video
Topic Series
Jeff Tollaksen
- Robert Lawrence Kuhn
- Jeff, we're at the FQXi Conference, looking at the nature of events: what happens in physics? It sounds very simplistic, but when you understand events in quantum physics, it gets very sophisticated. What can we learn about the nature of time by studying the nature of events in quantum physics?
- Jeff Tollaksen
- I'll try to maybe give a slight slant to what's new that we can say. The old story really came from the beginnings of quantum mechanics and Einstein and relativity. In essence, Einstein, by discovering relativity, he did away with the whole notion of an absolute now. So the notion of a now is a relative thing. It depended on the relative emotions between observers, so on and so forth, and he, Einstein commented that one of the biggest mysteries to him was the fact that we have this – this subjective experience of time, this becoming experience, which, as a matter of principle, could never be part of our objective structure of nature. And so he, Einstein went so far as to write the widow of a friend of his when this friend passed away, and he wrote, you know, Michelle, he's still there. Right? He hasn't really died. He's part of this, you know, what was called a block universe. All those moments in time in the past are still there. They're equally as real as we are right now. So that's kind of taking that view to the extreme. So the second thing is you say events, and what does that mean? Well, there's the old notion of events that just sort of points, like a precise mathematical idealistic point in space.
- Robert Lawrence Kuhn
- And time.
- Jeff Tollaksen
- And time, but that's the next thing. The next thing is what I understand an event to be is kind of more like process. And so if you can say that an event is something that's spread over space and time, that's more like a process kind of way of thinking about it. We've done a lot of work on that kind of thing. So we look at the underpinnings of – the basic elements of quantum reality that we can see and so we've invented ways of observing events, processes, as a – in a fundamental sense, which suggests that you can have, say, one particle and you can observe it in a way so that it's not really here in time or there in time, but only when you look at both times together is there a particle there. If you look at there, nothing there. If you look at there, nothing there. But we look at both times, there's something there and that sort of expands the notion of a thing into at least two points in time.
- Robert Lawrence Kuhn
- So, what that says overtly is that, unless it has two separate points in time, it doesn't exist. That's what you said. Now, that doesn't seem to make sense.
- Jeff Tollaksen
- That's right. There's – there's no operational meaning to say that the particle's is at this moment in time or the particle is in that moment in time; its state exists, for example, at two different moments in time only, and it doesn't break down into one moment plus another moment. So we see all kinds of states like that, and the reason that's important is because we started to ask deeper questions about the nature of time. For example, just as a curiosity, I was wondering if – if the old notion of time by Heraclites, you remember this was, you know, thousands of years ago, Heraclites says: you never step twice into the same river. And so, to me, that seemed like a very different notion of time. I mean, the kind of time notions and concepts that we've grown up with are very different. They suggest that we have individual objects in the universe and they just change their state and time, and the next time they're the same thing, but just maybe change their state and time. Heraclites seemed to suggest that each moment is like the whole universe is born new. It's completely new, you know. We think we're the same person, but we're born again. And I was curious if physics could accommodate this. Turns out it can't. It's not possible for physics to make a picture of this, unless you have a picture of this process, of these events that are spread in time. If you allow for that kind of physics, then you can paint such a picture.
- Robert Lawrence Kuhn
- How does one affect the other? If you have the two particles that only exist when you have them at two points in time, how does that affect this sort of macroscopic understanding of the nature of time?
- Jeff Tollaksen
- So, it turns out that if you want to have a picture in which the universe keeps getting reborn again and again–
- Robert Lawrence Kuhn
- Every moment.
- Jeff Tollaksen
- –every moment, then it turns out that the only way to connect these universes together, like the universe at one moment in time with the universe at the next moment of time, is to have one of these process-like things that is spread in time. So we have – I don't know if I can do it with my fingers here, but you have – you have, here's one moment in time, here's another moment in time. You have to have a processing that can connect those two universes, otherwise, it's like a barrier of lead between them, but those process event type things can connect them.
- Robert Lawrence Kuhn
- So that each one of those is like a point in time and so it keeps recreating itself.
- Jeff Tollaksen
- It keeps recreating, and the thing that makes you think that you're the same person, right, is this process thing, which connects the you from the previous universe to the you in the next universe and it sort of passes the you along, so you keep getting – you're always new, right? It's a beautiful idea, and it actually led to so many beautiful new mathematics and ways of thinking about the deep physics that it even let us solve or develop a picture. I don't know if it's the final answer, but it even let us solve a picture for our notion of becoming, our subjective becoming, the thing that Einstein said nobody would ever be able to do. So we're able to have our cake and eat it. We were able to make Einstein happy because we had this – this – each moment of time in the universe is this, you know, is like his big block universe, but we're also able to have a subjective becoming.