Thought Experiments


There Is No Now

Excerpted with permission from The Island of Knowledge: The Limits of Science and the Search for Meaning by Marcelo Gleiser. Available from Basic Books, a member of The Perseus Books Group. Copyright © 2014.

What goes on when you see something, say, this book you are reading? Leaving aside the whole business of how the brain processes visual information, let’s just focus on the information travel time. To make life simple, let’s also just consider the classical propagation of light, ignoring for now how atoms absorb and reemit light. Light is bouncing around the room because either the window is open or the lamp is on, or both. This bouncing light hits the surface of the book, and some of it is absorbed, while some is reflected outwards in different directions. The page and the ink used for printing absorb and emit light in different ways, and these differences are encoded in the reflected light. A fraction of this reflected light then travels from the book to your eyes, and thanks to the brain’s wondrous ability to decode sensorial information, you see the words on the book’s page.

Credit: Flickr/Alex Harries, adapted under a Creative Commons license.

It all looks instantaneous to you. You say, “I’m reading this word now.” In reality, you aren’t. Since light travels at a finite speed, it takes time for it to bounce from the book to your eye. When you see a word, you are seeing it as it looked some time in the past. To be precise, if you are holding the book at one foot from your eye, the light travel time from the book to your eye is about one nanosecond, or one billionth of a second. The same with every object you see or person you talk to. Take a look around. You may think that you are seeing all these objects at once, or “now,” even if they are at different distances from you. But you really aren’t, as light bouncing from each one of them will take a different time to catch your eye. The brain integrates the different sources of visual information, and since the differences in arrival time are much smaller than what your eyes can discern and your brain process, you don’t see a difference. The “present”—the sum total of the sensorial input we say is happening “now”—is nothing but a convincing illusion.

Even if nerve impulses propagate fast along nerve fibers, their traveling times are still much slower than the speed of light. Although there are variations for different types of nerves and for different people, the speed is around 60 feet per second. That is, nerve impulses travel about 1 foot in sixteen milliseconds. (A millisecond is one thousandth of a second.) For comparison, light travels 2,980 miles in the same amount of time, a little more than the driving distance from New York to San Diego.

Here is an imaginary experiment that illustrates the implication of these time differences. Imagine two lights programmed to flash simultaneously every second. One of the lights is fixed at 10 yards from an observer, and the other can be moved away on a straight rail. Imagine separating them by increasing distances as they flash together every second. An observer will start perceiving a difference in the flashing times when the distance between the two lights is larger than about 2,980 miles. Since we can’t see this far, our perception of the simultaneous now seems very credible for huge separations. An alternative, and more realistic, experiment could be set up to test this theory: have two lights flashing at slightly different times, and check when observers notice a difference. If my conjecture is correct, observers will start to notice differences when the timing interval is larger than about twenty milliseconds or so. This timescale sets the limit of visual simultaneity in humans.

The arguments above lead to a startling conclusion: the present exists because our brain blurs reality. To put it another way, a hypothetical brain endowed with ultrafast visual perception would catch the difference between the two flashing lights much earlier. For this brain, “now” would be a much narrower experience, distinctive from the human “now.” So in addition to Einstein’s relativity of simultaneity involving two or more moving observers, there is also a relativity of simultaneity at the cognitive level resulting from the subjective perception of simultaneity or “now” for the individual or, more generally, for every kind of brain or apparatus capable of detecting light.

Each one of us is an island of perception. Just as when we look out into the ocean and call the line where water and sky meet the horizon—a limit to how far we see—our perceptual horizons comprise all the phenomena that our brains compute as happening simultaneously even if they are not: the perceptual horizon delineates the boundary of our “sphere of now.” Since light is the fastest speed in Nature, that’s the one I’m using to define our sphere of now. (Had we used the speed of sound, of only 1,126 feet per second in dry air and at 68 degrees Fahrenheit, the sphere of now would have a much smaller radius. Two lightning strikes miles apart look simultaneous but wouldn’t sound simultaneous.)

To summarize: given that the speed of light is fast but finite, information from any object takes time to hit us, even if the time is tiny. We never see something as it is “now.” However, the brain takes time to process information and can’t distinguish (or time-order) two events that happen sufficiently close to one another. The fact that we see many things happening now is an illusion, a blurring of time perception. Since no brain is the same, every person will have their own limits of time perception and their own sphere of now. In fact, every brain, be it biological or mechanical (light-sensitive detecting device), has a different processing time and will have its own sphere of now; each one will have a distinctive perception of reality. From current neurocognitive experiments, it seems reasonable to suppose that on average a human’s time perception is on the order of tens of milliseconds. The distance light travels in this time interval is the approximate radius of an individual’s sphere of now—a few thousand miles.

