Everything Exists at Once: Past, Present, and Future
By: Ella Alderson
Tags: Physics, Space, Time, Astronomy, Universe

“Time” is the most commonly used noun in the English language. The word itself is so versatile: we can kill time, do time, save it and spend it. Time even takes on a medicinal role when it comes to healing both physical and emotional wounds. Most of us wish we had more of it, and yet time persists both as an object of value and an enemy of every person on Earth. It is, eventually, the thing which kills all of us. And yet for all its pervasiveness in our everyday conversations, describing what time is doesn’t come easily.

Thinking of it in a common sense sort of way, one would imagine a universal clock which ticks at the same rate at all times and for all people. One second passing for me is also a second which passes for you and for every other person on this world or on any other. It is an event outside of our control, simply a characteristic of the universe like gravity or light. We experience it as a sweeping movement from the past and into the future, carrying us with it and leaving us helpless to do anything about it. The most unsettling part of time is also its most refreshing: the future unfolding before us, dictated by our actions and by an unpredictability than can bring both great or terrible happenings our way. But that part of our lives hasn’t yet been written.

Except it might’ve. The future might already exist and those three ways we separate time — past, present, and future — are nothing more than an illusion created by our minds.

This is the picture of the universe that emerged from Einstein’s theory of relativity. Unlike the universal clock imagined by Newton, relativity gives us time as a very individual experience. A second for me isn’t the same second that you experience. In fact, events don’t even have to unfold in the same order for two observers in the universe. Whereas you might see a fish taken out of its tank, killed, and cooked, in a different part of the universe someone might witness the dead fish taken out of the pan, brought back to life, and placed into its murky tank. How events play out depends on the reference point of the individual.

This is possible because of the relationship between space, time, and motion. To give an example from everyday life, think of where you are right now. You are in your bedroom at 7 PM. You are on the bus at 11:53 AM. You are in a restaurant at 3:40 PM. You cannot have one without the other. That is, you will never be at a place without a time or exist at a time without also being someplace.

Relativity merges space and time into a single fourth-dimensional structure known as spacetime. We should think of time the same way we think of space; just as all of space exists outside of our world and any point within space can be described by coordinates, all of time exists as well and any events that have happened or will happen already exist, described by their own coordinates within the universe. And the same way all coordinates in space are valid, all coordinates (or events) in time are valid as well, meaning that there should be no such distinctions as “past”, “present,” or “future”. The universe and life within it is not an organic thing that’s constantly changing and morphing. Instead it’s like a video where the present moment is merely a frame within that video. And that video, had we access to it, would reveal every event to ever take place in our universe, from beginning to end. This cosmos is known as the “block universe”, a place where change isn’t real and there’s nothing special about the present moment. Considering this on a philosophical scale brings into question the idea of free will.

The most accurate measurement of time is taken using the frequency of cesium atoms. 9,192,631,770 oscillations of this atom is equal to exactly 1 second. Image of URWERK AMC Atomic Master Clock.

But there’s another important relationship here: that of time and motion.

The Hafele-Keating experiment of 1971 proved that relativity was real. Atomic clocks were taken aboard a commercial airline by two scientists — J. C. Hafele and R. E. Keating — and the clocks were flown around the world, once to the East and once to the West. Upon returning, the clocks from the airline were compared to those which had stayed at the observatory in Washington. The airline clocks were found to have gained .15 microseconds. Modern experiments since then have continued to prove this aspect of relativity time and time again.

The discrepancy between the two sets of clocks is due to time dilation. In simple terms, time dilation is the relationship between a moving object (in experiments they’ve witnessed this effect with muons and photons) and how quickly time will move for that object. The faster the speed of the object, the slower time passes for it. If you left home to board a spaceship in the year 2000 and the spaceship went at 99% the speed of light for 5 years, when you came back the year on Earth wouldn’t be 2005, it would be be 2036. And yet you’d only be 5 years older than when you left. Meaning that, yes, you’ll have travelled into the future 31 years. In this way, when an object is standing still, all of its motion is through time. It’s only when the object begins to move that its motion is now shared between time and space — the more motion through time, the less it has through space and vice versa.

This is important because going back to the example of the video, one would believe that any observers can agree on what happens on any given frame — that is, any given moment. But this changes because of the relationship between time and motion. For an observer who’s moving, what’s happening in the frame will be different than for an observer that’s standing still. Movement gives the person a different rate of time and thus a different perception of the frame and what’s happening within it. While relativity happens on Earth all the time, the differences are so small that they’re imperceptible. However, if two observers are separated by enough distance (say tens of billions of lightyears) their movement can change their perception of the frame to include events in our past or in our future. But if this is true and our future or our past can be part of the perception of another observer, that must lead us to the conclusion that both these things already exist. The future is not unfolding and the past is not inaccessible.

This moment — this “now” — and the constant ticking of the clock, ever passing and ever fluid, sending us toward a mysterious future might only be in our heads. An impression created by our brains.

Gravity is another factor which also affects the passage of time. Miller’s planet, from the movie “Interstellar”, existed on the cusp of a black hole. Because of the black hole’s immense gravity and speed, an hour on the planet was equal to 7 years back on Earth. Image from “Interstellar”.

But that doesn’t explain why we observe a clear direction to time. It goes from the past and into the future, even though the laws of physics don’t prevent events from going the other way. This “arrow of time” is one of the greatest mysteries of our universe. It’s believed this directionality has to do with entropy (the amount of disorder in our universe, to boil it down to a quick definition) and the idea that entropy must always increase. It’s a fundamental law present since the Big Bang and one which seems to simply be an initial condition of the universe, continuing its course ever since that iconic explosion 13.8 billion years ago. But there are experiments that dispute the idea that entropy is the reason time flows forward.

The idea of a universe in which all events exist simultaneously is both a grim and a comforting one: things and people which we’ve lost aren’t gone, merely a little out of our reach at the moment. But it also means we might not have as much say in the future as we hope. Of the many things we can do with time, it seems there is one which we haven’t yet managed: to understand it.