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PhysicsNut

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Posts posted by PhysicsNut

  1. So, at how many light years r does the number of photons per cm^2 drop low enough that the star will only appear intermittently to the observer due to photon sparsity?

     

    At 500 million light years a photon would hit every cm^2 every 50 seconds, that should be enough for the star to appear intermittently, sadly i don't have much of an idea how many cm^2 are in the average human eye (i forget how large a cm is -_-)

  2. One Watt of visible-light photons comprises of order 10^18 photons arriving per second. Our sun puts out a total power of more than 10^26 Watts, so that's 10^44 photons/sec if all of the light were in the visible spectrum. A light year is 10^18 cm, so a sphere of that radius has a surface area of ~10^37 cm^2. At a light year, you have ten million photons per cm^2 per second arriving from a sun-like star. That number drops off as r^2, assuming no attenuation.

     

    Oh wow, ok, thank you! that explain everything.

  3. Thank you for the answer.

     

    I have another question on the same basis, as light from the start reaches Earth every person on that side of the Earth can see it simultaneously, but for that to happen would the light have to hit every point on that side of the Earth including people's eyes, but how would that happen? Are photons being emitted at such an unimaginable rate that they hit every point on a very distant planet such as Earth at almost the same time so every person sees pretty much the same image?

  4. I am wondering how does light from a distant star constantly reach Earth? the surface area of the star is far smaller than the surface area of a sphere that has a radius that's the distance between the star and Earth, so incoming light from the star should rarely hit any points in space on or near Earth.

     

     

    There is probably a very simple explanation to this which will make my question seem silly since my knowledge of Physics is pretty minimal at the moment.

     

    EDIT: there is obviously something important about light that i don't know because when the light from the star reaches Earth it would also have to hit every point on Earth that can be directly reached from the light's incoming position so people can see it (because it has to hit people's eyes)

  5. Has any (small) vehicle actually been used to test whether it can accelerate faster than the speed of light? I'm sure many observations have been made of particles launched with high amount of force, but I'm talking about a vehicle that can move through interstellar space at high speed, stabilize, and then accelerate again and again, etc. until it nears C without impinging electric fields, etc. to contend with.

     

    As someone already said light doesn't accelerate, but if you are asking whether a vehicle can accelerate to speeds faster than the speed of light, then by simply accelerating no, because photons don't have any mass and so nothing can travel faster than them, but theoretically a vehicle can travel faster than the speed of light if it bends time in front of it and behind it.

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