“Now” is not only a cognitive illusion but also a mathematical trick, related to how we define space and time quantitatively. One way of seeing this is to recognize that the notion of “present,” as sandwiched between past and future, is simply a useful hoax. After all, if the present is a moment in time without duration, it can’t exist. What does exist is the recent memory of the immediate past and the expectation of the near future. We link past and future through the conceptual notion of a present, of “now.” But all that we have is the accumulated memory of the past—stored in biological or various recording devices—and the expectation of the future.

The notion of time is related to change, and the passage of time is simply a tool to track change. When we see something moving in space, we can follow how its position changes in time. Say it’s a ball; as the ball moves, it will describe a curve in space, an imagined sequence of points from initial position A to final position B. We can tell where the ball is between A and B by ordering its location sequentially in time: at zero it is leaving the soccer player’s foot—point A; at one second it is hitting the upper-left-hand corner of the goal—point B. The curve in between A and B links the position of the ball at the intermediate times between zero and one second. A ball, however, never occupies a single point in space, and time can never be measured with infinite precision. (The most accurate locks use electronic transitions in atoms to achieve a precision of about one billionth of a second per day.) Mathematically, though, we brush all this aside and compute how the position of the ball changes in time instantaneously: for every moment of time we claim to know its position. Clearly, this is only an approximation, albeit a very good one.

We represent the flow of time continuously so that each instant of time has a (real) number attached to it. In our example of the soccer ball, time will cover the number line from zero to one. How many instants of time are there between zero and one second? Mathematically, there is an infinite number of them, since there are infinite numbers between zero and one. (You can keep subdividing intervals into smaller and smaller bits: a tenth of a second, a hundredth of a second, a thousandth of a second, and so on.) But even the most accurate clocks have limited precision. We may represent time continuously, but we measure it in discrete chunks. As a consequence, the notion of “now,” a time interval of zero duration, is only a mathematical convenience having nothing to do with the reality of how we measure time, let alone perceive it. I will have more to say about this and what it means about our notion of reality when we get to quantum physics, where nothing is ever continuous.

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Marcelo Gleiser

    Marcelo Gleiser is the Appleton Professor of Natural Philosophy and Professor Physics and Astronomy at Dartmouth College. Gleiser received a Presidential Faculty Fellows Award, given by the White House and the National Science Foundation, for his research in cosmology and dedication to teaching. A Fellow and General Councilor of the American Physical Society, his research focuses mainly on the physics of the early universe and the emergence of complex structures in Nature, including life. In addition to The Island of Knowledge, he is the author of three previous books, The Dancing Universe, The Prophet and the Astronomer, and A Tear at the Edge of Creation, Gleiser lives in Hanover, New Hampshire. Twitter: @MGleiser

    • Matt Kreinheder

      Great article Dr. Gleiser. I especially like the concept of a “sphere of Now”, a very cool way to language an abstract concept. I agree that “now” is much more a felt experience than a definable and finite number. But then, why try to use pure objective measures to define a subjective experience? If now is a purely experiential event then no calculation will be able to locate it. It seems that when we can’t specifically pin point something in time and space its value (in this predominately left brained, logical society) is diminished. Thanks again for writing this!

      • Marcelo Gleiser

        Thanks for your comment; a calculation can always “locate” something, given that it is an abstraction. So, it’s a location but not in real, physical space or time. What I intended in this part of the book was to show how such an intuitive notion such as “now”, that we use all the time, is actually a fabrication!

        • Hominid

          That depends on your frame of reference. Stand on the RR tracks before a speeding locomotive & you’ll soon discover that there is a now.

          • Marcelo Gleiser

            To how many decimal points you want to specify the exact moment of impact?

            • Hominid

              You’re delusional – there will be an impact.

            • Marcelo Gleiser

              I hope I’m not delusional…Of course there is an impact! that’s not the point. The point is that it is impossible to specify with absolute precision when the impact occurs. “Now” is an approximation, that’s all. It’s not that we can’t conceive of it cognitively. But we can only measure time with a finite amount of precision. That’s just how science is done. Not need for insults, just an effort to comprehend the meaning of concepts used in the physical sciences.

