←back to thread

Does Earth have two high-tide bulges on opposite sides? (2014)

(physics.stackexchange.com)
294 points imurray | 1 comments | 22 May 25 18:58 UTC | HN request time: 0.211s | source
Show context
srean ◴[22 May 25 19:51 UTC] No.44066091[source]▶
The problem of predicting tides was so important that it attracted many Physics and Maths heavy weights. You can well imagine how important predicting tides would have been for D-day landing.

One related fascinating historical artifact is the special purpose analogue computer designed by Lord Kelvin in the 1860s based on Fourier series, harmonic analysis. Think difference engine in it's cogs and cams glory, but special purpose.

https://en.m.wikipedia.org/wiki/Tide-predicting_machine

Possibly one of the first examples of Machine learning, with Machine in capital 'M'. It incorporated recent tidal observations to update it's prediction.

Note that sinusoids are universal approximators for a large class of functions, an honour that is by no means restricted to deep neural nets.

George Darwin (Charles Darwin's son) was a significant contributor in the design and upgrade of the machine.

https://en.m.wikipedia.org/wiki/George_Darwin

Other recognizable names who worked on tide prediction problem were Thomas Young (of double slit experiment fame) and Sir George Airy (of Airy disk fame).

replies(4): >>44066143 #>>44066655 #>>44069709 #>>44070084 #
rhdjsjebshjffn ◴[23 May 25 03:50 UTC] No.44069709[source]▶
> You can well imagine how important predicting tides would have been for D-day landing.

Is this intended to communicate positivity or negativity?

Predicting tides was known to the ancients; it would be lovely to explore the hubris of the modern narrative.

Edit: fundamentally, if hacker news has taught me anything, it's that "downvote = makes me feel bad and doesn't want to answer questions". The entire concept of democratic news aggregation was a lie.

replies(4): >>44070984 #>>44071082 #>>44071318 #>>44072128 #
grues-dinner ◴[23 May 25 08:24 UTC] No.44070984[source]▶
I think there are two ways to interpret that sentence: "it would have been important": one which implies tidal prediction was unavailable at D-day but would have been useful, and one that implies it was indeed available (subjunctive conditional or "the Anderson case", apparently, per Wikipedia)

I don't think anyone is claiming tide times were so unpredictable in 1945.

replies(1): >>44073710 #
1. pfdietz ◴[23 May 25 15:25 UTC] No.44073710[source]▶
They were predictable. Interestingly, Rommel misunderstood how tides affected landings. He thought the landings would be done at high tide, so the invading troops wouldn't have to advance across wide expanses of beach. In reality, the allies wanted to invade on a rising tide, so the landing craft, grounded to let out troops, would refloat and be able to move back out. Also, invading at lower tide meant beach obstacles would be exposed and unable to damage the landing craft.