Sunday, 30 October 2005

Selected Week News #3

The Man Who Would Murder Death
By Thomas Bartlett
From The Chronicle of Higher Education

The article tells about Dr. Aubrey de Grey, who´s a former Computer Scientist who turned to research on aging and has, to be polite, a lot of unusual ideas about preventing death by becoming old. Sounds a little like science fiction, but biology is evolving very quick now and this century will bring as much revolutions as we saw on physics and information technology last century. It´s interesting to be aware.

Wilma the Capacitor
By Paul Noel and Mary-Sue Haliburton
From Open Source Energy Network

This article suggests that hurricanes can act as natural particle accelerators and have capacitor properties that explain why they simply do not disperse. I remember that I learned that vortices are very stable fluid configurations per se, but a hurricane has a lot of interactions with the environment and I don´t know how all this interactions interfere in the stability.

Walking Small: The First Bipedal Molecule
By Ker Than
From LiveScience

Almost everyday I see some article about nanodevices. This is a very interesting one talking about a molecule that has a shape that let it walk as if it was a bipedal bug. All this little machines will play an important role mainly in the medicine of this century, but also in a lot of other fields like material engineering and chemistry. Just wait and see.

Wednesday, 19 October 2005

Quantum Gravity: LQG

Loop quantum gravity, or LQG for short, is one of the most popular approaches to quantum gravity. It is in the second place right behind string theory. It is a theory that try to quantize gravity using just plain quantum mechanics as we already know it, without incorporating any other new principle. Compared to strings, a very humble theory.

The trick to make this approach to work is to describe general relativity using a set of new variables, called Ashtekar variables, and impose the quantum commutation relations for these variables instead of for position and momentum as is usual. These commutation relations are mathematical relations that in non-relativistic quantum mechanics are responsible for the uncertainty principle, that says that if a particle has a well-defined position at an instant it has no defined momentum and vice-versa. When you add relativity things become a little more complicated, but the spirit remains the same. Indeed, this method of quantizing a theory by imposing quantum commutation relations IS what we call to quantize a theory. Quantum mechanics is not a very understood theory. It works, but we don't know exactly what happens. What we do know is that if we expand the solution of classical equations in Fourier series and impose the quantum commutation relations for some variables, it works. That is how QED was quantized, and it worked with an astounding precision.

The approach is called LOOP quantum gravity because the variables to be quantized are variables known as Wilson loops. Formally, a Wilson loop is the trace (i.e., the sum of the diagonal components of a matrix) of the holonomy of a vector transported along some closed path (a loop) in spacetime. Holonomy is an operator that gives the resulting vector after the transport has been made. If you do this transport in a flat spacetime (with no gravitational fields), the resulting vector is the same as the initial vector. But if the spacetime is curved (like the surface of a sphere), the result is not the same vector.

Using this variables, physicists were able to find solutions for the resulting quantum equations for general relativity (GR). Some additional results have been found, for example, they found quanta of area and volume for the spacetime (something that physicists liked, because we think that spacetime is fundamentally not continuous, but discrete) and, like string theorists, the correct entropy formula for black holes (in special cases). LQG is far more simple than string theory, although this simplicity is relative once that the geometry involved in LQG is very sophisticated, and to date achieved as much successes as strings (theoretically, because experimentally, they're in the same level: no confirmation at all). There are some physicists that even believe that strings and LQG can be combined in a single theory, because both have interesting physics insights and results and some similarities. As the popularity of strings id coming down due to the lack of testable predictions, that of LQG is coming up. The only thing that rests for us physicists is keep working on the problem to see what Nature could reveal to us in the future.

Picture from the article: "Quantum gravity: The quantum of area?" - John Baez - Nature 421, 702-703 (13 February 2003). Original caption:

In loop quantum gravity, space is envisaged as a fabric of woven threads. Where these threads puncture a surface, such as the event horizon of a black hole, they define its area.

Sunday, 16 October 2005

Selected Week News #2

Online Game Could Boost You into Space
By Leonard David

If you like to play, and if you're good, you can try to win this trip. The official page of the contest is

Hurricane Center Has One Name Left: Wilma
By Robert Roy Britt
From LiveScience

The interesting part of this article is the explanation of how hurricanes are named. I didn't know that as in my country we don't have hurricanes...

New “hobbit” bones bolster separate species claim
By Andy Coghlan
From New Scientist

It is one more species of man that has appeared during evolution. Quite interesting because it gives some reality to old legends.(And show that the scientists that named it liked the "Lord of the Rings".)

Duped and Clueless: How Easily We Fool Ourselves
By Ker Than
From LiveScience

This is a new experience showing once more a fact that science already observed before: our memories are constructed by our brains and can differ from reality. The brain can even construct the memories incorporating elements that are totally fictitious as if they were real. It's scaring to know that what you remember could never have happened, isn't it?

