There is indeed a small difference in the relative age between someone who remains earthbound and those who go into Earth orbit on the International Space Station (ISS) – even if this is a minuscule effect.

This is a quirk of relativity, which comes into play due to the speed at which astronauts on board the ISS are travelling – at a breakneck speed of almost 28,000km/h.

This is a quirk of relativity

The difference in the relative time which passes on board the ISS is not large enough to be easily noticeable, however, even though clocks need to be adjusted on board the ISS to counter this exact phenomenon.

Indeed, astronauts who spend six months on board the ISS age by about 0.005 seconds less, during that time, than all of us here on Earth.

This in essence means that when astronaut Scott Kelly returned home from a 12-month stay on board the ISS, he had, in fact, aged around one-hundredth of a second less than his twin brother who remained on Earth – US senator Mark Kelly.