            • Hominid

              That’s not physical science – it’s philosophy. THAT’s the point. Of course we can’t define time – or a whole lot of other things. That’s the inadequacy of theoretical physics – which is most likely a consequence of the limits of cognitive acumen. Rigorous science attempts to approximate the universe that exists outside the mind. In that universe, there is definitely a ‘now’ even though we might perceive it a bit late.

            • diana

              yeah, but, when?

      • Hominid

        Predominantly, not predominately.

        Wherever did you get the notion that society is left brained and logical? It’s exactly the opposite.

        • Doppleganger11

          Technically, both words-though distinct-can be used in this context.

          Society doesn’t have a mind of it’s own, people do.

    • Peter Martin

      “Up is down !” – George Costanza

    • Peter Kershaw

      Well said. My thoughts were along the same lines as Mr. Kreinheder’s comment. Nothing spoils the experience of the flow of time (living) quite like math. There’s a fabrication for ya.

    • Hancock

      A neurologist friend told me of an experiment where the subjects were told to hold a mirror in their lap and look at a monitor displaying numbers in a sequential order, like 1, 2, 3, etc., they were told to hold the mirror so that they could see in their peripheral vision the reflected numbers, all the subjects could see the numbers on the screen in sequence, but the numbers in their peripheral vision skipped in the sequence, like 1, 3, 5, 6, 9, 10, 12. Some of the subjects reported that there was a noticeable delay in the number sequence reflected in the mirror. Which is a great example of how the brain prioritises information.


      Brain mapping and this area of study is quite mature. Most humans are easily controlled.

    • Jesse G Herrera

      Sometimes when I am driving late at night on the highway, I will notice that I am now at Point B. I remember Point A, but I don’t remember the space or history between Point A & B. Where did that time go? Maybe my brain went out to lunch for few minutes? I’ve wondered about everything I see, that I am seeing right now. Is it real? For it to be real, there must be a “now”, but by time I’ve thought about it, I’m at another “now” like when I was driving.

    • Rick Chesler

      We know there’s no such thing as “now” because by the time you say the word “now,” the point int time you were referencing has already past. Everything is either in the future, or the past. “Now” is just a colloquial term that means “in the present,” it’s not a technical term.

    • Rev. Jasper P. Schwingster

      May Jesus forgive you of this blaspheme.

      • eric.wallter

        Err… and what exactly are you referring to, Reverend? I mean, what ‘blasphemy’ are you talking about?

      • isnamthere

        And may santa claus leave no coal in your stockings, or the easter bunny leave no pellets in place of your jelly beans.

      • shunga munga

        If there were a Jesus, and he were the Jesus you presumably are referring to, he is dead, and there is no evidence other than a moved stone to support the risen from the dead theory. But in the spirit of some accounts of this Jesus’ teachings, I forgive you for missing the point of the mythologies.

    • Hobartcat

      Wow. So, our perception is illusory. I’ll alert the media.

    • Thoughtful_Rationalist

      After reading this stimulating article, the Buddhists, who prize living in the NOW, will be so disappointed.

    • David Wright

      Like quantum mechanics, these short time lags are not important to us biologically. Only some of our techo devices have to account for these lags.

      To say it is false that “I am reading this” is an exaggeration. During the moment it takes to process information, I am reading. No actions are instantaneous because any action requires the passage of time. Time is the fourth dimension.

      • Bruce

        Good perspective and understanding David. If I may add this little bit. Using your statement “I am reading this” there are several constructs to the statement. The sense of a someone (I am) the action (reading) are both a feeling of “beingness” and a “doinginess” but the common denominator is the detached “Isness” that is a dispassionate witness and gives reflection to any movement, activity that sense of beingness.

    • Heather

      How do you apply this theory to blind people? Time and the perception are not perceived only by vision. Also…
      ““Now” is not only a cognitive illusion but also a mathematical trick, related to how we define space and time quantitatively. One way of seeing this is to recognize that the notion of “present,” as sandwiched between past and future, is simply a useful hoax. After all, if the present is a moment in time without duration, it can’t exist. What does exist is the recent memory of the immediate past and the expectation of the near future. We link past and future through the conceptual notion of a present, of “now.” But all that we have is the accumulated memory of the past—stored in biological or various recording devices—and the expectation of the future.”

