Did Our Cosmos Eat Baby Cosmoses, Triggering Dark Energy?

The expansion of our cosmos is accelerating. Possibly it’s some enigmatic form of dark energy, but last year scientists put forth the radical idea that the accelerated expansion is because of our universe absorbing adjacent baby cosmoses. More recent research has revealed that while the idea still might work, it’s far more complicated.

Astronomers first discovered dark energy way back in 1998, when two separate teams found that distant supernovae were in fact far dimmer than they should be, indicating that the expansion of the universe was accelerating. Since then, various other lines of evidence have led to the same conclusion, but the ultimate cause of the accelerated expansion is still a mystery.

Dark Energy Is a Cosmological Constant

Easily the simplest explanation for dark energy (the name given to the accelerated expansion) –– is what’s known as a cosmological constant. An idea first presented by Albert Einstein, the equations of general relativity let us to add simple constants. In essence, in this particular view the expansion of the cosmos accelerates because there is a baked-in acceleration.

While very simple, as most scientific theories go it’s not exactly satisfying. It’s like saying that dark energy exists as…it exists. But physicists have badly struggled to come up with better ideas, and the issue has been aggravated recently with the emergence of the purported Hubble tension, where different measures of the present-day expansion rate are giving significantly different outcomes.

Are We Merging with Baby Universes?

Last year, a pair of astrophysicists proposed a fresh idea: possibly the accelerated expansion wasn’t due to a cosmological constant or some exotic physical process. Instead, our cosmos might be expanding at a relatively sedated rate. But perhaps our cosmos isn’t alone, and we are surrounded by smaller baby cosmoses. As our cosmos expands, we absorb our neighbor baby cosmoses, which make the volume of our cosmos suddenly jump – giving the appearance of accelerated expansion.

While the initial idea appeared promising, it had only been tested against an inadequate number of observations. Most recently, astrophysicists at McGill University took a closer look and put the baby cosmos idea to the real test. They compared the predictions of this model against data from the Planck satellite measurements of the cosmic microwave background, the DESI galaxy survey, and supernovae datasets. They reported their outcomes in a paper appearing in the journal preprint server arXiv.

These astrophysicists found that the simple baby cosmos concept couldn’t match all the available data. But they did find that there might be in fact a middle ground, where the cosmos still merges with baby neighbours but also maintains a little bit of cosmological constant.