Anyways, one of the coolest things about Einstein's Theory of Relativity is how it proves that Time Travel is possible. It states that the faster an object/observer moves towards the speed of light (relative to another object at rest) that time slows down for the object/observer relative to the object at rest. This is called "Time Dilation". Gravity can also effect and create "Time Dilation". You may be saying to yourself "this is all good in theory, but how is this relevent in my life?" Well, you know those satellites buzzing around in space? Well, they are all affected by this effect of "time dilation" because they are moving faster relative to our speed... plus they are further away from Earth (meaning that they are in a weaker gravitational field). So, that means time is moving at a different rate for those satelites up there than it is for us down here on Earth. In fact, for our GPS navigational devices to even work, they had to program the clocks on those satellites to compensate for the time difference! So you see, understanding how "time" works is essential for us to be able to use our GPS systems everyday. With this in mind, now think about all the astronauts that went into space and back. They are all "time travelers". Because after they left Earth, their relative speed (in relation to Earth) changed and also their relative distance to Earth (which effects how the gravitational field effected their time dilation). The people at NASA understand all this and the problems that can arise from it. Once we do further manned missions, this will become a bigger issue because the further we must travel means the faster we must travel... which equals a bigger "time dilation" effect.
So, back to the business of Time Travel. I've illustrated that Time Travel to the future is "relatively" easy (lol, I kill me!). All you have to do is travel as fast as you can (relative to Earth) and back. Time for you would have effectively slowed down while time perceived on Earth would have sped up. You'd return "younger" than those on Earth.
Traveling Backwards in Time:
But what if you want to travel back in time? Well, traveling backwards in time is another whole enchilada. .. and could prove much more "disasterous". We've all learned about all the crazy shananigans that could happen if you could travel back in time. You could change history, kill your own parents and thus never be born.... etc. There are all sorts of time paradox's that seem to prevent us from going to the past. So what does Einstein say about this? Well, he said that if you could somehow travel faster than the speed of light, that you would start going backwards in time. But traveling faster than the speed of light seems to be an impossible feat, because the faster you travel towards the speed of light, the more effective mass you gain. In fact, if you travel at the speed of light, you'd have "infinite mass"... and no amount of diet or exercise would help you at that point.
But joking aside, let's say that there was another way to travel backwards in time. I don't know what it is, but if there is indeed a way, I'm sure that someone, someday will find it. For now, let's suppose that sometime in the future, someone has found a way to travel backwards. If this is true, then doesn't it mean that we have "time travelers" visiting us now and throughout history? Hard to fathom huh? Doesn't it also mean that time ceases to be "linear" if we can weave in and out through it? And what if we can go back and change the past? Would it be "our past" or would we create another parallel universe every time something is changed? Thinking about all these possibilities can give you a headache. But the question is: is it possible? Yeah, sure... I believe that everything is possible. And if there are indeed time travelers among us, that would make the world a much more interesting place to live.
Seeing the Past? Yes, seriously!
But even if worst comes to worst and "going" back in time isn't possible, it's important to remember that "seeing" the past is. Believe it or not, you and I "see" into the past all of the time and most of us probably don't even realize it. It all goes back to Einstein. See, he also discovered that the speed of light has a speed limit. It can only travel through space at a certain pre-determined maximum speed limit. Why? I have no idea. I've always wondered why light can't travel faster than a certain speed. If anybody can "illuminate" me on this, it'd be great :) I mean, I can understand why matter can't travel faster (because of the whole infinite mass thing) but light doesn't have mass... nor do radio waves. So why can't either travel faster? One weird interesting side-note is that the expansion of Space itself can 'expand' faster than light... or so they say.
At any rate, for some reason, light can only travel at a certain maximum speed. This means that it takes time for it to travel through space. So whenever you stare at the Sun (and I did this quite a bit as a child, which explains alot) you are actually seeing the Sun as it was over 8 minutes ago. Yes, it's true. You are seeing into the past... about 8.3 minutes into the Sun's past. And when you look up at the stars, you are effectively peering hundreds, thousands, millions, ga-jillions (lol) of years into the past... depending on how far away the oject you are viewing is. And this is of course why astronomers get so excited about powerful telescopes. The more powerful the telescope, the further in time you can see. This never ceases to boggle my mind and has so many implications. For example, some of those stars that you see in the sky could have died long ago... and yet we see them with our naked eyes, like ghosts of the distant past.
So is time travel possible? Yes, absolutely. Time is relative, and in a way, we are all "time travelers". We just haven't mastered the technology yet. But I think, someday we will. The question should be: how can we better understand the relationship between Time, Space, and Matter? And how can this understanding be applied to help us advance towards the future? I'm sure that Einstein never dreamt that his Theories would someday help us navigate our way through our busy streets and help us explore new cities, without getting lost... and that's merely one way that it's helped us. So as the future approaches, I'm sure that there will be many more ways that our understanding of time and science will help us navigate through an uncertain and challenging future.
One last note:
And, if by chance, there are "Time Travelers" out there visiting us... look me up! I'm ready... and my bags are packed... Seriously!
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