Martin Rees is not your average astrophysicist (if you can be an “average” astrophysicist). This British cosmologist has been president of the prestigious Royal Society of London, rector of the no less reputable Trinity College, and serves as Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge. In addition, if his resume was not impressive enough since 1995 he has held the honorary title of Astronomer Royal, which places him on the same path that other famous astronomers, such as Edmund Halley or Sir Harold Spencer Jones, have walked before him.

During his career he has studied such exciting and complex phenomena as the role that dark matter can have in the formation of galaxies, the existence of gravitational waves, the formation of black holes, or how quasars are distributed far and wide. of the universe. He has also published several hundred scientific articles and nine popular books. This article is precisely dedicated to the last of them. And it is that in a chapter of ‘In the future: perspectives for humanity’ Rees raises the possibility that the experiments we are currently carrying out in particle accelerators could destroy the Earth Or even the entire Universe.

During his career, Martin Rees has studied such complex phenomena as the role that dark matter can have in the formation of galaxies, gravitational waves or the formation of black holes

Only a handful of scientists can afford to write something like that in a popular book and come out unscathed. Martin Rees is one of them. He approaches this idea by relying on the approaches of other scientists, but by explaining these theories in his work as he does, he gives them at least minimal credibility. And for this reason, it is worth investigating them, but only as a curiosity with scientific ambition. Without worrying us in the least. And it is that in the last section of the article we will see what Javier Santaolalla thinks about these ideas, a Spanish doctor in particle physics who participated in the CERN experiments that led to the discovery of the Higgs boson.

A voracious black hole capable of devouring everything

This is not the first time that someone has defended the possibility that the collision of the particles that we collide in the accelerators causes the formation of a tiny black hole that could increase its mass by absorbing the surrounding matter. But on this occasion, the person who describes this idea is Martin Rees, so it seems reasonable to accept that it could stop being a “wizard” to be considered a scientific curiosity. In his book, Rees affirms that according to the General Theory of Relativity enunciated by Albert Einstein, the energy necessary to produce a microscopic black hole is much higher than that generated by the collisions that we produce in current accelerators.

In addition, and this is something that Rees does not reflect in his book but that has been defended countless times by many particle physicists, if a microscopic black hole were to occur during collisions, it would evaporate in a minimum fraction of time due to the effect of radiation by Hawking. And it would not behave like a stable object or engulf matter insatiably. Explaining in depth how this form of radiation described by the recently deceased Stephen Hawking works would require us to dedicate a full article to it, but it is enough for us to know that black holes emit radiation, and therefore lose mass until they disappear completely. And that the least massive are the ones that evaporate the fastest.

What Martin Rees brings to this discussion, and what makes it interesting beyond what we already knew, derives from some implications of superstring theory. This theory is a hypothesis described by several theoretical models that are candidates to establish themselves as a Theory of Everything, and that, therefore, seek to bring together the four fundamental interactions of nature: gravity, the electromagnetic force, the weak nuclear interaction, and the strong nuclear interaction. In his book, Rees argues that these theories describe spatial dimensions that coexist with the three with which we are all familiar and that could “reinforce the grip of gravity.”

The relationship between these additional spatial dimensions and the gravitational pull Martin Rees is talking about is not clear because his explanation in the book is very brief. In all probability, its brevity is due to the fact that the physics on which the superstring theories that theoretical physicists currently propose are built is extraordinarily complex. In any case, what is really interesting is that Rees gives visibility to the possibility, predictably minimal, that the reinforcement of gravity caused by these extra spatial dimensions causes a particle in very specific conditions to implode, giving rise to a black hole presumably tiny, at least in its early stages.

Earth could transform into a huge strangelet

The word strangelet is peculiar. And it is not at all casual. A strangelet is a hypothetical particle that, according to some theories of current physics, could be a constituent element of strange matter. As you can see, we enter, hand in hand with Martin Rees, in a swampy terrain that does not go beyond the hypothetical. Before proceeding further, it is necessary that we review some notions about the strange matter, a peculiar form of matter composed of only three types of quarks of the six that there are in total: up ( up ), down ( down ), and strange ( strange). ).

The quarks are fundamental particles that interact with each other to form subatomic particles like protons or neutrons, which are, in turn, particles that can be found in the nucleus of atoms. As an example, a neutron is made up of one up quark and two down quarks, which are held together by strong nuclear interaction. The most surprising characteristic of foreign matter is that it is not made up of the protons and neutrons with which we are familiar because it is subjected to such high pressure that these particles are dissociated into their constituent elements, which are precisely the quarks of which we have spoken a few lines above.

If a strangelet comes into contact with the nucleus of an ordinary matter atom it could transform it into strange matter

At the same time, the enormous pressure to which these fundamental particles are subjected causes them to be very close together, causing the foreign matter to have an enormous density. An interesting feature of this form of matter that has been described by theoretical physicists is that it is more stable than ordinary matter that we are all familiar with, which is made up of protons, neutrons, and electrons. Interestingly, some astrophysicists are convinced that the interior of some neutron stars is under such high pressure that the neutrons could appear dissociated in the form of strange matter. A startling fact: the density of a neutron star is such that a “die” of a cubic centimeter would weigh a billion tons.

