May 212016
 

Not for the first time, I am reading a paper that discusses the dark matter paradigm and its alternatives.

Except that it doesn’t. Discuss the alternatives, that is. It discusses the one alternative every schoolchild interested in the sciences knows about (and one that, incidentally, doesn’t really work) while ignoring the rest.

This one alternative is Mordehai Milgrom’s MOND, or MOdified Newtonian Dynamics, and its generalization, TeVeS (Tensor-Vector-Scalar theory) by the late Jacob Bekenstein.

Unfortunately, too many people think that MOND is the only game in town, or that even if it isn’t, it is somehow representative of its alternatives. But it is not.

In particular, I find it tremendously annoying when people confuse MOND with Moffat’s MOG (MOdified Gravity, also MOffat Gravity). Or when similarly, they confuse TeVeS with STVG (Scalar-tensor-Vector Gravity), which is the relativistic theory behind the MOG phenomenology.

So how do they differ?

MOND is a phenomenological postulate concerning a minimum acceleration. It modifies Newton’s second law: Instead of \(F = ma\), we have \(F = m\mu(a/a_0)a\), where \(\mu(x)\) is a function that satisfies \(\mu(x)\to 1\) for \(x\gg 1\), and \(\mu(x)\to x\) for \(x\ll 1\). A good example would be \(\mu(x)=1/(1+1/x)\). The magnitude of the MOND acceleration is \(a_0={\cal O}(10^{-10})~{\rm m}/{\rm s}\).

The problem with MOND is that in this form, it violates even basic conservation laws. It is not a theory: it is just a phenomenological formula designed to explain the anomalous rotation curves of spiral galaxies.

MOND was made more respectable by Jacob Bekenstein, who constructed a relativistic field theory of gravity that approximately reproduces the MOND acceleration law in the non-relativistic limit. The theory incorporates a unit 4-vector field and a scalar field. It also has the characteristics of a bimetric theory, in that a “physical metric” is constructed from the true metric and the vector field, and this physical metric determines the behavior of ordinary matter.

In contrast, MOG is essentially a Yukawa theory of gravity in the weak field approximation, with two twists. The first twist is that in MOG, attractive gravity is stronger than Newton’s or Einstein’s; however, at a finite range, it is counteracted by a repulsive force, so the gravitational acceleration is in fact given by \(a = GM[1+\alpha-\alpha(1+\mu r)e^{-\mu r}]\), where \(\alpha\) determines the strength of attractive gravity (\(\alpha=0\) means Newtonian gravity) and \(\mu\) is the range of the vector force. (Typically, \(\alpha={\cal O}(1)\), \(\mu^{-1}={\cal O}(10)~{\rm kpc}\).) The second twist is that the strength of attractive gravity and the range of the repulsive force are both variable, i.e., dynamical (though possibly algebraically related) degrees of freedom. And unlike MOND, for which a relativistic theory was constructed after-the-fact, MOG is derived from a relativistic field theory. It, too, includes a vector field and one or two scalar fields, but the vector field is not a unit vector field, and there is no additional, “physical metric”.

In short, there is not even a superficial resemblance between the two theories. Moreover, unlike MOND, MOG has a reasonably good track record dealing with things other than galaxies: this includes globular clusters (for which MOND has to invoke the nebulous “external field effect”), cluster of galaxies (including the famous Bullet Cluster, seen by some as incontrovertible proof that dark matter exists) and cosmology (for which MOND requires something like 2 eV neutrinos to be able to fit the data.)


MOG and the acoustic power spectrum. Calculated using \(\Omega_M=0.3\), \(\Omega_b=0.035\), \(H_0=71~{\rm km}/{\rm s}/{\rm Mpc}\). Also shown are the raw Wilkinson Microwave Anisotropy Probe (WMAP) three-year data set (light blue), binned averages with horizontal and vertical error bars provided by the WMAP project (red) and data from the Boomerang experiment (green). From arXiv:1104.2957.

There are many issues with MOG, to be sure. Personally, I have never been satisfied with the way we treated the scalar field so far, and I’d really like to be able to derive a proper linearized version of the theory in which the scalar field, too, is accommodated as a first-class citizen. How MOG stands up to scrutiny in light of precision solar system data at the PPN level is also an open question.

But to see MOG completely ignored in the literature, and see MOND used essentially as a straw man supposedly representing all attempts at creating a modified gravity alternative to dark matter… that is very disheartening.

