Would you go back in time to prevent your own birth for $1b?

[uppi]

Light will always take the fastest path* between two points.

*more rigorosly, the path of least action

If you want to be rigorous, you have to say that light takes the path of extremal (and thus stationary) action. This does not have to be a global minimum.

It is easy to see, that the statement that light takes the fastest path is untrue in general: Imagine a long rod of a highly refractive material. If you shine in a beam of light along the axis of this rod, perpendicular tot he end face, it will take the straight path through the rod, although there would be much faster paths around the rod.

 

[dutchfire]

Yeah, that is indeed the most rigorous way to state it.

 

[Racsoviale]

The biggest two problems I see arising with this scenario is that either you get hunted down by Van Damme for doing something that changes history too much, or Schwarzenegger realizes this prevents the machine take-over. Either way you're screwed and that's even before we get into the paradox thing.

 

[warpus]

Have you ever read Robert Silverberg's novel Up the Line?

First of all, I apologize for taking so long to get to your response and not keeping up with this thread! (and this is directed at everyone who read and posted in this thread) I've been really busy lately, mostly with work and have had to dedicate my forum-posting time to the formal debate.. with some "recreational" Tavern threads thrown in here and there for s&g. I'm exhausted right now and tomorrow I'm waking up at 6am to go to see my sister in Ottawa for thanksgiving weekend.. I'll be back on Monday night when I'll have to put together a demo for work for a meeting on tuesday.. At least I'm not driving in either direction so I can sleep in the back tomorrow, so that's good, but I'm definitely stressed the hell out..

I have actually not read any of Silverberg's work .. I have read a lot of other sci-fi though and that is usually what I read. How is his stuff? Would you recommend "Up the Line?"

Right now I'm in a bit of a Iain M. Banks phase... and unfortunately I made a point to not reading the rest of your post about the novel in case it's one of his best and I end up reading it or something.. Sorry! It had to be done!

If you recommend it I will have to keep it in mind as an option once I'm done with Banks and (yeah, I know you're going to hate this) the latest Dune novel. Good sci-fi authors are hard to find and I kind of go through them in phases for that reason.. Once I find somebody good I just read more of him or her until I've read all the books that sound like they have an interesting premise or until I get bored of the style.. I might have read some Silverberg and I have probably read a couple of his short stories, but I totally can't remember anything..

 

[warpus]

It calculates your position in four-dimensional spacetime (and that's why you need the information from at least 4 satellites for it to work accurately).

You might not believe in time as the fourth dimension, but your GPS receiver has to rely on that fourth dimension in order to have a chance at accuracy. So if you use GPS you rely on something you do not believe to exist.

This deviates quite a bit from the intended theme of the thread, but.. how does GPS work? I mean.. I thought I knew how it works but I didn't think it considered relativistic (is that even a word?) space-time. Is that what it has to do for GPS to be precise to some level of degree?

I could just look it up, but you obviously know what you're talking about when it comes to this stuff.

...

Oh dear.. I have been reading the thread and what.. .. Ondskan.. what ..

Do you actually suggest that if I were to fly through the sun, make a hole through it, and at the same time project light around it that if I was flying at near light speed I could actually travel in time?

No.. no.. this thread was definitely not supposed to be about people flying through the sun.

 

[warpus]

I finished reading the thread and I don't understand where the yellow frog comes in but I have learned a bit about refraction!

@Crezth, dutchfire, and uppi

You guys seem to know your stuff... Is it possible to analyze my scenario using hard physics? Or would you have to know the exact nature of the time-machine and how it works to do something like that?

My understanding of physics is limited, but I do have 1st year University level physics knowledge (or used to have) and have done a bit of recreational reading about quantum physics (unrelated to all this I think.. but), the history of physics, the nature of space-time, Einstein's theories, etc... which isn't much at all but I can make sense of the concepts due to my math background and have at times understood some of them on some level.. maybe not the advanced stuff, but I definitely had a decent grasp at some point of space-time, why it's called "relativity", some of the implications, etc.

So anyway.. What if the time machine is a wormhole? Say you anchor one end of a wormhole somewhere today and hold on to the other end and let it travel through time with you while the other opening stays behind? And then use that to send someone back and perform the mission? Is that a decent enough framework that could be analyzed, at least in a "thought experiment" way? How would my scenario play out?

The reason I bring a wormhole into this is because it is my understanding that wormhole-like connections between 2 points in space-time are valid mathematically in terms of being consistent with general relativity.. and the anchor is a way to get rid of the "how do you make the connection?" question

 

[Valka D'Ur]

I have actually not read any of Silverberg's work .. I have read a lot of other sci-fi though and that is usually what I read. How is his stuff? Would you recommend "Up the Line?"

