Secrets of the Universe: Revealed!
Ah ha! So you fell for the old, "Secrets of the Universe" ploy, eh? Well, since you're here I might as well get on with things.
The following is from a blog of mine. As promised, I hope to have an intelligent discussion regarding time travel. It is targeted towards those who have little to no scientific background. So don't worry about not being familiar with any of this. I hope to not scare anyone away! Here it goes:
Last night as I was on my computer, Alicia felt adventurous and read the beginning to "A Briefer History of Time" by Stephen Hawking. I was quite pleased that she actually found it at least mildly interesting, and of course it got me thinking. I picked up the book myself and began reading. Now, I had already read the previous version, "A Brief History of Time". (The before mentioned book being a newer, updated, more concise version of the latter) But the new version has some worthwhile additions, and it was right about then that "Back to the Future" came on TV.
Which brings me to the topic of this blog: Time travel. What exactly is meant by this, what is the real science behind it, and what is actually possible? I didn't wind up watching the movie on TV like I had with "I, Robot", but I've seen it before. It's a good flick if you haven't yet.
First, to be able to talk about "Time Travel", we have to talk a little bit about "Time". Everyone has at least a mild understanding of what time is, even the ancient people did. The first time detecting devices were sun dials build in upwards up 5,500 years ago. But the first real "clocks" were water clocks made by the Egyptians around 1400 BC. These were machines that regularly dripped water from one container to another, and the amount of water in the bottom container could tell you how much time has passed. Our modern day clocks are essentially the same thing, but with more updated methods of achieving the same goal. We constantly run out of time, we never have enough, and no matter what we seem to do it just keeps marching along. So let's look at some of the assumptions that we've made about time so far that we might not have realized we've made.
Assumptions:
1) Time has two directions, forward and back.
2) Time tends to move from back to forward at a regular rate.
3) Time is independent of other factors such as space. (Meaning that time acts the same way to somebody in Europe as in Arizona)
These seem like perfectly reasonable assumptions, yes? So from these, we might conclude that (in the immortal words of Groucho Marx) "Time flies like an arrow, fruit flies like a banana" And this is the common conception of Time that most have. This is where we base our questions of "Time Travel" on. We wonder if it is possible to travel back into the past, or into the future. But we shall see in a moment that things are not always as they seem.
The revolution regarding how we understand time all began with Albert Einstein. For some years before him, it was observed that light when traveling through space seemed to always go at the same speed. Now give this a thought for just a second. Speed is relative, which means that there is no physical difference between you running into a parked car on your bike at 15 mph, and a car moving at 15 mph hitting you on your bike stopped at a crosswalk. When you say the speed of something, you must say what it is moving "in relation to". So when we say that we're going 75mph on I-10, we really mean to say "we're moving 75 mph in relation to the ground on the I-10". Because of course in relation to the other cars on the road you're not moving at all, and in relation to the cars on the other side of the road, you're moving at 150 mph!
So when we say that light "always moves at the same speed"... the important question to ask is "moving in relation to what?" Many people tried to come up with answers to this question, even coming up with notions of a "light ether" that light moves in relation to. But none of these ideas were consistent with what observation was telling us. Then finally Einstein stepped in and laid the truth on everyone.
The speed of light is constant, relative to anything and everything! To any observer, regardless of where you are or how fast you're moving, if you see light then it's moving at the speed of light. Sounds simple enough, right? What's the problem? Well it means that the very nature of existence is relative. That means that the light coming from your car's headlights move at the same speed in relation to both a passenger in the car, a person standing by the road, and a person coming the opposite way down the road. Each of these people will observe the light from the car passing different places at the same time!
These discrepancies are not illusions, or tricks, they are real. Light doesn't just "appear" to be moving at the same speed always, it IS always moving a the same speed for all observers. What happens is as you travel faster and faster, time slows down for you. And the closer you travel to the speed of light, the more noticeable the effects are. These small disagreements are called "Time Dilations". That means if you had two clocks (that keep perfect time) and sent one on a plane trip around the world and back, when you put them back next to each other, they would disagree on what time it is!
You can see immediately that time is far more complex than previously thought. It is not just like an arrow. It speeds up, slows down, and is different for anything depending on your stance.
So does it still even make sense to ask questions regarding "Time Travel"? Only partially. Time still does have direction, it's just that it is relative. So when we want to travel back in time, there is no supreme ultimate clock with which to base our travels. (As in Back to the Future)
Now that we have a more accurate understanding of the nature of time, we can explore the methods and philosophies behind time travel.
The first and most important idea I would like to bring up is "The Principle of Consistent Histories". This principle states simply that history must have one single and unchanging record of what has happened. Put another way, the Colts must have either won the Super Bowl last year or not. It cannot be both, it cannot be neither, and it the fact of whether they did or not cannot change. Quantum theory demands that the future (and present) be represented in uncertain terms, but the past but have a definite concrete answer.
This rules out immediately traveling into your own past. You can think about this in terms of the "Grandfather Paradox". If you were able to travel into your own past, you could shoot and kill your own grandfather. So then you would never be born. But since you were never born, you wouldn't be able to go back and kill your grandfather, so you would be alive. So which are you, alive or dead? They should both be true, and both be false, if you could travel into your own past.
What IS feasible is traveling into the "past" of a parallel universe. It really isn't proper to speak of this as time travel though because this other universe's time is entirely separate from ours. It would just so happen that the events occurring when you got there are similar to the ones that happened in our past.
One other important idea to mention is that of a "Worm Hole". The idea is rather just like what the name implies. It is a hole in space itself that leads to another area in space. These are not proven to exist, but could in principle exist, depending on the contour of space. Albert Einstein also showed that time is a dimension of space, it is literally the 4th dimension. In fact he coined the term space-time. When we speak of space, we also necessarily speak of time and vice versa. (which means that not only when you speed up does time slow down, but space itself contracts!) If we were to somehow "tear" space and come up on the other side, it would be a different region of space at an arbitrary point in time. This is the closest thing to real time travel that can be achieved by today's reasoning.
The problem with worm holes is the only way we can think to move space enough to tear it is using black holes, and getting too close to one of those is not a very good idea. So it would seem that the prospects for real time travel is kind of slim.
But you could still do some time traveling using today's technology, no joke. If you were to board a space ship and go really fast for a while. Just take a trip around the solar system for a couple of years traveling at speeds in upwards of 1% of the speed of light. When you came back thousands of years will have passed on earth. Everyone you know will have been long dead, and every place you loved will be rubble. But think of the crazy cool video games they'll have!
What do you all make of this? Is it possible to make a good time travel movie that actually does make sense in a scientific way? Does any of this just seem to weird to be true?
Thanks for reading!
