If you are human, you are going to die. This isn't the most comforting thought, but death is the inevitable price we must pay for being alive. Humans are, however, getting better at pushing back our expiration date, as our medicines and technologies advance.

If the human life span continues to stretch, could we one day become immortal? The answer depends on what you think it means to be an immortal human.

"I don't think when people are even asking about immortality they really mean true immortality, unless they believe in something like a soul," Susan Schneider, a philosopher and founding director of the Center for the Future Mind at Florida Atlantic University, told Live Science. "If someone was, say, to upgrade their brain and body to live a really long time, they would still not be able to live beyond the end of the universe."

Scientists expect the universe will end, which puts an immediate dampener on a mystery about the potential for human immortality. Some scientists have speculated about surviving the death of the universe, as science journalist John Horgan reported for Scientific American, but it's unlikely that any humans alive today will experience the universe's demise anyway.

Related: What happens when you die?

Many humans grow old and die. To live indefinitely, we would need to stop the body from aging. A group of animals may have already solved this problem, so it isn't as far-fetched as it sounds.

Hydra are small, jellyfish-like invertebrates with a remarkable approach to aging. They are largely made up of stem cells that constantly divide to make new cells, as their older cells are discarded. The constant influx of new cells allows hydra to rejuvenate themselves and stay forever young, Live Science previously reported.

"They don't seem to age, so, potentially they are immortal," Daniel Martnez, a biology professor at Pomona College in Claremont, California, who discovered the hydra's lack of aging, told Live Science. Hydra show that animals do not have to grow old, but that doesn't mean humans could replicate their rejuvenating habits. At 0.4 inches (10 millimeters) long, hydra are small and don't have organs. "It's impossible for us because our bodies are super complex," Martnez said.

Humans have stem cells that can repair and even regrow parts of the body, such as in the liver, but the human body is not made almost entirely of these cells, like hydra are. That's because humans need cells to do things other than just divide and make new cells. For example, our red blood cells transport oxygen around the body. "We make cells commit to a function, and in doing that, they have to lose the ability to divide," Martnez said. As the cells age, so do we.

We can't simply discard our old cells like hydra do, because we need them. For example, the neurons in the brain transmit information. "We don't want those to be replaced," Martnez said. "Because otherwise, we won't remember anything." Hydra could inspire research that allows humans to live healthier lives, for example, by finding ways for our cells to function better as they age, according to Martnez. However, his gut feeling is that humans will never achieve such biological immortality.

Though Martnez personally doesn't want to live forever, he thinks humans are already capable of a form of immortality. "I always say, 'I think we are immortal,'" he said. "Poets to me are immortal because they're still with us after so many years and they still influence us. And so I think that people survive through their legacy."

The oldest-living human on record is Jeanne Calment from France, who died at the age of 122 in 1997, according to Guinness World Records. In a 2021 study published in the journal Nature Communications, researchers reported that humans may be able to live up to a maximum of between 120 and 150 years, after which, the researchers anticipate a complete loss of resilience the body's ability to recover from things like illness or injury. To live beyond this limit, humans would need to stop cells from aging and prevent disease.

Related: What's the oldest living thing alive today?

Humans may be able to live beyond their biological limits with future technological advancements involving nanotechnology. This is the manipulation of materials on a nanoscale, less than 100 nanometers (one-billionth of a meter or 400-billionths of an inch). Machines this small could travel in the blood and possibly prevent aging by repairing the damage cells experience over time. Nanotech could also cure certain diseases, including some types of cancer, by removing cancerous cells from the body, according to the University of Melbourne in Australia.

Preventing the human body from aging still isn't enough to achieve immortality; just ask the hydra. Even though hydra don't show signs of aging, the creatures still die. They are eaten by predators, such as fish, and perish if their environment changes too much, such as if their ponds freeze in winter, Martnez said.

Humans don't have many predators to contend with, but we are prone to fatal accidents and vulnerable to extreme environmental events, such as those intensified by climate change. We'll need a sturdier vessel than our current bodies to ensure our survival long into the future. Technology may provide the solution for this, too.

As technology advances, futurists anticipate two defining milestones. The first is the singularity, in which we will design artificial intelligence (A.I.) smart enough to redesign itself, and it will get progressively smarter until it is vastly superior to our own intelligence, Live Science previously reported. The second milestone is virtual immortality, where we will be able to scan our brains and transfer ourselves to a non-biological medium, like a computer.

Researchers have already mapped the neural connections of a roundworm (Caenorhabditis elegans). As part of the so-called OpenWorm project, they then simulated the roundworm's brain in software replicating the neural connections, and programmed that software to direct a Lego robot, according to Smithsonian Magazine. The robot then appeared to start behaving like a roundworm. Scientists aren't close to mapping the connections between the 86 billion neurons of the human brain (roundworms have only 302 neurons), but advances in artificial intelligence may help us get there.

Once the human mind is in a computer and can be uploaded to the internet, we won't have to worry about the human body perishing. Moving the human mind out of the body would be a significant step on the road to immortality but, according to Schneider, there's a catch. "I don't think that will achieve immortality for you, and that's because I think you'd be creating a digital double," she said.

Schneider, who is also the author of "Artificial You: AI and the Future of Your Mind (opens in new tab)" (Princeton University Press, 2019), describes a thought experiment in which the brain either does or doesn't survive the upload process. If the brain does survive, then the digital copy can't be you as you're still alive; conversely, the digital copy also can't be you if your brain doesn't survive the upload process, because it wouldn't be if you did the copy can only be your digital double.

Related: What is consciousness?

According to Schneider, a better route to extreme longevity, while also preserving the person, would be through biological enhancements compatible with the survival of the human brain. Another, more controversial route would be through brain chips.

"There's been a lot of talk about gradually replacing parts of the brain with chips. So, eventually, one becomes like an artificial intelligence," Schneider said. In other words, slowly transitioning into a cyborg and thinking in chips rather than neurons. But if the human brain is intimately connected to you, then replacing it could mean suicide, she added.

The human body appears to have an expiration date, regardless of how it is upgraded or uploaded. Whether humans are still human without their bodies is an open question.

"To me, it's not even really an issue about whether you're technically a human being or not," Schneider said. "The real issue is whether you're the same self of a person. So, what really matters here is, what is it to be a conscious being? And when is it that changes in the brain change which conscious being you are?" In other words, at what point does changing what we can do with our brains change who we are?

Schneider is excited by the potential brain and body enhancements of the future and likes the idea of ridding ourselves of death by old age, despite some of her reservations. "I would love that, absolutely, she said. "And I would love to see science and technology cure ailments, make us smarter. I would love to see people have the option of upgrading their brains with chips. I just want them to understand what's at stake."

Originally published on Live Science.

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Will humans ever be immortal? | Live Science