The dream of antigravity

Man has always wished to be able to fly. Seeing how birds do it and not being able to do it has obsessed him, to the point of causing quite a few accidents. It is a craving that even very young children know. Some mishaps caused by the viewing of the movie Superman at the end of the seventies may be proof.

At the end of the 19th century, two fundamental interactions were known: electromagnetic and gravitational. In one respect, both are quite different. Electrically charged bodies can have a positive or a negative charge. A positive and a negative charge attract each other; two positive or two negative charges repel each other. Likewise, magnetic bodies have two ends with magnetism of a different type, north and south. If we bring two magnets together, the north end of one and the south end of the other attract each other; ends of the same type repel each other.

A conversation with ChatGPT

Last January I decided to test the latest hit in Artificial Intelligence, ChatGPT from OpenAI. To do this, I carried out two independent sessions (I don’t know if the program connected them to each other). My questions had to do with the following scientific topics:

• The first session dealt with a series of questions about the general theory of relativity, cosmological theories, and the standard cosmological model.
• The second session dealt with the special theory of relativity, the limit of the speed of light in a vacuum, and the possibility of time travel.

After the first session, my conclusions are the following:

Do black holes have hair?

Black holes are strange objects. They are accumulations of extremely compact matter, which exerts such huge gravity that at less than a certain distance (the event horizon) nothing can escape their attraction, not even light. Hence their name.

The existence of black holes had been predicted in the 18th century by the English geologist John Michell and the French astronomer Laplace. At that time nobody paid attention, but from 1915, when Einstein formulated the theory of General Relativity, the interest in these mysterious objects grew. It was soon concluded that when a massive star exhausted its ability to produce nuclear fusion reactions, no force of nature would be able to overcome the gravitational pull of the remaining matter, resulting in a black hole. But for a long time there were doubts about their real existence, for the theory seemed to predict that the matter located inside a black hole would occupy a zero volume and therefore would have an infinite density. As physicists usually suspect that infinity is a mathematical concept that cannot happen in real life, there were two possibilities: either black holes do not exist, or Einstein's theory would have to be modified so that they wouldn’t have an infinite density.

Compatible, incompatible, possible, impossible

I wish to clarify the four concepts of the title, which are sometimes confused when talking about physical theories and their application:

• An event (real or imagined) can be compatible with a theory. In this case, if the event were real, it would not pose any problem for the theory, which admits in principle the possibility of that event taking place.

More scientific misrepresentations from the media

On my first day every year, lecturing in the degree on Telecommunications Engineering, I used to say this to my students:

Don't believe any scientific news published in the press or in generalist media. Most of them are false or have been misunderstood.

In previous posts I have mentioned several cases of scientific misrepresentation by the media, although sometimes the fault lies not with the journalist, but with the scientist, who tries to sneak in philosophical ideas based on reductionist materialism as if they were science. In this post I'm going to comment on three relatively recent news stories, published in the Spanish press, and try to explain what is really behind them.

Scientific models: adjustment or validation?

Leonard Nimoy
as Mr. Spock

One of the ways in which science advances is by building models, which are often made up of more or less complex sets of mathematical equations, and trying to verify whether or not these models adapt to the functioning of the real world, as described by our senses and our instruments.

When building and using a model we must consider two distinct phases:

• Model adjustment: it consists of assigning values ​​to the parameters of the model to ensure that it fits the data we already have about the real world. A model not adjusted to such prior knowledge would be totally useless.
• Model validation: it consists of using the model to make surprising predictions that nobody could have foreseen without the help of the model. If these predictions are confirmed, they become surprising accurate predictions, validating the model. However, the validation is never final, for a new surprising inaccurate prediction could invalidate it in the future.

Let's look at a few examples:

Newton, the greatest scientist of our civilization

Isaac Newton

As I said in the previous article, in my biographical dictionary 1000 great scientists (1996) and an unpublished book, I proposed an objective quantification of the importance of different scientists, using measures such as the number of lines that various encyclopedias assign to each. Six scientists, one Greek (Aristotle), of whom we have already spoken, and five from the West (Descartes, Newton, Darwin, Freud and Einstein) were tied with the highest score in these studies. Among these five, is there one who can be considered the greatest scientist of our civilization?

In 1964 Isaac Asimov conducted another study (The Isaac Winners) on the relative importance of men of science, which resulted in a list of the 72 best scientists of all time, in his opinion. This list is simply qualitative and does not establish a relative order among the names that appear in it, although Asimov (again in his opinion) asserts that Isaac Newton, who happened to be his namesake, was the greatest scientist of all time.

