## Monday, April 1, 2013

### Discoveries that Killed Entire Philosophies

EDIT: Just realized it's 1st of April today. Had I known that before I wrote this post, I may actually have tried to come up with some clever trick. However, that didn't happen: this post is completely serious, no hidden jokes or traps.

Every belief - no matter how innocent looking - implies certain conclusions. Put differently, every belief tells us something about what to expect (or not expect) in a certain situation. This makes it possible to make predictions based on beliefs, that is, to experimentally test our beliefs. This lies at the heart of the scientific method.

Yesterday's philosophy is today's science. Physics used to be called "natural philosophy". Cosmology has traditionally been considered part of religion and philosophy. Today they are quantitative science, making accurate predictions down to decimals. This transition occurred because we humans have historically underestimated how much we would one day be able to discover by rational means.

Here's some big philosophical beliefs that have been shattered by scientific discoveries.

## Clockwork Universe - A Predetermined World

Birth: 1687 (Newton)
Death: 1915-1930 (Einstein, Planck, Bohr)
History:
After Newton discovered Newtonian Mechanics in 1687, it became clear from his equations that any future state of the universe could in principle be predicted from the current state. This is best explained by Laplace in 1814:

"We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes."

A clockwork universe is thus characterized by determinism.
Einstein's discovery of Special Relativity in 1915 put doubts of this world view, as it coupled space and time, and the discovery of Quantum Mechanics finally destroyed it, as it became clear that, on atomic scale, the best can do is give probabilities for location / momentum of particles. A fundamentally non-deterministic universe had to be accepted.

The implications of Quantum Mechanics (QM) are still a matter of ongoing research (it will be so until all but one interpretation of QM has been eliminated). Bell's theorem demonstrates that reality is either a multiverse (all possible outcomes happen in separate universes) or non-local (instantaneous transfer of information between one end of the universe to the other is possible).

## Divine Origin - The Gift of Life

Birth: 500 B.C. (Empedocles)
Death: 1859 (Darwin)
History:
The idea that man was created in its full form by divine power is very old. It can be traced back to the ancient Greek philosopher Empedocles, although the idea most likely existed long before that. The beginning of the end for such a world view came with Darwin's discovery that species evolve into other species in time, as they adapt to their environment. Man, as all other species, was thus created from some "seed of life".

Darwin also destroyed another idea: the belief that physical traits can be altered throughout an organism's life. Lamarckian evolution is a theory in which Giraffes grow longer necks because they keep trying to reach higher fruits (they stretch out their necks). Darwin made this idea obsolete, by correctly explaining that Giraffes with necks too short simply die out, so that long necked Giraffes become more common in the next generation.

Today, evolution can be observed directly in microorganism (as their evolution is much faster than that of larger species). The mechanism by which the information gets passed on was discovered to be the double helix DNA strands. The decoding of DNA information (genotypes) into observable traits (phenotypes) is ongoing research.

## Formalism - A Dream of Mechanization

Birth: 1920 (Hilbert)
Death: 1931 (Gödel)
History:
At a time when mathematicians rose to the challenge of mechanizing all of mathematical reasoning (and, in doing so, founded what is today known as Artificial Intelligence), Hilbert had a vision: a system of rules to go from one fact to the next, thus discovery all truths. The end result? A machine that, given some input such as "does $x^n+y^n=z^n$ have any integer solutions?", the machine would output "yes".

This dream came to an abrupt end in 1931 when Gödel proved two things: first, the machine Hilbert envisioned would never be able to answer some questions, and, second, that machine cannot reliably answer the question "Is every answer you give me correct?". These are Gödel's famous incompleteness theorems.

One may then ask an interesting question: If the machine cannot answer some question, what would happen? We can imagine that in the best case, the machine would answer with "Don't Know". So for every question, we have three possible answers: "Yes", "No", and "Don't Know". Church and Turing later proved that even this is not possible: in the "Don't Know" case, the machine will "think" forever (this is known as the Church-Turing theorem).

## Static Universe - Eternal Existence

Birth: 1917 (Einstein)
Death:1929 (Hubble)
History:
The idea of a universe that has always existed, and will always exist, is probably very old, but Einstein made it explicit when he introduced the so called "Cosmological Constant" into his equations to force the universe to be static in size (non-shrinking and non-growing). This made for great disappointment in 1929, when Hubble observed that everything is moving away from us in space - the universe is expanding!

If we reverse the expansion of the universe, we see that it all began at a single point, and so Hubble also discovered the Big Bang theory.

It was initially thought that the expansion of the universe would be slowing down due to the discovery of dark matter. This left open the possibility that the universe would one day stop expanding, and start contracting back into the big bang. Later discoveries showed the opposite of such expectations: the expansion of the universe is speeding up all the time. The reason for this is completely unknown, and called "dark energy" (or sometimes also "cosmological constant", although it needs not be constant). What is clear, however, is that the universe will thus continue expanding forever, implying higher entropy / lower temperature / lower energy per cubic meter of space. In short, the universe is dying.