Is time travel possible?
Yess!...Kinda. Let me explain...
Before we get into the how and the why, let me tell you what I mean when I say ‘Time-travel’ (If you think about it, technically you’re always travelling through time 🤷). The idea set by science fiction is often quite miss leading, the idea that you can travel back and forth through time and that travelling to the past will cause the branching of timelines (I’m looking at you marvel 😐). This is simply not true ❌. As per our current knowledge, it is impossible to travel to the past; it's been verified mathematically, and even reasoned logically through thought experiments. Even the mere thought of travelling to the past poses perplexing paradoxes🥴. But what is possible and indeed does happen in the universe is time moving at different rates for different observers that are subject to different surroundings. We're going to explore real time travel to the future is possible! 🚀
Over a hundred years ago, Einstein explained that time itself is a physical entity that is not only measurable and subject to observable changes due to external influences but also is fundamentally linked or ‘woven’ into the ‘fabric’ or continuum of space-time. Confused 🥴? Let's break that down🧐.
I’m guessing you figured out the ‘Over a hundred years ago’ part 😂. Moving on, time is described as a physical entity which means that just like speed 🏃♀, it can be measured with respect to another body. For instance, you can say perhaps that a bike 🏍 is moving with a velocity of 60 km/hr with respect to the ground. Or you could say the bike is moving twice as fast as the car🚘. But then if you were in a spaceship 🚀 in distant space 🌌, you wouldn't be able to tell your speed since there is nothing to compare it to 🤷. Now think of time ⏳ in a similar way. In our day-to-day life, we tend to think of time as flowing at a constant rate and it never occurs to us that time ⏳ too can pass at different rates for different observers just like a bike 🏍 and a car 🚘moving at different speeds. Hence time is ‘relative’.
Now, what are the ‘external influences’ that cause changes in the rate of passage of time? (⛈It's not the weather!🌧) Well, it's simple - the velocity of the body in comparison to the velocity of light and its nearness to a massive object. Okay, maybe not that simple. But you’re smart, you’ll understand 🤓.
Einstein's famous theory of relativity tells us about how these factors influence the rate of passage of time ⏱. According to the theory, the faster you travel (or in other words, the closer you get to the speed of light 💡) the slower time passes for you. Bizarre isn't it? 😲 This is called time dilation. This means that every time you fly in a plane ✈️ (or even just move quickly), time for you is in fact passing slower (although by an extremely tiny 🤏 but measurable amount ⏱) than say your friend who is waiting to receive you at the airport. An experiment actually done in 1971 called the Hafele-Keating experiment did just this! They synced two atomic clocks 🕛🕛 and flew one of them around the world 🌏 on a plane and kept the other on ground. On comparing the two clocks after the flight, the readings were indeed out of sync by a minuscule but readable value 🕐🕜.
Another influence on the rate of passage of time is the effect of gravity. Simply put, the closer you are to a massive object (massive implying something with a large mass) the slower time passes for you. So a body that's closer to the sun ☀️ experiences time slower than a body on earth 🌏. This phenomenon is wonderfully depicted in the movie interstellar.
Finally, what is a space-time continuum you ask 🌌+⏳? (And there really are two ‘u’s in the word continuum). Well, Einstein stated that space and time combined form one fundamental entity - spacetime. Think about it 🤔, when you travel through space 🚶♂️, let's say from your house to your friend's house 🏠, you travel not only in space (distance) but also in time. You take a couple of minutes ⌚️ to get there. Turns out this is a fundamental trait of the universe, everywhere you go is also innately described by ‘everywhen’ you go too 😲. Furthermore, changes in space cause changes in time too! 🤯 And vice-versa of course. Remember how I mentioned above that being close to a massive body 🪐 slows down time for you? This is indeed because the massive object influences or ‘warps’ spacetime. The influence on space causes you to feel the effects of gravity while the influence on time causes it to pass slower for you. I’ll explain just this idea of the ‘warpage’ of spacetime in another blog soon 🤓.
Now consider this, you sit in your super cool spaceship 🚀 and blast out into space🌌, travelling at crazy high speeds (obviously less than the speed of light 💡) and then you decide to camp at a safe parking orbit around a blackhole 🕳 to take a good look 👀 at it, and then you zoom back to earth 🌏 after your interstellar adventure (seriously watch interstellar! 🍿). For you, it may have been a month-long trip considering your super high speeds (you couldn’t possibly do that since the nearest known black hole is over 1000 light years away), but back on earth, it may have been years and years later that you’ve returned, since time passed much slower for you compared to those on earth! Generations would have gone by, and you would have returned to a completely different world with technological capabilities we can only dream of 🤯. There you have it, time travel! 🤩 (Still not, but you get the idea 😅😁).
This particular blog barely scratches the surface of what there is to know about the concepts of relativity and time dilation and I didn’t get to write further in depth considering the length of reading time. Let me know if you’d like to learn in further depth about general and special relativity, we’ll dive deeper into it in a future blog!
Meanwhile here are a some excellent sources to explore these topics yourself:
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