Thursday, September 14, 2006

Philosophia Naturalis #1

Welcome to the première edition of a new science blog carnival. Since the idea and objectives of the carnival have been explained here, I won't repeat those comments now. Let's get right down to business.

It's been 50 years since "artificial intelligence" emerged as a recognized subject of enquiry in computer science (see here). And for even longer than that, a few individuals -- such as Alan Turing -- have speculated about the possibility that computers could "think". AI has been controversial the whole time. Turing proposed a test, the Turing Test, which he offered as a criterion for computers having the ability to think. There has been plenty of skepticism that a computer could actually pass the test anytime soon. And it has also been argued that even if a computer could pass it, that would not mean the computer could really think. Scott Aaronson of Shtetl-Optimized takes on one form of this argument in Alan Turing, moralist.

Reaching back somewhat further in time, Scott also channels Aesop with this fable of The physicists and the wagon. Not to be outdone, Dave Bacon, the Quantum Pontiff, fires back with a tale of The Computer Scientist and the Abominable Approximation. The dueling fabulists are really talking about quantum computers and the differing approaches of physicists and computer scientists.

Writing in eSkeptic Phil Molé argues against the possibility of AI from a different point of view. In A.I. Gone Awry he describes three different approaches that have been tried for implementing AI, and he explains why he thinks none of them can work.

Another example of philosophical controversies that are actively roiling the waters of modern science is the pitched battle going on in high-energy physics over string theory. Despite the theory's mathematical elegance, after several decades of active study, physicists have not yet come up with any clear way to test the theory, and many are now skeptical that such a test will turn up any time soon, if ever. Peter Woit of Not Even Wrong is one of the better-known skeptics, and Lee Smolin is another. Both have recently published books on the subject. In The Trouble With Physics Woit reviews Smolin's book.

The nice thing about science, the largest part of it anyway, is that most controversies are eventually resolved by an accumulation of evidence that strongly favors one hypothesis over all others. This seems to be happening now, finally, regarding the issue of "dark matter" in cosmology. Just a few weeks ago, new evidence was reported that strongly supports the existence of dark matter as an explanation for many puzzles about the seemingly anomalous behavior of visually observable matter. Sean Carroll at Cosmic Variance gives a comprehensive summary in Dark Matter Exists of what was found and what it means.

Having established that dark matter is real, the question remains: What is it? Another writer at Cosmic Variance, Mark Trodden, addresses this question in Identifying Dark Matter. This is a problem in particle physics rather than cosmology per se, though cosmological observations will almost certainly contribute to pinning down the answer. Basically, physicists are pretty sure that the standard model of particle physics isn't complete. There must be other particles and possibly other forces beyond those we know about. Not only are they needed to extend the standard model, but they're natural candidates for the "stuff" of dark matter.

There's a "standard model" of cosmology too -- it's called the Big Bang. Though this model also has its skeptics, the present evidence in its favor is quite strong. And the recent findings about dark matter further bolster the theory. Actually, a big reason that skeptics of the Big Bang persist is that there are many misconceptions about the theory. Jon Voisey at The Angry Astronomer clears up some of them in The Big Bang – Common Misconceptions.

One aspect of the Big Bang about which there remains some uncertainty is the distance scale and correspondingly the amount of time that has elapsed since the initial singularity. Rob Knop at Galactic Interactions explains in Is the Universe a couple of billion years older than we thought? how astronomers try to measure distances. He then writes about recent research that raises questions about what we thought we knew regarding the cosmological distance scale -- and consequently how the figure of about 13.7 billion years for the length of time since the big bang could be 15% too low.

This length of time, otherwise known as "the age of the universe", is closely related to another quantity, the "Hubble constant". It's not really a constant, by the way, since it changes over the lifetime of the universe. It's more accurately called the Hubble parameter, and it expresses the rate at which distant galaxies are receding from us as a function of their distance, which is the key fact that Edwin Hubble discovered about 80 years ago. The value of this parameter at the present time is symbolized by H0, and it's usually expressed in units of kilometers per second per megaparsec. If you unwind that, the units are proportional to the reciprocal of time, and so 1/H0 has units of time. To a first approximation, this is the "age of the universe". (A decade or so ago, some astronomers thought H0 was larger than today's best consensus value. So it was feared that the universe could not be as old as the oldest known stars. This was unsettling to many people.) The upshot of the new distance measurements is that H0 might be even smaller than the current consensus, making the universe even older. Mollishka at {mollishka's title goes here} points out here that measurements of H0 still aren't that exact.

Although scientists haven't thought for quite a long time that Hubble's "constant" is really constant, there are other important "constants of nature" whose actual constancy has only recently (less than a decade) been seriously studied experimentally. Accounts of such investigations show up from time to time in the popular media, such as here. Reacting to that story, Rob Knop in Are the fundamental constants changing? writes to point out that possible variations in constants such as the speed of light, if they exist at all, are likely to be quite minute, even over the entire lifetime (14 or 15 billion years) of the universe. So it's undestandable that research that claims to have found such variations is very controversial. (In a subsequent correction, Rob notes that there is a more credible piece of research on this than the example he first chose.)

Based on Rob's remarks, Chad Orzel of Uncertain Principles picks of the conversation. In two longish articles (part 1, part 2) he delivers a detailed explanation of what is involved in trying to investigate possible variations in a dimensionless constant such as the "fine structure constant". This latter number, which is suspiciously close to 1/137, plays a very large role in quantum physics. Among other things, it affects atomic spectra, and so can in principle be studied by examining spectra from very distant quasars. It depends in turn on four other physical constants -- the speed of light, the charge of an electron, Planck's constant, and the permittivity of free space. Any one of these, or even perhaps all, could be changing very slightly with time... so this is a rather interesting question.

