What is time

A: Nice to see you in this sunny day. Say, is this bike new?

B: It is yeah. I bought it today. It is a fixie.

A: A fixie? So you’s a hipster?

B: No, it is just a type of bike that has no freewheel mechanism. Your chain is directly tied to the pedals. This means that you can go both forward and backward, as well as to reduce your speed by just using the pedals. But riding this bike got me thinking about the following question - “what is time”?

A: That does not seem terribly related.

B: It is not.The thought that sparked it was the following: it seems to me that the difference between time and space is similar to the difference between a fixed gear bicycle and a normal one.

A: Hm, what have you been smoking?

B: But it is true! Einstein proved that there is no universal time. So moving through space is the same as moving through time. With just one exception - from space you can go forward and backward, and generally in any direction you want, just as with a fixed gear bicycle. While with time you travel in just one direction. Once you spin the wheels you cannot go back.

A: That does not seem right. Because in time you also cannot slow down or go faster, right?

B: I can. I can perform one action in one hour, and I can perform the same action in two hours. Why do you say that I cannot slow down?

A: You can slow down but time itself cannot slow down - one hour will always take one hour to pass.

B: No see, you are explaining what an hour is in terms of itself. You can spend a lot of time trying to justify your intuition but if you think about it, clocks are actually nothing more than sources of uniform motion which are synchronised with one another for the purpose of being used as a frames of reference by people. The first clocks were based on the uniform motion of the sun. Most of the ones that we use today contain setups that enable artificial uniform motion. There is nothing unique about uniform motion, though. For example most artificial setups break down easily, and even the sun will break down eventually. And there isn’t a single clock in the universe on which you can rely on to tell the time.

A: That makes sense. And our perception of time is evolutionally bound to these uniformal events for survival purposes?

B: Right. The human mind is designed for practical purposes. That is why it is so hard to grasp stuff like this.

A: But if we cannot thrust our brains, and if the clocks are a lie, then why you say that we cannot go back in time? I mean, I can go back to the same place that I was yesterday and feel the same way as I did yesterday. Who can tell me that it is not yesterday?

B: Well, if you, for example, left something there yesterday, then you will find it there. This is how you’d know which event is after which.

A: Well, by the relations you have with other objects essentially, for example we see a swallow flying from one place to the other and when it gets there we assume that some time has passed.

B: Hmm, are you sure that is the only way?

A: If I lock you in a room without windows, can you determine how much time you’ve been there.

B: We can make an experiment and see.

A: I feel that other people had already made this experiment for us. The only way for you to know that time is passing is to literally count the minutes and seconds as they go. But I’d argue that using your internal clock is an exception which justifies the rule - our intuition of time is solemnly based on the perception of the way that our environment changes, with our body being considered a part of this environment. I am at my kitchen. I place one egg at my pan. I look through the window and see a swallow flying towards me. Some time passes and I notice that it is sitting on my window. I know from experience that its movement takes roughly five minutes so I can assume that my egg is ready. There aren’t always real birds crossing my streets, so I make up a mechanical one - that is the cuckoo, that lives inside my clock.

B: So you are saying that the notion of time is married to the law of causality?

A: The law of what?

B: Bro, do you even read other philosophers?

A: Leave me alone.