# An ocean in the sky

## Main Question or Discussion Point

Hi all!

In the absurd hypothesis that we could take all water from earth's oceans and distribute it equally through the sky ceiling (as shown below). We have the point of view of an observer in the land.

Questions:

1. We know that the water pressure rises as we come closer to Earth's core, so the "flying ocean" would have less pressure at its "bottom", right?

2. If the previous is true, would the pressure difference be considerably lower than actual seabed one?

3. If observer in land would be launched in the air, entering the "sky ocean" from the "bottom", would he be crushed by the seabed pressure as if it were submerging into the Mariana's Trech, for example?

I know this is fairly nonsense but it's a scenario for a fiction.

:)

Thanks people!

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Borek
Mentor
would have less pressure at its "bottom"
Define "bottom". Is it up (far from the observer) or down (close to the observer)?

mfb
Mentor
1. We know that the water pressure rises as we come closer to Earth's core, so the "flying ocean" would have less pressure at its "bottom", right?
Less than what?

If you magically exchange the current oceans with a layer of air as indicated in the sketch, the system is far away from an equilibrium: the air below will start at its old pressure, but suddenly all the water above pushes down on it - the water would fall down and compress the air below it. Shortly before the water reaches the surface, air pressure will be so high it gives some resistance to further compression - but then you still have something like 3km of water that fell down some significant distance and still moves downwards. It will completely crush everything on the surface. Shortly afterwards all the land is covered by 3km of water with some highly compressed air bubbles (the pressure at the surface is the same as it is now 3km below the ocean surface) moving upwards. The water will then start to rush back into the oceans, the flow rates should be sufficient to level down everything the flood reaches.

Drakkith
Staff Emeritus
1. We know that the water pressure rises as we come closer to Earth's core, so the "flying ocean" would have less pressure at its "bottom", right?

2. If the previous is true, would the pressure difference be considerably lower than actual seabed one?

3. If observer in land would be launched in the air, entering the "sky ocean" from the "bottom", would he be crushed by the seabed pressure as if it were submerging into the Mariana's Trech, for example?
1. Compared to where the ocean bottom used to be? Maybe. It depends on the depth of the seafloor you're comparing the new one too. Very deep trenches in the current seafloor will have much higher pressures than the bottom of this floating ocean simply because the current ocean is much deeper at those locations than your new floating ocean would be.

2. Again, it depends on the depth of the seafloor that you're comparing the floating ocean too.

3. Probably, though the pressure wouldn't be nearly as much as the mariana's trench.

jedishrfu
Mentor
Are you writing a science fiction story?

Less than what?

If you magically exchange the current oceans with a layer of air as indicated in the sketch, the system is far away from an equilibrium: the air below will start at its old pressure, but suddenly all the water above pushes down on it - the water would fall down and compress the air below it. Shortly before the water reaches the surface, air pressure will be so high it gives some resistance to further compression - but then you still have something like 3km of water that fell down some significant distance and still moves downwards. It will completely crush everything on the surface. Shortly afterwards all the land is covered by 3km of water with some highly compressed air bubbles (the pressure at the surface is the same as it is now 3km below the ocean surface) moving upwards. The water will then start to rush back into the oceans, the flow rates should be sufficient to level down everything the flood reaches.
Hi MFB,

Wow, they said this forum was good. :)

Yes, that's the case. And the outcome is what I've imagined. \o/
But my point is (and here I'll also answer jedishrfu: yes, it's a science fiction novel) that for some not important reason, the water will remain in the sky, causing the air pressure in the surface to increase. My doubt is that in this "suspended ocean" if it's bottom (that would be the highlighted red zone in the image as "High pressure zone", and from the observer point of view (as Borek said, down (close to the observer)) would have the same/equivalent pressure as the seabed since it moved away from the earth's core.

The water would be distributed in the same depth on the sky ceiling, since we have enough space to allocate it and still have room for air down below.

Let's say someone tried to enter the "ocean" like a rocket coming from land and entering directly the ocean "bed", would it be crushed by water pressure as it was in a depth like, let's say, the Mariana's trench?

I hope I was clear this time... sorry if I confused you guys
:)

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mfb
Mentor
It is meaningless to ask "what would the laws of physics predict if the laws of physics do not apply".

Drakkith
Staff Emeritus
My doubt is that in this "suspended ocean" if it's bottom (that would be the highlighted red zone in the image as "High pressure zone", and from the observer point of view (as Borek said, down (close to the observer)) would have the same/equivalent pressure as the seabed since it moved away from the earth's core.
I believe I already answered this in post #4. The gravitational forces is practically the same, still well over 99% of what it is on the surface, so the pressure per depth wouldn't change much in that area. Along with that there would be a slight drop in pressure since the weight of the atmosphere is no longer pressing down on the ocean (since it is underneath).