parmenides

_

What is time? Rather than something that ‘flows,’ a philosopher suggests time is a psychological projection

Time isn’t an illusion, unlike optical illusions that trick your eyes. There’s nothing to ‘trick’ because it has no physical basis.
BSIP/UIG Via Getty Image

“Time flies,” “time waits for no one,” “as time goes on”: The way we speak about time tends to strongly imply that the passage of time is some sort of real process that happens out there in the world. We inhabit the present moment and move through time, even as events come and go, fading into the past.

But go ahead and try to actually verbalize just what is meant by the flow or passage of time. A flow of what? Rivers flow because water is in motion. What does it mean to say that time flows?

Events are more like happenings than things, yet we talk as though they have ever-changing locations in the future, present or past. But if some events are future, and moving toward you, and some past, moving away, then where are they? The future and past don’t seem to have any physical location.

Human beings have been thinking about time for as long as we have records of humans thinking about anything at all. The concept of time inescapably permeates every single thought you have about yourself and the world around you. That’s why, as a philosopher, philosophical and scientific developments in our understanding of time have always seemed especially important to me.

Ancient philosophers on time

A stone bust of a man with curly hair and a beard. — Parmenides of Elea was an early Greek philosopher who thought about the passage of time.
Sergio Spolti/Wikimedia Commons, CC BY-SA

Ancient philosophers were very suspicious about the whole idea of time and change. Parmenides of Elea was a Greek philosopher of the sixth to fifth centuries BCE. Parmenides wondered, if the future is not yet and the past is not anymore, how could events pass from future to present to past?

He reasoned that, if the future is real, then it is real now; and, if what is real now is only what is present, the future is not real. So, if the future is not real, then the occurrence of any present event is a case of something inexplicably coming from nothing.

Parmenides wasn’t the only skeptic about time. Similar reasoning regarding contradictions inherent in the way we talk about time appears in Aristotle, in the ancient Hindu school known as the Advaita Vedanta and in the work of Augustine of Hippo, also known as St. Augustine, just to name a few.

Einstein and relativity

The early modern physicist Isaac Newton had presumed an unperceived yet real flow of time. To Newton, time is a dynamic physical phenomenon that exists in the background, a regular, ticking universe-clock in terms of which one can objectively describe all motions and accelerations.

Then, Albert Einstein came along.

In 1905 and 1915, Einstein proposed his special and general theories of relativity, respectively. These theories validated all those long-running suspicions about the very concept of time and change.

Relativity rejects Newton’s notion about time as a universal physical phenomenon.

By Einstein’s era, researchers had shown that the speed of light is a constant, regardless of the velocity of the source. To take this fact seriously, he argued, is to take all object velocities to be relative.

Nothing is ever really at rest or really in motion; it all depends on your “frame of reference.” A frame of reference determines the spatial and temporal coordinates a given observer will assign to objects and events, on the assumption that he or she is at rest relative to everything else.

Someone floating in space sees a spaceship going by to the right. But the universe itself is completely neutral on whether the observer is at rest and the ship is moving to the right, or if the ship is at rest with the observer moving to the left.

This notion affects our understanding of what clocks actually do. Because the speed of light is a constant, two observers moving relative to each other will assign different times to different events.

In a famous example, two equidistant lightning strikes occur simultaneously for an observer at a train station who can see both at once. An observer on the train, moving toward one lightning strike and away from the other, will assign different times to the strikes. This is because one observer is moving away from the light coming from one strike and toward the light coming from the other. The other observer is stationary relative to the lightning strikes, so the respective light from each reaches him at the same time. Neither is right or wrong.

In a famous example of relativity, observers assign different times to two lightning strikes happening simultaneously.

How much time elapses between events, and what time something happens, depends on the observer’s frame of reference. Observers moving relative to each other will, at any given moment, disagree on what events are happening now; events that are happening now according to one observer’s reckoning at any given moment will lie in the future for another observer, and so on.

Under relativity, all times are equally real. Everything that has ever happened or ever will happen is happening now for a hypothetical observer. There are no events that are either merely potential or a mere memory. There is no single, absolute, universal present, and thus there is no flow of time as events supposedly “become” present.

