Cosmology - The thread of the skein

The thread of the skein

J.R. Silva Bittencourt

The thread of the skein

Greek legend tells that Minos, king of Crete, was involved in a confusion with Poseidon, sovereign of the seas, when betraying his confidence. As a form of punishment Pasifae, the wife of Minos, came to have the Minotaur, son with human characteristics mixed with those of a bull.

Minos determined that Dedalus build a labyrinth to trap the beast, in the basement of his palace in the town of Knossos in Crete. Every year, seven young women and seven Athenian boys, taken prisoner in battle, were sent there to be sacrificed. Theseus, a Greek hero, volunteered to kill the Minotaur. Having met Ariadne, daughter of Minos, she decided to help him in the task. For this, she gave him a ball of wool, which would serve to mark the way from the entrance in the labyrinth, avoiding to lose himself when he tried to return. Our hero took advantage of the element of surprise and killed the Minotaur, in addition to releasing the hostages. To leave the place where others could not, Theseus tracked the way back making use of the ball of wool, delivered

by Ariadne.

This Greek legend could be adapted to the modern observation of the stars in the night sky, especially in the case of distant stars and galaxies.

Without the bravery of our hero Theseus and without half the effort expended by him, when we point our telescope towards a star, the Minotaur lies dead beside us. With the mission accomplished, we must now get out of the maze, which we will not be able to do without our wool ball.

Modern astronomy has been adding to Physics several areas of knowledge, among them Philosophy and Chemistry, which has allowed us to arrive at some curious conclusions. By stating that the speed of light is constant in the vacuum, without depending on whether the source or the observer could be immobile or in motion, Einstein has revolutionized the field of ideas. The first consequence of this postulate is the realization that absolute motion can not be measured in a vacuum; the second, that the light does not move instantly from one point to another of the space. More and more of the lay people are naturally understanding the ramifications of these findings. No information about the distant universe comes to us instantaneously, which means that we are looking at the stars as they were in the past, some of them looking like they were millions of

years ago. The physicist Stephen Hawking, referring to the 8 minutes that the light of the Sun needs to spend to reach our position, remembers that if the sudden death of the Sun occurred we would not see the event directly. That is, if this happened during the day, the sky would remain illuminated for another 8 minutes. Now, if there is no directly accessible information before these brief minutes are exhausted, darkness will instantly impose itself on us in the past, placing the apex of the light cone of the star's future and the apex of our own cone of light of the past in the same dimension of time (present). Thus, at this very moment we would be separated from the Sun only by a subtle fold of space, or by an inversion in the direction of the arrow of time. I used to say that if the Sun's death were a runaway truck, when it passed us we would not even have time to write down its license plate.

If we could follow a photon that was emitted at this moment by a distant star, we would have to reverse the thought we usually apply in the case of the observation of the image of another star, whose light has already reached us. The relativistic view makes things a bit confusing because, in relation to this photon being emitted in the present moment of the star, our position is that it will be in the past

when it hits us, due to the time that will be spent by the light to overcome the distance that separates us.

The space around the star seems to have altered its geometry in a position then placed relatively in the future, allowing it to secondarily assume its enormous mass and could then manifest itself in delay, through the emission of photons. The light from there at this very moment will be nestling into the cone of light of the star's future, until it reaches our position. Any event underway within this abstract cone could not be measured directly and, therefore, would cease to exist because of lack of access. The wool ball has not yet reached the position where the Minotaur is waiting to be shot.

When that happens, deep in the labyrinth of space and on a beautiful blue planet, we point our telescopes in the direction of the image of the star and we are collecting, little by little, the ball of wool of its scattered light. So, like Theseus trying to escape the labyrinth, we are tracing the star from the past, which means that we will try to reach it by a fictitious path, which has already been trodden by light. Some astronomers are fond of using effect phrases like "we are formed from the dust of the stars", or "our atoms can be traced back to the nucleus of distant stars and galaxies". If they truly

believed in this, they should not expect the light to come to us from within our own cone of light of the past, for in that case it could not be traced back by our memory. This figure is very representative of our interaction with dark matter: -Whatever the circumstance and without depending on the considered level of matter, we will always be looking at the universe from some place in the past. That is, when the events can be registered, they will no longer be there (at least in the way it can be observed now).

Santa Maria, RS, Brazil, 03/30/2018.