You find yourself in the cretaceous

[DBT]

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.

If you can travel to the past, and you do travel to the past, having travelled to the past, your past trip must necessarily have happened. You simply complete the time loop upon your departure, arrival and activity while in the past.

That is, unless you open a portal to an alternate reality, you never actually went back in your own universe, therefore there is no record of your presence in your own past and never will be.

 

[bilby]

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.

It's been repeatedly explained to you in this thread that in a block time model of the universe, nothing changes.

I suppose it's fun to ignore what people say and claim that they said the exact opposite. But it's very boring for those of us you are inflicting it upon.

I suppose it's possible that you really just haven't grasped the concept, so here's an example timeline for you:

4,500,000,000 years ago - Earth is formed
67,000,000 years ago - Untermensche appears in his time machine
66,999,998 years ago - Untermensche is eaten by a T. Rex
Tomorrow - Untermensche climbs into his time machine and disappears, intending to travel to the Cretaceous.

That's a single, unchanging and unchanged series of events. At every time on that timeline, and every time in between, the universe has one and only one set of events occurring. Nothing changes; There is no time at which there was once X, but is now Y.

That's what block spacetime is like. You can travel back to the past, but doing so changes nothing, because if you look at what was happening in the past, you see exactly what was always there.

 

[Treedbear]

...
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".

Well if the universe is entirely deterministic (something I agree with) then every effect is determined by some cause or causes. If I could go back in time there would need to be something preventing me from killing my grandpa. Aside from that being a more favorable state for my world, why would the universe happen upon that course rather than just ending it all? Does it have some stake in it's own continued existence? How do you actually explain that a time traveler appearing now in the present could not then kill his grandfather? Seems to me that would require purpose and design. A simpler solution is that time travel to the past is just not possible. Otherwise why not just declare that although time travel is theoretically possible, a time machine will just never be built? You did propose that the "future is as it always has been." Basically it's because all else being equal, simpler is better.

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.

I guess I overlooked the fact that your many worlds model abandons the block-time model. I should have questioned that because how then can you go back in time? The many worlds models don't say anything about the existence of the past or future. They are just a way to rationalize the existence of "free will" in a deterministic universe by making it "possible to have made a different choice". So the many worlds model doesn't present a paradox that I'm aware of. Grandpa spawned an infinity of grandchildren and I happen to be one of them. But he's gone and the others are of no consequence to me.

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?

Only the one I mentioned which is that time travel is impossible because the past and future do not exist. They are both only concepts of the mind. The records of the past are used to explain the present and to predict the future. I fail to see any conflict between that and the relativity of time and space.

 

[Jokodo]

Well if the universe is entirely deterministic (something I agree with) then every effect is determined by some cause or causes. If I could go back in time there would need to be something preventing me from killing my grandpa. Aside from that being a more favorable state for my world, why would the universe happen upon that course rather than just ending it all? Does it have some stake in it's own continued existence? How do you actually explain that a time traveler appearing now in the present could not then kill his grandfather? Seems to me that would require purpose and design. A simpler solution is that time travel to the past is just not possible. Otherwise why not just declare that although time travel is theoretically possible, a time machine will just never be built? You did propose that the "future is as it always has been." Basically it's because all else being equal, simpler is better.

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.

I guess I overlooked the fact that your many worlds model abandons the block-time model. I should have questioned that because how then can you go back in time? The many worlds models don't say anything about the existence of the past or future. They are just a way to rationalize the existence of "free will" in a deterministic universe by making it "possible to have made a different choice". So the many worlds model doesn't present a paradox that I'm aware of. Grandpa spawned an infinity of grandchildren and I happen to be one of them. But he's gone and the others are of no consequence to me.

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?

Only the one I mentioned which is that time travel is impossible because the past and future do not exist. They are both only concepts of the mind. The records of the past are used to explain the present and to predict the future. I fail to see any conflict between that and the relativity of time and space.

Well if all 4 (or more) dimensions of space time are affected by relativistic distortions and there is no preferred reference frame, than "the present" doesn't exist, only as a mirage: it's the collection of points with a t coordinate equal to yours within your reference frame. If the present doesn't exist and neither do past and future, we're forced to conclude nothing exists.

 

[untermensche]

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.

