image, was taken by a certain Bill Anders when he was flying almost 400,000 km from the Earth. Anders was one of the first three members of our species who flew to another celestial body (albeit without landing on its surface; that came a bit later.)
Yesterday, I read a very interesting article about Anders, both his trip on board Apollo 8 and his life afterwards. The article also touched upon the topic of religion.
The message radioed back by the crew of Apollo 8 is probably the most memorable Christmas message ever uttered by humans. (Or maybe I am biased.) And yes, it starts with the words from Genesis, but I always viewed it the way it was presumably intended: as an expression of awe, not as religious propaganda.
The curious thing, as mentioned in the article, is that it was this trip around the Moon that changed the traditional Christian viewpoint of Anders about Earthlings created by a God in his own image.
“When I looked back and saw that tiny Earth, it snapped my world view,” Anders is quoted as saying. “Are we really that special? I don’t think so.”
Well, this pretty much sums up why I am an atheist. I’d like to believe that it’s not hubris; it’s humility.
An article we wrote with Slava Turyshev about the Pioneer anomaly and its resolution, at the request of IEEE Spectrum, is now available online.
It was an interesting experience, working with a professional science journalist and her team. I have to admit that I did not previously appreciate the level of professionalism that is behind such a “members only” magazine.
I began this blog of mine a little over ten years ago, although it took a bit longer than that before I was able to bring myself around and actually call it a “blog”. (I originally called this a “Day Book”, a term I borrowed from Jerry Pournelle.)
In 2002, I wrote about Brian Herbert’s prequels to his father’s, Frank Herbert’s, Dune series of books.
In 2003, I introduced my Halloween cat. I wrote about Moscow schools banning Halloween. I wrote about electronic voting in Ontario using a Linux-based system, and about a stray cat in our neighborhood that may have been killed by the Humane Society.
In 2004, I wrote about Halloween cats (including our very first cat, Marzipan and his Halloween dance) and about the shutdown of Mirabel airport.
In 2005, I was wondering if Condoleeza Rice, with her glowing eyes, might actually be a Goa’uld System Lord from Stargate SG-1.
In 2006, it was time to celebrate NASA’s decision to reinstate the final Hubble repair mission after all.
In 2007, I was speculating about ant colonies and group consciousness.
In 2008, I had nothing to say. Fittingly, this was the last time I used my old, homebrew blogging engine.
After switching to WordPress, in 2009 I complained about daylight savings time. I still think that switching to daylight savings time is a ridiculous gimmick that does far more harm than good in a post-industrial society.
In 2010, I was complaining about snow in October.
2011 was a scary Halloween indeed: it was on that very day that the world’s population supposedly reached 7 billion. Also on that day, the debt-to-GDP ratio of the United States reached 100%. And there was a major snowstorm in New England.
And here comes 2012, the scariest Halloween yet since I started blogging: a good one third of Manhattan is still in darkness, large sections of New Jersey are ruined, millions are still without power, scores are dead, and the remnants of Sandy are heading in our direction, bringing rain, cold, perhaps even some snow.
But for what it’s worth, Happy Halloween to all!
Earlier this morning, I came across the following headline on Google News: “Fewer crashes when docs report bad drivers, study finds“.
The headline almost made sense. Yes, bad drivers cause crashes, indeed the main reason why modern operating systems crash these days is bad third-party drivers. So being able to identify and report a bad driver kind of makes sense, but how would you do that? And what does it have to do with your docs? Did the author mean perhaps that a document, say, an HTML page, could display a warning about a bad driver instead of invoking the driver (e.g., to display video) and risk crashing the browser or the computer?
Then, about three tenths of a second later, I realized that the headline was about road accidents and medical doctors.
Once again, I was doing something dangerous: despite being a programmer, I chose to carry not just a screwdriver but also some power tools.
Two weeks ago, I had a plumbing crew remove our old bathtub. It was way overdue:
It took them no more than a couple of hours to reduce the bathtub to this:
And by mid-afternoon, they were done. The new bathtub was installed. Actually, let me emphasize: ONLY the new bathtub was installed:
From this point on, I was on my own. It was by choice: I dislike having workmen in my house and in any case, these are skills that, I think, are well worth learning.
Having never done tiles (or for that matter, sheet rock) before, I was taking things slowly. (Hey, I am also just a few months shy of fifty, somewhat overweight, and I usually spend my days in an armchair sitting in front of a computer.) Even so, a few days later, I was done with all the preliminary work: notably, the installation of tile backer drywall:
The plastic sheets were put in there so that we could use the bathroom even while it was still under construction.
Next came the tiles. The tricky bit (for me anyway) was to cut tiles around the faucet and other fixtures. I was able to cut pretty decent holes using a tile cutter bit in my “Roto-ZIP” tool:
And thus it came to be that a little less than two weeks after the plumbers left, the tiling was done:
There was, of course, still more work to do. First, I had to wait a few days for the adhesive to set before grouting the tiles. Once I completed the grouting successfully, I had to wait another few days before I could spray the new grout with sealant. It was only at this point, namely today, that I sealed the edges of the tile using silicone. Finally, once the fixtures were reattached, the job was at last done:
Needless to say, I am mighty proud of myself. In fact, I’ll probably be insufferably proud for the next few days (that is, unless the tiles start popping off, in which case my insufferable pride will rapidly turn into an overwhelming sense of embarrassment.) There is still a little bit of cleaning up to do, and eventually, repaired bits of wall around the tiles will need to be repainted. I may apply a bit of paint for protection, but the real paintjob will have to wait; I am considering replacing the vanity (the sink definitely needs to be replaced) and I am also considering replacing the floor tiles, which are old and have developed a few minor cracks over the years.
