Wednesday, October 24, 2007

Are the laws of physics emergent ?

Last monday I attended a fascinating conference by Robert Laughlin (who won a Nobel Prize for his remarkable work on fractional quantum hall effect). The meadow of his arguments is this: the behavior of the world is ultimately governed by emergent phenomena.

Let's say a kid wants to know how some simple device works, he will surely try one thing: dissasembling the device, look at each part and figure out how they work. This is what Laughlin calls the reductionist approach. Physicis has been carried this way for the past centuries, this is how we arrived to our knowledge of elementary particle physics, by dissambling the matter in to smaller chunks at increasing energies.

Emergent phenomena arraises when collective behavior suddenly becomes different from the behavior of it's individual parts, this pinpoints to one of the fundamenal characteristics of emergent phenomena: universality. This means that the collective behavior is esentially independent of the properties of it's individual parts.

This was exemplified in a funny way by Laughlin who showed Newton burried under a big pile of apples, which is an obviously different behavior from that single apple in Woolsthorpe. Note that for the sake of beeing buried under a big pile of something it won't make a difference to be buried beneath apples, watermelons or potatoes.

One of the really perturbing things mentioned by Laughlin was that Newton's first law is actually emergent and comes from a broken symmetry, this was totally unexpected for me, but maybe one enlightned reader can bring some light to this issue (please!).

But, are fundamental laws of physics emergent? There is no doubt that emergent phenomena is important and quite interesting. And of course, every reasonable physicist will tell you that we don't need to know the detailed behavior of quarks or QED for describing biology or weather.

Whatsoever I don't honestly believe we can have a complete/satisfactory knowledge can be acquired in this way, we actually need to know from where this laws emerge from. As an example, how are we going to figure (say) the properties of fundamental particles? It seems to me that if you keep asking "why?" you eventually need a detailed description, the sort of fundamental physics we have always think about.

And, this might be just a wrong perception but it seems to me that the "reductionist approach" is far more general, at least in the sense we only need to know the law of gravity (and dynamics, of course) to compute the behavior of an arbitrary number of apples, this also applies to any other system where gravity is acting. On the other side you need to have a "lot's of falling things law", "orbital's motion law", "single falling ball law", etc...

Saturday, October 20, 2007

Halley's debris

During the year, earth's orbit crosses the paths of hubris left behind by comets. When this debris enters the atmosphere it is heated by friction and it's temperature raises dramatically making them quite easy to spot, this are the so called shooting stars.

When the earth crosses a dense stream then the number of shooting stars (usually close to one per hour in the whole sky) meteor showers occur. Some well known meteor showers are the Perseids and the Leonids (usually boring, the Leonids can produce the most spectacular meteor showers evey 33 years including the meteor shower of 1833, usually considered the most spectacular ever).

Tomorrow's night (October 21-22) the Orionids will reach their peak, in the north you can expect 20 meteors per hour and 40 in the south.

Use this starmap (from meteorshowersonline) to watch the orionids, the stream of meteors will look as emerging from a radiant, the radiant is quite close to red bright star Betelgeuse.

Remember that this means 20 meteors in the full sky, and to be honest this shower isn't as reliable as the Perseids, nonetheless it is a nice weekend activity.

The source of the Orionids stream is the famous Halley's comet, so you are actually watching little pieces from this comet as they enter the earth, quite amazing if you think about it, there are even missions where high altitude planes collect this comet dust.

Wednesday, October 17, 2007

Cool Nerd King

Are you facing the ultimate question: Am I a nerd? The website offers you the answers you always wanted. In particular in my trip to the oracle I got: says I'm a Cool Nerd King.  What are you?  Click here!

Oficially I am a cool nerd king, whatever that means. Submit your results to the comments section!

First light ... and some Sudoku!

Well, hello to all of you, kind blog readers, whoever and wherever you are. This is my first post, or making reference to what observational astronomers say when a new telescope captures its first image ever, this is my first light.

I think Luis already mentioned the main points concerning myself. I've been fascinated with Physics, Astronomy and Computers since I was very little, so getting into numerical astrophysics was an inevitability of fate, it seems. In case I seem too geeky, I should note that I also enjoy movies, music, videogames and drinking beer/tequila like there's no tomorrow.

