Why do astronauts age differently?
Time dilation and microgravity… Cool.
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Everyone has their own life experiences. Some range over 40 years, and some range over 2. And the ones with 2 years’ experience seem to make the ones with 40 feel like it was 80… A variety of things can lead to changes in aging—stress, illnesses, exercise, and diet, to name a few. But all these have one thing in common: they seem to speed up or slow down the physical effects of “aging”. They change how you look, how you feel, but none of them actually increase or decrease the amount of time that you’ve experienced. A 40-year-old is still 40 years old—regardless of the condition they’re in. But what if there was a way you could slow down time? What if you really could age more slowly than everyone else? Would you do it? Wait. Don’t answer that yet—you might want to hear what we have to say.
Today we’re going to explore the concept of “Time Dilation”, what it means, and why people usually think it means something else. It’s going to get pretty meta, so if you have any questions, make sure you ask in the comments below.
Our story begins in the world of General Relativity. Our hero, Albert Einstein, stands in front of a chalkboard. He looks perplexed. Why you might ask? He’s just stumbled upon a very unnerving discovery: time isn’t constant. One second here isn’t one second everywhere else. “How will the world react to this news,” he thinks, “I hope no one will make a movie about a hot tub that can go back in time”—the one incorrect hypothesis Einstein ever had. Now you may be thinking, “well, what was on that blackboard?” I have no idea, to tell you the truth, but I’d guess it looked something like this: [1]
This is one of Einstein’s “Field Equations” that he used to define “spacetime”. Spacetime is a concept within General Relativity that represents both three-dimensional space and time as one, unified fabric. Because the two are connected, we can reasonably conclude that one can affect the other. For our purposes, the only takeaway that we need is that the gravity you experience and the speed at which you’re going both can directly affect how time passes. That being said, Earth’s gravity and orbital velocity are not nearly strong or fast enough to significantly affect our time. Therefore, most time in the universe passes very similarly to ours here on Earth. But in the case of Black Holes, or near the speed of light travel, these effects are much more noticeable. Some of you may recall in the movie Interstellar, the astronauts visit a planet that is so close to a Black Hole’s gravitational field that every hour passing on the planet is 7 years on Earth. While we can’t actually prove this until we go and visit a planet like that with an iPhone stopwatch, it’s theoretically possible.
But I don’t like theoretical. And I don’t think you do either. I want to see proof. So, we have to find somewhere close to home that we can either experience an extreme amount of gravity or travel at extremely fast speeds. The gravity option is out, unfortunately. The heaviest object we have in our solar system is the Sun, and even the Sun doesn’t have enough mass to really see these effects. Not to mention we’ve not even gotten humans past the Moon. The speed option, if we have accurate enough clocks, is attainable. We’ve discussed in a past newsletter what it would take to get to a significant percent of the speed of light and in summary: it’s a lot. But we have gotten people up to speeds that just might be enough. Where? The International Space Station. Astronauts on the ISS travel around the Earth at 4.76 miles per second. Surely that’s fast enough to slow down time.
Amazingly, it is. According to Einstein’s theory, the rate at which time passes for astronauts traveling at this speed is less than it is on Earth. Therefore, they are technically living in a state of slowed time. Crazy. Although cool in theory isn’t always cool in practice. These astronauts are only going 0.003% the speed of light. Because of this, they can spend months on the ISS and return home only having experienced microseconds less than their human-bound counterparts. Regardless of the quantifiable results being rather unimpressive, the qualitative results are—astronauts, because they’re traveling so fast, experience time dilation. As a result, time passes for them more slowly than it does for the rest of us.
Unfortunately, I must admit, it doesn’t matter. They can’t stay up there long enough to really be younger than they otherwise would be when they return. That’s because of all the other effects of space. Radiation exposure, microgravity, and sterile conditions are not generally kind to the human body, and onboard the ISS they significantly offset any anti-aging effects of time dilation. So, they experience less time, but they actually age more.
I’ll leave you with this: what is time travel? What does it mean to slow down time? You never actually experience more or less time. You can’t reduce or increase the amount of time that’s passed. You can only experience relative changes. (Hence the theory of relativity) By going at crazy high speeds or passing by a Black Hole, you don’t speed up others’ time, nor do you slow yours. They still live at the same pace they did before—and so do you. To you both individually, one second will still feel like one second. What changes is the difference. So, Matt, you’re asking, can I time travel or not? Technically yes. But not how you’d think. You can’t speed up time, you can only reduce the number of days it takes you to get to the future. Make sense yet? Doesn’t matter. Because as with anything, it’s all relative.
Thanks for reading this week’s edition of It’s Not Rocket Science. I hope it broke your brain about as much as it did mine. And don’t forget to join our community if you haven’t already. See you next week!
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Special thanks to Julia Lubarsky for inspiration.
For more details…
[1] https://en.wikipedia.org/wiki/Time_dilation
[3] https://en.wikipedia.org/wiki/Einstein_field_equations
[4] https://en.wikipedia.org/wiki/International_Space_Station
Fascinating Matthew, I have so many questions but not enough time to ever understand!