What is time anyway?

That’s a question that has been debated for thousands of years. Philosophers, in particular, have put deep thought into this subject.

At its most basic, time is a way to measure duration—how long something takes. For example, it takes me five hours from where I live to reach the beach, but just one hour to be in the Appalachian Mountains.

Time and Movement

Most of the time, we experience time through movement. One Greek philosopher argued that if nothing moves, then there is no time. You could say that time is a consequence of a process—but isn’t it also the enabler of one?

Time and Perception

Time also has a perceptual aspect. We perceive the duration of events differently depending on our mood, focus, and level of interest. That means we all live with a personal sense of time.

But that’s not true for objects. The moon doesn’t perceive time. It simply moves through space at a consistent velocity, unaffected by feelings or awareness.

Time in Science and Theory

Time is relative—dependent on speed, gravity, and, once again, on motion. Albert Einstein postulated this in his theory of relativity, which has since been proven. The movie Interstellar is based on these ideas, as is Planet of the Apes in a more imaginative way.

Voices on Time: A Compilation of Quotes

Here’s a collection of quotes that explore time from different angles—philosophical, scientific, and even humorous. If you have a favorite to add, feel free to share it with me!

“Neither does time exist without change.”— Aristotle, Physics, Book IV, Chapter 11, 218b (~350 B.C.E.)

“Time is the number of motion (change) in respect of before and after.”— Aristotle, Physics, Book IV, Chapter 11, 219b

“So it is in you, my mind, that I measure periods of time...Who will lay hold on the human heart to make it still, so that I can see how eternity, in which there is neither future nor past, stands still and dictates future and past times? Can my mind have the strength for this?”— *Augustine of Hippo, The Confessions

“If nothing passed away, there is no past, and if nothing arrives, there is no future, and if nothing existed there would be no present time.”— Augustine of Hippo, The Confessions (4th century CE)

“Time is composed of atoms—that is to say, of many parts that cannot be subdivided, on account of their short duration.”— Maimonides, The Guide for the Perplexed, I.73 (~12th century CE)

“Absolute, true, and mathematical time, in and of itself and of its own nature,without reference to anything external, flows uniformly.”— Isaac Newton, Philosophiae Naturalis Principia Mathematica (1687)

“The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”— Stephen Hawking (1991)

“It seems there is a chronology protection agency, which prevents the appearance of closed timelike curves and so makes the universe safe for historians.”— Stephen Hawking, Physical Review (1992)

“I have experimental evidence that time travel is not possible. I gave a party for time-travelers, but I didn’t send out the invitations until after the party. I sat there a long time, but no one came.”— Stephen Hawking, Seattle Science Festival (2012)

“If nothing happened, if nothing changed, time would stop. For time is nothing but change. It is change we see occurring all around us, not time. In fact, time doesn’t exist.”— Julian Barbour, The End of Time (1999)

“Space and time emerge from the laws rather than providing an arena in which things happen.”— *Lee Smolin, The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next (2006)

Books to Read (in no particular order)

If you're curious to explore more, here are just a few books worth checking out:

• The Order of Time by Carlo Rovelli

• From Eternity to Here by Sean Carroll

• A Brief History of Time by Stephen Hawking

  
  

Final Thoughts

Time surrounds us, shapes us, and often escapes our grasp. Whether it’s a measure, an illusion, or something still beyond our comprehension, it continues to fascinate and challenge us.

What does time mean to you?