Horizon, Host: Ted Simons

July 17, 2013


Host: Ted Simons

Krauss on Science


  • World famous physicist Lawrence Krauss makes his monthly visit to Arizona Horizon to talk about the topic of time.
Category: Science   |   Keywords: krauss, science, ASU,

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Ted Simons: World renowned physicist Lawrence Krauss appears on "Arizona Horizon" each month to discuss science news and issues. This month our conversation centers on the physics of time. Thanks for joining us. Good to see you again.

Lawrence Krauss: It's always good to be back.

Ted Simons: This is something that I'm trying to wrap my mind around, the concept of time.

Lawrence Krauss: Time is an amazing -- I know you're fascinated by it, but it is a perplexing quantity. Because it seems so different. The future is different than the past, at least for most of us, we hope. And yet the problem is the time -- The question is, is time real? Is time any -- Have any object reality of course it does. It does, because we can't repeat the -- We can repeat the conversation we just had, but perhaps not exactly the same way. That's done. That's in the past. But what the first wrinkle, if you wish, and I want to be -- To make a fun for that book "a Wrinkle in Time," but the first wrinkle was Einstein, who showed that time clockers tick at -- Clocks tick at different rates for different observers, depending on their relative conditions. If I'm moving with respect to you, my clock is ticking more slowly than yours. And we test that every day in undergraduate laboratories. But the thing I wanted to point out, it's not so esoteric. We depend on it every day. I depended out twice today when I was using my GPS. Einstein showed not only if you're moving while your clocks get slower, but if I'm standing on top of the table and I'm a little higher than you, my clock is ticking a little bit slower. The effects are so small, you'd think they would be irrelevant. But GPS works. All these satellites up there, they're traveling about 12,000 miles up, maybe 10,000 miles an hour, and they -- And the way it works, two of them beam a signal down at you, or signal up from you and back again, and they measure the time And they triangulate. So the difference in time between those two round trips is how they can find out where are you. You got a better triangulation if you have three of them. But if we didn't take into account the fact they're moving, and high up, it turns out in order to have a accuracy of a meter, light travels sort of 60 centimeters every nanosecond, every billionth of a second, so I have to have accuracy of a few billionths of a second to have a meter accuracy, or maybe a few millionths of a second to get 10 meters. It turns out the clocks are ticking at different rates because they're at different heights and speeds, and if they didn't take that into effect, then within about a minute, all GPS would stop working. We have to take into account the fact that their clocks, their atomic clocks are ticking more slowly than ours, so it's not so esoteric. Every day we have to use the fact their clocks are more slowly than ours.

Ted Simons: That's us adjusting to what time is as far as how we experience it. What is time?

Lawrence Krauss: You know, in physics, that's a really good question. In physics it's a parameter that allows us to say when things happen. In that sense it's like space. But it just seems weirder. What is space? Space is -- Tells me where you are. You're at some point in space and I'm in a different point in space. And we can tell a lot about what's happening by where we are when we come together here in the studio when our points of space converge, we have an event. We have one of these little dialogues. And time has a way of labeling events. What Einstein told us is space and time are tied together in a four-dimensional universe in which each point is a point in space and a point in time. But it gets weirder. Because I can do a circle in space, right, I can walk around this table and come back. But if time and space are together as part of the universe, why can't I do a circle in time? Because we all know as far as we can see that we just move forward in time. Can I travel backward in time? And that's a fascinating question. In fact, I've written about it, and in fact when I wrote a book called "The Physics of Star Trek" it caused a stir because Stephen hawking wrote the forward and he previously said time forward is impossible, but in the forward he said it was possible, because I said it in the book and I was right. But he said time travel is impossible, because if it wasn't we'd already be inundated by tourists in the future. I said they all went back to the 1960s. But that paradox, you see, if you can do time travel, and all the most for many people their favorite science fiction episodes involve time travel. We have cause -- In our world, cause always precedes effects. We predict things, a cause, and then an effect. But if I had time travel, you could go back in time and kill your grandmother before your mother was born. And then your mother wouldn't be born, but then you wouldn't be born, and if you weren't born how did you go back in time and kill your grandmother? Many physicists like Hawking had said time travel must be impossible because all these paradoxes as a result. But we've learned the universe is the way it is whether we like it or not. We don't know, Einstein's theory, because it connects space and time, tells us in principle time travel is position, because you could create a geometry where you could do a circle in time. Of the thing that creates that geometry, space and time, their fabric is determined by energy and matter. So the left-hand side is space and time, the right side is energy and matter, and so if I can imagine a mathematical universe with time travel, on the right side all I have to do is come up with the right configurations of matter and energy to do that and I'm going to interrupt you one more time. That's the open question. We know that the geometries can exist but what we don't know, can you create the configurations of matter and energy that would produce time travel? That's an open question at the forefront of physics and that's one of the things I worry about.

Ted Simons: Is it safe to say that you can travel, we will be able at some point to travel back in time, but only back in time if we have a certain parameter or if something has -- In other words, no one from the future can come back now, but in the future we can come back to a previous future because we've laid the ground work --

Lawrence Krauss: No.

Ted Simons: You're saying no.