I absolutely recommend "Up the Line". However, you will have trouble finding it anywhere other than in a library or (if you're lucky) a second-hand book store. Not sure about eBay or other online sellers. I bought my copy back in the '80s (and was lucky enough to meet Silverberg a few years later and have him autograph it ).

One thing about this particular novel, though: Some of it may make modern readers a little uncomfortable, as there are several "politically incorrect" bits of dialogue, character traits, and some very definite sexist attitudes from some characters. I belong to a Yahoo! group called "Time Travel Novels" and some of the people in that group couldn't finish it. I had to really talk my fellow admin into it, since she decided to give up right before the main character got into one MAJOR amount of trouble!

The basic story involves Jud Eliot, student of Byzantine history, getting hired by the Time Service as a Courier. His job is to escort groups of tourists into the past to have a one or two-week holiday in Byzantium, hitting some of the highlights (ie. watching an Imperial coronation, the Crusaders, battles) and also having a leisurely time at the chariot races, shopping, and doing what tourists do pretty much anywhere/when. There's a chapter where Jud is learning about time paradoxes and how not to get into trouble with them, and Silverberg has definitely made an effort to present this as logically as possible.

It's not the only time travel novel Silverberg has written - he also wrote Hawksbill's Station, about political prisoners marooned back in pre-human times (the men and women are separated by several hundred million years, so there's no danger of human descendants coming along and overtaking their proper time/place in evolution). This is a pretty grim book, though, and I much prefer Up the Line, which is an absolute hoot.

(btw, if it were ever made into a movie, which I doubt it would be, but a person can hope... I'd cast Joaquin Phoenix as Jud and a younger Lou Gossett, Jr. as Sam; that should give you some idea of how I perceive the characters )

If you recommend it I will have to keep it in mind as an option once I'm done with Banks and (yeah, I know you're going to hate this) the latest Dune novel.

I saw Sisterhood of Dune in the bookstore today. I finally gave up on waiting for Winds of Dune to make it to the bargain table at Chapters/Coles, and got it on eBay. I'll probably do the same for this new one, since I don't feel it's right to criticize KJA/BH if I haven't actually read what I'm complaining about. At least this way they won't get any royalty money out of my wallet.

 

[warpus]

I absolutely recommend "Up the Line". However, you will have trouble finding it anywhere other than in a library or (if you're lucky) a second-hand book store. Not sure about eBay or other online sellers. I bought my copy back in the '80s (and was lucky enough to meet Silverberg a few years later and have him autograph it ).

Nice! I don't have any of my books autographed except a Robert J Sawyer novel and I can't even remember which one...

Any other Silverberg books you recommend? Or anything else about time travel actually?

My favourite time travel novel has got to be Pastwatch: Redemption of Christopher Columbus. It's enjoyable from both points of view: that of the natives and the alternate history take on human history .. but also that of the time travellers.

One thing about this particular novel, though: Some of it may make modern readers a little uncomfortable

Oh, that won't bother me one bit.. I've come across stuff like that before.. such as Asimov's "fantasy" in one of his novels where a grandpa is having sex with a 12 year old for the betterment of the human race. I think it was one of the Rama novels.

I saw Sisterhood of Dune in the bookstore today. I finally gave up on waiting for Winds of Dune to make it to the bargain table at Chapters/Coles, and got it on eBay. I'll probably do the same for this new one, since I don't feel it's right to criticize KJA/BH if I haven't actually read what I'm complaining about. At least this way they won't get any royalty money out of my wallet.

I can't remember which one I liked more: Winds of Dune or Paul of Dune, but I do remember enjoying one of the more recent Dune books more than most of the other prequels.. which I actually don't mind - but I just have to be in a "space opera" type mindset when I read them - and not a "classical Dune" mindset at all. Anyway, one of the more recent ones was a good read - I started reading Sisterhood but got distracted - from what I've read so far it seems like it could have potential

 

[Arakhor]

I've always been interested in time-travel and alternate history scenarios, but I haven't actually read that many, since I'm completely uninterested in military history. I did like Robert Silverberg's novella Sailing to Byzantium though and I think that edition came with a novella about a Canadian time agency overshooting Ancient Rome and marooning a couple of agents in Egypt's New Kingdom.

 

[dutchfire]

This deviates quite a bit from the intended theme of the thread, but.. how does GPS work? I mean.. I thought I knew how it works but I didn't think it considered relativistic (is that even a word?) space-time. Is that what it has to do for GPS to be precise to some level of degree?

I could just look it up, but you obviously know what you're talking about when it comes to this stuff.

GPS clocks need to be very accurate to give tell you where you are exactly. Since relativity messes with clocks, you need to take that into account when you want to be very accurate. According to the almighty wiki, the effects are such that to receive a 10.23 MHz signal, the satellite has to emit it at 10.22999999543. This relative effect of 10^-10 is caused by relativistic effects. The point is mainly that a small clock error translates to a huge distance error since the speed of light is "large"*.

