My 10 Favorite Scientific Discoveries of the 20th Century

In a post published two weeks ago, I commented on an article in Science News that tried to answer this question: which were the ten most important scientific discoveries of the last century? Some of my readers asked what is my personal opinion. This is my answer.

To begin with, I will point out that scientific research can advance in four different ways:

1. Theoretical science, which tries to discover fundamental laws in the universe.
2. Experimental science, which confirms or falsifies theories by carrying out experiments.
3. Observational science, which instead of experimenting, observes. Astronomy, for instance, uses these methods, as experimentation is almost never possible.
4. Technology, the practical application of science, whose goal is to build devices that work.

I will point out, quoting Popper, that a theory cannot be considered scientific unless it can be falsified by experiment or observation. Furthermore, for the theory to be valid, it must have made at least one surprising accurate prediction: i.e., an unexpected prediction, later confirmed by experimentation or observation. I talked about this in another post.

This is the list of my ten favorite scientific advances of the 20th century. I have excluded from this list any theory that is not scientific or that has not been validated after its formulation. Among the theories excluded for being unscientific, I will cite cosmic inflation, string theory, and the various multiverse hypotheses. Among those excluded for not having been validated, I will cite the existence of dark matter and dark energy, and the standard cosmological model.

The order of the ten discoveries I have selected is roughly chronological and does not try to establish a scale of importance.

1. Planck's quantum theory and quantum mechanics: Planck explained black body radiation, and his theory was validated by Einstein by explaining the photoelectric effect, and by Bohr by building a better model of the atom than Rutherford’s; its extension, quantum mechanics, fused the concepts of wave and particle and made at least one surprisingly accurate prediction: the EPR experiment, designed by Einstein, Podolsky, and Rosen precisely to break down this theory.
2. Einstein's General Relativity: it explained Michelson's experiment and the precession of the orbit of Mercury. It made the following surprising accurate predictions: the deflection of light from a star as it passes near the sun (confirmed by Eddington in 1919); the redshift of sunlight (confirmed in 1959); and the existence of gravitational waves (confirmed in 2015).
3. The expansion of the universe and the Big Bang theory: The first was proposed by Georges Lemaître in 1927 and by Edwin Hubble in 1929; the second, a consequence of the first, by Lemaître in 1931. It explained the redshift of most galaxies. The Big Bang theory led to two surprising accurate predictions, made in 1948 by Georges Gamow, Ralph Alpher, and Robert Herman: the average composition of baryonic matter and the existence of a cosmic background radiation, both confirmed in the 1960s.
4. The discovery of the limits of mathematics: Initially made by Kurt Gödel in 1931 and expanded by Alan Turing, Alonzo Church and other researchers, it put an end to an exaggerated optimism, according to which we were about to know everything. This disappointment spread to physics, as I pointed out in other posts.
5. The existence of elementary particles and the standard model of particle physics, atomic physics and nuclear technology: During the 20th century, many particles were predicted and subsequently discovered, such as the neutron and positron (1932), the pi meson (1947), the antiproton and antineutron (1955-6), the W and Z bosons (1983) and the Higgs boson (2013). During the 60s and 70s, the standard model organized elementary particle physics and unified two fundamental interactions: electromagnetism and nuclear weak interaction. In a parallel way, 1938 saw the discovery of nuclear fission, which led to the construction of nuclear fission reactors. Nuclear fusion explained the origin of the sun's energy and opened a possibility of obtaining energy that has not yet borne the expected fruits. (Unfortunately, this also led to the large-scale destruction of two cities, Hiroshima and Nagasaki; fortunately, the hydrogen bomb still hasn’t been tested in this way, although the threat remains).
6. The spectacular development of information and communications technology: This has resulted in four generations of computers; micro-informatics; satellite and waveguide communications; smart mobile telephony; the development of data-analysis algorithms and their use with large amounts of data through the Internet and the World Wide Web.
7. Genetics, DNA, the deciphering of the genetic code and genetic engineering: After Morgan's experiments, which explained Mendel's laws, and Avery's proposal, which located genes in the DNA molecule, came the discovery of the structure of DNA by Watson, Crick and Rosalind Franklin, the decipherment of the genetic code, and the start of a revolutionary new technology: bioengineering.

8. 

   Ant head seen through
   an electron microscope

   Advances in medicine, which have led to an unprecedented increase in human life expectancy through the worldwide eradication of a terrible disease (smallpox); the containment of other diseases (such as polio) through vaccines, antibiotics and other drugs; and many impressive advances in medical technology: electron and tunnel-effect microscopes, ultrasound, scanners, MRI… (Too bad some doctors are using these advances to murder unborn children more effectively!)

9. Chemistry has advanced in several different ways: by developing polymers (although plastic garbage threatens now to suffocate the world); by designing new medical drugs (although it has also given us new deadly addictive substances); by its integration with biology, making biochemistry one of the main tools of our time, which has provided us with DNA analysis through the PCR reaction, among many other things.
10. Plate Tectonics, which revolutionized geology, biogeography and paleontology, explaining many enigmas and allowing predictions about the future evolution of the Earth and its surface.

This list can be compared to that in Science News. Or, everyone can create their own list. It will be noted that my list contains three lines of discoveries related to physics, one to astronomy, one to chemistry, one to geology, one to biology, one to medicine, one to mathematics, and one to technology.

The same post in Spanish

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Manuel Alfonseca