Is history repeating itself?

Alexander Vilenkin

The idea that history repeats itself is a commonplace notion, often expressed through sayings such as man is the only animal that trips twice over the same stone. However, that is not what we are addressing here, as such repetitions are always partial—events never recur in exactly the same way. Here, we will discuss whether it is possible for history to repeat itself in such way that events unfold exactly as they did before.

In principle, there are two ways history could repeat itself:

·         In time: According to theories of cyclical time—accepted by various civilizations—time repeats itself. Greek astronomers like Hipparchus and Ptolemy calculated that the cycle of the precession of the equinoxes (the wobble of the Earth's axis) lasted about 36,000 years (one degree every 100 years). Believing that the position of the stars determined human destiny, some concluded that every 36,000 years—when the stars returned to the same positions—history would repeat itself exactly, and the same people would be born again. Although Saint Augustine rejected this theory in The City of God, some Scholastics revived it, and the Church was forced to condemn their ideas as heretical. I discussed cyclical time in two previous blog posts: Cyclic Time and Linear Time and Is Time Infinite?

Second-generation planets

Betelgeuse, a red giant

Theories regarding planet formation have evolved over time. In the early decades of the 20th century, it was assumed that the planets of the solar system were formed when a passing star came close to the Sun and, through gravitational attraction, stripped away material that subsequently coalesced into planets. Given that such close encounters between stars must be extremely rare, this theory implied that the existence of planets around a star would be a highly uncommon phenomenon.

Current theory differs. It is now believed that when a cloud of gas and dust contracts to form a star, a portion of the cloud remains outside the protostar, forming a disk that flattens around the system's equator. Gradually, the gas and dust concentrate and condense around larger nuclei, eventually giving rise to planets. This theory explains why nearly all planets in the solar system orbit the Sun in roughly the same plane. It suggests that the existence of planets should be commonplace; indeed, the discovery of thousands of planets around nearby stars lends strong support to this theory.

A city on the Moon?

Lunar transport vehicle, film 2001

Building a lunar colony is a favorite theme in science fiction. I would cite one of my favorite stories featuring such a colony: The Menace from Earth by Robert A. Heinlein (1957). A lunar colony also appears in the novel and film 2001: A Space Odyssey by Arthur C. Clarke.

Recently, with the return of humans to the Moon (still in its early stages, as astronauts have only orbited the Moon), there has been renewed discussion about the possibility of building a permanent lunar facility. There is even talk of establishing a city, with a population of over 100,000.

A piece in Physics World—referencing another article published in Frontiers in Space Technologies—addresses this issue by examining the needs of a lunar colony and the potential cost of maintaining it.

A planet, or a satellite?

ESO/M Kornmesser

On July 23, the journal Nature published an article announcing the discovery of what it called an “exosatellite,” although in my opinion, this is a wordplay with the meaning of the word satellite. Let's look at the concepts involved:

·         In our solar system, there is a central star, the Sun, around which eight planets, several smaller planets, and many thousands of asteroids and comets revolve. In addition, almost all the planets have satellites, much smaller than the planets. The largest in proportion to its planet is the Moon, whose mass is 81 times less than that of Earth. There are four satellites larger than the Moon: three of Jupiter (Ganymede, Callisto, and Io) and one of Saturn (Titan). Many exoplanets have been discovered in systems of this type.

Ontological proof of God’s existence

Elizabeth Anscombe 

In 1078, Saint Anselm of Canterbury proposed a proof of God’s existence in his work Proslogion, which has given rise to various versions that attempted to improve it (usually without success) and to attempts to demolish it. Even today, it continues to provoke the attention of philosophers and corrections to its translation. This is Saint Anselm's argument, originally written in Latin, as it is usually translated:

i.      That than which nothing greater can be conceived at any rate exists in the mind of the fool who says there is no such thing.

ii.   If that than which nothing greater can be conceived is only in a mind, it can be thought to exist in reality too, which is greater.

iii. Therefore if that than which nothing greater can be conceived is only in a mind, it is not that than which nothing greater can be conceived.

iv.  But it is a contradiction to say that something than which nothing greater can be conceived is something than which a greater can be conceived.

v.    Therefore that than which nothing greater can be conceived exists in reality as well as in the mind.

