Dark energy offers incredible hints about conditions in our universe

Based on what we have observed so far, it seems that our Earth is the only one with intelligent life. But there are a number of reasons why we might not detect the light of civilization elsewhere in the Milky Way, and a number of factors that might influence whether or not it appears.

The Drake Equation must be reconstructed.

More than half a century ago, these variables were assembled into a tool called the Drake Equation , allowing scientists to tinker and ponder.

But one variable was missing from the Drake Equation. Recently, a team led by physicist Daniele Sorini of Durham University in the UK added a variable to the Drake Equation as the basis for a new calculation: the effect of dark energy on the rate of star formation in the universe.

The Drake equation requires the introduction of additional variables.

"Understanding dark energy and its impact on our universe is one of the greatest challenges in cosmology and fundamental physics. The parameters that govern our universe, including the density of dark energy, may explain our very existence," Sorini explains .

Dark energy is an unknown force that causes the expansion of the universe to accelerate instead of slowing down due to the gravitational pull between galaxies. While we don't know what it's made of, we can estimate how much dark energy there is. It's not a small amount, accounting for about 71.4% of the matter-energy content of the universe.

Another 24% is dark matter; only the remaining 4.6% is ordinary baryonic matter , which includes all the stars, planets, black holes, dust, humans, and everything else we could theoretically see and touch.

One of our assumptions about life is that it needs a star. It may not need one, but the likelihood of life arising on an object so far from its energy source is so remote that it is not useful in determining the Drake Equation.

So, assuming that life requires a star, knowing the rate of star formation in a universe we live in might tell us something about the chances of finding life in it.

Stars form from clouds of dust and gas that collapse into dense clumps. They then accumulate enough mass that the density and heat in their cores trigger nuclear fusion. The outward pull of dark energy plays a role in how quickly this reaction can occur. Dark energy counteracts the inward pull of gravity, otherwise all the matter in the universe would condense into clumps too dense to form stars.

The researchers calculated this matter conversion rate for different dark energy densities in a cosmological simulation to determine the most efficient rate at which stars could form. And they found that the most efficient rate was when 27% of the matter in the universe was converted into stars.

We live in a non-ideal universe.

What makes this interesting is that the 27% optimum doesn't exist in the universe we live in. Our universe has a 23% transition rate. This isn't the first time we've found evidence that humans didn't arise in the most optimal conditions for life. This suggests that intelligent life could arise elsewhere in the universe.

"To our surprise, we found that even significantly higher dark energy densities were still compatible with life. That suggests we may not be in the universe most likely to form life," Sorini commented .

There are many other factors that could influence the likelihood of intelligent life appearing . The rate of star formation is just one of them. Others include the number of stars with planets and the number of planets with conditions suitable for sustaining life. Then there are variables we don't know, like how the building blocks of life are distributed and combined into an evolving system.

But each study contributes insights that may one day allow us to see a more complete picture of the universe than we see today. This, in turn, will help us narrow down how and where to look for other civilizations that may be scattered throughout our galaxy.

"It would be interesting to use this model to explore the emergence of life across different universes and see whether some of the fundamental questions we ask about the universe now need to be reinterpreted," commented theoretical physicist Lucas Lombriser of the University of Geneva in Switzerland .