Could humans really zoom through space at the speed of light?

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Dec 3, 2017

If Homo sapiens are ever going to be an interplanetary species, boldly going where no one has gone before means we’re going to have to figure out a way to at least come close to the cosmic speed limit of 186,000 miles per second—the speed of light.

Physics has something to say about it. In his theory of special relativity, which revolves around the idea that the speed of light stays constant no matter how fast you move in relation to the light you’re chasing, Einstein stated that the obstacles standing between us and light-speed travel were the relativity of time and the energy needed to propel an object through space, which would keep increasing the further it was headed (and increasing infinitely if it had no destination). The fact that time does not have a steady rate sounds like something out of Doctor Who, but Einstein said it, so your argument is invalid. Time is relative to how fast you’re moving in space. Meaning, it can accelerate or decelerate with you depending on how fast you’re shooting through space compared to something else. Enter the phenomenon otherwise known as time dilation.

This would get even more sci-fi if you hypothetically reached the speed of light and time just stopped, but we’re not there yet. We can at least imagine what would happen. If an astronaut were able to physically handle traveling at light speed (more on that later) and blasted off to Proxima Centauri, our nearest neighboring star at 4.25 light-years away, much less time would elapse for the astronaut than everyone back on the home planet. The astronaut will have aged much less than other Earthlings upon touching down.

So we can’t send projectiles through space at the speed of light yet, but would the human body even survive such a thrill ride? The fastest anyone has ever rocketed through the cosmos was when the capsule of NASA’s Apollo 10 mission reached a staggering 24,790 mph relative to Earth. When the space agency launches Orion in 2021, the spacecraft could break even that record. It would take more to break us.

Humans wouldn’t be able to handle a vehicle that went from zero to light speed at once. Inertia, the force responsible for objects with mass resisting changes in motion, would make that lethal. Newton told us so in his first law of motion. G-force could also kill you before you made it out of the solar system, never mind Proxima Centauri. Accelerative force upon a mass is measured in gravitational or G-forces, with one G being the equivalent of the pull of Earth’s gravity (at sea level) toward its center at 9.8 meters per second squared. Vertical G-forces from negative acceleration will send blood rushing to your head, and vice versa. Most people can only handle about 5 Gs before dangerous things start happening. The human body can take more for short periods, especially in a high-tech high-G suit, but it isn’t exactly advisable for someone who hasn’t been through intense pilot or astronaut training.

You shouldn’t lose sleep over potential death by G-force, because unless you really are a pilot or an astronaut, the rest of us won’t be subjected to speeds where that would be a real hazard until people are regularly taking off to exoplanets.

Proxima Centauri, the final (or at least next) frontier. Credit: NASA

We still haven’t figured that one out. Spaceships could someday accomplish that through nuclear fission, fusion or the most out-there theoretical tech of all, antimatter annihilation. Nuclear fission already happens in nuclear reactors and will be needed to turn H2O into viable rocket fuel if we someday want to live in pods on Mars. Nuclear fusion, the same reaction of atoms fused into heavier atoms that keeps the sun blazing, hasn’t yet been figured out in terms of revving up spacecraft to warp speed. Antimatter annihilation involves matter and antimatter molecules crashing into each other head-on to release a blast of energy. It has been done on a nano scale, but is nowhere near powering a rocket.

So are we really being held back by our inability to reach the speed of light? For now, but remember that technologies we thought were impossible even several decades ago have come into being sooner than humanity ever thought they would. That could be both exhilarating and terrifying.

(via NBC Mach)