“Physics’ Biggest Unanswered Questions”

“Why is the universe so exquisitely balanced such that life can exist?”
Based on the odds, we really shouldn’t be here. Galaxies, stars, planets and people are only possible in a universe that expanded at just the right speed during its early days. This expansion was governed by the outward push of dark energy warring with the inward gravitational pull of the universe’s mass, which is dominated by the invisible kind called dark matter. If these quantities were different—if dark energy had been just a tad stronger after the universe’s birth, for example, space would have expanded too fast for galaxies and stars to form. But a smidge less dark energy would have caused the universe to collapse in on itself. So why, asks Erik Ramberg of Fermilab in Batavia, Ill., are they so perfectly balanced to enable the universe we live in? “We don’t know of a fundamental reason why that balance should exist,” Ramberg says. “There’s no doubt that the amount of dark energy in the universe is the most exquisitely fine tuned number in the history of physics.”