What Is Time? Why Our Sense of a ‘Flowing’ Time May Be a Psychological Projection

What Is Time? Why Our Sense of a ‘Flowing’ Time May Be a Psychological Projection

We commonly say “time flies,” “time waits for no one” or “as time goes on.” Those expressions suggest that time itself is a process moving through the world and that we — as occupants of a fleeting present — are carried along. But what exactly is it that “flows”? Rivers move because water travels; what is the moving substance when people say that time flows?

Ancient skepticism: Parmenides and others

Philosophers have wrestled with this puzzle for millennia. Parmenides of Elea (6th–5th century BCE) argued that if the future does not yet exist and the past no longer exists, it is unclear how events could change status from future to present to past. If the future were real now, it would already be part of the present; if it is not real, then how can anything emerge from nothing?

Related worries appear in Aristotle, in the Advaita Vedanta tradition of ancient India, and in Augustine of Hippo. These thinkers highlighted apparent contradictions in common-sense descriptions of temporal change.

Newton’s clock and Einstein’s revolution

Isaac Newton conceived time as an absolute background — a universal, evenly ticking clock that enables objective measures of motion and acceleration. In the early 20th century, Albert Einstein overturned that intuition with his theories of relativity (special relativity, 1905; general relativity, 1915).

Empirical work showed that the speed of light is constant regardless of the motion of its source. Taking that fact seriously leads to the relativity of motion: there is no single privileged rest frame. Observers in different frames assign different spatial and temporal coordinates to the same events.

A classic thought experiment illustrates this. Two lightning strikes equidistant from a station platform may appear simultaneous to an observer standing on the platform. A passenger on a train moving toward one strike and away from the other will judge them to have occurred at different times because the travel time of the light differs for that passenger. Neither observer is mistaken — they simply occupy different frames of reference.

Eternalism: all times are equally real

Under relativity, the standard consequence is eternalism: past, present and future are equally real in the four-dimensional structure of spacetime. There is no single, objective “now” that moves. If there is no universal present that events objectively “become,” then the everyday idea of a flowing passage of time is not a physical process.

Instead, change is the fact that the world has different properties at different times — different slices of spacetime show different states. For example, I may remember fewer events at one moment and more at another. That difference across temporal locations is what we call change.

Why do we feel time passes?

Given that physics leaves no room for an objective flow of time, why do we instinctively feel a passage of time? One common answer calls the feeling an “illusion.” But that term risks suggesting a sensory error like an optical trick. It is more accurate — and less misleading — to call the sense of passage a psychological projection.

Think of color: a red rose reflects light at particular wavelengths; our visual system converts that input into the experience of redness. The rose’s physical properties and our perceptual processing together produce color experience. The experience is not a mere illusion, nor is the rose “redness” independent of perception — it is a way our brains represent information about light and surface.

Similarly, the feeling of temporal passage arises from how humans represent and organize their experiences. It is a cognitive way of making sense of sequences of events, memory, anticipation and attention. We routinely attribute descriptive properties to instruments (for example, saying a GPS “thinks” we took a wrong turn) without implying the instrument is conscious. In the same practical way, we describe the world using temporal language even if physics describes time without a flowing present.

Conclusion

Theories of relativity challenge the idea of a single, moving present. While physics supports a block-like, four-dimensional view of spacetime in which all times are equally real, our psychology constructs a sense of passage that helps us navigate experience. The error — the projection — is conflating this perspective-laden representation with the structure of reality itself.

Republished from The Conversation. Written by Adrian Bardon, Wake Forest University.

Disclosure: Adrian Bardon reports no conflicts of interest beyond his academic appointment.