I’ve recently been kicking around my personal list of what might constitute the greatest scientific achievements of the 20th century. There are so many things to consider and the list is necessarily so subjective that I’m not going to pretend to be giving a highly considered, thoroughly vetted list. I have put thought into this, but there will surely be dozens of examples I could easily find myself reconsidering if brought to my attention.
5) The Expanding Universe
In 1929 Edwin Hubble made the discovery that the Universe is actually expanding. This had direct implications throughout physics and astronomy. It was the reason Einstein called his cosmological constant “the biggest blunder” of his life.
Hubble used Cepheids, commonly known as “standard candles”, to get the relative distances of various galaxies. He then plotted this against their known redshifts. What he discovered was that these redshifts increased as a linear function of distance. That is, the Universe was uniformly expanding. In 1998 it would be discovered that this expansion was actually increasing in speed, contrary to expectations.
4) Cosmic Microwave Background Radiation
In the early 60’s, Robert Dickie was searching for the radiation that should have been left over if the Big Bang model was correct. He had assembled a team to look for what science had predicted, but he was beaten to the punch by Arno Penzias and Robert Wilson. And they weren’t even looking for the CMB.
Using a Dickie radiometer (designed by Dickie himself), Penzias and Wilson happened upon an interfering sort of fuzz while doing other research in 1965. They assumed it was coming from some nearby source, perhaps New York. After ruling out all the obvious possibilities (including pigeons), they were unable to conclude precisely what it was. They published a paper describing their results, which Dickie then used to correctly interpret as the discovery of the CMB. Penzias and Wilson won Nobel Prizes in 1978.
3) The Structure of DNA
There’s the saying that nothing in biology makes sense except in the light of evolution. This is crucially true, but the essence of the saying can be broaden to another area in biology: nothing in biology makes sense except in the light of the structure of DNA as discovered by James Watson and Francis Crick in 1953. I dare say, aside from Darwin’s discovery of how evolution happens, the discovery of the molecular shape of DNA has been the most significant event in all of biology. Interestingly, it shouldn’t have happened the way it did. Watson and Crick were one of several teams studying the structure. One member of another team, Rosalind Franklin, had actually produced accurate images of the molecule on her own, but determined she wasn’t ready to present her findings quite yet. Her teammate, Maurice Wilkins, would have none of that and decided to show her images – covertly – to Watson and Crick. They almost immediately recognized its significance (and to an extent Franklin hadn’t quite grasped): DNA formed as a double-helix with a uniform width all the way up its length.
Franklin’s work has unfortunately been drowned in history because of Wilkins’ betrayal, not to mention the fact that she is a woman in science – and that’s no easy task (especially in 1953).
Watson, Crick, and Wilkins received their Nobel Prizes in 1962 – Franklin got nothing.
2) General Theory of Relativity
Albert Einstein described his general theory of relativity in 1915, updating Newton’s ideas on gravity. He presented one of the most brilliant ideas man has ever had, fundamentally changing our understanding of how the Universe works. His science knocked down the notion of absolutes within spacetime, indeed, even helping to define the term. (Credit does not go directly to him, but his theory of special relativity was key in the development of the concept, and general relativity is an expansion of special relativity.)
Einstein received his Nobel Prize in 1922 (for 1921). (It was given for work as it specifically pertained to his special theory of relativity, not his theory of general relativity.)
1) Life on Mars
For the life of me, I don’t understand why no one seems to care about this. NASA recently announced it had reexamined a meteorite discovered in 1984 and confirmed that it contained within it microbial life which did not originate on Earth. While that may seem unfitting for a post about 20th century discoveries and events, the meteorite was originally described in 1996 to much fanfare. Over time a quiet consensus grew that the shapes in the rock could be formed via geological processes. The recent analysis blew those concerns out of the water.