We are aware of time travel and stuff like the time machines from various movies and the famous cartoon Doraemon. Did this ever happen to you; You set an alarm for 6 a.m. and wake up. After a few seconds of further sleep, it’s already 10:45 a.m. ! So, you might say, we time travel every day! Jokes apart, is time travel really possible? A gentleman with the name of John Titor, in 1998 claimed that he arrived from the year 2034. He described his time traveling in great detail and vanished! Did he finish his mission? Or was he real at all? How do we know?
Time Dilation and the Crazy Space Stuff
Suppose you and I wear identical watches. We synchronize them right before I blast into space. In my space shuttle, I am traveling at a speed of 28,000 Km/h, relative to the earth. I do few orbits around the earth and return. When we compare watches, we discover that less time has passed for me! A very tiny amount of time, but it’s there.
This is time dilation. And it simply means according to Einstein’s theory of relativity:
“Time measured along different trajectories is affected by differences in either gravity or velocity, each of which affects the time in different ways.”
We see a real-life example of time dilation on the International Space Station (ISS). Compare the passage of time on ISS with that on earth for 6 months. You see astronauts have aged approximately 0.005 seconds less than people on earth. Of course, a very insignificant amount of time! But it can be apparent if the astronauts could travel closer to the speed of light.
Interestingly, the effects of time dilation are fairly minor, even up to around 75% of the light speed. However, once we reach 75% or so, the effects become substantial!
So, to travel in time, we need to move fast!
Bear with me now, things will get weirder. The strongest aspect of special relativity is that distance shrinks in the direction of motion when the speed is comparable to light.
If you were a passenger on a train and you could somehow travel at 99% of light speed, for every year you spent on the train, 223 years have passed back at the station! Fascinating?
But is it really time travel? Perhaps not in the sense that we usually see (like in Doraemon), but according to spacetime, it is! If you were to return home from your 99% light speed trip, you would be roughly 1 year older and people on earth would have aged 223 years more. So, you have traveled 222 years into the future relative to your time in space.
The film interstellar is not a fiction!
Let’s take another example. In the film Interstellar, Cooper and his team land on a large watery planet, on which gravity is 30% stronger than on earth. This planet is situated extremely close to a supermassive black hole called Gargantua. It orbits the black hole at 55% of light speed. Gargantua’s mass is equal to that of 100 Million suns and spins at 99.8% speed of light. The combination of all these factors had the effect of slowing down time relative to the astronaut left aboard the ship by staggering 61000 times. That means one hour on the planet is equal to seven years aboard the ship. When the team makes it back to the vessel after a little over three of their hours, their friend had aged by 23 years.
The craziest part is that this isn’t just science fiction. Those calculations are all correct and that’s exactly how it will happen in real life. So, in real essence, the crew has traveled 23 years into the future in just three hours.
This was time dilation. Now let’s look at another way to travel through time.
Cryonics is the branch of science that deals with preserving humans and it has been in practice since the late 1960s. Its proponents suggest that:
“Death is not a singular event, but a process that may be stalled!”
The body of a person is frozen at negative 130 degrees Celsius, minutes before his death. The theory says that, reducing the patient’s body temperature will help retain enough brain information. This will keep the brain in an accessible state for doctors and scientists of the future to revive it.
The practice might not be fruitful. The temperature is so low that it causes significant damage to the human body, regardless of prior-preservation safeguards. Regarding this, the doctors of today rely on the development of future technology that will repair the brain at the molecular level and restore to functioning condition. Also, it’s currently illegal for a human to be frozen before death. One person opted to be cryopreserved. What happened to him? Bedford was the first person among other 300, who opted to be cryonically preserved in 1967. Since then, the world has seen him only once. Skin on his neck was inflamed and his nose had collapsed.
If technology advances far enough to revive cryopreserved humans, they will have essentially time-traveled to the future. It’s not as easy as the show “Futurama” makes it seem. But it is theoretically possible. And that’s time traveled in a nutshell.
So far, we have only explored traveling to the future. Imagine, you traveled to your future and landed in the year 2080 but you couldn’t find a way to come back! Isn’t that a horrible idea? Is it possible to travel back to the time?
The Grandfather Paradox
Let’s say, you own a time machine that lets you travel through time. One day you get the bright idea to travel to the year 1940s to mess with your grandpa. You ride your time machine and suddenly find yourself standing beside your grandpa, who is enjoying the scenery at the cliff of a valley. Since you have never been the biggest fan of your grandpa, you decide to push him over the edge. Gravity does its things, and a few seconds later, grandpa is no more!.
But wait, if you killed your grandfather before he met your grandmother, then you will never be born! Because you are not born, you cannot go back and kill your grandpa. Doesn’t that mean grandpa is alive and you will be born? Now you can go back and kill him. So, the loop goes on and on. We call this the ‘Grandfather Paradox’. And this is part of what makes time travel interesting!
Grandfather Paradox deals with time travel on a significant scale and explains why traveling in the past is not possible.
The Bootstrap Paradox
It can happen that someone from the future will show up in our time. But if this is possible, why did they not show up so far? For them, traveling to 2050 is the same as traveling to 1950 or 2020, just extend the time limit. Even if nobody came yet, and might arrive in the future and give us the key to unlock the mystery, won’t that be a paradox? This is called the bootstrap paradox.
So is it possible to travel backward in time? According to some theories, specific types of motion in space might allow time travel into the past and future simultaneously.
“Specific types of motion in space might allow time travel into the past and future “if” these a certain kind of geometries and motions were possible.”
However, that’s a big “if”! It would require something called a closed time-like curve. Another possibility would be the existence of wormholes, which are technically permitted by general relativity. According to Hawkings, everything including time itself has wrinkles in it. There are tiny tunnels in the quantum world that form, disappear and reappear.
Some people believe that if you were to kill your Grandpa, before the possibility of you being born, you would just end up in a parallel universe. Others say
“You killed your grandfather, but still you’re born in that timeline!
Grandma needs to answer some questions.”
You really can move forward in time by traveling at immense speeds or through cryopreservation. But traveling to the past is likely impossible. Of course, the science of Quantum physics and time travel is incredibly vast and well beyond the grasp of most common people. So we may be missing just one crucial element to understand how space-time works. Once found, the mystery of time travel can be unlocked.