I Tweeted the following inscrutable remark. Probably best left unexplained, but upon reflection I can’t resist.
My consciousness freely travels up and down my world line, but sadly it only carries the memories appropriate to the moment it inhabits.
The point is that (some) people don’t think about the flow of time in the right way, and this leads to a couple of unfortunate consequences: a difficulty in understanding the psychology of time, and a scattering of entertaining but illogical science-fiction scenarios.
Modern physics suggests that we can look at the entire history of the universe as a single four-dimensional thing. That includes our own personal path through it, which defines our world line. This seemingly conflicts with our intuitive idea that we exist at a moment, and move through time. Of course there is no real conflict — just two different ways of looking at the same thing. There is a four-dimensional universe that includes all of our world line, from birth to death, once and for all; and each moment along that world line defines an instantaneous person with the perception that they are growing older, advancing through time.
But if you don’t play too much attention to the way these two views fit together, you are tempted to imagine that “you” might actually, in some set of laws of physics if not actually in our own, go visit different moments in your own life, carrying along the consciousness of your “present” self. Something like that happens in SF stories from Slaughterhouse-Five to Back to the Future. But it’s not consistent — it requires the implicit introduction of a kind of “meta-time” that keeps track of when we visit the ordinary time with which we are familiar. That’s not how nature works; my tweet was trying to point out the inconsistency of taking this idea seriously, subject to the strictures of 140 characters or less. (To be earnestly explicit: if you did manage to travel up and down your world line at will, you would indeed have whatever memories were appropriate to the moment you were inhabiting — which means it would be exactly like not traveling at all.)
Sometimes, unfortunately, people go further than science fiction. I’ve run into folks who believe that our conscious perception of time passing is actually evidence against modern physics — arguing that we need to change the known laws of physics to account for the flow of time. It’s always conceivable, in principle, that what we think we understand at a basic level is completely wrong. But the evidence had better be pretty overwhelming. The brain is a complicated thing, and I don’t think that our present inability to provide a complete and comprehensive theory of conscious perceptions should be held as compelling evidence that the laws of physics are in need of overthrowing.
To the folks talking out-of-body experiences … floating above the surgical table and looking down, etc …
The problem I have is that I think I understand a little about light, optics, and how the eyes work; and it all obeys physical laws. But if your consciousness floats up out of your body and you look down and can “see” yourself, then how are you “seeing” this reflected light without physical eyes. And if your consciousness can see without physical eyes, then why do we need eyes in the first place?
Oh yea, floating above the surgical table and “hearing” the surgeon talking to the nurse presents the same problem. If your consciousness can sense these acoustic waves without ears, then what’s the point of physical sense organs … or physical laws? I wonder if when your consciousness continues to float upward beyond the atmosphere it can still hear sounds?
If you need glasses to see clearly, and your consciousness floats up out of your body and looks down at your physical self on the operating table, do you see yourself in or out of focus?
Sean, when I was first exposed to quantum theory decades ago, I considered the possibility that information projected into the past better explained such phenomena as non-locality (spooky action at a distance) and the paradox of Schrodinger’s Cat than the more outlandish (to me) Many Worlds (or multiverse) interpretation then being bantered about. After all, Many Worlds may seem reasoable for coin tosses, but ask me to write down a real number between zero and one, and we’ve just split off an infinity of new worlds. Furthermore, I conjectured that the Big Bang could have produced not just our universe moving forward in time, but an equivalent (antimatter?) universe moving backwards in time … analogous to pairs of virtual particles materializing from the vacuum. Of course this was mere speculation; no chalk was wasted attempting to take it beyond bong babble. And in fact I don’t think it could fit with your proposal that entropy produces an Arrow of Time. But what am I missing that seems to be obvious to more educated physicists which rules out information projected into the past as a plausible explanation of quantum phenomena?
I have heard that closed timelike worldlines are mathematically possible
in GR. If so, and I could follow one, it seems I could – in principle –
“visit” my own past and meet my past self. (No doubt the actual
world has no such worldlines, but this is perhaps not known for
certain.)
