Time Travel

[ghostrunner]

What would stop you from doing that?

Fate. When you went back to observe the "first" time, you'd see yourself changing the event.

Damn.

[AdmiralKird]

I remember reading somewhere that one theory posits that as soon as time travel gets invented the universe will be destroyed. (haven't read the rest of the thread, sorry if it was mentioned).

So for all our sakes, I hope it's not possible.

Rest at ease, if it is possible its already been invented and used somewhere else in the universe. There are probably races within our own galaxy that consider our intelligence vastly inferior. It would be akin to how we feel about the animals' intelligence relative to our own. I don't believe the human race is that smart.

[Arthur Dent]

In a physical model in which time travel is possible, someone has long since screwed up the universe.

i've made this point before. and particulaly about time machine. If one was built, we'd have seen them by now.

So I actually read the posted article, and the author makes a good point about this:

According to Einstein's picture of the universe, space and time are curved and very closely related to each other. This means that traveling through time would be much like traveling through a tunnel in space—in which case you'd need both an entrance and an exit. As a time traveler, you can't visit an era unless there's already a time machine when you get there—an off-ramp. This helps explain why we're not visited by time-traveling tourists from our own future. Futuristic humans don't drop in for dinner because we haven't yet invented time travel.

There's a similar point about theoretical faster than light travel. You could do it if you send the construction crew to the destination slower than light.

[jim]

Not only is time travel into the future possible, we are all doing it right now!!

Stasis is my only hope.

Help me, Obi Wan.

Well, when did you type this message? What time is it now? Voila, you just traveled through time. No big deal.

What can change is the rate at which you travel through time relative to an independent observer. So if you and me set our clocks at noon, and I jumped into a car and traveled at 1/2 the speed of light for a half hour according to me, my clock would say 12:30 but yours would say 1:00. Your watch is just fine, it's just that I altered the rate at which I traveled through time. Hollywood would say that I time traveled into the future, which is true but unremarkable. The unintuitive point of this is that I traveled through time "slower" than you did.

I'll have to check when I get back to work, but I'm certain I read something in our daily rag at work about how time travel in black holes is like traveling through space, and traveling through space is like time. Space and time are just different dimensions on of one thing called spacetime, and apparently the gravitational force of a black hole is so strong that it warps spacetime so much that you actually "flip" dimensions. So if you could survive a fall into one, you would find it impossible to move backward in space but you could freely move either forward or backwards in time. That makes some sense actually, because if you get caught in a black hole you are only going to be able to go one direction in space, right?

Maybe this flipping happens in worm holes and not black holes? Dunno, I'll ask someone smarter than me.

Some interesting time issues on the event horizon of a blackhole as well. If I observed you falling into a blackhole from some safe distance, what would seem like a second to you would be minutes, hours, days, or years to me. As you fell in, you would essentially be reaching a point where your travel through the time dimension virtually stopped, but of course as I'm sitting here typing this I'm flying through time at my old rate.

By the way, as bizarre as this idea sounds it was actually experimentally proven. This was done back in the 70's I think, putting synchronized atomic clocks on airplanes etc.. and flying them. Just like Einstein predicted, they "slowed" down as they were flying. I put the slowed in quotes because of course to the clocks and the people on those airplanes, relative to them there was nothing "slow" about their clock. It was just different than an observer not on the plane. Since the ratio of an airplane speed compared to the speed of light is so small, you don't really notice when you get off that flight in Tokyo that you the people on the ground actually are a little ahead of you timewise. But just because it's too small to be noticed by humans doesn't mean it doesn't exist.

So there you go, time travel happens all time and it's no big deal. Can't go backward, but theoretically you could "stop" time by traveling at the speed of light. If you could go faster than the speed of light, you would be going backward in time. But you can't.

It's all relative.


Although I wonder about some of the balls Albert hits.

[Arthur Dent]

So if you could survive a fall into one, you would find it impossible to move backward in space but you could freely move either forward or backwards in time.

Which direction is backwards in space?

[jim]

So if you could survive a fall into one, you would find it impossible to move backward in space but you could freely move either forward or backwards in time.

Which direction is backwards in space?

Not sure, and it's a bad word choice meant more to describe something intuitively that isn't very intuitive. I'm going on very hazy memory here, but now that I am trying to remember what I read I think maybe the time and one of the space dimensions interchange? So maybe you could travel on the x and y axis freely but only forward on the z-axis, or something like that.

Something happens where the time dimension acts like space and you can go in a positive or negative direction on it, not sure of the other details. And it's not impossible that I am mixing up articles and am completely confused on this.

[jim]

Teleportation is not science fiction any longer, not related to time travel but kind of on the same theme...

http://www.nytimes.com/2004/06/17/scien ... eport.html

[TimeForGuinness]

In a physical model in which time travel is possible, someone has long since screwed up the universe.

i've made this point before. and particulaly about time machine. If one was built, we'd have seen them by now.

So I actually read the posted article, and the author makes a good point about this:

According to Einstein's picture of the universe, space and time are curved and very closely related to each other. This means that traveling through time would be much like traveling through a tunnel in space—in which case you'd need both an entrance and an exit. As a time traveler, you can't visit an era unless there's already a time machine when you get there—an off-ramp. This helps explain why we're not visited by time-traveling tourists from our own future. Futuristic humans don't drop in for dinner because we haven't yet invented time travel.

I think I tried to say this a few pages back.

[TimeForGuinness]

Let's see...if electromagnetic waves travel at the speed of light, then if you were to travel faster than the speed of light, you could catch up to the first television broadcast and rewatch it. It's kinda like going back in time.

A similar concept is looking up at the stars. All you are seeing is their past finally making it to you. That star may be burnt out, and it's history is just flying by you. Kinda cool.

Ever watch someone from a distance hit a sledgehammer on a rail? You see it, then a second later, you hear it. If light were to travel that slow, you'd be viewing something that actually happened a second earlier. But because light travels so fast, the reflection of light off of someone swinging a sledgehammer seems instantaneous. If you put enough distance between yourself and the guy swinging a sledgehammer (gagillion miles), then what you're viewing has already happened, relative to the guy with a sledgehammer.

So, I guess if you travel faster than light, go really really far away, was able to focus on the light just reflecting from the Earth...then you might be able to see Albert Pujols' first home run again. It's no different than pointing a telescope at another sun, you're just watching it's past light catch up to where you are.

[jim]

Let's see...if electromagnetic waves travel at the speed of light, then if you were to travel faster than the speed of light, you could catch up to the first television broadcast and rewatch it. It's kinda like going back in time.

If you could do that, it's not kinda like going back in time, it IS going back in time. But you can't.