Probability of the existence of extraterrestrial life

In a previous post I talked about the probability of the existence of extraterrestrial intelligence and mentioned the difficulty of its calculation, as we don’t know of any planet where they exist, apart from Earth, and to calculate the probability of an event one must know the number of favorable cases and the number of possible cases. For extraterrestrial life, we ​​don’t know either.

In another post I detailed the conditions that should be necessary if life similar to ours were to be possible on a planet similar to Earth. These conditions are many, which reduces the probability that we will find life on some extrasolar planet located in our vicinity. In fact, among the almost 10,000 planets detected so far (of which just over half have been confirmed), 65 are at a distance from their star that could be favorable for life (the Goldilocks zone), but only three of them orbit around stars similar to the Sun (of the stellar class G).

500 posts in PopulScience

This is the 500th post I have published on the Spanish version of this blog, just after 11 years since the creation of, on January 15, 2014. The English blog, PopulScience, where I almost always publish the same posts, translated into English, came about later. I did not publish the first article until August 12, 2014, so it was half a year late. However, over the years, it has gradually recovered the lost ground, to the point that right now there are 498 posts, only two less than the Spanish blog.

Why is this? It is very simple: in the United States the summer holidays are shorter and end in mid-August, while in Spain the whole month of August is a non-working month. When I take a vacation from the blog, I stop publishing posts in the Spanish version for most of July and all of August, and start the new course at the beginning of September. On the English blog, however, I start in mid-August, and so every year I catch up on two or three posts. After eleven years, I have almost made up for the half-year delay that the English blog was behind. This summer, God willing, the two blogs will be on a par.

Giant Viruses

John Maynard Smith

In 1966, H.J. Muller defined living beings as follows: Any being capable of multiplying with inheritance and variation. With this definition, which prioritizes reproduction and evolution as the definition of life, viruses should be considered as living beings. Other biologists, such as John Maynard Smith, thought that this criterion was too broad. It would mean that nucleic acids are alive, since they are capable of reproducing with inheritance and variation. That is why they propose adding another criterion: A living being is capable of reproducing and metabolizing. This would exclude nucleic acids, and therefore viruses, which are nucleic acids enclosed in a protein capsule, and viroids, which are isolated nucleic acids.

The tree of life, the family tree of all species of living beings, seems to indicate that all beings formed by one or more cells descend from a single individual, the first living being, which is called LUCA (Last Universal Common Ancestor). As I said in another post, some think that perhaps LUCA was not a single individual, but a network of individuals. But where do viruses come from?

Universe or multiverse?

In the posts in this blog I have often said that theories about the multiverse (there are many) are not science, but speculations, because it is impossible to design an experiment that demonstrates the existence or non-existence of these multiverses.

In an article published in May 2023 in the journal Springer Nature, entitled Is Everyone Probably Elsewhere?, the authors claim that it would at least be possible to distinguish between the following two hypotheses:

1. Our universe is unique, it does not belong to any multiverse.
2. Our universe belongs to some multiverse. Of course, we would have no idea what type of multiverse it would belong to.

Physics, Mathematics and Mathematical Physics

Eugene Wigner

Eugene Paul Wigner was a Hungarian physicist who received the Nobel Prize in Physics in 1963 for his contribution to the theory of the atomic nucleus and elementary particles. In a famous article published in 1960, Wigner said:

It is important to point out that the mathematical formulation of the physicist's often crude experience leads in an uncanny number of cases to an amazingly accurate description of a large class of phenomena. (“The unreasonable effectiveness of mathematics in the natural sciences”. Communications on Pure and Applied Mathematics 13: 1-14).