It's been repeatedly explained to you in this thread that in a block time model of the universe, nothing changes.

Yes. The past can't change. A person from the future can't go back there and change it.

Time travel is impossible.

I know.

Your claims that a person from the future going back to the past does not change the past that has occurred once already without that time traveler is laughably blind.

67,000,000 years ago - Untermensche appears in his time machine
66,999,998 years ago - Untermensche is eaten by a T. Rex

Untermensche did not exist 67,000,000 years ago to appear anywhere. That was the time before Untermensche.

If Untermensche is suddenly and miraculously thrown into that time then the past has changed.

 

[untermensche]

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.

If you can travel to the past, and you do travel to the past, having travelled to the past, your past trip must necessarily have happened. You simply complete the time loop upon your departure, arrival and activity while in the past.

That is, unless you open a portal to an alternate reality, you never actually went back in your own universe, therefore there is no record of your presence in your own past and never will be.

If you travel to the past you have changed the past.

This is not hard if one is merely honest.

 

[Jokodo]

If you can travel to the past, and you do travel to the past, having travelled to the past, your past trip must necessarily have happened. You simply complete the time loop upon your departure, arrival and activity while in the past.

That is, unless you open a portal to an alternate reality, you never actually went back in your own universe, therefore there is no record of your presence in your own past and never will be.

If you travel to the past you have changed the past.

This is not hard if one is merely honest.

Snipping out the explanations that have been given and instead continuing to attack you own straw men is as far from honest as it gets.

 

[DBT]

If you can travel to the past, and you do travel to the past, having travelled to the past, your past trip must necessarily have happened. You simply complete the time loop upon your departure, arrival and activity while in the past.

That is, unless you open a portal to an alternate reality, you never actually went back in your own universe, therefore there is no record of your presence in your own past and never will be.

If you travel to the past you have changed the past.

This is not hard if one is merely honest.

Did you read what I said? It appears like you didn't.

 

[untermensche]

If you can travel to the past, and you do travel to the past, having travelled to the past, your past trip must necessarily have happened. You simply complete the time loop upon your departure, arrival and activity while in the past.

That is, unless you open a portal to an alternate reality, you never actually went back in your own universe, therefore there is no record of your presence in your own past and never will be.

If you travel to the past you have changed the past.

This is not hard if one is merely honest.

Snipping out the explanations that have been given and instead continuing to attack you own straw men is as far from honest as it gets.

You can't change the past.

A person from the present traveling to the past changes the past.

Therefore it is impossible.

You want to claim that a person moving from the present to the past does not change the past.

You want to claim that a time traveler visiting you last night is not a change to your previous experience from last night.

Go tell that to some child that will believe you.

 

[untermensche]

If you can travel to the past, and you do travel to the past, having travelled to the past, your past trip must necessarily have happened. You simply complete the time loop upon your departure, arrival and activity while in the past.

That is, unless you open a portal to an alternate reality, you never actually went back in your own universe, therefore there is no record of your presence in your own past and never will be.

If you travel to the past you have changed the past.

This is not hard if one is merely honest.

Did you read what I said? It appears like you didn't.

You will not read what I wrote and respond to it will you?

People live in their present, not the past.

For a person in their present their past is complete, finished. It can't change.

Some time traveler can't come visit them in their past. This is the same for all observers including dinosaurs.

Impossible.

 

[DBT]

Snipping out the explanations that have been given and instead continuing to attack you own straw men is as far from honest as it gets.

You can't change the past.

A person from the present traveling to the past changes the past.

Therefore it is impossible.

You want to claim that a person moving from the present to the past does not change the past.

You want to claim that a time traveler visiting you last night is not a change to your previous experience from last night.

Go tell that to some child that will believe you.

Your visit and your activity are a part of the past before you take your trip. You complete the loop when you board the time machine, depart and return. That is the history. Nothing is changed.

 

[Jokodo]

Snipping out the explanations that have been given and instead continuing to attack you own straw men is as far from honest as it gets.

You can't change the past.

A person from the present traveling to the past changes the past.

Therefore it is impossible.

You want to claim that a person moving from the present to the past does not change the past.

A person moving from a present to a past of which they are a part does indeed not change that past.