      Time was created by our lack of ability to remain present with all of ourselves at once…Now. When we experience pain or discomfort we attempt to separate ourselves from it by leaving it in the past as baggage that is to be left behind. While avoiding an experience we also project into a fantasy of something better to take us away from being present now, creating a perception of a future, hence sayings like, “Tomorrow’s a new day” or “Look to a brighter future”. When we react with denial or repression to pain we project our perceptions of ourselves into the past and future which seemingly gets us out of having to be responsible now, for everything we have avoided. P.T.S.D.(Post Traumatic Stress Disorder).
      The way to experience Now is to be fully present with everything we are in denial of which is all the things about ourselves that were ever and still are in pain that we wanted to leave in some place called, ‘the past’ where we could appear helpless to go back to while reaching into a future of expectations to get out of the Now.
      To experience Now, is in y/our ability to remain present with all of yourself all of the ‘time’. Now, is real when we allow it.

    • Blueprinter

      I don’t like feeling pain, whether it’s real or not. I don’t care if it’s real or not, I want it to go away NOW! Or as ‘fast’ as possible. (Whatever fast means, because if there is no NOW, and there is no past, and there is no future, then what is there?) So, as far as I’m concerned, pain and pleasure, and how long it lasts is what I want to influence.

    • Amrit Sorli

      what a nonsense that there is no now

    • Amrit Sorli
    • David Tomasello

      Wow! Interesting stuff.I feel more intelligent now

    • Larry Swain

      The most accurate “clocks,” not “locks.”

    • Gustavo Gomes

      Great ideas Dr. Gleiser. I am specially interested in bringing the same rationale to space. How many numbers are between 0 and 1 centimeter? Infinite, right. But I can not divide one centimeter of cloth forever, I will have to stop at some particle. So materially finite and mathematically infinite. Wouldn’t be mathematics playing us a trick?

    • abc123

      My apologies to Dr. Gleiser but the concepts this article presents are really not new or groundbreaking. It is not a great leap from learning the speed of light to the realization that “now” is stitched together by our minds. If it wasn’t, it certainly could have been deduced in the early twentieth century or earlier by someone observing a loud event in the distance and hearing it a second or two later.

      What also continues to surprise me is how Eastern philosophy’s long standing realization of these concepts and exploration of their philosophical implications is rarely mentioned. Individuals in the Vedic culture of northern India were turning their awareness inward to explore the various complexities of the mind – including analyses of how sensory input is stitched together to form experiences – at least 5000 years ago if not earlier. The mind’s construction of experience, the sense of now and, to a large extent, the sense of individuality is sort of the central tenet eastern philosophy and psychology.

      Admittedly the metaphysical tone and terminology used to describe this inner research might make it difficult for the modern western mind to accept the fact that this research was in fact scientific in approach and rigor and not conducted for religious purpusoses, at least not exclusively, but done to expand our knowledge of our bodies and brains.

      The experience of many experienced meditators is that of having transcended the interruptions of sensory perception and inner thoughts & emotions to reach a state of mind where all you expetience is a state of pure awareness. Awareness of what you might ask? Its a mystery. Does awareness need an object? The folks that have reached this state will tell you not to take their word for it but test it yourself.

      I apologize if these ideas are addressed elsewhere in the author’s work.

      • Hominid


        • shunga munga

          What one is ignorant of usually sounds like it. The paradox of one reaching a state of pure awareness is that the analog I ceases to exist. Perceptions of time change. An hour passes instantaneously while seconds resonate like a gong, but as abc123 has written and any practitioner will tell you it is difficult if not impossible to intellectually describe experience, not unlike explaining the taste of an orange to one who never has.

    • Daren

      Of course there is a now. Our perception of it is stitched together as best as we can. But the reality of the now exists outside of our ability to perceive it.

    • The Master

      I disagree with the premise that ‘now’ is a time interval with zero duration. ‘Now’ is of infinite duration; it is always ‘now’ in our perception. Of course what we perceive is the past, but the past is the frame within which we experience the present.

    • Richard McCargar

      Man, this is old. On top of that, it ignores the fact that our minds work in such a fashion as to be useful to us in our everyday lives.

      Is this guy a late-teen pot-smoker?

