Sign up for the Blank Horizons mailing list here.
“Through our eyes, the universe is perceiving itself. Through our ears, the universe is listening to its harmonies. We are the witnesses through which the universe becomes conscious of its glory, of its magnificence.” – Alan Watts
Living forwards and backwards
In Richard Linklater’s film Waking Life, two characters have an incredibly profound conversation about dreams and the nature of time. One mentions that a lot can happen in dreams even though very little time passes by in the real world. What feels like an hour-long dream might actually take only a minute of real time. “I wake up and it is 10:12, and then I go back to sleep and I have those long, intricate, beautiful dreams that seem to last for hours, and then I wake up and it’s … 10:13.”
When we die, the characters in the film say, there are about six to twelve minutes in which the brain remains active even though the rest of the body has shut down. If just one minute of brain activity in the dream state can contain many hours of conscious experience, then how much can get compressed into the span of those six to twelve minutes? Could an entire lifetime’s worth of memories and experiences unfold in those moments? After all, many people claim that they have seen their lives flash before their eyes right before undergoing a near-death experience. In these so-called “life review experiences” (LREs), memories are rarely recalled in a chronological fashion; our minds don’t replay the events of our lives in the order in which they happened. In fact, during the flashback, all sense of time is lost; all the moments blend together in an undifferentiated, timeless unity. In the words of someone who experienced an LRE, “A moment, and a thousand years … both and neither. It all happened at once, or some experiences within my near-death experience were going on at the same time as others, though my human mind separates them into different events … I was not in time/space.” In these flashbacks, the past does not flow into the future; time does not move. All events happen simultaneously in the eternal, unchanging landscape of the Now.
The characters in Waking Life ask a bold and profound question: what if you are living in a life review experience right now? What if your life has already happened, and everything that you are experiencing is contained within a flashback that you will have of your own life right before you die? What if this moment – the one that seems to be happening right now – is just a memory that your brain is replaying, and what you’re really living through is the six to twelve minutes of brain activity that occur after your heart has stopped beating? Would there be any way to know?
These questions may inspire you with deep awe and wonder, as they did to me, or they may strike you as totally speculative and entirely unfounded. Of course we’re not living in a flashback, you might say. We live through all of our experiences in the present moment, and all of our memories are recollections of the past. We know that we aren’t living inside of a memory because the past can never coincide with the present. The notion that we are currently experiencing a flashback of our own lives, therefore, runs counter to our deeply ingrained belief that time flows from past to future, but never in the reverse.
My aim in this essay is to challenge the idea that time moves in only one direction. I’m not arguing that time travel is possible, but rather that time doesn’t really pass in the way that we think it does. Nevertheless, we have to contend with the undeniable fact that certain events take place before others, and some happen after others. If any change occurs in the universe, then it would seem that the distinction between “past” and “future” must be real. I do agree that our minds arrange the events of our lives into a linear, temporal order, such that each moment appears to flow into the next one. However, the limited scope of our normal, everyday perception confines us to experiencing only one moment at a time. Beyond the veil of our perception, all moments are happening together, at the same time. The totality of past and future are transpiring right now, in the Absolute Present, where no single moment ever arises or fades away. All of time is unfolding during each moment that we experience, but in a realm that we cannot access through our regular state of consciousness.
In Part I of this series, I discussed the notion that each moment contains all other moments in the context of Buddhist philosophy, particularly as it pertains to the topics of spiritual practice and enlightenment. Here, I’m going to talk about some findings in contemporary physics that may substantiate my view of time. It is worth noting that many in the scientific community are skeptical of these ideas, so take them with a grain of salt.
In a previous post, I discussed the concept of symmetry, which is a transformation that leaves a physical system unchanged. The laws of physics exhibit symmetries in space and time; if I conduct an experiment at 2PM on December 28 in Los Angeles and obtain a particular result, then I would (generally) expect to get the same result at a completely different time of day on the other side of the world. The dynamical equations that govern the evolution of the universe hold true at all points in the universe, no matter what time it is. Furthermore, as the physicist Emmy Noether demonstrated in the early 20th century, every symmetry is associated with a particular conservation law in physics. For example, if a physical system is symmetrical with respect to time (that is, the laws that describe the system are not dependent on time), then its energy will be conserved. Many physicists have sought to find underlying symmetries in the universe in order to uncover hidden dynamical laws.