Why stick to just your own world line?
“…(some) people don’t think about the flow of time in the right way, and this leads to a couple of unfortunate consequences…”
This reminds me of another common misapprehension. Many if not most people have the impression that when we gaze outward into intergalactic space, we are looking at what we call ‘the universe’, potentially, at the whole of everything. It’s easy to forget that we can never obtain more than a cross-sectional and fleeting ‘snapshot’ of all that’s ever transpired in the universe – that is, just the info that’s just arrived at our position that has traveled on the anterior light-cone. Even our view of the potentially ‘observable universe’ is grossly restricted.
It’s also worth noting that the conventional western way of thinking about the direction we are heading in time, FACING the future ahead of us and turned away from the past behind us, doesn’t reflect our situation very accurately: at any given point in the present, we don’t see the future before us but only have a view (a ‘memory’) of the past. Some isolated cultures have cultivated this ‘past-facing’ tradition in their impression of time, with the unknown future out of sight behind them. Their ‘backing into the future’ way of looking at it is, to my mind, superior to the one western societies assume. But the western way is well-entrenched: they are ‘forward-looking’ cultures, I suspect, because of the constant preoccupation and feedback stimulus of looking ahead down the road, navigating toward a destination, negotiating to reach a goal, etc.
Craig #23 says, “But the particles that make you up are constantly being replaced over time. How do you square that with the world line idea?”
Simple: ‘you’ aren’t the particles but the dynamic interactions between them. Your mind is a ‘process’ generated by a brain consisting of a complex system of billions of interconnected neurons and your neurons and the rest of the cellular components in your body down to the molecular and atomic level are all processes in dynamic flux, but which have evolved the ability to maintain a relatively stable equilibrium configuration over your lifespan. The pattern of interactions persisting in time is ‘you’ and that’s the ‘worldline’ referred to, but if you examined that ‘worldline’ at increasing magnification, you would see that it isn’t a single line at all, but rather a gnarly hideously-frayed spaghetti-like cable with particles (other ‘lines’) leading to and from it, coming and going all the time, a cable always threatening to unravel while the biochemical pattern works to maintain its integrity with replacements and repair mechanisms. The ‘self’ is not as adamantine and pure as some of us would like to suppose.
My consciousness freely travels up and down my world line, but sadly it only carries the memories appropriate to the moment it inhabits.
Do you have any empirical evidence for this, or is this merely a rationalist speculation. Come to think of it, can you even produce any empirical evidence that you are conscious. Suppose you are facing a panel of extremely talented but very skeptical scientists equipped with the best experimental equipment out there. Can you convince them you have consciousness.
“There is a four-dimensional universe that includes all of our world line, from birth to death, once and for all; and each moment along that world line defines an instantaneous person with the perception that they are growing older, advancing through time.”
No.
There is a 4D solution at any instant that is consistent with all the information we possess. As that information is updated, the solution changes. It is the path through this solution space that is of interest.
“Modern physics suggests that we can look at the entire history of the universe as a single four-dimensional thing. That includes our own personal path through it, which defines our world line.”
Let’s see what can know about the world by looking at it. Well we can know the past existed, since the information we directly observe comes to us, dependent on distance and via a constant speed of light. Since this information is being consistently updated, we can define the time that we receive it to be the present. We can only infer that the future will exist, since our experience and our knowledge of the laws of physics suggests that it will. Here’s the kicker. The future is not guaranteed to exist. Something unknown could happen to the entire universe – say a collision in the multiverse or “whatever” – that destroys our entire universe such that time ceases to exist. Bearing any unlikely such event, does the future exist and is it already determined? If it were determined, why doesn’t classical physics apply to all physical objects regardless of scale?
