Wednesday, 28 September 2005

Stereograms & Lena

After posting that stereogram of a dinosaur I took a look at Google to see if I could find other interesting pictures. I found an interesting site (okay, that´s the first to appear in my search) named simply Stereogram Page with some useful information and stereograms. Although I suggest to look more pages if you became really interested in the matter, I found in the site an interesting picture (the one at the beginning of the post).

This picture is not interesting because of the beauty of the lady in the photo, but because that girl is Lena. I met Lena for the first time a couple of weeks ago in the room of another physicist. While he was talking to me about a work he´s doing on image treatment, he showed me a photo of a girl (just the face) and asked me if I knew her. I said I didn´t and he told me who she was and a little story.

The photo was one of Lena and he told me that the picture is extremely popular in the scientific community of image treatment but people didn´t know who was Lena untill someone decided to look for the first paper where the image appeared and asked the authors where they found the photo. They said they scanned it from an old Playboy magazine. These guys then tried to find her and they succeeded: she was already a sweet old grandmother. So, they took her to a congress on image treatment and she was extremely applauded. He told me the story and then showed me the original photo, full body. It´s sad I don´t have enough space to put it here... :o)

Monday, 26 September 2005


Sunday, 25 September 2005

Quantum Gravity

There are four known fundamental interactions in our universe: strong, weak, electromagnetic and gravitational. When quantum mechanics was found to be the correct framework to formulate our physical theories, a program to describe these four interaction in a quantum way started. Successful quantum descriptions of the first three (strong, weak and EM) were found. EM was the most simple to be quantized, since Maxwell wrote his equations in such a general way that they didn´t need to be modified (they even didn´t need to be modified to adapt to relativity too! I´ll write a post about this in the future, if I remember…). The resulting theory is known as QED, or Quantum Electrodynamics and is largely confirmed by experiments. The quantum theory of strong interactions is known as QCD, or Quantum Chromodynamics and is also confirmed by experiments. The weak interaction is described by Electroweak Theory, that has the additional bonus of unifying the weak force and EM interactions in a single framework. Together, these three quantum theories form theoretical framework named the Standard Model that explain all the known microscopic physics that our today technology has access without being contradicted by any experiment.

This seems to be very nice, but there is a hole in all of this: gravity. In the microscopic world, gravity is so weak that we can ignore gravitational interactions and the results of experiments will not change in a perceptible way. But we have strong arguments supporting that we must quantize gravity in the same way as we did to the other forces. We tried it, but we failed miserably. Technically, if we try to quantize gravity using the same techniques that succeeded in quantizing the other three forces, we discover that gravity is nonrenormalizable. This is a technical word that means that in our calculations we find a lot of infinities that we cannot make disappear and so, we cannot calculate things with our theory and cannot make predictions. We are lost!

Be calm, not everything is lost. Our failure only means that gravity is more complex than we though and we need to be a little smarter to find the correct theory. This is good, because we have a real tough challenge and we physicists like challenges! Well, let´s get back to gravity. Since our simplest tentative didn´t work, we had to try other approaches. The first and most widely known by the general public approach which gave us some hope of finding a quantum gravity (QG) theory was String Theory, but its complexity reached such enormous proportions and after decades it didn´t yet provided a correct testable QG theory. Strings are an ambitious theory, because it not only tries to quantize gravity, it tries to unify all the four forces of Nature in a single unified theory, as people usually call it, a theory of everything (TOE).

But in the last two decades, a lot of theories alternative to strings appeared. The most popular now is Loop Quantum Gravity (LQG). These theories are not so ambitious as strings, because they only try to quantize gravity, not to unify all forces. Other approaches include: causal sets, causal dynamical triangulations (CDT), twistors, spin foam models and others. Remember that these are TENTATIVE theories and none was tested yet.

This is the big problem of QG in physics today. It is one of the most challenging problems of physics and a very active area of research. With this post, I´m starting a series of posts that will explain the existing approaches to QG with more detail. I hope that you enjoy this journey. But be patient, it is long and tortuous. Prepare yourself but remember that the most important is ALWAYS to have fun.

Saturday, 24 September 2005

Prove me Wrong!

One of the most fundamental features of a truly scientific theory is that it must be falsifiable in principle. By falsifiability I mean the characteristic of a theory that enables it to be tested by means of experimentation. A theory that cannot be falsified by an experiment is just metaphysical or philosophical. It is beyond the scope of science. For example, if I say that people only die when the time comes, it cannot be disproved in principle. That is because there is no experiment or situation where this theory can be shown to be wrong: if someone dies, the time arrived, if doesn´t, the time hasn´t arrived.

