You find yourself in the cretaceous

[bilby]

...
Nothing about this model prohibits strands from looping back in the t-dimension - but any such loops were always a part of the block. They can't change anything.

For someone who is so aggressively confident in his assertions about time travel's impossibility, you seem remarkably ill informed about some of the more well known hypotheses on the nature of spacetime.

How do you get around the Grandfather Paradox? Seems like you'd need to do a lot of debugging to keep it from crashing the OS. Of course maybe the multiverse is littered with crashed block-time programs and we live in one that just happened to work. Or to have worked so far (*). Or maybe there's some self-limiting factor on how frequently time travel gets employed. But that would be pretty damn lucky.

*ETA - On second thought that's a cheap excuse because it requires the block-time operates in a time-dependent sequence detached from the future.

In a block universe there is no possibility of changing the past or the future. Your existence is a clear demonstration that you didn't kill your grandfather, so any attempt to do so failed, will fail, is failing, has always failed.

This doesn't rule out the possibility that you always tried, and failed in some fashion that leaves the present and future as they are. Indeed, if you tried, you can't not try. There's zero freedom in a block universe.

Of course, there are other models of spacetime that preserve "freedom", while massively increasing the complexity of the model. Personally I don't see a good reason to eschew parsimony in order to defend a belief in something as abstract as "freedom", but if you abandon block time in favour of one of the 'many worlds' interpretations, killing your grandfather is possible, but only changes which timeline you are in - moving from a present in which he wasn't killed, to the past; Killing him (and by doing so joining a different timeline in which you will never be born); and then returning to the present but in the new timeline, allows you to commit grandpatricide without ceasing to exist. But at the expense of requiring the existence of every possible universe that differs from any other by any event.

In either scenario, the paradox is resolved by your grandfather surviving (at least in the timeline from which you first depart in your time machine). The more un-parsimonious hypothesis gives you the freedom not so much to kill him, as to move to an alternate reality timeline in which you killed him, while in your home timeline he still survives your attack.

In either case, nothing about the wider reality can change. You just need to pick whether you lean towards an hypothesis with one spacetime and no freedom, or one with a huge number of spacetimes and the illusion of freedom granted by the ability to choose which parts of that spacetime you explore. That freedom is a mere illusion however, because for every possible choice, both (or all) options get chosen, and the multiple 'yous' in existence after that choice all believe that their path was the one freely selected.

 

[untermensche]

We have no ability to go back in time presently

There’s yer problem.
Our inability AND “presently” have nothing to do with what is possibly already the case.

Did you have dinner with some organic creature from the future last night?

I'll assume no.

But you are saying it is possible that in the distant future some creature, not likely human, will be able to have dinner with you last night.

So that is moving from you not having dinner with the creature to having dinner with the creature.

And you want to claim this is miraculously not a change.

Get real.

 

[Treedbear]

...
Nothing about this model prohibits strands from looping back in the t-dimension - but any such loops were always a part of the block. They can't change anything.

For someone who is so aggressively confident in his assertions about time travel's impossibility, you seem remarkably ill informed about some of the more well known hypotheses on the nature of spacetime.

How do you get around the Grandfather Paradox? Seems like you'd need to do a lot of debugging to keep it from crashing the OS. Of course maybe the multiverse is littered with crashed block-time programs and we live in one that just happened to work. Or to have worked so far (*). Or maybe there's some self-limiting factor on how frequently time travel gets employed. But that would be pretty damn lucky.

*ETA - On second thought that's a cheap excuse because it requires the block-time operates in a time-dependent sequence detached from the future.

In a block universe there is no possibility of changing the past or the future. Your existence is a clear demonstration that you didn't kill your grandfather, so any attempt to do so failed, will fail, is failing, has always failed.

This doesn't rule out the possibility that you always tried, and failed in some fashion that leaves the present and future as they are. Indeed, if you tried, you can't not try. There's zero freedom in a block universe.