The Rise of the Body Bots
By Erico Guizzo and Harry Goldstein
From IEEE Spectrum Online

A detailed article about the latest developments in the area of exoskeleton building. You can see that probably very soon they will be avaiable for a variety of practical applications.

Friday, 14 October 2005

Particle Physics Art

My brain works visually. That's why I prefer geometry to algebra (okay, I like both, but I like geometry more). And that's why I like to put beautiful (at least to me) pictures in the beginning of every post.

Sometimes in physics theories reach phenomena that our eyes cannot. Then we need to rely only on math and have no clear visual picture of what is going on. But I suspect that a lot of other scientists also like visual inputs and that is the reason Feynman graphs and other diagrammatic methods became so popular in physics: they not only give us a better way to calculate things, but they give us some visual picture of the process and we can feel more confortabe with what we are doing. Somehow, we feel that we are understanding it better.

Particle physics is an area where pictures are always welcome, because we can only experiment particles indirectly, by means of paths in accelerator's collisions. Rigorously, quantum mechanics' math treats particles as point structureless entities. But although they're points and has no structure, they have a lot of properties like spin, momentum, polarization, mass and other quantities associated, most of them with the collective name of quantum numbers. The best we can say is that not having images in our brains to visualize those things is boring. Then I saw yesterday an article entitled "gallery: jan-henrik andersen" from where I took the picture in the top of this post (that represents a photon) talking about this designer that worked together with particle physicists to create graphical representations of the particles that would reflect their properties. The article has a lot of beatiful images and you can download a PDF file, althoug the resolution of the pictures in this file is not so good as in the site. I really enjoyed his work.

Just one more observation: these are artistic REPRESENTATIONS of the particles, remember, as I already said, that our view of particles today (at least the elementary particles) is that they are just points.

Thursday, 13 October 2005

Busted Archimedes

In the beginning, I used to like Mythbusters, but as the episodes unfolded I started to be suspicious of their results and then I finally realized that they do not test things with the required care. I stopped seeing then, because I saw that you cannot trust entirely in their results and, sometimes, the results were so obviously flawed that made me upset. One of these days was when they tested the story about Archimedes against the Roman fleet.

The story says that Archimedes devised a way to combat the Roman warships trying to invade Syracuse by focusing the sunlight on them with soldier's shields arranged in some ordered way. Mythbusters tested the story in a highly controversial way and concluded that it was false. Well, I didn't like the way they made the test and commented with my fiancee that they probably would be wrong, because the test was full of misconceptions and strange asumptions. Well, today I was browsing slashdot and found that some guys from MIT made the test more carefully and indeed found evidence in favor of the story. At least, it is not totally discarded as the TV guys said.

Mythbusters have good intentions, but they must be more careful if they want to get more credit. My advice is ALWAYS to be suspicious about what they say, sometimes it's right, but sometimes it's not. I would give this advice to them, but I guess they'll probably not listen to me...

(The picture is: Archimedes Death Ray. Wall painting, Florence, Italy)

Monday, 10 October 2005

Quantum Gravity: Strings

String theory is the most known approach to quantum gravity. It started as a tentative to describe the strong interaction in the 60's, but soon after QCD was discovered and shown to be the correct approach. Strings went forgotten for some time and were rediscovered by Green and Schwarz in the 80's. One of the main flaws of strings in the description of the strong force turned out to be what called the attention to it as a possible theory to describe QG: in the spectrum of the theory you always had a spin-2 massless boson that was undesirable in the description of strong interactions. But, if a graviton exists, it should be exactly a spin-2 massless boson, and so the idea that strings could describe QG was born. And gravitons are not the only particle that appears in the spectrum of the theory, other particles with lower spin appear too and so strings were believed to describe not only gravity, but all other interactions.

Okay, but what does the theory say? First, you must keep in mind that string theory is just a tentative theory, and not very successful yet. The theory appears to be consistent and appears to give general relativity and quantum mechanics in the correct limits, but it is not rigorously proved yet. Worse, the theory cannot predict anything testable yet, although it can be tested in principle (if not, it would not be a scientific theory). Well, let me give an idea of the picture of the universe painted by strings. String theory has a simple underlying idea that changes everything. In ordinary quantum mechanics, elementary particles are considered points in space, i.e., they are 0-dimensional. In string theory, they're supposed to be tiny strings, little 1-dimensional objects. Note that strings are not made of something, in fact, they're the fundamental stuff that makes everything.

