How long has the Universe been accelerating?
“The Universe has been accelerating for the past six billion years, and if we had come along sooner than that, we might never have considered an option beyond the three possibilities our intuition would have led us to. Instead, we get to perceive and draw conclusions about the Universe exactly as it is, and that’s perhaps the greatest reward of all.”
One of the biggest surprises in our understanding of the Universe came at the end of the 20th century, when we discovered that the Universe wasn’t just expanding, but that the expansion was accelerating. That means the fate of our Universe is a cold, lonely and isolated one, but it’s a fate that we wouldn’t have uncovered if we were born when the Universe was just half its current age. By understanding the Universe’s expansion history and determining what the different components are that it’s made of, we can figure out exactly how long the Universe has been accelerating. We find that dark energy rose to prominence some 7.8 billion years ago, and the Universe has been accelerating for the last 6 billion years. As the acceleration continues, more and more galaxies become unreachable from our perspective, even at the speed of light; that number’s already up to 97% of the galaxies in our visible Universe.