When it comes to searching for life elsewhere in the universe, we think of the rovers on Mars, or of sending probes to Jupiter’s moon Europa or Saturn’s moon Enceladus. Or we think of looking for habitable exoplanets or exomoons. The universe we’re in feels infinite with possibilities, but – in contemplating alien life – could we go beyond even our own universe? Writing at NBC News Mach on May 28, 2018, Seth Shostak of the SETI Institute in Mountain View, California, ponders this very theoretical, yet exciting idea of the possibility of life in parallel universes.
Shostak’s article is based on two related papers, published in May, in the peer-reviewed journal Monthly Notices of the Royal Astronomical Society. He focuses on explanations related to a hypothetical substance in our universe known as dark energy. The effect of dark energy appears to be a faster expansion of our universe over time.
The idea of parallel universes isn’t new. You find it in many fields of thought. But, in the physics community, the debate about this concept – which is sometimes called the multiverse hypothesis – has heated up in recent years. As Shostak explained in his Mach article:
The idea that other universes might exist arises from the realization that the Big Bang might not have been a unique event but a common one. How common? Stanford University physicists Andrei Linde and Vitaly Vanchurin have estimated that the number of unique parallel universes – ones that are independent of the cosmos you know and adore – could be written as a one followed by 10 thousand trillion zeroes. That’s not a number that has a name, and certainly not one you will ever encounter in the real world. I figure it would require 10 billion notebooks just to write this number down.
How does dark energy relate to these possible parallel universes?
In their previous studies, physicists have concluded that our universe might have less dark energy than other universes, if those universes do exist. Parallel universes might have so much dark energy that stars and planets cannot form. In other words, in most universes, it might be the case that more dark energy leads to even faster expansion of the universe, preventing star- and planet-formation, making life unlikely.
The new studies, from scientists in the U.K., Australia and Holland, suggests dark energy doesn’t play a such a crucial role in whether parallel universes can support life, or not. As Shostak said:
Using computer models, the research team found they could vary the strength of dark energy from zero to several hundred times its value in our universe, and everything remained copacetic. Dark energy didn’t need to be any particular strength for galaxies and stars to form.
From the vantage point of life in other universes, that might be good news.
There are still other factors to consider however, such as differences in nuclear or gravitational forces. Some other universes may still be completely sterile, unlike ours which has formed in ways that are ideal for life to exist. Shostak explained:
[Our universe’s] physical properties are remarkably suitable for the existence of life. If the forces that hold atoms together were even a bit different, the atomic reactions that power the stars wouldn’t work, and our cosmos would consist of nothing but hydrogen. Tweak those constants another way, and stars would burn themselves out so quickly that there would have been no time for the evolution of microbes, dinosaurs, or you. If the strength of gravity were just slightly altered, our universe would have either expanded too rapidly after the Big Bang for stars and galaxies to form – or would have collapsed in a Big Crunch.
It was also thought that dark matter was essential for galaxies to form, but, recently, the 10-billion-year-old galaxy NGC 1052-DF2, 65 million light-years away in the constellation Cetus, contains 400 times less dark matter than had been expected. That finding was published on March 28, 2018 in the peer-reviewed journal Nature. As Pieter van Dokkum at Yale University commented:
You don’t expect a galaxy to have no dark matter because dark matter is not something a galaxy can just opt out of.
All of this is conjecture, informed by the tools of modern physics and by high-powered computer modeling. It is speculative, but interesting food for thought. Parallel universes, dark energy and dark matter are the kinds of subjects which have long been relegated to science fiction, but today’s science is shedding new light on just how incredible the cosmos really is.
Thus, while we’re still searching for evidence of alien life in our own universe, the possibility of an almost infinite number of such universes – some inhabited – is truly mind-blowing.
Bottom line: As discussed previously at EarthSky, new research has suggested that the Big Bang may have been only one of countless others, that parallel universes might exist, but that life might not be possible in those other universes. Writing at NBC News Mach, Seth Shostak of the SETI Institute provides some insights on new studies, suggesting that might not be so.