We have known for a long time that the Universe is expanding. However, the speed at which it does so is a headache. Depending on which method is used to measure it, a different result is obtained. Now a much more precise way to measure it has finally been found, but it doesn’t really unravel much of the mess. It messes it up even more.
An overlay of techniques. Through a superposition of different techniques, an international team of scientists has made the most precise calculation so far of the expansion speed of the Universe: 73.5 ± 0.81 kilometers per second per megaparsec. The figure coincides quite well with those that have been calculated in the past using data from the nearby Universe. However, it is quite far from what is calculated when data from the dawn of the Universe is used. This indicates that there is something in the physics of that furthest point in the cosmos that we have no idea about. Far from being solved, the mystery has become more complicated.
A balloon that inflates. When we talk about the Universe expanding, we refer to the fact that galaxies are increasingly distant from each other. But not because the galaxies themselves move, but because the space between them widens. We can see it as a balloon on which a series of dots are painted. As the balloon inflates, the dots appear farther away, even though they have not moved from their place.
Hubble voltage. Traditionally, the expansion rate of the Universe is calculated in two ways. Or by measuring the distances between stars and galaxies in the nearby Universe, or by measuring the cosmic microwave background. This is the electromagnetic radiation that remained as remnant of the Big Bang. That is, the oldest light that we can find in the Universe, since it was formed in the explosion with which it was formed. Therefore, the data is not taken from the nearby Universe, but from the most distant and ancient one, the one approaching the Big Bang.
The figure obtained with both types of calculations should be the same. However, with the nearby Universe a speed of 73 kilometers per second per megaparsec is obtained, while with the most distant Universe a speed of 67 kilometers per second per megaparsec is calculated. This incoherence is known as Hubble tension. and indicates that, possibly, the Universe is expanding faster and faster. That’s why the closest one expands the fastest.
This graph represents the tension that exists between measurements of the expansion rate of the late and nearby Universe, versus what would be expected based on measurements of the early Universe, specifically the cosmic microwave background.
It could be a mistake. One of the hypotheses that seek to explain the Hubble tension is that, in reality, there is some error when measuring the expansion speed in the nearby Universe. There are many methods to calculate the distance between stars and galaxies and there could be an error. Therefore, an international team of scientists has decided to use a superposition of techniques to make a more precise calculation.
Different types of stars. This method consists of simultaneously analyzing a large amount of data obtained from ground and space telescopes. These focus primarily on the brightness of Cepheid stars, red giants, supernovae, and galaxies of known brightness. The three types of stars mentioned are characterized by having a characteristic brightness, which is used to map the Universe and, therefore, also to calculate distances. With this superposition of techniques, the figure of 73.5 ± 0.81 kilometers per second per megaparsec was obtained.
There is no mistake. When one of the superposition methods was eliminated, the alteration in the expansion rate of the Universe was minimal. The figure was practically the same. This indicates that the number has been measured perfectly. There is no mistake. So if the Hubble strain is not due to error, why does it occur?
The mystery continues. After obtaining these results, the Hubble tension remains the prelude to a mystery. However, it is true that there are some hypotheses. For example, it is believed that the different figures in the distant and near Universe They may be due to the intervention of dark matter. There’s a lot we don’t know about her, so maybe it could explain what’s going on. On the other hand, there is the hypothesis that the Earth is in a place with spatial characteristics. It would be an area where there is relatively little matter, comparable to an air bubble in a cake.
As explained in 2023 by one of the scientists who support this hypothesis, Indranil Banik“the density of matter is greater around the bubble, so gravitational forces emanate from this surrounding matter, attracting the galaxies in the bubble toward the edges of the cavity.” “That’s why they’re moving away from us faster than you would really expect.” Now we will have to solve that part of the mystery. At least we know that there is no error in the calculations and that the Hubble tension is a reality.
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