“It’s neither possible nor survivable to travel near the speed of light relative to our good old Earth,” says Gerd Kortemeyer, emeritus associate professor of physics at Michigan State University. This is the sweeping declaration that sums up the titanic challenges for those who fantasize interstellar travel at near lightspeed speeds. The romance of near-light-speed travel, so picturesquely idealized in science fiction, runs into the brutal realities of physics and human physiology.
The speed of light, about 299,792,458 meters per second, is the cosmic speed limit. It’s not a number, but one of nature’s fundamental constants, which Kortemeyer describes. Even though massless particles such as photons move at this speed, anything with mass, including humans and their vehicles, encounter impossible obstacles. The amount of energy required to bring a 10-metric-ton vessel up to 99% of light-speed, for instance, is over 200 times the annual energy consumption of Earth, assuming the utopian condition of ideal fuel efficiency—a state contravening the second law of thermodynamics.
But the theoretical pursuit of such speeds is a tapestry of fascinating phenomena. Time dilation, according to Einstein’s special theory of relativity, states that time for passengers traveling at relativistic speeds would slow relative to Earth dwellers. That would imply starship crews could age but months as decades pass on Earth. The “Rip Van Winkle Experience” becomes reality as return travelers find their home planet beyond recognition.
But even if we did have the energy, there’s another obstacle, and that is the human body. Our Earth-conditioned physiology just can’t cope with the stresses of high-speed accelerations. The impact on g-forces is enormous. With constant accelerations required to approach near-light speed, blood supply can be cut off, causing G-induced loss of consciousness (G-LOC). Today’s pilot fighters, who wear G-suits and are used to withholding from Gs by fighting against them, can tolerate up to +9Gz, but forces needed for sustained interstellar travel are several orders of magnitude higher.
To this, the traversal of space at such velocities infects the interstellar medium with hostile conditions. Space is not empty; it contains particles in it, and at relativistic velocities, they are lethal projectiles. A piece of dust can strike a spacecraft with the intensity of a thermonuclear explosion. This requires tenacious shielding, and above the enormous energy and engineering achievements, there are also enormous technology handicaps.
The Large Hadron Collider (LHC) offers a glimpse of the boundaries of near-light-speed travel. It accelerates subatomic particles to 99.99999896% of the speed of light, exhibiting the energies at play. But these are not human-transport spaceships. The success of the LHC is to show the technologies needed to extrapolate such attainment to human transport.
In hypothetical engineering, hypotheticals such as the Bussard Ramjet and antimatter drive have been considered. Such hypotheticals, though thought-provoking, are confronted with daunting challenges. The Bussard Ramjet, for example, would need a scoop the size of a small moon to collect sufficient interstellar hydrogen to propel itself. Antimatter, having the highest energy density, possesses storage and production problems currently unovercomable.
Finally, the dream of near-light speed travel is a tempting blend of high science and science fiction. The obstacles are monumental, but the quest for this dream keeps pushing technology forward and our understanding of the cosmos. As we explore into these frontiers, we are forced to weigh the siren’s call of the stars against the cold hard realities of physics and human capability.
