What even is Time? | Josheta Srinivasan

Ok. I get that this is an ambitious question, ~~nearly~~ impossible to answer at this time (no pun intended), just because there is yet to be a singular, fully convincing answer. Regardless, the week I spent on Time as a special topic at the end of my Intro to Philosophy class last semester, was perhaps the most entertaining part of the semester; I really did enjoy it. So, I do want to explore and build on what I’ve learnt from that class and aim to do so for the next few posts.

That being said, in this post, let’s survey some theories and explanations for this incredibly intuitive yet surprisingly elusive concept of time.

The Groundworks

Time is such an abstract concept. But, just like any other abstract concept, the most productive way to at least start grasping at its meaning might be to inspect how we use it: in speech, in practical life, in measurement, etc.

Let’s start with how we measure time. With a clock. Sure, but what exactly does that mean, i.e. what is the clock doing/ exactly measuring? Let’s start with the absolute basic: It goes in circles… okay, more specifically, it goes in circles through numbers from 1 to 12 (or 24). And pretty much that’s all it does, doesn’t it? Every day, consistently circling through a bunch of numbers…

In more primitive times (no pun intended, again), time was kept by following the sun or the moon. In fact, the earliest account of timekeeping discovered is the markings on a bone from the Democratic Republic of Congo (18000 BCE) which may have served as a way of tracking days according to sunrises and sunsets. However, a more conclusive historical timekeeping dates back to 8000 BCE, where a hunter-gatherer society from Eastern Scotland dug pits in the shape of the phases of the moon. Furthermore, these pits seem to line up with a point on the horizon connecting to the midwinter sunrise, possibly making this a lunar ‘calendar’.

Later on, sundials unearthed from 1250 BCE demonstrates the use of the sun to divide each day into 12 hours – day and night – although the ‘hours’ themselves were inconsistent: an hour was longer in the summer and shorter in the winter.

Time and Change

So, what seems common across all these forms of measuring time? Routine. The lunar calendar followed the routine waxing and waning of the moon, the sundial followed the routine rising and setting of the sun and our clock right now follows the routine circling through 12 (or 24) numbers. And what does routine consist of? A systematic change. So, our way of understanding time seems to be represented by change. This makes sense. We do perceive the passing of time through a series of changes: the leaves turn brown and time has passed from summer to autumn; the whiteboard gets full and time has passed from the beginning of the class to the end. We also perceive time through the ‘change’ in our memory, as in we remember something more than we did a second ago and a second has hence passed.

But to define time in terms of change might not provide many answers. Firstly, change is just as elusive as ‘time’. I mean what is change? Sure, broadly speaking, it is to make something different, but that ‘difference’ raises philosophical question marks about identity: how can something ‘change’ to bear incompatible properties but still be the ‘same’ thing. For example, if a particular leaf changes color from green to yellow as we approach autumn, is it still the same ‘leaf’? What then does identity consist of if not one’s properties? More importantly, however, change seems to be dependent on time just as much as time on change. Change is essentially a measure alteration of properties or characteristics (broadly speaking) over time, then how can it give us an answer about what time is, if its definition is itself built on time?

Time and Motion

Another way to make sense of time is by monitoring our language; i.e. how we speak about time. When we talk of time, we say time passes or that we ‘pass’ time; that it flows, marches on, etc. Just from these metaphors for time, it seems as though time is closely tied with motion.

Once again, this raises more questions than providing actual answers. We make sense of motion as the change in position over time (in physics, speed is the measure of motion, which is measured by distance divided over time). I guess we could define this more generally as the displacement through one dimension relative to displacement over another.

Yet again, how can this give us an answer about time, if displacement itself is dependent on time?

We could look at the present moment as moving instead, like a photo negative, where each frame is a ‘present’. For instance, right now I’m drinking coffee, and then I put the coffee mug down, and then I wash my coffee mug. The present moment, as it were, moves from drinking coffee to putting the coffee mug down to washing the coffee mug. But the present moment, if it moves, has to move through something correct? What is this something? Does it move through space? No. Then, time? Alas, we reach bewilderment once again.

