Physicists Don’t Know Exactly What Time Is. However, They Suspect That It’s an Illusion

“Space and time are so fundamental that we can talk about them without ever identifying with the utmost precision what they really are. We could compare space to a set of dominoes, glue them together on a plane, and then place another similarly constructed plane on top of them. Of course, space isn't like that, but this analogy may help us understand its nature somehow.”

“In any case, we can first try to understand the relationship between space and time. If we have a flat space with two ants in it, we can draw them at one moment in time, and then at a later moment, we can draw a plane over it with the same two ants but in different positions. In this way, we could build a kind of sandwich in which space runs in the horizontal direction of my drawing, and time runs in the vertical direction.”

“But what we've just done is more than a drawing. Since the late 19th century and culminating with [Albert] Einstein’s work in 1905 (the special theory of relativity), we know that something extraordinary relates to space and time: a maximum speed. You cannot go faster than the speed of light.” This is how the prestigious Spanish particle physicist Álvaro de Rújula explained the relationship between space and time to me. Still, the most exciting idea from his words is that, in reality, physicists don’t really know what these concepts are.

The Reconciliation of General Relativity and Quantum Mechanics Will Enlighten Us

Theoretical physicists have been flirting with unifying general relativity and quantum mechanics for over a century—practically since the two branches of physics first saw the light in the early 20th century. General relativity describes gravitational phenomena as the result of the interaction of objects with mass and the space-time continuum. Quantum mechanics, on the other hand, studies the behavior of nature at the scale of subatomic particles.

It takes work to reconcile the description of the very large and the very small. In fact, if it were not so difficult, theoretical physicists would probably have achieved their goal by now. After all, many of them have been trying for decades. Most physicists agree that when science establishes a theory of everything that can prove its robustness, they’ll probably understand the nature of time better than they do now. Anyway, Einstein’s theories of special relativity (1905) and general relativity (1915) reveal two fundamental features of time.

The first is that it depends on the observer’s velocity. If two observers, one motionless and the other in motion, observe the same phenomenon, such as, for example, a lightning strike, they won’t perceive it simultaneously. The second characteristic of time is that it depends on the strength of the gravitational field. Time doesn’t pass with the same rhythm at our feet and heads when upright. It passes more slowly at our feet because the earth’s gravitational field is more intense at the points closer to our planet's center of gravity.

Physicists have experimentally verified these two features on countless occasions. Nevertheless, as Casas explains in the wonderful article he published in The Conversation, the most reasonable thing to do now is to accept that the passage of time is probably an illusion—a collective hallucination. 

Our perception invites us to observe it as a sequence of events that runs unchangingly and in a single direction. Forward. However, the laws of physics don’t support this observation. They don’t say that time moves from the past to the future. One day, we'll hopefully have a theory of everything one day to help us understand this concept better. Fingers crossed.

Image | Jordan Benton

More info | The Conversation

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