Is there a universe?

The Spanish Wikipedia defines the universe thus:

The universe is the totality of space and time, all forms of matter, energy and momentum, plus the laws and physical constants that govern them. However, this term is also used in slightly different contextual senses and refers to concepts such as cosmos, world or nature. Its study, at the highest scales, is the object of cosmology, a discipline based on astronomy and physics, which describes all the aspects of this universe, together with its phenomena.

Before applying to the universe, the Greek word cosmos meant order and beauty. Notice that this sense is maintained in one of its derivatives, the word cosmetic. The Latin word mundus also has the two meanings: as a noun, it means the world, the totality. As an adjective, clean, neat, elegant. Presumably the first sense was copied from Greece, and to translate the world cosmos they adopted the same word that represented in Latin its other meaning. Finally the word nature (physis in Greek) has phenomenal connotations (rather than to the universe, it refers to what happens in it). From this word come physics (the study of nature) and metaphysics (beyond physics).

Alternatives to the Big Bang

The Big Bang theory has a problem, which can be explained by the following set of questions:

• The farthest we can see is the cosmic microwave background radiation, which originated about 380,000 years after the Big Bang. We cannot see directly what happened before, because it is hidden behind that radiation.
• It is true that we cannot see, but we can deduce what happened in those first 380,000 years by applying the standard physical theory, i.e. general relativity. It is also possible to check those deductions, for they offer predictions, such as the average composition of the cosmos, which fit well with the experimental data.
• The problem is, general relativity does not take us to time zero, the Big Bang itself. This theory can be applied only from 5×10^-44 seconds after the Big Bang (the Planck time), as quantum effects were predominant before that time, and we do not have a physical theory that unifies quantum mechanics with general relativity.

The theory of everything

In Joe Dacy’s science fiction novel Esquelle and the lost enclave (2015), which belongs to the hard science fiction genre, skillfully combined with espionage, adventure and political fiction, and covers 1500 years of future history, including the invention of time travel and the manipulation of the past, one can find the following quotation:

At this point, the Theory of Everything is actually the Theory of Not Very Much

Is Joe Dacy II right? Do we think we know a lot, but we know very little? What is this Theory of Everything, with such a grandiose name?

This name has been invented by a few physicists and cheered by the press, on the same line as the name of the God particle applied to the Higgs boson, possibly discovered in 2012. Yes, I say possibly, as it is not certain. Although the particle discovered had the predicted mass and decomposed in some of the predicted particles (not all of them), it has not yet been proved that the Higgs field exists.

What is meant by the name of Theory of Everything is that we know everything about the physical fundamentals of matter, that we do not need God.

What does physics tell us about time travel?

In the previous article we considered a few paradoxes that could bring us to doubt the possibility of time travel. But what does physics say about this? Is there any theory that would make time travel possible? Is it true, as some say, that Einstein’s special theory of relativity implies that it will be possible to travel in time?

First of all, we must refute a fairly widespread misconception. We often hear people saying something like this:

If it were possible to travel at speeds greater than the speed of light, we would travel backwards in time, because the passage of time would become negative.

Is this true? Consider the equation that defines the relationship between proper time and external time for a body moving with a uniform rectilinear speed, according to the special theory of relativity:

Where t is the time experienced by travelers who move at speed v; t₀ is the equivalent external time (the time experienced by an object at rest); and c is the speed of light. 

We can see that, for v < c, the term inside the square root is positive and less than 1, its root would also be less than 1, and therefore t < t₀ (the time experienced by the travelers is shortened).

The mystery of too many variables

Standard theory of particle physics

We have now two great physical theories:

·         On one side, quantum mechanics, which applies primarily to very small objects (those scarcely affected by gravity), and is the basic tool for the standard theory of particle physics.

·         On the other, general relativity, which applies to very large objects (from the planets to the whole universe, those for which almost nothing matters except gravity), and is the main tool for the standard cosmological (Big Bang) theory.

Unfortunately, the two theories are not mutually compatible, so that physics is far from having resolved its outstanding issues. Moreover, these two theories depend on about forty independent variables. Many physicists think that they are too many. If it were true, it would mean that the configuration space of nature has about forty dimensions. If it is difficult to imagine a four-dimensional space, what about forty!