The Origin of the Universe and the Immortality of the Soul

Aristotle

The philosophical and scientific works of Aristotle were lost to Western Europe for centuries and were rediscovered through Arabic translations. Their rediscovery gave rise to a Western European philosophical movement, Scholasticism, with such prominent figures as Albertus Magnus, Thomas Aquinas, Duns Scotus, William of Ockham, Jean Buridan, Albert of Saxony, Nicholas Oresme, Gregory of Rimini, and many others.

I will recall here a curious debate that took place among the Scholastics between the 12th and 14th centuries, which may seem pointless to us today, but which was quite important in its time. For those who wish to learn all the details of the debate, I recommend Pierre Duhem's book, Le Système du Monde, volume VII.

The debate originated from the detection of an incompatibility between two statements due to Aristotle:

Time and Motion

Pierre Duhem

Time and motion are intimately related, because there can be no motion without time. In fact, Aristotle understood it the other way around, thinking that if there were no motion, there would be no time. He defined time in terms of motion, as the number of changes in terms of before and after. And the basic motion, upon which all others depend, would be the rotation of the sphere of the fixed stars.

·         Saint Augustine, in his Confessions, dedicated Book XI to the philosophical study of time. He rejects Aristotle's theory, denying that time depends on the existence of motion, and doubts that time exists outside our minds, although his famous quote reveals his uncertainty about time: What is time? If no one asks me, I know; if I want to explain it to a questioner, I don’t know.

AI failures and successes

In previous posts, I've mentioned several cases where AI tools (such as LLMs) failed to answer my questions. To balance things out, this time I'm going to talk about two failures and one success.

The problem I posed was the following: There was a quote I wanted to use in one of my book reviews, but I wasn't sure of the exact words or the author, although I suspected it might be by C.S. Lewis. As I remembered, the quote was:

Every decade in England and every year in the United States, someone says to have discovered what Shakespeare really meant.

Hypothetical science and dark matter

Bullet Cluster, hot gas in pink, dark matter in blue

In several previous posts in this blog, I have pointed out that physicists and cosmologists frequently forget the real world and construct theories based on speculations not based on concrete data, observations, or experiments, but only in their imagination. Let’s look at a few examples:

·         Is physics losing touch with reality? In this post, published in 2017, I used as examples the various theories about multiverses, the theory of everything, and some ideas that would make it possible to build a time machine (in principle, but hardly in practice).

·         Is physics: science or literature? In this post, published in 2018, I referred to Freeman Dyson's procedure for extracting energy from stars and the idea that an advanced civilization could resist the accelerated expansion of the universe.

·         Pathological science, wishful science, or ironic science? This post, published in 2023, points out eleven cases of scientific research without experimental basis.

The dark side of AI

Those companies that market Large Language Models (LLMs), such as OpenAI (ChatGPT and GPT-4), Google (GEMINI), Meta (Llama), Anthropic (Claude), and Deepseek, establish controls to prevent their tools from being used for nefarious purposes, such as assisting a young person in committing suicide, providing instructions for building Molotov cocktails or atomic bombs, helping to design viruses potentially usable in biological warfare, or teaching how to manufacture dangerous drugs.

The problem is that these controls are fallible, as demonstrated by cybersecurity expert Dave Kuszmar, who published a summary of his research in an article that appeared in the IEEE's Spectrum magazine in August 2026. Their fallibility makes them dangerous, but the companies in question seem to ignore the dangers and remain silent when they are brought to their attention.

