Does Time Exist? (Or, how Aristotle got metaphor wrong)

I remember some time ago hearing the physicist Sean Carroll, who's written quite a bit on the subject of time, mention that he and a colleague of his, fellow physicist Julian Barbor, disagreed strongly on the existence of time. Being physicists, they're debating the subject purely from the perspective of whether time can or should be disregarded from equations. But what about the broader idea that time doesn't really exist?

Obviously, it seems prima facie absurd. Time is an absolutely central and fundamental part of the human experience. It's integral to virtually every scientific field, and has been a topic of philosophical musings for millennia. How can time not exist?

But wait a second... couldn't the same have been said of color? Color is a deeply seated part of our phenomenological experience, but cognitive neuroscience has shown that color does not exist "out there", so to speak — that is, it is not a property that inheres in the world, but is an interactional property between wave lengths, light-sensitive cones in our eyes, and our brains [1]. What if time is something similar? Not "out there", inhering in the universe itself, but an interactional property dependent on embodied brains?


Aristotle on metaphor

Let's back up (that's a metaphor). The philosopher Aristotle believed that metaphor was poetic and rhetorical, and not part of our everyday language or fundamental to the process of reasoning. In The Poetics, he wrote,

Metaphor consists in giving the thing a name that belongs to something else; the transference being either from genus to species, or from species to genus, or from species to species, on the grounds of analogy. 

In other words, he thought that metaphor occurred when words which have a specific meaning and use were used in other circumstances, that it was a novel — not fundamental — linguistic expression. Or, as Lakoff puts it in Philosophy in the Flesh,

Metaphor [according to Aristotle] is a matter of words, not thought. Metaphor occurs when a word is applied not to what it normally designates, but to something else.

Empirical evidence has shown Aristotle to be profoundly mistaken. Metaphor is a process of thought, not merely of words. And there is perhaps no better example of this than time.


Time as a metaphor

If time exists as a property of the universe unto itself, wholly independent of human minds, then it seems we do not have direct access to it through our senses alone. For us, time expresses a relationship between events and we cannot think about it without embodied metaphor. Even physicists like Sean Carroll, who defines the "arrow of time" as the increasing entropy of the universe, are employing a metaphor (since arrows are objects that go from one place to another in a straight line) to describe a relationship between events.

In our everyday language, we conceptualize time as expressing a relationship between objects in motion. We use metaphors that derive from our embodied, spatial experience — forward, backward, behind, in front of, toward, through, etc. There are, broadly speaking, two embodied metaphors of time that we generally employ.

1. Stationary-observer metaphor. In this metaphor, the observer does not move. Time is conceptualized as objects moving in relation to the observer. The objects are events. Events in the future are objects which move closer to the observer, and objects in the past are moving away from the observer. The observer faces toward the future events, and faces away from the past events. If the observer is contemplating the past, they may "look back" on events behind them.
2. Moving-observer metaphor. In this metaphor, time is conceptualized like a river or road, and the observer is traveling along it. As before, events in the future face the observer and events in the past are behind the observer, but in this metaphor they are points that the observer reaches as they travel along the road or the river. The perceived speed of time can be conceptualized as varying by describing the type of path, such as a road that "meanders" or a river that "rushes".

Examples of (1):

• "I'm looking forward to my vacation. It's coming up soon!"
• "The deadline is approaching quickly."
• "I feel happy when I look back on my years in college."

Examples of (2):

• "We're coming up fast on the last week of classes." (Notice that the same phrase, coming up, is used with a different subject depending on the metaphor)
• "The day just flew by!"
• "Could this meeting drag on any longer?"

These are a few of dozens, if not hundreds, of examples. Not only is metaphor part of our everyday language — and not, as Aristotle thought, simply poetic and rhetorical — but it's absolutely integral to our very ability to abstract a concept such as time.  

When philosophers engage in speculating about the 'metaphysics' of time, they're choosing from the cognitive subconscious a pre-existing metaphorical conceptualization of time. They then, using a pre-determined set of logical axioms, work out the consequences of the metaphor according to those particular axioms. The consequences will vary according to the set of axioms used. The whole time, they've taken the metaphor to be literal, and ultimately declare that they're arrived at a deep 'truth' about reality. Lakoff expounds further (hey, that's an embodied metaphor too!):

When the concept [of time] itself is defined by metonymy and multiple metaphors, it is odd to ask what the objectively real correlate of that concept is. If you insist on asking that question, you will wind up doing one of the things that philosophers have typically done: choosing some aspect of the concept that you want to focus on and claiming that that one aspect really is time, either time as a flow, or time as a continuous unbounded line, or time as a linear sequence of points, or time as a single spatial-like dimension in a mathematical theory of physics. What you will probably not be able to do is arrive at a single, unified, objective, literal understanding of that subject matter that does full justice to all aspects of the concept.

This doesn't mean that metaphor renders time meaningless; far from it. Just as color is an essential part of our phenomenological experience even if it does not inhere in the universe, metaphors of time are absolutely essential to our phenomenological experience, our conceptualization and understanding of science, and to our process of reasoning.

So, does time really exist? I think it's perfectly sensible to say it does, since it's such an essential part of our experience (see "non-eliminative physicalism"). But it may be most sensible to say that "time" is ultimately an emergent, interactional property that arises from the cognitive subconscious, and not a property that inheres in the universe itself independently of our embodied brains.