What is Time?

Relativity, entropy, and the mystery behind a familiar illusion

Time is the invisible architecture of our lives. We organize entire civilizations around its pulse, yet it remains one of the universe’s deepest mysteries.

In everyday life, time feels rigid. It appears to flow forward at a steady pace. Minutes become hours, hours become years, and the past seems to fall away effortlessly. But modern physics tells a very different story.

According to Albert Einstein and his theory of General Relativity, time is not a universal clock ticking identically everywhere. Instead, it is woven together with space into a single, four-dimensional structure called spacetime.

Massive objects like planets, stars, and black holes warp this structure. This curvature does not only affect the path of light, it also changes how time passes. Gravity literally stretches time. If you spend a year orbiting a massive black hole while I stay on Earth, you would return to find that decades had passed for me, but only a few months for you. Your "now" and my "now" are only aligned when in proximity.

If time is a dimension, as the Block Universe theory suggests, then our perception of passing time might be a trick of the mind. A feature of human perception, rather than a physical law. In this model, the past hasn't vanished, and the future isn't a blank slate. Instead, every moment that has ever happened or will ever happen exists simultaneously in a four-dimensional structure. This suggests that while we feel we are drifting down a river, we might actually be standing still in a vast, ocean of events.

But why do we perceive that time only flows in one direction? Why can we remember the past, but not the future? In science, this is explained through entropy, the universal principle that systems tend to move from order to disorder. For example, a broken glass doesn’t spontaneously reassemble because there are countless ways for it to be broken, but only one way for it to be whole. This gradual increase in disorder gives the universe a direction, creating the 'arrow of time.'

Within that framework, we emerge as sophisticated entropy-processing machines. We record memories (low-entropy traces of what was) to navigate the uncertainty of what is to come (high-entropy). For our brains, this arrow is a filter, distilling the overwhelming complexity of a four-dimensional reality into a linear narrative we can inhabit. Without the forward motion of entropy, there would be no change. And without change, there would be no meaning.

https://www.youtube.com/watch?v=9gqGvOj8pfI