First, the difference between internal and external pressure in fish determines how deep they can dive. Some fish also have a gradual increase in internal pressure when diving (which may be the cause of the penetration of the fish's body). The pressure inside the submarine is basically the same (the pressure suitable for the human body), and as the submarine dives, the pressure difference between the inside and outside will gradually expand. Nowadays there are double-hull submarines, and the pressure in the middle layer (mezzanine) is higher than that inside, but when the submarine is diving, the pressure difference between the middle layer and the outside is much smaller than that of the single hull. So the depth of the dive is even deeper. On the other hand, the inside of the submarine needs to be loaded with people, and the air pressure inside needs to be adapted to the air pressure, and the huge pressure outside the submarine causes a pressure difference. Sperm whales can balance the pressure inside and outside the body, so they dive freely.
Second, because of the balance of internal and external pressure, whales can dive for thousands of meters. Pressure equalization is a necessity, but equilibrium does not mean that the pressure is gone. The whale's flesh walls are still under tremendous pressure, with the outward thrust from the inside, and the inward water pressure from the outside. For example, if you are constantly flushing water in your body, you can also achieve pressure balance, and you can also dive for thousands of meters, but the flesh wall of your chest cavity can't withstand so much pressure at all, and it will be thinned and crushed, so the whale can dive so deep, the fundamental reason is that its tissue structure is hard enough, and people also understand the principle of pressure balance, absorbing water when diving, and spitting water when floating.
Third, people who have a little thinking about this problem should understand that the internal and external pressure is the same, and any item with a mass greater than water can sink as deep as it sinks, such as tin cans, glass bottles, etc. There is space on the submarine, there is gas, if with the submarine diving, the gas can be pressurized and the sea sinks, the pressure can still reach the desired depth, the key is that it cannot be the same pressure as the sea water, even if it can be done, other items can not withstand it, so the submarine can not dive, but the sinking can be done, and the sinking can be done.
Fourth, the density of water is 800 times greater than that of air (standard sea pressure), and the outer part of the submarine 700 meters below the surface of the water is subjected to a pressure of 70 atmospheres, but the inside is only 1 atmosphere because of the need to meet the needs of human survival, and the shell is a rigid structure, and the huge pressure difference will crush the submarine shell. The whale is not a rigid structure, the soft and elastic body can change shape and size with the pressure without breaking, do not believe that if you press the balloon full of air into deep water, the balloon will become smaller, and the internal air pressure will increase to the same as the water pressure, but it will not **.
Fifth, first of all, it is impossible for fish to be crushed to death by atmospheric pressure, because the swim bladder does not adapt to the low pressure and bursts, killing the fish. The situation of whales is slightly different from that of fish, which is basically similar to that of humans. In a high-pressure environment, more oxygen and other gases are dissolved in the blood of animals than in a low-pressure environment, and the sudden low pressure will cause the gas to suddenly separate from the liquid (blood), forming an air clot, blocking the blood vessels and causing death. In order to avoid the above situation, the floating speed should be controlled to 5 10 meters per second, so that the excess gas can be expelled from the lungs, and there will be no danger. That's what whales do. Another theory is that the whale's ** is thicker and constantly shrinks during the ascent, creating corresponding pressure on the body.
Which one do you find more convincing? Feel free to leave your objective opinion?