Change just means that the situation is different at different times. At any moment, I remember certain things. At later moments, I remember more. That’s all there is to the passage of time. This doctrine, widely accepted today among both physicists and philosophers, is known as “eternalism”.

This brings us to a pivotal question: If there is no such thing as the passage of time, why does everyone seem to think that there is?

Time as a psychological projection

One common option has been to suggest that the passage of time is an “illusion” – exactly as Einstein famously described it at one point.

Calling the passage of time “illusory” misleadingly suggests that our belief in the passage of time is a result of misperception, as though it were some sort of optical illusion. But I think it’s more accurate to think of this belief as resulting from misconception.

As I propose in my book “A Brief History of the Philosophy of Time,” our sense of the passage of time is an example of psychological projection – a type of cognitive error that involves misconceiving the nature of your own experience.

The classic example is color. A red rose is not really red, per se. Rather, the rose reflects light at a certain wavelength, and a visual experience of this wavelength may give rise to a feeling of redness. My point is that the rose is neither really red nor does it convey the illusion of redness.

The red visual experience is just a matter of how we process objectively true facts about the rose. It’s not a mistake to identify a rose by its redness; the rose enthusiast isn’t making a deep claim about the nature of color itself.

Similarly, my research suggests that the passage of time is neither real nor an illusion: It’s a projection based on how people make sense of the world. I can’t really describe the world without the passage of time any more than I can describe my visual experience of the world without referencing the color of objects.

I can say that my GPS “thinks” I took a wrong turn without really committing myself to my GPS being a conscious, thinking being. My GPS has no mind, and thus no mental map of the world, yet I am not wrong in understanding its output as a valid representation of my location and my destination.

Similarly, even though physics leaves no room for the dynamic passage of time, time is effectively dynamic to me as far as my experience of the world is concerned.

The passage of time is inextricably bound up with how humans represent our own experiences. Our picture of the world is inseparable from the conditions under which we, as perceivers and thinkers, experience and understand the world. Any description of reality we come up with will unavoidably be infused with our perspective. The error lies in confusing our perspective on reality with reality itself.

Adrian Bardon, Professor of Philosophy, Wake Forest University

This article is republished from The Conversation under a Creative Commons license.

_

03 + 05 : 13parmenides św. augustyn zenon

Physicists and philosophers have long struggled to understand the nature of time: Here’s why

Time itself isn’t difficult to grasp: we all understand it, despite our persistent struggle to describe it. The problem is one of articulation: a failure to precisely draw the right boundaries around the nature of time both conceptually and linguistically.
(Donald Wu/Unsplash), CC BY

Daryl Janzen, University of Saskatchewan

The nature of time has plagued thinkers for as long as we’ve tried to understand the world we live in. Intuitively, we know what time is, but try to explain it, and we end up tying our minds in knots.

St. Augustine of Hippo, a theologian whose writings influenced western philosophy, captured a paradoxical challenge in trying to articulate time more than 1,600 years ago:

“What then is time? If no one asks me, I know; if I want to explain it to a questioner, I do not know.”

Nearly a thousand years earlier, Heraclitus of Ephesus offered a penetrating insight. According to classical Greek philosopher Plato’s Cratylus:

“Heraclitus is supposed to say that all things are in motion and nothing at rest; he compares them to the stream of a river, and says that you cannot go into the same water twice.”

Superficially, this can sound like another paradox — how can something be the same river and yet not the same? But Heraclitus adds clarity, not confusion: the river — a thing that exists — continuously changes. While it is the same river, different waters flow by moment to moment.

While the river’s continuous flux makes this plain, the same is true of anything that exists — including the person stepping into the river. They remain the same person, but each moment they set foot in the river is distinct.

How can time feel so obvious, so woven into the fabric of our experience, and yet remain the bane of every thinker who has tried to explain it?

An issue of articulation

The key issue isn’t one most physicists would even consider relevant. Nor is it a challenge that philosophers have managed to resolve.

Time itself isn’t difficult to grasp: we all understand it, despite our persistent struggle to describe it. As Augustine sensed, the problem is one of articulation: a failure to precisely draw the right boundaries around the nature of time both conceptually and linguistically.

