Our closest star is Alpha Centauri is just 4.37 light-years away. Alpha Centauri is not just a star it is a solar system that contains three stars Rigil Kentaurus, Toliman and Proxima Centauri. Rigil Kentaurus is just like our sun a spectral class type G star. Toliman is a class K star orange to red color. Together they form a binary star system, Proxima Centauri is a small and faint red dwarf and is closest to our sun. Proxima Centauri has an Earth-like exoplanet in the habitable zone Proxima Centauri b. The planet was discovered in August 2016 by ESO Very large telescopes. It was discovered by the wobble method. Just like other planets orbiting red dwarfs Proxima b is tidily looked. It is the eternal day on one side of the planet and night on the other side. The planet does not transit its star and that makes it difficult to get any reliable information about the planet atmosphere and composition. But there is a chance that the planet has an ocean and an atmosphere. Red dwarfs are known to have deadly radiation that could have a negative effect on life.
As the star is just around the corner 4.2 light-years away could we travel to the planet and look for aliens? The New Horizons probe, which lifted off in 2006 on a mission to Pluto and the Kuiper Belt moves at a speed of 84000 km / h it will only take us 54 thousand years to reach Proxima b at that speed.
A research and engineering project using solar sail will be capable of making that journey in just twenty-five years. So how does solar sail works? The sails are being pushed by the massless particles in light called photons. Due to the wave-particle duality of quantum particles, light could be described both as particles and waves and particles have momentum. Even though a photon has zero rest mass, it has energy. This could be derived from the relativistic equation E2 = (mc2)2 +(pc)2 if the mass is zero then E = pc. Most people would recognize the equation where the momentum is zero as Einsteins most famous equation E = mc2
The photoelectric effect that Einstein got his Nobel prize for in 1921 is also based on this phenomena. Where light shining on some material it will cause emission electrons. This effect is proportional to the frequency of the light f=c/λ.
Where the energy is E=hc/λ and the momentum p =h/λ, where λ is the wavelength of the light and h is a universal constant called Planck's constant 6.62607004 × 10-34 m2 kg / s and c the speed of light in a vacuum.
By using very tiny nano craft that just weights a gram and the sails would be four meters wide but just a couple 100 atoms thick. By then using high energy lasers blasting a 100-gigawatt beam on one solar sail from earth could accelerate the craft up to 20% of light speed within an hour. In space, there is no friction so the craft will keep its speed for the rest of the journey to Proxima b
Breakthrough Starshot initiative is planning to send hundreds or even thousands of nano crafts. The technology is not developed yet and it is very difficult to make the sails hold. Russian billionaire Yuri Milner and other investors have paid $100 million to cover the first 10 years of development. So it is not just science fiction it could be possible in a near future.