Shows about time travel

[arfa brane]

In the Netflix SF series Travelers, they get around the problem of sending a human consciousness, i.e. someone's mind, into the past with a quantum "stack". What this does has something to do with entanglement, plus some unspecified way of transmitting information across an Einstein Rosen bridge (or something).

But objections aside about whether or not a future human race will build such a thing, what else is the problem about the idea that transmitting any kind of information back into the past can alter it?
(Especially if that information means you can "inject" active human agents into your past with missions to carry out changes to that past?) How would you determine the success or failure of your agents?

 

[Michael 345]

what else is the problem about the idea that transmitting any kind of information back into the past can alter it?

The past does not exist

 

[Gawdzilla Sama]

"Let the dead past bury its dead."

 

[Q-reeus]

...what else is the problem about the idea that transmitting any kind of information back into the past can alter it?...

Can you think of a sensible way around the Grandfather paradox? Every attempt I'm aware of comes apart at the seams when examined closely.

 

[Gawdzilla Sama]

Can you think of a sensible way around the Grandfather paradox? Every attempt I'm aware of comes apart at the seams when examined closely.

Best solution I've seen is that when you shoot your 5 yo grandfather he dies and doesn't die. Time branches at that point.

Impossible to prove but fun to play with.

Anybody else read the story about a guy who goes back to kill his hateful wife when she was 6 years old and gets razzed by a 12 year old. He shoots the 6 yo and returns to find his wife still there.

"So, she lied about her age too?"

 

[Q-reeus]

Best solution I've seen is that when you shoot your 5 yo grandfather he dies and doesn't die. Time branches at that point.

Impossible to prove but fun to play with.

Anybody else read the story about a guy who goes back to kill his hateful wife when she was 6 years old and gets razzed by a 12 year old. He shoots the 6 yo and returns to find his wife still there.

"So, she lied about her age too?"

An example of coming apart when examined closely. Time branching or rather spacetime branching is another spelling of Many Worlds interpretation of QM.
It boils down to traveling to somewhere else rather than somewhen else (even though the latter always involves 'space-travel' too - but in a different way to the other fantasy version). Some notionally respectable theorists take it to the (il)logical conclusion known as 'quantum suicide'. Look it up and apply if one has 'faith'.

 

[Gawdzilla Sama]

Until you shoot Grandpa there is one timeline. At the point you pull the trigger there are two timelines.

 

[Q-reeus]

Until you shoot Grandpa there is one timeline. At the point you pull the trigger there are two timelines.

Think again. Every single thing counting as an interaction, in MW picture results in a splitting into two new worlds. The number of 'new worlds' being so generated every nano-second is staggering beyond comprehension. Or belief. Furiously exponential growth without evident limit doesn't sit well with many folks. Like me.

 

[sculptor]

Yesterday is a memory, tomorrow is but a dream. Today is a gift and that is why it is called the present.

 

[Gawdzilla Sama]

Yesterday is a memory, tomorrow is but a dream. Today is a gift and that is why it is called the present.

Thank you Master Oogway.

Q-reerus, what if takes more than just an atom going one way rather than the other to make a "split"?

 

[Q-reeus]

...Q-reerus, what if takes more than just an atom going one way rather than the other to make a "split"?

Wikipedia is probably as good a place as any other to get a feel for MWI: https://en.wikipedia.org/wiki/Many-worlds_interpretation
Opinions among various theorists vary as to what constitutes a 'split' or even a 'world', but for sure there is no room for your notion of a clean before and after single split determined by a gun shot.
I've had enough SCiFi discussion for one day. Best of luck to all our many copies spewing out into the Grand Totality.

 

[Gawdzilla Sama]

I have fun with the notion. And The Cat Who Walked Through Walls would just day "blert!"

 

[Michael 345]

Best solution I've seen is that when you shoot your 5 yo grandfather he dies and doesn't die. Time branches at that point.

Impossible to prove but fun to play with.

Anybody else read the story about a guy who goes back to kill his hateful wife when she was 6 years old and gets razzed by a 12 year old. He shoots the 6 yo and returns to find his wife still there.

"So, she lied about her age too?"

Not read the story but a great take on the ol Time Travel

 

[hansda]

The past does not exist

Is it that, past merges with the present?

 

[Gawdzilla Sama]

Not read the story but a great take on the ol Time Travel

Yeah, "Get your data straight before making such an effort."

My two favorite time travel stories are "All You Zombies" and "By His Bootstraps". Can you see a pattern?

 

[QuarkHead]

MW picture results in a splitting into two new worlds. The number of 'new worlds' being so generated every nano-second is staggering beyond comprehension.

I don't think this is quite right
To every eigenstate of a quantum system there are associated eigenvalues, usually many, often infinitely many. To make a measurement on the state of the system, is to "choose" an eigenvalue.

Copenhagen-ists claim that this makes all other eigenvalues unavailable (this is sometimes called "collapse of the wave function"). Many-World-ists merely claim that these eigenvalues are still and always available in eigenspace.

 

[arfa brane]

The only answer I can think up about a future AI knowing if a mission does change the past, then it must be able to see that past and how it changed--it would have to have information about both pasts, one in which the mission fails and one in which it doesn't, and in either case it would have to know it would have a probability of one of being in the future of either of these two pasts.

That's some information processing, for sure. How much information?
In one of the episodes, you see the same mission run, fail, and reset a few times before it succeeds--it's one of the missions that can't fail so the Director resets it 5012 times, the episode begins with attempt 5002 or so.

A problem with this episode is that the mission is also about recovering a meteorite from a lake, without which the AI would not exist--the meteorite's material ushers in a new kind of quantum device and eventually the quantum stack itself. So the mission must have not failed.

 

[Q-reeus]

I don't think this is quite right
To every eigenstate of a quantum system there are associated eigenvalues, usually many, often infinitely many. To make a measurement on the state of the system, is to "choose" an eigenvalue.

That's true in any version of QM. With most interpretations of the interpretation known as MW, there is a physically real branching taking place. Two new worlds.

Copenhagen-ists claim that this makes all other eigenvalues unavailable (this is sometimes called "collapse of the wave function"). Many-World-ists merely claim that these eigenvalues are still and always available in eigenspace.

A few MW theorists may see it that way, but most MW advocates believe every measurement/projection/choice results in a forking into separate actual worlds. That forever after never interact with each other. It's an exponential growth recipe.
That Wiki article sets out all the nuances and variations.

 

[Michael 345]

Is it that, past merges with the present?

NO

 

[Janus58]

A twist on the MW model that I always thought would make a good premise for a SF story would involve indeterminacy working in both directions. You don't travel to the past, but to a past; One of the many possible pasts that could have led to your present. The further back you go, the greater the variety of possible pasts.