Also, if time does exist, doesn’t there have to be a definable beginning or end? Otherwise it’s just infinity which to me suggests the absense of time.
I partially read “The Discoverers” by Daniel Boorstin several years ago and he discussed how different societies conceptualized of time and how they kept time. And it has had me wondering ever since. Then I started exploring Zen Buddhism which emphasizes the present moment as the only tangible reality, along with the illusion of the ego, which only furthered my questioning.
EDIT – I am aware that the concept of time is based on the revolution of the Earth and it’s moon. However, that is just how humans conceive of time. That’s not proof of time itself.
EDIT 2 – The explanation of timespace and relativity is the best from an objective point of view. No matter how much I read or watch, it was always a bit hard to grasp but it makes sense in terms of change or entropy. The reality of time being flexible vs the human perception of time being linear and unchangeable gets closer to what I am asking.
EDIT 3 – “Exist” is a tricky word.
In: 7871
So you’re sort of halfway to understanding time as a concept, because you’ve started to question the idea that the things that we usually use to mark the passage of time — seconds and minutes and hours, and even things like ‘planetary rotations’ and ‘lunar orbits’ — are largely arbitrary, and would change depending on where you’re based relative to other things. A slightly trickier question, though, is how do we know that one second is the same length as every other second? Maybe if there was an ‘outside perspective’ of time, one minute could last *this* long, and another minute could last *thiiiiiiiiiiis* long, but they feel the same length to us because one of them was squished together with us inside of it. Each one of them contains a minute’s worth of ‘stuff’, but just because they *feel* the same length to us, how do we know they actually *are* from some external and objective reality?
Weirdly, this isn’t as crazy as it sounds. [*Time dilation*](https://en.wikipedia.org/wiki/Time_dilation) is an effect of relativity, in which — from an ELI5 perspective — a second as perceived by one person might be a very different length to a second as perceived by a different person depending on how fast they’re going. You can define a second as the time it takes a pendulum of a certain length to swing once, and that time will be the same for both Person A and Person B… but Person A’s pendulum might swing dozens or hundreds of times more often than Person B’s pendulum from Person A’s perspective during the same interval, depending on their relative speeds. (Relativity is complicated, and things get very unintuitive very quickly.) We can calculate these values consistently and show them to be real — in fact, things like GPS satellites *depend* on us being able to calculate these values consistently — but they’re still different from the point of view of each observer. So how can we define *time* at all, if it’s not the same everywhere? If time depends on how fast you’re moving, how do we know that it actually even exists at all?
One way is to think about *time* not in terms of measuring it, but in terms of whether we can detect time ‘happening’ in the first place. (Now we’re not interested in whether a second is a second, but whether a second is *anything meaningful at all*.) In that sense, what we call ‘time’ is really just a measurement of *change*. (After all, the only way to detect the passage of time is to note how things vary from one point to the next. You can think of it like taking two photos; if you can’t detect any changes between the photos, how do you know that it’s two photos taken seconds or minutes or weeks or years apart, rather than just two copies of the same photo?) One of these is the principle of *cause and effect*, namely that if an action A causes an effect B, A must have happened before (or rather, at an earlier time than) B. One way to think of ‘time’, then, is as a measurement of causal effect. Time *must* be progressing, because change keeps happening, and because change happens in one direction only, the value we assign to ‘time’ — perhaps thought of as the countdown that has progressed from the start of everything to what we call ‘now’ — has to keep increasing. The classic example is unscrambling an egg: from our perspective, the unscrambled egg must always come before the scrambled egg, and so it can be seen that time can only act in one direction; as a result, A must predate B. (The slightly more scientific formation of this thought is that [entropy](https://en.wikipedia.org/wiki/Entropy) — the level of ‘disorder’ in a system — cannot decrease over time without putting work into the system; just as you can’t expect the milk you stirred into your coffee to randomly unstir itself, you can’t undo the natural processes that split apart an atom by radioactive decay. State A comes before State B, and so if you could line up all of those necessary A-before-B states from the beginning of time to now, you’d end up with what is effectively a timeline that shows a progression. You might not know how long it took between each *step* of that timeline, but you’d still be able to show that progression was happening.)
Again, this is a *very* ELI5 explanation, but [this is a pretty good rundown of why figuring out whether time is ‘real’ is a bigger — and smarter — question than it first sounds.](https://bigthink.com/starts-with-a-bang/does-time-exist-182965/) The short version is that *time* can be definitely said to exist, at least according to our current understanding; it’s just the specific measurements that are fiddly and weird and often pretty arbitrary.
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