The human body is not magical, it’s a machine, that takes advantage of the laws of physics and that machine has flaws, such as dying from old age. The human body is in essence, the most advanced technology on the planet. Nanotechnology is an emerging field and eventually we will come to a full understanding of the human body and create technology just as sophisticated.
There are researchers studying what is called Telomeres. Telomeres are protective caps on chromosomes and with each cell division, the Telomeres are shortened. As you age, the accumulative damage eventually starts causing cells to malfunction. There is also an enzyme in our DNA called Telomerase and it can repair Telomeres. Scientists have already created a virus, that activates the gene in mice, to cause them to produce the Telomerase enzyme and repair their Telomeres. In a study, mice have regrown hair and lived 33% longer from a single treatment. Some forms of cancer also produce the Telomerase enzyme and are essentially immortal. It’s also possible with enough treatments, you could reverse-age from 80 to 20 within a few years. Repairing Telomeres may be part of the solution but there could be other “bugs” in the human machine that need to be fixed as well, such as neurons in the brain dying and not being replaced. We will just have to wait and see. The following is a YouTube video that talks about the possible causes of aging:
In my universe, I have immortality. I limited the population of Earth to 100 billion people. I handled population growth by transitioning to subterranean cities, underwater cities and floating cities; basically instead of a giant continuous city, we have a giant continuous Central Park on the roof. The economy was engineered using a modified land tax, which only taxes surface land that has been modified from it’s natural state. This incentivized more skyscrapers, subterranean cities, floating and under water cities, by allowing tax dodging and making it the path of least resistance. I handled food production by switching to indoor hydroponics with solar powered artificial lighting and carbon dioxide enrichment. Using known technology, we can increase our food production by 12 times. If you include genetically modified organics, that number could be increased further. You can also do multi-story farms and increase the yield per area even more. We will also eventually have to recycle fertilizer. By 2600, Mars and Venus are terraformed and there are a billion people living on space stations in the Sol system. I estimated by the year 4000, we will need to give up immortality or give up having children. Fractal Federation also colonizes 1400 star systems, so people who want to remain immortal can immigrate to a new star by digitizing their mind using nanomachines and doing an intersteller mind transfer. With theoretically possible memory density, we could store every particle in the human brain, the velocities and positions, down to picometer precision, inside a volume of space smaller than a penny. We could have a virtual population in the septillions, where people live in a virtual reality with all five senses and can use time-shared android bodies when they need to do something in the real world. If we mined the entire Solar system, put every useful element into circulation, recycled everything, and came up with every variation of technology using as many different raw materials as possible, we could maximize the population and/or quality of life. Most people might think that immortality is a bad idea because of limited resources but I personally think we’ll be fine for another two thousand years. We can decide then.
I made a spreadsheet with all the elements in the star system. The data on asteroid and moon composition is very limited. It looks like the first thing we will run out of is Nitrogen for space station atmospheres. We could have 86 trillion people living on space stations. If we abandon Venus, Earth and Mars; and use their Nitrogen, we could increase the maximum population by a lot more. Using Nitrogen for planetary atmospheres is a less efficient approach. Not to say we have to abandon planets, we could just build massive layered planet-wide cities and suck all the atmosphere into the pressurized buildings. We could also have a huge continuous subterranean city, with a natural ecosystem on the roof, then build a dome over the entire planet. Right now most of the atmosphere is creating 1 bar of pressure, other than that, it’s not being used. If we pressurized the whole planet, it would free up a lot of Nitrogen.