When we look at the idea of time, it’s easy to imagine it as a flowing river we move through. But modern physics tells us something much stranger: time and space are inseparable. For example, astronauts who spend six months aboard the International Space Station return with their watches lagging behind Earth clocks by 0.01 seconds.

This tiny difference isn’t a mechanical flaw—it’s time itself behaving differently depending on how we move through space. From Zeno’s paradox in ancient Greece to Einstein’s relativity, humans have spent over two thousand years realizing that “time travel” is really about moving through a four-dimensional spacetime, not jumping across an abstract river of time.

Going to the past or future is really visiting a different space coordinate. Time is just another way of describing where we are in space, like latitude and longitude on Earth.

Physics Teaches Us: Paths in Spacetime Are Unified

Einstein’s special relativity in 1905 overturned Newton’s idea of absolute space and time. When an object moves at 0.8 times the speed of light, its length shrinks to 60% of its stationary size, and its time slows to 60% as well. This isn’t coincidence; it’s built into spacetime itself. Experiments with fast-moving muons at CERN confirm this: their lifetimes stretch by 300% when moving quickly, giving them “extra existence” in time as they travel further in space.

General relativity adds another layer: strong gravity curves space, bending time along with it. Near a black hole’s event horizon, one hour could equal seven years on Earth. This doesn’t mean time is slow—it’s that space itself is compressed into an extreme geometry, and time, as its companion dimension, stretches and shrinks naturally. Kip Thorne’s wormhole models even turn time travel into a spatial problem: passing through a tunnel connecting two points in spacetime could transport someone a kilometer in space while crossing a century in time.

Quantum experiments echo this unity. In the double-slit experiment, a photon’s “past path” changes based on future measurements, showing that time depends on space observations. In 2023, research on “quantum time crystals” revealed that atoms can vibrate in states representing both past and future, linking time uncertainty to spatial probability. The conclusion is clear: time isn’t independent—it’s a macroscopic expression of space’s quantum structure.

Practical Space Travel: Moving in Space Is Moving in Time

The most striking effects of interstellar travel come from moving across space itself. Traveling to Proxima Centauri, 4.2 light-years away, at 0.9 times light speed, astronauts experience only 2.3 years, while nine years pass on Earth. This real-life twin paradox shows that time differences come from distance and speed—not from “jumping through time.” Even Voyager 1’s atomic clock runs slightly faster than Earth clocks as it leaves the Sun’s gravity. We don’t need a “time machine”—just a change in spatial position.

Black holes and neutron stars act as natural “space-time converters.” Near a black hole, moving closer to the singularity also moves our time coordinate backward. Roy Kerr’s rotating black hole model suggests closed time-like curves may allow a traveler to circle a black hole and access their own past. Time travel is possible without breaking physics—just follow specific spatial paths, like walking along a meridian on Earth to change both space and time zones.

Observing the Universe Is Observing Time

Cosmic microwave background radiation offers proof of spacetime unity. Photons from 380,000 years after the universe’s birth carry information about early space. By observing radiation in different directions, we’re looking at slices of space from different times: one direction might reveal a nebula 13.8 billion years ago, another a galaxy cluster from 10 billion years ago. Observing the universe is, in essence, traveling through spacetime. Our gaze alone acts like a spaceship crossing the cosmos.

Philosophy and the Collapse of Linear Time

Philosophers like Heidegger described human existence as “unfolding in time,” but modern physics shows this unfolding is also spatial. The past isn’t gone—it exists in space as “was,” and the future isn’t potential—it exists as “will be.” Bergson’s “duration” concept and other philosophical insights hint that time’s linearity is an illusion; reality is a continuous, inseparable mix of space and time. When astronauts observe time passing and distance traveled, they’re recording the same reality in two ways.

Looking Back from Orion

From the Orion arm of the galaxy, our distinctions between “time” and “space” feel tiny. When we finally build ships that cross light-years, going “back to the dinosaur age” might mean traveling to a star system 6,500 light-years away—where light from the Cretaceous era still lingers, waiting for us to arrive in space. The ultimate secret of time travel is simple: there is no independent river of time, only an ocean of space.

Every journey we take is a voyage through this spacetime sea. Understanding this will not only push interstellar travel forward but also reshape how we understand existence: past, present, and future coexist, waiting for us to explore through space itself.

Embrace Spacetime

Lykkers, the next time we gaze at the stars, let’s remember this: every journey through space is also a journey through time. Each step, each light-year we travel, takes us deeper into the universe’s mysteries. By thinking in terms of spacetime rather than a straight line of time, we can experience the cosmos—and ourselves—in a richer, more connected way.