Ten Things Everyone Should Know About Time

“Time” is the most used noun in the English language, yet it remains a mystery. We’ve just completed an amazingly intense and rewarding multidisciplinary conference on the nature of time, and my brain is swimming with ideas and new questions. Rather than trying a summary (the talks will be online soon), here’s my stab at a top ten list partly inspired by our discussions: the things everyone should know about time. [Update: all of these are things I think are true, after quite a bit of deliberation. Not everyone agrees, although of course they should.]

1. Time exists. Might as well get this common question out of the way. Of course time exists — otherwise how would we set our alarm clocks? Time organizes the universe into an ordered series of moments, and thank goodness; what a mess it would be if reality were complete different from moment to moment. The real question is whether or not time is fundamental, or perhaps emergent. We used to think that “temperature” was a basic category of nature, but now we know it emerges from the motion of atoms. When it comes to whether time is fundamental, the answer is: nobody knows. My bet is “yes,” but we’ll need to understand quantum gravity much better before we can say for sure.

2. The past and future are equally real. This isn’t completely accepted, but it should be. Intuitively we think that the “now” is real, while the past is fixed and in the books, and the future hasn’t yet occurred. But physics teaches us something remarkable: every event in the past and future is implicit in the current moment. This is hard to see in our everyday lives, since we’re nowhere close to knowing everything about the universe at any moment, nor will we ever be — but the equations don’t lie. As Einstein put it, “It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence.”

3. Everyone experiences time differently. This is true at the level of both physics and biology. Within physics, we used to have Sir Isaac Newton’s view of time, which was universal and shared by everyone. But then Einstein came along and explained that how much time elapses for a person depends on how they travel through space (especially near the speed of light) as well as the gravitational field (especially if its near a black hole). From a biological or psychological perspective, the time measured by atomic clocks isn’t as important as the time measured by our internal rhythms and the accumulation of memories. That happens differently depending on who we are and what we are experiencing; there’s a real sense in which time moves more quickly when we’re older.

4. You live in the past. About 80 milliseconds in the past, to be precise. Use one hand to touch your nose, and the other to touch one of your feet, at exactly the same time. You will experience them as simultaneous acts. But that’s mysterious — clearly it takes more time for the signal to travel up your nerves from your feet to your brain than from your nose. The reconciliation is simple: our conscious experience takes time to assemble, and your brain waits for all the relevant input before it experiences the “now.” Experiments have shown that the lag between things happening and us experiencing them is about 80 milliseconds. (Via conference participant David Eagleman.)

5. Your memory isn’t as good as you think. When you remember an event in the past, your brain uses a very similar technique to imagining the future. The process is less like “replaying a video” than “putting on a play from a script.” If the script is wrong for whatever reason, you can have a false memory that is just as vivid as a true one. Eyewitness testimony, it turns out, is one of the least reliable forms of evidence allowed into courtrooms. (Via conference participants Kathleen McDermott and Henry Roediger.)

6. Consciousness depends on manipulating time. Many cognitive abilities are important for consciousness, and we don’t yet have a complete picture. But it’s clear that the ability to manipulate time and possibility is a crucial feature. In contrast to aquatic life, land-based animals, whose vision-based sensory field extends for hundreds of meters, have time to contemplate a variety of actions and pick the best one. The origin of grammar allowed us to talk about such hypothetical futures with each other. Consciousness wouldn’t be possible without the ability to imagine other times. (Via conference participant Malcolm MacIver.)

7. Disorder increases as time passes. At the heart of every difference between the past and future — memory, aging, causality, free will — is the fact that the universe is evolving from order to disorder. Entropy is increasing, as we physicists say. There are more ways to be disorderly (high entropy) than orderly (low entropy), so the increase of entropy seems natural. But to explain the lower entropy of past times we need to go all the way back to the Big Bang. We still haven’t answered the hard questions: why was entropy low near the Big Bang, and how does increasing entropy account for memory and causality and all the rest? (We heard great talks by David Albert and David Wallace, among others.)