Perhaps the future only exists in a superposition of possible futures and the past only exists in the information that it is encoded in the EM radiation that travels through space because the *map is not the territory*. With all due respect to you, Minkowski, and say Max Tegmark, the constructions we devise to model reality through the rationalization of physical phenomena with mathematics is only an *approximation* of reality, it is not reality, itself. Just as there are no known true spherical objects in the universe (only ones that are approximately so), there is no evidence that the past, present, and future exist as a whole in some four dimensional spacetime. This “block universe” is just one of our constructions to help us model physical reality. The “succession of present moments” is another concept of the universe and the nature of time that works as a map of reality and IMO fits better with the indeterminate aspects of QM observations.
We all have direct evidence of the present moment, it’s what we know by looking at the world. The present moment flows at different rates dependent on our motions and positions wrt the proximity to massive objects in complete agreement with the theories of relativity, without the need for a block universe. We have no evidence that the past and future actually exist in parallel to the present moment, only evidence that such rationalizations have been useful, especially in modeling the physics of relativity.
We do have evidence that the universe is expanding. What is the universe expanding into? It’s expanding into the future. Just as new space is created by the expansion, new time is created as well. Doesn’t this serve as a quite satisfactory explanation of what creates the succession of present moments?
Dan: I don’t see how we can define a ‘moment’ let alone a present one, in any sense that is independent of the observer like Einstein said. It is true that the map is not the territory- but Minkowski’s map was better than Newton’s. To the extent the universe is truly evolving like some species, it’s certainly doing so not in our ‘present’ but some other frame of reference that has nothing to do with the human experience.
Ray
Of course your questions are great. How about an extended mind? There was a conference in 2009 to do with this. Can this explain somehow? If people are seeing during NDEs can optics get bypassed? There are very good cases. Is there a subtle body doing the seeing?
Lloyd Rudy (from above) – “he was up there!”
http://www.rcpsych.ac.uk/pdf/SIG%20Website%20April%203rd%2009%20Programme.pdf
Answers on one sheet of A4 only please.
It’s worth distinguishing the world line of a person from a person’s passing through time and experiencing the evolving, unfolding universe (or at least having the phenomenology as of passing through time and the phenomenology as of the universe unfolding)
What’s interesting to me is not that we have these fascinating discussions about the nature of time and how gravity works, but that we think our brains are evolved enough to understand the nature of the universe at all. We’re like goldfish in a bowl who think we know how the world works because we’ve seen our owner use a can opener. We see the universe from our own extremely limited perspective, and all we can do is form theories about it. It seems to me the height of hubris to imagine that, from our dusty little perch partway out one of our galaxy’s spiral arms, we can proclaim we have knowledge of how the whole, intricate mechanism is built. In fact, I’m sure we have much more to discover than we have ever learned. Invoking terms like “dark energy” and “dark matter” to try to explain things we don’t understand is proof enough. Not that we should stop striving to understand the nature of a universe in which we play a miniscule part, but doing it with a modicum of humility might more accurately reflect our place in it.
Gene #37,
OK, let’s assume that the block universe exists. If A is a random event in the set of all events that creates the block, we can trace back in time to the singularity to say that A occurred when the universe is XX.X billion years old. If we hold the time constant, and vary the three spatial dimensions, we trace out the surface of a hypersphere, with a radius of XX.X billion years. This surface intersects the world line of every particle in the universe, even though the local time of each particle is determined by local conditions and the laws of GR (all physics is local), this hypersurface represents the “present” state of the universe. As this hypersurface expands, it creates new space and new time. We can not prove that addition hypersurfaces, interior and exterior to the “present” hypersurface, exists in actuality (there is no evidence for their existence in reality) rather than in the Platonic sense. We do not need to posit their existence to adequately describe the universe. Therefore by Occam’s razor, it is simpler to assume that they do not exist.
If you would like to learn more about this model and its surprising consequences, I have written a essay for FXQI’s essay contest that can be found here: http://www.fqxi.org/community/forum/topic/826
Sean Carroll noted that “… Modern physics suggests that we can look at the entire history of the universe as a single four-dimensional thing … This seemingly conflicts with our intuitive idea that we exist at a moment … Of course there is no real conflict — just two different ways of looking at the same thing.”
