Harvard professor says humans could reach the Milky Way's center in just 10 years. Here's how

Wormholes—hypothetical tunnels through space-time—have been a staple of space-centric science fiction, and were perhaps most famously represented in the film Interstellar (2014), where the crew used a wormhole to traverse an unimaginably vast distance through space. While fascinating, the unfortunate truth is that wormholes remain purely theoretical objects and astronomers have yet to find any evidence that usable wormholes exist. As Harvard astrophysicist Avi Loeb points out, wormholes would require exotic matter or negative mass to keep them open, barring which they would instantly collapse.

So, does the absence of wormholes make long-distance space travel, such as exploring the Milky Way galaxy, an impossibility for humans? Not quite. The laws of physics already provide a real and scientifically sound mechanism for humans to traverse impossibly vast distances in a decade or so, and Loeb highlights precisely that in a recent blog post.

A major obstacle to humans travelling vast distances through space is our physiology. In zero gravity, astronauts lose about 1-2% of their bone density every month, making super long-distance space travel a technical death sentence. However, this can be worked around, argues Loeb, by constructing a spacecraft that can continuously accelerate at 1g or 9.81 m/s^2. This would enable astronauts inside the spacecraft to experience the same gravitational pull we feel on Earth's surface, and this artificial gravity would preserve bone density and human health throughout long journeys.

In addition to helping astronauts maintain their health, a spacecraft accelerating at 1g would also be able to reach astonishing speeds, and would be able to travel close to the speed of light within a year.

The center of our galaxy, the Milky Way, lies a whopping 26,000 light-years away from Earth, meaning that it would take millennia to reach even at the cosmic speed limit. However, thanks to a phenomenon called time dilation that stems from Albert Einstein's theory of relativity, such a journey could take just decades.

As the accelerating spacecraft approaches the speed of light, time would tick considerably slower inside the ship relative to clocks back on Earth. In simple terms, while the actual journey to the galactic core of the Milky Way would indeed take 26,000 years or more for observers on Earth, for the astronauts inside the ship, it would take roughly 10.6 years with constant acceleration—comfortably achievable within a human lifespan, says Loeb. In fact, even if the astronauts onboard our hypothetical spacecraft decided to decelerate for half of the trip, a journey to the galactic center would take just 19.8 years, he adds.

The aforementioned idea does not break any laws of physics, and works on paper, but actually engineering a ship capable of constant 1g acceleration is where the hurdle lies. Sustaining such acceleration all the way to the core of the Milky Way would require an unimaginable amount of energy—55,000 times larger than the rest-mass equivalent of the payload. Loeb says that for a human with a hypothetical body mass of 150 kgs, energy requirements would be as much as the total energy stored in the global nuclear arsenal today.

If that weren't all, actually engineering such a spacecraft would add more obstacles. Not only would engineers need to figure out a way to produce enough energy to propel the mass of the ship, crew, and fuel, but they would also need to figure out a way to shield the crew from the extreme radiation that they would be subject to while travelling at near-light speeds.

But could we, or another advanced civilization, potentially overcome these extreme energy barriers? Loeb suggests that it is possible, but not through conventional means. Making such a spacecraft would require mysterious or exotic matter with negative mass—if engineers can pair normal mass with an equal amount of negative mass, the spacecraft's total mass would effectively be zero, thereby drastically reducing the energy required for acceleration.

While humans don't have access to such matter or technology, Loeb suggests that it's unlikely that we're the universe's best engineers, given its vastness and age. Therefore, an encounter with an advanced extraterrestrial civilization could help us bridge this knowledge gap—"In our first encounter with interstellar travelers, we can ask them for path length and duration of their journey. These two numbers would immediately educate us whether they solved the engineering challenges facing a decade-long travel of a spacecraft with a positive mass through the Milky-Way. Otherwise, they might have mastered the production of a negative mass," writes the Harvard astrophysicist.