Good News For Time Travelers!

[austenandrews]

Re: Good News For Time Travelers!

 

Now that you brought this up' date=' the only one of your grandparents guaranteed to cause a paradox is your maternal grandmother.[/quote']

Is there no chance your mother was adopted and didn't know it? What if your maternal grandmother had an identical twin, who then married your grandfather and bore a genetically-exact version of your mother?

 

You can't thwart Rod Serling so easily.

[Nyrath]

Re: Good News For Time Travelers!

 

Some observations:

2. The other great big problem with time travel apart from "where are all the time travelers?" is this: Given the assumptions excellently summarized by Dr. Anomaly, sooner or later someone will go back far enough that they screw up the events that led to the invention of the time machine (assuming the past can be altered). Time machine-possible-universes automatically delete the timelines that lead to the development of time travel. By their very existence, time machines assure their non-existence.

 

Larry Niven, in "The Theory and Practice of Time Travel", had a similar concept. In a universe where time machines had been invented, sooner or later some joker would go back in time and change history. And changes would happen in the new history. History would be in an unstable state, constantly evolving.

 

This would stop once history reached a stable state. Which would be a history where nobody ever invented a time machine.

 

In other words: history would inevitably evolve to a state which had no time machines, and stay in that state.

[Nyrath]

Re: Good News For Time Travelers!

 

PS. I haven't read the referenced article yet. It sounds like just another scientist's "radical new theory". I'll wait for Wal-mart to start selling time machines before I worry about what's possible.

It is actually not that radical. Secretly, most physicists were hoping for something like this.

 

On the one hand, the pillar of all physics, indeed of all science, is the principle of cauality. Initiate a cause and its effect will follow. Drop a brick over your foot and your foot will be crushed. Send electricty through water and obtain hydrogen and oxygen.

 

If sometimes you dropped a brick and it flew up, sideways, or turned into little fairies covered in rainbow glitter, you might as well give up being a scientist.

 

On the other hand, (a) time travel seems to destroy causality due to its ability to create paradoxes and ( other than that, relativity, quantum mechanics, and all other known laws of physics allow time travel. In fact, they describe several methods that are theoretically possible.

 

This has been annoying physicists for quite a few decades now.

 

In theory, there were four possibilities to fix the situation, but no details on how these would work. They are all ways to prevent time travel from creating a paradox, thus allowing time travel and causality to co-exist.

 

The new paper describes a way that quantum mechanics can create possibiliy #2: Consistency Protection. If the paper withstands peer review, physicists can heave a sigh of relief and go back to what they were doing.

[austenandrews]

Re: Good News For Time Travelers!

 

I don't think it's clear that "Relativity time travel" and "QM time travel" are the same animal. I admit, I don't know enough about the mathematics to have a concrete feel for what Greenberger and Svozil's equations do or don't imply. But they're expressly generalizing that a beam-splitter, with one beam reentering the same splitter at an earlier time, is equivalent to a time traveler going into the past. Is that a valid assumption?

 

It's probably safe enough to call the beam-splitter analogous to a time traveler either going or not going into the past. But can we assume the beam-splitter is a sufficient model for the entire period from his reentry to his initial departure? Can we assume the whole universe between the two events is represented by a single wave function that feeds back on itself?

 

Unless I'm mistaken, this paper is only saying that if time travel acts like a feedback mechanism, then temporal feedback necessarily enforces causality. Which is pretty cool, no question. But while only physicists can truly review the assumptions, from my naive perspective, the paper has a pretty narrow scope compared to relativistic time-traveling consequences.

[Duke Bushido]

Re: Good News For Time Travelers!

 

I FEEL SO FREAKIN' VALIDATED!!!!

 

Party at my place; let's go!!!!!

[McCoy]

Re: Good News For Time Travelers!

 

"When Greenberger and Svozil analysed what happens when these component waves flow into the past, they found that the paradoxes implied by Einstein's equations never arise. Waves that travel back in time interfere destructively, thus preventing anything from happening differently from that which has already taken place (http://www.arxiv.org/quant-ph/0506027). "If you travel into the past quantum mechanically, you would only see those alternatives consistent with the world you left behind you," says Greenberger."