A direct question to Sean Carroll if you are still reading this thread:
Both special relativity and quantum theory include strongly deterministic threads, e.g., the reciprocity of “now” in SR frames and the advanced EM wave solutions of Feynman’s thesis.
If you have a moment, would you share your views on how to reconcile the idea of a real, non-trivial “now” with those parts of physics that seem to imply predetermined worldlines?
Ouch, I just looked up a Perimeter Institute paper on alternatives to the block universe.
As someone with a long-term fascination about methods and heuristics for determining when complex information is worth analyzing closely, and conversely when it should be discarded quickly, that paper reminded me of simple point: If an argument is based on a huge number of ideas that individually sound impressive, but which on average have never been well verified, the real chances of the argument being valid are… well… vanishingly close to zero. (This is also a simple way of explaining why I am am incapable of being impressed with the enormous work and detailed reasoning that has gone into string theory over the past several decades.)
So, if I may add a qualifier to my last question: Sean Carroll, would you happen to have any simple, well-focused, and perhaps even experimentally meaningful approaches to reconciling your idea of a real “now” with the idea of a block universe? My emphasis here is on “simple.” If an issue this fundamental to how existence operates cannot be explained by using only a very small number of conceptual building blocks, it’s time to go back to the whiteboard and start over again.
Matt in 6:
“Sean, I wonder what the implications of this on discussions of free will/decision making are? If the four-dimensional universe includes our world line are we simply deterministic machines with our consciousnesses providing an “illusion” of the ability to make decision when from the full-dimensional view it is simply following its worldline?”
Our ability to make decisions and the decisions themselves are just as real as anything else in the block universe, not illusory. But of course the decisions are all there in spacetime, it’s just we experience them serially.
We wouldn’t gain anything in terms of control were we somehow able to extricate ourselves from our worldlines, since exerting control is a particular sort of pattern in the worldline itself, namely when getting what we want follows from what we do, http://www.naturalism.org/spacetime.htm#inevitability
As Wes comments, GR does not rule out the possibility that points on your worldline may have a spacelike separation, sharing a single ‘now’ according to some observers. At one of the points you would have memories of being at the other. Are those memories appropriate to the inhabited moment? I’d say so: most would call the person with the extra memories a time traveller…
Whether nature or intelligence can fiddle with the spacetime curvature enough to allow this is of course still unknown. Does anyone have a massive near-infinite cylinder rotating at relativistic velocities handy?
Dan: A most interesting theory, and good luck in the contest. Still, I don’t understand its advantages. It is true that we can construct a hypersurface and watch it expand ‘as if’ it were like a balloon in a room that fills up with air as we look at with our watches. The problem is there is no unique way to do it. In a sense, its not that I maintain all hyperspheres exist, its that I don’t think any of them do in any fundamental sense. Even the ADM formalism has its limitations, and I doubt that a future theory of quantum gravity will fix the situation.
Gene #46,
Thanks, for the feedback. Unfortunately, the contest is already over and I didn’t receive a prize. I felt like a winner nonetheless, since I managed to make it thru to the judging, which was no easy task. My essay was a little off the topic of the contest and it was a lot to cover given the limitations of the essay length.
I’m presently working on a more rigorous version to submit to a respectable journal. I believe that the Concordance Model has some definite fatal flaws that can be amended by a new model without a wholesale revision of our fundamental laws. I will need a little luck, a lot more hard work, and some ironclad proofs, if I want to have any effect on the status quo.
Re: Sean’s Tweet.
Sounds like bad poetry written by a bored 15 year old after flipping through A Brief History of Time.
Time Flow in Stephen King’s “The Langoliers”
In the 1995 a sort-of science fiction novel by Stephen King was made into a movie called The Langoliers. As you would expect for a Stephen King book, the set up was primarily a horror-drama with the usual selection of ornery and outright demented people, as one of King’s scary-smart young girls with telepathic powers that he seems to favor for many of his stories.
