Every time I think about this I get tangled up. That may be because I'm not competent to grasp it (a possibility I definitely do not dismiss). But it could also be that a lot of this comes out of the math (it does) and NOBODY can really see it outside of the equations--we can't just "intuit" it and say "of course". After all, even the religious folk get screwed up. As genesis says, "...the earth was waste and void, and the spirit of God was stirring above the waters." OK, so there was already water before there was anything? What was the waste? Mining slag? Rubble? Is a void solid--you can't see it but can bump into it? Is it just "empty space"--you can run right through it? Both of those things have properties--so they are not "nothing" (which should have no properties).Thanks, a good explanation ... I do remember learning about the 'ultraviolet catastrophe' but long since it dropped from active memory.
For me, explanations that approach things by way of going through the history of ideas and scientific challenges tend to be the easiest to follow.
In comparison for instance the wikipedia page on the fine structure constant isn't massively helpful for a person like me who doesn't have any physics background.
Maxwell's equations (deduced from real experiments by Faraday and others) describe light as a "force field" traveling in waves through space. Herz in some clever experiments with radio waves--a form of light--actually figured a way to detect them and measure the wavelength (distance between peak and trough, twice the distance from peak to 0). But people wondered how you could have a wave when there was nothing to carry it--certainly space is practically a vacuum, but starlight sails right through. So they invented the idea of "ether" to carry the waves. People tried to find it, figuring the earth was moving through it--both orbiting the sun and rotating on its axis--so sometimes there should be an "ether head wind" and sometimes and "ether tail wind". Nothing (sic) was detected. So it could be that the ether is carried along with the earth. Then what does the sun say (sunlight has to come through the ether too). "Hey, bro, I'm bigger than you--stop messing with my ether!"? (This idea that there are "special places" where physics is different is what Einstein countered in relativity.)
Oxford publishes some cheap paperback books written for "laymen" by "experts"--the "Very Short Introduction" series. There are more than a hundred now I think: Consciousness, Viruses, the Trojan War, Biblical Archeology, The New Testament, The New Testament as Literature, etc. But there is one called "Nothing--A Very Short Introduction". It is fun to read about all the trouble people had accepting that there could be a vacuum where God had not deigned to create, and the chain of experiment leading to theory leading to experiment that lead to the "quantum vacuum"--even if in the end you can't "see why it must be so", but can accept that the evidence for it is pretty strong.