LessWrong Vienna, 18. 1. 2014

Until now we have travelled with Barbara to Vienna using a bus, but today we tried a train. The price is almost the same (13 € per person, round-trip ticket), and the train station in Vienna is at the same place (near the underground station Südtiroler Platz). The train is faster and more convenient. On its way back it has larger intervals, and sometimes it ends in Petržalka, which is not very convenient for us. When buying a round-trip ticket is does not matter whether we return to the main station or to Petržalka. Considering all these data, the train is obviously better.

Walking through Vienna we went astray a bit, because the underground stops are closer to each other than we expected. So not only we went by the parallel street, but when we passed near our destination, I probably though we are merely somewhere in the third of the distance, so we went needlessly far. Then some good people helped us return back, in time to catch the beginning of the lecture.

The lecture started in Cafe Votiv at three, we had reserved a room with a flipchart. Alex told us about quantum physics, in English. The lecture was clear and comprehensive, it was obvious Axel was familiar with this topic. Furthermore, he didn't speak any nonsense - which is exactly what people often do when discussing this topic. Well, an expect and a rationalist, that's a pleasure to listen to. I have no chance to repeat the lecture with sufficient value in a blog article (I guess Alex should make a YouTube video once). I'll only mention a few details that started make more sense to me after this explanation. As a former teacher, I highly appreciate showing us the specific experiments. Previously I imagined that to observe quantum effects one needs a complex apparatus in a lab, but in fact one needs a laser pointer, a piece of cardboard, and a floor. One thing is to read a book about a mysterius experiment, another thing is to try it for yourself.

As the scientists were discovering the laws of physics, the philosophers were speculating whether the universe is deterministic or not. Whether we could unambiguously predict the future of the universe if we had at some moment information about all its particles: where they are and how fast they move (and how much they weigh, what is their electric charge, etc.). Before discovering quantum physics it seemed the answer in an obvious "yes", then it seemed the answer is an obvious "no", and today it starts to seem (the opinions of the physicists are still split) that the answer will be "yes" anyway. With some technical notes about the precise meaning of the word "deterministic", because - as it happens in science all the time - the devil is in the details.

(Let me express my opinion that it's precisely this importance of the details why philosophers usually can't answer their own questions, and although they spend thousand years studying them, the answer will finally come from a scientists in a lab, who may even be unaware of the philosophical consequences of their research. According to my experience, "philosophising" usually means that people express themselves in very nebulous and wide categories. Which makes them miss all those important details. Of course when someone else later shows them the details and convinced them about their important, the philosophers can quickly classify them under some nebulous category and pretend it was what they were trying to say all the time. Which is why they are always one step behind the science, and can only discover what science has already discovered. Metaphorically speaking, if you put a philosopher on the shore of America, he will be able to argue the necessity of its existence from the first principles and write a large book about it, but yesterday he didn't even suspect the existence of the continent, although the sailors were already watching the seagulls on the horizon.)

In case of determinism, the trick is what exactly we mean by "predicting the future". If we mean wearily calculating step by step, atom by atom, with infinite precision; in other words, simulating the entire universe - this is called "weak determinism" - according to some current interpretations of quantum physics this would be possible, and according to others it wouldn't be. (Watch for the word "collapse"; if the theory contains it, it is non-deterministic, e.g. the classical Copenhagen interpretation; and if the theory avoids it, it is deterministic, e.g. the Everett many-world interpretation. There are other interpretations, too. As far as I know, they agree upon the specific equations, but differ in an opinion about what specifically do these equations describe.) But if we expect an ability to predict the future somehow more efficiently, to somehow approximate the result from the data using some simplified calculation, without simulating step by step - this is called "strong determinism" - that is clearly impossible.

To refute the strong determinism, we even don't need the quantum physics, merely the classical problem of three bodies. Sometimes the physical system develops in such way that the tiny change in the original setup causes dramatic differences later and leads to different future. If we imagine a planet orbiting about the Sun, what would happen if the planet started a thousand miles nearby? Not much; it would orbit along pretty much the same track, plus or minus a fraction of a percent. Its position thousand years later would be pretty much as in the former example. Now imagine that around the Sun rotates the planet and one comet with an excentrical course, which intersects the course of the planet. One day these orbiting bodies collide. Then the difference of a thousand miles can cause the comet to miss the planet, to whizz around and skew its course because of the gravity. The new course of the comet will markedly depend on how many miles and in which direction from the planet it flew. The state of the system (specifically the position of the comet) in a thousand years will greatly depend on tiny changes in the original state. This is a simple example, but the more complex examples, such as weather, these things happen all the time, so it's practically impossible to predict the weather more than three days in advance.

The difference between the strong and weak determinism may seem like a needless technical details, but informaticians use it frequently (although they don't use these names) and it's one of the key topics of the theoretical informatics. The halting problem: using a simulation we can follow the program step by step until it stops, or perhaps forever if it doesn't (weak determinism); but we can't algorithmically determine in advance whether it will stop or not (strong determinism). And since such program can run in the real world, on the computer, and the outcome may have visible consequences, even the real world cannot be strongly deterministic. This is true not just for the computer, but for any physical system. The idea is that (1) simulating a process step by step is not the same as being able to tell the result directly, and that (2) even a tiny difference in the start can cause dramatic changes in the later behavior.

By the way, once was popular a kind of half-atheism called "deism", according to which the universe was once in the past created by a supernatural being, but that being does not influence the further development of the universe, which only (deterministically) follows the laws of physics. The founders of USA were mostly deists (although current religious Americans are trying to deny it).

