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.

Time Travel and Christ’s Crucifixion

Christ crucified, wood carving
by Manuel Alfonseca Santana

If time travel were possible, the greatest incentive for travelers would be to witness firsthand famous events of the past, such as the assassination of Julius Caesar and many others. The fact that we have no record of the presence of strangers in any of these cases is a significant argument against the feasibility of time travel.

There is no doubt that one of these events, perhaps the most famous of all, would be the Crucifixion of Christ. If time travel were possible, there should have been an avalanche of visitors from future times at Golgotha ​​to witness the most important event in the history of humankind.

In fact, this idea has been used in science fiction literature. In a novella titled There Will Be Time, Poul Anderson has his protagonist travel to Jerusalem on the day of the Crucifixion to witness Christ's death. Upon arriving, he discovers a large crowd, almost all of whom are time travelers.