4 ms·

Even if you could refocus all of the sun into a single direction, over stellar distances, wouldn't it have dispersed into nothing more than a bright star? What

Even if you could refocus all of the sun into a single direction, over stellar distances, wouldn't it have dispersed into nothing more than a bright star? What is the range of a putative Sol death ray?

naasking 3y ago
How would it disperse? There's little matter to disperse it over interstellar distances. Very little energy would be lost if it were properly focused.
hansvm 3y ago
"Dispersion" as I think you're describing is an artifact of the fact that most light sources radiate spherically, and more focused alternatives simply reflect the edges of that sphere to obtain some focus at larger distances, still radiating off in a 1/r^2 nature eventually. If you actually take every photon from Sol and point it in a single direction (think "LASER" rather than "mirrors"), the range is infinite, give-or-take the fact that you'll hit some objects on the way, and the intensity is on par with the intensity next to the surface of the sun.
- fbdab103 3y ago
  Even laser beams diverge, so that is where my intuition is headed. Plus the engineering implausibility of perfectly aligning every photon to go in the same direction.
  - hansvm 3y ago
    I see. If we're willing to suspend disbelief enough to say that we can focus a star in a direction, I think it's reasonable to assume we'll get the rest of the engineering "good enough." The only hard limits I'm aware of are the engineering (which we're ignoring), and diffraction (which is small, I'll touch on). Diffraction-limited lasers have a wavelength / diameter term in the mix, so the relative increase in beam diameter is miniscule at any reasonable scale (doubling at 650M light years, tripling at twice that, quadrupling at 3x that, and so on linearly). Surface power scales with the inverse of that squared. The engineering is pretty obviously going to be the dominant term. Even with some lasers we've already created (not to mention more exotic forms of wave propagation), dispersion (diameter) would be on the order of 750x at 1 light year, or ballpark 1.1e2 watts per square metre if I haven't screwed up too much arithmetic, contrasted with the 1.4e3 or so we experience on Earth when measured in a plane normal to the Sun and the roughly 6.3e7 you get on the surface of the sun and the roughly 5.6e4 where no matter your orientation if you didn't have protection or active cooling you couldn't prevent death by overheating just via sweating (that last threshold you hit from this hypothetical laser at 0.045 light years -- a small chunk of the way into the oort cloud). How much better will we get the engineering between now and then? Who knows, but the math in that regime is _almost_ linear, and if you halve the angle of dispersion you double the distances in question for a given power flux.

naasking 3y ago

How would it disperse? There's little matter to disperse it over interstellar distances. Very little energy would be lost if it were properly focused.

hansvm 3y ago

"Dispersion" as I think you're describing is an artifact of the fact that most light sources radiate spherically, and more focused alternatives simply reflect the edges of that sphere to obtain some focus at larger distances, still radiating off in a 1/r^2 nature eventually. If you actually take every photon from Sol and point it in a single direction (think "LASER" rather than "mirrors"), the range is infinite, give-or-take the fact that you'll hit some objects on the way, and the intensity is on par with the intensity next to the surface of the sun.

fbdab103 3y ago
Even laser beams diverge, so that is where my intuition is headed. Plus the engineering implausibility of perfectly aligning every photon to go in the same direction.
- hansvm 3y ago
  I see. If we're willing to suspend disbelief enough to say that we can focus a star in a direction, I think it's reasonable to assume we'll get the rest of the engineering "good enough." The only hard limits I'm aware of are the engineering (which we're ignoring), and diffraction (which is small, I'll touch on). Diffraction-limited lasers have a wavelength / diameter term in the mix, so the relative increase in beam diameter is miniscule at any reasonable scale (doubling at 650M light years, tripling at twice that, quadrupling at 3x that, and so on linearly). Surface power scales with the inverse of that squared. The engineering is pretty obviously going to be the dominant term. Even with some lasers we've already created (not to mention more exotic forms of wave propagation), dispersion (diameter) would be on the order of 750x at 1 light year, or ballpark 1.1e2 watts per square metre if I haven't screwed up too much arithmetic, contrasted with the 1.4e3 or so we experience on Earth when measured in a plane normal to the Sun and the roughly 6.3e7 you get on the surface of the sun and the roughly 5.6e4 where no matter your orientation if you didn't have protection or active cooling you couldn't prevent death by overheating just via sweating (that last threshold you hit from this hypothetical laser at 0.045 light years -- a small chunk of the way into the oort cloud). How much better will we get the engineering between now and then? Who knows, but the math in that regime is _almost_ linear, and if you halve the angle of dispersion you double the distances in question for a given power flux.