My current research is focused towards numerical models of DEM L316, a pair of supernova remnants in the Large Magellanic Cloud that were caught in action, ie: two supernovas that might have exploded near to each other and thus may now be colliding.


Now, time for some Sudoku! For those of you who don't know, Sudoku is a simple number game, where one must fill the blanks in an incomplete 9 x 9 number grid, following a simple rule: a number may only appear once in each row, each column and in each of the nine 3 x 3 blocks of the grid.

I spent most of my afternoon writing a Sudoku solver. Since I'm a bit rusty with my programming skills, I thought it'd be a good exercise. The program is written in C++ and I've compiled it under SuSE 10.3 (which I've just installed on my laptop and works wonderfully).

You can download my Sudoku solver here.

It's a gzipped tarball. I've also included a binary compiled in SuSE 10.3. In order to compile the source in your own distro, if you have the GNU C++ compiler just type "g++ -o sudoku sudoku.cpp". The grid to solve is entered in the data file sudoku.dat, which should be in the same directory as the binary. I've included the hardest grid I've found (for my solver) as example; it takes 605,484 trials to solve it.

The algorithm behind the program is simple. It's a brute-force recursive algorithm. This means my algorithm solves Sudoku by trying a valid number in the first empty position, then trying a valid number in the next grid position, then the next, etc ... all this done through a recursive function. When the function finds it cannot place a number in a particular position, it goes back to the last grid position, and tries the next valid number there... again, all this done recursively.

In the end, it works very well and fast enough (despite being an exhaustive algorithm). It takes well under a second on my C2D T7100, 2GB RAM laptop to find the solution to any grid I've fed the program. The program is nice since it makes use of recursion, which is a powerful feature of programming languages. As the creator of Ghostscript, L. Peter Deutsch, put it:

To iterate is human; to recurse, divine.

As is to be expected, the greater the number of blanks to fill, the more trial number placements the program must do to achieve a solution. However, there is no clear correlation between the reported difficulty of a particular grid and the trials needed by my code to solve it, other than the fact that harder puzzles usually have a larger number of empty squares to fill.

Thursday, October 11, 2007

And Now for Something Completely Different...

A man with string theory up his nose.

As our gracious host has already pointed out, I'm actually a physics student, so it's an honor to be able to write for this fine astronomy blog. In any case I'm beginning to understand the AdS/CFT correspondence, which as you may already know, deals with the apparent duality that exist between some string theories and quantum field theories.
What we can aspire to do with this approach is to investigate quantum field theories without relying on perturbation theory, which limit our understanding of nature. For example, Quantum Cromodynamics (QCD) enjoys asymptotic freedom at high energies, this means that since interactions are weak at those energy scales it's sane to use perturvative methods. However in cases where energy scales are small, we simply do not know how to perform calculations. As always numerical methods are useful to some extent, but even they have a hard time dealing with some situations (they involve dealing with some dynamical quarks, as far as I know). Other option is to study the AdS/CFT correspondence and gather bits of information about gauge theories in general. It all boils down to this: either, A) Find a string theory dual to QCD to be able to make calculations or B) Understand properties about gauge theories in general so you can make predictions about QCD. The second option is more viable and has had success in the past. But I'll explain that some other time.

Since I'm just starting studies on this subject I hope I'm not making some false statements, (I'm not, as far as I know). Feel free to comment on the subject should you feel otherwise.

On a side note, Toots Thielemans is playing tomorrow at Netzahualcoyotl Concert Hall, one of Mexico's most beautiful concert halls in my own opinion. This will be interesting...

What makes this blog thick?

Counter services are one of those little modern wonders, allowing to track the number of visitors to a site, the country of origin, the browser they are using and most importantly what keywords they used to arrive to the site.