Time and Space

I briefly touched upon motion as a displacement through one dimension relative to displacement over another, and this idea of ‘dimensions’ is what we look at next. In this view, time is compared to the spatial dimensions: width, height, and depth. Now we do the same thing that we did for our other comparisons: what is space then. The most abstract concept of space characterizes it as a set of points. Let’s consider a singular dimension: a space in one dimension can be characterized by sets all real numbers: i.e. <x> where x can take on any real number. A space in two dimensions is all the possible points in the two-dimension; this can be characterized by all possible <x,y> such that both x and y can be any real numbers. Similarly, space in three dimensions is the set of all possible <x,y,z> such that x, y, and z are any real numbers. So, mathematically, a space in n-dimension is the set of all possible such that each is any real number.

Four-Dimensionalism is the view that time can be looked at as a space-like dimension: time would be the fourth dimension (hence the name). So, each point in space can be represented as <x,y,z,t>. So, the universe is some kind of four-dimensional block (this view is called the Block Universe), which presumes that everything, the past, present, and future, is fixed and baked into the universe. Also, it proposes each object (including ourselves) is four-dimensional: some sort of a ‘space-time worm’ wherein time is a property of ourselves just as our height or foot length is. It is pretty confusing to think about this at first but I’ll elaborate on this view in another post.

A competing view called Three-Dimensionalism claims that it is a mistake to conflate time to be a space-like dimension because they are far too different. It claims that the dimensions have an entirely different relationship to time: that objects are three dimensional and persist through time. This, of course, once again gives us no account of a way to define time.

Relativity and Time

This has more to do with describing the way time works as opposed to giving it a definition per say but, nevertheless, it’s pretty fascinating, especially at first glance: Time and Einstein’s Theory of Relativity. If I were to summarize this in one phrase, it’d probably be “Time is elastic”. More elaborately (still not that elaborate), this phenomenon of the elasticity of time is called “time dilation” which proposes that time does not pass at a constant rate but rather ‘passes slower’ for a fast-moving object compared to a stationary (or slower-moving) on. TLDR: Time slows down for objects in motion. Obviously, this isn’t very noticeable in our daily lives but becomes more apparent at speeds close to that of light, c.

There was an experiment done in the 1970s (the Hafele-Keating experiment) to test this proposal: scientists put four atomic clocks (the most accurate types of clocks we currently have) on a commercial plane and left reference clocks on the ground at the United States Naval Observatory, they flew around the world twice and came back to find that the times of the clocks on the plane differed from the ones on the ground consistent with Einstein’s theory for time dilation.

Obviously, this is pretty mind-boggling initially just because we’ve been accustomed to look at time as this constant and absolute concept, and the fact that it is ‘relative’ or ‘elastic’ seems very self-contradictory.

I am going to end this post with the following consideration: Maybe time is sui generis, which is a Latin adjective meaning “of its/his/her/their own kind, in a class by itself; unique”. This essentially means that time might just be fundamentally irreducible to anything else. In this case, obviously, there isn’t much that can be done to define time; the only thing we can do to understand time is to study how it relates to everything else we know.

And that’s it, for now! I’ll probably write more about four-dimensionalism and three-dimensionalism later. Till then, See ya!

References:

A project by Quanta Magazine. Text by Dan Falk. Design and illustrations by Eleanor Lutz and Olena Shmahalo., & Quanta Magazine moderates comments to facilitate an informed, S. (n.d.). Arrows of Time. Retrieved June 21, 2020, from https://www.quantamagazine.org/what-is-time-a-history-of-physics-biology-clocks-and-culture-20200504/

Atherton, K. (2017, November 13). A brief, 20,000-year history of timekeeping. Retrieved June 21, 2020, from https://www.popsci.com/brief-history-of-timekeeping/

Motion. (n.d.). Retrieved June 21, 2020, from https://www.dictionary.com/browse/motion

Crew, B. (n.d.). Physicists Have Broken The Record For The Most Accurate Clock Ever Built. Retrieved June 21, 2020, from https://www.sciencealert.com/physicists-have-broken-the-record-for-the-most-accurate-clock-ever-built

Hafele and Keating Experiment. (n.d.). Retrieved June 21, 2020, from http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/airtim.html

Sui generis. (n.d.). Retrieved June 21, 2020, from https://www.dictionary.com/browse/sui-generis

Ludwig, Kirk. “Time.” Online lecture, April 23, 2020.

Images and Gifs retrieved from:

https://gifer.com/en/gifs/moon-phases