Alien spaceships — when they come — will still be detectable at near-light speed

[Reefa]

The universe is an unfathomably big place, so there’s plenty of opportunity for intelligent life to evolve out there among the stars. Of course, with the universe being so gigantic, me might never get to meet these beings. Even at near the speed of light, it would take years to cross the gulf between stars. The good news, according to a pair of researchers at government contractor Raytheon, we’ll be able to see any aliens as they come our way at such amazing relativistic speeds.

Everything we know about physics and the workings of the universe tells us that nothing can match or exceed the speed of light. You can pour all the energy you want into accelerating a spacecraft, but it will always be a few fractions of a second behind a photon. This feat is still beyond our current technology, but the mathematics work. So could a more advanced civilization from a distant star come here at 99% the speed of light?

There wouldn’t be any planets or asteroids to get in the way of a spacecraft traveling in between stars. But it would interact with light and radiation in a way slower craft would not. This is the key to detecting very speedy travelers, according to the new paper by Ulvi Yurtsever and Steven Wilkinson at Raytheon.

As a spacecraft approaches relativistic speeds, it will begin interacting with photons in the cosmic microwave background (CMB) radiation. This is the energy left over from the Big Bang billions of years ago, and it’s everywhere. Every cubic centimeter of the universe contains somewhere north of 400 microwave-energy photons from the Big Bang. The ship would collide with a great deal of these particles moving at such speeds, which would produce drag that slows it down.

Assuming an alien ship has enough power to overcome this drag, how can we see it coming? According to the paper, the movement of a relativistic craft would cause a scattering pattern in the cosmic microwave background radiation. This frequency shift should be detectable on Earth with current astronomical instruments. Yurtsever and Wilkinson calculated that the disturbance would be in the terahertz-to-infrared region of the spectrum, and that this signal would appear to move as the spacecraft zipped through space.

There are still a lot of unanswered questions when it comes to relativistic space travel. While space is mostly empty — it is called space, after all — there is still the occasional speck of dust. At slower speeds, the dust is harmless. But at near the speed of light, a grain of it could be potentially deadly. It may also not be feasible to fight through the drag of the cosmic background radiation, making it more efficient to travel at slightly slower speeds that don’t produce the ripple effect described in the paper.

Of course, this all assumes there isn’t some science-fictional technology that allows for travel faster than the speed of light. If that’s possible, maybe the aliens are already here, and we’re just not smart enough to know it. If aliens come for a visit the old-fashioned way, though, we just might see them coming.

http://www.extremetech.com/extreme/202274-alien-spaceships-when-they-come-will-still-be-detectable-at-near-light-speed