Casimir Effect.

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Vanadium 50
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It's still not clear to me that the fact that there is a force between two nearby ships means that its analogous to the Casimir effect.

The existence of a force is not sufficient to prove this. There's a force between a baseball and the ground, but it has nothing to do with Casimir. If the force is due, as Pythagorean suggests, to wave amplitude (and traveling wave amplitude) it's a different thing.

Also, from my own (albeit slight) experience on the water, I don't think this force has the right functional dependence to be a Casimir-analogue. If it were, the force would become unstoppable shortly after it became noticed. Remember, Casimir forces grow very quickly with decreasing separation.
 
  • #27
nrqed
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From Bob S
One of my neighbors is a PhD physicist who was a naval commander before retirement. He says there definitely is an attractive "force" between two ships when they are very close, and it is attributed to the relatively calmer wave structure between them.
Originally Posted by Vanadium 50
From "Interstellar Technologies"? Are you sure that's a reputable site?

(My neighbor is the only person I know who can write out the proof of the Brachistochrone problem w/o referring to his book collection. He is very sharp.) This effect, whether due to true Casmir forces or not, is taught to graduates of the U.S. Naval Academy in Annapolis. This has nothing to do with the trustworthyness of Interstallar Technologies.
Here is another version from Chemistry Daily
http://www.chemistrydaily.com/chemistry/Casimir_effect:
An effect analogous to the Casimir effect was observed by 18th century French sailors. Where two ships are rocking from side to side in conditions with a strong swell but light wind, and the ships come closer together than roughly 40 m, destructive interference eliminates the swell between the ships. The calm sea between the ships has a lower energy density than the swell to either side of the ships, creating a pressure that can push the ships closer together. If they get too close together, the ships' rigging can become entangled. As a countermeasure, a handbook from the early 1800s recommends that each ship should send out a boat rowed by 10 to 20 sailors to physically pull the ships apart.
Here is another from http://scienceweek.com/2004/sa041119-6.htm (see ref 5.)
3) Although the Casimir effect is deeply rooted in the quantum theory of electrodynamics, there are analogous effects in classical physics. A striking example was discussed in 1836, in P. C. Caussee's L'Album du Marin (The Album of the Mariner)(5). Caussee reported a mysteriously strong attractive force that can arise between two ships floating side by side -- a force that can lead to disastrous consequences. A physical explanation for this force was offered only recently by Boersma (1996), who suggested that it originates in the radiation pressure of water waves acting differently on the opposite sides of the ships. His argument goes as follows: the spectrum of possible wave modes around the two ships forms a continuum (any arbitrary wave-vector is allowed); but between the vessels their opposing sides impose boundary conditions on the wave modes, restricting the allowed values of the component of the wave-vector that is normal to the ships' surfaces. This discreteness created in the spectrum of wave modes results in a local redistribution of modes in the region between the ships, with the consequence that there is a smaller radiation pressure between the ships than outside them.

References (abridged):

1. Casimir, H. B. G. Proc. Kon. Ned. Akad. 51, 793-795 (1948).

2. Bordag, M., Mohideen, U. & Mostepanenko, V. M. Phys. Rep. 353, 1-205 (2001).

3. Kenneth, O., Klich, I., Mann, A. & Rezen, M. Phys. Rev. Lett. 89, 033001 (2002).

4. Boyer, T. H. Phys. Rev. A 9, 2078-2084 (1974).

5. Caussee, P. C. L'Album du Marin (Mantes, Charpentier, 1836).

Fascinating!! Thanks for posting all this information
 
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I just did a seat-of-the-pants Casimir effect calculation which I will post if anyone's interested.
 
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perhaps you could email instead of posting. mphilo@xtra.co.nz
I would also be interested if anybody knows the correlation between calc numbers and experimental numbers. I expect only about an 80% correlation if em has not been accounted for.

nrqed. your post about the ships is what I said, in different words.
I see an analogy between the ships, frequencies in a waveguide, and the Casimir effect.
Of course the analogy is not exact, when are they ever ? we're talking water, rf, and quantum stuff. But it is similar.

