Deep envisions several of its 'sentinel' units parking beside each other to from an underwater research center. Credit: DeepShareHumanity (or at least an eclectic subset of it) has been obsessed with exploring the deep seas for hundreds of years. Rudimentary forms of submarines and diving bells were envisioned as far back as the 16th century. More recent advances in submarine and submersible technology in the past hundred years, however, have made it possible for divers and explorers to spend an increasing amount of time underwater, in some cases for weeks on end. Now, according to The Guardian, one British company called Deep is taking that interest to an extreme. With the deep financial backing of an anonymous investor, the company is working towards creating a permanent human settlement under the sea.Deeps plan revolves around the creation of specially designed, house-sized submersibles they call sentinels. Equipped with multiple bedrooms and a communal area, these mobile research stations could one-day house residents at 80 meters below the oceans surface. If realized, the underwater homes could give scientists and researchers more prolonged access to unexplored areas of the deep sea than previously possible. It could also draw the attention of wealthy underwater deep-sea tourists eager to manifest their dreams of living for weeks or possibly months surrounded by the ocean.What will the underwater homes look like?If successful, Deeps small-house-sized sentinel units will let scientists and other would-be oceanic explorers live below the surface for longer periods of time and with some greater semblance of normalcy. The sentinels are currently being tested at Deeps facility in Gloucestershire near Wales. The floor units feature a recreation area, six bedrooms, a kitchen, and crucially, a bathroom with running water and a toilet. Deep envisions up to six people living in these underwater homes at a time. Several sentinels could also be placed next to each other to form a kind of underwater research station. The facilities are constructed using a special steel they say can withstand pressures of up to 200 meters below the surface. Initially, Deep plans to have its living facilities sit at a depth of 80 meters before plunging further down.The multi-floor sentinel units feature six bedrooms, a recreational area, and running water. Credit: Deep The overall mission of the project is to aid in scientific research and ocean exploration. By spending more time comfortably at lower depths, Deep says researchers may have a sustained presence in the ocean which will allow for more detailed studies of remote areas still filled with mysteries. Recreation areas onboard the sentinels can also function as an underwater laboratory. For now, according to The Guardian, Deep is preparing its participants to spend 28 days underwater. But Mike Shackleford, Deeps chief operating officer, says the long-term vision is much more ambitious.The goal is to live in the ocean, for ever, Shackleford told The Guardian. To have permanent human settlements in all oceans across the world.How human could survive underwaterLiving underwater requires some psychological adjustments. Deep sea divers typically breathe in a mix of helium and oxygen to avoid nitrogen narcosis. Something similar happens when living in a sentinel. After a certain period of time in deep water, the inert gases breathed in by a diver, or in this case, a sentinel resident, dissolve into body tissues and eventually reach an equilibrium with the pressure in their particular depth. This, Deep Director of Scientific Research Dawn Kernagis says in a blog post, is referred to as the principle of saturation. That equilibrium, or saturation, is the key to comfortably staying in deep water for prolonged periods of time.Once saturation is reached, the diver can stay at the bottom for days, weeks, and months without needing any additional decompression time, Kernagis said. All they need is a place to stay down there and the basics to sustain life (food, water, oxygen).The longest anyone has ever spent continuously underwater is 100 days, so its still unclear what if any physiological damage would occur to residents in deep sea environments for several years at a time. The more immediate concern, according to research published in The Lancet, is how a half dozen people will handle living among each other in tight corridors. Disturbances in sleep caused by a lack of sunlight and the stresses of a cramped environment could take a toll on residents mental health.That all may sound promising, but turning that theoretical idea into a reality will present challenges on multiple fronts. Currently, Deep is testing in a highly controlled, 260-foot-deep lake. Moving this out into the ocean will introduce new variables like extreme weather and possible disturbances from wildlife or other vessels. Theres also the uncomfortable specter of the OceanGate Titan submersible, which infamously imploded in 2023 killing all five passengers onboard. Unlike OceanGate, Deep says it is working closely with Det Norske Veritas (DNV), an international accreditation agency, to make sure its submersible and underwater homes meet safety regulations. Still, even with the best preparations, the ocean presents a unique challenge. Shackleford noted as much in The Guardian report.Basically, everything wants to kill you, he said.Humans are testing the limits of livabilityPrivate companies and nation-states alike are racing to build new habitats for humans in a place once considered unlivable. The Bjarke Ingels Group, an architecture firm based out of Denmark, in 2019 introduced the concept of Oceanix City a floating archipelago of platforms the firm says could one day house 12,000 people. Outside of Earth, NASA says its looking into a surface habituation system to allow future astronauts to stay on the moon for prolonged periods of time. China, meanwhile, has laid out an ambitious initial roadmap to build out a lunar base on the moons South Pole by 2035. SpaceX founder Elon Musk has, for years, envisioned a future human colony on Mars, though its unclear if thats even technically possible with modern technology.For now, at least, the most accessible alien world might be the still largely unexplored dark depth below the ocean surface.