    • donqpublic

      Since I can never cognitively experience “now” or the “future” ( the Kantian thing in itself?) because of a cognitive processing lag, then I gather now and the future are not objects of empirical science but mere illusion (a Humean psychological cultural construct or fabrication?). Indeed, when peeling back the cognitive processing layers of consciousness I can never see the “I” that’s doing the processing in the here and now: cowabunga dude, I’m an illusion of constant conjunctions of things in time, just like you and the universe. I’m just a bad habit. But I can still have fun exploiting and oppressing illusions like you for fun and profit; funny how unreality (values) can seem so real and satisfying when at some other illusion’s expense. Damn, being on the progressive right side of history and celebrating the end of history and the last man is an illusion and a fraud after all; the girls are going to be pissed.

    • EscondidoSurfer

      All of this makes the sublime truth from God when he revealed his name as “I am” (Yahweh) all the more profound. The biblical claim of a God who defines himself in this way is striking, let alone the claim that he is able to fully inhabit all of creation within his “now,” freely taking whatever time is needed to accomplish his purposes. Such truths should be a matter of deep reflection by all those who regard his revelation as trustworthy in light of the inability of science to grasp what “Now” really means.

    • James Hedman

      Your reliance upon Zeno’s Paradox as an analogy is lame.

    • ttrr

      Dear Marcello, the reality is the opposite – there is ONLY now.

    • ttrr

      … and time as we perceive it is an illusion, needless to say.

    • Iarwain Benadar

      to summarize the article: we are all bound by perception in a relativistic universe. “Now” can only be apprehended though a larger domain that surrounds, yet is unbound from, perception. I define this larger domain as “knowledge” — “now” with a “k”.

    • TomKinney

      This comports, somewhat, with something I’ve been thinking about;
      the fact that humans are constantly “learning their (personal) lessons” about
      life only in hindsight. We continue to repeat our mistakes, which like karma,
      seem to be sown into our system from our beginnings. As if we were
      entirely predisposed to having a given condition; that of having to learn the same lessons over and over again. As if life were some sort of test. But who’s the tester and what’s the point of the test?

      And those most vital questions we don’t seem to be able to grasp—as if they’re always just beyond our comprehension—in our current physical form, the point being that we must relive our built-in mistakes over and over again. And, saddest of all, we die not having been successful–beyond a limited point–without having corrected our mistakes.

      Here the author is talking about the slightest amount of time that elapses
      between reading something and when what we have read reaches our
      brain. But we’re always just a shade behind ourselves in everything we do, as if
      time is a sort of cosmic trickster never letting us catch up. Always late to
      the party.

      Anthony Peake, new age quasi-scientist, has supposed that when we
      are in the act of dying, time slows down exponentially from a second to a half
      second to a quarter second, etc., ad infinitum, so that the actual moment of
      death never actually occurs. What then happens? Perhaps we leave the sphere of
      time altogether to enter yet another dimension, or world, or whatever, a
      timeless place in which we dwell eternally beyond all these physically
      constraining paradigms.

      Or not.

      Who knows?

    • mikie

      So, if I’m reading this on a LCD monitor, does the info get to me sooner, since the light in the room doesn’t have to first bounce off the page before getting to my eyes?

    • Gordon Shumway

      I’m far more concerned with why we park in driveways and drive on parkways.

    • Gabriel

      An instance has no time duration, like a point is dimensionless in space. Both define a “singularity”; an imaginary construct of our intellect. What precisely is zero and infinite? On the other hand, a moment is defined as roughly 90 seconds. It seems that for our practical sensorial experience “now”, in the present tense, means something more appropriate like a moment. Logic, reason, and mathematics sometimes let us experience its own limits to understand the reality of the cosmos we live in. Does Achilles ever pass the turtle and wins the race?

    • Morgan Buenger

      Very interesting thought provoking article Marcelo, thank you.
      There is no mathematical now, just like there is no mathematical time that is independent of location. You mentioned the sphere of now, well time is also a sphere defined by an orbit, not a rectangle. Mathematical time that is an arrow shooting into eternity in a straight line without relation to locality does not exist in reality. Hence the non-existence of the linear now. The universe is not square, so there is no square mathematical now either. Time is always related to a local orbit. The now we commonly refer to is a round now that is related to our orbit around our sun Sol. The arch degrees of this path we share. If we perceive the visual stimuli individually at different times due to processing speed limitations/differences of our brains that does not mean that we don’t have a common now.
      Mathematics is a tool, not to be confused with reality. For example: the soccer ball leaving the foot of the player mathematically never reaches the net because we can always divide the distance of impact by 2. However far you say the ball is from the net there are infinite divisions of space and time. While you are calculating that the Germans shot 7 goals into the net against Brasil during the World Cup semifinals. And that is reality now. Sure the tv and radio broadcast signals and transmission lines across the world and our individual bio-electro-chemical perceptions created lag times but the times the balls touched the net were very/vary specific Nows in terms of a location on the sphere of time that is our orbit around Sol in arch degrees.
      I hope this makes sense.

