Why is it said that people with overly vivid imaginations cannot become divers?

Why do people with too much imagination end up not being able to become scuba divers? What did you see? Nothing, right? Then why do you feel a racing heart? Your eyes clearly didn’t see anything, yet you can’t control the fear. Don’t force yourself to push through—this isn’t sensitivity or drama. It’s the most primal fear of the unknown deep ocean, hardcoded into human DNA. The calm you see is all an illusion. In this sea that looks empty, what’s hidden is scarier than every horror movie you’ve ever watched.

Below the surface of the ocean, there’s a world that should never be uncovered. As the light fades little by little, life exists in ways that completely defy common sense. This is the low-light layer, stretching down to a depth of 1 kilometer. Sunlight is so weak that photosynthesis can’t happen, and the paradise of plankton disappears. No plants, no green energy—only debris drifting down slowly from the upper layers, like a silent snow. And these are waste and biological remains. Scientists call it marine snow.

To humans, this stuff isn’t noteworthy. But to the creatures here, it’s everything needed to survive. Where there’s food, there’s life—though it’s no longer the kind of life we’re familiar with. Animals in the low-light layer look stranger than the next. Many are entirely transparent, like glass, floating in the water, with even their internal organs visible clearly, like a ghost.

To be honest, even now scientists haven’t fully figured out why so many species evolve into transparency—are they doing it for stealth, or so they don’t draw too much attention? But some species develop ideas completely the opposite. They don’t hide or conceal themselves; instead, they evolve their own light. It looks beautiful—specks of starlight, glowing patterns that are like neon lights on the seabed. But don’t be fooled. Here, light is actually a survival tool. Some creatures lure prey with light, while others use it to find mates.

The coolest part is that bioluminescence is for disappearing. This trick is called counterillumination. For example, the firefly squid grows light organs all over its belly, adjusting brightness to match the faint light coming from the ocean surface. That way it can erase its silhouette right away. In other words, it glows in order to hide in the light. Even more clever is the blood-bellied comb jelly: it emits red light, but in the deep ocean red light can’t travel far, so in the darkness it’s just pure black. Even if it swallows prey that glows, the light won’t show up—like it comes with a body-concealing function.

In this world, survival follows a single logic: whoever can’t be seen, can live. Even more interesting is that during World War II, naval sonar discovered a bizarre phenomenon—one layer of the seafloor would rise at night and sink again by morning. Later people learned it wasn’t the seafloor at all, but an entire layer of life. A hidden world moves in sync. This is called diel vertical migration. Every night, billions of creatures rise from the deep sea toward the surface. A vast deep-sea army takes advantage of the darkness to feed at sea level, then as daylight comes they collectively sink back down. This is the largest synchronized migration on Earth—more than all the animals on land combined.

Once you cross 1 kilometer, sunlight vanishes completely. This is the aphotic zone, down to 4 kilometers deep, with no day or night—only eternal darkness. The water temperature is near freezing, and the water pressure is hundreds of times that at the surface. The environment is extraordinarily harsh, yet in exactly this place evolution becomes the most extreme.

Most bizarre of all is the anglerfish, with an extremely outrageous breeding strategy. The male is weak and spends its entire life trying to find a female. Once it finds her, it clamps down hard. The two bodies then slowly fuse, until only a sperm pouch remains. From then on, it lives off the female for its whole life. Even with submersibles, human understanding of the aphotic zone remains fragmentary.

Diving further to 4 kilometers is the abyssal plain—an endless mud desert covering 70% of the ocean’s global area. Deep-sea gigantism is popular here. Things like giant isopods and the giant squid are much larger than their shallow-water counterparts. When a whale falls, it’s a feast. Scavengers swarm in, bone-eating worms strip the bones, and a single carcass can support an entire ecosystem for decades.

There are also vampire squid. Although the name is scary, it basically picks up trash and eats it. It can live even in the oxygen-poor deep sea, with an oxygen-carrying ability so extreme it’s hard to believe. Life here grows slowly, and reproduction is scarce, yet they live remarkably long. Greenland sharks can live for 400 years or more—making them the longest-lived vertebrates in the world. In this place, time seems to slow down too.

Another 6 kilometers down to 11,000 kilometers is the ocean trench. If you throw Mount Everest in, the peak would still be more than a kilometer underwater. Water pressure reaches over a thousand times atmospheric pressure—humans simply can’t survive. Yet life still takes root there. A lionfish has a soft, transparent body. It looks like it would tear with a poke, but it is the deepest-known vertebrate. It has no hard bones; its cells are specially reinforced, and under high pressure it still swims and thrashes around as if lively.

Inside the trenches, there’s also hydrothermal vents that send shivers down your scalp. Here, microorganisms don’t rely on sunlight. They can support a complete chemosynthetic food chain using only hydrogen sulfide and methane spewed from the Earth’s crust. Even today, over 80% of the ocean remains unknown. The deep-sea fear you feel right now isn’t because there are monsters in there—it’s because we know nothing about what’s there. Beneath the calm lies the most疯狂, most震撼, and most terrifying truth on Earth.