In the mid-1990s, the physicist Itzhak Bars began to suspect that a symmetry between position and momentum may account for the Heisenberg uncertainty principle, which states that it’s impossible to simultaneously measure both of these properties in a particle with total precision. Bars found that this symmetry would require two additional dimensions: one of space, and one of time. In total, the universe would have to consist of six dimensions.
The added dimension of time in Bars’ model permits time to move in two directions: forwards and backwards. Nevertheless, the model imposes strong constraints on an object’s range of motion within those six dimensions, making it impossible to travel back in time. In fact, according to Bars, “[For] all intents and purposes, the six-dimensional world behaves like a far more restricted world, one with only four dimensions.”
If Bars’ six-dimensional universe so closely resembles the four-dimensional world that we think we live in, then it would seem that the extra dimensions of space and time in Bars’ theory are nothing more than mathematical devices that have no actual bearing on reality. However, Bars argues that these dimensions are not only real but can also dramatically reshape our understanding of the physical universe. When Bars modeled a very simple physical system – a particle moving in a straight line without any forces acting on it – with his theory, he discovered that the system was merely a “shadow” of a larger six-dimensional structure. There were at least two other shadows, each one corresponding to a different set of phenomena: one in which an electron orbited an atom, and another involving a particle in an expanding universe. Generalizing this finding, Bars claims that the four-dimensional world that we readily perceive is merely a shadow of a six-dimensional reality, one that we cannot access through our observational awareness.
Furthermore, all of the shadows coexist with each other simultaneously, but each one has its own dimension of time. In other words, time may pass differently in our universe than it does in the other universes in the six-dimensional structure of reality. Some of the shadows that Bars describes for his one-particle system include universes where space-time is flat, rather than curved (as it is in our cosmos); in others, time doesn’t even exist! At just one moment in the six-dimensional reality, the particle may be farther along in its path in one shadow, farther behind in another, and on an entirely different coordinate plane. (1) The crucial implication of two-time physics, therefore, is not that time can flow backwards, but instead that multiple configurations of the same system, existing at multiple different times, can all coincide with each other in a higher-dimensional universe. According to our conventional, Newtonian notion that time passes linearly from past to future, it takes more than one moment for a particle to evolve from one state to the next. But in two-time physics, it can express both states in a single instant. Two separate paths taken by the particle are merely two perspectives on one trajectory that is realized in the present moment. (2)
Critics of two-time physics might note that it doesn’t deal that much of a blow to our Newtonian conception of time due to the restrictions that it places on an object’s motion in time. Even Bars will admit that within one universe, time essentially flows in only one direction. We will have to look elsewhere in physics, then, for evidence that the future can influence the past.
In 1984, the preeminent quantum physicist John Wheeler proposed a “delayed-choice” thought experiment that aimed to suggest that these “retrocausal” influences may, in fact, be plausible. Wheeler’s idea is a spin on the famed double-slit experiment in quantum mechanics, which demonstrates that even a single particle, or photon, of light can be in several places at the same time before it is measured. The physical state of a photon is encoded by a “wave function,” which describes the probability that it will be at a particular location in space. If the photon can be in two possible states, then it could be in a superposition of the two corresponding wave functions. Hence, when faced with the choice of passing through one of two slits, it can enter through both simultaneously. However, we can never actually see a photon passing through two slits at once; we can only gain indirect knowledge of this phenomenon by noticing the interference pattern that the light forms on a screen placed behind the slits. Indeed, when it is detected with a measuring apparatus, the wave function collapses into one discrete point, such that the photon can only ever be observed at a single point in space and time. Therefore, when photon detectors are placed near the slits, the light only travels through one of the two slits, not both.