Kuszmar has developed at least seven procedures to bypass the controls of commercial LLMs and obtain dangerous information. The first two were these:

Persons cited in Populscience

Poisson distribution of person names

I enjoy compiling statistics on many things. Naturally, I also do it for this blog. One of the statistics I often compile is that of the names of people (scientists or otherwise) most frequently mentioned in the blog, which now has 564 posts. I presented such a table in January 2024, when 449 articles had been published, in the post titled Ten years of Divulciencia-Populscience, and I think it's time to update it. Here is the corresponding table, showing 40 people who have been mentioned at least 10 times.

Human Dignity: Religion, Politics, or Natural Morality?

The sentence against Socrates

In connection with his visit to Spain, and in particular his address to the Parliament, Pope Leo XIV has been criticized in some media outlets for having argued that democratic parliaments must be subject to certain basic moral norms, such as those associated with human dignity. It has been said that the Pope was speaking as head of the Catholic Church, that the Spanish Parliament is not composed solely of Catholics, and that he should not have questioned the legitimacy of the Parliament to enact laws, based on the majority rule. This is the paragraph that has attracted the most disagreement:

Paradoxes of Time Travel

In several previous posts, I have discussed various paradoxes that time travel could cause if it were possible. Travels to the future controlled from the past do not cause paradoxes. That they are possible is obvious, since we all travel to the future at a rate of twenty-four hours each day.

It is also possible to travel to the future if one is in a coma and later awakens; or through hibernation, if it were possible, which it is not at the moment, but it may become so someday; or by traveling through space at relativistic speeds, which would result in a time dilation that, upon returning to the starting point, translates into a journey to the future. This last procedure is not possible right now, but it could become so someday, apart from the technical difficulties of achieving it.

Units of Length

It was natural for humans to use their own dimensions as a basis to measure distances. Thus arose the inch, the width of a thumb; the span, the width of the palm of the hand with spread fingers; the foot, the length of a human foot; the cubit, the distance from the elbow to the tip of the middle finger; the fathom, the distance between the two hands with outstretched arms; the pace, the distance between the two feet while walking; and so on.

This system of measurement has two problems. The first: that these lengths depend on each person. The second: that they are not simple multiples of one another. To solve the first problem, standard values ​​were introduced. To solve the second problem, some of the measurements were slightly modified. Thus, in England, the inch was approximated by one-twelfth of a foot. This introduced a third problem, because each country chose different standard values ​​and made approximations in its own way.

A new Goldilocks zone

We are familiar with the Goldilocks zone, considered necessary for the emergence of life in a planetary system. It is the region where the surface temperature of the planet allows for the existence of liquid water, which is generally considered essential for life as we know it, although in science fiction literature (remember Fred Hoyle's The Black Cloud) there are life forms that might not require this condition.

Planets very close to their star would have a temperature too high for the existence of liquid water; all the water would vaporize, and in some cases escape the planet's gravitational pull. On very distant planets, the temperature would be too low, and all the water would be in a solid state (ice). In both cases, it is thought that the emergence of life would not be possible.

The Death of Words

C.S. Lewis

In an article published on September 22, 1944, in The Spectator with the same title as this post, later included in the collection Of This and Other Worlds, C.S. Lewis pointed out that the meaning of many words evolves until they become mere synonyms for “good” or “bad,” and when this happens, the word is dead, because its original meaning is eventually forgotten, while the new one is useless, since the number of synonyms for “good” or “bad” continues to grow.

Lewis notes that many words, throughout history, have undergone this evolution, which transforms them from descriptive terms into insults or praises (synonyms for bad or good). He gives as examples villain, which from inhabitant of a village came to mean  a mean, evil, or unprincipled person (synonyms for bad); bastard, which from illegitimate child came to mean a person, especially one who is mean or unpleasant (another synonym for bad); or to say that someone is a gentleman, which initially referred to a profession or social category, and came to mean a man of good breeding, education, and polite manners (that is, a synonym for good).

About the Encyclical Magnifica Humanitas. Can it be called Luddism?

