There would be no dark energy in the Universe! Here’s why

In 1998, cosmology, that is to say the scientific study of the properties of the Universe, was disrupted by observations of supernovae, cataclysmic explosions of stars, outside our galaxy and making it possible to measure large distances. Adam Riess and Saul Permutter, winners of the Nobel Prize in Physics in 2011 for this discovery, then stunned the world by showing that the expansion of the Universe, far from slowly slowing down, was on the contrary accelerating.

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To explain this behavior, physicists were therefore obliged to add a new force to the equation dedicated to the behavior of space-time, a force which was called “dark energy”. We had identified the problem, but we didn’t understand it at all. What the hell was that dark energy!

The expansion of the Universe is not the same everywhere, and that changes everything

The announcement in question here is just as resounding, creating a hubbub within the global scientific community: for researchers from Christchurch in New Zealand, the expansion of the Universe would be neither uniform (the same…) nor isotropic (…in all directions), which would change absolutely everything.

Indeed, the “laws” of the Universe must be the same everywhere in the cosmos. Thus, we cannot at all imagine discovering a planet where gravity would direct things upwards, because it could not exist, given that its matter would not clump together. In their article, the New Zealand astrophysicists explain that the expansion is not the same at equivalent distances, perhaps depending on a factor that escaped us until now, or even that it would only be a kind of illusion pushing us to invent dark energy.

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What if the expansion of the Universe was just a gravitational illusion?

We often hear that time in space passes much faster than on Earth. This is partly true. Although these effects are proven by advanced technology, such as GPS using orbiting satellites, they are often extremely small. Basically, the passage of time depends on factors such as the (relative) speed of an object and the masses present. To summarize, a clock placed in the dense center of a galaxy will see “its time” very slowed down compared to another clock frolicking in the void between two galaxies.

A clock in the Milky Way would run 35% slower than in a galactic vacuum

The idea of ​​the cosmological model known as the “time landscape” is that the large voids between the galaxies have seen — relative to us — their time accelerate due to the absence of matter. These intergalactic voids would therefore have allowed the expansion to act more, not because it would be stronger there, but just because it would have had more time to do so. This model predicts in particular that a clock in the Milky Way runs 35% more slowly than another in a large cosmic vacuum.

If Albert Einstein’s general relativity predicts that matter slows down time, this time landscape model relies on a way of establishing averages to integrate the effects of cosmic voids into the behavior of space-time. Physicists call this effect feedback, and not everyone agrees on its importance. Some say it is negligible; others, like New Zealand researchers, think on the contrary that at these cosmological scales it becomes sufficiently important to generate this effect responsible for the illusion of accelerated expansion.

The Euclid space telescopes and soon Nancy Grace Roman will be able to test the “time landscape” model

Euclid, an ESA space telescope already in orbit and responsible for magnificent photos, should help to better understand the origin – absolute or relative – of the expansion of the Universe. It would take around 1000 observations of supernovae to distinguish which of the standard cosmology model or that of the “time landscape” is the right one. It will undoubtedly also be necessary to use NASA’s future telescope, the Nancy Grace Roman Telescope, successor to the James-Webb, which we will tell you about soon…

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