Now what was interesting about this purely-for-entertainment work was that King put some non-trivial effort into developing a theory of the flow of time, one in which he then places his characters to stress them out and make them do the sorts of things you expect in Stephen King novels. In a nutshell, King’s theory of time goes roughly like this: The “now” in which the universe exists moves not through some abstract definition of time, but through a quite literal empty space in which “now” is more like a spaceship in motion than a system in evolution. Change takes place within the spaceship, but in a way that is independent to some degree of motion through the literally space-like time dimension.
That’s sort of interesting, but what really captured my attention about King’s model of time flow was that he placed incomplete versions of the universe both in front of and behind the moving location that defined what “now” is. King’s leading-edge incomplete universe was bright, fresh, and full of the promise of change, while his lagging universe was stale, fading, and clearly head towards a bad end. This being a Stephen King movie, he of course placed the crew of an airplane first in the lagging universe, where they would await… what?
The Langoliers, of course. The Langoliers might best be described as the ideal nightmares of someone who is frightened horribly by large drill bits and empty spaces. Their purpose? Recycling of course! The Langoliers are the überscary (well, by 1990s CGI standards they were) chompers and eaters of the past, leaving it in place only long enough to (I guess) reinforce the real “now” further up the chain. Once the Langoliers recycle the ragged trailing edge of reality, however, it is gone forever — all that is left is a gaping, empty vacuum from which “now” is hurrying away at breakneck speed.
And therein lies what I like most about Stephen King’s version of the flow of time: He simply creates an intuitive model that deviates in the most fascinating and heretical ways from “standard” spacetime physics. Why shouldn’t he? His only purpose was entertainment.
Yet it’s a fascinating model about which to ask some of the same questions that perplex far more learned models of the flow of time. For example, can you travel in the past in King’s version of spacetime? Yes and no, since you can go a short ways back, but no further, and even that distance is ragged and unpredictable. Can you visit the dinosaurs? Definitely not, since they only exist as memories stored within the Present. The past in King’s universe is nothing more than the lonely and empty road left after the first, last, and only bus there will ever be passes over it. Only the memory of dinosaurs lives on in the images and information within the bus of now, just as the bones we find in our actual universe are nothing more than memories of a past that is no longer accessible as a existing place.
In King’s universe, can you change the present by altering the brief past that lags behind it? No, because that past is only a subset whose impact on the present fades quickly as you move farther away from now. Can space be curved? Well, yes, but probably only in the sense that the bus that represents all of now can be curved or bent, since only that part contains space as we would perceive and measure it with instruments. Are there infinite worlds? No. Are there infinitely long world lines, what is often called the “block” (as in “solid like a block from start to finish”) universe? No, only short dangling world lines that extend a ways into both the future and the past. Can the waves of quantum mechanics grow without limit? No, because there is no room for them to grow; they are captured and must resonate within the bound of the Bus of Now.
If Now can be bent, might the wormhole solutions of general relativity allow travel back in time within King’s flow of time? Probably… but you would only find empty space when you got there, since time in King’s universe is an infinite sequence of empty spaces through which the occupying mass of Now moves. Can Sean Carroll’s vision of complementary universes moving in opposite direction in time be accommodated? Sure, but in an almost trivial way: Both universes change in the same way, they just literally travel in opposite directions down the long road of empty spaces. In King’s universe time is not so much space like as it is two separate variables, one for distance along the path of empty spaces (t), and another, call it tau (that’s not standard incidentally) for “change like a clock hand moving.” That kind of choice is a programming or data representation issue, and so is not necessarily fundamental to physics if precise equivalence is maintained. Cramming multiple meanings into a single variable is what computer types call overloading. It can be a handy technique for expressing issues compactly, but some willingness to recognize provably equivalent alternatives can also be helpful for finding cleaner or more understandable ways of representing ideas.