The publication of Pope Leo XIV's Encyclical Magnifica Humanitas has prompted some people to accuse it of being an exercise in Luddism and a return to the Middle Ages (many of these people know little about the medieval period), sometimes accompanied by gruesome images of robots being burned at the stake, undoubtedly generated using AI tools. The speed of their responses is so surprising that one may wonder if they are judging the text without having read it. Are they right? Can the encyclical be accused of Luddism?

Let's begin by defining the word Luddism, as it appears in the Merriam-Webster dictionary:

The beliefs or practices of the Luddites: one of a group of early 19th century English workmen destroying laborsaving machinery as a protest. Broadly : one who is opposed to technological change.

It is, therefore, a term primarily applied to the use of violence against technological advancements. Violence is certainly difficult to justify, although in Ned Lud's case it is understandable, considering what happened at the time as a consequence of the introduction of machinery (looms) in textile factories. Some employers took advantage of this to dismiss their workers, telling them something like this:

Craig Venter, rest in peace.

Craig Venter

Craig Venter died on April 29, less than six months shy of his 80th birthday. This biologist revolutionized genomics research with two major achievements:

·         Deciphering the human genome. The Human Genome Project, whose scientific director was Francis Collins, was launched in 1990 by a multinational consortium with huge funding and the support of several governments. Its goal was to decipher in 15 years all the genes in human DNA. In 1998, eight years later, Craig Venter founded Celera Corporation and decided to apply the shotgun sequencing method, which he had developed, to decipher the human genome in parallel with the Human Genome Project, but much faster and with far less funding. His efforts culminated successfully, as in 2000 Venter and Collins jointly announced the success of both projects, several years ahead of schedule, and presented partial results, which were completed in 2003.

The future of science

Friedrich Nietzsche

With the loss of the impetus of Christianity, cyclical conceptions of history have resurfaced in the West. Let us see how Nietzsche expresses this in Thus Spoke Zarathustra (Part III, 2.2), at the same time as predicting the replacement of man by the Superman, so he should have been immune to it:

And that spider creeping slowly in the moonlight, and that same moonlight, and you and I, standing before this door chatting about eternal things—must we not all have existed once before? And must we not come again and travel that path that stretches before us, that long and dreadful path? Won't we have to return eternally?

Twentieth-century atheist cosmologists often expressed a preference for a cyclic cosmology, which in their view would make God unnecessary to explain the existence of the universe. Although some of those theories (steady-state cosmology and the alternation of the Big Bang and the Big Crunch) are no longer in vogue, thanks to the data we now have about the origin and future of the universe, new theories continually emerge to replace them.

The Synthesis of Science and Faith in Western History

S.Augustin, by Louis Comfort Tiffany
Lightner Museum

By studying the history of science, one fact becomes evident: while other civilizations reached remarkable technical, mathematical, or astronomical heights, within European Christendom germinated a systematic, accelerated, and extraordinary scientific development, incomparable to that of any other civilization, past or present. Why this spectacular difference? The answer is not a matter of chance, but of worldview. Science and faith are not adversaries, but pieces of a puzzle designed with astonishing precision.

The supposed war between science and faith is a false diatribe fueled by nineteenth-century prejudices. While science deals with the material and experimental world, philosophy and faith deal with being and purpose. The error of scientists like Stephen Hawking was to declare that philosophy is dead and then, immediately afterward, propose theories (such as model realism or the multiverse) that are philosophical speculations.

Quantification of science

Chapter 2 of my book, The Quantification of History and the Future of the Western World, is dedicated to quantifying science, something I had done in the introduction to my dictionary, 1.000 grandes científicos (1,000 Great Scientists, Editorial Espasa, 1996), although in this new book I have introduced new tables and figures, and expanded upon the analyses carried out there. Here I will summarize some of the results of this chapter.

