What’s the matter with dark matter?

Comparison of observed and expected
rotation curves of galaxy M33
(Wikipedia)

Nine years ago, I published here a post entitled Dark Matter or New Theory, where I pointed out that the motion of stars in galaxies does not match theoretical predictions. The problem can be solved in two ways:

1.      Assuming that galaxies have much more mass than we can see. The mass we cannot see was called dark matter, where the word dark means that we don't know what it is.

2.      Assuming that Newton's laws should be corrected in the outer part of galaxies, where the acceleration of stars is very small. Various corrections to Newton's equations have been proposed that would satisfactorily solve the problem, which are called MOND (MOdified Newtonian Dynamics) theories.

Traitors to the Human Species

The Three Body Problem is a gripping science fiction novel by Liu Cixin, which contains a wealth of information about ancient and modern Chinese history. But I fear it distorts science. And my first golden rule of good science fiction is not to distort science. I think distortions are dangerous because uninformed readers can be led to believe that certain false things are true.

I’m not worried about the assumption that string theory is true. It could be, although it has lost a lot of backing in recent years. But the description in the novel of the three-star system Alpha Centauri has nothing to do with reality, even though that description is crucial to the plot.

Should Barbie chat with children?

ChatGPT and similar tools, called LLMs (Large Language Models), are being used with greater frequency in our daily lives. Google, for instance, has integrated its GEMINI tool with its search engine. Sometimes, when the program behind the search engine deems it appropriate, the question asked is sent to GEMINI, and the response of the LLM appears first, albeit with this warning at the end, in small print:

AI responses may include mistakes.

Of course, they may include mistakes! These responses are not generated by understanding the question, but by using information previously obtained from the Internet, and applying an algorithm based on extracting words that typically appear in that information after the previously generated words. See a post in this blog where I explained that algorithm. Since the information extracted from the Internet can be true or false, and the algorithm can introduce new falsehoods where none existed, the answers obtained may be correct, partially correct, or completely wrong, therefore Google's warning is valid.

More bad uses of scientific language

George Boole

To continue with the previous post, I’ll add here a few more cases of bad translations between English and Spanish, many of them due to the existence of false friends between those languages. In other cases, the English word is used as-is, although there is a Spanish word that can be used instead.

Bad uses of scientific language

Journalists and scientists perpetrate sometimes abuses of scientific language. In this post, I’ll mention a few.

·      Heard on the radio news: Meteorology is to blame for the spread of this fire. I suppose we must sue the meteorologists. According to Wikipedia, Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. Apparently, saying that excessive heat or dryness is to blame for the spread of the fire is too vulgar, and the news needs to be phrased in a more scientific way.

·     DNA (deoxyribonucleic acid) is a molecule that contains the genetic information of living beings. The idea of ​​identifying it with the properties that define a different entity, such as a cultural construct or a society, is an ingenious metaphor, but through overuse and repetition it becomes hackneyed. We hear frequently about the DNA of a football club, or the DNA of a company, or the DNA of the work of an artist.

·      A variation on the previous case consists of using the word genome instead of DNA with the same meaning, as in this example, which appeared in an article in the Spanish newspaper El País with the following headline: The household genome: the new consumer battle is fought at home.

Mysterious Particles

Some physicists sometimes act as if the hypotheses they propose to explain the mysteries of the universe are always true. But a hypothesis is nothing more than a proposal to explain a natural phenomenon, and it cannot be considered a confirmed theory until it has provided one or more surprisingly accurate predictions. This last detail, which is essential, is usually omitted.

In 2020, I read two popular books on cosmology and particle physics (the two branches of physics are closely related):

Can density be infinite?

First photo
of a black hole

Einstein’s general theory of relativity allows for the existence of objects with infinite density (singularities). There are two types:

1.      Black holes, accumulations of matter in a null volume, either at the center of a galaxy, or as the result of a supernova explosion.

2.      The universe, at its initial moment (the Big Bang).

A star like the sun is in equilibrium because the gravitational attraction, which tends to make it contract, is equal to the expansion caused by the nuclear reactions taking place inside the star. When a star much larger than the sun exhausts its nuclear fuel (first hydrogen, then helium, then other elements), as there are no longer nuclear reactions to stop the contraction, the star implodes. When the implosion rebounds, the star throws large quantities of matter into space: a supernova explosion, which for some time makes the star brighter than a whole galaxy. But there is always a remainder of matter, which gives rise to a new type of object.