Now here’s a more hypothetical question that I don’t think King had in mind, but I don’t want to be too quick to judge him on that either: Is there a plausible physical interpretation for why a universe would have leading and lagging edges to it, that is, partial versions of itself that cannot exist or change in isolation, but which somehow assist the main Now of the universe to function and work?
This more than anything else struck me about King’s flow of time, because I think you can make a surprisingly deep argument that whatever the universe is, it does indeed require roots that extend into both the past and the future. The reason is that at a profound level, much of physics seems to operate on a principle sometimes called minimization of action, action being an odd product that has the same units as Planck’s constant. One way to get a tiny bit of a graphical feel for how this minimization of action works is to imagine particles as rubber bands that are stretched between points in the distant past and other points in the distant future. Near the middle of these bands is the Present, where forces and potential energies cause the rubber bands to stretch and move sideways in interesting ways. The tension of the rubber bands can then cause them to interact and interplay with each other can, producing in many cases results that seem strangely prescient, almost as if the particles could see in limited ways into the future — which of course with those rubber bands extending into both the future and the past is sort of what happens.
I should mention that this whole peculiar issue of particles being smarter than they have any real right to be, at least when it comes to responding to energy potentials, is one of the reasons why some physicists like to extend those rubber bands all the way from the start of the universe to the end. At that point they become what are called world lines, and the resulting universe of infinitely long rubber bands becomes the “predetermined” block universe I mentioned earlier.
King inadvertently (?) proposes a scheme that is far more appealing to computer folks, which is to make the worldlines virtual. That is, to help the Present respond meaningfully to its array of diverse forces and potentials, King’s worldlines appear to extend as far as they need to into both the future and the past… but no farther. Once their action minimization duties are completed, the rubber bands in effect snap back towards the fabric of Now and become available for building new virtual world lines to explore new possibilities and potentials.
And that gives another answer to a question someone might want to ask about King’s flow of time:
Why is quantum computing so hard? Well, in King’s universe that’s easy to answer: The worlds being used to calculate more powerfully are virtual only, so they can only exist for as long as the lagging edges of the recent past can be coaxed into hanging around. Eventually, inevitably, and without exception, they will snap back into the fabric of Now upon which their existence depends. And when that happens, any quantum computing will be over. The overall result in King’s universe is that quantum computing becomes a matter of balancing cantankerous noodles on their ends. It can be done, for a while, but in the end it will always collapse back into the ordinary physics of Now.
And last but not least, there’s an ugly beast — the Langolier. What would it be in such a universe? Would a real-physics analog to the destruction of packets of virtual worldlines a thing of beauty, or would it be as ugly, scary, nasty, and poorly understood as King’s Langoliers?
I vote for ugly, because the beast already has a name in real physics, and it’s not much liked in many circles: wave collapse. That is, to make virtual worldlines real and a part of actual physics, you unavoidably must also make their destructors just as real. Many physicists do not like even the idea of operators of this type, which have never been well quantified and which have annoying properties such as changing or collapsing entire regions of spacetime. One answer to that is to avoid such operators. Another is to get creative and look for some entirely new ways to do math.
And the end: Why have I bothered with all of this?
Because I just wanted to point out that in physics, interesting and even entertaining ideas can lead to conclusions that are no more absurd than wondering if the ability to think and remember might require the redefinition of all of physics.[1] Three cheers then for Stephen King, who took the time to explore some wild ideas for how time works for the purpose of entertaining, yet surprisingly wound up with a collection of ideas that both resonate and conflict with modern physics thinking in a number of truly fascinating ways.
———-
[1] I know nothing of all that argument, but I would make this observation again: If Now is just a set of memories, as in the King universe I just described above, then any measurement of a time difference unavoidably depends in part on memory and intelligence. Why? Because the past cannot be observed directly, even if you believe it still exists. Thus you can at best only measure time as it exists between the real instruments looking at Now, and the intelligent memory constructs that we call Then. Forget about observers being needed in quantum mechanics: Every invocation of time or t in classical physics calls for an intelligent observer, and does so just as forcefully as do the precepts of quantum mechanics.
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