First: I think a balloon would still be a balloon, but what becomes of us living under pressure…
There are various of species living under these conditions, but can people turn into “submerged things” not by evolving, but just getting used to it gradually
Well, the balloon would have to be pressurized in order to not compress tightly around your body and kill you.
I think a rigid structure would be a better idea than a balloon.
A balloon is going to shrink drastically as the water pressure increases with depth. At the deepest parts of the ocean, a balloon at normal pressures is going to be compressed to the point of being really tiny.
If you dramatically increase the pressure inside the balloon it will stay inflated, but human beings can only tolerate so much air pressure. Given time to acclimate to the pressure, humans could survive down to about a thousand feet below sea level, but that’s about it. Divers who work at these depths also use a mix of helium and oxygen, since normal air becomes too dense and thick to breathe at those pressures. If you have normal air in your balloon, the max depth would be much shallower.
The ocean floor is way too far down and the water pressure there is far too great for us to be able to tolerate it.
You die. But the reality is odd.
To be in a balloon the air pressure must equal the water pressure, so the density of air is very high. You can’t live with ordinary air at those pressures. Your first problem is actually the oxygen. At the pressures you see at ocean depths, the concentration of oxygen is toxic, and you would die (in agony) very quickly. So you need to get the concentration of oxygen down. This is termed the partial pressure. IE, that part of the total pressure you experience. You need to get the oxygen down so that the number of atoms per unit volume of the gas you breath is similar to that you breath at sea level. You also need to get rid of the nitrogen, as that has unfortunate effects as well.
Your next problem is that the air at depth is much thicker than at the surface. There are a lot more atoms in the gas, and the viscosity will become a problem. At best you can use a mixture of helium and oxygen - with very little oxygen. But even then, at the pressures you get a deepest ocean floor, the air is actually too thick, and you won’t survive for terribly long.
The obvious answer is perflurocarbons perfusing your lungs (ie as in The Abyss.) Maybe one day.
Only if your balloon is made of something extremely strong, uncollapsable, and water/air proof, and can maintain an atmosphere pressure inside it that humans can live with.
Basically we’re talking about a submarine or bathyscaphe, which is exactly that sort of balloon.
Beyond a certain depth, breathing air at the local pressure causes nitrogen narcosis. This is a problem for SCUBA divers who must carefully manage their dive in order to survive it. If you’re protected inside a balloon of sorts, with (for the sake of discussion) unlimited supplies of air and food, then the narcotic inebriation is much less of a problem - but the narcosis still gets bad enough to kill you at depths greater than ~300 feet.
Below a couple hundred feet you’re also at risk for oxygen toxicity: yes, too much oxygen in your body is a bad thing.
SCUBA divers using Trimix (a custom blend of oxygen, nitrogen, and helium) can manage the risks of oxygen toxicity and nitrogen narcosis, allowing them to operate at greater depths, but even then the limit is about 1000 feet. This is much shallower than the “deepest floor of an ocean” - which would be the Challenger Deep, almost 36,000 feet to the bottom.
ISTM that breathing liquid would be difficult, especially for relatively large organisms like us. As has already been pointed out in this thread, the low density of helium helps make trimix/heliox easier to breathe at depth than plain old air, and a liquid is going to have a density *hundreds * of times that of air. You’d need some kind of breathing assist device, a pump to cram the liquid into your airway during inhalation along with a vacuum to suck it out during exhalation.
My impression was that this was the intent - and that you actually stop breathing yourself altogether, and rather let a perfusion pump circulate the fluid. But it is after all still mostly science fiction. The oxygen transportation of the liquid is (I think) much better than air, so you don’t need to circulate the fluid all that fast.
For 20 minutes…
At what pressure would some vital piece of human cellular machinery collapse, due to solubility or whatnot?
I am not sure, but i now have a vision in my head of some poor guy with every bodily fluid being squeezed out of every orifice large and small in his body until the poor guy dies of something rupturing
Trimix will get you to around 500ft, but eventually the helium contributes significantly to High Pressure Nervous Syndrome. There are ways to try to manage that, including other gas mixtures such as Hydreliox (Hydrogen, Oxygen, and Helium), Heliox (Helium and Oxygen) or for the truly whacked out folks there is straight Hydrox (Hydrogen and Oxygen).
Hydrox. It’s not just a cookie.
So living at ambient pressure on the sea floor is not really practical below 200ft or so. A depth of 500ft is pushing it for short visits. And the nervous system starts to go all to hell as you approach 1000ft.
The limiting factor may relate to gas solubility in the myelin sheath of certain nerves. Nerve conduction seems to be compromised by gas dissolving in myelin. This is one hypothesized mechanism of action to cause Nitrogen Narcosis. Taken to extreme, go deep enough and some nerve key to respiration or cardiac function is probably going to short out.
That’s correct; it’s just not possible with current technology and physiological science to go deeper for any sustained period. Using saturation diving – where the diver lives in a pressurized environment underwater breathing exotic gas mixes – brief excursions have been made at 700 meters (2,300 ft) but they had problems: Saturation diving - Wikipedia
If total liquid ventilation (TLV) was perfected, deeper dives might be possible. But even though TLV has been experimentally used on humans, none of the available oxygen-carrying liquids will transport adequate CO2 from the lungs. So the subject’s bloodstream would have to be intercepted and scrubbed of CO2 – basically a portable heart/lung machine – in addition to managing the liquid breathing apparatus.
What, like, 20 minutes?
(in the 1960s)
The occupants were not exposed to ambient pressure. The Trieste was designed to resist the enormous pressure of the water at such extreme depth. That is something a balloon (as specified in the OP) could not do.
Are gravity and pressure related in any ways?
The pressure is caused by the weight of the water, so yes.
… how much gravity would a 100m water sphere make - not much?