Bryan Johnson is a software entrepreneur who

Johnson is just one of many ber rich people spending billions to prevent themselves from growing old. But eventually, they may run up against a fierce obstacle in their quest for eternal youth: the laws of physics. So is immortality possible?

The thermal motion of thousands of water molecules smashing into our cells molecular machines can break the bonds between molecules. Over time, this wears out our cells.

There are a few possible reasons why we age. The evolutionary argument is that each generation of creatureswhether human, animal, or plantmust grow old and die to make way for a new generation. In that case, the fact that our bodies stop repairing themselves at a point isnt a design flaw, but a feature.

Alternately, or possibly in tandem, is the wearing-out theory of aging. There are various molecular machines, that do everything from replicating cells to moving nutrients where they need to be in our bodies, biophysicist and nanomechanics expert Peter Hoffmann, Ph.D, eloquently explains in an article for Nautilus Magazine. As these machines go about their business, they are surrounded by thousands of water molecules, which randomly crash into them a trillion times a second. This is what physicists euphemistically call thermal motion. Violent thermal chaos would be more apt, he writes.

This thermal motion, Hoffman says, provides a source of energy that these molecular machines can harness for their work; but it is also responsible for breaking bonds between molecules. When he and his colleagues replicated this action in a lab, they found the survival probability of the bonds plotted against applied force looks just like human survival plotted versus agewhich suggests a possible connection between breaking protein bonds and agingand between aging and thermal motion.

In other words, just through living, we experience basic wear and tear. Unlike inanimate objects, we can repair our systems after such damage, but there are still limits.

Leonard Hayflick, Ph.D, has worked as professor of anatomy and microbiology, and is among the foremost experts on aging. He developed what is known as the Hayflick Limitthat is, the number of times human DNA cells can replicate before they become senescent, or stop replicating and take on a different form associated with age. After a lifetime of study, Hayflick supports the wear-and-tear explanation of aging.

Everything in the universe ages for the same reason your car is brilliant because it knows how to age without any instructions, either in the car itself or in the blueprints, Hayflick says in a 2015 presentation on biological aging held at the University of California, San Francisco. So why is the second law of thermodynamics the probable cause of aging? It governs the behavior of all molecules; it can explain the ultimate cause of all other theories of aging; it is testable using current technologies; its falsifiable; it is universal and applies to both animate and inanimate objects.

Entropy is the condition of things moving from a more-ordered state to a less-ordered state; Rudolf Clausius first postulated the concept in the 1850s. The second law of thermodynamics, the law of entropy, states that if the physical process is irreversible, the entropy of the system and the environment must increase; the final entropy must be greater than the initial entropy.

For instance, when you eat an apple, the fruit starts out in a low-entropy state, and its entropy increases as you chew it, digest it, and incorporate it into your bodys fuel system. Entropy increases among billions of different molecular processes in our complex bodily systems. The longer you live, the more entropy you will have experienced, and each new occasion of entropy can create a slew of new entropic processes, in turn.

Some of the damage that occurs in our bodies can be reversed, but with some 37 trillion different cells of 200 different types all affecting one another, there are cascading impacts. Your bodys repair systems simply cannot keep up, catching and reversing every last bit of molecular damage.

Your body is a hierarchical network of interlocking systems where everything acts with everything in a very complicated way, Hoffmann tells Popular Mechanics. If your DNA is a bit damaged, it affects the repair mechanisms, which can get a bit slower. This builds up. In principle, you could fix everything, but in practice, its just not possible, because of the complexity of the system. Recent studies have shown, for example, that transcription of DNA into proteins is compromised as organisms age. Since proteins do most of the work in cells and are responsible for the structure and function of the tissues, that can result in what we experience as aging.

Could blood transfusions from a young body increase an older persons lifespan? While research with mice shows a life-lengthening effect, the findings dont necessarily translate to humans.

Obviously, if you live in such a way that you reduce damage to your cells and organsyoure not sedentary, you dont drink too much, you provide adequate nutrition for your body to run onyou slow down the aging process, because you arent overtaxing the bodys ability to repair itself. Some scientists have found older mice that receive blood transfusions from young mice live longer, though the findings dont necessarily translate to humans.

But are there other ways humans can systematically slow aging? Yes, to a point, Hoffmann says.

Cooler temperatures sometimes help. Low-calorie diets can, too. Research on nematodes and mice show that exposure to medium-static magnetic fields might slow aging in the whole system. However, other studies show that exposure to electromagnetic fields can accelerate aging; scientists are still exploring the factors that affect these varied results. Aging, Hoffmann acknowledges, is a very complex process.