Wheeler imagined a version of the double-slit experiment conducted on a “cosmological scale.” His thought experiment involves a very, very distant quasar (an extremely bright celestial object) and two galaxies that lie between it and Earth. The light emitted from the quasar is deflected by the galaxies as it travels towards our planet. Before it is observed, the light exists in a superposition of locations; that is, it will bounce off both of the galaxies, even if they are separated by many light years. However, if astronomers on Earth pointed a telescope at the night sky, they would find that the light emanating from the quasar only traveled around one of the galaxies, since the act of measurement would collapse the superposition of its wave functions. If they choose to look at, say, the left galaxy, then they will find that the light was deflected by that galaxy. On the other hand, if the astronomers did not directly observe the light and instead carefully reflected it onto a screen (similar to the one in the double-slit experiment), then they would perceive an interference pattern, implying that the light had traversed both of the galaxies simultaneously. Astoundingly, Wheeler’s thought experiment implies that the way we measure light in the present can retrocausally affect the behavior of the light in the past. If we detect the photons from the quasar with a telescope, then it took one route; if we use a screen instead, then it took both routes at the same time. A completely random choice that we make right now could influence the path that the light took billions of years ago, long before the evolution of human life.
It may be impossible to test Wheeler’s thought experiment with our current scientific tools, but evidence has emerged for retrocausality elsewhere. In particular, it has served as an effective framework for resolving one of the most baffling puzzles in quantum mechanics, which was most fully realized in some experiments that were conducted by the physicist John Bell in the 1960s. Two photons are generated at a common source, and then each one is propelled towards a “measurement box” controlled by one of two humans, Alice or Bob (see Fig 1). Each person will choose the angle at which the box will polarize the light (i.e. restrict its vibrations to one direction). The photon is then detected on one of two possible output channels, which reflect the direction of its polarization.
Fig 1. A diagram of an experiment similar to the ones that Bell ran. Taken from here.
Over many trial runs, the photons will begin to show striking correlations in their output results. Their polarization directions will tend to be anti-correlated with each other; that is, if one photon is detected on output channel 1, then the other one will, on average, be detected on output channel 2. Yet presumably, each photon has no way of knowing the measurement setting that was chosen for its counterpart. The results of the Bell experiments would be the same if Alice and Bob had used random number generators to decide their polarization angles, thereby ensuring that there are no patterns between their respective choices. The photons also cannot “communicate” with each other to formulate a plan that would maximize the differences in their output results. They cannot “agree” ahead of time to, for instance, pick channel 1 if the selected angle is 45 degrees but pick channel 2 instead for all other angles. In fact, if the photons were replaced with human agents who could decide, in advance, which output channel they would choose for each possible polarization angle, they could not achieve a success rate as high as the one in the Bell experiments. Even the best possible plan would result in a lower rate of correlation than the one exhibited by the photons. Thus, Bell reasoned that each photon must “know” the polarization angle of its partner. Furthermore, Bell realized that the behavior of the photons should, in principle, be correlated, or “entangled,” with each other even if the measurement boxes were at opposite ends of the universe.
Many thought that Bell’s experiments were unequivocal confirmation of a phenomenon known as “action-at-a-distance.” Information about a photon’s polarization could instantaneously be transmitted to its entangled partner, even if the pair was separated by millions of light years. But action-at-a-distance violates a central tenet of one of our most successful physical theories, general relativity, which claims that nothing can travel faster than the speed of light. Einstein, one of the scientists who first discovered action-at-a-distance phenomena in quantum mechanics, thought that quantum theory was incomplete because it couldn’t account for these disparities with general relativity.
In the 1940s, the physicist Olivier Costa de Beauregard, who agreed with Einstein, began to suspect that retrocausal influences, which had not been incorporated into quantum theory, may explain action-at-a-distance. Bell’s experiments, as well as those of his predecessors, assumed that the polarization of a photon in the present is independent of the photon’s properties in the past, also known as “hidden variables.” This seems to make sense; Bob’s decision to polarize a photon at a particular angle shouldn’t have anything to do with its behavior prior to arriving at the measurement box. But Costa de Beauregard argued that the way an experimenter chooses to measure a photon can actually affect its pre-measurement hidden variables. In other words, a decision made right now can alter the photon’s past! (3) Due to some physics that I won’t get into (since I don’t fully understand it yet), changing the hidden variables of a photon subsequently has an effect on its partner, thereby resulting in their entangled behavior.
Unlike action-at-a-distance, retrocausality does not conflict with general relativity, hence its appeal. However, it does conflict with a very fundamental assumption that we make about time: the past is already fixed, and there’s nothing we can do to change it. As the philosopher Huw Price, a major proponent of retrocausality, says, “According to the retrocausal proposal, quantum theory shows that the division between what is fixed and what is open doesn’t line up neatly with the distinction between past and future. Some of the past turns out to be open, too, in whatever sense the future is open.”
