More recently, scientists have pointed out that if one tweaks many of the dimensionless physical constants — numbers like pi that are independent of units and simply exist as fundamental ideas — none of the cosmos we see would exist. One of these numbers is omega, the density parameter, which pits gravity’s pull against the expanding push of dark energy. If gravity were stronger, the universe would have long since ceased expanding, and would have collapsed back down in a reverse Big Bang, often called the “Big Crunch.” If dark energy were stronger, then the universe would race away from itself so that no matter would stick together and stars, planets, and people could never form.

If the cosmos were truly a random and senseless arrangement of particles, it seems eerie or suspicious to many that these two forces balance so delicately.

But we can remember the tautological approach: if the universe were any way other than what it is, we wouldn’t be here to worry about it. Of course the universe seems fine-tuned to us; it’s the only one we know.