The universe turned out to be wrong

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Cosmologists are faced with a serious scientific problem, which indicates the imperfection of human knowledge about the Universe. The complexity concerns such a seemingly trivial thing as the expansion rate of the Universe. The fact is that different methods indicate different meanings - and so far no one can explain the strange discrepancy.

Cosmic Mystery

Currently, the standard cosmological model "Lambda-CDM" (ΛCDM) most accurately describes the evolution and structure of the universe. According to this model, the universe has a nonzero positive cosmological constant (lambda term) causing accelerated expansion. In addition, ΛCDM explains the observed structure of the CMB (cosmic microwave background), the distribution of galaxies in the Universe, the abundance of hydrogen and other light atoms, and the very rate of vacuum expansion. However, a serious discrepancy in the expansion rate may indicate the need for a radical change in the model.

The theoretical physicist Vivian Poulin of the French National Center for Scientific Research and the Laboratory for the Universe and Particles in Montpellier argues that this means the following: something important has happened in the young universe that we do not yet know about. Perhaps it was a phenomenon associated with an unknown type of dark energy or a new kind of subatomic particles. If the model takes it into account, then the inconsistency will disappear.

On the verge of a crisis

One of the ways to determine the rate of expansion of the Universe is to study the microwave background - the relic radiation that arose 380 thousand years after the Big Bang. ΛCDM can be used to derive the Hubble constant by measuring large fluctuations in the CMB. It turned out to be equal to 67, 4 kilometers per second for each megaparsec, or about three million light years (at such a speed objects that are distant at the appropriate distance diverge from each other). In this case, the error is only 0.5 kilometers per second per megaparsec.

If we get about the same value using a different method, then this will confirm the validity of the standard cosmological model. Scientists measured the apparent brightness of standard candles - objects whose luminosity is always known. Such objects are, for example, type Ia supernovae - white dwarfs that can no longer absorb matter from large companion stars and explode. By the apparent brightness of standard candles, you can determine the distance to them. In parallel, you can measure the redshift of supernovae, that is, the shift of wavelengths of light to the red region of the spectrum. The greater the redshift, the greater the speed at which the object is removed from the observer.

Thus, it becomes possible to determine the rate of expansion of the Universe, which in this case turns out to be equal to 74 kilometers per second for each megaparsec. This does not match the values obtained from the ΛCDM. However, it is unlikely that a measurement error can explain the discrepancy.

According to David Gross of the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara, in particle physics, such a discrepancy would not be called a problem, but a crisis. However, a number of scientists disagreed with this assessment. The situation was complicated by another method, which is also based on the study of the early Universe, namely, baryonic acoustic oscillations - oscillations in the density of visible matter filling the early Universe. These vibrations are caused by plasma acoustic waves and are always of known dimensions, making them look like standard candles. Combined with other measurements, they give the Hubble constant consistent with ΛCDM.

New model

There is a possibility that scientists made a mistake when using Type Ia supernovae. To determine the distance to a distant object, you need to build a distance ladder.

The first rung of this ladder is the Cepheids - variable stars with a precise period-luminosity relationship. Cepheids can be used to determine the distance to the nearest type Ia supernovae. In one of the studies, instead of Cepheids, red giants were used, which at a certain stage of life reach maximum brightness - it is the same for all red giants.

As a result, the Hubble constant turned out to be 69.8 kilometers per second per megaparsec. There is no crisis, says Wendy Freedman of the University of Chicago, one of the authors of the paper.

But this statement was also called into question. The H0LiCOW collaboration measured the Hubble constant using gravitational lensing, an effect that occurs when a massive body bends rays from a distant object behind it. The latter could be quasars - the nuclei of active galaxies fed by a supermassive black hole. Due to gravitational lenses, several images of one quasar can appear at once. By measuring the flicker of these images, scientists have derived an updated Hubble constant of 73.3 kilometers per second per megaparsec. At the same time, scientists until the last did not know the possible result, which excludes the possibility of fraud.

The result of measuring the Hubble constant from natural masers formed when gas rotates around a black hole turned out to be 74 kilometers per second per megaparsec. Other methods gave 76.5 and 73.6 kilometers per second per megaparsec. Problems also arise in measuring the distribution of matter in the Universe, since gravitational lensing gives a different value compared to measurements of the microwave background.

If it turns out that the discrepancy is not due to measurement errors, then a new theory will be required to explain all the data currently available. One possible solution is to change the amount of dark energy causing the accelerated expansion of the universe. Although most scientists are in favor of doing without updating physics, the problem remains unresolved.