Unfortunately, Price doesn’t really explain how the past could possibly be “open.” Although Price does endorse elsewhere the notion that time doesn’t flow in only one direction, the retrocausal view itself does not necessarily entail that time passes in both a forwards and a backwards direction. It only states that the present can influence the past, not that the present can become the past. Unless retrocausality presupposes or claims that time can flow in more than one direction, it cannot plausibly uphold the stance that the present can actually change the past. If time only passes from the past to the future, then the past must be fixed. Past moments are gone; they already happened. I could offer a number of philosophical arguments to support this claim, but since it’s so intuitive, I don’t think they are necessary. Suffice it to say that the arrow of time describes not merely the direction in which moments flow but also the direction in which causality occurs. A present cause can only ever produce a future effect. Hence, all efforts to effect change in the past are doomed to failure.
Rather than asserting that decisions in the present can literally alter the past, a more coherent formulation of retrocausality would instead suggest that the past, the present, and the future are not quite as distinct as we think they are. Perhaps entanglement occurs not only between particles that coexist with each other but also between particles that are separated in time. Just as the two photons cannot easily be separated from each other, past events and future events might be inextricably linked with each other in a timeless simultaneity. Alice’s measurement doesn’t reach back into the past in order to alter the photon’s hidden variables; rather, both events are happening “now” in a moment that transcends the passage of time. Cause neither precedes nor follows effect but instead coincides with it.
A 2013 experiment conducted by physicists at the Hebrew University of Jerusalem lends support to this idea that “temporally nonlocal” events can be entangled with each other. The design of the experiment, which is fairly convoluted, is depicted in Fig 2. (4) At time I, a pair of entangled photons 1 and 2 are generated. Immediately afterwards, at time II, photon 1 is measured, thereby collapsing its wave function and destroying the entanglement. Photon 2 now moves through space in search of its “collapsed” partner as the experimenters create a new, entangled pair consisting of photons 3 and 4 (time III). Then, at time IV, photon 2 becomes entangled with photon 3, thereby setting photon 4 “free.” Finally, at time V, the experimenters measure the polarization of photon 4.
Fig 2. Diagram from the 2013 experiment showing “entanglement swapping between photons that have never coexisted.”
The team of physicists discovered that photons 1 and 4 were entangled even though they never coexisted with each other. This finding would appear to suggest that the measurement of photon 4 at time V retrocausally alters the polarization state of photon 1 at an earlier point in time. Or, in an alternative interpretation, the measurement of photon 1 at time II “reaches into” a future time and affects the polarization of photon 4 at that moment. Which view is correct?
Well, what if both of them are? As the philosopher Elise Crull insightfully points out in her analysis of the 2013 paper, Einstein’s theory of relativity demonstrated that simultaneity is not absolute, but rather is relative to an observer’s frame of reference. Two observers that are moving relative to each other will disagree about which events are happening in the present moment. Hence, as Crull writes, “The various frames of reference in the Hebrew University experiment (the lab’s frame, photon 1’s frame, photon 4’s frame, and so on) have their own ‘historians’, so to speak. While these historians will disagree about how things went down, not one of them can claim a corner on truth. A different sequence of events unfolds within each one, according to that spatiotemporal point of view. ”
In one frame of reference, measurements in the present cause changes in future polarization states; in another, the direction of causality flows backwards in time. Not only are both frames of reference equally valid, but they also coexist with each other. Even though one observer’s Now will not be the same as another’s, all events, when they are experienced, will happen in the Now. Events that photon 1 experiences in the present may be in photon 4’s past; and the events that the researchers perceive right now could be in one photon’s future. Because there is no single Now, all moments – past, present, and future – are Now.
As we will see, the theory of relativity doesn’t merely yield the conclusion that the dividing line between “past” and “future” is an arbitrary one; it may also refute the flow of time altogether.
The block universe (and our role within it)
We tend to think that the points in space that are in front of us are just as real as the points in space that are behind us. We know, for example, that the Statue of Liberty exists even if it’s so far away that we can’t see it. But points in time that are in the future are considered to be less real that points in time that are in the past. Future events are possibilities, but the past is certain, etched in stone. Hence, for many centuries, physicists thought that time and space were fundamentally separate from each other.
