While some scientists are working on personal cloaking devices to hide individual humans from one another or from alien invaders, two astronomers have proposed a way to hide the entire planet Earth from alien detection using lasers. Which ones would you send your crowd-funding money to?
Columbia University astronomers David Kipping and Alex Teachey expose the details of their planetary cloaking device in the Monthly Notices of the Royal Astronomical Society. Their idea is based on the theory that alien civilizations are searching for us much the same way we’re searching for them – by looking for a dark spot in the light of a star when a planet passes in front of it. These so-called “transits” are the patterns detected by our own Kepler Mission in its quest to find new exoplanets. A planet’s “transit” would show that it’s in the “habitable zone” where temperatures, radiation, atmospheric conditions and water levels make it suitable for life.
To cloak the entire planet, Kipping and Teachey propose hiding Earth’s telltale transit spot from alien watchers by emitting a continuous 30 MW (megawatt) laser for about 10 hours annually. That’s not much energy – it’s the same as the energy collected by the International Space Station in a year – and would only block visible light. To create a laser beam that hid all wavelengths, called a chromatic cloak, a large array of tunable lasers needing 250 MW of power would be required, according to Alex Teachey.
Alternatively, we could cloak only the atmospheric signatures associated with biological activity, such as oxygen, which is achievable with a peak laser power of just 160 kW per transit. To another civilisation, this should make the Earth appear as if life never took hold on our world.
Wait just a have-you-thought-this-through minute, you and Stephen Hawking shout. Wouldn’t a truly advanced and possibly evil civilization be able to determine this is artificial light and decide Earth is an inhabited planet suitable for invading? Kipping thinks we might to do this intentionally.
There is an ongoing debate as to whether we should advertise ourselves or hide from advanced civilisations potentially living on planets elsewhere in the Galaxy. Our work offers humanity a choice, at least for transit events, and we should think about what we want to do.
How do we know aliens aren’t cloaking their own planets from us using this same technique? Good point, say the authors. We should be looking for signs of artificial transits too.
While we’re waiting for this cloaking technology to be available, maybe we can connivance everyone on Earth to stand outside for a few hours with laser pointers aimed skyward. Sounds like a great new New Year’s Eve tradition.