 

Isn't this basically Silver Age Time Travel rules? You go back into the past to make a change, and something, no matter how improbable, prevents you from it? Like when Superboy traveled back to prevent the assassination of Abraham Lincoln, but was stopped by an adult Lex Luthor who had ducked into the past to hide from Superman? And while returning to the present, you must say "And once again I've learned, no matter how hard you try, you can't *choke* change the past!"

[Dr. Anomaly]

Re: Good News For Time Travelers!

 

Isn't this basically Silver Age Time Travel rules? You go back into the past to make a change' date=' and something, no matter how improbable, prevents you from it? Like when Superboy traveled back to prevent the assassination of Abraham Lincoln, but was stopped by an adult Lex Luthor who had ducked into the past to hide from Superman? And while returning to the present, you must say "And once again I've learned, no matter how hard you try, you can't *choke* change the past!"[/quote']

Not really; it varied considerably from writer to writer in the Silver Age. Characters would make remarks like that, about the "rules" of time travel or history, only to have it work differently in another story by a different writer. There were several occassions in the Silver Age stories of the Legion where interfering in the past changed the future (their present).

[Duke Bushido]

Re: Good News For Time Travelers!

 

okay,

 

I wanted to review the thread before making more comments, but I was so buzzed by the validation that I had to go out and ride a few miles-----

 

Here's the deal, and I've been pumping it for years.

 

You've got two ways to go here:

 

either time travel doesn't exist, and never will (and it doesn't, and never will. More later), or it one day will.

 

First, let's look at the 'one day we will do it' angle.

 

Okay, assuming that time travel will/does exist, paradox is impossible. Period. period. period.

 

The simple reason is that no matter what you go into the past to do, you have already done it, so there is no way that you can possibly screw it up by going and doing it. Poof. Paradox, if I may borrow from Adams, vanishes in a puff of logic.

 

I know it's not glamorous, and doesn't make good fiction (like time travel itself, actually), but think about it.

 

Let's say that you are born in 3000 and in 3050 you go into the past. Let's say that you go back to 1000, just to look around. Fine. So you were already mucking about in 1000, years before you were actually born. Woo-hoo; let's right a short story!

 

Two thousand years later you will be born, build a time machine, and go back. It's pre-ordained by your already having been there. But no matter what you do when you get there, you cannot possibly ever affect any change to 'your' version of history, simply because no matter what you could possibly do, you've already done it.

 

Are you going to shoot Hitler? Well, you won't, simply because you didn't. (unless you did; I don't think anyone's really sure yet). Going to drop an asteroid on the earth and wipe out the dinosaurs? Well that one seems to have gone over well; you should enjoy actually being there to see yourself doing it.

 

Any possible thing that you do or do not do won't change a cussed thing because it is already what you did or did not and therefore absolutely nothing will be different. You'll go on continuing to believe in free will, and the world will remain unchanged.

 

Now yes, it's quite possible that I might be construed to advocate predestination, but I'm just not that deep. Besides, I don't. I'll spare you that lengthy dissertation...

 

Of course, that's only if time travel could actually exist.

 

 

And here's why it won't. Oh, and whoever it was that quoted whoever else it was about the future tuourists, thanks! That was hillarious.

 

People are people. We can all aspire to lofty ideals and we can pretend that each and every one of us holds inside the best, most noble traits of the race, and that we can all be counted on to do the absolute best possible thing in the interest of your fellow man. As I said, we can aspire to it, and we can pretend that we believe it.

 

But we all know it's not true.

 

While there are good and great people, and wonderful people, and the best of people that you can describe with whatever descriptives you might use on your idea of the best of people-----

 

The bulk of humanity is pretty self-centered, and scatterbrained. No; I'm not being snide. Think of all the people every single day who go out of their way to steal, lie, and kill for whatever trivial reason they have.

 

Given that we have time travel, we by default have infinite time. And given that we have infinite time, we are forced to accept that we have infinite people. And given the tendencies of people on the whole, one of them is going to one day screw up and spill the beans.

 

And once those beans are spilled, well time goes forward. It will spread and spread and spread, onward and upward through time, until eventually everyone is well and goodly aware of time travel itself, how it's done, and how to do it. And when that day comes, there will be those (Okay, I'm still trying to give people too much credit, maybe. It's quite possible that it won't take a very big spread to find the greedy person).

 

Anyway, there will be at least one person who decides that the temptation for wealth through time travel, or education through time travel, or whatever, is too great to resist, and starts hopping all through time.

