Our universe expands more or less like a balloon that is inflated little by little. The expansion is not caused by galaxies moving through space, but by space itself expanding. This is why the balloon metaphor is used. If we imagine them as dots drawn on a balloon, they move further and further apart as the balloon inflates. Today we know, moreover, that this expansion is accelerating over time. It is believed that this is due to a mysterious force, dubbed dark energy. But it is so mysterious that we don’t know how it will behave over time.
Now, an international team of scientists has taken a step to verify this by measuring the emission of neutral hydrogen from the universe. To do this, they used a method that already existed, but they perfected it.
Chim he Canadian Hydrogen Intensity Mapping Experiment (CHIME) is an experiment that measures hydrogen from different places in the universe. Since hydrogen is the most abundant element in the universe and the main component of stars, it’s a good sign to see how galaxies are separated.
So far, CHIME has measured accumulated hydrogen from various points and distances. If a point has a lot of intensity measured, it means that there are many galaxies. If there were less, it was explained that there were few. But there are two problems here. On the one hand, CHIME also measures background noise from Earth interference and emission from the Milky Way. On the other hand, to know if it was really capturing the position of the galaxy, the data needed to be compared with the galaxy map taken by the telescope. This was very expensive. Therefore, the authors of two recently published studies made a series of changes to the software that allow hydrogen to be measured directly.
Why hydrogen?. At the dawn of the universe, matter was a dense, hot gas through which pressure waves traveled. However, about 380,000 years after the Big Bang, matter cooled a little, where these waves stopped propagating and remained “frozen”. We can compare it to a pond whose water freezes as soon as a stone is thrown, so that the ripples it creates are drawn forever. The result is a footprint 500 million light-years across, within which, given the conformation of the universe at the time, it is more likely to find clumps of matter.
To understand how the universe expands and what forces are causing it, we need to track that footprint, whose apparent size changes with distance. For example, a painter represents a tree smaller if it is further away or larger if it is closer to the observer. Since this matter must contain a large proportion of hydrogen in its composition, the ideal to follow is to measure this element. This is where CHIME comes into play.
which has already been seen. The scientists who developed CHIME’s software used data from 94 observing nights of the experiment taken in 2019. At this time there was no need to resort to established catalogs for measuring hydrogen levels. And the best thing is that what they found is consistent with the predictions of the Standard Cosmological Model, so it looks like the method works. However, the evolution of dark energy cannot be analyzed with only 94 nights. They hope to do so now, with 7 years of observations available to them thanks to CHIME.
Three possible scenarios. Dark energy could evolve in many ways, though these scientists consider three: an eternal expansion, a big rip, or a big crunch. The first scenario would be the least dramatic, since expansion would continue forever, without reaching a critical point. On the other hand, dark energy will become increasingly intense at large tears, so that the expansion will accelerate until it overcomes the forces holding matter together. First galaxy clusters will be separated, then individual galaxies, then stars, then planets and finally stars will disintegrate into atoms.
In case of major crisis, the opposite will happen. Dark energy will weaken and all matter will condense so that the universe collapses. It will be like a big bang backwards. At the moment, it is impossible to know which scenario will occur; But, perhaps, with 7 years of CHIME observations we can achieve this. Now, at least, we know that the new method works.
Picture | Kaim cooperation
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