Okay, you have 1-dimensional objects, but now you need to know how they move. As string theory must agree with relativity in the correct limit (the limit where the string seems to be a point), the movement of the string is supposed to behave in an analogous way as the particle in relativity. The particle in relativity traces a curve in space that is a geodesic, i.e., it is the short path from one point to the other with the distance given by some metric defined by the mass-energy distribution in the space. But as the string is 1-dimensional, instead of a minimal path we define that the string will move such that it traces a minimal area from one position to the other. This is the fundamental principle of strings. After defining this, you can do some calculations. But this description is not a quantum description yet and then you need to apply some mathematical rules that characterize quantum systems and you get what people call the Bosonic Strings, because this kind of string gives only bosons during the calculations.

Well, the universe is not only composed by bosons, which are the particles responsible by the interactions (strong, weak, EM and gravity), but by fermions too. Fermions are the particles that compose matter. Quarks and leptons (which include electrons). You include fermions in string theory by adding a kind of symmetry in Nature named supersymmetry. It is a principle that says that to every boson there exists a corresponding fermion. This hypothesis is a fundamental component of string theory, but it has not been proved yet in experiments. If it turn out to be wrong, string theory is probably wrong too.

The last curious feature of strings is the hypothesis that the universe has not 4 dimensions, but more. This comes from a mathematical problem that requires that, in order to string theory to be well defined, you need that the number of dimensions in the universe must be a specific number: 10. The problem is that we only experiment 4 dimensions in our daily lives and string theorists had to adapt and old trick first developed by Theodor Kaluza and Oskar Klein in the past to reduce the number of dimensions perceived by us, a theory that appropriately has the name of Kaluza-Klein Theory. The best way we devised till now is by means of a mathematical process where the extra-dimensions are wrapped in a geometrical cosntruct named a Calabi-Yau manifold, which is represented in the picture in the beginning of this post. This hypothesis has not been tested too. That is because our technology cannot probe the distances necessary to do the tests, but soon it will be possible. If we cannot find these extra dimensions, again string theory will be wrong.

String theory is ambitious. The idea is to describe all interactions in a unified framework. This ambition has a drawback: the theory is exceedingly complicated and to this date you cannot calculate anything numerically to compare with experiments. The predictions of extra dimensions and supersymmetry are important to strings, but even if they're found, they will not be sufficient to prove the theory for you can have other theories with these principles. A recent result of strings was the calculation of the entropy of a special kind of black hole with the correct factor given by the Bekenstein-Hawking formula. But as black holes are not experimental facts yet, it is just a marginal success.

Theoretical developments of strings lead in the past years to a myriad of new possibilities and mathematical techniques. Now it is believed that strings are part of a much more (to this date undefined) complex theory called M-Theory. Strings are not the only component of the theory now, but you have objects of any dimensionality called branes. But as the time passes and predictions and experimental observations do not happen, the scientific community is becoming more and more suspicious of the correctness of string theory. This has led to new theories of quantum gravity alternatives to strings. If they're related to it somehow, nobody knows. In the end, the answer is always with the only one who knows the correct laws: Nature.

Saturday, 8 October 2005

Selected Week News #1

Mystery Ocean Glow Confirmed in Satellite Photos
By Robert Roy Britt
From LiveScience

For the first time a strange glow in the ocean already described by sailors is photographed by satellite. The only explanation that was though till now is that it should be luminescent bacteria (that emmit light by a process called, a little obviously, bioluminescence), but more studies are needed to find the truth. It is interesting to think in how many natural phenomena we have yet to study in our own planet. I will not be surprised if more ghost and aliens sightings would be explained by natural phenomena we don´t understand yet.

Python Eats Gator, Explodes
By Denise Kalette
From LiveScience

Poor snake! That´s what happens when men break the natural balance by introducing alien species in different habitats. But in the end, I think that the world is getting so connected that it will be very difficult to maintain isolated natural habitats. Sad, because the number of species will diminish drastically and some substances that would be discovered among these organisms will probably take too much time to be synthetized by us.

Micro-organisms may be turned into nano-circuitry
By Will Knight
From New Scientist

The picture is of diatoms, a kind of microorganism with dimensions of the order of nanometers that some scientists think they could use to construct circuits.

IgNobel 2005
The IgNobel Prize is back and the laureates were already announced this year. If you don´t know what it is, it´s a prize given to the most weird reasearchs and achievements of the year. Sometimes these guys are a little unfair, but surely always fun.

Thursday, 6 October 2005

Reflections about the Bomb

Yesterday I saw a documentary about the Manhattan Project (MP) on the History Channel. I always though what would be if some government put together as many brilliant scientists and spent as much money as in this project in a similar project with an objective that would benefit mankind. Suppose that you bring together the most brilliant minds in the world in the area of Medicine and give them as much resources as the USA spent to build the atomic bomb for them to find the cure of AIDS. I bet that they would find a solution in a couple of years or less!!!

