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Diffraction limit determines the fundamental beam divergence angle theta = lamda/pi/D, where D is the beam diameter, lamda is wavelegth of elwctromagnetic radiation (eg. light). To minimize theta, we need to either increase D or decrease lamda. Lets assume we would be able to make far infrared high power lasers, at say 10,000 nm = 1e-5 m wavelength. Lets assume we would be able to make D, the diameter of our laser beam, similar to the diameter of a typical planet, for Earth it is ~13,000 km = 13e6 m. Theta = 1e-5 / 3.14 / 13e6 ~= 1e-13 radians. Sun is ~ 25,000 light years from the center of our galaxy, ~= 25e3 y 3e8 m/s 31.5e6 s/year ~= 1e20 m. Laser beam diameter, there far away, would be: 1e-13 *1e20 = 1e7 m, similar to the diameter of Earth, not much further diverged, focused and delivering the wast amount of energy all over the planet thereby evaporating it to a gas. Indeed, what you say about the melting far away planets is possible, in theory. |