This is pretty decent: http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Relativity

*In the units we are used to. Scientists will ofter work with c=1

I am afraid I cannot really answer your other question. Time travel is rather abstract, and rather "out there" in terms of physics theories, without knowing exactly how you would time travel, it is hard to say anything about it. And if I knew how you could time travel, I'd be patenting it right now.

 

[warpus]

GPS clocks need to be very accurate to give tell you where you are exactly. Since relativity messes with clocks, you need to take that into account when you want to be very accurate. According to the almighty wiki, the effects are such that to receive a 10.23 MHz signal, the satellite has to emit it at 10.22999999543. This relative effect of 10^-10 is caused by relativistic effects. The point is mainly that a small clock error translates to a huge distance error since the speed of light is "large"*.

This is pretty decent: http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Relativity

*In the units we are used to. Scientists will ofter work with c=1

I am afraid I cannot really answer your other question. Time travel is rather abstract, and rather "out there" in terms of physics theories, without knowing exactly how you would time travel, it is hard to say anything about it. And if I knew how you could time travel, I'd be patenting it right now.

Interesting, thanks!

How much more specific in how the time machine works would I have to get for you to be able to analyze it and predict effects? The "use a wormhole" thing seems rather specific, and remember, I am not after the details as to the time travel but rather how the universe resolves paradoxes. There are particles that travel through time, right? Do any paradoxes arise? How does reality take care of them?

 

[Souron]

So anyway.. What if the time machine is a wormhole? Say you anchor one end of a wormhole somewhere today and hold on to the other end and let it travel through time with you while the other opening stays behind? And then use that to send someone back and perform the mission? Is that a decent enough framework that could be analyzed, at least in a "thought experiment" way? How would my scenario play out?

The reason I bring a wormhole into this is because it is my understanding that wormhole-like connections between 2 points in space-time are valid mathematically in terms of being consistent with general relativity.. and the anchor is a way to get rid of the "how do you make the connection?" question

I'm not one of the people you listed, but I'll answer anyway.

That creates a situation where the earlier in time wormhole influences what goes into the later in time wormhole. So it's self causing. I have heard of at least one scientific paper claiming this is impossible, though I don't know the reason given. It could be something like "it could create perpetual motion, which is impossible." I don't have a link to the publication.

Wormholes between places that do not have a causal relationship have not, as far as I know, been ruled out.

 

[strijder20]

There are particles that travel through time,

Duh You're made of them.

 

[warpus]

I'm not one of the people you listed, but I'll answer anyway.

That creates a situation where the earlier in time wormhole influences what goes into the later in time wormhole. So it's self causing. I have heard of at least one scientific paper claiming this is impossible, though I don't know the reason given. It could be something like "it could create perpetual motion, which is impossible." I don't have a link to the publication.

Wormholes between places that do not have a causal relationship have not, as far as I know, been ruled out.

It's not fully self-causing though, because what you do is this:

1. Create a wormhole and anchor 1 end to the "present"
2. You leave it there and you hold on to the other end of the wormhole
3. You use the end you have been holding onto to go back in time to the exact time & place when the anchor end of the wormhole was deposited.

I suppose you could have meant something else by "self-causing", but I wanted to clarify. I have read about the above scenario in Scientific American I believe, as a plausible time-travelling scenario, in that it would be mathematically consistent and wouldn't violate any known theories. The obvious issues are "How do you create a wormhole like that?" and "How do you anchor a wormhole in space-time?" but wormholes connecting points in space-time are mathematically possible given our present understanding of the Universe, so those 2 questions were left as variables not to be thought about during the thought experiment.

 

[Souron]

By self causing I mean that the stuff going through the wormhole could influence itself, not that the wormhole itself creates itself. More formally, the wormhole end in the future is within the realm of influence, the "light cone", of the wormhole end in the past. That allows stuff to enter the future end, go to the past, then enter the future end again, or influence what goes in, which amounts to about the same.

The problem only exists if light can travel from one end of the wormhole to the other, without going through the wormhole. If two the two ends are far enough apart, and don't persist too long, then there is no problem.

 

[Ondskan]

I don't get it. People believe in god and astrology, in the moonlanding being fake and in getting aids by sharing cups. Yet nobody believes like me that this goes against common sense?

wow. I'm like the fringe of the fringe

 

[Crezth]

As stated, "common sense" is not a particularly useful epistemological construct for understanding the universe.

 

[Ondskan]

You shut your piehole. We are not going through this agian.

 

[Crezth]

yessuh

 

[warpus]

Ondskan, I highly recommend that you limit your posting prowess to the Tavern.