Jan 202017

Enough blogging about politics. It’s time to think about physics. Been a while since I last did that.

A Facebook post by Sabine Hossenfelder made me look at this recent paper by Josset et al. Indeed, the post inspired me to create a meme:

The paper in question contemplates the possibility that “dark energy”, i.e., the mysterious factor that leads to the observed accelerating expansion of the cosmos, is in fact due to a violation of energy conservation.

Sounds kooky, right? Except that the violation that the authors consider is a very specific one.

Take Einstein’s field equation,

$$R_{\mu\nu}-\tfrac{1}{2}Rg_{\mu\nu}+\Lambda g_{\mu\nu}=8\pi GT_{\mu\nu},$$

and subtract from it a quarter of its trace times the metric. The trace of the left-hand side is \(-R+4\Lambda\), the right-hand side is \(8\pi GT\), so we get

$$R_{\mu\nu}-\tfrac{1}{4}Rg_{\mu\nu}=8\pi G(T_{\mu\nu}-\tfrac{1}{4}Tg_{\mu\nu}).$$

Same equation? Not quite. For starters, the cosmological constant \(\Lambda\) is gone. Furthermore, this equation is manifestly trace-free: its trace is \(0=0\). This theory, which was incidentally considered already almost a century ago by Einstein, is called trace-free or unimodular gravity. It is called unimodular gravity because it can be derived from the Einstein-Hilbert Lagrangian by imposing the constraint \(\sqrt{-g}=1\), i.e., that the volume element is constant and not subject to variation.

Unimodular gravity has some interesting properties. Most notably, it no longer implies the conservation law \(\nabla_\mu T^{\mu\nu}=0\).

On the other hand, \(\nabla_\mu(R^{\mu\nu}-\tfrac{1}{2}Rg^{\mu\nu})=0\) still holds, thus the gradient of the new field equation yields

$$\nabla_\mu(\tfrac{1}{4}Rg^{\mu\nu})=8\pi G\nabla_\mu(T^{\mu\nu}-\tfrac{1}{4}Tg^{\mu\nu}).$$

So what happens if \(T_{\mu\nu}\) is conserved? Then we get

$$\nabla_\mu(\tfrac{1}{4}Rg^{\mu\nu})=-8\pi G\nabla_\mu(\tfrac{1}{4}Tg^{\mu\nu}),$$

which implies the existence of the conserved quantity \(\hat{\Lambda}=\tfrac{1}{4}(R+8\pi GT)\).

Using this quantity to eliminate \(T\) from the unimodular field equation, we obtain

$$R_{\mu\nu}-\tfrac{1}{2}Rg_{\mu\nu}+\hat{\Lambda} g_{\mu\nu}=8\pi GT_{\mu\nu}.$$

This is Einstein’s original field equation, but now \(\hat{\Lambda}\) is no longer a cosmological constant; it is now an integration constant that arises from a conservation law.

The vacuum solutions of unimodular gravity as the same as those of general relativity. But what about matter solutions? It appears that if we separately impose the conservation law \(\nabla_\mu T^{\mu\nu}\), we pretty much get back general relativity. What we gain is a different origin, or explanation, of the cosmological constant.

On the other hand, if we do not impose the conservation law for matter, things get interesting. In this case, we end up with an effective cosmological term that’s no longer constant. And it is this term that is the subject of the paper by Josset et al.

That being said, a term that is time-varying in the case of a homogeneous and isotropic universe surely acquires a dependence on spatial coordinates in a nonhomogeneous environment. In particular, the nonconservation of \(T_{\mu\nu}\) should lead to testable deviations in certain Parameterized Post-Newtonian (PPN) parameters. There are some reasonably stringent limits on these parameters (notably, the parameters \(\alpha_3\) and \(\zeta_i\) in the notation used by Clifford Will in the 1993 revision of his book, Theory and experiment in gravitational physics) and I wonder if Josset et al. might already be in violation of these limits.

 Posted by at 9:43 pm
Jan 202017

It is well known that the despicable Biff Tannen character from the Back to the Future movies was based on a certain real-life despicable mogul by the name of Donald J. Trump. In particular, the “rich Biff” of 1985, having established a casino and real estate empire after receiving a sports almanac from the future back in 1955, was modeled after everyone’s favorite Trump.