I'd call that the "Having One's Cake and Eating It Too" hypothesis. We happen to live in the best of all possible worlds in which nature has self-booted itself into a stable crystalline state. Seems like wishful thinking. Going back in time you might be prevented from out-right killing your grand pap but tiny changes would tend to compound themselves after thousands of iterations. And since only the logic makes it inevitable it requires no time at all for the dog to catch its tail and for cause and effect to contradict each other.

Of course, there are other models of spacetime that preserve "freedom", while massively increasing the complexity of the model. Personally I don't see a good reason to eschew parsimony in order to defend a belief in something as abstract as "freedom", but if you abandon block time in favour of one of the 'many worlds' interpretations, killing your grandfather is possible, but only changes which timeline you are in - moving from a present in which he wasn't killed, to the past; Killing him (and by doing so joining a different timeline in which you will never be born); and then returning to the present but in the new timeline, allows you to commit grandpatricide without ceasing to exist. But at the expense of requiring the existence of every possible universe that differs from any other by any event.

In either scenario, the paradox is resolved by your grandfather surviving (at least in the timeline from which you first depart in your time machine). The more un-parsimonious hypothesis gives you the freedom not so much to kill him, as to move to an alternate reality timeline in which you killed him, while in your home timeline he still survives your attack.

In either case, nothing about the wider reality can change. You just need to pick whether you lean towards an hypothesis with one spacetime and no freedom, or one with a huge number of spacetimes and the illusion of freedom granted by the ability to choose which parts of that spacetime you explore. That freedom is a mere illusion however, because for every possible choice, both (or all) options get chosen, and the multiple 'yous' in existence after that choice all believe that their path was the one freely selected.

I don't agree. If you went back to a time in the past (your past, not the beginning of a parallel path in another universe) and killed your grandfather it would still be the grandfather from your past and a requirement of your existence. If you killed a different grandfather that's off on some other time-line then it's a different scenario. Effectively a red-herring, because you (the original version of you) still exists in your original universe's past and is bound by the causal logic that it requires. You (the you defined by the continuity of its existence) would cease to exist and so never could have existed. Therefore any other you's spawned from the creation of any parallel universes would also never come to be. Just a bunch of facsimiles. Most of them don't even drink beer. Besides, you can have all that along with the illusive free will without needing to go back in time.

 

[bilby]

In a block universe there is no possibility of changing the past or the future. Your existence is a clear demonstration that you didn't kill your grandfather, so any attempt to do so failed, will fail, is failing, has always failed.

This doesn't rule out the possibility that you always tried, and failed in some fashion that leaves the present and future as they are. Indeed, if you tried, you can't not try. There's zero freedom in a block universe.

I'd call that the "Having One's Cake and Eating It Too" hypothesis. We happen to live in the best of all possible worlds in which nature has self-booted itself into a stable crystalline state.

Leaving aside the foolish snark about 'best of all possible', yes.

The block time universe is entirely deterministic. Appearances to the contrary are illusory.

Seems like wishful thinking. Going back in time you might be prevented from out-right killing your grand pap but tiny changes would tend to compound themselves after thousands of iterations.

There are no changes. None. Everything, past, present, and future is as it always has been. There are no "iterations".

And since only the logic makes it inevitable it requires no time at all for the dog to catch its tail and for cause and effect to contradict each other.

Of course, there are other models of spacetime that preserve "freedom", while massively increasing the complexity of the model. Personally I don't see a good reason to eschew parsimony in order to defend a belief in something as abstract as "freedom", but if you abandon block time in favour of one of the 'many worlds' interpretations, killing your grandfather is possible, but only changes which timeline you are in - moving from a present in which he wasn't killed, to the past; Killing him (and by doing so joining a different timeline in which you will never be born); and then returning to the present but in the new timeline, allows you to commit grandpatricide without ceasing to exist. But at the expense of requiring the existence of every possible universe that differs from any other by any event.

In either scenario, the paradox is resolved by your grandfather surviving (at least in the timeline from which you first depart in your time machine). The more un-parsimonious hypothesis gives you the freedom not so much to kill him, as to move to an alternate reality timeline in which you killed him, while in your home timeline he still survives your attack.

