How to time travel? Understanding time travel #1

  One fine day on a casual talk on phone with one of my friend, he accidentally, out of nowhere, pulled out the topic of time travel. And then what! Our 2 minutes' casual  call lasted for an hour! So let's understand time travel as I tell you our conversation...

  He asked me how to time travel. As per my little knowledge on that topic, I told him the very first way I knew: travelling with the speed of light. Time is relative, thus, if you and I are on a place A with two accurate atomic clocks. Assume that I travel to a place B with the fastest speed and come back to you while you are still standing on place A, our clocks will show different times. Thanks to the concept of time dilation, that does happen. Imagine I took an hour to go there and come back to you on place A. It will show one hour passed on my clock, but your clock will show more time than an hour. The difference is although negligible.

  So as to understand this concept better, my friend gave me another example. Imagine I travel with the speed of light for one year and come back to you, I will be way younger than you and for you with normal speed, probably a decade would have been passed. 

  Travelling faster will take you to the future, was my firm opinion and indeed it is. Travelling faster than light would have been a great idea, but it would have needed infinite amount of energy which can't be produced using today's technology. Even if it is done, it would still lead to serious consequences.

  But if some how possible, can I still time travel with speed of light? That's the question my friend asked me and I was like lost in finding answers. Because his explanation was more against this and reasonable too. His view was that I am still not travelling in the future. The time has just elapsed a bit early for me. That's where we discarded this method to time travel by using speed.

  If that was not possible, my friend suggested me an alternative: going to places with high gravity. Jupiter for instance has high gravitational force than Earth. A year on Earth could be some 8-10 months on Jupiter. And it can be 5-6 months near the sun and a month on big stars. And a fraction of a second on supermassive black hole. He continued to explain that time dilates under the influence of gravity due to the gravitational wave theory by Sir Albert Einstein. 

  And I caught him! Again this will be elapsing of time and not travelling. So far now, this was clear that time dilation was different from time travel. And both the ways mentioned above were the methods to dilate time and not for time travel. But we needed to check this difference:

Time dilation may be regarded in a limited sense as "time travel into the future": a person may use time dilation so that a small amount of proper time passes for them, while a large amount of proper time passes elsewhere. This can be achieved by traveling at relativistic speeds or through the effects of gravity. Source

  There has to be a method then. Right? We thought the same. But then he remembered the early physics class of our 11th grade. And he told that what if we were able to retrace a path of a particle backwards somehow? He was obviously unclear. Them he explained what he meant: If a particle goes straight, it is travelling a specific path in space and experiencing time as well. But if we change its forward direction to backwards using advanced technology and some sort of simulation, we could be able to see it's earlier positions and thus it's past. Done! We travelled back in time and saw it's past.

  But! I had 2 objections. Number 1, when we retrace its path and see the past actions of that particle, we can't alter it. Thus we are not travelling to the past, but actually we are just looking at it. It's like taping something, playing it in reverse and saying "Eureka! I travelled in the past!" And although that is considered, my second objection broke him. Although we retrace its bath backwards, the particle is although moving backwards in space, but the time is still running forward! 

  And that was the moment we understood, while we were about to simplify things regarding time travel, we ended up with complicating it more without the solutions for methods of time travel...

  I know you have got many questions: What is the twin paradox and the grandpa paradox? What are dimensions? Is concept of time travel in Doraemon's episodes correct? Hold on! 'Understanding Time Travel Series', is a seperate post series on my blog to help you understand better about time travel. And to help me in that, the friend I was talking to will help me: Thilakraj Bhandary. 

  Let us know in the comments section do you know any other method of time travel? and your thoughts as well...

Posts before October 2021 have been marked as "Old Posts". Less likely, but they might have out dated or incorrect information, ugly looking bits of code, no labels, etc. Don't get me wrong, many of these posts are top-notch and interesting too.

I thought it would be better not to delete or revamp these posts, even if they suck. The bitter truth is that old works always suck, but I take that as a positive tool to convey that I am growing. Besides there's no better way to showcase my journey without these old, messy, poorly written posts!

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