Laser is a high-energy coherent and extremely concentrated focused electromagnetic wave. But it will eventually pay remotely. I am not a green laser pointer expert by any means, but I think one of the reasons is that the beam itself consists of multiple wavelengths. There are countless wavelength starting points between any two consecutive peaks in the spectrum.
And each of these individual wavelengths also changes frequency from start to finish within itself, so regardless of the method of generating the initial laser frequency, made of ruby, emerald or other gemstones, the emitted wave will contain multiple wavelengths. And no matter how finely we perceive or measure it on the earth, the intermodulation between different wavelengths will eventually cause the light beam to lose its coherence.
But it will take several miles to achieve. 🙂 I don’t know what it is, but the amount of diffusion or expenditure that occurs between sending a laser pulse to the moon and receiving it should give some rough figures. And they should have been able to ignore the influence of the mirror itself.
It’s always a long time. The universe may exist forever, or it may not exist. If it exists forever, the extremely small probability of a given photon intercepting matter (which is very sparse in the universe) will continue to increase until such collisions become inevitable. If you literally mean eternity, the answer is no. If you mean “forever” on a human scale, yes. It is possible that the light will move on almost forever.
Think about the fog around you. Will the light stay away? Even if the weather is clear, your laser pointer beam will spread through small particles in the air. Your laser beam can go into space. There, he will not find too many items to be lost, and will stay longer. It will travel infinitely-as long as you keep your laser pointer on the earth.