So, which are the more popular keywords in the last 100 visits? Let's take a look:

mexican scientist, mexican astronomer
Yes. That's just what we are.

mexican astronomy
You have just come to the right site, you can have a little glance at astronomy done in Mexico from firsthand participants, mostly students, but still firsthand participants.

iraf ubuntu, ubuntu iraf, ubuntu iraf package, install ds9 ubuntu
Fine, enjoy the scripts. You can still say you compiled IRAF yourself, just to impress your (geeky) friends.

astronomy package octave
Sorry, but octave is an interpreted numerical language quite similar to Matlab and it lacks astronomy specific packages (you can update me on that), maybe if you have some astronomy package for Matlab it will work on octave.

mexican scientist famous, important mexican scientist
Get back in a few years...

What!!! Who is google stalking me? I should lock the door right now...

Claudio Toledo: our latest adquisition

Juan Claudio Toledo (also known as Meithan West in the underworld) has joined our blogging team. He is a grad student at Instituto de Astronomía, UNAM, where he works on astrophysical fluid dynamics and interstellar medium (yes, this blog is populated by ISM researchers).

He is currently working on numerical simulations of astrophysical fluids (this usually means a fluid that is self-gravitating and usually ionized), so hopefully he will bring his numerical expertise to this site.

With his addition this blog is now almost a chilango blog!!! Well, that should be remedied soon!

Welcome Claudio!

Tuesday, October 09, 2007

Eric joins the team

I proudly announce the addition of Eric Pulido (from a dual approach) to our blogging staff. He is currently a physics grad student (yes, this blog is driven primarly by students) at Universidad Nacional Autonoma de Mexico, as far as I can say his interests are in theoretical physics, mostly at string theory and cosmology (allowing me to call him an "astronomer").

Besides bringing his stringy expertise to this blog his addition will move the center of gravity of this blog a bit in to Mexico City.

Welcome Eric!

Nobel to giant magnetoresistance

I have always been very impressed by this modern devices capable of storing vast ammounts of data in a quite reduced space.

This devices had been possible by giant magnetoresistance, an effect discovered in multilayered materials (Fe/Cr/Fe trilayers and Fe/Cr multilayers). The effect manifests itself as a significant disminution in the resistance of the material in the abscence of a magnetic field, this has been implemented in the reading heads of hard drives allowing the data to be stored in really weak magnetic fields.

Giant magnetoresistance is widely regarded as the birth of spintronics, in particular in giant magnetoresistance the spins of the electrons of the nonmagnetic metal align parallel or antiparallel with an applied magnetic field in equal numbers.

This work got the nobel to Albert Fert and Peter Grünberg, who had just won the Wolf Award this year, so this prize wasn't a complete surprise for anyone, and it is actually the recongnition to some really remarkable research that has lead in to devices that everyone uses on a daily basis.

Monday, October 08, 2007

Ok, I'll read the manual

In my latest procastination attack I stumbled over this masterpiece of contemporary humor. If you change the toaster by my computer then the situation starts to feels quite familiar for me. Check xkcd for more great comic strips (just in case you didn't knew it before).

Sunday, October 07, 2007

Nobel Hype 2007

The next week the winners of the Nobel prize will be announced. As usual there is always some fuzz speculating who will win. As usual I declare my own ignorance of the whole selection process. Whatsoever I can always say who are the obvious candidatates in the astro related areas: Alan Guth, Paul Steinhardt and Andrei Linde for inflation (although Andreas Albrecht was also crucial and a quite similar mechanism was proposed before by Starobinsky), and the leaders of the Supernova Cosmology Project and the High-z Supernova Search Team that found evidence of the acceleration of the expansion of the universe. Now, considering the prize went to cosmology the last year I don´t think it will be awarded again to a related area this year. Dark matter also deserves a nobel, but it's history is too long, although Vera Rubin is the usual suspect. Thomson scientific has a stadistical based prediction, saying that Martin Rees will win the prize.

What about other areas of physics? Well I am certainly less savvy about that, I have always believed that James Bjorken who found the scaling law for QCD deserves the prize and also Yoichiro Nambu along with Jeffrey Goldstone for the bosons that appear in simultaneously broken symmetries. The SNO experiment showing that neutrinos indeed oscillate is another crucial contrubution.

On the rest of physics I don't feel like making some sort of prediction, but of course, your predictions are always welcome.