My son and I went to the movies the other night to see Project Hail Mary. It’s a terrific Sci-Fi flick based on Andy Weir’s awesome novel by the same name. The plot is about an astronaut crew that travels for decades and light-years to a distant star to figure out a way to save the earth from some really bad astronomical goings -on that are unfolding back here at home. I won’t spill the beans on any more of the plot so go see the movie if you haven’t already. It got me thinking about time/space travel that’s a fascinating mind experiment, and it leads to all kinds of mental rabbit holes to dive into.
Time travel is certainly not new to any of us. Way back in 1895, HG Wells started off the whole Sci-Fi genre with his first novel, The Time Machine, which tells the story of an unnamed traveler who jumps into his time travel contraption and ends up in the year 802,701—way out there and kind of random sounding—but that's typical HG Wells. The traveler discovers that humanity has “evolved” into two separate forms with the dominant and aggressive underground dwellers, the Morlocks, who prey on the feeble, defenseless Eloi guys who live on the surface and farm all the crops that the bad boys steal. By setting the action nearly a million years in the future, Wells likely based his new humans on Darwin’s model of evolution and natural selection—kind of “fast-forwarding” through the slow evolutionary process Darwin described in his landmark study, The Origin of the Species, in 1859.
The reason time/space travel is so fascinating for me is that looking up at the stars in the night sky, you realize that if you could only magnify the images enough, the light you see from a star 5,000 or 10,000 light-years away is a look 5,000 or maybe 10,000 years back in time to the past events up there. The other thing about the time/space travel thought experiment, in keeping with the superagers and aging themes of the last few articles, the longer and faster you travel in space, the slower you age so the longer you live. It has to do with something way over my head related to Einstein’s Theory of Relativity, which proved the faster you travel, the slower time elapses.
So those astronauts in Project Hail Mary not only traveled to the other side of the galaxy but they didn’t age as much as the guys who sent them on their journey—a little bit of payback, I guess—another reason to see the movie to get what I mean. It’s called “time dilation,” and it’s one of the most mind-bending things about Albert Einstein’s Theory of Relativity. Time moves more slowly for a person in motion compared to a person at rest. This effect also applies in gravitational fields. Someone closer to a gravitationally dense body like a black hole would be subject to a slowdown in time compared to others farther away. It’s not like life would proceed in “slow motion” for those folks; everything would seem normal within their own frames of reference. The relative differences would only be noticed when everybody meets up and compares their respective aging, likely prompting that vapid greeting, “Oh my, you haven’t aged a bit,” only true in this case.
In our own existence, we really don’t have to concern ourselves with time dilation, as humans move much too slowly to ever notice it. However, physicists keenly tuned into the tiniest ticks of time have documented time dilation in a very human activity that we all love, flying airplanes. Forty years ago, physicist Joseph C. Hafele and astronomer Richard E. Keating bought tickets for themselves as well as four highly precise Hewlett-Packard atomic clocks to take two commercial airplane trips around the world, one heading east and the other one heading west, to test Einstein’s theory. After the trips, they compared the times on the atomic clocks in the airplanes with the time of the atomic clock at the United States Naval Observatory. If Einstein’s theory of relativity was correct, the clocks heading east should have been behind those on the ground, while the ones traveling west should have been ahead and that’s exactly what the two guys found. Physicist Heino Falcke explained why it is in his recent book Light in the Darkness that clocks that flew east with the Earth’s rotation relative to the clock on the ground were 60 nanoseconds behind after the flight. The clocks on the flight traveling west, counter to the Earth’s rotation, had a larger difference in velocity relative to the clock on the ground and were a full 270 nanoseconds ahead of the clock in the laboratory. I’m not sure that amount of time was worth all the ticket prices—but that’s science.
Adding to our thought experiment on time travel, we can compare former NASA astronaut Scott Kelly after his historic one-year mission aboard the International Space Station (ISS) with his identical, but earthbound twin, Mark, who is the slightly older brother. The unprecedented space ride, which ended this past March, brought Scott’s total time in orbit to 520 days—all of which he spent zooming around Earth at 17,500 mph. “So, I used to be just 6 minutes older, now I am 6 minutes and 5 milliseconds older,” Mark said when his brother showed up for their birthday party. Another high price to pay for a moment extra. Aging of space travelers is a really interesting topic and the subject of a study published earlier this year on astronaut aging. It turns out that, besides going far and fast, spaceflight exposes astronauts to a combination of environmental stressors such as microgravity, ionizing radiation, circadian disruption, and social isolation that cause other changes in their rate of aging. In their study, the authors looked at 32 DNA markers of biological age in 4 astronauts during the Axiom-2 mission, which was a private spaceflight operated by Axiom Space. The mission was launched on May 21, 2023, atop a SpaceX Falcon 9 from the Cape and orbited for 10 days.
They compared these genetic markers preflight, in-flight (day 4 and 7), and post-flight. It turns out that space travel time slowing is not all in one direction for astronauts. According to those 32 DNA markers, on average, biological acceleration increased aging 1.91 years by flight day 7, but don’t jump on the next commercial space flight; everything changed again when these space flyers came back to Earth. Biological age reversed and decreased in all the crew members, with older astronauts returning to preflight estimates and younger astronauts showing a biological age significantly lower than preflight levels. This suggests that spaceflight induces rapid, yet reversible, genetically linked changes associated with aging, making spaceflight a good way to study human aging and might make it possible to understand our aging process and to find positive find interventions to extend life-span.
So, yeah, you are “time-traveling” relative to individuals on the ground when you take long-distance flights, particularly on those traveling west, but you’ll never notice. It’s still a fun mind game to think that another way to get to be one of the “superagers“ we talked about last month is to jump into your plane, crank it up, and fly around the planet. But, to add a mere one second to your age relative to friends and family on the ground, you’d have to fly west around the globe 3.7 million times! That would put a pretty big dent in your fuel budget and take up all of your spare time and then some. Probably a better way to live longer and add some time on is to follow all the good advice on diet, exercise, and healthy lifestyles we’ve talked about for months. Especially important to growing old is to, as always, FLY SAFE.
