Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Harri on 06/03/2020 09:04:43
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As the title says, just what would I find in a square centimetre of space? If that bit of space was in the vacuum of outer space?
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As the title says, just what would I find in a square centimetre of space? If that bit of space was in the vacuum of outer space?
Not much, its a very low density, the content would vary but consist mainly of Neutrinos, Hydrogen, Helium, Lots of radiation, and virtual particles(zero point energy). The odd asteroid or comet might pass through your cubic centimeter of space also.
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As the title says, just what would I find in a square centimetre of space? If that bit of space was in the vacuum of outer space?
It depends on where in "outer space" you are. The interstellar medium can vary from a density of 1e-4 atoms per cm^3 to 10^6 atoms per cm^3. While 1 million atoms may seem like a lot, it is still 1/10,000 as many as you would find per cubic centimeter in a man-made high-vacuum chamber.
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And ... how much of that square centimetre is 'empty'? Is there such a thing as empty space?
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I think the answer might be "infinitely less than you find in a cubic centimetre of space".
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And ... how much of that square centimetre is 'empty'? Is there such a thing as empty space?
In a way, all space is empty. Take for instance an apple. How much of some cubic centimeter of that apple is empty? Well, no known fundamental particle occupies a finite volume. It cannot, else it would have the left side and the right side and it would not be a fundamental particle. Hence the entire apple is empty space. Sure, the cc has plenty of electrons and other things in it, but none of them occupy any of the volume in it.
OK, that's one answer. The QM answer gives a different way of looking at it.
Quantum mechanics has interpretations that kind of fall into two camps: Local and counterfactual ones. Some are neither. A counterfactual interpretation (state exists even if not measured) would say that there is actually a measurement independent state to any system, which in our case is some cubic centimeter in a random spot in space, likely well between galaxies. For that, the lower bound of the numbers given by Janus would be a fair description. Such interpretations need to posit information transfer faster than light, and so are not considered local interpretations.
On the other hand, a local interpretation (denying faster than light cause and effect) would not say there is in fact an electron at location X inside that cc. An electron's position only exists when measured, and nothing is likely getting measured there. So such interpretations would simply say that were a measuring device to be placed there, it would likely detect particles and radiation at the levels given by Janus. But by no means can it be said that a given particle is in fact within that cc if not measured.
So the wave function of that little volume of space might be wildly complex, describing all manner of probabilities of things that may or may not be measured if something were to put a detector there, but if there was a detector there, it wouldn't be empty, would it?