In light of this and today’s historic events, it is only appropriate to imagine how the real-life Biff, I mean Trump, would have fared in one of the movies’ iconic scenes:

I hate manure…

Yes, I know it is more than a little crass to share this tweet. Even so, it is far less distasteful than the many racist caricatures that followed Obama’s inauguration and frankly, it makes it a lot easier to deal with this historic day.

 Posted by at 4:24 pm
Jan 142017

So here is another thing I don’t expect to see from Donald Trump: Publishing an article in the highly respected multidisciplinary journal Science.

His predecessor, the still sitting Barack Obama did just that: his article about “The irreversible momentum of clean energy” was published yesterday, January 13, 2017. In it, he makes the case that economic growth does not depend on energy-related emissions, and that combating climate change does not require accepting lower growth or a reduced standard of living.

 Posted by at 9:33 pm
Jan 142017

I just saw this US Defense Department video about a swarm of high speed drones released at altitude by an F/A-18. The drones communicated with each other, self-organized, and went on to execute predetermined tasks autonomously.

In case anyone is wondering why I worry about the future of AI, this is a perfect demonstration.

Meanwhile, the Defense Department is also continuing its trials of the Sea Hunter, a 132-ft, 145-ton unmanned, autonomous vessel designed to hunt submarines.

Don’t worry, the brave new world is coming…

 Posted by at 9:22 pm
Jan 102017

I just finished listening to Obama’s farewell address.

Now why do I have the feeling that this may be the very last time in my life that I’ll be hearing an American President preach goodness and decency instead of contempt and hate? Uplifting thoughts instead of fear and loathing?

Meanwhile, there appears to be a multitude of clowns on the Interwebs who think repealing Obamacare is okay, because they are insured through the Affordable Care Act:

What can I say? Enjoy your improved healthcare starting next month, folks. Glad I live in pinko commie Canada where we have had decent (albeit far from perfect) medicare for half a century. Of course once Trump, along with his BFF Putin, manage to blow up the world, none of this will matter anymore.

 Posted by at 10:05 pm
Jan 082017

Here is a quote from one of my favorite novels, Jack London’s Smoke Bellew:

“The world’s gone smash. There’s nothin’ regular an’ uniform no more. The multiplication table’s gone loco. Two is eight, nine is eleven, and two-times-two is eight hundred an’ forty-six—an’—an’ a half. Anything is everything, an’ nothing’s all, an’ twice all is cold-cream, milk-shakes, an’ calico horses.”

Why this particular quote? Because I was reading about Trump’s infamous medical report, prepared by a Harold N. Bornstein, MD, from the great city of New York. The doctor is real, but the medical report is… weird (reproduced below.) Apparently, Mr. Trump tests positive for everything.

But what is even weirder is the doctor himself and his Web site. Once a respectable site advertising a family practice, today it redirects to a site that sells an annoying teddy bear.

I kid you not. A site that sells “The Original Annoying Happy Birthday Teddy, the bear that never stops singing ‘Happy Birthday to you…'”.

So perhaps that explains why I think that anything is everything, an’ nothing’s all, an’ twice all is cold-cream, milk-shakes, an’ calico horses.

Or maybe I got high on something without realizing it.

I mean… is there anything about America’s esteemed President-Elect that is not a boldfaced lie?

 Posted by at 1:14 am
Jan 042017

The Emperor has no clothes.

Sycophants praise his choices. The lush fabric. The elegant, fashionable tailoring. The beautiful stitching.

Yet the Emperor has no clothes.

Unfortunately, even his critics no longer acknowledge this fact. They criticize his clothes. They question his taste in garments. They reject the gaudy colors. They ridicule the bad workmanship.

But none have the courage to tell the world the truth: This Emperor is naked.

And thus it came that the lessons of history are once again forgotten, and all its mistakes are yet again set to be repeated.

 Posted by at 1:34 pm
Jan 022017

I captured this close captioning gem several days ago but then promptly forgot about it.

I know, I know, it’s not easy to caption a conversation in real time. But it was still hilariously funny. Thanks for a good morning laugh.

For what it’s worth, as I recall the word that was actually used was “agree”. How that turned into “pee”, I have no idea.