 

And with time travel, even all that infinite time will no longer be orderly and sequenced, so we can assume, through time travel, that all people then exist all at once. So what happens, as soon as the cat is out of the bag, is that there are millions and millions ---billions and billions? Trillions and trillions?-- of people hopping about through time. Once again, one of them is bound to screw up, and leave the secret laying about somewhere in the past. Why, with the numbers potential of infinite time, millions and millions of them will screw up and leave the secret all through time.

 

And as a direct result, time travel will be readily accessible to all times and all people.

 

Time travel is the only thing with which this is truly possible, but its lack of existance presently proves its lack of existance in the future. Time travel does not now exist, and therefore never will.

 

Period.

 

And that's why I felt so validated earlier. All my friends-- gamers, readers, writers, bikers, wrenches, racers, drinkers-- all seem to enjoy sci-fi (apparently that's my biggest qualifier for friendship.... Who knew?), and have always dismissed my ideas on the subject outright, though I suspect that is mostly because they do not want to deny their own fantasies about the subject. But this science report thingy just kind of made me feel good. Not for bashing hopes, but because it indicates that I might have had a point for all these years.

 

I just felt good. I might go for another ride!

[keithcurtis]

Re: Good News For Time Travelers!

 

OK, I've read the article, and the referenced abstract. While the math is beyond me (or at least beyond the time and effort I am willing to spend), it seems that the theory doesn't go far enough. "Killing your grandfather" is a human paradox. The existence of time travel would imply paradox on every level of existence, right down to the subatomic level. You weren't in existence 150 years ago, so any attempt to put your atoms back there would cause a paradox, regardless of any gross human consequences. In other words, by their deterministic past model, any universe you are living in is one in which you (and all your component atoms) did not exist in the target point in the past. Therefore, any attempt to put your atoms back there would fail. The waveforms would interfer and collapse, again using their terminology.

 

 

On the other hand' date=' (a) time travel seems to destroy causality due to its ability to create paradoxes and ( other than that, relativity, quantum mechanics, and all other known laws of physics allow time travel. In fact, they describe several methods that are theoretically possible.[/quote']

 

Mathematically possible, not theoretically possible. There's a difference. The relativity equations, IIRC, all require "negative energy". I've never found a good explanation of "negative energy". What is it? How can it be generated?

 

Keith "In the end, the best use for time travel is a literary device" Curtis

[austenandrews]

Re: Good News For Time Travelers!

 

OK' date=' I've read the article, and the referenced abstract. While the math is beyond me (or at least beyond the time and effort I am willing to spend), it seems that the theory doesn't go far enough. "Killing your grandfather" is a human paradox. The existence of time travel would imply paradox on every level of existence, right down to the subatomic level. You weren't in existence 150 years ago, so any attempt to put your atoms back there would cause a paradox, regardless of any gross human consequences. In other words, by their deterministic past model, any universe you are living in is one in which you (and all your component atoms) did not exist in the target point in the past. Therefore, any attempt to put your atoms back there would fail. The waveforms would interfer and collapse, again using their terminology.[/quote']

I believe the notion is that any system, not just a microscopic one, can theoretically be expressed as a quantum waveform.

 

Mathematically possible, not theoretically possible. There's a difference. The relativity equations, IIRC, all require "negative energy". I've never found a good explanation of "negative energy". What is it? How can it be generated?

NGD threads, mostly.

 

I suddenly have the idea of a negative energy generator using a time machine. The universe is constantly generating & annihilating virtual particle pairs, right? If you could create a time machine that removes the positive-energy particle by sending it back in time, you'd be left with a negative energy generator. Use the negative energy generator for a local FTL effect to create a time machine. Of course you'd cause a huge explosion at some point in the past, but you can't make an omlette without breaking a few (cosmic) eggs.

 

Or even better, send the negative energy back in time, just long enough to start up the time machine in the first place. The machine would run until someone shut off the generator, which would fail to send back negative energy, which would cause the generator to deactivate just before someone flipped the switch. If the delay time was short enough, the paradox would be undetectable and no one would be the wiser.

 

(So sue me, I've been reading Douglas Adams lately. )

[keithcurtis]

Re: Good News For Time Travelers!

 

I believe the notion is that any system, not just a microscopic one, can theoretically be expressed as a quantum waveform.

