Scientific American staff editor George Musser joins podcast host Steve Mirsky to discuss his article in the September issue about the possibility of time itself coming to an end. Web sites related to this episode include http://bit.ly/bn3GYO
Steve: Welcome to Science Talk, the weekly podcast of Scientific American, posted on September 21st, 2010. I'm Steve Mirsky. Our September single-topic issue looks at the ends of things including the possible end of time itself. Staff editor George Musser is our astronomy and astrophysics expert. He is the author of The Complete Idiot's Guide to String Theory. Despite that title, he himself is not a complete idiot, and he is the author of the article "Could Time End?" in the September issue. We had a conversation about the piece at the Scientific American offices.
Steve: First George, I have to congratulate you on the coinage, as far as I know, of a new word. I believe it would be pronounced "pre-bangian", although I am leaning toward "prabahngian".
George: I like the latter actually; I'm not sure I'm really the coiner of that coinage.
Steve: You've seen it elsewhere—prebangian?
George: Then again I may have seen it in something else I wrote. So maybe I coined off myself.
Steve: And you're plagiarizing [yourself].
Steve: So obviously by prebangian we mean before the big bang.
Steve: Before the big bang is a, it seems to be a conflicted notion but the whole article made my head hurt. Could time end?
George: I succeeded! Your head hurts.
Steve: It really did. And then the subhead just makes your head hurt further because the subhead after "Could Time End?" begins: "Yes and no." What are you getting at here?
George: Well, that goes back to the whole question of pre-bangian or prabahngian.
George: Prabahngian, and the question is whether there was a period before the big bang; and it's similar to the question, if you kind of flip around, of whether there's an end to time or not. So whether there's a beginning to time or not and end to time or not are sort of flip sides [of the question].
Steve: Right. That's the important question, because if you subscribe to the idea that time began at the big bang, then the idea that there was some things prior to the big bang puts the whole issue of time back on the table as [having a] beginning or not.
George: And the "yes and no" formulation is just meant to convey that no matter which choice you make, you run into certain paradoxes and certain conundrums that you need to solve. Now these are present in Einstein's theory, Einstein's general relativity theory, which says that essentially an end or beginning to time is inevitable for a certain type of matter in the universe; and yet at the same time, the conditions which matter would be subjected to at the beginning or end are seemingly impossible. Now that kind of seeming contradiction also carries forward into quantum gravity theories. So you might have those theories which just attempt to flesh out Einstein's theory, say, that there was a period before the big bang, that time may have stretched on eternally into the past and therefore would go eternally into the future, there's no beginning or end. But then you run into paradoxes such as entropy—if entropy continually increases and it's been increasing forever, it should be maxed out by now. Then there is, if time begins or ends, the other option, then you're just left with a) understanding what [does it] mean for time to begin or end, and how do you have an edge to that which seems to be edgeless inherently?
Steve: We'll get to all of those.
Steve: Or may be some of them, but you have six really basic doomsday scenarios for the universe. So here's the first one—the big crunch.
George: This is what the astronomers used to think would happen in the far future of the universe, that the gravity of all the material would slow the cosmic expansion and then reverse it like [throwing] a ball up and having it fall back down to the ground; it [would] all come smashing back together in something like the big bang except in the reverse—the big crunch.
Steve: And it would be, from a physics point of view, it would be equivalent, just with time going in the other direction.
George: Well that was always that the hope, but it turns out when you actually [look] at it, you run into that problem with entropy, and entropy would [have built] up, so in the intervening, you know, billions and billions of years, and so the crunch would not be the big bang [in reverse].
Steve: The big whimper.
Steve: This is what astronomers now think will happen. As dark energy begins to press outward or continues really to press outward, [and] cosmic expansion is accelerated, the universe will be basically just empty out. All the galaxies would be flung apart, and we'll just have this kind of lonely void around us and then the galaxy itself will disintegrate, and it'll all just kinda wind out and gets miserable from there. This is the "ending in ice" option.
Steve: [The ice option?]
George: No the whole, was it Robert Frost?. "The world will end in fire or in ice." [So instead of] ending in fire, this is ending in ice.