Head spinning yet? If not, perhaps you'd like to contemplate the question of the direction of time. This is a matter of deep concern to everyone: Why the heck do we keep getting older instead of younger? Alejandro Satz at Reality Conditions writes about the direction of time by way of a review of Huw Price's 1996 book Time's Arrow and Archimedes' Point. According to Alejandro, Price describes several well-known asymmetries ("arrows") of time, in spite of the time symmetry of practically all physical laws. The book then goes on to consider possible explanations for the asymmetries. Alejandro is planning to continue his review in the "future" -- or is that the "past"?

Winding down now, let's turn to simpler subjects, like math.

Perhaps you've heard anecdotes like this: Harried math grad student stumbles into class late. She sees a couple of assertions written on the blackboard and assumes they are homework. A week later she returns and hands the professor a written-out proof of one of the assertions. Professor is flabbergasted, since the assertion in question was a famous unsolved problem. Evidently that's not just an Urban legend. Apparently it's even happened more than once, as Luis Alberto Sanchez Moreno of Astronomer. In the wild. explains.

With the apparent resolution of the Poincaré conjecture much in the news lately, many folks are interested in learning more about the fundamentals of topology. (Well, we can dream, can't we?) One of the most basic concepts is that of a "continuous function". Fortunately, we have "Paranoid Marvin" of Antopology ready with a good primer: Continuity Introduced.

Mathematics, of course, is not entirely about higher dimensions and similar abstractions. It has applications just about everywhere. I recall seeing a report that came out in the past year of someone, probably a lonely grad student, who came up with a mathematical model of sexual attraction, but I don't have time to go looking for it just now. However, mathematical biology is currently an active field, and Deepak Singh is enthusiastic about a paper that uses finite element modeling to study a biological process. He suggests that "in a few years, those interested in studying protein structure and function will require a healthy training in multiscale modeling (quantum chemistry, molecular dynamics, coarse grained simulations, continuum dynamics), bioinformatics, and mathematical modeling."

And now for something completely different... Did you know that there was an area in the upper midwest of the U. S. between lakes Superior and Michigan that was unglaciated even in the depths of the last ice age? I didn't. It's called the Driftless Area, and "Pascal" of Research at a snail's pace (this is about glaciology, see?) explains how it happened.

And that concludes today's opening performance of Philosophia Naturalis. We'll be back here again in just four short weeks, on Thursday, October 12. Watch this blog for further details. Or just go back to the original announcement for information on how you can suggest articles for inclusion here -- which I hope you will consider doing, because, well, sharing your interests is a Good Thing.

Update 9/30/06: The next edition will be posted at Nonoscience on October 12.

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12 Comments:

Blogger pascal said...

I like it. A good compliment to the Tangled Bank.

9/14/2006 04:56:00 AM  
Anonymous Arunn said...

Nice carnival; good theme; and interesting collection of posts although some of them (from Cosmic Variance for instnace) I read earlier.

Check here for another one, in which you may be interested in submitting your posts.

Keep up your good work with physics at this blog.

9/14/2006 07:43:00 AM  
Anonymous Anonymous said...

One fun ride, I must bring the wife and kids!!

9/14/2006 10:05:00 AM  
Blogger Daniel Doro Ferrante said...

Very nice: Having a "Carnival of Physics" is not only refreshing, but soothing as well! :-)

Now i'll have to start writing some of my posts in english... and find the nerve to submmit them. ;-)

Take care.

9/15/2006 08:35:00 AM  
Blogger Charles Daney said...

Now i'll have to start writing some of my posts in english... and find the nerve to submmit them. ;-)

Daniel, Please do!

Unfortunately, Portuguese just isn't my strong suit.

9/15/2006 10:25:00 AM  
Anonymous Anonymous said...

"Harried math grad student stumbles into class late. She sees a couple of assertions written on the blackboard and assumes they are homework."

I had a professor who liked to throw in a few unsolved problems into our homework just to see if there was a genius in his midst though he didn't tell us that he was doing this. Some of those problems were hard but I didn't realize just how hard they actually were until later.

9/15/2006 10:56:00 AM  
Blogger L. Riofrio said...

Nice links. Since I work on a changing c, it is great to see this subject discussed. I hope to hear even more from you about c change. I also like to see photos in a blog, and include them every day.

9/15/2006 11:09:00 AM  
Blogger Charles Daney said...

Arunn:

I'll be glad to have you host a future edition of the carnival. Please send me your email address so we can arrange this.

Charles

9/17/2006 12:00:00 AM  
Anonymous Belizean said...

Bravo! A spendid debut.

9/18/2006 01:13:00 PM  
Blogger John Baez said...

I don't think the fine structure is "suspiciously close" to 1/137. Its reciprocal has been measured as 137.03599911 with error bars of about .00000046. That's fairly close to 137, but definitely not 137.

9/26/2006 02:51:00 PM  
Blogger Bee said...

Hey, you changed the template! Good choice, much better readable, not so messy. -- B.

10/16/2006 11:26:00 AM  
Blogger Charles Daney said...

Thanks, Bee. I think it looks better too. <g>
-- Charles

10/17/2006 12:48:00 AM  

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