Ask Ethan: Does Dark Energy Mean We’re Losing Information About The Universe?
“The universe’s expansion means our visible horizon is retreating; things faraway are vanishing continuously. (Albeit slowly, right now.) This would seem to imply we are losing information about the universe. So why is it the idea of losing information in a black hole’s event horizon is so controversial, if we’re constantly losing information to another horizon?”
As you look to greater and greater distances, you’re looking back in time in the Universe. But thanks to dark energy, what we can see and access today isn’t always going to be accessible. As galaxies grow more distant with the accelerated expansion of the Universe, they eventually recede faster than the speed of light. At present, 97% of the galaxies in the Universe aren’t reachable by us, even at the speed of light. But that isn’t the same as losing information. As a galaxy crosses over the horizon, its information never disappears from the Universe connected to us entirely. Instead, it gets imprinted on the cosmic horizon, the same way that information falling into a black hole gets imprinted on its event horizon. But there’s a fundamental difference between a black hole’s decaying horizon to the cosmic horizon’s eternal persistence, and that makes all the difference.