I´m a physicist, so I´ll talk about physicists. Work together with the scientists of MP is the dream of every physicist: they were a group that could do almost everything! Fermi, Bethe, Bohr, Feynman, Oppenheimer and a lot of other great physicists were there. If the government asked them to create a teleporting machine, they would have did it! They would discover everything if it was not impossible, and if it was, they would get as close as possible. But sadly this kind of project only is created to destroy, not to construct.

Most of the physicists at MP didn´t like when the bomb was deployed among civilians, although some were people that lost so much in the war that were driven by hate and didn´t realize the atrocity that was being made (e.g., Edward Teller). The documentary told that the scientists of MP signed a document asking for the bomb not being used in the war, just tested in an isolated place. A little naïve, I admit, but sometimes we scientists are very naïve.

Well, I was researching a little about the project and the bomb and found this interesting letter from Einstein to the president Roosevelt. This was the letter that initiated MP. Einstein was afraid that the Nazis would build the bomb before any other nation and drop it, so he warned USA about the danger. Einstein didn´t work in MP, but he was as naïve as all the others thinking that the USA would never use the bomb, even after constructing it.

I would like very much to see one day projects like MP to find the cure of AIDS, of cancer, of Alzheimer, to build teleporting machines, spaceships and other things. I just fear that somehow the governments will distort it and use it to make war and control other nations. Sad.

Tuesday, 4 October 2005

Nobel of Physics 2005

The Nobel Prize of Physics of 2005 was given today to two american scientists, John Hall and Theodor Hänsch, and to one german, Roy Glauber. They share the prize for their works on Quantum Optics.

Hall and Hänsch won the prize for works in quantum optics that advanced the field of spectroscopy and enhanced the precision of spectrometers. Spectroscopy is the set of techniques used to analyze the light emmitted by atoms or molecules. Each atom or molecule absorbs light in a particular way and emmits this energy back to the environment in a specific pattern that defining a signature. This is how astronomers can tell you the elements in the composition of a distant star: they analyze its light and identify the pattern of different elements. This pattern also revealed that the electrons in atoms were placed in specific orbits ordered by integer numbers, what Bohr explained in his model for the atom. But this is another story.

Glauber is a guy that I only lnew from a classic work in statistical physics where he introduced what is called today as "Glauber Dynamics". It is a way to introduce and study a dynamics in the Ising model (someday I'll talk more about it), which is originally a static model intended to describe magnetic materials. But he won the prize working on quantum optics too and it seems that he somehow is the father of this area, he was the first to apply quantum mechanics to describe optics.

I found an interesting document explaining the contributions of these three physicists in the homepage of Hänsch. I think I could hardly explain that better. I copied the document and put it HERE.

You can find more information on the Nobel Prize Page itself.

The image was taken from the site of the Vienna University of Technology where it has the caption:

The purple light originates from helium atoms excited by intense laser light. The laser pulses propagate along the axis of the purple lobes (horizontally) through the helium gas, and the X-ray beam (not visible) is radiated in a beam several hundred micrometers in diameter in the same direction. Photo by courtesy of: J. Seres, Vienna University of Technology.

Sunday, 2 October 2005

A Sign for Half the Universe (?)

When I was leaving my room in the university last Monday, a friend of mine was unease with some problem and then I asked him if the problem was a minus sign I´ve heard he talking about with another friend. He said to me that the problem was deeper, although sometimes a minus sign could be a deep problem. I answered saying: "It was for Dirac, wasn´t?".

I intended to refer to the fact that Dirac turned an undesirable minus sign in the solution of an equation in a great success. Let me tell the whole story. Paul Adrien Maurice Dirac was a British physicist that was working on a quantum relativistic wave equation for the electron and found one which has as solutions for the energy of the electron two values, one positive and one negative. Usually, the procedure would be to discard the negative energy solutions and keep going on with the positive ones. But Dirac noted that he could interpret the negative energy solutions as a new particle that had almost all the characteristics equal to the electron, but with the opposite charge. He called the particle "positron" (for positive-electron or positive particle or whatever…) and it was found experimentally some time later. He just predicted antimatter!

I had a professor called Henrique Fleming that used to say that Dirac discovered half of the universe. That was because matter and antimatter, apart from their opposite electric charge, seems to have the same characteristics and there is no reason why the universe should have more matter than antimatter. Okay, there is a deeper reason for supposing the equality. It´s because in processes that create particles with mass from ones that has no mass, matter and antimatter are created in the same proportion, such that the electric charge is conserved in the whole process. It is indeed a great mystery for physicists why in the observed universe matter dominates antimatter. There are some speculations, but just it.

Dirac discovered a lot of other things. He was one of the greatest physicists of the 20th century and probably you will heard more about him in the future posts. Antimatter is another interesting subject too and I´m planning to talk more about that later. So, as you can see, a little minus sign in an equation could lead to a big difference. I suggest you to ever remake your calculations, who knows what secret may be lurking behind a “-“.