When you find someone defending a theory by defying you to prove that the theory is wrong and saying that if the theory cannot be proved wrong it must be right, be sure that the person is not a scientist or is a bad scientist. Theories that cannot be proved wrong are not good, they´re useless. A theory that cannot be falsified has no predictive power, i.e., you cannot predict the outcome of new experiments, cause if you could, the theory could be tested just by doing that particular experiment and verifying if the result is the same as the prediction. The more predictions of a theory are confirmed, the more the theory is trusted, but rigorously you can never say that a theory is completely correct. I´ll post something later showing how this relates to Bayesian inference.

It seems too simple, but this simple requisite is the main reason why a god cannot enter in science. That´s because gods cannot be falsified in principle. There is no experiment or situation that prove that they don´t exist. The same way, any theory that include gods are not scientific too (e.g., intelligent design).

So, adding to the items you must check to judge a theory, try to find a way to test it. If it cannot be tested in principle, if the theory cannot make a prediction but just fit the already known experiments, be very suspicious of it: probably it is not worth the time you will spend trying to understand it.

Thursday, 22 September 2005

Why not to lie?

Do not expect a text about moral principles. And I will not say that to lie is a sin, because I don't believe in "sins". Talking always the truth is not good because it will take you to heaven, but there are a lot of rational reasons to do that and I'll try to enumerate some.

We are social beings. We interact with other individuals. Very few of us live in total isolation. Therefore, our life depends on our relationship with other persons. Based on this, the first reason to tell always the truth is that people will always trust you. It's a great advantage! Sometime someone will tell a lie that will harm you saying that you did something you didn't. If everybody knows you only speak the truth, you'll be safe. Your word will be enough. But if you tell lies, then people may not trust you even if you are innocent. There is an additional bonus: most of people will tell you always the truth too. People will feel compelled to pay back your favor of telling them the truth by doing the same thing. It's highly probable that this will happen. People will even tell you secrets. Just because they know that if you promise so, you won't tell the secret to anybody else. And there is always someone who needs to share a secret with other person.

Another reason is that it will make you always try to do the right thing. And you'll probably benefit of this. That's because if you do something very wrong, you will have to lie to hide that. Therefore, you will try to do everything right. If you don't, you'll need to tell the truth and something bad can come of this.

Now, consider what happens when you tell lies. People get angry with you if they know. People will not trust you and this can harm you. It´s difficult to make friends if they don´t trust you. What happens is that you will end up with no friends, probably with a lot of enemies. Sometimes people gain with a lie. But in the average, the gain will bring more problems than good things. Unless you prefer a risky and lonely life, this is not the best thing to do.

Even the lightest lie can make damage. There is no little harmless lie. You're never doing any good for someone if you lie, although sometimes you may think so. Suppose people are worshipping some idol because they think that idol can do miracles. The community is happy because that renews their faith. You discover that the miracles are fake. If you don´t tell them to keep their faith, you open the doors to someone who can use that faith for own benefit. And trust me, there is always someone eager for doing this.

Once I even had a talk with another physicist that told me that maybe you can derive moral reasons from a rational model. Statistical physics is an area of physics that studies the behavior of interacting systems with a lot of components. Exactly like every society. This is interesting, but I´d better talk about this in another post…

Picture: Pinocchio - Jim Salvati

Monday, 19 September 2005

Beware of Revolutionary Theories!

I was reading some posts in Physics Forums and found something you see a lot of times in the Internet. Physics Forums have the advantage that a lot of serious physicists and mathematicians participate in the discussions and, sooner or later, things like that disappear, although sometimes people could be really insistent.

What I'm talking about is "Revolutionary New Theories". People saying that they found a theory explaining all science in a revolutionary way. Sadly, the scientists never believe in the theory and the author feels marginalized. Then, he starts to write a web page so he can publish his "discoveries".

It is not too hard to a experienced scientist to identify these kind of false theories. I will not explain that in detail, I will just direct you to the sites below where you can find almost everything you need to know about that:

Crackpot Index - by John Baez

Are you a quack? - by Warren Siegel

Read it and take your own conclusions. What I intend to do in this post is just to give two little and quick tips to identify these kind of false stuff.

1. How many formulas can you find in the work? There is NO WAY to do science without math. Sorry, but that's true. If the work claims to be a professional work (for experts) and have almost no math, it is probably just waste of time. Note that when I say "professional" I'm excluding books and articles to divulgate science to non-professionals. I'm talking about works to be read and analyzed by scientists.

2. Take the name of the "theory" and of the author and try to find any paper related in arXiv. Today, almost every physicist and mathematician post there a preprint of their work. It is not a reviewed journal, but if the theory is not even there... something is wrong.

Remember that the above tips are just TWO little features you need to pay attention. The sites I linked above have a lot of more things you should check.

Be careful, Internet is good for acquiring knowledge, but it includes wrong knowledge too.