The following table shows the list of the 24 greatest scientists in the history of Greco-Roman and Western civilizations. The complete study considers the names of 1,000 scientists, who have been ordered according to the number of lines dedicated to them in the sources and encyclopedias used as the basis for the selection. Personally, I don't agree with all the results, but if I were to give in to the temptation to alter them at any point, that would have been an end to the objectivity I was seeking.

Quantification of literature

William Shakespeare

The analyses conducted about the literary field in the book The Quantification of History and the Future of the Western World cover almost three thousand years of Greco-Roman and Western literary history. This is a biographical analysis, based on recording the birth, flourishing, and death dates (if known), as well as the nationality of the writers. Each of the 210 historical figures considered has been assigned a quantitative rating, represented by a number between zero and ten. This number was calculated based on the number of lines dedicated to each author in the texts or encyclopedias used as the basis for the study.

Can history be quantified?

Can the history of culture be quantified? I believe many historians would answer this question in the negative. The prevailing view seems to be that historical events are unique and unrepeatable, and any attempt to discover laws or recurring patterns in these phenomena is usually met with extreme suspicion. Let us remember as an example the antagonistic reaction provoked by works such as The Decline of the West by the German philosopher and historian Oswald Spengler, or A Study of History by the British historian Arnold Joseph Toynbee, whose conclusions, however, were based on qualitative analysis. It is not surprising, therefore, that to find true quantifiers of history, one must turn to authors who were not professional historians.

The case of Galileo

The case of Galileo is one of the most widespread modern historical myths, widely used by anti-Catholic propaganda, along with the anti-Spanish Black Legend. It surfaces even in the most unexpected places. For example, in the book A Song for Nagasaki, an excellent biography of Takashi Nagai, scientist, convert, and atomic bomb survivor, whose beatification process is underway, his biographer Paul Glynn, an Australian Catholic priest, states twice that Nagai's conversion was delayed due to his concern about the atrocities committed by Catholics throughout history, and cites four: a) the Crusades; b) the Inquisition; c) the genocide of native Americans in South America; and d) the case of Galileo. It is curious that Nagai says nothing about this in his autobiography, and it is surprising that a Catholic priest would fall for such historical fallacies.

New Ways to Scam the Unwary

Wallet scam
Spanish film "Los Tramposos"

About 30 years ago, I received my first attempt at the Nigerian scam: a letter from someone unknown to me offering me the chance to participate in a capital evasion operation involving several million dollars, which they proposed depositing into my bank account, offering to share the profits in return. Of course, I didn't reply, although I kept the Nigerian stamp that came with the letter. I suppose that if I had replied, they would have asked for access to my account to make the transfer, and instead, it would have been emptied.

Since then, I've received dozens of similar attempts, since a certain time via email, always originating from some African country. This scam is, in a way, similar to the wallet scam, because in addition to the swindler, the victim also tries to commit fraud; in one case against the supposed mentally challenged person offering the alleged money, in the other against the governments affected by the capital evasion.

The inconstant constant

Georges Lemaître

In a previous post, The Hubble-Lemaître Law, I explained how Georges Lemaître discovered in 1927 the expansion of the universe, but as he published in a French-language journal, it didn't make a great impact, and for almost a century the discovery was attributed to Edwin Hubble, who published in 1929 in a much more widely circulated English-language journal. This injustice was corrected on October 29, 2018, by the International Astronomical Union, and I echoed the renaming of the law in my post, published three days later in this blog.

The Hubble-Lemaître Law says this: The farther away a galaxy is, the faster it is receding from us. Its recessional velocity is proportional to its distance. The constant of proportionality is called the Hubble constant, which has the dimension of 1/time. In the International System of Units, this dimension would be expressed as seconds⁻¹ or 1/second, but in practice, its definition (speed/distance) is used, with the following units: km/s/Mpc, which means: the increase in the recessional velocity of a galaxy (in km/s) as its distance from us increases (measured in Megaparsecs). One Megaparsec (Mpc) is one million parsecs, and one parsec is equal to 3.2616 light-years.