I understand that. People have been focussing on the grandfather paradox, a primarily human, social cause-effect relationship. This engenders a feeling that "If I can just find a loophole" mentality. ie. He's not my real grandfather, I get stopped by another time traveller, etc. I was pointing out that the theory they are positing works right down to the elemental particles of creation. There's no need for the Grandfather Paradox; it clouds the issue. Just the creation of matter in the past where there was none before is a paradox.

NGD threads, mostly.

 

I suddenly have the idea of a negative energy generator using a time machine. The universe is constantly generating & annihilating virtual particle pairs, right? If you could create a time machine that removes the positive-energy particle by sending it back in time, you'd be left with a negative energy generator. Use the negative energy generator for a local FTL effect to create a time machine. Of course you'd cause a huge explosion at some point in the past, but you can't make an omlette without breaking a few (cosmic) eggs.

 

Or even better, send the negative energy back in time, just long enough to start up the time machine in the first place. The machine would run until someone shut off the generator, which would fail to send back negative energy, which would cause the generator to deactivate just before someone flipped the switch. If the delay time was short enough, the paradox would be undetectable and no one would be the wiser.

 

(So sue me, I've been reading Douglas Adams lately. )

 

I'd buy one. You'll need some unobtainium and a quantum seive, though.

 

Keith "and maybe some kryptonite" Curtis

[John T]

Re: Good News For Time Travelers!

 

I'd buy one. You'll need some unobtainium and a quantum seive, though.

 

Keith "and maybe some kryptonite" Curtis

What, no Handwavium? I thought that was a critical ingredient.

 

Actually, time travel is possible, but the current universe will be destroyed before anyone, anywhere can invent it.

 

John T

 

PS - not that I actually BELIEVE that, just sayin'...

 

PPS - And a trivia question, for anyone that thinks they have an answer (I don't). I'm fairly sure that Harlan Ellison first coined the term "Handwavium", and "Kryptonite" is, of course, from the Superman comics. Does anyone know where/from whom the term "Unobtanium" first sprang?

[austenandrews]

Re: Good News For Time Travelers!

 

I understand that. People have been focussing on the grandfather paradox' date=' a primarily human, social cause-effect relationship. This engenders a feeling that "If I can just find a loophole" mentality. ie. He's not my real grandfather, I get stopped by another time traveller, etc. I was pointing out that the theory they are positing works right down to the elemental particles of creation. There's no need for the Grandfather Paradox; it clouds the issue.[/quote']

I agree. When people say "if you go to the past, you find that you can't do anything that causes paradox," they miss the point. It's not just "no matter how much I try, I can't do X!" It's an alignment of the waveform at a fundamental level, where not one electron can be out of place. Macroscopic paradoxes are moot if microscopic paradoxes are eliminated.

 

Just the creation of matter in the past where there was none before is a paradox.

I'm not sure I agree with that as a general principle. We're not talking about creating matter, but about "transporting it through time." In the case of this research (if I have it correctly) the waveform that travels back in time interacts with itself. Just a feedback mechanism. But in the larger sense, I don't know of anything that forbids time travel based on conservation of energy. Fundamentally two electrons in the exact same state are the same electron, right? Quantum entanglement. I see nothing inherently paradoxical about an electron "meeting itself" in the past, for instance, or spontaneously "appearing" somewhere it previously didn't exist. If that makes any sense.

 

I'd buy one. You'll need some unobtainium and a quantum seive, though.

"Unobtainium" was one of my favorite bits from The Core. It gave me a giggle.

[austenandrews]

Re: Good News For Time Travelers!

 

PPS - And a trivia question' date=' for anyone that thinks they have an answer (I don't). I'm fairly sure that Harlan Ellison first coined the term "Handwavium", and "Kryptonite" is, of course, from the Superman comics. Does anyone know where/from whom the term "Unobtanium" first sprang?[/quote']

http://en.wikipedia.org/wiki/Unobtainium

[Duke Bushido]

Re: Good News For Time Travelers!

 

The relativity equations, IIRC, all require "negative energy". I've never found a good explanation of "negative energy". What is it? How can it be generated?

 

Keith "In the end, the best use for time travel is a literary device" Curtis

It can't. You have to ungenerate it. Or possibly un ground it. Then the lines should fill back up, leaving you with enough negative energy to reverse all the cieling fans in two small towns. You don't want to know what happens to the light bulbs.....