Then, Einstein’s theory of relativity demonstrated that time and space are, in fact, inextricably linked with each other; they are two components of a larger entity known as space-time. Many physicists and philosophers think that the theory of relativity implies that we live in a “block universe.” That is, the three dimensions of space and the one dimension of time (past-future) form a four-dimensional block. “Past” and “future” merely describe points in the block that are farther behind and farther ahead of the moment in the block that we are currently experiencing. Just like the points in space, all of the points in time are equally real, including those that we haven’t yet observed.
Fig 3. A diagram of the block universe theory. Taken from here.
The implications of this model are startling and profound. Every event that will ever happen in the universe already exists in the four-dimensional block. As one film says, “All of history is fixed and laid out like an infinite landscape of simultaneous events that we simply happen to travel through in one direction … The past never vanishes away, and the future has already happened.” The present moment doesn’t dissolve into the past, nor does it flow into the future, since time is completely static in this picture. The future doesn’t become real once we experience it in the present, since the future is, and always has been, a set reality.
To put it another way, all of time can be thought of as a book, and the role of consciousness in the universe is to turn the pages. We can only experience one page – in fact, one word – at a time, but the book was written long before we started reading it. The pages that lie ahead of us are not empty; they have already been filled with words.
It would seem, then, that we play no part in writing the book; we have no influence over the events that will take place in the universe. I think that this deterministic outlook is too fatalistic and, in fact, deeply misguided because it denies intelligent life of any significant role in the universe. Without consciousness, nothing would happen in the universe, since all the moments of time would just exist in a sort of timeless simultaneity. Conscious experience – the act of unfolding the stationary landscape of time into a linear progression of moments – is the precondition for any and all change.
Furthermore, unless change is perceived, individual moments of time could not exist, even though every moment has always existed as part of an unchanging structure. If all the events in time happened concurrently, as the block theory suggests, then there would only be one moment in the entire history of the universe. In fact, there would be no history, since a single instant would have no duration (or perhaps an infinitesimally short duration) in a universe where time doesn’t pass. The one moment in which all of eternity occurs doesn’t last for any substantial or meaningful interval of time. But this is a logical contradiction; how could eternity be infinitely fleeting? How could the block theory claim that the cosmos is eternal, while also yielding the apparent conclusion that it doesn’t persist through time at all? If the universe is in fact endless and everlasting, then the one moment in which all of eternity takes place must be perpetually expressing itself as a duration that has no end. In other words, the whole of eternity is happening not just at one duration-less instant, but at all the instants of time. Everything is occurring at once, over a span of infinite moments. Since the moments can’t all coincide with each other, they must exist not merely at different points on the four-dimensional landscape of the universe, but at different times as well. If any two moments are separated in time, then some kind of transition, or change, must transpire between them, even if they are identical in content. Even the statement “the block universe is exactly the same from one moment to the next” implies that the moments themselves are distinct from one another, and furthermore that one moment can change into another. Moreover, if the history of the universe is infinitely long (as according to the block theory), then the gaps between all the moments of time must collectively sum up to infinity, so there is infinite change in the universe. Hence, paradoxically, the universe is always changing, but at the same time, it is never changing, since the same thing (i.e. everything) is occurring at all moments of time.
For example, if my birth and my death are events that always exist because they are points within a timeless structure, then, by the definition of “always,” my birth and death must be happening at all moments of time, along with all the events in between – that is, everything that occurs during my life. Each moment flows into the next one, but every moment is exactly the same.
In the words of the Zen philosopher Eihei Dogen, who I cited in Part I of this essay series, time persistently makes a “passageless passage.” We move forward into a future that has always been in the timeless present. We shape the universe over time, but the universe is already shaped for us.
Through our consciousness, the universe realizes itself at every moment. It is constantly becoming what it already is.
(1) It’s worth noting that I’m drawing these conclusions on my own; Bars never states them explicitly. Given my total lack of expertise in physics, I could be completely wrong.
(2) I once again stress that this may be an erroneous interpretation of two-time physics.
(3) It is very important to note that, even in the retrocausal picture of the universe, the present can causally influence the past but cannot signal into it. The distinction between signaling and causal influence is a tricky and subtle one, so I’ll leave it up to two experts – the philosopher Huw Price and the physicist Ken Wharton – to explain it on my behalf.
(4) My explanation of the 2013 study largely paraphrases a summary given by the philosopher Elise Crull.