 Posted by at 5:23 pm
May 202016
 

CNN reports that ACARS messages received from MS804 in the minutes before its disappearance indicate a fire on board.

I was able to find online a copy of the screenshot discussed by CNN:

CNN’s talking heads are still discussing the terrorism theory, but in light of these data, it looks increasingly unlikely. It is very difficult to imagine a terrorism scenario that begins with one of the cockpit windows.

 Posted by at 8:25 pm
May 182016
 

In the fourth volume of the Hitchhiker’s Guide to the Galaxy “trilogy”, we learn that just before the Earth was about to be destroyed by the Vogons to make way for a new interstellar bypass, the whales left. They left behind a simple parting message: “So long and thanks for all the fish.”

Which makes me feel rather alarmed now that I am learning that hundreds of North Atlantic right whales went missing. I hope it’s not a bad sign.

 Posted by at 7:55 pm
May 182016
 

A question on Quora made me reminisce about old computer games that make me feel somewhat nostalgic.

I’ve been involved with computer games both as a player and in a professional capacity for a very long time.

Long before I laid my hands on a personal computer, I was an avid player of Trek on a PDP/11. This was a game written for text terminals, simulating the mission of the Starship Enterprise through Klingon-infested space:

Another game of similar vintage, which I used to play on a peer-to-peer QNX network, is Hack:

Then there was the Commodore-64. Here are two Commodore-64 games that I remember fondly. Impossible Mission:

And Jumpman:

After the Commodore-64 came the Amiga. One of the first games I played on the Amiga 500 was the absolutely surrealist Mind Walker:

Very weird game. Memorable, algorithm-generated music. Ahead of its time.

Moving on to the PC (actually, I first played these on the Atari ST), there are the classic INFOCOM games. (Yes, I am taking the liberty of classifying pure text adventure games as “video games”.) Best known perhaps is Zork:

But there was also the unforgettable apocalyptic story of Trinity:

The equally unforgettable A Mind Forever Voyaging in which you get to play a disembodied artificial intelligence:

And the hilarious Hitchhiker’s Guide to the Galaxy with its fiendishly impossible puzzles:

Still on the text game front, back in 1991 I began playing what was for me the first multiplayer online game, British Legends, aka. MUD (Multi-User Dungeon):

Meanwhile, on my PC, I was busy playing Duke Nukem, its platform versions first, eventually moving on to Duke Nukem 3D (which exists to this day in a community supported 32-bit high-resolution version, complete with NSFW imagery):

And then came Myst, the “killer app” for CD-ROMs:

Last but not least, a game that gave me tremendous amounts of joy, Lands of Lore: Guardians of Destiny (with none other than Patrick Stewart lending his voice acting skills to the CD version):

I remember all these games very fondly. And they are all still eminently playable, and very enjoyable, to this day.

 Posted by at 3:42 pm
May 112016
 

No, I am not using expletives.

Or rather, I’ve been using some expletives, but *#0808# is not code for one of them.

It is an actual code that I can enter into my Samsung phone to get to a service menu that allows me to re-enable USB functions that somehow got turned off.

Although it took only about 15 minutes to find this particular code, it marked the end of a rather frustrating 24 hours. Last night, as it was just about to complete installing 24 Microsoft updates, my workstation locked up. The incomplete installation of updates managed to mess up my Microsoft Office setup, and made it impossible to install some still missing updates. Which meant that I had to use System Restore to get back to a known-good state first, and then redo the updates.

As a result, much of my day was consumed (and it’s not like I slept much last night either.) And as if that wasn’t enough, my phone also suddenly decided that it didn’t want to connect to my workstation anymore… hence my need for the aforementioned code.

All is well that ends well, though, and in the end I managed to install everything. It’s just that those hours of my life that I lost, I’ll never get them back.

It also reinforced my conviction that I made the right decision when, a few days ago, I decided to invest some money and purchase parts for a new workstation and server. It’s about bleeping time… this machine served me well for over seven (!) years, and seven years in this profession is almost an eternity.

Still waiting for some of the parts though. Although I ordered everything from the same supplier, NewEgg.ca, the shipments come from at least four different locations in North America.

 Posted by at 8:47 pm
May 052016
 

And just when you least expect it… Russia celebrates its victories in Syria over ISIL with a class act, an amazing concert by the Mariinsky Theatre Orchestra of St. Petersburg, held at the ancient amphitheater that is at the center of Palmyra’s Roman era ruins, badly damaged (not to mention desecrated with barbaric public executions) by the Islamic State.

