According to Wikipedia, the Casimir Effect
(which is real) is "a physical force exerted between separate objects, which is due to neither charge, gravity, nor the exchange of particles, but instead is due to resonance of all-pervasive energy fields in the intervening space between the objects." The effect is best observed with things such as parallel plates of metal in a vacuum.
Another example often used to illustrate the effect is that it can be seen operating on ships lying close together in a strong swell because "waves with wavelengths longer than the distance between the ships would be suppressed in the space separating them. This could perhaps pull the ships together."
But Nature.com reports
that former NASA scientist Fabrizio Pinto has challenged this notion. The claim about the Casimir Effect acting on ships apparently traces back to a 1996 article by Dutch scientist Sipko Boersma, who came across a statement in an 1836 nautical book warning that "two ships should not be moored too close together because they are attracted one towards the other by a certain force of attraction." Pinto found a copy of this 1836 book and discovered that it was talking about ships moored in a calm sea, not in a strong swell. But Pinto is suspicious even of this claim. Nature reports:
Pinto says he hasn't found any real evidence for the effect, in either sailing or scientific literature. Naval architect Jason Smithwick of Southampton University says he has never heard of such an effect. "I could imagine how it might possibly happen, but it would take a very specific set of circumstances," he told firstname.lastname@example.org. "It's nothing that naval architects have ever worried about." Pinto thinks that the whole tale is symptomatic of physicists' approach to the history of their subject. "Physicists love lore about their own science," he says. "There are other stories that are unfounded historically."
Nature lists a few of these other popular (but false) stories
that physicists like to tell, including the claim that Galileo proved objects fall at the same speed by throwing things off the leaning tower of Pisa, or that Newton was inspired to discover the law of gravity after an apple fell on his head.