On cosmic scales, humans are extremely fragile. Made of mostly water, our bodies are soft meat bags with surprisingly malleable minds, both of which are easily damaged in ways most difficult to heal.
And we don't live long.
Among other things, this means even our most advanced means of propulsion are incapable of transporting humans to other stars in a single lifetime. This is because even the closest stars (like Proxima Centauri) are unconscionably far away — so far that to reach them, we'd need colossal amounts of energy, and a ship capable of supporting human life for thousands of years as generations are born, live, and die in endless succession, like a master's thesis on existentialism.
However, there's a way around the pitfalls of human frailties, and the abyssal depths of time and space. For example, the idea of wormholes offers a theoretical gateway connecting any two points in space and time with one another, like a cosmic bridge.
Wormholes, like mass, warp the fabric of space-time
Also called an Einstein-Rosen bridge, a wormhole is a theoretical fold in space and time, creating an intersection of the fabric of space-time with itself, where one place and time is directly accessible to a totally different time and place.
Films like "Interstellar" in 2014 and "Event Horizon" in 1997 include the same apt analogy for wormholes: consider a piece of paper with a line drawn between two points, then folded over so the points touch. Put simply, traversing a wormhole is like pushing your pen through the paper, from A to B, in one smooth motion.
The words come easy, but the physics don't. When Einstein introduced his theory of General Relativity, he showed the world how — unlike magnetic forces, which pull and repel matter — gravity actually warps the fabric of space-time. This has bizarre effects on bodies in space.
For example, if the Earth and sun were invisible, an astronaut on the moon might think it moves in a straight line, while it actually follows a curve under the sway of gravitational attraction from the Earth's mass — which warps the fabric of space-time.
The holes in wormhole theories
It was Einstein and another physicist, Nathan Rosen, who proposed the possibility of tangling space-time so tightly that two points shared the same location, while also remaining distant, according to the "linear" path (just like how the line between A and B on a piece of paper is still there, even after you fold it to touch both points). If we climbed into the gravitational well of one side of a wormhole, we'd find ourselves in the other location — millions or billions of light-years away from where we started.
While wormholes are theoretically possible, for a long time, engineering their creation faced too many challenges to seem feasible. They include gravitational collapse, and the possibility for ordinary matter plugging the bottleneck section of the wormhole — preventing all transit from one aperture to the other.
Some physicists suspect exotic matter might help pry these stellar stargates open, but a recent study published in the journal Physical Review Letters suggested a way to keep wormholes open for traffic without exotic matter. The team of researchers — from the Complutense University of Madrid — argued that thinking of matter as if it were composed of fermions could open a new window into wormhole theory, and the idea of traversing them.
Wormholes connect two points in space and time
Changing the mass and charge of fermions could create a traversable wormhole, according to study author Jose Luis Blázquez-Salcedo. Most crucially, the maximum force of acceleration wouldn't exceed 20g (or 20 times Earth's sea-level gravity). This means humans could potentially survive the physical perils of a near-instant trip across interstellar space. But there's a catch. It can only work if the total mass inside the wormhole is larger than a much bigger theoretical limit — determined by black holes. Additionally, such wormholes could be microscopic — far too small for any human. But, lucky for us, another study (also) published in the journal Physical Review Letters suggested it's possible to create wormholes large enough for humans and their starship.
"From the outside they resemble intermediate mass charged black holes. Their big size comes from demanding that a human traveler can survive the tidal forces," according to the second study. "They take a very short proper time to traverse, but a long time as seen from the outside."
In other words, while a wormhole traveler may experience less than a second of elapsed transit time, if they then turned back and went home, they might be dismayed to learn that thousands of years had passed, and everyone they'd ever known was long dead.
The fabric of space-time can collapse or expand at any speed
As yet, no one is drawing up plans for a vessel capable of ferrying humans to-and-fro on either side of an intergalactic wormhole, which is a bummer. Obviously, folding the fabric of space-time enough to make it intersect with another point in space and time is beyond present-day technological capabilities, but there exist ways of avoiding the long wait of rocket-propelled travel between the stars.
Recent research into faster-than-light travel conceived a new kind of hyper-fast "solitons" using sources only reliant on net-positive charges — enabling travel at any speed. Solitons are "warp bubbles" — compact waves in space-time that retain their shape at a constant velocity. Instead of trying to move physical objects (like people, or ships) past the speed of light — which would encounter several problematic paradoxes — we could theoretically move the soliton warp bubble, since the fabric of space-time itself can expand or contract at any speed.
It is paradoxical to travel through space. Commonsense ideas about motion can have bizarre and counter-intuitive consequences, especially when we think about modifying the fabric of space-time enough to create a wormhole. But on the cosmic scale of the universe, going anywhere interesting means traversing unimaginable distances — where cosmic forces we experience as constants on Earth can reach monstrous heights, challenging our preconceptions of reality.