Does Earth have two high-tide bulges on opposite sides? (2014) • Hacker News Board

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

#61

Post by detourdog » Fri, May 23, 2025, 9:17 AM UTC

dghlsakjg wrote: post #48

CommenterPerson wrote: post #44

Six months ago, I spent a week at the shore. It happened to be full moon. We were out walking late at night while the moon was high up, and had to slog through ankle deep water on the way back. It was like clockwork roughly 12 hours apart. Did read through stackexchange. It is indeed complicated. But the top response feels like paralysis by analysis. If we analyzed turbulent flow too much we would be unable to build…

Your clock was off. Tides advance ~30 minutes per day. But not exactly 30 minutes. Sometimes more. Sometimes less. Sometimes it doesn’t follow a semi diurnal pattern. Water can’t pass through landmasses, and that is a huge factor. If the earth had no landmasses, the tides would be entirely as you expect. However, if you look at a global visualization of tidal heights, you will see that a small landmass, NZ is a great…

Wind can have a large effect the Chesapeake Bay's tides during large wind events in the atalanitc can effect water levels by feet.

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

#62

Post by verzali » Fri, May 23, 2025, 9:20 AM UTC

coolcase wrote: post #43

senderista wrote: post #31

Earlier quoted context omitted.

No, don't! Use the simplest model that applies in your context!

I agree, I meant to add "as a mind bending exercise to realize how complex nature is!"

Its all models in the end. Half of physics is just putting things in the easiest frame or model to solve the problem you want to solve. And the other half is often simplifying things down to the proverbial spherical cow in a vacuum.

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

#63

Post by [deleted] » Fri, May 23, 2025, 9:33 AM UTC

rhdjsjebshjffn wrote: post #50

srean wrote: post #6

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 speci…

> 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 de…

[deleted]

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

#64

Post by fransje26 » Fri, May 23, 2025, 9:41 AM UTC

alejohausner wrote: post #15

In the animations, New Zealand stood out: the high and low tide chase each other counterclockwise around the islands!

Nicely spotted!

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

#65

Post by srean » Fri, May 23, 2025, 9:52 AM UTC

ahazred8ta wrote: post #53

parpfish wrote: post #21

Earlier quoted context omitted.

And to top it all off, that dang apple hit him on the head

Newton - "the sole mortal who could grapple, Since Adam, with a fall or with an apple." — Byron A calculus fit to compute on, White light and a head to drop fruit on, A mind to absorb it, And soar into orbit — That's all that it takes to be Newton. — Gina Berkeley

My favorite:

Nature and Nature's laws lay hid in night:

God said, Let Newton be!

And all was light.

-- Alexander Pope

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

#66

Post by taneq » Fri, May 23, 2025, 10:12 AM UTC

ghaff wrote: post #40

zabzonk wrote: post #39

Earlier quoted context omitted.

destruction (or nearly) via tidal mechanics happens in several of larry niven's short sf stories

As I recall there were issues with the math in Neutron Star though still a very good story.

I went to look up a relevant story I remembered, and Neutron Tide is indeed it.

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

#67

Post by tylervigen » Fri, May 23, 2025, 10:36 AM UTC

The explanation is phenomenal. I particularly like the elevation heat map, which helps me intuitively grasp what is going on.

This raises a question for me though: why do we show the tidal bulge graphic in any educational context? Like OP, the "far bulge" was always the most surprising and difficult-to-grasp part of the image. But this explanation would indicate that the far bulge is almost totally pointless as a concept, given the complexities of the system. Given it's the least intuitive part of the image, it invites additional consideration. But it's all the wrong consideration!

The model would be more useful if it only showed the bulge on the moon side, and excluded the far side bulge. It would still be wildly imprecise, kind of like the orbital model of atoms is wildly imprecise, but at least it would be a slightly more accurate (and useful) initial mental model.

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

#68

Post by mkl » Fri, May 23, 2025, 10:42 AM UTC

That animation is great. I found the person who made it: https://ceoas.oregonstate.edu/directory/svetlana-erofeeva

That links to this website which has a similar animation for the current day: https://www.tpxo.net/

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

#69

Post by MostlyStable » Fri, May 23, 2025, 10:57 AM UTC

I took a graduate level physical oceanography course and never learned this and still believed the tidal bulge story.

To be fair to the course, it was much more interested in currents than tides (I don't remember really discussing tides in any depth at all)

This is a great answer!

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

#70

Post by tomxor » Fri, May 23, 2025, 11:08 AM UTC

II2II wrote: post #38

tomxor wrote: post #29

Earlier quoted context omitted.

> So it's a bunch of complicated splashy water that is excited by the moon moving past This explanation is so much better. If people want to use big words they can say fluid dynamics, but yeah, it's a complex system with a big orbiting body pulling on it regularly, that gives the complex system rhythm but not order.

That would be akin to describing a computer as a complicated arrangement of switches that control each other through pulses of electricity to do useful stuff. While it may satisfy a bunch of people who aren't really interested in how computers work, and it may even inspire a few people who are intrigued by how such a simple notion could produce incredible results, it doesn't really explain how computers work.

Splashy complicated water is an accurate but imprecise description, which is exactly what you want for an introduction. It's a complex chaotic system.

Computers are a terrible analogy for this type of minimal explanation of natural phenomena because computers are layers of designed complexity built by exploiting an understanding of multiple distinct natural phenomena... At the composite scale computers are a very unatural human construct, not something emergent that can be accurately expressed informally.