In either case, nothing about the wider reality can change. You just need to pick whether you lean towards an hypothesis with one spacetime and no freedom, or one with a huge number of spacetimes and the illusion of freedom granted by the ability to choose which parts of that spacetime you explore. That freedom is a mere illusion however, because for every possible choice, both (or all) options get chosen, and the multiple 'yous' in existence after that choice all believe that their path was the one freely selected.

I don't agree. If you went back to a time in the past (your past, not the beginning of a parallel path in another universe) and killed your grandfather it would still be the grandfather from your past and a requirement of your existence.

That's not you disagreeing; That's you proposing a different model from the two I just outlined.

There are others; I personally rule them out, because I think the grandfather paradox is an insurmountable contradiction that renders such models impossible - but of course I could be wrong. I would be interested to know how you would resolve that paradox in such a model of spacetime.

If you killed a different grandfather that's off on some other time-line then it's a different scenario. Effectively a red-herring, because you (the original version of you) still exists in your original universe's past and is bound by the causal logic that it requires. You (the you defined by the continuity of its existence) would cease to exist and so never could have existed. Therefore any other you's spawned from the creation of any parallel universes would also never come to be. Just a bunch of facsimiles. Most of them don't even drink beer. Besides, you can have all that along with the illusive free will without needing to go back in time.

OK, so you agree that such 'mutable past' models founder on the grandfather paradox.

So what is left? I only see a few possibilities:

• Block time
• Many worlds (multiple diverging block times)
• Many worlds only to eliminate paradoxes (regular choices don't create new timelines unless a paradox would arise if they didn't)
• Causal policing - mutable time in which paradoxes are somehow disallowed or physically prevented
• Anything goes - paradoxical results occur, regardless of their illogic
• Time travel is impossible - but somehow absolute time still isn't a thing, per Einstein

Are there any others?

 

[none]

yeah the red line.

 

[Jokodo]

We have no ability to go back in time presently

There’s yer problem.
Our inability AND “presently” have nothing to do with what is possibly already the case.

Did you have dinner with some organic creature from the future last night?

I'll answer. No, I didn't. I also didn't have dinner with a creature from the Americas (except in the limited sense that I had tomato sauce on my Pizza; today, I went have any Americans on my table, even in that limited sense). That doesn't mean the Americas don't exist, or Transatlantic travel is impossible, or does it?

I'll assume no.

But you are saying it is possible that in the distant future some creature, not likely human, will be able to have dinner with you last night.

That's not what Elixir, bilby Bomb#20 or I are saying, no. What we are saying is that it might (not will - you're still the one making proclamations of absolute knowledge) be possible to travel in time with technology not yet discovered, but under the most plausible interpretation this doesn't change the past/present. Therefore if anyone from the future would choose to travel back and have dinner with me yesterday, I would already have had dinner with them, and from the fact that this doesn't appear to be the case, we can infer that one of the following is likely true:

- time travel is impossible
- time travel possible but never becomes practical
- time travel is possible and practice but it impossible to choose the exact coordinates of your destination, so 99.999% of time travellers end up in empty space and most of the rest are crushed in the interior of stars.
- time travel is possible, including choosing your coordinates with arbitrary precision, but hugely expensive so no one would do it except for good reasons. A dinner conversation with either of us just isn't a good enough reason.
- time travel isn't particularly expensive but we're a boring destination anyway.
- probably missed some too

The logical jump from "no travelers visited me last night" to "time travel is impossible" has several unspoken assumptions, one of which is "if time travel were possible, the first thing any time travelers would do is visit me".

Maybe try some humility?

 

[untermensche]

But you are saying it is possible that in the distant future some creature, not likely human, will be able to have dinner with you last night.

That's not what Elixir, bilby Bomb#20 or I are saying, no. What we are saying is that it might (not will - you're still the one making proclamations of absolute knowledge) be possible to travel in time with technology not yet discovered, but under the most plausible interpretation this doesn't change the past/present. Therefore if anyone from the future would choose to travel back and have dinner with me yesterday, I would already have had dinner with them, and from the fact that this doesn't appear to be the case, we can infer that one of the following is likely true:

It is the exact same thing as some human visiting a dinosaur.

