Almost a century ago Einstein had to get rid of his cosmological constant. 5,000 robots have just proven him right

What will the end of the universe be like? It is one of the great questions for science due to its implications, but it is also one that sometimes goes unnoticed. Perhaps because we don’t like to think about how things end (even though there are billions of years left), or perhaps because the consensus on this matter is overwhelming.

Although maybe not so much.

New clues. A new study has just found clues that indicate a possible weakening of dark energy, the mysterious force that makes the universe expand. This could lead to the universe contracting instead of expanding faster and faster, but in the more immediate term it could force us to revise our “standard model” of cosmology.

Labda-CDM. This standard model is the one that links dark energy and cold dark matter or ΛCDM (Lambda – Cold Dark Matter). The key to the expansion of the universe is in the lambda parameter. This represents a constant, the cosmological constant.

Although we do not know exactly what it is, dark energy is the force that stretches the very scenery of the universe like chewing gum, causing galaxies to move away from each other instead of attracting each other due to the effect of gravity. Just a quarter of a century ago we discovered that the universe is not only expanding but doing so rapidly as a result of this constant expansive energy.

Now the question is, what if this constant… is changing? (And decreasing, to be more precise.)

5,000 robots studying the sky. To answer this question, the DESI instrument (Dark Energy Spectroscopic Instrument) has been mapping the universe around us for the last year. This instrument is made up of 5,000 small cylindrical robots with fiber optic sensors, and is installed on the Nicholas U. Mayall Telescope in Arizona.

DESI studies the imprint of baryon acoustic oscillations (BAO), being able to measure its signal across different time points in cosmological history, between 11,000 and 3,000 million years ago.

The instrument has been working for a year and still has five years of activity left, so the results are preliminary. However, these are the most precise measurements obtained so far. A bibliography of data, drafts and working documents have been made available to the public through the project website.

Einstein’s “big mistake.” This project will continue to peer into the far reaches of our universe for years to come. If at this time their first results are confirmed, theoretical physicists will have work. For many it will also be a relief.

In 1917, physicists such as Albert Einstein and Willem de Sitter realized that when applying the formulas of general relativity to the behavior of the cosmos, the model described was not static. Something that broke the molds of what was believed until then but that would end up giving rise to modern cosmological models. Einstein’s solution was to adapt the new cosmological model, to introduce a lambda that would put things in their place. And that they didn’t move from there.

It took more than a decade until Edwin Hubble observed the expansion of the universe for the first time. Einstein’s lambda would be buried for decades and the German physicist would die thinking that this was his big mistake.

““Big Crunch.” Almost a century later, history repeats itself. Something that we thought was constant may not be so constant. As in Einstein’s time, the contemporary lambda that represents dark energy is still an instrument with which we fill in the gaps in our models so that they fit what we observe.

If these latter observations are confirmed it could mean that our standard cosmological model requires another significant change: removing a constant and introducing a variable. This could have important consequences for physics (perhaps it could help us resolve the large disagreement between observations of the expansion rate of the universe).

It also reopens the door to an abandoned hypothesis, that of Big Crunch. This hypothesis postulates that the universe will end up imploding in a “big Bang reverse”. This hypothesis had been discarded since it was believed that cosmic inflation would stretch galaxies and move them away from each other faster than gravity attracts them. A hypothesis that now we may have to rescue from the trash as the lambda constant was once rescued.

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Image | NASA, ESA, CSA, STScI, Webb ERO Production Team