An Interesting Read on Time Travel

[nlc315]

Finals have been going on recently, and so naturally I've been searching for sources of procrastination. Poker helped for sure, but I found a book on time travel very interesting:

"Time Travel in Einstein's Universe: The Physical Possibilities of Travel Through Time by J. Richard Gott"

The author brought up traveling into the future is already posssible via relativitic principles...all one would need is a rocketship able to travel the speed of light for a few years, and then come back. More time would have passed on earth due to time dilation, and in effect, you would have traveled into the future.

It talked about various time travel paradoxical issues. One issue was traveling back in time, and killing your grandmother. Obviously, if you killed your grandmother, she would have been unable to have your mother, and you couldn't have been born....but then, if you couldn't have been born, then you wouldn't have been able to travel through time and kill her to begin with.

To explain this, he proposed the idea if traveling to the past was possible, that changing it to alter the future would be completely impossible. Because you would have been a part of the past when it happend, you were involved in how it happend in the first place. Basically, that past events were depended upon you being there so any actions you had would have already had consequences in the future you came from.

He also brought up time loop-like paradoxes. For example...I read Shakespeares' Hamlet. Then I go back in time, and tell Shakespeare the story he wrote. Then he write it and publishes it. Years later I'm born and I read it....so who actually wrote Hamlet? No one actually created the story...

What does everyone think about this?

I'm going to add my own story to this already long post. Shortly after reading this, I was trying to study for my physics final in the library. I was very quiet, and I was getting a lot done, when suddenly a bird, that I presume was in the tree next to the window I was studying by, began churping and wouldn't stop!! It seemed very loud, probably because of my otherwise very quiet surroundings. I looked up, and thought to myself, "ok, I'm going to really study physics VERY VERY hard, and I'm going to invent a time machine one day. And when I do, I'm going to come back here on November 28th, at 10:30 a.m. and kill that damn bird so I can get some studying done!"

And it stopped....

[alphatmw]

which part of this was the interesting part?

[MaxWeiss]

Yeah, information loops like your Shakespeare thing always got to me. Should travel backwards ever exist or a good mathematical model of how it can be done ever proven, I would be very interested in how to resolve information loops. It seems to me that there is a definite "start" and "end" to the loop, it is just not in our space-time. The information did come from somewhere. Who knows? I know very little about the topic, but I enjoy the thought of the possibility even though I doubt it will happen.

[John21]

I made a post about questioning the concept of time a while back, and my ideas were completely refuted. My central premise was that time doesn't exist in ultimate reality, and since then, I've tried to look at the issue of time from a slightly different perspective, and this is where I'm at:

We define a second in time by a duration of 9 billion periods of radiation of a caesium atom. So blah, blah, blah to define frequency/velocity/wavelength - we can conclude that:
period = (distance/distance)/time -- so basically this approach to define time leads to an abyss. (I didn't end up defining time, instead I just gave another definition of a period. That was the mistake I made in trying to refute the concept of time in my first argument.)

So now I'm looking at how my current definition of frequency impacted my conclusion. The aspect that stuck out was that we define time by the quantity of "events" that occur. Hence, a period of time is a number of events that occur in a second; but the specfic interval is related to other events; and those intervals are measured by other events, etc…

I'm at a point where all we really have left are intervals, which are established with timeless moments. So, I'm being forced to conclude that time is simply the measure of the change of events, which we have attributed to and against other changes of events.

This is just my sketchpad of thought and probably incoherent, but maybe it would be easier to work backwards from my conclusion:

For change to occur we require some sort of motion, and our problem has been the concept of requiring time to have motion - rather than requiring motion to have time.

It's quite a paradigm shift to look at motion as the genesis of time. But when I look at the human mind and the concept of past, present and future - I'm wondering if we haven't done more to interject our own mind onto reality, rather than use our mind to accurately interpret it.

[recipro]

[ QUOTE ]
He also brought up time loop-like paradoxes. For example...I read Shakespeares' Hamlet. Then I go back in time, and tell Shakespeare the story he wrote. Then he write it and publishes it. Years later I'm born and I read it....so who actually wrote Hamlet? No one actually created the story...

[/ QUOTE ]

Yeah, this is like how Fry is his own paternal grandfather. It makes you wonder where his (and his father's) x-chromosones came from.

