Even Orion won’t represent the peak of our speed potential, though. “There is no real practical limit to how fast we can travel, other than the speed of light,” says Bray. Light zips along at about a billion kilometres per hour. Can we hope to safely bridge the gap from 40,000kph to those speeds?

Surprisingly, speed – defined as a rate of motion – in of itself is not at all a problem for us physically, so long as it’s relatively constant and in one direction. Therefore, humans should – in theory – be able to travel at rates just short of the “Universe’s speed limit”: the speed of light.

But assuming we can overcome the considerable technological obstacles in building faster spacecraft, our fragile, mostly-water bodies will have to contend with significant new hazards that come with such high-speed travel. Speculative dangers could arise, too, if humans achieve faster-than-light travel, either by exploiting loopholes in known physics or through paradigm-shattering discoveries.

Withstanding G-forces



However we attain speeds in excess of 40,000kph, we will have to ramp up to (and down from) them patiently. Rapid acceleration and deceleration can be lethal to the human organism: witness the bodily trauma in car crashes as we go from a mere tens-of-kilometres-per-hour clip to zero in the span of seconds. The reason? A property of the Universe known as inertia, whereby any object with mass resists change to its state of motion. The concept is famously expressed in Newton’s first law of motion as “an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an outside force”.

“For the human body, constant is good,” explains Bray. “It’s acceleration we have to worry about.”