We sometimes say that dogs are living in the now. Sometimes we say that of people who live in the moment and don’t think much about the future (or about the consequences). Whether we mean that as a compliment — as we generally do with dogs — or as an oblique implication of shallowness depends on the point we’re making.
There is the tale of the ant and grasshopper; it divides people into workers who plan for the future and players who live in the now. The former, of course, are the social role models the tale holds heroic. The grasshopper is a shifty lay-about, a ne’er do well, a loafer and a moocher, but that’s not the point.
The point is our sense of «now» and of time.
The previous post, Wondering About Wetness, was about whether we sense wetness, but I touched also on whether we sense time. (Which generated some interesting comments.) I’d mentioned then that time was a topic for another time.
Now is the time for time!
To start, time is a mystery a bit like consciousness in being something we experience every waking moment, but don’t understand very well.
Consider the «now». The invisible, constantly moving, razor edged, singularity that separates past from future. It exists for me as I write this; it exists for you as you read this.
The «now» draws a moving line between two realms that appear very different to us. The one, known, unchangeable history; the other, unknowable, changeable future. (Or so it seems. If the universe is fully deterministic, perhaps the future is as fixed as the past.)
From our vantage point in the «now» the future appears less and less predictable the further ahead we look. The weather forecast for tomorrow is usually right (or close enough), but sometimes they still get it wrong. The weather a year from now? About all you can forecast is the season.
For us there seems a clear discontinuity — the «now» — between the past and future realms. This is just one of time’s great puzzles!
When we interact with people, we share the «now» together. That’s different from that other great mystery, consciousness. Inside each of us is an «I» that directs our actions and thinks our thoughts. We can’t share the «I» with anyone (at least not so far), but we do easily share the «now» (or at least we seem to — more on this in a bit).
It’s a good thing we can! Imagine how hard life would be if «now» for each of us was very different. It would be hard to have a conversation or even hand something to someone. Everyone would be literally out of sync!
But we have no idea what «now» really is all about, why it exists. We don’t understand why time exists, what it is, or why it runs in one direction. As far as the laws of physics go, there’s no reason things can’t run backwards.
You ask, “Ah, but what about broken eggs and such?” Well, it turns out that the laws of physics have no problem making a broken egg whole. The egg-breaking process works fine in reverse. You do have to apply exactly the right forces in exactly the right directions at exactly the right times, but it is possible.
The point: Breaking an egg is easy. Unbreaking one is hard. Very, very hard (but not prohibited).
We think that enormous difference in difficulty may account for why time runs forward. It might even account for why time exists at all.
We think. But we aren’t sure.
There is a view that the enormous difficulty of unbreaking an egg creates an Arrow of Time that points in the direction of breaking eggs. Also of hot things cooling and cold things warming. These things are due to the laws of thermodynamics.
Entropy, in a sense, is the Arrow of Time. (One apparent difference: you can use energy to reverse entropy locally.) The natural state for entropy is to increase, and in the closed system that is the universe, it always does.
The thing is, thermodynamics (and entropy) apply to systems with lots of parts. The molecules of air in a room, or of steel in a bolt, comprise systems of unimaginable size. It is the emergent collective behavior of all those parts that give rise to thermodynamics.
Given the link to thermodynamics and entropy, is time an emergent collective behavior? Is time a consequence of the universe rather than a fundamental aspect of it? Does time come from reality, or is it a key part of it?
Speaking of cosmology, Minkowsky Space (which Einstein used to describe Special Relativity) treats time as if it was a physical dimension similar to the three we seemingly inhabit. As such, time becomes the “fourth dimension” and movement in time is treated as movement in (4D) space.
An xkcd comic I especially like comments on how we’re forced along that time “dimension” against our will.
And in only one direction. And always at the same (to us) speed.
Time may subjectively speed up or slow down, but no correct clock you ever carry with you will run faster or slower.
So time isn’t really a dimension. We can choose to move back and forth — or not at all — in physical dimensions. There is also that time has a start point, the Big Bang. Where is the start point for any physical dimension?
If we don’t understand time, figuring out «now» is whole other level.
There’s a philosophical version: The universe is 13 billion years old. Why are we here now? The universe is likely to last a trillion years (at least), so why are we here so early? I’m not asking (or rather, you’re not reading) those questions «now».
I mean the «now» that separates past and future.
Even if the future was determined, isn’t it weird we’re experiencing reality in serial fashion? It’s like we’re all riding in cars being pulled through a time landscape.
And if chewing on that hasn’t scrambled your egg, what if I told you that the «now» you experience depends on your location and velocity?
Einstein’s Theory of Relativity has an astonishing consequence: There is no such thing as simultaneity. We seem to share simultaneous experiences, but it’s just a local effect. If you’re talking about people on a distant star—or, worse, distant galaxy—the question, “What are they doing right now?” is almost meaningless.
In the math that describes this distance (as well as speed) plays a role. As it happens, at the distance of the Andromeda galaxy, just walking past someone is enough to create differing accounts between you of «now» in that distant galaxy.
We seem to share the «now» but in fact our little cars are all spread out, some ahead, some behind. Nearby cars going along together do share the «now» but that becomes less true as you consider cars farther away. Yet there is a diffuse moving “cloud” «now» that began at the Big Bang and will continue into the distant future.
So there’s time, and there’s the «now», and finally the question of whether humans sense time (which requires defining exactly what we mean by “sense”).
As I pointed out previously, “Cogito ergo sum,” is a thought that occurs serially in time. The concept of “before” applies to the first word relative to the others just as “after” applies to the last word (even “first” and “last” imply time).
The functioning of any machine (or any algorithm, for that matter) is a process in time. Movement is defined as distance over time. All chemical and physical processes occur in time. Our thought process — our “stream of consciousness” — occurs in time.
If you agree we “sense” love and grief, then time should be a shoe-in. If you at least agree we have a sense of balance, then perhaps we sense time as a mental signal from below our self-awareness horizon. Even if you restrict sensing to the five traditional senses, to have those requires time, so all sensation might be said to include time.
Perhaps we are actually as unaware of time as fish are of water. In both cases, we do know when we’re out of it!
“Stay timely my friends!”
 For the record, in terms of planning about the future, I’ve always identified more with the happy hopper than the industrious crawler. A tragedy of life is that the good do sometimes die young, no matter how industrious or good or careful they are. I’ve known two things a long time: that life can be short, and that when it ends, I want to be able to say I enjoyed as much of it as possible.
 Or so I claim.
 An interesting question: To what extent does the past become hard to know accurately as you look further back? Any knowledge set describing the past (including your memory) is subject to decay over time plus having to handle an ever-increasing amount of knowledge.
 An all-time favorite: “Time flies like an arrow. Fruit flies like a banana.” (Often misattributed to Groucho Marx. It’s believed to come from an early book about computer parsing of natural language.)
 That is to say, a law telling us that, not only can we never win but, we can never break even. Just like Las Vegas.
In every energy transaction the universe extracts a small tax to fund its ever-growing supply of entropy. At some point — the heat death — there won’t be enough ordered energy left to pay the tax, and that will be the end of energy transactions, of being able to do work.
 The strong link between time and entropy gives us a bit of a puzzle. If entropy always increases, and the universe is fairly ordered now (after 13.7 billion years of increasing entropy), the very early Big Bang universe must have had extremely low entropy. The conundrum is: How is the Big Bang, in any way, a highly ordered state?
An interesting thing to ponder is, given the speed at which quarks and electrons move, they must all have their own frames of reference!
 Well, obviously you are (and I did), but you know what I mean.