Tides - 4

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"Time and tide wait for no man"...Proverb

There is a tide in the affairs of men
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures. 

...Shakespeare

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Tides are periodic bulging and shrinking of seas.

In the high tide sea level rises, and the sea floods the beach.

In the low tide the sea recedes far away from the beach.

High tides and low tides occur twice a day one followed by the other about six hours apart.

Thus there are two high tides and two low tides alternating every day.

High tides at times can be very impressive.

One night I was walking back to my home in Krishna Nagar by the road in front of the RK Mission in Vizagh.

There were no street lights and it was pitch dark...maybe New Moon (Amavasya).

Suddenly I found my feet wet. And I realized that the sea had swallowed the beach entirely, jumped over the low embankment in that spot, and was trying to swallow the road as well...like a hungry cobra.

And I had to take a non-existent sidewalk and cling to the trees and bushes and inch my way forward through those patches...not to get wet or lost...

At places where a river joins the sea, and the river's mouth narrow, the sea in its high tide can flow back vengefully into the river, reversing its course, and flooding its embankments far far into it. 

That is the Tidal Bore in rivers.

The leading edge of the bore is highly visible like a traveling hump.

This is a common enough occurrence in the river Hooghly by Calcutta....the bore having traveled inwards all the way from Ganga Sagar maybe.

The tidal bore can at times be so high that it could devastate the small boats sailing under the Howrah Bridge.

And then travel to Dakshineswar where Sri Ramakrishna Paramahamsa would be waiting on the bank with his team of followers in order to watch it. His abode was by the river Hooghly which he used to call reverentially: "Ganga".

And also scare the monks of Belur Math on the other bank:

https://timesofindia.indiatimes.com/videos/city/kolkata/watch-high-tide-causes-panic-in-belur-math-in-west-bengal/videoshow/68558540.cms

https://www.youtube.com/watch?v=C6XdTxyUH68

World's highest tides (about 50 feet) are seen in the Bay of Fundy (Nova Scotia):

Twice each day, 160 billion tonnes of seawater flow in and out of the Bay of Fundy — more than the combined flow of the world’s freshwater rivers! The Bay of Fundy’s tides transform the shorelines, tidal flats and exposed sea bottom as they flood into the bay and its harbours and estuaries.

https://www.youtube.com/watch?v=OP0cpXpw8yk

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Tides are complicated events. Their size and extent depend on the longitude, latitude, lay of the shore, seasons, and rivers flowing into the sea...

But science can now predict their timings fairly accurately...unlike earthquakes, tsunamis, and Didi's tantrums.

This is because tides in our seas are due to an interplay of the combined gravities of the Moon and the Sun.

In a sense they are the highly visible terrestrial events due to celestial bodies.

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In our university physics we heard of two pinnacles of precision:

1. Astronomical

2. Spectroscopic

1. Astronomical:

For instance we learned that medieval astronomers tracked the movements of planets over centuries accurately and recorded them. Copernicus used them to propose his heliocentric theory (planets, including our Earth, move around the Sun rather than the other way round) and so destroyed the primacy of our Earth, its pundits and politicians. Newton used his 'Inverse square Law of Gravitation' to account for the intricate motions of planets due to their mutual gravitational interaction, called perturbations. And predicted the next arrival of the Halley's Comet accurately. That was his crowning glory.

But Newton's Gravity Theory failed to account for a tiny tiny tiny anomaly in the motion of the innermost planet, Mercury, difficult for us to see unaided in our lifetimes, mostly due to the arrival of electricity and sky lights :)

Mercury was found to revolve around the Sun in an elliptical orbit (as predicted by Kepler and derived by Newton). And due to perturbations of the gravity of other planets, its orbital ellipse slowly slowly slowly rotates like in a rosette pattern.

Most of this precession of the perihelion of Mercury could be accounted for by Newton's Gravity Theory, except for a wee amount that came to be correctly calculated two centuries later by Einstein's Gravity Theory (wrongly called The General Theory of Relativity).

How tiny was the discrepancy?

It is mind-blogging (I had checked Einstein's calculations and gave them out as an MSc Project...along with the two other classical tests of Einstein's Theory):

It was 43" of an arc per century (hundred years)!

One second (") of an arc is 1/60 of a minute ('). One minute of an arc is 1/60 of a degree (deg). And a circle has 360 degs (when I heard last). 

How the hell could the Middle Age Western Astronomers measure and record it (while our Kalidas was busy writing his Meghdoot, as lovely a thing as any)?

2. Spectroscopic:

We had 6-hour labs in our Spectroscopy in our University at Waltair.

In our MSc Exam in 1963, for appearing in this lab, we had to wake up early to catch the first bus and reach the Lab by 7 O' Clock. And then for all of 6 hours we were stuck there (no coffee-breaks).

Most of those experiments involved taking emission spectra of carbon, copper etc sticks when they were lit up by arcs.

And we measured the wave numbers (frequencies) of the spectral lines we recorded on our glass plates (developing them in our dark room) using 7-figure log tables (4 figures were no use...not accurate enough).

That meant that the good old spectroscopists measured spectral lines of various elements and recorded them accurately to seven decimals (that was called 'Term Zoology' for fun, and youngsters like Heisenberg who invented Quantum Theory had it at their finger tips).

The latest measurement of the 'Fine Structure Constant' has an accuracy up to 14 figures!

Like "pi" was taught us to be 22/7, this 'fine structure constant' was first measured to be 1/137 and led to many hilarious "Magic Number Theories", all wrong.

It is nothing so simple. Its value a decade ago was:

The team in Paris measured the value of the fine-structure constant as 1/137.035999206, to an accuracy of 11 digits. The result appears in a study published in Nature.

And it agrees fairly well with the super-duper-hyper computer calculations of the Quantum Electrodynamics popularized by Richard Feynman.

Phew!

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To be Continued

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