Einstein's Fridge: How the Difference Between Hot and Cold Explains the Universe

by Paul Sen

Think of one dot as our Milky Way, and imagine that a circular boundary is drawn around it and its nearby galaxies. Inside this boundary, the balloon is expanding slower than the speed of light, whereas outside it is expanding faster. Only objects inside this boundary are visible to us; everything outside the boundary is invisible. But because the rate at which the balloon is expanding is increasing, more and more of these objects will disappear as they flow across the boundary. This process should sound familiar. It’s as if our universe is “an inside-out black hole.” Instead of stuff flowing inward across a one-way boundary never to be seen again, stuff is flowing outward across a one-way boundary never to be seen again. That means that, like the event horizon surrounding a black hole, there is an event horizon around our universe. The denouement of this argument? Just as the informational content of all that's fallen into a black hole is encoded on its event horizon, perhaps information describing everything that's flowed out of our universe is somehow stored on its equivalent—the “cosmic horizon.”