If you put 2 thin plates very close together in a vacuum, they are attracted to each other- this is known as the Casimir effect. The odd thing is- this attraction is not due to gravity (which is much much weaker) or electrostatic charge. This attractive force seems to come for free - out of nowhere! Creepy.
I've been fascinated by this since i first heard about it a few years ago- but have never been able to understand the mechanism behind it. What i needed was an anaolgy nearly totally devoid of physics- and now i've found one..as part of a really interesting lecture on "nothingness" by Dr John Barrow- i.e. the history of zero, vacuums etc.
Here is the best bit:
"I discovered a few years ago a wonderful nautical version of this (Casimir) force. Back in the 1820s, the French Navy produced a handbook of advice to their sailors, and one of the pieces of advice to captains is rather extraordinary. There’s no reason for the advice, it’s just based on experience, and the experience was that if you had two large ships and you were sailing in a strong swell but there were not high winds, then if the boats were to come quite close together, 30 or 40 yards close to one another, then the captain should set down small boats full of 20 or 30 men, and they whould attach lines and pull the boats apart, because experience showed that once the boats which were gently swaying together got closer than about 30 or 40 yards, they would be pulled together and their riggings would become entwined and there would be disaster. If you calculate this, you find that it’s exactly the same effect in the large, that you get an out of phase generation of waves between the boats, so the crests of one wave match the troughs of the other, so it’s in effect there is no wave motion between the two boats, but the waves coming in and rebounding off the outside push the boats together. Mathematically, it’s exactly the same type of effect, but not with quantum waves, just with classical waves. In fact, a little mathematics shows you, if you have two ships that weigh about 700 tons or so, then a couple of small boats with 20 or 30 men will be able to overcome the force that pulls them together, so it’s a nautical Casimir effect.".
So... Could this vacuum energy from empty space power a perpetual motion machine and solve the worlds energy and climate crises forever? No. Just like a brick falling to Earth gravitationally- you'd have to keep pulling the two Casimir plates apart again and again- and each time you did so, you'd use up just the same amount of energy created in the first place.
Dr Barrow's other lectures look equally interesting- here's a list of 'em.