[FortunaMaximus]

[ QUOTE ]
which part of this was the interesting part?

[/ QUOTE ]

Give him a break. This is new to somebody once in awhile.

Time is not directional. It's human perception that has it flow in one direction.

Yeah, well, grandfather paradoxes. <weary shrug> Easy enough to explain away when you realize a backwards causality violation just sprouts another temporal branch.

Information is an emeergent property that doesn't rely on a location in time to exist. To wit: Look at a picture of Neptune. Think yourself there. You didn't violate c, did ya. But you know Neputune's there.

You have to assume a lot, and in rediscovery, you find the facts are still there. The value of Hamlet's words aren't in who wrote it and when it was written, but that there are millions of copies... That were printed at different times in different languages, and still carry the same message. (Although what's Xhosa for fardels anyway?)

Sometimes Denmark's foggy, sometimes it's sunny... Sometimes it's on a Caribbean beach. It is, for better or for worse, still the Denmark of the Bard's devising.

[Morrek]

[ QUOTE ]
Shortly after reading this, I was trying to study for my physics final in the library. I was very quiet, and I was getting a lot done, when suddenly a bird, that I presume was in the tree next to the window I was studying by, began churping and wouldn't stop!! It seemed very loud, probably because of my otherwise very quiet surroundings. I looked up, and thought to myself, "ok, I'm going to really study physics VERY VERY hard, and I'm going to invent a time machine one day. And when I do, I'm going to come back here on November 28th, at 10:30 a.m. and kill that damn bird so I can get some studying done!"

And it stopped....

[/ QUOTE ]

Awesome

[Utah]

[ QUOTE ]
Time is not directional. It's human perception that has it flow in one direction.

[/ QUOTE ]We simply dont know enough about time to say that it is non directional. At least I am not aware of experimental evidence showing this.

[PLOlover]

[ QUOTE ]
We simply dont know enough about time to say that it is non directional. At least I am not aware of experimental evidence showing this.

[/ QUOTE ]

Actually I think experimental evidence in partical accelerators about particle decay shows a bias for the forward direction of time.

I think there was an article or series in Scientific American magazine called "Arrows of Time" or somthing like that circa 1985-90 where they went over all the evidence for the flow of time, backwards and forwards.

[nlc315]

[ QUOTE ]
For change to occur we require some sort of motion, and our problem has been the concept of requiring time to have motion - rather than requiring motion to have time.

It's quite a paradigm shift to look at motion as the genesis of time. But when I look at the human mind and the concept of past, present and future - I'm wondering if we haven't done more to interject our own mind onto reality, rather than use our mind to accurately interpret it.

[/ QUOTE ]

I disagree with this if I'm interpreting what you meant correctly. We consider motion being dependent on time often using vector-valued functions for basic physics problems. We'll take the path of a projectile, or whatever, and express the equation(s) describing this motion in parametric form, often using t as the variable, and considering the motion now, as a function of time.

I often wonder about relativity's view that c is that cosmic speed limit... Let's consider an object...say, a planet, or I dunno, a big star or something, revolving around it's own axis... Now, let's imagine it's spinning with an angular velocity of c. Would an observer in an inertial reference frame few this as a speed violation of c? What would this say to the concervation of angular momentum? How would this affect space-time?

[Torgeir23]

This is a subject I have been thinking about a lot lately. Now, I'm not going to pretend to be a great physicist or methematician, but I thought I would share my two cents anyways.

So far I have thought of two different approaches to the 'grandfather' problem.

The first one is to imagine a multiverse instead of a universe. Imagine that this universe does not exist alone but is only one possible universe out of every possible universe. Basically, there exists a universe for every possible direction a universe could take. If you travel back in time you would basically travel back in time to the universe where you did travel back in time and kill your grandfather and you therefore do not exist in that universe.

Another thought I have had is that if you view time as another dimension, people are traveling through that dimension on a linear road. In order to exist, people, or anything, would have to be present in in all 4 dimensions. You canbnot see a two dimensional object, in order to see an object it would need three dimensions. But a three dimensional object which does not exist in time would be impossible to see as well. So by traveling back in time, the rest of the world would have traveled forward in time as time passes by, and there would therefore be nothing to see in the past. Not really sure what this theory implies though, and have thought of it while being stones most of the time.... Just interested to see what people better qualified in this field have to say about it really