We already have some intuition about the nature of foreign matter, so we can go back to our strangelets, which, as we saw at the beginning of this section, are the constituent elements of this form of matter. What some physicists postulate, and Martin Rees collects in his book, is that if a strangelet comes into contact with the nucleus of an ordinary matter atom it could transform it into strange matter, releasing a large amount of energy and more strangelets in the process. The latter would presumably be thrown in all directions and when in contact with other atomic nuclei they would produce a chain reaction that would transform ordinary matter into foreign matter.

Rees echoes the hypotheses defended by some physicists that describe the possibility that the collisions of particles that we carry out in accelerators under certain circumstances give rise to the appearance of strangelets. And these when coming into contact with the ordinary matter of which our planet is made (and also ourselves) could transform the entire Earth by contagion into a hyperdense sphere of strange matter, around 100 meters in diameter. Imagine the entire mass of our planet compressed to such an extent that it is confined to such a small sphere. It certainly doesn’t seem like a nice thing. Fortunately, it is only a hypothesis that, as we will see in the last section of the article, has been dismantled by many more physicists than those who defend it.

A phase transition could tear the space-time continuum

The third accident collected by Martin Rees in his book as a possible result of the collisions that we carry out in particle accelerators is even more dramatic than the previous two. In his explanation, Rees resorts to a very illustrative metaphor that argues that the space that contains all the particles and the fundamental forces that govern the physical world could exist in several “phases”, in the same way, that water can be in three states different: liquid, solid or gaseous. What is interesting about this perspective is that, according to Rees, some physicists argue that the vacuum of space could be fragile and unstable.

The instability of the vacuum in certain circumstances caused by the collision of the particles in the accelerators could cause the space to change phase suddenly

During his explanation, he further develops the analogy of space and water by describing the possibility of supercooling water beyond the temperature at which it freezes. However, this is only possible if the water is totally pure and perfectly still. Any disturbance, no matter how minimal, would cause the water to leave this supercooling state and revert to the form of ice. Something similar could happen with space. The fragility and instability of the vacuum in certain circumstances caused by the collision of the particles in the accelerators could cause space to change phase suddenly, thus tearing the space-time continuum and giving rise to a catastrophe that would not only affect the Earth but, perhaps, the entire Cosmos.

All of this is of theoretical interest, but we don’t have to worry

After describing the three “accidents” in which we have just investigated, Martin Rees states that the most accepted theories are reassuring because they ensure that the risk involved in the experiments we are carrying out in current particle accelerators, such as those at CERN, is zero. The reasons given by the bulk of the scientific community to defend this statement are overwhelming: cosmic rays, which are made up of particles with energy much higher than that which we handle in accelerators, frequently collide in the Cosmos, and, as far as we know, they have not produced any catastrophe.

However, we do not have to go back to the ends of the galaxy to reinforce this argument. Those same high-energy cosmic rays are constantly striking the atomic nuclei in our planet’s atmosphere and it is evident that they have not caused the formation of black holes or strangelets, nor the breakdown of the space-time continuum. In any case, to investigate a little more about this matter and clarify it as much as possible, we have spoken with Javier Santaolalla, a Spanish Ph.D. in particle physics and telecommunications engineer who has worked in some of the most respected scientific institutions, such as the French Space Agency, CIEMAT or CERN. In fact, within the latter organization, he was part of the team of physicists that made the 2012 discovery of the Higgs boson possible.

Javier’s first explanations, as expected, are deeply reassuring: “Martin Rees speaks of very unlikely and exotic theories. In his description, there is a lot of speculation because all the scenarios he raises are very strange. We can be sure that the collisions we carry out in particle accelerators are safe if we look at cosmic rays. They are much more energetic than the shocks that we are producing now and those that we will produce in the future, and we have not observed that any planet has collapsed or disappeared due to the action of these very high-energy particles.

Martin Rees talks about very unlikely and exotic theories. We can be sure that the collisions we carry out in particle accelerators are safe if we look at cosmic rays

In addition, Javier points out several very interesting ideas that undoubtedly enrich this discussion: “One theory has even predicted that the Higgs field could be shaped in such a way as to give rise to a tunnel effect capable of tearing the Universe apart. To me personally, as an experimental physicist, these theories make me think that we are so lost about how we should advance our knowledge of fundamental physics that strange ideas like these appear. I believe that the Universe is simpler than all that, and I defend that the theory that will come later will not introduce such speculative and rare ideas.

Before concluding my conversation with Javier, I refused to miss the opportunity to ask him if during his stay at CERN he had ever spoken with a veteran physicist about the possibility that the experiments they were carrying out could lead to an accident. «On one occasion during my stay there I spoke with a veteran physicist and he recognized that hypothetically, in some very particular scenario, even taking into account the cosmic rays, some unwanted effect could be produced. But again it is a hypothetical approach that is based on a very particular scenario, ”Javier recalled.

And he concluded his explanation by noting: «These ideas arise on paper to propose something that could hypothetically be possible, but in practice, it is very likely that they are not correct. In addition, even though they are correct, they must face the improbability of the appropriate circumstances for that effect to take place. For these reasons, this all sounds more like science fiction than science. The LHC will continue to function; it will continue to carry out collisions without any problems and the world is not going to disappear because there is no plausible evidence that we need to worry about.