8. Complexity comes and goes. Other than creationists, most people have no trouble appreciating the difference between “orderly” (low entropy) and “complex.” Entropy increases, but complexity is ephemeral; it increases and decreases in complex ways, unsurprisingly enough. Part of the “job” of complex structures is to increase entropy, e.g. in the origin of life. But we’re far from having a complete understanding of this crucial phenomenon. (Talks by Mike Russell, Richard Lenski, Raissa D’Souza.)

9. Aging can be reversed. We all grow old, part of the general trend toward growing disorder. But it’s only the universe as a whole that must increase in entropy, not every individual piece of it. (Otherwise it would be impossible to build a refrigerator.) Reversing the arrow of time for living organisms is a technological challenge, not a physical impossibility. And we’re making progress on a few fronts: stem cells, yeast, and even (with caveats) mice and human muscle tissue. As one biologist told me: “You and I won’t live forever. But as for our grandkids, I’m not placing any bets.”

10. A lifespan is a billion heartbeats. Complex organisms die. Sad though it is in individual cases, it’s a necessary part of the bigger picture; life pushes out the old to make way for the new. Remarkably, there exist simple scaling laws relating animal metabolism to body mass. Larger animals live longer; but they also metabolize slower, as manifested in slower heart rates. These effects cancel out, so that animals from shrews to blue whales have lifespans with just about equal number of heartbeats — about one and a half billion, if you simply must be precise. In that very real sense, all animal species experience “the same amount of time.” At least, until we master #9 and become immortal. (Amazing talk by Geoffrey West.)

250 Comments

250 thoughts on “Ten Things Everyone Should Know About Time”

  1. TIME [Posted 9-11-11]

    We know time not by what it is,
    but by what happens within it.
    “Time will tell,” and it does;
    but it speaks not of itself.
    Only of events, and of memories of events.

    Darwin drew diagrams of a solitary leaf
    as it stirred upward and downward through the day.
    “And doubtless, when swallows come in the spring,
    they act like clocks,” said Descartes.

    Steel columns, heated to redness, in time buckle
    and suddenly lower millions of pounds
    to impact like a pile driver on the floor below,
    which interrupts the fall, but in the interruption,
    amplifies the weight to trillions, and fails.

    Which interrupts the interruption,
    creating a vertical pendulum, a keeper of time,
    accelerating as it collapses.

    Time then continues after, as it had before.
    But never the same.
    For we know time not by what it is,
    but by what happens within it.

    Copyright 2001 Albert G Fonda
    (Written 10/26/01, 8:05 to 8:15 AM, as-is.) (I cried – as much as an engineer can.)

    Darwin and Descartes from Jonathan Weiner, in “Time, Love, Memory” (Knopf, 1999)

    Pile-driver insight from my petroleum engineer son Mark

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  5. Interesting idea, a lack of motion and what effect that would have on time. However, it couldn’t happen. Without motion, the sun wouldn’t be able to produce heat or shine, I think. There should cease to be any gravitational pulls anywhere, and…what? A lack of motion would have to inexhorably lead to motion so, I don’t think it’s possible.

    On the past future bit. I like to think of our present selves as being a collection of our past experiences and our future hopes rather than just existing “in the moment”. So, I’d be really interested to read more on our linear understanding of time.

  6. “3. Everyone experiences time differently.”

    It seems to me that the subjective experience of accelerating time with increasing age is a function of the volume of organic remembrance. That is, at an early age, the volume of remembered experience is small relative to what it is at an advanced age. Of course, situationally induced recollection from within this growing pool of remembrance is the behavioral trigger for making this assessment.

    Tom

  7. @ Big Flava 224, you say you could live without your telephone and tv. good for you. also, try to live without medicine, vaccines, modern medical technology, vitamin supplements… oh wait… you can’t and neither can your family. as to the rest of your ignorant comment where you refer to energy and mass as “blather”, i won’t waste my time responding.

  8. Is it really mysterious that touching one’s nose and foot “simultaneously” should be experienced as happening at the same time? For electrical impulses (which move at the speed of light) the increased distance is hardly significant, and in any case it seems obvious that we’re not equipped to perceive the resulting microscopic difference in timing (nor are we capable of perfectly synchronizing the act of touching both spots anyway).