Specifically, physicists and philosophers tend to conflate what it means for something to exist and what it means for something to happen — treating occurrences as if they exist. Once that distinction is recognized, the fog clears and Augustine’s paradox dissolves.

The source of the issue

In basic logic, there are no true paradoxes, only deductions that rest on subtly mishandled premises.

Not long after Heraclitus tried to clarify time, Parmenides of Elea did the opposite. His deduction begins with a seemingly valid premise — “what is, is; and what is not, is not” — and then quietly smuggles in a crucial assumption. He claims the past is part of reality because it has been experienced, and the future must also belong to reality because we anticipate it.

Therefore, Parmenides concluded, both past and future are part of “what is,” and all of eternity must form a single continuous whole in which time is an illusion.

Parmenides’ pupil, Zeno, devised several paradoxes to support this view. In modern terms, Zeno would argue that if you tried walking from one end of a block to the other, you’d never get there. To walk a block, you must first walk half, then half of what remains, and so on — always halving the remaining distance, never reaching the end.

A painting shows a man in robes leading other men in robes. — The Greek philosopher Zeno of Elea showing his followers the doors of Truth and Falsehood in a 16th century fresco at the El Escorial in Madrid.
(El Escorial, Madrid)

But of course you can walk all the way to the end of the block and beyond — so Zeno’s deduction is absurd. His fallacy lies in removing time from the picture and considering only successive spatial configurations. His shrinking distances are matched by shrinking time intervals, both becoming small in parallel.

Zeno implicitly fixes the overall time available for the motion — just as he fixes the distance — and the paradox appears only because time was removed. Restore time, and the contradiction disappears.

Parmenides makes a similar mistake when claiming that events in the past and future — things that have happened or that will happen — exist. That assumption is the problem: it is equivalent to the conclusion he wants to reach. His reasoning is circular, ending by restating his assumption — only in a way that sounds different and profound.

Space-time models

An event is something that happens at a precise location and time. In Albert Einstein’s theories of relativity, space-time is a four-dimensional model describing all such occurrences: each point is a particular event, and the continuous sequence of events associated with an object forms its worldline — its path through space and time.

But events don’t exist; they happen. When physicists and philosophers speak of space-time as something that exists, they’re treating events as existent things — the same subtle fallacy at the root of 25 centuries of confusion.

Cosmology — the study of the whole universe — offers a clear resolution.

It describes a three-dimensional universe filled with stars, planets and galaxies that exist. And in the course of that existence, the locations of every particle at every instance are individual space-time events. As the universe exists, the events that happen moment by moment trace out worldlines in four-dimensional space-time — a geometric representation of everything that happens during that course of existence; a useful model, though not an existent thing.

The resolution

Resolving Augustine’s paradox — that time is something we innately understand but cannot describe — is simple once the source of confusion is identified.

Events — things that happen or occur — are not things that exist. Each time you step into the river is a unique event. It happens in the course of your existence and the river’s. You and the river exist; the moment you step into it happens.

Philosophers have agonized over time-travel paradoxes for more than a century, yet the basic concept rests on the same subtle error — something science fiction writer H.G. Wells introduced in the opening of The Time Machine.

In presenting his idea, the Time Traveller glides from describing three-dimensional objects, to objects that exist, to moments along a worldline — and finally to treating the worldline as something that exists.

That final step is precisely the moment the map is mistaken for the territory. Once the worldline, or indeed space-time, is imagined to exist, what’s to stop us from imagining that a traveller could move throughout it?

Occurrence and existence are two fundamentally distinct aspects of time: each essential to understanding it fully, but never to be conflated with the other.

Speaking and thinking of occurrences as things that exist has been the root of our confusion about time for millennia. Now consider time in light of this distinction. Think about the existing things around you, the familiar time-travel stories and the physics of space-time itself.

Once you recognize ours as an existing three-dimensional universe, full of existing things, and that events happen each moment in the course of that cosmic existence — mapping to space-time without being reality — everything aligns. Augustine’s paradox dissolves: time is no longer mysterious once occurrence and existence are separated.

Daryl Janzen, Observatory Manager and Instructor, Astronomy, University of Saskatchewan

This article is republished from The Conversation under a Creative Commons license.