You're moving forward through time at a rate of one second per second. Congratulations—you’re technically a time traveler! Sure, it's a bit lame compared to what we see in movies, but it’s a starting point. Let’s start here so we can eventually dive into the fun aspects of real time travel—like riding dinosaurs or high-fiving Einstein.
Time isn't something that just passes; it’s a dimension, a direction you can move in. Our universe is thought to be four-dimensional: three spatial dimensions and one time dimension, all combined into a fancy concept we call spacetime. What you experience as the passage of time and your life unfolding is actually you moving through the time dimension. But there's a catch: while you can move forward, backward, left, and right, up and down in the spatial dimensions, in the time dimension, you can only move forward. You only get older, never younger. You can’t make detours.
However, this is just an illusion—you actually have much more control over how you move through time. To understand how this really works without diving into a math lecture, we’re going to make a lot of physicists grumpy by simplifying and bending the truth a bit. So bear with me.
Here’s a strange rule: everything in our universe moves at the speed of light through four-dimensional spacetime. Your speed through spacetime is the sum of your speed through time and space. It’s impossible to stay perfectly still; even if you aren't moving through the spatial dimensions, you are still moving through time—rushing face-first into the future.
You can slow down your movement through time by moving faster through space, but no matter what, you’re always moving at the speed of light through spacetime. If you could somehow be perfectly still in space, you’d still be moving through time at the speed of light. Conversely, photons (light particles) move at the speed of light through space, but they don’t experience any time passing, as their speed through the time dimension is zero. From a photon's perspective, time is frozen—if a photon hits your eye, it seems like it was just on the Sun's surface a moment ago, with nothing happening in between.
Of course, we’re telling a simplified science story here. In reality, things are more complicated. For one, it’s impossible to truly stay still relative to space itself—you can only stay still relative to other objects. And technically, you can’t really define a reference frame for photons like we just did. If you want more details, check our sources. But for now, let’s get back to the story.
So, everything in the universe moves at the same breathtaking speed, but that speed is split between space and time. This leads to all sorts of interesting consequences, including real, observable time travel.
Imagine a bus driving past you. It’s moving a little faster through space than you are, so it moves slower through time compared to you. In other words, the bus experiences time slightly slower than you do. While this sounds like weird physics magic, it's pretty simple: move faster through space, and you go slower through time; move slower through space, and you go faster through time.
Now, let’s add another person who’s moving even faster or slower than you. You’d both end up traveling different distances in the time dimension. This brings us to a popular thought experiment: the "twin paradox." Imagine we force one of a pair of twins into a rocket and send them into space at super-fast speeds, while the other twin stays on Earth. Since the space-traveling twin is moving quickly through space, they move more slowly through time compared to their sibling. When the traveling twin returns to Earth, they’re younger than the twin who stayed behind—ready to start years of therapy for being abducted by theoretical physicists.
This makes sense within the universe's rules—it’s called "time dilation." Essentially, your position in time is subjective and only true for yourself. With a fast enough rocket, you could travel as far into the future as you’d like. In theory, you could witness the end of the universe or the final thing that will ever happen.
There’s also another way to leap forward in time: gravitational time dilation. Massive objects bend spacetime, causing time to slow down near them. On Earth, the effect is tiny—our planet’s gravity makes time pass about 0.000000007% slower than in deep space, which isn’t very useful for time travel. But it's a start. If you were near a really strong gravitational field, like the area around a black hole, time would pass much slower for you. If we send our twin near a black hole, they wouldn’t notice anything odd—their watch would tick as usual. But for someone watching from afar, the twin would seem to almost stand still. Only when they returned would they realize that time had passed differently for them.
So, we have a couple of ways to time travel into the future: moving really fast or being close to massive objects like black holes. But these options are pretty limited—especially since they mostly involve leaving everything behind, including everyone you know, forever.
But what if we want to travel backwards in time? Is there a loophole in the universe’s rules? The theory of relativity, which is one of our most solid scientific theories, doesn’t explicitly forbid faster-than-light motion. If you moved through the spatial dimension faster than the speed of light, you’d end up moving through the time dimension with negative speed—essentially traveling backward in time relative to the rest of the universe.
In theory, faster-than-light particles, called tachyons, could exist, and they’d have some wild properties—like getting faster as they lose energy and, of course, traveling backward in time. Scientists have looked for tachyons, but we don’t have any evidence that they actually exist. If tachyons were real, you could use them to interact with the past—maybe even send messages to your past self to change things that have already happened.
Unfortunately, there’s a big problem with this idea: anything that starts out slower than the speed of light can't reach the speed of light. The energy required to reach the speed of light is literally infinite. Even if you gathered all the energy in the universe, you couldn’t accelerate a grain of sand to the speed of light. You can get as close as you want, but you can never reach it. And, so far, we don't have any evidence that tachyons exist outside of theoretical calculations.
So, for now, it seems time travel to the past is strictly impossible. The past remains a far-off land that we can observe in pictures, movies, and memories, but we can’t return to it. While this might feel disappointing, it leaves us with the most important time: right now—the present. This moment is where you truly exist and where you have the power to shape your future. And that’s worth a lot.