Steve: I got you. When you said ice option, I thought I had missed some great sci-fi classic.
Steve: The big rip.
George: So this is a variant on the big whimper, where dark energy pushes everything out, accelerates expansion, but it itself becomes intensified. So the acceleration accelerates and it actually not only pushes the galaxies apart from one another, but it actually rips them apart, and then after ripping apart the galaxies, turns its attention to stars, rips them apart, then planets get ripped apart; we, if we are still alive, by that point—everything, atoms, protons even.
Steve: Not we, but some living organism.
George: Well, I hope to live forever. So perhaps it will be me.
Steve: Good luck with that. The big freeze.
George: Okay. Now we're getting into some of the more, you know, the newer, newly discovered ways that time could end.
Steve: Big freeze, ironically not the ice option.
George: Yes. Yes, I shouldn't have brought up Robert Frost, I guess. So there's a, when the whole idea dark matter, excuse me, dark energy came up, there are different options for what the dark energy could be, and they led to some of these newer, more newly discovered ways the universe could end, the big rip being one of them. The big freeze is similar, but what happens is the matter isn't completely torn apart to shreds, it's simply locked into place. So whatever matter is leftover is locked into place, it's unable to move and the universe just kind of [seizes] up, and that also can certainly count as time ending.
Steve: Another possibility: the big break.
George: Again, this is our friend dark energy up to its old tricks. In this case, it basically shuts off abruptly. So what had been [a]n acceleration goes into an infinite deceleration and everything just, kind [of,] screeches to a halt, and in the process time probably—although it's not completely clear, depends on a model—would also just become toast.
Steve: Why would dark energy do that suddenly?
George: Well, it all depends on what dark energy is. No one really knows, but you could imagine it's some kind of quantum field that might have the property that [it] would not remain constant but might intensify, might shut off, might do all sorts of shenanigans.
Steve: Shenanigans. And finally: the big lurch.
George: Here's one that doesn't really require dark energy to do something weird. [But just] matter itself can, kind of, work itself up to a frenzy; the pressure, forces in the universe might become infinite and again time might or might not be a casualty of that. So it's all "the big"—big [this, big that, big whimper,], big crunch, big rip, et cetera.
Steve: But the big lurch is, according to astronomical calculations, there is a finite probability of it actually happening and relatively soon.
George: Yeah, just in some millions of years. It's not so much there's a probability of it; [it's just that] the knowledge of the relevant cosmological observables, the parameters, just isn't established enough to rule it out.
Steve: I see. You quote Oxford philosopher Richard Swinburne, who says it's illogical for time to have an ending; it's not logically possible for time to have an end. So that's a philosopher's point of view. Is that reflected in the physics at all or is that a bias on his part for some reason?
George: No, what's interesting, when you look at the philosophy of time, which of course, as philosophy often does, goes back to [Plato and Aristotle,] the same kinds of dilemmas and controversies that arose in philosophy carry right over into physics. So one might argue that it's logically impossible for time to end in physics. It just, how can it [end?]. The equations of physics are situated within time, they talk about motion, they talk about things unfolding and changing, and that's just a process that by definition can['t] end? But on the other hand, one might argue that time must end. And this is what's so beautiful about Einstein's theories is [that they kind of] embody both sides of that paradox. So the equations for a given type of matter say that time must end, singularities must occur in the universe. But at the same time, the conditions that matter undergoes within the singularities are physically impossible—things become infinitely dense. So there's a tension there between something that must occur and something that cannot occur. So what happens in physics is not exactly the same, but it's pretty parallel to what happens in philosophy.
Steve: Let me bring this up because it was an idea that I hadn't really thought about till maybe [five] or [six] years ago, and I think it leads you to a lot of strange places: A photon that was created at the big bang and has been flying across the universe ever since, has not experienced any passage of time. For that photon, it is still the same moment of creation because a photon by definition is traveling at the speed of light, so it's not experiencing any passage of time. So what that then means—and I know that this is old hat to anybody who works in you know, GPS—that different things that are all around us are actually moving at different times, at different rates of time passing. And you say it very succinctly in the article, that you can look at gravity, I mean, if I drop the apple from the tree onto Newton's head, the apple is moving from a place where time is moving at a certain rate to a place where time is moving more slowly. That's one way to define gravity. It's very weird. I mean, even the [three] feet that the apple falls, is a differential, there exists a differential in the rate of the passage of time.