The dinosaur does not have dinner with the human one night but then somehow does have the human for dinner the same night.

The night of the dinosaur changes.

The past changes.

Impossible.

 

[Jokodo]

But you are saying it is possible that in the distant future some creature, not likely human, will be able to have dinner with you last night.

That's not what Elixir, bilby Bomb#20 or I are saying, no. What we are saying is that it might (not will - you're still the one making proclamations of absolute knowledge) be possible to travel in time with technology not yet discovered, but under the most plausible interpretation this doesn't change the past/present. Therefore if anyone from the future would choose to travel back and have dinner with me yesterday, I would already have had dinner with them, and from the fact that this doesn't appear to be the case, we can infer that one of the following is likely true:

It is the exact same thing as some human visiting a dinosaur.

The dinosaur does not have dinner with the human one night but then somehow does have the human for dinner the same night.

The night of the dinosaur changes.

The past changes.

Impossible.

The only thing that's impossible is you making an argument that's not a straw man.

Everything else is just improbable at best.

 

[Jokodo]

I ended up adding a couple spoons of chocolatl/cocoa to my apple strudel (otherwise consisting of Anatolian wheat for the dough, Kazakh apples, Sri Lankan cinnamon and Iranian walnuts, and a bit of sugar) so maybe the Americas do exist? I'm confused, I'm not yet used to the godly power of making continents appear and disappear with the choice of ingredients for my meals, maybe untermensche can help with his extensive experience of making worlds disappear by refusing to understand them and looking the other way?

 

[untermensche]

It is the exact same thing as some human visiting a dinosaur.

The dinosaur does not have dinner with the human one night but then somehow does have the human for dinner the same night.

The night of the dinosaur changes.

The past changes.

Impossible.

The only thing that's impossible is you making an argument that's not a straw man.

Everything else is just improbable at best.

Why is it feeling like your claims of time travel are really a form of the no true Scotsman fallacy?

You don't address the scenario in any way.

You are claiming the past can change with a claim that time travel is possible.

Impossible.

The past is completed. It cannot be added to.

No entity from the future can penetrate it in any way shape or form to observe it. That would change the past.

Impossible.

 

[Jokodo]

It is the exact same thing as some human visiting a dinosaur.

The dinosaur does not have dinner with the human one night but then somehow does have the human for dinner the same night.

The night of the dinosaur changes.

The past changes.

Impossible.

The only thing that's impossible is you making an argument that's not a straw man.

Everything else is just improbable at best.

Why is it feeling like your claims of time travel are really a form of the no true Scotsman fallacy?

You don't address the scenario in any way.

You are claiming the past can change with a claim that time travel is possible.

Impossible.

The past is completed. It cannot be added to.

No entity from the future can penetrate it in any way shape or form to observe it. That would change the past.

Impossible.

In the kind of universe bilby, Bomb#20 and myself are talking about: If a time traveler from the 22nd century will visit the Cretaceous atnd be eaten by a Utaharaptor, then (and only then), there was a Utahraptor that ate a human from the 22nd century. The past doesn't change: it either does, or more likely does not, contain an out of time entity. If it does, it always did. There's only one version of the year 85,345,256 BP (Of the slug in spacetime where that Utahraptor lives, to be more precise), and it either does or does not contain a human time traveler from 2321. Similarly, if you had dinner with a time traveler from 22,456,267 AD on April 22 2021, then someone from the year 22,456,267 will end up travelling to our time and find nothing better to do then spending his time with you (a pretty ludicrous idea, and not because of the time travelling part). The past or present do not change.

The "True Scotsman" fallacy is, if anything what you're engaging in: You are claiming that all ways to conceive of time travel lead to contradictions. We are telling you that there is at least one internally consistent conception that doesn't (not that there aren't contradictory ones - no-one makes that claim), which you ignore as if it were "No True Timetravel". Though most of the time you don't even have the honesty to acknowledge our explanations, but rather clip them out of the posts you reply to and pretend it never even happened.

