what the hell is quantum foam
ok, this one starts with an explanation of the heisenberg uncertainty principle
on a quantum scale there are certain sets of properties that are linked: usually we talk about time/energy and position/momentum. heisenberg uncertainty is that if you measure one accurately, you have to know the other inaccurately. the derivation for this is interesting but mathematical and hard to explain so i’ll give you something that is not a derivation but an example: suppose you have an electron in a box. out of all the possible places in the world that electron could be, you know it’s not in any of the places outside the box. what i don’t know is the electron’s momentum: it could be moving in any direction at all, bouncing off the walls of the box at great speed in unpredictable directions. well, take the lid off the box and look inside. but remember, we’re operating on tiny quantum scales. the only way my eye/microscope/quantum probe can look at this electron is if a photon bounces off the electron into my eye. and, once it’s bounced off the electron, the electron is going in a different direction!
how can we get an accurate momentum reading? we have to measure the electron twice: get a snapshot now, then a snapshot a second later, and figure out its velocity moving from A to B. but if we do that, the most accurate we can say about its position during that time is “uhhh somewhere between A and B”. if we take snapshots far apart, we get precise momentum values but have to wave hands about position. vice versa is true if we take snapshots really close together. and you can think of all kinds of ways to improve the experiment, but no matter what, something else always pops up. same happens for energy of an electron and the amount of time that’s passed.
ok blah blah blah who cares. or at least, if you didn’t follow what i said above, don’t worry about it and just trust what i say coming on.
let’s look at a ruler, and i’ll use meters because it lets me make the point a little more concisely. my meter stick is exactly one meter long. in this meter there are exactly ten decimeters, in each decimeter there are exactly ten centimeters, in each centimeter ten millimeters, etc. i can go on down forever, to infinitely small and precise measurements.
except that i cannot get infinitely precise. or at least, we said above, that the more precise my position measurement gets, the less precise my momentum measurement gets. and the same for time and energy. so at some point in my metrical divisions, i get to a point where i have to stop worrying about that. if i imagine an imaginary box and keep making it smaller, at some point the box gets so small i can’t be sure how much energy is in there. yes, even if i put nothing in there to start with. yes, this looks like getting energy out of nothing. i put 0 energy in, roll dice, get 2 energy out.
what does this actually mean? if i look inside that tiny tiny box (about a trillionth of a yoctometer, for those playing along at home) i might find tiny particles popping in and out of existence. they would probably, in fact, be particle-antiparticle pairs: an electron and positron that appear out of nowhere, get a little distance away from each other before getting pulled back towards each other and annihilating in the way of matter, antimatter, and sasunaru. we’ve long known that this can happen if you have a lot of energy: if i have 100 energy [units] lying around, 1 of them might turn into matter/antimatter for a split second and then annihilate back into energy, while the other 99 just keep being energy. well, it turns out that if we have 0 energy, this can still happen, and we have -1 energy for a minute. (DONT WORRY this isnt that catastrophic. deciding where to put 0 energy is not the same as deciding where to put 0 dollars. its still a little worrying but not catastrophic)
so that’s what quantum foam is: this champagne fizz of particles and antiparticles popping into existence and back out of existence all the time. people have actually measured the effects of this: some guy called casimir said ok, if we hold two metal plates a really small distance away from each other, there’ll be a ton of fizz outside and less fizz inside, so you should feel a tiny tiny pressure inwards, and this has been done! it works!
a couple other things are implied by this. some people say space also has curled up dimensions, as you might remember, and that at this scale they “unfold” or are traversible in a way that they’re usually not. tbh i dont really get that part but they have some pretty interesting evidence. another thing is that particle/antiparticle pairs always have to be in pairs. you’d need a pretty big something to split them up. something like, say, a black hole. and we do in fact have evidence that a bunch of stuff radiates away from black holes (Hawking radiation) in exactly the way you would expect from this (and it does reduce the black hole’s size/matter/energy, despite nothing escaping the event horizon itself). and a lot of people get really excited about energy from nothing (if you remember hearing about “zero-point energy” or “vacuum energy” it was this).