Born2bwire. I think that external em would add to the Casimir force. Why would it not ?
If it's there and given the cutoff inside the plates, there is going to be an imbalance with many more frequencies external than internal, resulting in more momentum transfer outside than inside.
 
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Born2bwire
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perhaps you could email instead of posting. mphilo@xtra.co.nz
I would also be interested if anybody knows the correlation between calc numbers and experimental numbers. I expect only about an 80% correlation if em has not been accounted for.

nrqed. your post about the ships is what I said, in different words.
I see an analogy between the ships, frequencies in a waveguide, and the Casimir effect.
Of course the analogy is not exact, when are they ever ? we're talking water, rf, and quantum stuff. But it is similar.

Born2bwire. I think that external em would add to the Casimir force. Why would it not ?
If it's there and given the cutoff inside the plates, there is going to be an imbalance with many more frequencies external than internal, resulting in more momentum transfer outside than inside.
The first paper on accurate measurements of the Casimir force got results in agreement of 5%, S. K. Lamoreaux, Phys. Rev. Lett. Volume 78, page 5 which used corrections for the non-zero temperature and finite conductivity of the scatterers. Again, the reason why they will not have an effect is that the presence of a scatterer does not change the total energy of the EM radiation nor, more importantly, is the total energy dependent upon the position of the scatterers. The Casimir effect, relies on the fact that the presence of and position of scatterers affects the energy of the system, whether it is the vacuum state or say the quantum fluctuation currents and charges. The change in energy due to the change in position results in the force along the direction of spatial variation.
 
  • #31
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As reported in the professional physics literature in 1995, an entirely classical, that is, non-quantum, treatment of the Casimir force is all is needed to explain the mysterious attractive force
Bob S: can you give me the exact reference of the paper you pointed out.

I'm very sorry if what i'm going to say cannot be used in fiction movies or starships stories, but it turns out that that the Casimir effect is one of the biggest and most misleading myths of quantum mechanics. The fact is that the "Casimir’s original goal was to compute the van der Waal’s force between polarizable molecules at separations so large that relativistic (retardation) effects are essential. [...] These results were derived using the
standard apparatus of perturbation theory (to fourth or-
der in e) without any reference to the vacuum."

ref{ Title:"The Casimir Effect and the Quantum Vacuum"
arXiv:hep-th/0503158v1
Journal:Phys.Rev. D72 (2005) 021301
Abs: In discussions of the cosmological constant, the Casimir effect is often invoked as decisive evidence that the zero point energies of quantum fields are "real''. On the contrary, Casimir effects can be formulated and Casimir forces can be computed without reference to zero point energies. They are relativistic, quantum forces between charges and currents. The Casimir force (per unit area) between parallel plates vanishes as \alpha, the fine structure constant, goes to zero, and the standard result, which appears to be independent of \alpha, corresponds to the \alpha\to\infty limit.}
 
  • #32
Born2bwire
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Bob S: can you give me the exact reference of the paper you pointed out.

I'm very sorry if what i'm going to say cannot be used in fiction movies or starships stories, but it turns out that that the Casimir effect is one of the biggest and most misleading myths of quantum mechanics. The fact is that the "Casimir’s original goal was to compute the van der Waal’s force between polarizable molecules at separations so large that relativistic (retardation) effects are essential. [...] These results were derived using the
standard apparatus of perturbation theory (to fourth or-
der in e) without any reference to the vacuum."

ref{ Title:"The Casimir Effect and the Quantum Vacuum"
arXiv:hep-th/0503158v1
Journal:Phys.Rev. D72 (2005) 021301
Abs: In discussions of the cosmological constant, the Casimir effect is often invoked as decisive evidence that the zero point energies of quantum fields are "real''. On the contrary, Casimir effects can be formulated and Casimir forces can be computed without reference to zero point energies. They are relativistic, quantum forces between charges and currents. The Casimir force (per unit area) between parallel plates vanishes as \alpha, the fine structure constant, goes to zero, and the standard result, which appears to be independent of \alpha, corresponds to the \alpha\to\infty limit.}
That is Jaffe's paper is it not? It is a good read.
 
  • #33
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That is Jaffe's paper is it not? It is a good read.
Yes, it is the Jaffe's paper. Very enlightening indeed.
 

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