Tangential question: Would it affect light too? I mean gravity bends light, so does that mean, if you cocked your eye along the water, it would look flat, because the light was dipping with the water surface?
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yeah! exactly.
that is the final part of that chain that i left out.
in the hill underwater analogy, where the water surface is flat despite the hill… since the hill is spacetime, to see what it’d look like to us, you’d normalize it. keep the depth of the water at each point just like it was, but pull the hill flat again. the hill had only a little water on top of it, so now - visually - you’ve got a well.
the water isn’t going to go anywhere because what it cares about is gravity, not what things look like to us crazy humans.
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i’m not an expert, so take this for what it’s worth, but i believe light and matter are affected by gravity in different amounts. so the curves for the two are different
there’s a reddit post where someone talks a bit about that
https://www.reddit.com/r/askscience/comments/21lo0t/just_how_much_does_earths_gravity_bend_light/
Light passing tangentially to Earth’s surface should be deflected by 0.16 millionths of a degree by gravity.
so basically it’s unnoticeable
(eta for clarity)
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Its still a pretty good marble.
If you took a regular marble with all its imperfections and expanded it to the size of the earth it wouldn’t be nearly as smooth as the Earth.
Basically what @AnthonyC said above
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Yeah, yeah, but…potato.
/s
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Water keeps moving downward until it can’t anymore, and after that it moves sideways until it thinks the force of gravity is straight down
If the actual force of gravity is “lumpy,” water will arrange itself so the potential energy is the same everywhere on the surface
The surface in the Indian Ocean seems “low” geometrically but it’s energetically higher than that because it’s farther from the lumps
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First, assume a 2-dimensional, circular cow…
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Band: Indian Gravity Hole
Album: biggest low in the geoid
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Wait a moment…
The experiment was devised sometime before 1783 by geologist John Michell who constructed a torsion balance apparatus for it. However, Michell died in 1793 without completing the work. After his death the apparatus passed to Francis John Hyde Wollaston and then to Cavendish, who rebuilt the apparatus but kept close to Michell's original plan.
Cavendish was following up on Michell? Do you suppose there is any chance that he was, well, Gros? Because we have the makings of one of the most obscure jokes of all time.
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Thanks! I thought after I asked the question, that that must be the case - otherwise we wouldn’t have a hard horizon when we look at the sea – it would just appear to fade out as per “flat earth”. But isn’t it weird that light and water are affected differently, considering Galileo and all that? I guess it’s a speed-of-light-quantum thingy.
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Different things are happening to them. Neglecting air resistance, if you were to fire a beam of light and a bullet and a stream of water from the same point, you would find they all bend downward, with the amount of curvature differing from their speed.
But the ocean surface is water that has already fallen as far as it can, and is now being held up by the pressure of the water below. So the shape is not a trajectory, it’s where there’s a balance between the two forces. If the gravitational field were all parallel like in physics 101 the water would actually lie flat even though things dropped above it would still fall.
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Brilliant. Thanks.
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That would be bananas!
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Seems like a good place to start looking for MH370.
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Ok, so this is all stuff I learned today.
There’s a massive “gravity hole” in the Indian Ocean where the pull of gravity is less than everywhere else on Earth and the sea level is is 100 meters lower than the planetary average.
So what happens to the air above the gravity hole? When you are floating in a boat directly over a gravity hole, and the boat 100 meters below the mean sea level, what would an altimeter say? How many meters below sea level would it indicate (if any)?
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Aren’t we all, my friend, aren’t we all.
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Huh, Google says it’s 378’ (100 m ) down. So much for my thinking that the sea, in its boundless joy, would leap free 100 m in that much unleashing. Perhaps someday China will make giant seaborne robots which assemble to form a stable-in-place breaker by which one can reliably surf some fraction of 200 m waves? But then name it Tse-on-Goa?
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There’s a hole in the ocean, dear eliza, dear eliza,
a hole in the the ocean, dear eliza, a hole.
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According to Wikipedia, it depends on what you use to measure it:
So analog tools (e.g. tide gauge) will probably tell you you’re at zero altitude. Raw GPS reading will say you’re at -100 meters, but a smart GPS receiver will correct that to 0.
Also, I found this interesting fragment of a map showing what the world would look like if Earth’s interior had uniform density and there were no gravitational anomalies - Bangladesh under water, land bridge between Australia and New Guinea, etc:
And now I’m wondering how much do we know about the dynamics of these gravitational anomalies. E.g. is the “hole” in the Indian Ocean getting deeper or regressing to the mean? Is the change faster or slower than plate tectonics? In the grand scheme of things, how does the change of sea levels due to mass fluctuations in the mantle compare with the effects of melting glaciers, plate tectonics and the post-glacial rebound?
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