 Posted by at 8:37 pm
Dec 252016

Today, I was trying to explain to someone the difference between entering a Web site’s address in the address field of a Web browser, vs. entering a search term in Google. I was not very successful. In the end, it doesn’t really matter… Google happily accepts a Web site address in its search field, and all modern browsers accept search terms in the address field, passing it on to the preconfigured search provider.

But this experience reminded me of a clip from Star Trek IV: The Voyage Home. It’s when Scotty and McCoy talk to a factory manager and Scotty tries to show the chemical formula for “transparent aluminum”. When McCoy suggests the use of a computer, on old Mac sitting on a desk nearby, Scotty first tries to talk to it; and when McCoy helpfully points at the mouse, Scotty picks it up as though it was a microphone tries talking into it.

What I realized is that thirty years later, we basically gave up on the idea of trying to educate users. If that computer was built today, with users like Scotty in mind, we’d just put a damn microphone into the bleeping mouse. It’s just easier that way.

 Posted by at 10:09 am
Dec 242016

Once again, I feel compelled to use the same image and same words that I have been using for many years, to wish all my family, all my friends, indeed everyone on the good Earth a very merry Christmas: the words of the astronauts of Apollo 8.

I know, I know, it’s the same thing every year. But there really aren’t any better words. Just imagine: three human beings, for the first time in human history, far from the Earth, in orbit around another celestial body. And back on Earth, one of the most troubled years in recent history: 1968. So on Christmas Eve, with about a billion people listening—a full one quarter of the Earth’s population at the time—they greeted us Earthlings with the opening passages from the Book of Genesis, the common creation mythology of several major religions.

And then Frank Borman ended the broadcast with words that are as appropriate today as we are heading towards more troubled times as they were back then: “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.”

 Posted by at 9:10 am
Dec 232016

Last night, after I watched the final episode of an amazing Brazilian television series, 3% (yes, that’s the title) on Netflix, I felt compelled to listen to the immortal song Aquarela do Brasil, especially the Geoff Muldaur version that was the title song for Terry Gilliam’s film Brazil.

As I was listening to the song, I realized that along with Vera Lynn’s We’ll Meet Again, it’s one of the songs I’d like to listen to when the world comes to an end.

Runner-ups include Nena’s 99 Luftballons and Anita Kelsey’s version (known from the film Dark City) of Sway (¿Quién será?)

As to why I am thinking about the end of the world…

 Posted by at 12:26 pm
Dec 182016

I have been so busy this week, I forgot to blog about our latest Maxima release, 5.39. Nothing spectacular, just incremental improvements over 5.38; for me, this was a big milestone though as this was the first time that I used a CentOS platform to prepare the release. (Which, incidentally, is why I haven’t done this months ago.)

And SourceForge, kindly enough, once again designated Maxima as one of the site’s Projects of the Week.

 Posted by at 1:23 am
Dec 152016

I saw this question on Quora and I could not resist: I just felt compelled to offer my take, against my better judgment.

So here is how, in my opinion, you make fastest Everyone Dies™:

My answer is purely hypothetical. It is about a yet-to-be-discovered planet and the civilization that lives there. It is a piece of science-fiction. Any similarities to real persons, be they living or dead, are purely coincidental.

  1. Pick an incompetent, thin-skinned, narcissistic tycoon as the next leader of the country possessing the most powerful military that ever existed on the planet, with a nuclear arsenal capable of killing everyone several times over.
  2. Pick a highly competent, murderous sociopath, a former secret agent of a totalitarian superstate, as the ruler of the country possessing the second most powerful military that ever existed on the planet, with a nuclear arsenal capable of killing everyone several times over.
  3. Let #1 think that he can trust and he can be BFF with #2 and thus go down in history as the greatestest and bestest leader ever.
  4. Let #2 think that he can rely on the naivety, incompetence, and egotism of #1 to accomplish the goal of restoring his country’s lost pride and possessions.
  5. Sit back and watch the show. Consider yourself blessed that you are a) in your fifties, b) have no children to worry about, and c) that you live near the downtown core of a capital city, so that when the inevitable flash comes, you will not even notice it as you are instantaneously vaporized along with your spouse, cats and all worldly possessions.

As I said, this is a piece of fiction, for entertainment purposes only. Any similarities you might notice to real persons or events are purely coincidental. Happy Holidays!