Lawrence Krauss: We don't know. We don't know if time travel is possible. The point sits possible in principle, because mathematics allows to you create a universe in which time travel is possible. Mathematically you could -- But this is physics. We don't know if there are principles of physics that determine the energy and matter configurations that are necessary to produce those. Clearly if we saw someone from the future would it anxious that question, for we could see particles that go back in time, but at this point none of that is around and because of all the paradoxes, many physicists think the laws of physics, the ultimate laws of physics would in fact preclude creating those conditions of energy and momentum and matter that would create time travel. So there's a big debate about whether it's possible. What we can say now is at least it isn't impossible. But let me -- One other thing. We may not be going where you want to go, but I want to dash one more of your hopes.

Ted Simons: Please.

Lawrence Krauss: If you went in a time machine this, is something I remember from H.D. wells, no one realizes that hey, it's time and space. So the earth, we feel like we're at rest, but the earth is going around the sun at 30 kilometers a second. OK? If you went back in your time machine a minute earlier, so you went back in time a minute, but stayed at the same point in space, the earth would have moved 1,800 kilometers away and you would be now the space without any air or anything else. So every time they talk about a time machine, I think of going back in time and popping out and discovering --

Ted Simons: Yes. You're not going to land in the same spot.

Lawrence Krauss: Because the earth is moving.

Ted Simons: Alright. At the speed of light, time pretty much stops.

Lawrence Krauss: Not just pretty much, it stops. That's one of the reasons why there are limits on how fast you can -- How close to the speed of light you can get.

Ted Simons: Let's say some future generations can hit the speed of light. Does that mean there's no past, there's no future? It's all now forever?

Lawrence Krauss: In fact there are particles that go the speed of light. They're called light. [laughter] And for them, if you really were sitting on a lights wave, the entire history of the universe would happen instantaneously.

Ted Simons: If anything happens instantaneously, what is time?

Lawrence Krauss: Well, for a light ray they there would be no time. But one of the things that's -- One of the Catch-22s of relativity is because we have mass, it takes an infinite amount of energy to get to the speed of light. So we'll be able -- In principle we can travel closer and closer to the speed of light and it is true, it's not science fiction, if you were going around in a spacecraft traveling at 99.99% the speed of light, could you go on a trip that would take two weeks, but you come back to earth and 50,000 years would elapse. We test that all the time. We have in fact one of the simplest tests of that is the amazing fact if you had a Geiger counter, it would be clicking. And one of the particles that would be clipping from are nuons. They're created when cosmic rays hit the upper atmosphere and they produce these particles. At rest it lives one millionth of a second. You could show even traveling at the speed it is, it wouldn't make it down to the earth. But the reason it makes it down to the earth is its clock is ticking slowly and it says oh, it's a millionth of a second, time for me to decay, but in our -- But it's much more than a millionth after second so it makes to it earth. So the very fact we can measure these cause and create particles on earth, is due to the fact their clocks are ticking slowly. It's not subjective. It's not as if we perceive time to be -- It really is. It really travels at different rates for different observers.

Ted Simons: If we -- If time is a glorified senses of measurement here, or how we purr Steve it -- Perceive it --

Lawrence Krauss: It's a way to label when it happens.

Ted Simons: If that's the case, is there such a thing as infinity, eternity?

Lawrence Krauss: I watch TV shows that certainly seems like there is. But we don't know. We don't know -- We know our universe had a beginning, a finite time ago. 13.8 billion years ago. We know that. But the future, we don't know. And it -- All the evidence is that our universe will expand forever and ever. And the future is indeed eternal.

Ted Simons: Back to your book, universe or nothing, you're saying there was -- I don't want to get too deeply into nothing, is there a beginning to time?

Lawrence Krauss: Everything that we know tells us yes. Namely because space and time are tied, at the very beginning it's equal zero when the entire universe, if you took the known laws of physics was in a single point. The laws of physics break down. And time itself may have arisen. So when people ask what happened before the big bang, we can give them the answer, that's not a good question. Because time itself may have begun in the big bang. Time may not have existed before the big bang. We don't know the answer because the laws of physics break down. When space and time become so small that the laws of quantum mechanics governing the space and time, all of our theories break down and our understanding of time and space go out the window. That's an open question. But it could shall the time began with the big bang. That this clicking this, classical clicking of a clock that we, use to delineate events and time just like with the ruler, we, delineate events in space. That all makes sense only after the big bang. Before the big bang, where quantum mechanics was governing the nature of space and time, rulers and clocks may have made no sense.

Ted Simons: If anyone were alive before then, they would be looking at us right now saying these people make no sense.

Lawrence Krauss: They may have been, but it's hard to imagine how you would be alive when all of the hundred billion galaxies in the universe were compressed in a region smaller than an atom. But you know what? At the limits of our knowledge, almost anything is possible.

Ted Simons: Last question -- Are there any breakthroughs on the horizon, anything that you think is coming up in terms of understanding time?

Lawrence Krauss: Well, I always tell you the same answer. If I knew what the next big breakthrough was I would be doing it. That's what's great about science. It's full of surprises. It could be that we learn that our universe isn't four dimensional. That there are more dimensions. That is a possibility. And that would change the whole nature of space time. And it might reveal new aspects of time. We don't know -- We may discover tomorrow that -- The only way we'll probably learn about the nature of time is to keep on looking for these weird and wonderful things. And if one of them is discovered I'll come back on the show and tell you. Or I'm come back in time --

Ted Simons: We'll make a spot for you. We're out of time. Good to have you.

Lawrence Krauss: Thanks.

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