Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Paradox-free time travel is theoretically possible

npr.org

Post reply on HN
Print view View original

91–100 of 215 posts

Re: Paradox-free time travel is theoretically possible

#91

Post by jlokier »

pmontra wrote: post #77
nirui wrote: post #51

Earlier quoted context omitted.

Oh actually, I've found the way to convenience myself about that: The "reality" is, when somebody travels through time, most of them (god knows how many) got killed in the process, but the story will just pick another "instance" who has survived the journey from the pool of "Multiverse" and continues.

I watched this short movie yesterday night "One-Minute Time Machine" https://www.youtube.com/watch?v=vBkBS4O3yvY Only 5 minutes and it's kind of along this line of thought. I won't spoil the details.

Genius!

Re: Paradox-free time travel is theoretically possible

#92

Post by ralfn »

dragonwriter wrote: post #79
mpalmer wrote: post #27

Earlier quoted context omitted.

Think what they're getting at is that it won't happen that way. Gun will jam, you die of a brain aneurysm. We don't exist in a universe where impossible things happen, so we can't bring them about. But yes, the article doesn't really sink its teeth into it.

The thing is, the time traveler’s existence in the past is a contradiction, so if the universe prevents contradictions it must prevent backwards time travel absolutely.

Yeah I fail to see anything addressed at all.

Just fluff words and old sci fi trope.

How is this presented as something published in a peer reviewed journal.

Is the article completely misrepresenting the research or is the research itself this level of nonsense.

I must be missing something here.

Re: Paradox-free time travel is theoretically possible

#93

Post by vidarh »

at_a_remove wrote: post #69
mpalmer wrote: post #27

Earlier quoted context omitted.

Think what they're getting at is that it won't happen that way. Gun will jam, you die of a brain aneurysm. We don't exist in a universe where impossible things happen, so we can't bring them about. But yes, the article doesn't really sink its teeth into it.

The thing about this "self-correction" is that nobody, but nobody has a mechanism to explain this force. Not how it works or worse yet, how it will know how to self-correct. What particular force decides that the friction on some surface will briefly rise and cause the gun to jam? How does it know to do that? In all of the paradox-forbidding time travel scenarios, nobody has ever mentioned anything deeper than "Well,…

I think the flaw here is assuming "knowing" rather than a mechanism that makes it impossible to express the paradox, or alternatively, impossible for you to find yourself in a world where an action that created a paradox happened.

One option: We tend to see time as mutable, but it's not clear that time needs to be mutable. Imagine time as a window into an immutable graph of deterministic state transitions, for example. You could come up with such a model where loops "back in time" were possible, but where the model simply can't express situations that leads to paradoxes, and where we by extension can't exist in a universe where people can ever take steps that would lead to a paradox.

Re: Paradox-free time travel is theoretically possible

#94

Post by schwartzworld »

skc wrote: post #88

This really got me thinking. Does anyone know of any great sci-fi stories centered around the lengths the universe goes to to prevent a curious time traveler from testing the grandfather paradox.

Probably not what you're asking for, but there's a classic Futurama episode that fits that description https://en.m.wikipedia.org/wiki/Roswell_That_Ends_Well

Re: Paradox-free time travel is theoretically possible

#95

Post by schwartzworld »

littlestymaar wrote: post #68

The time-travel paradox arises only if you presuppose the existence of free will: if we don't, and just consider human beings as physical objects acting deterministically, then there can be no paradox: the time traveler will simply do what was already had been done in his past.

Ah yes, can you change the past or was there a time traveler version of you running around failing to change things the whole time? See season 5 of Lost for endless discussion on this point. You also can avoid paradoxes if it turns out that time travel just puts you on an alternate timeline.

There's a different paradox with this version of time travel though. Suppose I'm a kid and future-Me comes back and tells me a story. "you will write down this story and publish it and it will be famous." I do as he asks and he's absolutely right, leading me to eventually return the favor to my past self in a time loop.

Where did the story come from?

Re: Paradox-free time travel is theoretically possible

#96

Post by guerrilla »

8bitsrule wrote: post #48

I've never seen the past or future. Only physical things still or moving, combining with other things or not ... What we call 'the past' is a mental picture of where physical things used to be positioned and their condition. But everything in 'that now' has changed. Just as when we 'travel' in physical space, when we get 'back home' it has changed. If I were to 'time travel' I'd be gone from now. But everyone else wo…

> So where was the 'instant of time' I travelled to stored so I could go there?

Not where, when. [1] The block universe ontology is pretty commonly offered as an interpretation of general relativity. People consider GR as pretty strong evidence for such an ontology. Personally I don't but I'm just saying your criticism isn't very good.

1. https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time...

Re: Paradox-free time travel is theoretically possible

#97

Post by littlestymaar »

schwartzworld wrote: post #95
littlestymaar wrote: post #68

The time-travel paradox arises only if you presuppose the existence of free will: if we don't, and just consider human beings as physical objects acting deterministically, then there can be no paradox: the time traveler will simply do what was already had been done in his past.

Ah yes, can you change the past or was there a time traveler version of you running around failing to change things the whole time? See season 5 of Lost for endless discussion on this point. You also can avoid paradoxes if it turns out that time travel just puts you on an alternate timeline. There's a different paradox with this version of time travel though. Suppose I'm a kid and future-Me comes back and tells me a…

Your story allows a “closed timelike curves” to exist, then it must be considered as a physical constant.

Where do c (the speed of light), G (Gravitational constant) or π comes from?

Re: Paradox-free time travel is theoretically possible

#98

Post by nimbleal »

forgingahead wrote: post #37
MetaWhirledPeas wrote: post #3

> Researchers ran the numbers and determined that even if you made a change in the past, the timeline would essentially self-correct, ensuring that whatever happened to send you back in time would still happen. I'm sure these researchers are pretty smart, but nothing in this article goes beyond the level of a grade-school debate. Maybe there's something enlightening in the paper. But if there was, you'd think it woul…

Given that this is NPR, a reference to Gell-Mann amnesia[0] seems appropriate: “Briefly stated, the Gell-Mann Amnesia effect is as follows. You open the newspaper to an article on some subject you know well. In Murray’s case, physics. In mine, show business. You read the article and see the journalist has absolutely no understanding of either the facts or the issues. Often, the article is so wrong it actually present…

I didn’t know this had a name, but it’s long been a cause of amusement (or despair!) for me. I too have noticed that any time I read an article on a subject on which I have even a passable level of expertise, I find it chock-full of errors.

Re: Paradox-free time travel is theoretically possible

#99

Post by mjburgess »

akvadrako wrote: post #83
littlestymaar wrote: post #68

The time-travel paradox arises only if you presuppose the existence of free will: if we don't, and just consider human beings as physical objects acting deterministically, then there can be no paradox: the time traveler will simply do what was already had been done in his past.

Not if he has more information because he has seen the future - then he'll likely act different.

Indeed.

What people mean by "time travel" isnt time-reversal. It's taking information from the future and injecting it into the past by moving the atoms of your now-body into the past.

This isn't "time travel" in any sense that physics uses the term. And is certainly impossible on very many grounds.

Physics has nothing to say on "time travel" in the popular imagination.

Re: Paradox-free time travel is theoretically possible

#100

Post by gitgud »

skc wrote: post #88

This really got me thinking. Does anyone know of any great sci-fi stories centered around the lengths the universe goes to to prevent a curious time traveler from testing the grandfather paradox.

[1] Predestination is a good Time Travelling Film, similar to the plot you describe.

[1] https://www.imdb.com/title/tt2397535/

Post reply on HN