Phantoms in the Universe?

The Standard Cosmological Model has introduced in physics two new concepts that didn't exist before:

• Dark matter: It seems to be five times more abundant than ordinary matter, but we don't know what it is, what it's made of. We only know that it appears to be affected by gravity, and so far, its existence has been concluded in two different ways: a) By analyzing the rotational motion of galaxies, which seems to require that there is more mass in them than what we can see. b) By studying the cosmic microwave background radiation, which has served as the basis for adjusting the standard cosmological model.
• Dark energy: We have no idea what it is. Some speak of a fifth fundamental interaction (or force), the quintessence, which would join the four we know: gravitational, electromagnetic, strong, and weak. Others offer different explanations, none of which have received experimental confirmation. The hypothesis of its existence is supported by two observations: a) Analyzing the expansion rate of the universe, after the 1998 discovery that this rate is accelerating. b) By studying the cosmic microwave background radiation, which has served as the basis for adjusting the standard cosmological model.

Alexander Friedmann
(Александр Фридман)

First of all, I must point out that in the two cases cited above, we do not have discoveries, but rather hypotheses that attempt to explain the data we know. As I explained in other posts, scientific hypotheses are only considered confirmed when they make surprising accurate predictions, which so far have not been achieved by either the dark matter or the dark energy hypothesis.

One of the most important recent instruments developed to observe the cosmos is DESI (Dark Energy Spectroscopic Instrument). It has been built to analyze millions of galaxies, from the nearest to the most distant, to try and deduce the properties of dark energy, the term in Einstein and Friedmann's cosmological equation represented by the constant Λ.

The first results of DESI have just been published, embodied in 270 terabytes of data about galaxies and quasars whose light started towards us up to 11 billion years ago. And the first analyses of these results do not confirm the predictions of the Standard Model. This has been considered a cosmological bombshell. These results seem to indicate (it must be confirmed) that the dark energy constant (Λ) is not constant, as had been assumed, but rather varies over time according to a process similar to the following:

1. Initially, its value would have been relatively low. The universe was small, all its mass was compressed in a small volume, and gravity was then the dominant interaction.
2. After a certain point, dark energy overtook gravity as the dominant interaction in an expanding cosmos. But this happened because another type of dark energy, phantom dark energy, had appeared, which at first did not exist but grew as the universe expanded. At that point in time, the expansion of the universe began to accelerate, as was discovered in 1998.
3. About 4.5 billion years ago, basic dark energy, along with phantom dark energy, reached its maximum density. Since then, it has been decreasing, for phantom dark energy is disappearing. The expansion of the universe is still accelerating, but not as rapidly as 4.5 billion years ago.

If these results are confirmed (their current statistical significance is 4.2σ, and to be considered confirmed, it should be at least 5σ), we would find ourselves in the following situation:

•         The dark energy constant (Λ) would not be constant, so Einstein and Friedmann's cosmological equations would not be correct. The theory would have to be reworked.

•         The quintessence hypothesis would be ruled out.

•         Dark energy, if it really exists, would be much more complex than previously thought.

•         As dark energy diminishes, after its phantom version disappears, the universe will decelerate its expansion, and its future would be unpredictable. It could continue expanding forever, more and more slowly; reach a maximum size and stay there; or begin to contract, ending in a Big Crunch.

The latest discoveries, therefore, increase the mystery and put an end to the feeling, which many cosmologists tried to foster, that we already know everything. As things stand, the standard cosmological model cannot be considered validated, as I have said several times in these posts.

The same post in Spanish

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Manuel Alfonseca