A Physicist Has Discovered Math That Makes 'Paradox-Free' Time Travel Plausible | Hacker News Reader

A Physicist Has Discovered Math That Makes 'Paradox-Free' Time Travel Plausible

sciencealert.com

14 pointsdoctor_eval13 comments

>Tobar's work suggests that the disease would still escape some other way, through a different route or by a different method, removing the paradox. Whatever the time traveller did, the disease wouldn't be stopped.

At least scifi-plotwise, the problem with this model of time travel is that it assumes arbitrary events are marked as "important", but from the perspective of the timeline, all events should be equally important -- or rather, none of them are.

And if every event is important, and must happen (in some fashion, even if you somehow stop it) and must be maintained... then you can travel to the past, and do nothing at all. Because everything must stay the same.

If you imagine that some key events are so special as to deserve recognition for maintenance, then there must be some author to this grand narrative

IMO the only time structure that has a chance of a plothole-free narrative is multi-universe (time travel = pick a universe thats exactly the same but delayed to point of interest, out of infinite selection). If you want to get real fancy, homestuck-style multitimelines hopping back and forth between each other

I don't think that every event is equally important or that any event is "special". Rather, the avoidance of paradoxes is. You just have to ensure the alternate history you get with respect to an action (or an event) doesn't preclude that event from happening. So if you go back to stop a disease from escaping a lab in Texas, that doesn't stop the disease from escaping two months later from a lab in California. The key is the avoidance of paradoxes.

The problem is, assuming the butterfly effect, anything you change could trigger the paradox -- and the further you go back, the less work you need to do find a trigger.

I mean you can't even cause the timeline in which you decide to go back to change; your memory would either have to be altered to match [a paradox: which memory was "first"? Neither] or you'd have a memory from a timeline that never existed [does that count as a paradox?]

It seems to me that determinism is the simple answer to this. If we're all basically just actors playing out a predefined movie then time-travel is just a loop within that movie.

Forgot about that model - one timeline, but your time traveling was always a part of it - this also is functional, but plotwise usually just amounts to a twist rather than something more interesting (i suppose tenet is a bit of an argument against that)

interesting thought

I have problems with time travel.

#1 How do I manage my space/time emergence point vs. my starting point... What about the vector my kinetic presence is upon ... If I manage to emerge upon the correct side of the planet, not inside a wall... am I moving in the appropriate direction, considering revolutionary, planetary, solar, galactic, etc.vectors..? OK a computer can figure that out... even if it is possible to pass the kinetic vector forward? (OK that kills a lot of old SF films...)

#2 isn't the universe expanding? If I take matter from now & shove it into the past/future, will it react at all with atoms from the other age? If that matter is me & my heart is beating, will the size of the oxygen atoms of that time be recognized by my red corpuscles... Wow 2-5 minutes viewing the future/past before my conscious brain melts... That's an E-ticket for sure. I think figuring out a way to extend/strengthen telomeres might be a safer way of traveling into the future.

Yes, keeping these thoughts in mind can really mess with the enjoyment of some SF movies. Ohm how I suffer

Good thoughts. Your first problem also need to address your position in space itself. The Earth and solar system are travelling at 230 km/s in reference to the galactic center. Going back in time 100 years would plop you well out in interstellar space if you didn't account for your universal location as well.

I think the problem is worse than this. There is no universal coordinate system, no 0x0x0 coordinate to measure everything from. The Earth is moving wrt the galactic center, the galactic center is moving wrt...what? The Andromeda galaxy? Why should that galaxy be special? And the local cluster is moving wrt...what? All the other galaxy clusters, I suppose, but what does that mean?

indeed . so the galaxy cluster might have moved by a really massive distance, assuming even if there is some universal coordinate system

This seems equivalent to assuming that time is a converging series in the sense that minor changes in the inputs will have only certain types of effects but the end result is fixed.

For example, using newton's method to compute square-roots always converges on the correct value, pretty much regardless of the initial guess. (It doesn't work for "potato".) The initial guess does influence how many iterations are necessary but that's it.

While that may be true wrt time travel, it's unclear why it should be true.

I just dont see how any point in time exist could exist "stored" in some form to be traveled back to.

How to overcome entropy?

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