Russia, of course, intervened not for reasons of altruism but because American indecisiveness offered them an opportunity to prop up Assad’s regime. Nonetheless, I much rather watch an amazing concert like this than public beheadings.

And the music was, in fact, amazing. It included a piece titled Quadrille, from contemporary Russian composer Rodion Shchedrin’s opera Not Love Alone. I think I ought learn a little more about contemporary Russian opera.

The concert was carried live (of course) by RT, complete with a televised greeting by Putin. Not unlike a similar concert that the same orchestra held in South Ossetia, after Russia’s brief war with the Republic of Georgia a few years ago.

 Posted by at 11:12 pm
Apr 292016
 

When you contribute on Quora as I do, Quora may reward you by declaring you a “most viewed writer” in select topics.

What I didn’t realize is that Quora’s powers reach not only beyond planet Earth, but also beyond the boundaries of our physical universe.

A few months ago, Quora declared me most viewed not just in this universe but in parallel universes:

But if you thought this cannot be topped, here is the latest: I am now a most viewed writer in the whole multiverse!

Wow. I really feel special.

 Posted by at 11:13 am
Apr 262016
 

This is an eerie anniversary.

Thirty years ago today, reactor 4 of the Chernobyl nuclear power plant blew to smithereens.

It’s really hard to assign blame.

Was it the designers who came up with a reactor design that was fundamentally unstable at low power?

Was it the bureaucrats who, in the secretive Soviet polie state, made it hard if not impossible for operators at one facility to learn from incidents elsewhere?

Was it the engineers at Chernobyl who, concerned about the consequences of a total loss of power at the station, tried to test a procedure that would have kept control systems and the all-important coolant pumps running using waste heat during an emergency shutdown, while the Diesel generators kicked in?

Was it the Kiev electricity network operator who asked Chernobyl to keep reactor 4 online for a little longer, thus pushing the planned test into the late night?

Was it the control room operator who ultimately pushed the button that initiated an emergency shutdown?

And the list continues. Many of the people we could blame didn’t stick around long enough: they died, after participating in often heroic efforts to avert an even greater disaster, and receiving lethal doses of radiation.

Some lived. This photo shows Arkady Uskov, who suffered severe radiation burns 30 years ago as he helped save colleagues. He, along with a few other people, recently revisited the control room of reactor 4, and were photographed there by Radio Free Europe. (Sadly, the photos are badly mislabeled by someone who didn’t know that “Arcadia Uskova” would be the name of a female; or, in this case, the genitive case of the male name Arkady Uskov. Thus I also cannot tell if “Oleksandr Cheranov”, whose name I cannot find anywhere else in the literature of Chernobyl, was a real person or just another RFE misprint.)

Surprisingly, the control room, which looks like a set of props from a Cold War era science fiction movie, is still partially alive. The lit panels, I suspect, must be either part of the monitoring effort or communications equipment.

It must have been an uncanny feeling for these aging engineers to be back at the scene, 30 years later, contemplating what took place that night.

Incidentally, nuclear power remains by far the safest in the world. Per unit of energy produced, it is dozens of times safer than hydroelectricity; a hundred times safer than natural gas; and a whopping four thousand times safer than coal. And yes, this includes the additional approximately 4,000 premature deaths (UN estimate) as a result of Chernobyl’s fallout. Nor was Chernobyl the deadliest accident related to power generation; that title belongs to China’s Banqiao Dam, the failure of which claimed 171,000 lives back in 1975.

 Posted by at 5:52 pm
Apr 212016
 

Her Majesty, Elizabeth II, Queen of Canada (and a bunch of other countries that I care a great deal less about as I don’t happen to live there) was born 90 years ago today.

She is my favoritest Queen. May she enjoy many more happy birthdays in good health.

 Posted by at 10:23 am
Apr 192016
 

I have been, and will continue to be, critical of many of the policies of Israel. I think that the policy of occupation, while tactically perhaps important, is a political dead end in the long term. I think it is in Israel’s best interest to help create a viable, strong Palestinian state, as any other solution leaves the Palestinian people in perpetual misery, and may ultimately lead to Israel’s own destruction.