You can take as much vitamin C, and B, and A, eat all the good fruits, live in a beautiful place and meditate every day and do your exercises, and if youre lucky, maybe you reach 110 years old, Hoffmann says, but not 160. Though the human lifespan has doubled over the past century, thanks to improvements in hygiene, medicine, nutrition, and other factors, most scientists believe were unlikely to surpass the upper lifespan limit Jeanne Calment set in 1997 when she died at 122.

On the other hand, given our size, the human lifespan already far surpasses what it should logically be. With some notable exceptions, longevity often corresponds with the size of the animal. A mouse lives for two years, on average, while elephants live to 60, and blue whales swim on until age 90. With that in mind, we should top out at around 40 years of age, as most people did before about the 20th century. Animals in the wild seldom grow old because they die from predation, disease, or starvation long before they have a chance to develop inflammation and other issues of cellular aging.

Is It Ethical to Spend Billions to Live Forever?

Theres an ethical issue to the billions invested in making rich people live longer, too, Hoffmann notes. While their discoveries might help all people live longer, theres a vast disparity between how the rich and the not-so-rich will experience those extra years. The U.S. has a uniquely negative perspective on age and dying. Though it is one of the richest countries, life expectancy in the U.S. ranks 43rd in the world.

And why is it going down? Hoffmann asks. Its because were not setting up our society to be aging friendly at all. ... We put more stress on people all the time, our healthcare system is inefficient and often inaccessible, we dont have the physical environment to exercise properly, good food is expensive, and bad food is cheap. We put chemicals on everything. ... I live in Florida, and people put piles of chemicals on their lawns. You dont see insects anymore.

On top of that, most people dont have retirement savings; U.S. Social Security is rarely enough to live on, and ageism bars older people from employment. Though age can come with advantages, such as wisdom borne of experience and a sense of peace and happiness that replaces the anxiety of youth, these things are seldom valued as much as elastic skin and physical prowess.

And since climate change is set to make some places uninhabitable within the next 30 years, and rates of anxiety and depression are skyrocketing, it might be worth putting those billions into making life better for people in the years they do have.

Studies point out that being old is the greatest predictor of developing a fatal disease; but aging itself cant be a diseasediseases have causes, and are not universal. Aging is universal to all living things, and its only cause is time. The risk of death increases as one grows old, but the risk of death is 100 percent for all things that are alive.

People living in Blue Zonesplaces like Okinawa, Japan; Sardinia, Italy; Ikaria, Greece; Nicoya, Costa Rica; and Loma Linda, Californiatend to experience uniform longevity, and have the highest rates of centenarians, or people who reach the age of 100 years or more. Locals in Blue Zones inadvertently follow lifestyles that adhere to four rules:

Those living in Blue Zones do not have special diets or treatments or supplements. But theyre not really trying to live a long time. And theyre definitely not trying to stop aging.

Bryan Johnson did receive blood transfusions from his son, just like the mice that researchers studied in the lab. He doesnt do it anymore, Johnson says, because there was no detectable benefit. He is reportedly showing several markers of being youngerincluding more youthful bones and more nighttime erections.

But now, Johnson has a new mission: not dying. Ever.

He thinks dying is pass, unnecessary. And most of Johnsons life is structured to avoid anything that could contribute to the bodily entropy that leads to cascading molecular failures in the bodysunlight, pizza, margaritas, staying up late, arguably some of the greatest pleasures in life. One reporter for TIME magazine reported visiting Johnson at his home and laboratory, where he gave her a taste of the chocolate he allows himself. It had been un-dutched, stripped of heavy metals, and sourced only from regions with high polyphenol density. In her words, it tastes like a foot.

For some, the pursuit of slowingand maybe even reversingaging might be a passion project, like being able to bench press 250 pounds or play Paganinis 24 Caprices on the violin. Perhaps one day, well discover quantum aging, and then all the rules will be out the window.

But until then, go ahead and indulge in the little entropic luxurieslike a nice red wine or a crusty baguettethat make the life you do have worth living.

Susan Lahey is a journalist and writer whose work has been published in numerous places in the U.S. and Europe. She's covered ocean wave energy and digital transformation; sustainable building and disaster recovery; healthcare in Burkina Faso and antibody design in Austin; the soul of AI and the inspiration of a Tewa sculptor working from a hogan near the foot of Taos Mountain. She lives in Porto, Portugal with a view of the sea.

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Immortality Is PossibleWe Just Have to Overcome One Stubborn Law of Physics - Popular Mechanics