Tim
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 Nov 30 awarded Enlightened Nov 30 awarded Nice Answer Jul 21 awarded Yearling Aug 8 comment How can a laser pointer have range of several kilometers in atmosphere? You're right, I had some things mixed up. But I fail to see why this does not apply to coherent light. Even laser beams diverge (slightly) and thus decay with $1/r^2$. Aug 8 comment How can a laser pointer have range of several kilometers in atmosphere? In a vacuum (which space is not), light travels more or less uninterruptedly. But because of non-zero divergence of any beam, the 'brightness' will slowly go to zero. Aug 8 answered How can a laser pointer have range of several kilometers in atmosphere? Aug 8 comment How can a laser pointer have range of several kilometers in atmosphere? As far as I know that's not correct, only beams that illuminate the whole unit sphere ($4\pi$ steradian) lose 'intensity' with $1/r^2$. The difference is in the divergence of the beams, the more convergent the beams are, the less they lose 'intensity' ('intensity' is a bit tricky here because there are various units that can be used). Jul 29 revised Could a human run horizontally inside a Wall of Death? typeset math using  Jul 29 suggested approved edit on Could a human run horizontally inside a Wall of Death? Jul 28 comment Roughly how many atoms thick is the layer of graphite left by a pencil writing on paper? I don't claim this is an accurate answer, the weakest part is very probably the maximum surface a pencil can write. I couldn't find any better estimates that quickly, so I settled for this. This answer is more about the method than the actual answer, with better data you can easily update the estimate. Jul 26 answered Roughly how many atoms thick is the layer of graphite left by a pencil writing on paper? Jul 25 answered Finding the max height of a ball launched as a projectile using work-energy Jul 25 comment number of electrons my laptop uses in a second Also note that the input electricity is AC, so the number of electrons passing through any circuit is time-variable. Jul 25 answered Maximal Gravity Jul 22 comment Light Energy Absorption In Mirror 1) this lacks necessary detail to solve the question, 2) this sounds somewhat like homework... Jul 21 awarded Supporter Jul 21 answered Projecting image without manual focussing Jul 21 awarded Editor Jul 21 revised Is apparent horizon curvature lesser due to refraction of light in the atmosphere? clarification Jul 21 comment Is apparent horizon curvature lesser due to refraction of light in the atmosphere? That's a somewhat more concise way of putting it, yes ;)