Saturday, 17 September 2005

Poor Evolution...

Evolution, like quantum mechanics and relativity, is one of the most misunderstood body of knowledge of our science by those who don´t study it. It is not just a scientific hypothesis. The evidence in favor of it is tantalizing and there is NOT any scientific alternative to it. Evolution made predictions that have been and continue to be verified day after day. It is genuine science, but people generally do not understand well their contents and this is the cause of lots of wrong press reports and affirmations about it. I will not talk here about the absurdity of those who believe that evolution is wrong and try to argue that intelligent design, that is not a scientific theory but just plain religion and misticism masked as PSEUDOscience, is valid. This is a meaningless discussion for me. I´ll talk about incorrect interpretation of the rules of evolution.

Sometimes you hear someone say that in the future all our fur and hair will desappear as a result of our evolution. This is wrong! Some characteristic only changes in a species when you have some selection pressure to change it. There is no advantage in the modern world of being bald or having no fur. So, what happens, is that probably the distribution of "furness" in our species will tend to a gaussian distribution, where a few individuals will have a lot of fur, a few will have no fur and the majority will have moderate fur.

About our teeth. They´re not disappearing as a result of evolution. Our maxilar today is not so large to accomodate all our teeth because we do not exercise it sufficiently so it can develope. We eat "soft food" today. Everything we eat is processed and we simply do not allow our jaws to reach the total size they would have if we eat, let us say, raw meat and raw vegetables. It is not evolution, it is convenience. There is no selection pressure in action that would force the number of our teeth to decrease.

On the other side, our intelligence is improving. Okay, this may be true (note: MAY BE!). That´s because the smartest people have more chance to survive and procriate than the others. Although, we know that today the more developed the country, the less the natality rate.

The key feature of evolution is natural selection. Changes only stick to a species if they give an advantage that allows the individuals having that feature to outfit the others and reproduce more, or survive where the others cannot. No selection pressure, no evolution. This is, indeed, a prediction that can be tested and everytime it is tested, it confirms evolution.

Thursday, 15 September 2005

Quantum Mechanics is Real

Last Friday I heard something from a student that I hear from a lot of people and makes me very upset. He said that "quantum mechanics is so abstract that it is not related to the real world". Ok, he's only fourteen, but the others were not so young. It is unbelievable that more than a century after the advent of quantum mechanics people still think that it is only a bunch of complex rules with no aim or utility! People only need to look around to see how quantum mechanics is TOTALLY related to our daily lives.

Computers are machines that are used everywhere, everytime. They are constructed with transistors, and transistors are quantum devices. Nuclear Magnetic Resonance (NMR) is a quantum mechanical device too. But the most quantum of all devices is also the most common. You can even buy it in any market. The LASER. Lasers are used to do so many things today that a complete list would take pages to write. The laser was originally created without any application in mind. Just an experimental exercise of quantum mechanics. Lasers CANNOT be even explained by classical optics. They need quantum mechanics to exist. I think I am not exaggerating if I say that computers and lasers are the basis of our modern technology. Therefore, our modern technology IS quantum mechanical.

Quantum mechanics is the most respected physics theory. There is not a single experiment today that contradicts quantum mechanics. The only problem with it is a philosophical one: its interpretation. The mathematical framework of QM is internally consistent and using it we can make predictions for experiments that are confirmed to one part in one billion! But as we cannot probe the diminute distances that are the range of applicability of QM directly with our senses, a picture of what is happening is difficult to construct. But (although a lot of people will disagree with me in this point) pictures are less important than the mathematical formalism. That is because we can test experimentally the theory even without a clear picture if we have a precise formalism that allows us to predict the outcome of experiments. And predicting what Nature will do on a given situation is what science is all about!

Next time you think about saying that QM is just nonsense mathematics & physics, look at your computer and your CD-player, remember about NMR and laser pointers, and give a look at the myriad of medical procedures that use one or more of the three devices I described above. And before saying anything, think seriously if you could really live the way you live today without QM.

The picture in the beginning of the post is a computer representation of orbitals in a hydrogen atom calculated using QM.

Wednesday, 14 September 2005

A New Hope

This is my 4th or 5th tentative of writing a blog. Let us see if this time it works. I hope it will.

I´m just finishing my PhD thesis and probably will not post long texts. And don´t expect regularity too! Well, but I have something to post right now. I was browsing slashdot and found an interesting article named "Don´t dumb me down" about how terrible is the scientific press. It tells about how the press distort and misunderstand almost every science news. Every scientist knows that it is hard to see any true story about science in common press. And it is even harder to explain to those who see it that it is (almost) completely wrong.

Well, I hope that from now on you´ll enjoy to follow me in this jorney by the sands of space and time. Farewell!