    • skipper

      What about conscious awareness of thoughts? The thought appears in our conscious mind awareness (in spoken words or picture). We consciously experience the thought (as spoken word or picture).
      Therefore all consciousness awareness even of thoughts lags
      reality by at least the speed of light.
      True enough?

    • carlos

      I think I understand what you are trying to describe.
      But it doesn’t seem right to try to force the ‘now’ to two separate instances or references, when the light beam originates from the book, and when the eye, or brain, perceive it.

      The way I understand it, is that it doesn’t really matter when the light bounced off the book, the ‘now’ for us would be when the brain processes the information (even if it is a delay image, and I’m also not accounting for conscience or anything like that).
      You could also see it from the book’s point of view if it had conscience, and then that ‘now’ would happen when the light beam bounced off, but i don’t think you should mix the two points of view.
      like one of the comments, now from the human perspective is around 90 seconds, I think it has to do with the amount of time it takes to store information in memory.
      From a maths or physics point of view, it might be something different because time is something different.

      In regards to the hypothetical brain experiment, I don’t believe you need a brain with ‘ultra fast perception’, I believe you would need a brain that is not constrain by distance; something like a a brain that can be everywhere at once,

      Thank you for writing this article, and giving people the chance to participate and explore new ideas and ways of seeing reality.

      *Sorry for my grammar, English is not my first language.

    • Mike

      so there is only the past and the future…

    • seescaper

      Suppose that we agree that there is only a past and a
      future. What we call the “now” is a construct that our brain uses to orient us as we move from past to future. So, past becomes future instantaneously—there is no time interval that is large enough to be measured that separates the transition.

      I seem to smell an aspect of the uncertainty principle here. As you try to nail down the exact time interval transitioning from past to future, the energy of the system would become increasingly uncertain. So one cannot define a time interval constituting the “now” with precision. When something is just
      in the process of “occurring,” there is an inherent uncertainty of whether it is part of the past or future. Here, in this fuzzy zone, the arrow of time can go either direction. This uncertainty phase is so brief that our brain and sensorium cannot appreciate it. Rather, our brains construct for us a “sense” of the present. Events occurring sufficiently “ago” in time we sense as occurring in the past, and for events that have not yet “occurred,” our conscious brains can attempt to predict by running a simulation of what might happen in the future.
      As we move in a transition to the future, there is again a fuzzy transition zone that is too small to perceive, so our brains smooth it out.

    • sand

      no distinction between past present and future. a. einstein

    • jess

      Werner!!!! Where are you hiding. EST 101, 1972

    • Peter

      I maintain that now is possible, indeed exists, even if the perception of it varies. Which is to say, we can indeed define now. And we do indeed define it, we do measure it and we do calculate very accurately every day. Which is why we have GPS. We have the technology to quantify, measure and calculate this. To say this is a mathematical trick which depends on how we define space and time is to take a strange position on the issue. Is this the same sort of mathematical trick we know as the Pythagorean Theorem, which depends on how we define a geometric plane, etc? Is all of mathematics a trick, dependent on how we define mathematical axioms? I suppose you could make that case. But to go down that road just muddles and mystifies the subject – perhaps intentionally, in an attempt to appear profound? At any rate I would prefer clarity over mystification. GPS knows where I am because of Pythagoras and Einstein – because we can calculate triangles and measure distance. Time is like distance, mathematically. It is one thing to say there exists optical illusions of simultaneity due to lag times in neural processes and photon exchanges, it is quite another to say simultaneity does not exist. All measurements are approximate. Any measurement we make that does not include the level of precision (or error) inherent in the measurement is meaningless. Defining such a level of precision is not a mathematical trick – it is simply necessary. Again, it is one thing to talk of illusions and to say what appears as the now is not the now – but it is another thing to say that we cannot calculate the now. We can. We do. Stop trying to mystify. Clarify, clarify.