Does flying make you age less? The physics behind a question that seems absurd

The short answer is yes. The long one is yes, but be prepared for disappointment.

When you are on an airplane cruising at 10,000 meters, time flows slightly differently for you than it does for those who have stayed on the ground. It's not a feeling, it's not a metaphor about the slowness of waiting at the airport. It is physics, and it is measurable. Einstein predicted it more than a century ago, and someone had the patience to verify it in the most literal way possible.

Two atomic clocks buy a plane ticket

It was 1971 and two American physicists, Joseph Hafele and Richard Keating, they had a budget problem. They wanted to test Einstein's theory of relativity in the field, but they did not have a space laboratory or particularly sophisticated equipment. What they did have were three atomic clocks, accurate to the nanosecond, and an idea that was as simple as it was brilliant.

They left one of the watches at the airport, in Washington. Then they bought plane tickets, arranged the other two clocks on the seats And they sent them on their way around the world, one to the east and one to the west. When the planes landed, they compared the times marked by the three clocks.

The results confirmed the predictions of the restricted and general relativity: the watches that had flown marked different times than the one left on the ground, with differences on the order of a nanosecond. Not an amount you would notice by looking at the watch on your wrist, but enough to prove Einstein was right across the board. The experiment is recounted in detail in Asymmetries, the INFN magazine., the National Institute of Nuclear Physics.

Because time doesn't flow the same for everyone

There are two effects that come into play when you are on a plane, and they go in opposite directions.

The first concerns altitude. At 10,000 meters, the earth's gravity is slightly lower relative to the ground. Einstein's general relativity says. Where gravity is less, time flows faster. So the altitude would tend to make you age slightly faster than those who stayed at home.

The second concerns speed. An airliner flies at about 900 kilometers per hour. Special relativity says that the faster you go, the slower time slows down for you compared to a stationary observer. This effect goes in the opposite direction of the former and, on commercial flights, prevails.

The net result is that While you are in the air you age a very little less Of those waiting for you on the ground. Very little means a few tens of nanoseconds per hour of flight time. A nanosecond is a billionth of a second. You do the math on how much longevity that works for you.

Exactly how much time do you earn

A frequent flyer who flies 100 hours per year accumulates an advantage of a few thousand nanoseconds. Matteo Rainisio, who flies well over 100 hours a year, maybe gains a few hundred thousand nanoseconds. In a lifetime of flying, we're talking fractions of a millisecond. Not enough to notice in the mirror, not enough to postpone the check-up at the doctor, not enough to justify the cost of a business class ticket as an investment in health.

To put the number in perspective: sleeping an extra night, taking a half-hour walk or eating a vegetable instead of a French fry has a billion-fold effect on life expectancy. Einstein is fascinating, but the Mediterranean diet beats relativistic physics when it comes to aging well.

The flip side of the coin to consider

However, there is a part of the story that is usually forgotten when it comes to aircraft and aging, and it goes in exactly the opposite direction.

At cruise altitude, the atmosphere is thinner and protects less from the cosmic radiation coming from space. The result is that during a flight you are exposed to a higher dose of ionizing radiation than you receive at sea level. For a passenger who flies a few times a year, this is completely negligible. But for someone who flies hundreds of hours a year, the issue is serious enough to be regulated. The Civil Aviation Authority classifies pilots and cabin crew as. workers exposed to radiation ionizing, with annual exposure limits and periodic monitoring, just as is done for those working in environments with other sources of radiation.

Ironically, the airplane ages you relativistically less and biologically more, for completely different reasons and with effects that are not even remotely equivalent.

So is it worth flying to live longer?

In a strictly physical sense, yes. In a practical sense, the question makes little sense. The nanoseconds gained through time dilation are real but irrelevant to any decision regarding your health or longevity.

What you can say, the next time you're stuck in a long haul with your knees against the front seat and your oxygen mask staring down at you from above, is that you're technically aging a little less than everyone you know. It's a marginal consolation, we admit, but it's supported by Einstein himself.