George: Exactly right. Now there's a couple of issues there to talk about—and [I think that's what's great about] this topic, just, everything you say about it, any sentence you utter, opens up a Pandora's box of questions to ask. So yes, in Einstein's theory, the passage of time varies with location and we can identify the force of gravity as that variation of the passage of time with location. So the fact that an apple would accelerate toward the center of the Earth, it's basically trying to maximize its distance that [it] passes in space time, and the way it does that is to accelerate downwards, [so it tends to spend] more time in its trajectory at a higher altitude [and] less time as it goes further down. And this is a general principle that you see throughout the universe, in black holes, in planets, that all the motions, all the cosmic dance that we see is an enactment of [these] variations of time that matter is playing out. At the same time, so to speak, material objects are influencing the passage of time, so [there's this] kind of back and forth between them, and that's how you can get time to end, is when that kind of interplay between matter and time just, kind [of], goes haywire, and time just calls it quits.
Steve: There's a part of your article where you talk about the fact that if the universe is in a particular point in its history, and the dimension that we perceive of as time is actually transitioning into another space dimension equivalent to the other three space dimensions, that things would actually look exactly the way they look right now. So how do we know that isn't what's happening?
George: Well, there's a group of physicists who argue that is what's happening. That the acceleration of the cosmic expansion, which is normally attributed to dark energy or some kind of failure of relativity theory, in fact is the transitioning of our time dimension into a space dimension, which is, of course, bad news for those of us who require time for our very mortal existence.
Steve: Why would time bother to become space?
George: This idea really arises in theories where space-time has higher dimensions. It's more than our three spatial, plus one temporal dimension. And in the particular theory I described, there still is a time dimension out there. It's just that our four dimensional slice of that higher dimensional reality no longer includes that time dimension. It's kind of like slicing an apple and slicing it horizontally versus vertically—you lose the time; the slicing that used to capture time no longer does.
Steve: So now that everybody's head is really throbbing and they're wondering what's the point of all this? What is the point of all this? I mean what…?
George: The main practical outcome of this is the attempt to unify physics. We all know that's one of the greatest scientific questions of our time. Why the natural world seems to have this unity to it, this cohesiveness to it and yet our theories are splintered, they don't cohere as the world does. So we're lacking something, we lack some deep understanding of how the world is put together if we're unable to capture its unity. And the biggest, arguably, the single biggest stumbling block to unifying physics is the notion of time, specifically the notion of time that arises in Einstein's theories is different from that which is part of quantum physics. Quantum physics has almost a Newtonian view of time. It's just kind of an absolute part of the framework of reality, and [in] Einstein's theory, or at least general relativity theory, it's a much more dynamic part of reality that's just dynamic as anything else, as atoms or particles or just us. So there's this tension between those two theories, and if you try force fit them together, the tension is often found in things that are temporal. [In one] attempt to unify them, time just kind of leaves the equations, just drops right out. It just can't handle the tension, it evaporates. The T in the equations just goes away, a reflection of just how you can't take these contradictory notions of time and make them mesh.
Steve: Now that the problems that seem to arise when you try to examine, you know, time at the beginning or at the end or what's going on in space, the singularities, do these reflect objective reality or do they more reflect a problem in our mathematics that indicates it's not as sophisticated as it needs to be to describe what's really going on?
George: I mean, I'll take the easy way out and say both. So first of all, I'm assuming in the article, kind of the underlying metaphysical assumption, is that there is an objective reality [and] our equation[s], the equations of physics, the laws of physics somehow capture it, just imperfectly. Some people will dispute that but we can leave that for another article. So there is an objective reality, but the question is whether our current theories really capture it fully, and arguably they do not. So there's a need for some kind of deeper theory. And what's interesting is that notions of what the deeper theory should be often suppose that it [has no] time in it, time [is] somehow ejected from that theory, it's no longer a part of it, the world at root is timeless. And, of course, the challenge is to capture the timelessness because all our conceptions of what reality should be or is tend to presume time at some level. We talk about motion, we talk about change, we talk about all these concepts that presuppose time. And the, kind of, metapoint I'm trying to make in the article, [when] I'm talking about the end of time, I'm also talking about how does time arise from that deeper timeless physics? Because we see time, we experience time, we live and die based [on] and within time. So the world is timeless, how do we reconcile the timelessness with the change that we do observe?