 Posted by at 10:30 am
Dec 132016

This morning, when I woke up, the regular status e-mails that my servers greet me with told me that there is a major CentOS update (version 7.3). Cool. Unfortunately, it meant that I needed to upgrade as many as five servers. This includes my main server, its physical backup, my backup server in NYC, another “in cloud” backup, and yet another server that I help administer. I began this process shortly after 8 in the morning, after I finished breakfast.

And as usual, a major upgrade like this brings to the surface little problems, little annoyances such as folders that had incorrectly configured SELinux permissions. No big deal, to be sure, but several such little things can consume hours of your time.

And then, it was also Microsoft Patch Tuesday, the second Tuesday of the month when Microsoft releases scheduled updates to Windows and other products. As soon as I was done with CentOS, my attention turned to my Windows machines, including my main workstation, its backup (actually, the same physical machine that also acts as my server’s backup in a dual-boot configuration), my wife’s desktop computer, two laptops, and last but not least, my old desktop that I still keep around as a backup/test computer.

Moreover, I also decided to update three virtual machines (one running Windows 7, the other two, Windows XP) that I keep around both for test purposes but also to have older software, older configurations available if needed.

Furthermore, when I update Windows, I tend to check and see if any other software packages need updating. On some computers, I run Secunia PSI, which keeps track of many applications. But even on other systems, I had to update Java (if installed), Adobe Flash, Chrome and Firefox.

And on older hardware, the process can be painfully slow.

To make a long story short, by the time I finished the bulk of this work, it was 7:30 in the evening. And one computer (a really low powered old netbook) is still doing its thing, even though it’s well past 11 PM now.

No wonder I didn’t accomplish much today.

Of course all of this needed to be done. Since I am a one-man band, I don’t have an IT department to rely on, but it is still important for me to keep my systems secure and well-maintained.

Nonetheless, it feels like one hell of a waste of a day.

 Posted by at 11:22 pm
Dec 042016

Last night, I went for a nice, long walk, maybe the last before the real snow comes and walking is no longer fun.

My route took me around several government buildings here in Ottawa Lowertown. Here is one of them, with some rather unusual light effects due to some low-hanging clouds and a partially closed bridge that is under renovation:

The picture doesn’t really give justice to the eerie, otherworldly light effects that I saw.

Later on during my walk, I looked through the glass front of an important government building that shall remain unnamed. Why? Because when I looked into the lobby, I saw not one but two uniformed security personnel… with their backs facing the front door, as they were both intently watching a television screen on which a hockey game was playing.

Ah, Canada! What a blessed country we are. And I am not naming the building because I don’t want these good people to get into any trouble, nor do I want to give any bad people ideas.

That said, I was tempted to snap a picture of these two. I decided not to do so… discretion is the better part of valor, and besides, who knows, maybe someone else was watching me, after all, through a security camera.

 Posted by at 11:50 pm
Nov 252016

I just read this article, arguing that the narrative, according to which “coastal elites” need to make an effort to understand rural America better, is woefully misguided and counterproductive.

The author’s point is that no, it’s not the coastal elites who fail to understand the woes of rural America. It’s rural America who fail to understand the causes of their own suffering. And a root cause among these is fundamentalist religion, which not only shape their belief systems (including racism and bigotry) but also expose them to demagogues, like TV preachers, who exploit them. Or, for that matter, billionaire presidential candidates who think living in the White House is so passé, as the toilets are not made of gold or whatever.

And thus it came that rural Americans routinely reject political ideas that benefit them, and routinely vote back into office Republican politicians, serving in local and state governments, whose policies do them the most harm.

The author admits that he has no good solution. But I think he is right about the fact that it’s not the coastal elites’ lack of understanding of rural America that is the problem.

 Posted by at 2:36 pm
Nov 232016

This was a potential nightmare scenario. Imagine if we found out that the swing state results of the Nov. 8 election were altered by hackers. Imagine if an investigation found that Hillary Clinton won these states after all, and hence, won the electoral college.

Remember the hanging chads of the 2000 election?

Remember the hanging chads of the 2000 election?