The ideas about the composition of the atoms developed gradually. First scientists observed that some chemicals react only in a certain ratio. For example some amount of a chemical X and some amount of a chemical Y creates a chemical Z. But if we add more chemical X at the beginning, we don't get as a result a different (more similar to X) chemical Z2; instead we get a mixture of the original Z and the additional X which did not react. This lead to a hypothesis of molecules, the compositions of certain numbers of atoms. The atoms themselves don't change, but they assemble into various molecules according to certain rules.

Later it was shown that the atoms contain electrons, which were supposed to just lay somewhere in the atoms, like raisins in a cake, and start moving only in specific circumstances, such as the electric current. It was also known that atoms can absorb and emit light in some circumstances. Then the radioactive substances were discovered, whose atoms also irradiated something else... something unknown which scientists called "alpha particles".

These particles were so much heavier than the electrons, that if we compared the electron to a raisin, then the alpha particle would be a cannon ball. The alpha particles were able to penetrate matter without problems; only sometimes they reflected. To continue the metaphor, it was as if we were shooting cannon balls to a wall made of paper, which most balls would pass without even slowing down... and once in a while some of them would reflect back. From similar experiments scientists deduced that the atom has a very little, very heavy core, around which the electrons orbit in mostly empty space, just like planets around the Sun. (Which may be what you learned at school.) This model has one problem, though: the electron has an electric charge, and if a charged particle rotates around a center, it emits the electromagnetic energy and loses energy; which means it would lose speed and fall to the core in a fraction of second. So the electrons don't orbit around the core. Also, to explain the chemical bounds among the atoms, it was necessary to suppose that an electron can orbit around the core not in any course, but only in a few specific tracks with specific capacity; and when the track becomes full, the next electrons can only take a further track. The first track can contain two electrons, the second one eight electrons, the third one also eight, the fourth one more... and this is how the rows of the periodic table are created. This theory nicely explains the chemical bounds among the atoms, but it does not explain why the electrons have to orbit on such tracks.

The quantum physics suggests that the reality is a bit "fuzzy". The particles in fact do not exist in one specific point, but "plus or minus" in some neighborhood of the point; just like they don't have one specific momentum, but "plus or minus" some momentum. To avoid a possible misunderstanding; I am not speaking about an imprecision of our measurements, but about how things really are. If you would draw a function of "whether this particle is right now at this place", the graph of the function wouldn't be a horizontal line with one infinitely sharp spike, but a curve. So would be a graph of the momentum. If one of these curves gets more narrow, the other gets more wide; there is a "∆x · ∆p ≥ ħ/2" relation. So the electron cannot be precisely at the center of the atom, because having a very specific place it would have very unspecific momentum, and some values of the momentum would make it fly away from the center. So it is in some compromise area where the uncertainty of the place is large enough for the uncertainty of the momentum to be small enough so the electron remains in the atom. (This is my extremely simplified interpretation.) There can only be two electrons in one place, not more. (This is a special property of electrons. For example, there can be any number of photons in one place.) Therefore in the nearest area around the core there are only two electrons; the next electrons can only be placed so they are not at the same place as the first two, and this is how gradually the orbitals appear and determine the properties of chemicals. (The more careful reader probably asks themselves why the protons and neutrons can be in the core of the atoms, if the electrons can't. If I understand it correctly, even the protons and neutrons are not at one point, but at some area around the geometrical center of the atom, but they are thousand times heavier than eletrons, which means higher momentum for the same speed, which means their area of compromise between the position and momentum is much smaller.) The elementary particles kinda are points with mass, but the quantum uncertainty precents them from getting too close to each other, and this is the reason why matter cannot pass through another matter.

I will not describe more complicated quantum stuff, because I don't understand it completely, and there is already enough nonsense about this topic on the internet; I am not going to create more. The important aspect is that the quantum physics calculations use complex numbers; any explanation without the complex numbers is wrong. The answer to the question whether "this particle is at this place" is not just something else than an unambiguous "yes" or "no", but it is also a value behaving differently than real numbers between 0 and 1, which we would intuitively expect when describing uncertainty. As a result, for example, adding two "possibilities" can create an "impossibility". (Like this: Can the electron pass through the slit A and get to the point X? Yes. Can the electron pass through the slit B and get to the point X? Yes. Both slits are open; can the electron pass through any of them and get to the point X? No. Because the sum of the two nonzero complex numbers from the former two questions happens to be zero.) I repeat, without specific equations using complex numbers further debate on this topic would only lead to nonsense. Physics does not have to obey our intuitions. (And please forget all the popular nonsense of the type: "quantum physics means the consciousness influences the matter". Nothing like that; only equations describing the movement of the particles.)

The best way to understand physics is to study physics. Analogies only get you so far; they predictably fail for things that don't have an analogy in the everyday life. - And this is as much as I remember from the lecture; the rest I have either misunderstood or forgot.

After the lecture we debated many things. We also spoke about religion, I don't quite remember why. Two members said that they grew up in a religious environment, and that the greatest change since they got rid of religion was getting rid of the ceaseless fear they didn't even know they had, because they had no experience of living without it. I asked whether it could be just their atypical way of experiencing religion (which would explain why they later abandoned it, and most religious people don't). They didn't think so, because when they speak with religious people today, they observe the avoiding of admitting the same things, or developing the same thoughts. I am happy that I personally don't have this experience.

viliam@bur.sk