Paradox-free time travel is theoretically possible • Hacker News Board

Re: Paradox-free time travel is theoretically possible

#161

Post by nautilus12 » Thu, Jan 21, 2021, 4:13 PM UTC

zaroth wrote: post #46

nautilus12 wrote: post #40

Earlier quoted context omitted.

I think the point about conservation of mass still applies. There are literally 2x yourself at a certain point in time, mass is not conserved.

Always conservation of mass is maintained by broadening the scope of the system under test. You can take matter out of a local system and make that local system less massive, but it’s not a violation of physics because the broader system maintains a steady state. So isn’t the simple layman’s answer that the “system” also spans the 4th dimension and you are just displacing mass around in a 4D space instead of the typi…

I dont think conservation of mass works like this between "disparate" points in the 4th dimension. It has to be continuosly connected. Otherwise things could appear out of thin air without causality. Reminds me of this software: https://4dtoys.com/ (4d is time in this case not another spacial dimension but the intuition about discontinuity still applies)

Re: Paradox-free time travel is theoretically possible

#162

Post by pontifier » Thu, Jan 21, 2021, 4:27 PM UTC

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…

I take it with a grain of quantum physics. When traveling back in time you are entangling the state of the moment of time travel with a past state of the universe, and the universe must collapse into a steady state with a single history... The history in which the time travel did nothing.

Re: Paradox-free time travel is theoretically possible

#163

Post by pontifier » Thu, Jan 21, 2021, 4:44 PM UTC

dghf wrote: post #75

v64 wrote: post #9

Sounds like they're describing the Novikov self-consistency principle [1] in a roundabout way. [1] https://en.wikipedia.org/wiki/Novikov_self-consistency_princ...

Are they, though? I thought the Novikov conjecture postulated that time-travel would change nothing at all: if you travelled back to the past, you had "always" travelled back to the past, and anything you did there was already part of history before you started on your journey (aargh, time-travel tenses are hard). Michael Moorcock's Behold the Man [0] would be a good fictional example. This, on the other hand, sugges…

Im reading "The Time Patrol" by Paul Anderson. It describes that even if an individual is killed, it's unlikely to matter much because a species is more like a collective DNA wise. They even go hunting in the past, have possible children there, etc. It's only in very specific cases that the time patrol has to step in to make sure that "X" specific significant event happens the way it's "Supposed to"

I haven't finished the book yet though :)

Re: Paradox-free time travel is theoretically possible

#164

Post by EliRivers » Thu, Jan 21, 2021, 4:49 PM UTC

yrimaxi wrote: post #154

vidarh wrote: post #144

Earlier quoted context omitted.

Exactly. E.g, a possible example immutable scenario that doesn't violate anything (with each number representing a discrete period of time) 1. An old man appears and says hi to me and disappear. 2. 20 years pass. 3. I obtain a time machine. 4. I travel back in time and return (in my absence from this time period, I'm at time step 1 saying hi to myself) The key being that we tend to see this as: 1a. Nothing happens. 1…

I don’t think this really gets at the paradox. What if you shot yourself?

You didn't shoot yourself. We know this to be true.

Re: Paradox-free time travel is theoretically possible

#165

Post by gpsx » Thu, Jan 21, 2021, 5:13 PM UTC

I don't understand how people view changing the past with time travel. If I go back in time I might experience a given point in time twice, but that point in time still only happens once. So if I go back to 1940 and kill my grandfather, then the first time 1940 happened he got shot. The second time...there is not second time. (Fortunately my parents were born in 1930s.)

Re: Paradox-free time travel is theoretically possible

#166

Post by yrimaxi » Thu, Jan 21, 2021, 5:28 PM UTC

EliRivers wrote: post #164

yrimaxi wrote: post #154

Earlier quoted context omitted.

I don’t think this really gets at the paradox. What if you shot yourself?

You didn't shoot yourself. We know this to be true.

Ok. I guess verb tense falls short in this case. :-)

Re: Paradox-free time travel is theoretically possible

#167

Post by YinglingLight » Thu, Jan 21, 2021, 5:30 PM UTC

throwaway9d0291 wrote: post #108

I watch a lot of both American-made movies and TV shows as well as a lot of Japanese anime. One thing I find curious is how different the models for time travel usually are. In American media, it seems more often than not, time travel is modelled as if the past and the future are simultaneously existing parallel worlds, where the future is affected by the past in "real-time", e.g. Back to the Future's Marty gradually…

Baron Trump's Marvelous Underground Journey. The Last American President. DJT's uncle John Trump & Tesla. John Titor. Breakaway civilization. 'UFO' sightings 1896 California. Sonora Aero Club.

'Truth' is far more fascinating than media for people who enjoy scratching that itch.

Re: Paradox-free time travel is theoretically possible

#168

Post by v64 » Thu, Jan 21, 2021, 5:47 PM UTC

dghf wrote: post #75

v64 wrote: post #9

Sounds like they're describing the Novikov self-consistency principle [1] in a roundabout way. [1] https://en.wikipedia.org/wiki/Novikov_self-consistency_princ...

Are they, though? I thought the Novikov conjecture postulated that time-travel would change nothing at all: if you travelled back to the past, you had "always" travelled back to the past, and anything you did there was already part of history before you started on your journey (aargh, time-travel tenses are hard). Michael Moorcock's Behold the Man [0] would be a good fictional example. This, on the other hand, sugges…

> I thought the Novikov conjecture postulated that time-travel would change nothing at all

Not exactly, from the wiki article:

> The simplest way to impose the principle of self-consistency in quantum mechanics (in a classical space-time) is by a sum-over-histories formulation in which one includes all those, and only those, histories that are self-consistent.

So it is possible to change the past, but only in ways that are self-consistent and don't give rise to paradoxes.

Regarding the ramifications for free will:

> Novikov supports this point of view with another argument: physics already restricts your free will every day. You may will yourself to fly or to walk through a concrete wall, but gravity and condensed-matter physics dictate that you cannot. Why, Novikov asks, is the consistency restriction placed on a time traveler any different?

Re: Paradox-free time travel is theoretically possible

#169

Post by EliRivers » Thu, Jan 21, 2021, 6:00 PM UTC

yrimaxi wrote: post #166

EliRivers wrote: post #164

Earlier quoted context omitted.

You didn't shoot yourself. We know this to be true.

Ok. I guess verb tense falls short in this case. :-)

It does, but that's also the point. The past is fixed in this model. If you go back in time, that's not new. You always did that. How the present looks now is a function of you having always done that. We know that you didn't shoot yourself, because you didn't.

Re: Paradox-free time travel is theoretically possible

#170

Post by offtop5 » Thu, Jan 21, 2021, 6:19 PM UTC

avereveard wrote: post #63

offtop5 wrote: post #62

Time travel stories always seem to be centered around what if fantasy. I think one of the movie adaptations of the time machine has the protagonist trying to save his wife. I would like to explore what would happen if one went years into the future to party ? Would certain time periods become tourist traps

You need to chart the future first, for even in moderately advanced countries you risk showing up during a riot or other agitations that could get you arrested and stranded, especially as our surveillance capabilities expand it will be hard to evade detection. And, if we assume we live in a one timeline hypothesis, all that work is still at risk from other time travelers altering a midpoint between now and where you…

Assuming I have enough gas in my time machine, I could just jump back. Eventually in this dream, it would be known , say Paris 2500 , is a cool spot . So people would travel there and spend money ( barter) .

Would love to see this explored in a novel