Casimir Effect Causes Ships To Attract Each Other
Status: Myth
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 news@nature.com. "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.Listed in chronological order. Newest comments at the end.
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It would make sense that it would only occur in a vacuum, as there's so many other factors elsewhere (especially at sea) to interfere.
Posted by Egret Narcosa on Sat May 06, 2006 at 12:22 PM
Maybe ships like to sail along on lonely water to keep company with each other, so that they should feel less alone.
Posted by t.kurione on Sun May 07, 2006 at 01:36 AM
I dunno, seems like two ships sitting side by side in a calm bay just might be attracted to each other by gravity alone.
There's a good demo of the gravitic attraction of small masses at "Bending spacetime in the basement":
http://www.fourmilab.ch/gravitation/foobar/
Seems to me if two masses of less than a kilo each can attract weights on a beam balance, two floating ships weighing several tons should have no trouble attracting each other.
Posted by Captain DaFt on Sun May 07, 2006 at 11:07 AM
There's a good demo of the gravitic attraction of small masses at "Bending spacetime in the basement":
http://www.fourmilab.ch/gravitation/foobar/
Seems to me if two masses of less than a kilo each can attract weights on a beam balance, two floating ships weighing several tons should have no trouble attracting each other.
I have observed this first hand several times - but there's nothing mysterious about it. A slight breeze will move a boat on calm water - if lined up just right, the upwind boat blocks the wind from the downwind boat. Boat "A" drifts towards boat "B"
Posted by Espano d'Orgone on Tue May 09, 2006 at 04:35 AM
I was a Naval Officer and the only times I have ever seen or heard of ships being sucked together was during underway replenishment.
This is when two ships are on parallel courses about 150 feet apart and both moving about 10 - 12 knots. The reason the ships want to move together is due to the Bernoulli Principle. The flow of the water and the close proximity of the ships creates a low pressure area between them.
I would not know about two ships close to each other at anchor, because there are a lot better reasons to keep ships apart when anchored. Often the scope of the anchor chain is around 7:1, so if you were anchored in 30 feet of water then you have 210 feet of chain. That length plus the length of your ship is the radius of the ‘swing circle’. While at anchor, the ship can be anywhere within that swing circle. Due to currents, tidal currents and wind two ships at anchor might not be pointing the same direction at the same time and will swing differently. That is why you don’t want your swing circles to overlap. I cannot imagine two ships being so close to each other at anchor that they actually move towards one another.
Posted by Jim in Columbus, Ohio on Tue May 09, 2006 at 09:04 AM
This is when two ships are on parallel courses about 150 feet apart and both moving about 10 - 12 knots. The reason the ships want to move together is due to the Bernoulli Principle. The flow of the water and the close proximity of the ships creates a low pressure area between them.
I would not know about two ships close to each other at anchor, because there are a lot better reasons to keep ships apart when anchored. Often the scope of the anchor chain is around 7:1, so if you were anchored in 30 feet of water then you have 210 feet of chain. That length plus the length of your ship is the radius of the ‘swing circle’. While at anchor, the ship can be anywhere within that swing circle. Due to currents, tidal currents and wind two ships at anchor might not be pointing the same direction at the same time and will swing differently. That is why you don’t want your swing circles to overlap. I cannot imagine two ships being so close to each other at anchor that they actually move towards one another.
In small molecules, such attraction is an example of the hydrophobic effect. This is explained as an entropy driven effect and the cause of crystal formation especially in water solutions. The free energy of the system is highest if the maximum number of water molecules can be in the bulk water as opposed to being associated with the small molecules. The small molecules get pushed together which frees more solvating water molecules. The small molecules are not sticky, they are pushed together.
A supposed model of the hydrophobic effect is that of cheerios in a bowl of milk. Near the end of the meal when there are few cheerios, these will be all touching each other or touching the rim of the bowl. They have been driven together by the Brownian motion of the water molecules.
This pushing effect has been used by some to explain Push Gravity. Things seem to be attracted but are actually pushed together by collisions of the ether. Apparently the gravity equations of force being inversely squared to distance is also in effect with Push Gravity.
Pushing seems like it might work to bring ships together if there were mild water movements in random directions as the ships would fall into each other's shadow of calmer water and be pushed less from that direction.
But it also might be gravity of the ships as mentioned by Captain DaFt. The question is which effect would be strongest and over what distances would each act.
Posted by George in Detroit, MI on Wed Jul 22, 2009 at 06:17 AM
A supposed model of the hydrophobic effect is that of cheerios in a bowl of milk. Near the end of the meal when there are few cheerios, these will be all touching each other or touching the rim of the bowl. They have been driven together by the Brownian motion of the water molecules.
This pushing effect has been used by some to explain Push Gravity. Things seem to be attracted but are actually pushed together by collisions of the ether. Apparently the gravity equations of force being inversely squared to distance is also in effect with Push Gravity.
Pushing seems like it might work to bring ships together if there were mild water movements in random directions as the ships would fall into each other's shadow of calmer water and be pushed less from that direction.
But it also might be gravity of the ships as mentioned by Captain DaFt. The question is which effect would be strongest and over what distances would each act.
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