Steve: So how do we?
George: Well, the basic idea is that there [is] an emergence process that occurs. Just as life emerges from inanimate matter, so time emerges from some kind of timeless material. How that happens in details is, we're talking at the cutting edge of perhaps beyond it. But physicists are kind of taking baby steps in that direction; and one [idea] is the thing I talk about at the very end of article, namely how a dimension of space, [and it] actually turns out also time, can kind of just pop out of the dynamics of the system. So you can have something that is in a certain number of dimensions and just the way [that system is] structured gives the illusion, almost like a pop-up [book] or a hologram, of an extra dimension. So that's an example of how you can get the emergence something from that which does not have it.
Steve: Why don't we go through the various scenarios that you describe in the article as attempts to get a handle on time and what the various problems with each are.
George: So the basic starting point is the idea that time has certain properties to it, you can just make a list of them: It goes from past to future; it has a sensation of flowing; it gives structure to causes and effects; it's distinct from space in some way; you can identify moments [in] time; you can identify events as taking place at certain moments in time. You can, in other words, just have this framework for understanding the world that [a priori you] may not think you could have. You could just imagine a world just being disconnected events without any relationship among them, without them occurring at particular times and lasting certain periods of time. So time has a lot of structure to it, and the basic conceit of the article is that structure can kind of just be peeled away one by one; and I'm talking about that peeling away occurring as time ends. So as we get closer to the end of time, be that a singularity or some cataclysm in the universe in the future, as we approach that, time will progressively lose some of those properties that we ascribed to it. And the other way to think about that is that if there is a timeless reality—ultimately, the ultimate reality of the universe is timeless—time emerges by acquiring those properties one by one. So the universe structures itself; it may have begun some in kind of chaotic state that corresponds to a timeless state and through some kind of structuring, time emerges. This is where we begin to run into some of your conundra and paradoxes because how can a process of emerging occur when you need a time to do something in it? So, there are ways that that can be, kind of, described. It helps to have time emerged progressively to describe it, because you could imagine one property of time [coming] about and that helps the next property to come, and its third property, and it kind of just [bootstraps] itself up. And in the article I'm talking about going in the other direction; that as we approach singularity or some of these other cataclysms I talk about, you might lose for instance, the arrow of time, this past-to-future quality to it; and it's been known for 150 or so years, maybe almost 200 years, that the arrow of time is a property not so much of time, but of the matter that occupies it. So the orderliness of matter in the universe gives us a sense that there's this progressiveness from past to future that doesn't actually exist.
Steve: And this is because of work done in thermodynamics.
Steve: This is Boltzmann you're talking about.
Steve: Dr. Boltzmann
George: To you.
Steve: Dr. Boltzmann. Right. Please, I should definitely treat him with more respect and his fundamental work with entropy and a measure of disorderliness, and that's really what we think of as time; the transition from states of more order to states of less order or more disorder.
George: Exactly. So, at the microscopic level, particles can just [as easily move] one way as the other, they go back and forth. Though they operate within time, they're not that sensitive to its directionality. The directionality occurs as you aggregate the particles. And if matter begins in a highly ordered state, just by probability, in other words, there's more disorder than, more possible states of disorder than [possible states of] order, so it will tend toward disorder. This is a syndrome we all experience in our lives—[Why does my desk] get so messy? Because it's hard to keep it clean—there's only one way it might actually be perfectly clean and there's kazillions of ways that it could be completely messy, so it naturally goes from one to the other. And this is just, kind of, a more established idea of time as a property, that it could gain or it could lose.
Steve: So, kind of, paradoxically—and I think we discussed this with Sean Carroll when I had him on the program a few months ago—the big bang, even though we think of it as total chaos, is actually mathematically, physically, thermodynamically, the point of the most order in the universe.
