Mikko Leino writes via e-mail:
Alright, Mikbro, let's see what we can do here.
The 'philosophy of time' is a blanket term that covers a lot of different meanings - questions about time say things about free will, determinism, natural language, skepticism and a bunch of other topics. But the most fundamental question about time is whether it exists, and if so what it is - what is the nature of time?
Some of you are, perhaps, presently thinking - "what the fuck would it mean for time to not exist?" After all, we have a clear sense of the passage of time - we measure it, mark it, divide it, and bitches take up so much of it. I know what it's like to not have enough time - but no such thing as time? That's fucking crazy.
So, consider this: what if everything 'froze' right now for three years and then started up again? I mean everything - we all stopped aging, atoms stopped moving, light stopped travelling - everything just fucking stopped. Is that possible? Is time still passing in that scenario? Perhaps it's been three years since breakfast this morning, and you would have no way of knowing. We've all figured out by now that the most badass superpower possible would be to control the flow of time, since you can derive so much other cool shit from it - what if everything froze except you, right now. No one would know except you - your best friend would feel like nothing changed, but you would have - well, let's not get into what you would have done. But we all know. Oh, we all know. Now what if your best friend can freeze everything at will, and you don't know it? Look at him, all smug and shit. You would never ever be able to tell, unless something about him instantly changed - you would perceive him three feet to the left suddenly, and it would feel like no time at all elapsed, but he would know that it took 20 minutes to draw that dick on your forehead that you don't know is there. So, is time a 'thing' unto itself, that moves regardless of what else is going on, or is it just the ordering of events in a sequence? This is the most fundamental question. Plato seemed to think that time was a 'thing' and Aristotle disagreed. Those bros couldn't agree on anything.
If time is just an ordering of events, do any of those events enjoy a special status as 'the present'? Again, at first glance that seems like a ridiculous question. The present is now - I was a baby, now I'm not. I'm going to be dead, now I'm not. Except that in 30 years maybe you'll think, "30 years ago Philosophy Bro started writing. He's still fucking awesome, but 30 years older." What gives your experiences now special status over your experiences 30 years from now, or a day ago?
J.M.E McTaggart famously laid out the A-, B-, and C-theories of time in the 1908 paper "The Unreality of Time". The A-series is time related to the present - we identify events in relation to now. 'The noodle incident' was 2 years ago', 'That pledge just stopped crying a second ago', 'We'll stop drinking 3 days from now' and so on. If we consider 'the noodle incident' an event, does it have the property of 'being 2 years ago' at this very moment? Tomorrow, it won't have that property, and a year from now it will have the very different property 'being 3 years ago' that it doesn't have now - this is the A-theory of time. The B-series is just time related to other times - 'The police investigation ended, inconclusively, 3 months later than the noodle incident', 'My best friend and I were interrogated simultaneously', 'I will break up with his widow 6 months after I start dating her', and so on. The noodle incident will always have the property of 'being 3 months before the end of the police investigation', no matter when you're looking from. That's the B-theory of time. The C-series is the redheaded stepchild of McTaggart's paper, and it's just 'moments' laid out in order, but with no direction - the potato-cannon incident and the Senate Hearing were two weeks apart, but the C-series doesn't tell us in which order they happened - we'd have to look at the B-series to know that. No one, really, is a C-theorist. Seriously. No one. The C-series is just a helpful tool to help us construct the A- and B-series.
Think of time like a filmstrip, running left to right in front of you. The B-theory of time tells you that no 'moment' on the film strip is special or privileged; the noodle incident will always be to the left of that one pledge crying. The A-theory of time says that there's a flashlight running from left to right, and that is the 'present'. At times the noodle incident will be to the left of the flashlight, at times to the right. But McTaggart says there's a problem with the A-series: The noodle incident can't be in the past and in the future, even though it will have both of those properties and every other time-property, too, at some point. A-theorists object - "bro, it won't always have those properties. It will only have the property of being 'three years ago' when the events that it has the property of being three years before, like the pledge crying, have the property of being 'now'." Except that that relies on something being now, which is what the A-theory is trying to prove. It looks circular, bro. Sorry. Of course, A-theorists have not given up easily, and there are plenty of resolutions to that circularity. For example, if we consider time like a growing block, the leading edge is 'now', and there isn't a circle - but that requires an open future. Shit's tricky is all I'm saying, and the question is far from answered.
So there's your overview of time: Maybe time is a real thing, or maybe it just arises naturally from the ordering of events; maybe the present is special, and maybe it isn't. Some people don't think the difference is particularly important, but it's sure as fuck interesting. There's a lot more to time that I won't cover here, but it could always show up in a different MM.
Want more? This SEP article is particularly helpful, even for the SEP, and was the primary source for this post.
You can also find McTaggart's paper online if you want to read the original.
As usual, Oxford Publishing puts out an excellent academic treatment: The Philosophy of Time (Oxford Readings in Philosophy)