A Radio Telescope on the Moon

One of the most interesting radio frequencies for radio telescopes is that emitted by hydrogen atoms when excited by an energy input. Upon returning to its ground state, the atom emits a photon with a frequency of 1.42 gigahertz. This frequency corresponds to the microwave region, which ranges from 300 MHz to 300 GHz. If we focus a radio telescope on a cloud of gas and dust in our galaxy, which is composed mostly of hydrogen, this frequency is easy to detect.

But what happens if we try to detect this frequency in very distant regions of the universe? The expansion of the universe affects these waves by lengthening them (that is, decreasing their frequency), in the same way as the frequency of the cosmic microwave background radiation, which was initially in the visible and infrared regions of the spectrum, is now in the microwave region, with its peak at a frequency of 160.2 GHz.

A Language Model Trained with Populscience

Since this blog has almost 550 posts, and it's becoming increasingly difficult to find the information you're looking for, my friend Manuel Márquez suggested allowing readers to ask questions to a Language Model (LLM) trained with the blog's content. I thought it was an excellent idea, so I used Google's NotebookLM tool, and you can use it from now on.

One of the features this product offers is the automatic generation of blog posts. To test it, as an experiment, I requested it to generate one, without specifying a particular topic. Of course, I’ll go on writing my posts without the help of the LLM. Before publishing it here, I corrected it manually, because there were many references to my name (which I removed), and also some curious errors, such as making its title 5 Keys to the Universe, 'AI,' and Evolution and then dividing the text into six points. The following is the resulting post, which summarizes the content of this blog in just two pages:

The Use of “AI” Tools

The second entry for the word tool in the Merrian-Webster dictionary states:

Something… used in performing an operation or necessary in the practice of a vocation or profession

Since the origin of the genus Homo, human beings have used tools, which together with skeletons or fossilized bone fragments are one of the main sources of information about our ancestors. Monofacial and bifacial pebble tools seem primitive today, but during human prehistory they served as weapons and tools and surely helped us survive.

Information technology, which has developed significantly during the last century, has provided us with many useful tools. Throughout the 21st century, these tools have become increasingly “intelligent,” tackling tasks that until very recently could only be performed by humans. But when using them, we should keep in mind some very general ideas, which should always be applied, but not always are:

The Kingdoms of Cladistics

In the previous post, I discussed cladistics, the new way of classifying living things based on their position in the tree of life, and mentioned some of the difficulties that arise when trying to adapt the previous classification system, based on the taxonomic tree and Linnaeus's classic categories—kingdom, phylum, class, order, family, genus, and species—to cladistics.

There are more difficulties. For example, let's consider the concept of kingdom, Linnaeus's highest taxonomic category. Traditionally, living things were divided into two kingdoms: animals and plants. These two kingdoms were clearly separate, with very different characteristics. Thus, animals were defined as organic beings that live, feel, and move by their own impulse, while the plant kingdom were beings that live but do not feel and do not move. It was acknowledged that these definitions were imperfect, because there were exceptions, such as sponges, which barely move but are animals, and some plants, like mimosas, which seem to sense certain stimuli and move in response.

Cladistics: A new classification of living beings

Tree of life
https://evogeneao.s3.amazonaws.com/
images/content/es/tree-of-life_2000.png

In 1735, the Swedish naturalist Carl von Linné (Linnaeus) created the binomial system of biological nomenclature still in use today, and a classification system for living things that is becoming obsolete. This system used at first seven successive categories: kingdom, phylum, class, order, family, genus, and species. The last two categories are used to name the species. Thus, according to Linnaeus's classification, the human species belongs to the animal kingdom, the phylum Chordata, the class Mammalia, the order Primates, the family Hominidae, the genus Homo, and the species sapiens. Its scientific name, according to Linnaeus's binomial system, is therefore Homo sapiens.