 

 

 

Oh, and Kieth--

 

thanks for all the discussion and logical reasons against time travel. I hadn't even considered spontaneous creation of matter, etc, ---

 

I'm validated again, and totally jazzed!

 

:D:D:D:D:D:D

[Captain Obvious]

Re: Good News For Time Travelers!

 

But what about the Casimir effect?

 

It's time travelers, I tell ya!

[Curufea]

Re: Good News For Time Travelers!

 

There should be no confusion that time is more or less constricting than any other dimension. We have three familiar ones already, and time should be treated like them - even though we still don't know the rules.

 

Time is not (as far as I can see) an overlord peering down on all other lesser dimensions with complete control over everything. It is our perception of the fourth dimension (if it's still called that) and can be expressed with formulas, which will help us shake off our anthropomorphisation.

 

The Grandfather Paradox is just a simplification.

[BlackSword]

Re: Good News For Time Travelers!

 

Given that, why haven't we seen huge "population explosions" around events of historical significance?

 

For a non-time travel version of what would happen, I refer you to Larry Niven's short story "Flash Crowd", and then invite you to imagine a similar problem but in relation to historical events that take place at a unique time as well as a unique location.

Maybe that is the case. Maybe there were only 10 people lining the streets for JFK's procession, and once the actual assasination and controvery about the assasination occured a bunch more popped in from the far flung reaches of the future to see. Or maybe in 2025 they just read the investigation documents and its really just a mundane reason.

[austenandrews]

Re: Good News For Time Travelers!

 

Maybe that is the case. Maybe there were only 10 people lining the streets for JFK's procession' date=' and once the actual assasination and controvery about the assasination occured a bunch more popped in from the far flung reaches of the future to see. Or maybe in 2025 they just read the investigation documents and its really just a mundane reason. [/quote']

It's no wonder people think there was a conspiracy. 90% of the witnesses mysteriously vanished without a trace afterward, returning to their home era. Which, of course, guaranteed that time travelers would be interested in the event.

[John T]

Re: Good News For Time Travelers!

 

http://en.wikipedia.org/wiki/Unobtainium

Thanks! I really need to remember that site when oddball questions pop into my head.

 

John T

[SteelDoom]

Re: Good News For Time Travelers!

 

My take on time travel is that if we could go back in time and alter our past then someone somewhen would change it some how. Eventually, a change would occur that would make the developement of that time travel device non existant. There for it can not happen because something has already changed to make it impossible!

[AmadanNaBriona]

Re: Good News For Time Travelers!

 

It's no wonder people think there was a conspiracy. 90% of the witnesses mysteriously vanished without a trace afterward' date=' returning to their home era. Which, of course, guaranteed that time travelers would be interested in the event.[/quote']

I have always liked the Red Dwarf episode where the boys go to Dallas, screw up history, discover that Kennedy ended up making a lousy president, and end up convincing him that in order to restore both Time and his proper legendary status, he should make sure he dies, by becoming the gunman on the grassy knoll.

Bloody brilliant idea, that

[austenandrews]

Re: Good News For Time Travelers!

 

I have always liked the Red Dwarf episode where the boys go to Dallas, screw up history, discover that Kennedy ended up making a lousy president, and end up convincing him that in order to restore both Time and his proper legendary status, he should make sure he dies, by becoming the gunman on the grassy knoll.

Bloody brilliant idea, that

You're right, that's awesome!

[keithcurtis]

Re: Good News For Time Travelers!

 

My take on time travel is that if we could go back in time and alter our past then someone somewhen would change it some how. Eventually' date=' a change would occur that would make the developement of that time travel device non existant. There for it can not happen because something has already changed to make it impossible![/quote']

Go back a few posts. That's been covered.

 

Keith "Go back a few posts. That's been covered." Curtis

[assault]

Re: Good News For Time Travelers!

 

The major flaw with Time Travel ever being a possible-to-develop technology is neatly outlined by Stephen Hawking :-

Where are the tourists from the future?

 

That's easy. Time travel hasn't been invented yet. No time machine exists yet. Therefore, time travel to this point in time is impossible.

 

(Unless some alien species has invented time travel, but we don't have access to their time machine(s).)