But not this year. For now, I prefer to return to my regularly scheduled programming job and put down my screwdriver.
Phew!
Busy celebrating our 20th wedding anniversary yesterday, I forgot that there was another important anniversary on September 12: it was fifty years ago yesterday that a certain John F. Kennedy uttered the words, “We choose to go to the Moon. We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.” And with those words, an astonishing sequence of events took place, and before the 1960s came to an end, two Americans indeed landed on the Moon… a technological feat the like of which the world has not seen since 1972, when the last of the Apollo Moon shots took place.
My wife and I have been married for exactly twenty years today. I hope the next twenty years will be at least as much fun for both of us as the first.
That the main function of the post office is to deliver letters may be obvious to many, but apparently it wasn’t obvious to a postal employee today when my wife tried to mail an oversize letter to Hungary. It would be about $30 surface, or $60 air mail, said the young employee to my wife who was so surprised at first, she was unable to respond. Thankfully, a senior clerk overheard the conversation and eventually came to her colleague’s rescue, explaining to her that a letter is not a parcel. Actual cost? $4.20, for a letter weighing between 50 and 100 grams. Though I am seriously beginning to wonder if at least half that price is due to the inefficiencies of inept postal employees…
Nature had a nice editorial a few days ago about the Pioneer Anomaly and our research, titled “…and farewell to the Pioneer anomaly” (so titled because in the print edition, it is right below the obituary, titled “Farewell to a pioneer”, of Bernard Lovell, builder of what was at the time the world’s largest steerable radio telescope at Jodrell Bank).
Farewell, yes, though I still hope that we will have the wherewithal to publish a longer article in which we provide the details that did not fit onto the pages of Physical Review Letters. We ought to update our review paper in Living Reviews in Relativity, too. We need to prepare for the release of the data used in our analysis. And, if possible, I’d like to spend time tackling some of the open questions we discuss near the end of our last paper, such as analyzing the spin behavior of the two spacecraft or making use of DSN signal strength measurements to improve the trajectory solution.
First things first, though; right now, my priorities are to a) earn money (which means doing things that I actually get paid for, not Pioneer) and b) get ready to have our upstairs bathtub replaced (the workmen will be here Monday morning), after which I plan to do the wall tiles myself (with fingers firmly crossed in the hope that I won’t mess it up too badly.)
Yes, sometimes such mundane things must take priority.
It was over thirty years ago, back in 1979-1980, that I first earned money from a software development contract. My first assignment? Aircraft simulation, specifically tabulating the minimum safe take-off distance of TU-154 aircraft at Budapest airport under various loads and weather conditions.
Alas, the Hungarian national airline, MALÉV, is no more. But as of today, I became the proud owner of a MALÉV TU-154 B-2, with the original MALÉV markings.
No, not the real thing, I’m not that rich (and even if I were that rich, I’d not be spending my money on obsolete Russian aircraft), just a beautiful diecast model. Still, it’s a nice reminder.
I completely forgot: four days ago was the 25th anniversary of my arrival in Canada as a landed immigrant. I never had a reason to regret my choice… in fact, politics of the day notwithstanding, I appreciate this country more than ever.
I just came across a photograph of a building that looks like one of the abandoned edifices in the ghost city of Prypiat, right next to the Chernobyl nuclear power station. Indeed, the picture appeared in a Facebook blog that features many pictures from Prypiat… but this wasn’t one of them.
Instead, the picture was taken in Hungary, on the south shore of Lake Balaton. The building is an abandoned hotel that before the collapse of Communism served as a resort, owned by the Hungarian Industrial Association. I spent nights at that resort. In particular, I spent nights in this very building shown in the picture.
What I found most striking is that the building looks exactly the same as it did 30-odd years ago (except for the decay, of course). It was apparently never modernized. Never really renovated. Presumably, it was privatized some time after 1989, served as a hotel for a while, and then it was abandoned… but it still looks exactly the same (insofar as I can remember) as it did back in the late 1970s.
I guess I now have a better appreciation of how residents of Prypiat feel when they come across present-day photographs of their once proud town. It is an eerie feeling.
Having been told by a friend that suddenly, there is a spate of articles online about the Pioneer anomaly, I was ready to curse journalists once I came across the words: “a programmer in Canada, Viktor Toth, heard about the effort and contacted Turyshev. He helped Turyshev create a program …”.
To be clear: I didn’t contact Slava; Slava contacted me. I didn’t “help create a program”; I was already done creating a program (which is why Slava contacted me). And that was the state of things back in 2005. What about all the work that I have done since, in the last seven years? Like developing a crude and then a more refined thermal model, independently developing precision orbit determination code to confirm the existence of the anomaly, collaborating with Slava on several papers including a monster review paper published by Living Reviews in Relativity, helping shape and direct the research that arrived at the present results, and drafting significant chunks of the final two papers that appeared in Physical Review Letters?
But then it turns out that journalists are blameless for a change. They didn’t invent a story out of thin air. They just copied the words from a NASA JPL press release.
And I am still trying to decide if I should feel honored or insulted. But then I am reminding myself that feeling insulted is rarely productive. So I’ll go with feeling honored instead. Having my contribution acknowledged by JPL is an honor, even if they didn’t get the details right.