George: Yep. And it's all be downhill from there. So that is one of the properties that arrow of time could lose, and it's not controversial among cosmologists that that would be the case. So the more fun and more newer research has to do with some of the other properties of time, and when I get into it some depth, is the concept of duration. So we assume that time can come in quantities, we measure it out. But determining whether a second or year or month or whatever has passed depends on having some kind of clock or periodic process to measure it. So a month is a lunar cycle essentially, a year is a solar cycle, or an Earth cycle around the sun. And if you, however, imagine a universe that has no planetary orbits or satellite orbits or any kind of orbit or any kind of vibrational pattern of an atom or a mechanism…
Steve: That's the key, because that's basically what we now think of as time—the vibration of a cesium atom is what we use as our basic unit of time.
George: Precisely. But just conceptually, any kind of process that occurs that is periodic. And that in turn requires there to be some kind of structure, in other words, [there's] some kind of cohesive body that is undergoing this periodic motion or periodic behavior. In the case of the Earth-and-the-moon system, it's the moon and the Earth together constitute one object that's bound to the Earth and hence goes around it at a fairly regularly pace. Same thing with the cesium atom, it's a bound object. And you can go all the way down in degrees of complexity to some kind of maybe hydrogen atom; and then you imagine hydrogen atom even splitting up, and you're just left with protons and electrons. And then the only structure the universe would have or indeed did have in its early path, in its early history, was the proton itself which is actually [a] tiny little structure in its own right, [it] has quarks and gluons in it. And if that, in a way, if that didn't exist, you have literally no mechanism, no structure in the universe able to undergo periodic motion of any sort any clocks would therefore become impossible and duration would be immeasurable.
Steve: And so time would stand still.
George: It's not so much that time would stand still, but that time would no longer be something you could define as coming in quantities, in units.
Steve: It wouldn't really exist in any meaningful way that would be recognizable to us.
George: Right. I mean, none of this is, I mean, this is all mind blowing stuff. But in this case, you could still imagine time is coming in a progression, that something occurred before or after something else; [you could] still line things up in a row. But you could no longer say they occurred a minute after the others did. You could still say it occurred after the other thing. So in that way, you've stripped away one of time's qualities and left some other qualities that are still there. You still have progression, you still have the sense of cause and effect, but you no longer have things taking [a] certain amount of time. I can see that your mind is already kind [of] spoofing, like, steam out your ears.
Steve: And you can smell the gears grinding as well. Now because it's as you said, a series of emergent properties; so if you go in the other direction [you] start to pluck one property out at a time, so now you're talking about this scenario where we do have a sequence, [but] we no longer have duration. So there is something that we recognize as time passing but we don't know if we took a year, million years, or two seconds.
George: [That's exactly right.] And I think the best analogy, [well, there are] lots of analogies you could use to [describe] emergent behavior; like how does an ice cube emerge out of liquid water, for example? It's [a] kind of structuring process it has to go through. Or again how does life emerge from inanimate matter? And we would commonly think of it occurring, kind of, in stages. So you've got the atoms [congregating] into, say, proteins, which then are part of a larger system that has certain biological functions; and [there] is a threshold below [which you] would say that's not even alive; and then you would have something [that's just] a cell and tissues and so forth; and then you'd get to something maybe you [could] call conscious or [sentient]. Same thing with time.
Steve: Same thing with time!
George: [Exactly the] same thing. It's so easy Steve, don't you see?
Steve: So what else do we talk about in the article in terms of, you know, scenarios for time ending or not ending.
George: So another property that time has just in our daily experience is it allows us to structure the world as cause and effect. So we know that when I took my brother's peanut butter sandwich he yelled at me, because I took my brother's peanut butter sandwich, and he hit me. Now if that can be inverted, you can get all sorts of disputes in the kitchen that never could be resolved. For instance, maybe I took his sandwich because he yelled at me.