You want to claim that a time traveler visiting you last night is not a change to your previous experience from last night.

Not at all. I'm claiming that a time traveler from the year 23,567 visiting me yesterday and identifying as such in a way that I can understand hasn't happened and will not happen - but that is not evidence that time travel is impossible. It could simply be that I'm not all that much of an attraction that any time traveler would choose to visit me out of every sentient being past and future they could converse with.

 

[Jokodo]

Did you read what I said? It appears like you didn't.

You will not read what I wrote and respond to it will you?

People live in their present, not the past.

For a person in their present their past is complete, finished. It can't change.

This is not in contradiction with anything we've said. It does not force the conclusion that time travel is impossible though. The only conclusion it forces is that a person who wasn't visited by time travelers wasn't visited by time travelers.

Some time traveler can't come visit them in their past.

Except if some time travelers have visited them in their past, of course

This is the same for all observers including dinosaurs.

It's true for dinosaurs that haven't been visited by time travelers, and false (even necessarily so, using your very own logic) for dinosaurs that have. We don't know whether the latter exist, but your ramblings do not show that they don't.

 

[Elixir]

This is not in contradiction with anything we've said. It does not force the conclusion that time travel is impossible though. The only conclusion it forces is that a person who wasn't visited by time travelers wasn't visited by time travelers.

Some time traveler can't come visit them in their past.

Except if some time travelers have visited them in their past, of course

This is the same for all observers including dinosaurs.

It's true for dinosaurs that haven't been visited by time travelers, and false (even necessarily so, using your very own logic) for dinosaurs that have. We don't know whether the latter exist, but your ramblings do not show that they don't.

Methinks y'all are up against what is commonly referred to as "invincible ignorance".

 

[untermensche]

A person moving from a present to a past of which they are a part does indeed not change that past.

Of course it does.

If no time traveler visited you yesterday then somehow a time traveler visits you yesterday the past has changed.

Are you saying a time traveler in the future can go back to any time except yesterday?

All observers exist in their present. They were born in their present and live in their present.

They are not part of time that existed before they were born.

If they somehow appear in that time they have changed it.

 

[untermensche]

Methinks y'all are up against what is commonly referred to as "invincible ignorance".

Me thinks you people are blind liars.

You claim a past changed is not really a past changed.

You claim a person born in the future visiting you yesterday has not changed yesterday.

 

[Jokodo]

A person moving from a present to a past of which they are a part does indeed not change that past.

Of course it does.

If no time traveler visited you yesterday then somehow a time traveler visits you yesterday the past has changed.

And if a time traveler did visit me yesterday, then a time traveler who visits me yesterday does not change the past, and indeed no time traveler visiting me yesterday would change the past.

Are you saying a time traveler in the future can go back to any time except yesterday?

I'm saying that assuming no time traveler visited me yesterday (which appears to be the case, unless they hid well), if time travel is feasible, nobody chose to visit my yesterday out of all possible destinations. That's not unlike saying if intercontinental travel is possible, no Australian visited me yesterday.

All observers exist in their present. They were born in their present and live in their present.

I'm fairly positive I was born in my past.

They are not part of time that existed before they were born.

Unless they traveled through time.

If they somehow appear in that time they have changed it.

Not if they already appeared in that time.

 

[untermensche]

And if a time traveler did visit me yesterday, then a time traveler who visits me yesterday does not change the past, and indeed no time traveler visiting me yesterday would change the past.

They didn't visit you yesterday in reality. You had no visitor yesterday.

If a person can go back in time though they can visit you yesterday.

So the reality of them not visiting you yesterday is changed to the reality of them visiting you yesterday.

This would be true of every moment in the past.

It would exist once with no time travelers since time travel wasn't invented yet.

Then it would exist with time travelers in it.

Totally changed.

 

[untermensche]

I'm fairly positive I was born in my past.

Many of what were your present moments are now your past.

And none can change.

No creature from the future can visit you in any of them.

 

[Jokodo]

I'm fairly positive I was born in my past.

Many of what were your present moments are now your past.

And none can change.

No creature from the future can visit you in any of them.

And no creature from Betelgeuze can visit me in any of then either. No creature from Bhutan can visit me in any of them. Does that rule out interstellar or intercontinental travel?