“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.)
“The past and future are equally real”
There are a lot of real problems with what you’re saying here.
First you’re saying that the future and past are implicit in the present. True, but that’s a lot weaker than the Einstein quote later that time is a fourth dimension. The past and future are IMPLICIT in the present, but do they actually exist, the way the room down the hall exists? Einstein is saying yes, you’re not quite.
But Einstein also said that “time is what we measure with a clock”, and I think that’s all we can say about time.
And personally I disagree with Einstein that time is like space. The Grandfather paradox is unsolveable if they are, but if they aren’t it isn’t a paradox at all, just a sign that we were looking at things wrong.
Wind is not moving. Flag is not moving. Mind is moving.
If the future is as real as the past, then free will must be an illusion. Cool. I can stop trying so hard now.
10 Things Everyone Should Believe About Time, Because Sean Believes Them. Everybody should have a position regarding metaphysics; thanks for sharing yours.
Time is the human attempt to measure the rate of decay of the universe; or measure the rate of evolution of the universe, to put it nicely.
Ya, everyone gets the same number of heartbeats, except for the exceptions. Birds squeeze off as many as 10 billion beats, and a human will knock off 4 billion without being all that amazing. Heartbeat makes a useful estimator of metabolic rate, which roughly equates to oxidative stress, but not all organisms handle that in quite the same way. The only real hard and fast rule in biology is that life will do pretty much whatever it pleases.
> So you’re saying the future too is fixed and in the books, and that this should be completely accepted. Given the implications for commonsense notions of human freedom and dignity, it’s unlikely this will ever come to pass, but I appreciate your advocacy.
In a sense, the future is fixed; it just has not happened yet. We might not like that idea, but that does not make it false. Everything up until now has happened in exactly one way, and that is how time will continue to pass. It does not make our decisions any less valid. Just that things were bound to happen this way.
People like to think they are more important than they really are, and that we are in charge. They do not like to feel helpless or worthless. But this concept is not rooted in objective reality. If you think about all the complex processes that had to occur for millions of years for us to end up in this precise moment, well, to think “I control my own destiny!” is a comforting thought, but patently false.
“The equations don’t lie”? I hope I don’t have to point this out to a physicist, but equations are models, not omniscient oracles.
I think you’re right,…. no, I’ve changed my mind. Time has passed between the two decisions without motion.
I have done a lot of science reading. If I had to describe spacetime in one sentence I would describe it as “a medium for energy to express itself”. Energy can exist in space as masss, it can exist as movement through space, over time, both space and time are nessesary for the objects in the universe to exist, and the energy of motion is the same ultimately “stuff” as energy that makes up the mass of the object that is moving. Space and time are also correlated and blah blah blah but I would definately regard time as a real “thing” just like I regard distance or area or volume as real “things”. To those who say that time doesn’t exist, and offer up a simple one or two sentence explination, or that the “future” isn’t “real” yet, probabily have not been shown how deep the relationship between space, time and energy goes.
“Eyewitness testimony, it turns out, is one of the least reliable forms of evidence allowed into courtrooms.” – That’s an old chestnut that I’ve seen used only by those who are defending evolution in an evolutionist-creationist debate, specifically to justify calling a study a science when no one was present to record the events the study pretends to study. As it happens, the statement is, if not untrue, at least misleading. Direct evidence–including some forms of witness testimony–is more reliable than circumstantial evidence. The fact that one can monkey with witness memory does not discredit all eyewitness testimony. As usual, evolutionists are liars.
“Other than creationists, most people have no trouble appreciating the difference between ‘orderly’ (low entropy) and ‘complex.'” If that were true, there would not be much point in talking about it at a physics conference. But, as usual, evolutionists are liars. Speaking of which, what is with this fascination for bringing up evolutionist’s arguments at a conference on time?
You must have a lot of frauds going to Norway.
106. Peteris Re: 80ms is too long. It could be that reacting to sound takes a higher priority over sight, so it could possibly take different times for different senses IMO. Touch may be even less complex to the point of taking even less time. Studies like that always seem to leave out common questions and generalize way too much. If only they would ask normal people BEFORE performing the study. 🙂
Aging related links:
http://www.thelivinlowcarbshow.com/shownotes/4190/478-evolutionary-biologist-michael-rose-on-achieving-biological-immortality-naturally/
http://www.bbc.co.uk/i/p00bg00v/
There is no present, only past and future.
@CuriousTech – Not sight; touch. 80 ms is too long to react to either sound or sight. In 80 ms, a car traveling 30 mph travels about 40 inches (0.528 inches/ms). We might not be able to react that fast, but we might notice if something appears just 3 feet in front of us. So, our resolution of reality is finer than 80 ms. BTW, research has also concluded that humans have more than one signal processing pathway in the brain, one of which is much faster than the other. The faster pathway becomes active in highly dangerous situations, and involves much less signal processing than the slower pathway.
When I was a teenager, I once rode my moped along a road in a 55 mph zone. I made a left turn and heard tires screeching on the pavement behind me. I looked down and saw the front bumper of a dark green car with chrome trim about 3 feet from my left side. I estimated in that moment that the vehicle was traveling about 35 mph. I looked back up and felt the muscles in my right arm begin to constrict as I attempted to steer away from the car. Then, I found myself floating in space, in a bright, white light. All of that had to have taken place in little more than 80 ms.
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What goes ’round comes back around….so to speak about ‘time’. Is that why the golden rule became our basic value of the universe?
“the past and future are equally real…”
Not scientifically proven. Not even remotely proven. Not even any legitimate scientific evidence for it.
Poor article.
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No matter how well medicine does the odds of being struck by lightning by your 2,000 birthday start to approach 100%
Who said, “Time does not pass. We do.”? Nothing in the universe is stationary – isn’t that right? From the micro to the macro, all things, particles, objects, etc. are in motion. And motion, or sequences of events, of movement and motion, is what gives humans a ‘sense’ of passing time.
“You and I won’t live forever. But as for our grandkids, I’m not placing any bets.”
-Of course not. Because as you say…you wouldn’t be around to collect.
It’s about the wave function collapse, stupid!
Greatest post this week! Great insights also. I always believe that each individual have their own amount of time. If you spent a lot of time sleeping, you will have lesser time than the one who’s awake. I always value time as top priority, more than comfort.
I have trouble with Thing number seven, 7.
It would be hard to quantify the degree to which human consciousness and awareness are orderly; and this multiplied by all observers in the Universe.
In fact, I wouldn’t doubt that the total entropy of the Universe remains constant, at zero.
Not only do I find the possibility intriguing, that knowledge and awareness increase proportionally to the increasingly disordered motion of particles in the Universe -and therefore cancel, but the idea the Universe contains any implicit, measurable, or distinct quantity whatsoever, across its entire domain, to me is anathemous.