    I also don’t believe the 80ms latency applies to all types of experience. Certainly 80ms have not elapsed between the time when I touch my nose and when the sensation is experienced. As a music producer, I know that I can perceive a latency as short as ~20ms when playing keys on a MIDI keyboard (the question of latency comes up when setting the buffer size of software to strike a balance between accurate timing and the increased strain on system resources when lowering it). Professional drummers with a very highly developed sense of timing can perceive even shorter latency values.

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  10. “there’s a real sense in which time moves more quickly when we’re older.”

    The link points to an article which mentions one of the reasons: when we’re young, we experience more first-time events, more interesting events etc and have more detailed memories, which makes that time seem longer looking back on it. (What the article doesn’t mention is that in the present the trend is reversed: interesting things fly by, and boring things take forever. Since we experience the present just once and always have our memories, it’s probably better this way.) However, there is another effect: for a baby, a year is a lifetime; for a very old person, one year more or less hardly matters. In other words, the older we are, each year corresponds to a smaller fraction of our lives. The first effect explains why it seems that time used to pass more slowly while the second explains why we old folks feel it passing quickly now.

  11. “10. A lifespan is a billion heartbeats”

    Do the math. In general, true, but for humans, it is significantly more. For parrots as well. Go figure. A billion human heartbeats is only 30 years.

    One might argue that the natural human lifespan is 30 years, and the extra 30–60 are the gift of science. True, but no cigar. Animals in captivity, with fewer dangers, better medical care etc do live longer, but not 3 times longer as their counterparts in the wild.

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  16. Indra Prasad Sharma

    At present time is measured with reference to the Sun being at our Zenith and only the galaxy exist. But if we take a more broader picture of the universe and various other galaxies then we need to shift to make a different reference point to measure various events at a time to follow the history of various activities of various creatures in various galaxies.

  17. In contrast to aquatic life, land-based animals, whose vision-based sensory field extends for hundreds of meters, have time to contemplate a variety of actions and pick the best one.
    As a biologist, I do think this is a sadly human-centered view that has not much to do with the actual sensory and cognitive abilities of animals. Because we are vision-based land animals does not mean that being one is compulsory to be intelligent or conscious.

    Firstly, not all land animals have a “vision-based sensory field”, not all of them live in the open ground where such large-scale vision is possible and not all of them are diurnal. Many land animals base their sensory field on smell, sound, echolocation etc. which bring information for consideration just as well as vision.

    And then again, many marine animals are highly visual and/or subsitute their eyesight with long-range echolocation, electroreception or such like.

    And it’s not like an animal has to constantly move forward like a clockwork machine and have to sense things from far away to have time to think before they are right in front of it and decisions have to be made. Animals can stop and take their time to investigate and think, and they often do. With predators, it’s not a good idea, but with pretty much everything else, you don’t need to see (or smell or hear) things from far away to have time in your hands.

  18. and yeppers, it would seem “change is fundamental, and time is a perceptual overlay”. (# 232)

    There is Form and there is Flow. Form creates and limits Flow, Flow creates and limits Form. Time may in fact be our snapshot view of this phenomenon.

    Consider the following:

    The stillness
    in stillness
    is not
    the real stillness.

    Only when
    there is stillness
    in movement
    can the spiritual rhythm appear
    which pervades
    heaven and earth.

    Ts’ai-Ken T’an

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  20. Monica Garliceanu

    Ever since I read about the 80 ms lag between things happening and us experiencing them, I’ve had a question in my mind: where does this leave the “quantum mind-body problem”? How can our consciousness cause the collapse of the wave function when by the time we are aware of an event, that event is already in the past?
    It seems to me that, by the time we open the box, the fate of the cat have been already sealed.
    Does anyone have a theory about this?

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  23. Hi Monica,

    Our perception is not limited to our thinking/being in the conscious mind. Intuition is an inherent awareness and we can “know” something without consciously thinking it.

    Actually, how else could one explain that over 5,000 years ago the great Masters understood polarity and many other aspects of Energy without the use of the technology scientists currently use. They sat very still, honed and heightened their awareness.

    Many of us have lost this ability by becoming slaves to our “busy” minds. In doing so, our minds are in the past or future. Can we be fully present? I think with practice, we can have the experience some of the time.

    🙂

    Funs

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