 

[untermensche]

In the kind of universe bilby, Bomb#20 and myself are talking about: If a time traveler from the 22nd century will visit the Cretaceous atnd be eaten by a Utaharaptor, then (and only then), there was a Utahraptor that ate a human from the 22nd century.

Yes.

Last Thursday the raptor went hungry.

But bizz bang buzz abra cadabra suddenly it seems last Thursday the raptor had a little time traveler for dinner.

Last Thursday changed like magic.

And according to you it could change countless times.

Suddenly it seems the raptor ate a dozen time travelers last Thursday.

The past has changed again.

But those time travelers in the future kept coming.

So last Thursday the raptor threw a party.

The past changed again.

 

[Jokodo]

In the kind of universe bilby, Bomb#20 and myself are talking about: If a time traveler from the 22nd century will visit the Cretaceous atnd be eaten by a Utaharaptor, then (and only then), there was a Utahraptor that ate a human from the 22nd century.

Yes.

Last Thursday the raptor went hungry.

No it didn't.

F in reading comprehension. Come back when you've made a moderate attempt to understand what we are saying.

 

[untermensche]

In the kind of universe bilby, Bomb#20 and myself are talking about: If a time traveler from the 22nd century will visit the Cretaceous atnd be eaten by a Utaharaptor, then (and only then), there was a Utahraptor that ate a human from the 22nd century.

Yes.

Last Thursday the raptor went hungry.

No it didn't.

F in reading comprehension. Come back when you've made a moderate attempt to understand what we are saying.

It sure did.

There have been no time travelers yet to feed it.

Last Thursday (in the time the raptor already lived) the poor thing didn't eat a thing.

But now suddenly by some miracle it seems last Thursday it feasted on time travelers.

The past changed.

I suppose it is fun to believe in silly miracles.

 

[DBT]

If time travel is possible, time travellers don't change the past, they are a part of it.

 

[untermensche]

If time travel is possible, time travellers don't change the past, they are a part of it.

That means the past changed.

If no time traveler had lunch with you yesterday but in the future some time traveler goes to yesterday and has lunch with you then yesterday has changed.

One yesterday, the real yesterday, no time traveler had lunch with you.

But you are claiming it is possible for some future time traveler to have lunch with you yesterday.

That would be a different yesterday.

A time traveler could change your yesterday.

An imaginary one of course.

 

[DBT]

If time travel is possible, time travellers don't change the past, they are a part of it.

That means the past changed.

If no time traveler had lunch with you yesterday but in the future some time traveler goes to yesterday and has lunch with you then yesterday has changed.

One yesterday, the real yesterday, no time traveler had lunch with you.

But you are claiming it is possible for some future time traveler to have lunch with you yesterday.

That would be a different yesterday.

A time traveler could change your yesterday.

An imaginary one of course.

It doesn't mean the past is changed. The past includes visits from time travellers before they even leave. They were in the past before time travel was invented. The trip is a loop between the past and present and once they leave on their journey, the loop is completed. The trip, the loop in time, itself becomes a part of the past once the traveler returns.

 

[none]

this whole thread is a message from the future.

 

[untermensche]

If time travel is possible, time travellers don't change the past, they are a part of it.

That means the past changed.

If no time traveler had lunch with you yesterday but in the future some time traveler goes to yesterday and has lunch with you then yesterday has changed.

One yesterday, the real yesterday, no time traveler had lunch with you.

But you are claiming it is possible for some future time traveler to have lunch with you yesterday.

That would be a different yesterday.

A time traveler could change your yesterday.

An imaginary one of course.

It doesn't mean the past is changed. The past includes visits from time travellers before they even leave. They were in the past before time travel was invented. The trip is a loop between the past and present and once they leave on their journey, the loop is completed. The trip, the loop in time, itself becomes a part of the past once the traveler returns.

You can't be in the past before time travel is invented. Nobody can.

That is our present condition.

Go ahead.

Be in the past.

Show us about being in the past before a time machine is invented.

 

[untermensche]

Only one possible way for time travel to work.

It only could work if the past can be changed from the present.

Time travel is the very definition of changing the past.

Putting yourself into a past you were not in before.