George: So our whole notion of what it means to be an agent in the world, you know, someone who is responsible for our behavior comes, from this destruction of cause and effect. And [in physics, there is] sort of a very precise meaning to that having to do again with Einstein's theories. And it comes about from the fact that time is dealt with a little bit differently than space. We always talk about there being four dimensions—three of space and one of time, and we think of a unified space-time. But as much as space-time is unified, there's definitely a different [role] being played in that unification by the space part as by the time part. In particular the time part has this structuring that you can have and talk objectively of causes and effects; something occurring before the other and perhaps giving rise or influencing that [event]. If time were to lose that property, it would essentially just become space, so time would shade [into] space; it would just melt and become a part of space. And then you can do all sorts of things. You can move in this newly "space-ified" time just as you would move through space, you can go back and forth.
Steve: This is obviously how [warp] drives work.
George: You know, it actually does relate to questions of traveling faster than light or not. Because if you could travel faster than light, you essentially would flip space and time; you would cause those two things to transition into one another. And you would get all sorts of paradoxes as we all know from Star Trek, going back and changing your civilization, causing [yourself] not to exist and things like that.
Steve: So will time end or does it just keep ticking along?
George: I think it's still an unresolved question. I try to make a case in the article that time could plausibly end; plausibly in the sense of some of the paradoxes you would associate with time's ending—how could time just be going along, going along, going along on and stop. You can, kind of, get away from this paradox by having a more gradual cessation of time's functions. But one could still imagine the situation where time does continue, and indeed the physicists have yet to really pull back and take time out of their theories completely. Even the most detailed theories of how time can shed its functions always have some kind of residue of time left over at the end; they haven't yet got to the last bit of it.
Steve: What do you mean by residue of time?
George: Well it's a very specific, technical meaning in this case that—and it's talked about at the very end of the article—that one can imagine the de-emergence of dimension of time; it would just, kind of, pull back as [though] a pop-up [book] had just collapsed back onto the page. And you can imagine that and time would go away, as that pop-up book collapsed back down and the universe would kind of revert to a more timeless state. But even in the theories time [would supposedly stand] still has a kind of a time in it. It's not time as we would experience it; it's, kind of, a primal sense of time. And the ultimate hope is that they can even get rid of that primal sense of time and have a theory that's well and truly timeless and there is nothing in it that is vaguely temporal or indeed geometric, spatial, and those properties come out through this progressive emergence. Am I making any sense to you, Steve? I don't know anymore.
Steve: Well, isn't that an occupational hazard when talking about this material?
George That's what makes it fun, too, isn't it?
Steve: Yeah definitely. It's exhilarating and maybe a little depressing at the same time.
George: Yeah, you know you might think it's more hopeful to think that the universe is stretching out into the indefinite future, and maybe the actions I take today will have this kind of ripple, and extend forever and forever in time. But one of the, kind of, ideas that I tried to leave the reader with in the article is that there is a tradeoff that [is being] made here: For us to be able to exist as mortal creatures, we have certain properties that we require, too. We have to have a sense of progression; we have to have a sense of causality, that something we do has an effect in the world; and we have to have some kind of structuring to our existence and we have to [be able to] our use [up] energy [and create] entropy and so forth. And it turns out all those attributes, in a sense, require time to die; that in order for us to live, time must have the capacity at least of dying, and even in the act of living we contribute to time's death.
Steve: Not just passing but dying.
George: Yes, in the particular sense, the easiest sense, perhaps, to understand is the arrow of time. So as you pointed out earlier that comes from this whole concept of entropy. Now for us to create in our bodies a kind of a localized order, we require the rest of the universe to become even more disordered. And the more we try to maintain the order that we have, the more disorder the rest of the universe has; in other words, we have to shed heat, there's an inefficiency in our technology, and in our bodies.
Steve: Right. Useful energy becomes nonuseful.
George: So the universe just runs down. And, you know, you can think of that as something to be depressed about but you can also think of that as, "Wow, the universe had this property that allowed us to exist."
Steve: Well, that's it for this episode. We will be back very soon with a look at one last piece from the September issue by Robin Marantz Henig on organ transplants and end of life issues, because time might not end, but you will. For Science Talk, the podcast of Scientific American, I am Steve Mirsky. Thanks for clicking on us.