There’s a famous quote that goes, “time and tide wait for none”. But what if I told you, that against common belief, time is not a constant but a relative phenomenon? Time feels like one of the only constants in life, with each day passing at the same pace. But Einstein had something else to say.
Let’s talk physics for a minute. When Albert Einstein proposed the theory of relativity, he said that time cannot be separated from the other three spatial dimensions. This is because the observed rate at which time passes for an object, depends on the object’s velocity relative to the observer. To this, he added that gravitational fields can slow down the passage of time for an object as seen by an observer outside the field. Thus, it introduced the fused model of the three dimensions of space and one dimension of time into a single four-dimensional continuum, called spacetime.
Think of spacetime as an intricately woven fabric that binds the forces of the universe together. We all perceive things differently because factors like when and where that control an incident reach us differently depending on our frame of reference. Spacetime isn’t flat- it is curved, with mass and energy continuously warping the spacetime around them.
Relativity encompasses two interrelated theories: special and general relativity. In a nutshell, special relativity is about how time slows down for us when we travel at very high speeds, and general relativity is about how time slows down with an increase in gravity. That’s because of time dilation effects. So, simply speaking, if you were to travel at a speed close to that of light, you would age slower than those on the ground. Let’s call this velocity time dilation. But here’s the catch. People on the ground would experience higher gravity, so shouldn’t time go slower for them too? This one is gravitational time dilation, and you would think that they both cancel each other out eventually, but velocity time dilation is more prominent, hence we notice a definite difference, though minuscule by earthly standards. When I say minuscule, I mean this:
After spending 6 months in the International Space Station, astronauts have aged just about 0.007 seconds less than us. That means when Scott Kelly returns home from his year-long mission, he’d be 0.01 seconds younger than his twin Mark Kelly, who remained on earth.
This brings us to one of the most controversial topics related to time dilation, the twin paradox. One twin blasts off into space, close to the speed of light, while one stays on earth. When the space twin returns, it’s a shocking result. The space twin has aged only a couple of years, while the earth twin has aged a decade. No this isn’t crazy, there’s substantial evidence to prove this.
Two identical atomic clocks were considered in the experiment: one was sent into space while the other remained on earth. The space clock returned running just behind the earth clock.
But before you book your ticket to space, there’s more when we discuss how aging happens. It involves metamorphoses, like bones going brittle, hair falling out, skin developing wrinkles, joints becoming weak and much more. The average human takes about a decade to feel the effects of aging but in space, it happens in fast foward. For instance, astronauts’ skeletal systems lose mass at an astonishing rate: 1-2% a month, against the 1-2% a year for average adults.
This is due to the lack of gravity. It plays a major role in keeping a lot of our bodily functions in check. The bones no longer must maintain the structure of the body or support their weight. This slows down the production of bone material. But these changes are often reversible- once the astronaut returns to the earth, bodily functions are usually restored to normal. Net effect? The astronaut gains 0.007 seconds.
But now that we know how velocity and gravity relate to time, here’s another bizarre thought:
People living on the first floor age slower than those on the fifth floor. So next time you want your holidays to last longer, retire to the basement and try moving very fast. Maybe that way, you’ll get a fraction of a second more. Remember, time isn’t absolute.