Let's imagine that we placed a cube with a side of 1 meter in the intergalactic space. How much energy in the form of electromagnetic waves will pass through a unit volume from all sources of radiation in one second?
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2 Answers
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Once you get away from bright, hot things like stars, the dominant radiation is the 2.7K cosmic background. That uniformly irradiates everything in a flux you may calculate using the Stefan-Boltzmann law. Your cube has a surface area of 6 square meters, and it's convex. For a convex object, the total projected surface area in all directions is just the surface area, so multiply the flux by $6\ m^2$ to get $\approx 19\ µJ$ per second.
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I think the author is trying to ask about the energy present in the space if it’s just an empty void I mean there’s nothing around it yes for surely if it is surrounded by some luminous object the energy passing through it would be flux dependent but I think here the author wants to ask as if what’s the zero energy field I mean we all know there are generation of virtual particles and anti particles which annihilate and form millions times in a million of seconds for example. We have geometry associated with it how to space is being curved the energy would depend on that also how much the area is also the time span for calculating the energy of that particular area, dark energy a would also be the part of it. I mean it’s a mixture of every single thing we could think of or maybe I am wrong. Like we always have that uncertainty in momentum and position for a particle or particles so we won’t be able to find out the actual energy ever as velocities would be uncertain too but we surely have some constraints built up it’s non-holonomic constraint and it will provide us with a range and uncertainty in equalities. I would love to know more if you have anything to say upon