Time traveling to see the past

I can hear you think that I'm stating the obvious. In order to see the past, you need to travel back in time, everyone intuitively understands the logic in that. But wait, because if it were obvious then I wouldn't have bothered writing this little article.

Time travel is, for all intents and purposes, a curious thing. It's "impossible" according to most leading physicists (at least, the ones we tend to take serious), but theoretically it might be possible as long as something is able to reach a speed that is greater than c, the speed at which electromagnetic radiation perpetuates. The idea is that there is no such thing as independent time, the temporal dimension is linked to the direction dimensions, and there is nothing that prevents motion in one dimension to "bleed into" another dimension. For instance, if you are traveling forward then you are probably moving around on the lef-right and up-down axis a little too, even if you don't intend to. The same is possible for time, but you need to go pretty damn fast if you want to have a noticable effect in the temporal dimension.

The idea is that the faster you go, the slower time goes for you (yes, even at normal speeds. If you take the airplane from China to South Africa, then the flight time for you in the air is actually slightly less than the flight time if you were to look at the clock in China when you left, and the one in South Africa when you arrived). this slowing down of time would continue until you reach c, which is physically impossible, and then if you were to somehow go even faster than c, you would actually be travelling backwards in time.

That's quite insane, because you'd still be travelling positively directionally, but negatively temporally, meaning you'd go forward, but everyone around you would see you going backwards. It's just flipped out sci-fi that way... Kind of like a pharcyde music video, but then infused with physics instead of hip beats.

But that's not the kind of time travel I was thinking of. You see, you don't need to "go back in time" in order to see the past. To see why, let's look at our universe, as if we're on the earth (I know, unrealistic concept given its size, but humour me a moment). Say you're standing on earth, and you're looking out over the ocean, and at the edge of the horizon there's a ship that you can barely make out. However, you have a radio setup that allows you to send radio signals to the boat, and obviously they have radio equipment to answer, and both your and the boat's equipment is pretty new and outfitted with a directional dish so that you don't waste energy just broadcasting all over the place, but specifically target each other.

He's the interesting bit. Someone on the boat has a powerful flashlight, and you have a powerful flashlight. You call up the boat with your fancy radio and say "turn on your flash light in exactly 10 seconds from ... now" and then you start counting with your atomic-clock-synchronised wristwatch and after 10 seconds you turn on your light, and pretty much at the same time you see the light on the boat being turned on.

Wow!

The remarkable bit is that both events seem to happen at the same time. Of course, this is ridiculous, they don't, but the distance - over though big for conventional purposes - is just not big enough to make a really noticable difference. There might be a half second delay, but what's half a second?

Now imagine you're standing on earth with a telescope, and you're looking out into the universe, peering at stars that are not the distance to the horizon away, but are 10 billion times further away. All of a sudden it would take an increase in luminosity of the star half a second for you to notice, it would take over 300 years for you to notice!

So what you're seeing now, is a picture of what the star used to look like, over 300 years ago.

The amazing bit is that no matter where you look around you, you're not seeing the present, but the past. Even if you look at the sun, you're seeing the sun the way it was 8 minutes ago, rather than the way it is now. You may be thinking "so what, we alreayd knew this", but the real fun starts now.

Consider the earth a point in the universe. In any direction you "point" a telescope, you will see a region of the universe as it some point in the past. Say we're looking at a star that is 60 light years away, then we see it the way it was 60 years in the past. Now, we take another point that is 2 light years closer to this star, and look at the earth - we see the earth as it was 2 years ago. Then we look at the start - we see it the way it was 58 years ago. Now we take another point that is 57 light years and 355 days closer to that star. If we look at the earth, we see it the way it was 60 years minus 1 day ago, but if we look at the star, we see it the way it was yesterday.

The impressive conclusion is that If we take the universe as a whole, then the universe contains a 3 dimensional picture of its own past, but the only way to see the full history is to look at every point in the universe *from* every point in the universe.

That's a hassle.

But it gets worse, because it's not just a hassle, say we wanted to look at the earth 400 years ago, then we somehow need access to a battery of telescopes, all of them about 400 lightyears away from the earth, all pointed at the earth, and all of them able to transmit their data at a speed of 400 lightyears per much less than 400 years. That would require the information to travel faster than the speed of light...

So here we have a problem: if we want to see the past without travelling in time, we need to get something else to do the time travelling for us.

So the good news is that there is a complete copy of the universe's visible history floating in the universe, and the bad news is we can't really access it.

Science sucks =(

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