Why is it a nightmare? Because it would likely lead to a constitutional crisis with unpredictable consequences. Donald Trump would be unlikely to concede. But even he did, tens of millions of his supporters would likely find the results unacceptable. Even the predictable disaster of a Trump presidency is preferable to a crisis of such magnitude.

And last night, the specter of just such a crisis was raised, in the form of a New York Magazine article (which was soon echoed by other news outlets), reporting on the doubts and suspicions of prominent scientists who noted a bias in the county-by-county results, more likely to favor Trump in counties where votes were counted electronically.

But not so fast, says fivethirtyeight.com. You cannot just compare the raw results without accounting for demographics. And once you take demographics into account, the apparent bias disappears. And while fivethirtyeight notes that it is difficult to validate the integrity of the voting system in the United States, nonetheless the burden of proof is on those who claim electoral fraud, and so far, the burden of proof has not been met.

I no more welcome a Trump presidency today than I did two weeks ago, but an orderly transition is still preferable to the chaos of a constitutional crisis.

Meanwhile, Clinton’s lead in the popular vote count increased to over two million votes (yes, they are still counting the votes in some states, including mighty California). This in itself is unprecedented: never in the history of the United States did a candidate win the popular vote with such a wide margin, yet lose the electoral college.

 Posted by at 6:31 pm
Nov 222016

A few days ago, I came across this excellent blog entry about many of the project management misconceptions, bad ideas, overused buzzwords that I ran into in my professional career.

For instance, the author defines “backwards causality” by the example, “let’s adopt the Spotify model!” Yes, of course. While you are at it, also ask a lottery winner what he did that led to his winfall, and make sure you follow those steps exactly, as it will surely guarantee a win.

Or how about the “big bang”, as in “we can’t afford to keep up two systems at the same time”? Even in my teeny-weeny home office environment, I run things in parallel. When I set up a new workstation, it runs parallel with the old for weeks. Same goes for a new server. When I last did a planned transition to a new Internet service provider, I ran things in parallel for a month, too. Sure, it costs money. But it costs a lot less money in the long run than a botched, irreversible transition.

Then there is “buy vs. build”, or the mythical commercial-off-the-shelf (COTS) beast. I have seen this so often, especially in this blessed government town! Sure, don’t develop your own word processing software, specifically designed for Her Majesty’s Canadian Government, as that would be foolish nonsense. But many government applications are unique to the government, and may also be unique to the country or jurisdiction. Yet I have seen this happen, in fact I have lost business as a result, when a government department somehow got it in their head that COTS is the way to go.

Closely related is the concept of a “platform”. As in, we’re not just selling a product… we are selling a platform! Yeah, right. Add an API to your software, perhaps bundle two or three remotely related applications with a common installer, and suddenly, you are a platform vendor. To would-be buyers out there: The word “platform” has no technical meaning. It is a marketing buzzword designed to serve one purpose and one purpose only: to suck more money out of your budget.

Speaking of money, how about “enterprise”? You know, it’s government, we cannot just go with some low grade consumer product, we need an “enterprise solution”! You know what makes a product “enterprise”? Mostly it’s the price, nothing more. So-called “enterprise-ready” software is usually the same solution you get elsewhere, just packaged differently.

Another lovely buzzword is the “roadmap”. OK, I plead guilty: in my misguided youth, I both talked about, and contributed to the development of “roadmaps”. And to some extent, they may even make sense: as in a vague, strategic overview of where an IT system is expected to be heading in the long run. But the moment you shoehorn that roadmap into Microsoft Project and start attaching numbers (dollars, dates) to it, it becomes a work of pure fiction. Don’t build roadmaps, do research, do planning, do analysis, do design.

And for goodness’s sake, don’t buy a “turn-key solution”. That is perhaps the greatest deception of all: the idea that an outside vendor can come in, study your business, analyze the requirements, design and implement a solution so that on the agreed-upon delivery date, a nice, shiny new system is ready, just waiting for you to turn the ignition key. That *never* happens. Every experienced system architect can tell you that successful systems don’t happen without customer/user involvement at all stages; that the best adoption strategy is often gradual (see also the “big bang” approach above); and that even the best system needs adjustments and tinkering as its shortcomings only become evident once it is tested through daily use.

Anyhow, these are good lessons. The original article is well worth the read, as it talks about many other points, too.

 Posted by at 4:19 pm