Astrophysics from Columbia University proposed a method that could reliably hide the Earth from alien's eyes. It is necessary to make it impossible to observe the planet when it passes in the background of the sun.
When the Earth crosses the disc of its native star, the visible brightness of the sun is reduced for a short time. Within knowledge about the direction of the point in space where the Earth can be monitored, people can deceive the aliens with the help of preventing the fall of the sun brightness.
According to the scientists, the mankind can mask the Earth in the optical range with the help of normal monochrome laser with power of 30 MW, just turning it on every year for about 10 hours.
Such value is comparable with the power of modern electric trains. "Invisibility cloak", which is able to hide a planet from all other wavelengths, needs the usage of reconfigurable lasers with a total capacity of 250 megawatts.
However, it is not necessary to hide the whole planet, if it is possible to hide the traces of biological activity in its atmosphere, for example high levels of oxygen.
According to scientists, for this purpose they will need a laser with a peak power of 160 kilowatts, and just turn that on at the time of the planet's transition on the background of the sun.
There is another application of such technology. Aliens may deliberately distort the star's luminosity level for outside observer when the planet passes on its background.
This intervention serves like a "beacon" for the search of extraterrestrial intelligence and also it can be a way of information transmitting. Astronomers offer to look such "beacons" in the SETI data archives.
The search for extraterrestrial intelligence (SETI) is a collective term for the scientific search for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other worlds.