The year Einstein proposed the theory of relativity, we see time and space with a different perspective. Since then, we are investigating the effects of matter moving at high speeds. As high as the speed of sound, rotation of Earth or the light constant.
The real question is, what happens if a Human is moving at such speeds and how does it affect another person standing still?
NASA recently sent an astronaut Scott Kelly to the International Space Station (ISS) for a one year mission. The purpose was to study the effects on the human body for long term flights in space. Particularly, to understand the challenges of a Mars mission. While Scott was orbiting the Earth, his body changes were being compared to his identical twin brother Mark Kelly, here on Earth.
The setting reminds us of a space-time paradox. A thought experiment in which an explorer goes to explore space for a long time. When he returns home, he finds that his twin brother is much older than him. As if time went faster for the brother on Earth.
The NASA Twin Study experiment was not aimed at this. However, the compiled results show a connection to this paradox. Let's first explore why this space-time paradox is logical and then link this theory to NASA's outcome.
The Space-Time Paradox
According to the theory of relativity , time is relative to the motion of observers and that light travels at the same speed for all observers.
Think of it this way, if a clock is stationary and you are traveling at a very high speed. You happen to pass by this clock and have a glimpse at it, you'll see that it's running slowly, or maybe it's completely static. This is because the speed at which the mechanical functions of the clock are working are slower than you. What you see is the time in the past, while you have already skipped that second and are in the future.
During this experiment of high-speed traveling, you haven't aged at all . Because all the processes in your body are working at the same speed as you. But can we prove this from a biological point of view?
Let's first learn what defines aging in our bodies.
The Biological Countdown Timer
After a certain age, multi-celled organisms start to deteriorate in health. Which eventually leads to a state when their bodies stop functioning aka death.
This aging phenomenon, especially in humans, is caused by a protein structure in the cells called telomeres. These structures protect our cells from deteriorating. However, with each cell replication, these telomeres start to lose strength, which is called telomere length. If the telomere length shortens to a certain extent, the cell becomes vulnerable to diseases. Thus causing death.
We can say that telomeres are the natural countdown timers in our bodies, that determines when will we expire. The telomere length can be affected by external factors like smoking and stress . Thus, accelerating our timer.
The twin study experiment by NASA included documenting the changes in telomere length of both brothers.
The Twin Study
NASA sent Scott Kelly a fifty-year-old astronaut, on a one-year long mission to the International Space Station (ISS). The purpose was to study how his body reacts over time by staying in space. This study will help future astronauts who embark on the Mars mission.
While Scot Kelly (Space Brother) was aboard the ISS, his identical twin brother Mark Kelly (Ground Brother) was being studied here on Earth. Samples from both brothers were collected before, during and after the year-long experiment. The space brother, tells in his book, Endurance , how NASA frequently collected blood and other samples from him, while on the ISS.
The blood samples helped in collecting the telomere length data and later comparing both space and ground brothers. The results were published in Journal Science .
An interesting outcome of this study was that the telomere length of the space brother increased while he was aboard the ISS.
Before the mission, both brothers had nearly the same telomere lengths. Meaning if we ignore issues like mental stress, both brothers should live roughly an equal age. However, while the space brother was orbiting the Earth, he had almost 14.5% longer telomere length.
It's unclear whether we can say the space brother was a few years younger than his ground brother. Because, the telomere length of the space brother, resumed to normal when he came back to Earth. It took almost 190 days, after return, for the telomere length to restore to expected.
Was relativity involved in this? It's hard to say. The blood samples from the ISS were sent back to Earth for processing. Therefore, the blood wasn't traveling the speed of ISS anymore. Moreover, the space-time paradox states that the space brother should be younger on return. However, we saw that the telomere length restored to its original state as before the mission. The space brother was again the same age as his ground brother.
From a biological standpoint, we can say that while orbiting in the ISS, if the space brother was shielded from all harms of space (radiations, etc.) then he would have lived longer than his ground brother.
The twin study report does not provide a clear reason. Seems like this wasn't something we expected to happen. One issue with the whole study is that telomere activity was lost during transit from ISS to Earth. This means we cannot see by eye the telomere length increasing. However, the cells that had longer telomere were clearly present in the blood samples.
This is an interesting finding. One I wasn't expecting while reading the report. Yet here we are with another bizarre phenomenon that space travel introduced us.
In order to get definite answers, we might have to conduct more experiments like this. This time, keeping the telomere activity intact -- Meaning, we should be able to observe a cell replication in order to understand what causes the telomere length to increase.
Studies like these take us closer to mission Mars. Considering that Scot Kelly survived a year in space, tells us a lot about how achievable this goal is.
 Redd, Nola Taylor. “Einstein's Theory of General Relativity.” Space.com, Space, 7 Nov. 2017.
 Lasky, Ronald C. “How Does Relativity Theory Resolve the Twin Paradox?” Scientific American.
 Shammas, Masood A. "Telomeres, lifestyle, cancer, and aging." Current opinion in clinical nutrition and metabolic care 14.1 (2011): 28.
 Kelly, Scott. Endurance: My Year in Space, a Lifetime of Discovery. Vintage, 2017.
 Garrett-Bakelman, Francine E., et al. "The NASA Twins Study: A multidimensional analysis of a year-long human spaceflight." Science 364.6436 (2019): eaau8650.