That said… anyone who suggests a moral equivalency between Israel’s policy of occupation and Palestinian terror ought to look at such artistic gems like this Hamas cartoon from yesterday:

Line Jerusalem-Hell

Line Jerusalem-Hell

I don’t think even the most rabid far-right press outlet in Israel would find it suitable to publish a cartoon that ridicules the suffering of Palestinian civilians. The fact that Hamas (and many other Arabic press outlets) think it’s okay to publish stuff like this speaks volumes.

I have little doubt that Netanyahu’s government will retaliate. I also have little doubt that they will not target civilian buses on Gaza; on the contrary, they will make quite an effort to avoid civilian casualties. I also have little doubt that they will not be successful, and given Israeli firepower, a number, perhaps a sizable number of Palestinian civilians will die, and Israel will be the target of severe criticism, much of it well deserved.

But as you wonder who the real injured party is in this never-ending conflict, look at that cartoon again and ask yourself: who is it who actually glorifies violence on civilians, who is it who believes that the indiscriminate killing of civilians is something to be encouraged and celebrated?

And in case this one cartoon is not sufficient, do yourself a favor and search a little bit on Google. Some of the published anti-Israeli cartoons are so depraved, even Hamas disowns them. No, not because they have any sense of remorse, simply the explicit depiction of the rape of an Arab woman by a Jew was too much in conflict with their, oh, Islamic sense of modesty I guess, and they were also concerned that they may have offended their West Bank brethren by making them appear too submissive. Ah, here it is:

Gaza man: “West Bank, get up and defend your honor and your children!”
West Bank woman: “Yes, I would like to, but I have no permit.”

Lovely artwork, isn’t it? Shows a deep concern for humanity, civil rights and all. Dr. Göbbels would be proud.

 Posted by at 9:24 am
Apr 152016
 

Not for the first time, one of my Joomla! sites was attacked by a script kiddie using a botnet.

The attack is a primitive brute force attack, trying to guess the administrator password of the site.

The frustrating thing is that the kiddie uses a botnet, accessing the site from several hundred remote computers at once.

A standard, run-of-the-mill defense mechanism that I installed works, as it counts failed password attempts and blocks the offending IP address after a predetermined number of consecutive failures.

Unfortunately, it all consumes significant resources. The Joomla! system wakes up, consults the MySQL database, renders the login page and then later, the rejection page from PHP… when several hundred such requests arrive simultaneously, they bring my little server to its knees.

I tried as a solution a network-level block on the offending IP addresses, but there were just too many: the requests kept coming, and I became concerned that I’d have an excessively large kernel table that might break the server in other ways.

So now I implemented something I’ve been meaning to do for some time: ensuring that administrative content is only accessible from my internal network. Anyone accessing it from the outside just gets a static error page, which can be sent with minimal resource consumption.

Now my server is happy. If only I didn’t need to waste several hours of an otherwise fine morning because of this nonsense. I swear, one of these days I’ll find one of these script kiddies in person and break his nose or something.

 Posted by at 11:50 am
Apr 102016
 

I’ve been encountering an increasing number of Web sites lately that asked me to disable my ad blocker. They promise, in return, fewer ads.

And with that promise, they demonstrate that they completely and utterly miss the point.

I don’t want fewer ads. I don’t mind ads. I understand that for news Web sites, ads are an essential source of revenue. I don’t resent that. I even click on ads that I find interesting or relevant.

So why do I use an ad blocker, then?

In one word: security.

Malicious ads showed up even on some of the most respectable Web sites. Ad networks have no incentive to vet ads for security, so all too often, they only remove them after the fact, after someone complained. And like a whack-a-mole game, the malicious advertiser is back in no time under another name, with another ad.

And then there are those ads that pop up with an autostart video, with blaring sound in the middle of the night, with the poor user (that would be me) scrambling to find which browser tab, which animation is responsible for the late night cacophony.

Indeed, it was one of these incidents that prompted me to call it quits on ads and install an ad blocker.

So sorry folks, if you are preventing me from accessing your content because of my ad blocker, I just go elsewhere.

That is, until and unless you can offer credible assurance that the ads on your site are safe. I don’t care how many there are. It’s self-limiting anyway: advertisers won’t pay top dollar for an ad on a site that is saturated with ads. What I need to know is that the ads on your site won’t ruin my day one way or another.

 Posted by at 9:19 am
Apr 092016
 

This beautiful image is a frame capture of the latest SpaceX first stage rocket, moments after its successful landing on the drone ship Of Course I Still Love You (yes, that really is the drone ship’s name) last night:

The landing was a little sloppy. I mean, look how far off-center the rocket happens to stand.

