Question: How much longer will the universe exist?
Robert Kirshner: Yeah. The time scale – the age of the universe now, we think is about 14 billion years. So, the universe has been expanding from this hot dense state in all directions, the Big Bang. And it’s been elaborated over time. Gravity has made things clump together so galaxies have formed, stars have formed, stars go through their lifecycle and they emit as they blow up as supernovae and put out heavy elements that are used by the next generation of stars and then they put planets. You have in your bones calcium atoms that were manufactured in supernovae, iron that’s in our blood, air that you’re breathing. Those nuclei, those actual atoms came from stars that blew up before the sun formed. So, you’re really part of this whole story, part of the universe. So that’s the story that we know has been going on in the past.
The piece in the future is much, much harder for us to say with confidence because after all, we always – there’s always that big voice that – astronomers know, the universe began in a powerful explosion 14 billion years ago. And that’s the voice in the planetarium and that’s the voice of authority. And it’s the voice of conventional wisdom. And we always talk like that. The trouble is, its what changes is nothing we say. So, now we say, “And the universe is expanding faster and faster—" Well, okay. That is our current picture, that is what we know and we’re trying to tell you the right story, but it would only take some very tiny deviation from the cosmological constant as the dark energy to produce a completely different affect. So, if there’s some slight, teeny little difference which we haven’t been able to measure, it could mean that the universe will expand for a while and then collapse in the future, or expand faster than exponentially, in which case things will get completely ripped apart. All of these weird things are possible, but our ability to measure them is really quite limited.
So it probably is a little bit better for us to be more modest about what we do know and what we can predict and what we can be sure is really going to happen. But I think we’re at a very interesting state where the evidence has gotten better over time, that we really live in a universe that’s really accelerating. The implication is that there is this stuff, this dark energy really, a negative pressure of something or other, in the universe. But you know, something that is related to the nature of gravity that we really don’t understand. There’s a big piece of fundamental physics that is missing. And this, in a way is great because it’s when you know everything and when everything is understood and it all fits together, that’s sort of a sign of something that’s done. Move on to something else.
When things don’t fit together and don’t quite make sense and you know that there’s a problem here, that’s great because of course, it means there’s going to be progress on this subject. The trouble is we don’t know when. And we don’t know which idea – at the moment, we don’t know which of the many ideas is really going to be the one that helps us solve this problem.
It probably will seem like a nutty idea when it’s new, you know, when we first hear about it, but that doesn’t mean that all nutty ideas are right. It just means we don’t have to figure out which of these things is really right. And to do that, we want to do big surveys to measure more precisely how the universe has been expanding. We want to measure precisely how matter has clumped together under the force of gravity. We want to study this history that’s available to us using telescopes to really see what the constraints are on this weird thing, this dark energy that seems so important. But that we really have very little grip on to – we have very little grip to tell which ideas are right and which ideas are wrong. And really, that’s what science is all about, is to pick out from the speculation and the kind of imagination which things agree with nature and so far, the measurements that we’ve made are kind of crude and we’ve got to do better.
Recorded on February 17, 2010
Interviewed by Austin