"Engage!" says Captain Jean Luc Picard and whoosh! the Enterprise engages its warp drive, all the stars get stretched as spacetime is compressed and the crew boldly go into the galactic unknown. Simple, right? Well, it probably won't come as a surprise to find that the science fiction version of traveling close to the speed of light isn't entirely... complete.
You know that "stretchy bright star" thing the Universe does when the Enterprise enters warp, or when the Millennium Falcon jumps to hyperspace? Well, it's wrong according to physicists at the University of Leicester.
A group of final year Masters students decided to understand what we would really see if we were to approach the speed of light. And far from the dramatic star trails, we'd actually see a blurred white blob in the direction we are headed. Why? Well, that comes down to some pretty fundamental physics as to how light works.
As our hypothetical starship rips through spacetime, any light from the stars ahead of us will be blueshifted. Like a police car with sirens blaring, it sounds high-pitched as the car approaches you and lower pitch as it moves away. This is known as Doppler shift - the sound waves (of the siren) are compressed as the car approaches and stretched as the car speeds away.
Electromagnetic radiation works in a similar way. The visible light emitted from the stars ahead becomes compressed as we speed forward. The wavelength gets shorter and shorter the more we accelerate. Very quickly, we'll see the light moved through the blue part of the visible light spectrum and then through the ultraviolet. The electromagnetic radiation from the stars no longer belongs in the visible spectrum, so our eyes can no longer detect the light. At close to the speed of light, the once-visible light (from our frame of reference) gets pushed into the X-ray part of the spectrum, making the galaxy ahead of us dark.
Forget all those psychedelic versions relativistic space travel, it's actually all gone dark and... well... dull.
But wait! This is the truly delicious part.
You know the primordial glow of the Big Bang that exists at the furthest-most reaches of the observable Cosmos? Suddenly the very faint electromagnetic radiation from the cosmic microwave background becomes really interesting.
Currently, only our most sensitive space observatories (such as NASA's Wilkinson Microwave Anisotropy Probe and ESA's Planck) can observe the faint radiation, measuring slight variations (or ‘anisotropies') in its distribution. But to any relativistic traveler, like the visible starlight that was blueshifted to X-rays, the cosmic microwave background radiation is blueshifted into visible light, creating a glowing disk of light in the direction of travel.
I can see it now:
"Engage!" says Captain Jean Luc Picard and whoosh! the starship engages its warp drive and the Enterprise's bridge rapidly goes dark. But as the starship accelerates, a foggy disk of white light gets brighter and brighter in the center of the screen, exposing the otherwise invisible background glow of the ancient Universe.
Image: What University of Leicester physics students suggest hyperspace travel would really look like. Credit: Univ. of Leicester