Still… I am seriously beginning to believe that Elon Musk may accomplish his ultimate goal within my lifetime: the beginning of the human colonization of Mars.

To live long enough to see the first human set foot on Mars… now that’s a dream worth living for.

 Posted by at 10:21 am
Apr 082016
 

I just finished reading an online-only novel, Armageddon, part of The Salvation Wars series, originally planned as a trilogy by author Stuart Slade.

The premise: God gave up on the Earth, and let it be known that from now on, it all belongs to Satan. However… Earthlings fight back. And pity the poor demon with his pitchfork when he is confronted with machine gun bullets, cluster bombs, incendiary bombs or Sarin gas, brought about by an impersonal modern military machine that is designed to destroy and annihilate its enemy… and then they haven’t even seen the worst of it yet.

And just as I was finishing the book, I came across this GIF meme: a machine, crucifying Christ at a rate of about one crucifixion per second. And suddenly, I started to feel really sorry for Hell’s demons.

OK, I may be the stupid atheist here, but I find this short clip more than creepy. It speaks volumes about the human race, about what we became and where we are heading, and none of it is nice.

 Posted by at 1:22 am
Apr 072016
 

News item from Google news: Ottawa taxi drivers plan to blockade city bus depots.

Oh really? You jackasses really believe that this is the way to gain support at Ottawa city hall?

OK, they now claim that it’s just a rumor. I am not convinced.

I hope your industry dies, like, yesterday.

Not long ago, I was committed to using regular taxis (on the rare occasions I needed one) and not rely on untested, unproven, new services like Uber.

It was the taxi industry and their thuggish reaction to Uber’s disruptive technology that convinced me otherwise.

Thugs have no place on our city’s streets. Not even when they are masquerading as licensed taxi drivers.

Perhaps if, instead of acting like a criminal gang, you had focused on making your cars cleaner, your service more reliable, your drivers better dressed and better behaved, most of us would still remain committed to your service.

 Posted by at 1:57 am
Apr 022016
 

Sometime last year, I foolishly volunteered to manage new releases of the Maxima computer algebra system (CAS).

For the past several weeks, I’ve been promising to do my first release, but I kept putting it off as I had other, more pressing work obligations.

Well, not anymore… today, I finally found the time, after brushing up on the Git version management system, and managed to put together a release, 5.38.0.

maxima

Maxima is beautiful and incredibly powerful. I have been working on its tensor algebra packages for the past 15 years or so. As far as I know, Maxima is the only general purpose CAS that can derive the field equations of a Lagrangian field theory; for instance, it can derive Einstein’s field equations from the Einstein-Hilbert Lagrangian.

I use Maxima a lot for tensor algebra, though I admit that when it comes to integration, differential equations or plotting, I prefer Maple. Maple’s ODE/PDE solvers are unbeatable. But when it comes to tensor algebra, or just as a generic on-screen symbolic calculator, Maxima wins hands down. I prefer to use its command-line version: Nothing fancy, just ASCII art, but very snappy, very responsive, and does exactly what I want it to do.

So then, Maxima 5.38.0: Say hi to the world. World, this is the latest version of the oldest (nearly half a century old) continuously maintained CAS in existence.

 Posted by at 9:31 pm
Apr 012016
 

Here is a rather entertaining piece of video evidence demonstrating that at least some lessons of history are not forgotten:

As they say, “We know where assholery leads… You will learn if even we were teachable!” Although judging from the comments on YouTube, not everyone is ready to learn these lessons yet.

Still… seeing several right-wing European politicians, including Hungary’s Orban (2:16), with Donald Trump’s toupee… priceless.

 Posted by at 1:50 pm
Mar 292016
 

Until recently, this used to be one of my favorite deep space images:

It is a frozen lake in the Ruach Planitia region of Neptune’s Moon Triton: an incredibly distant, dark and desolate world.

OK, the image is still one of my favorites, but on my list of favorites, it’s just been taken over by this one:

That, ladies and gentlemen, is a large (about 30 km) frozen lake (most likely frozen nitrogen), in the Sputnik Planum region of the planet Pluto.

Who would have thought that Pluto, the recently demoted ex-planet, a frozen world at the edge of the solar system, would have such complex climate and such a fascinating geological history?

Wow.

 Posted by at 9:35 am