Thursday, May 17, 2018

Are the digits of Pi real?

Martin Gardner
In an article published in Discover magazine in 1985, Martin Gardner wrote this:
As it happens, the thousandth decimal of pi is 9... The question: Was [this assertion] true before the 1949 calculation? To those of the realist school, the sentence expresses a timeless truth whether anyone knows it or not... [Others] prefer to think of mathematical objects as having no reality independent of the human mind.
This problem is quite old, as we have been discussing it for over two thousand years. The question about whether mathematical objects really exist or are a pure creation of our mind is a particular case of another problem, much more general, that debates whether ideas and concepts (like the dog species) really exist, or just this dog and that dog exist. This is the problem of universals, famous in the Middle Ages, which has not yet been solved to everyone’s satisfaction. In fact, at present, this debate is more virulent than ever.

Thursday, May 10, 2018

What’s a scientific theory

Karl Popper
Although it is fashionable to assert that Karl Popper’s theories about the evolution of science are outdated, his definition of what is a scientific theory is unassailable:
A theory is scientific if and only if it is possible to design an experiment that proves that this theory is false.
A paradigmatic case is the Copenhagen Interpretation of Quantum Mechanics. In 1935, Einstein, Podolsky and Rosen designed an experiment that could prove this theory false. A few months later, Niels Bohr published another article in the same magazine, in answer to the previous article. Almost 30 years later, as I explained in another post in this blog, the EPR experiment, which up to that point had been mental, could be carried out and confirmed Bohr’s predictions, rather than Einstein’s. As this theory was able to resist an attempt to prove it false, it must be considered a scientific theory.
Of course, this success of the theory does not imply that it should automatically be considered correct or true. Scientific theories (always according to Popper) never become so. This theory has successfully withstood an attempt to prove it false, but the next attempt could do it.

Thursday, May 3, 2018

The standard cosmological model

Map of the Cosmic Background Radiation
In 1927, the Belgian priest and astronomer Georges Lemaître discovered Hubble’s law.
Yeah that’s right. Hubble did not discover the law until 1929. What happened was that Lemaître published it in French in a low-impact journal (Annales de la Société Scientifique de Bruxelles), while Hubble published it two years later in English in the Proceedings of The National Academy of Sciences, received much more publicity and his name got associated with the discovery.
Combined with Einstein’s cosmological equation, Lemaître-Hubble’s law implies that the universe is expanding. In an article published in 1931 in Nature, Lemaître drew the consequence by proposing the Big Bang theory, so called in derision by its opponent Fred Hoyle in 1950. The name caught on.
In 1948, Ralph Alpher, George Gamow and Robert Herman made two surprising predictions, based on the Big Bang theory: the average composition of the mass of the cosmos (three quarters hydrogen and one quarter helium), and the existence of the cosmic background radiation. Both were confirmed during the sixties. From that point, the Big Bang theory became the standard cosmological theory.

Thursday, April 26, 2018

Evolution in the twenty-first century

A little over thirty years ago, during the eighties, some of the fundamental concepts of evolution seemed to be quite clear. Let us look at a few:
  • The DNA of every living being is an encrypted message that perfectly describes how to build the corresponding phenotype (the adult individual). All the information is in the genes. (Mechanistic reductionism).
  • Most DNA is unnecessary (junk DNA) and has been accumulated due to errors and repetitions in the transcription of the genomes of living beings.
  • The best metaphor to represent the organization of a genome is a set of beads on a string.
  • Genes are the repositories of inheritance, and each gene specifies a biological function.
  • Evolutionary processes take place through random mutations that act on a single gene, which are subject to natural selection, which results in small incremental increases in the adaptation of living beings to the environment.

Thursday, April 19, 2018

The end of the selfish gene

The German biologist August Weismann (1834-1914) was one of the most influential biologists of the late nineteenth century. His most important contribution was the theory of germinal plasma, also called in his honor Weismannism. According to this theory, there are two classes of cells in all multi-cellular living organisms (see Figure 1):
Figure 1
  • Somatic cells, represented in the figure by an S, that make up most of the body and do not play any role in inheritance.
  • Germ cells, represented in the figure by a G: the gametes, ovules and sperm, which pass the genetic information to the next generation.

Thursday, April 12, 2018

Epigenesis and epigenetics

Fertilization of the egg by the sperm
In the previous post we saw that at the beginning of the 19th century the theory of epigenesis seemed to have won the game. However, after 1850, and for just over a century, a cascade of new discoveries tipped again the balance towards the theory of preformation. Let us see what they were:
  1. The existence of a nucleus within animal and plant cells.
  2. The confirmation that the nuclei of the male and female gametes are fused during fertilization. This put an end to spermism and ovism and made it clear that the new being begins in the zygote.
  3. The confirmation that certain structures (the chromosomes) appear during cell reproduction inside the nucleus of the cell, which seem to play a very important role. It was also found that in the chromosomal endowment of the zygote, half of the chromosomes come from the father and the other half from the mother.
  4. A new science (Genetics) was originated in the experiments of Thomas Hunt Morgan, who showed that the chromosomes are linked to Mendelian inheritance.
  5. The works of Oswald Avery, who showed that DNA, a nucleic acid that appears in chromosomes, is the basis of Mendelian inheritance.
  6. The discovery of the structure of DNA (a double helix), made in the early 1950’s by Francis Crick, James Watson and Rosalind Franklin.
  7. The deciphering of the genetic code, which took place during the 1950s and the 1960s.

Thursday, April 5, 2018

Preformation and epigenesis

The history of the evolution of scientific theories about embryonic life (the origin of living beings) is very curious. I will try to summarize it in a couple of posts.
Throughout the history of science, the problem of the embryonic development of multicellular organisms has been one of the most arcane mysteries that man has tried to solve. Faced with this problem, two conflicting solutions have essentially been proposed:
         Preformation: During embryonic development there is just a growth of the pre-formed embryo, whose constitution and composition are completely ready-made from its origin. Everything is done from the beginning, whether in the egg, the sperm or the zygote.
         Epigenesis: Embryonic development is a process. Not everything is decided from the beginning; everything happens because something - a vital force, or an external or internal action - forces the embryo to develop in one way, rather than another.