You find yourself in the cretaceous

[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.

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?

You want to turn limitations of the universe into magic freedoms somehow.

On one hand you say time travel is possible.

That means a creature can go back to moments in the past.

At the same time you say they can't go back to your yesterday to change it.

If they can't go back to your yesterday they can't go back to any other yesterday.

 

[Treedbear]

...

...
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.

Here's an interesting one -

According to the growing block universe theory of time (or the growing block view), the past and present exist while the future does not. The present is an objective property, to be compared with a moving spotlight. By the passage of time more of the world comes into being; therefore, the block universe is said to be growing. The growth of the block is supposed to happen in the present, a very thin slice of spacetime, where more of spacetime is continually coming into being. Growing block theory should not be confused with block universe theory, also known as eternalism.

The growing block view is an alternative to both eternalism (according to which past, present, and future all exist) and presentism (according to which only the present exists). It is held to be closer to common-sense intuitions than the alternatives.
...
Recently several philosophers, David Braddon-Mitchell (2004), Craig Bourne and Trenton Merricks have noted that if the growing block view is correct then we have to conclude that we do not know whether now is now. ... However, some have argued that there is an ontological distinction between the past and the present. For instance, Forrest (2004) argues that although there exists a past, it is lifeless and inactive. Consciousness, as well as the flow of time, is not active within the past and can only occur at the boundary of the block universe in which the present exists.

So there you go. I'm arguing against myself here but according to this theory we are free to invent a time machine in the present and future. But the past is locked-in and so there's no ability to change if it were possible to go there. And no free will but how would anyone know that. It's really a hybrid model. But it just seems too contrived for me to accept. As scary as it may seem I think there's no good reason to believe anything but the present exists. If you could stop time you'd have one unchanging universe. Not a stack of sequentially ordered many-worlds. Although I will admit it is less objectionable that a purely block-time model in which all of eternity exists devoid of precedence or contingencies.

 

[bilby]

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.

No, it was always that way and always will be. Or are you suggesting that nothing can change from one instant to the next?

If I said that an electron and a position appeared, would that also constitute an unacceptable claim to you? Because that is a regular thing that happens all the time. And an untermensche appearing is just the same thing on a much larger scale. Obviously it's very unlikely to happen spontaneously, but very unlikely things happening as a result of a deliberate action involving the manipulation of large amounts of energy is completely in accord with everyday experience for any post-WWII human.

 

[Elixir]

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

Me thinks you people are blind liars.

Ooooh.... ad hom. A two-fer. Very convincing.
You probably should have picked one. You still can, if you go back into the past

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

No, that's YOUR claim about others' claim. That what they have proposed exceeds your ability to understand - that is the "problem", and it's all yours.
Don't throw a tantrum though, if you can help it.

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

That may have happened. How would you know?
Another thing for you to consider... How did I know you were going to say that???
[cue spooky music]

 

[Loren Pechtel]

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.

You can have time travel without being able to put yourself in the past. Simply having communications will have substantial effects.

 

[Jokodo]

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?

You want to turn limitations of the universe into magic freedoms somehow.

Quite the opposite. What I've been discussing is a fully deterministic universe: The past is what it is, and so is the present, and indeed the future. If it seems contradictory to you, this is only because you can't give up on your magic freedoms and insert them while they may be inapplicable.

On one hand you say time travel is possible.

False again. I'm saying we do not know that it's impossible. It may be impossible, but not for the reasons you're telling us.

That means a creature can go back to moments in the past.

Possibly, yes.

At the same time you say they can't go back to your yesterday to change it.

Half right. Apparently (best as I can tell), nobody from the future went to my yesterday. That doesn't mean it's impossible. Just like, best as I can tell, no-one from Bhutan or Betelgeuze went to meet me yesterday. In a deterministic universe in which time travel is possible, all three are simply contingent facts: No-one in Bhutan 3 days ago decided to purchase a plain ticket to come visit me in Austria yesterday, no-one from Betelgeuze decided to board a starship to visit me 6000 years ago (or however long it takes them to cross those 600-odd lightyears, and no-one from the year 22,021 decided to board a time machine to visit me in 2021. For all we know, no physical laws would have prevented any of those, but it's apparently not what happened. Not everything that can happen happens, and to conclude from the fact that something didn't happen that it somehow violates a basic law of the universe is not a sound conclusion. It's just silly.

If they can't go back to your yesterday they can't go back to any other yesterday.

They could have gone to my yesterday. They didn't. Not the guy from Bhutan, not the lady from 22021, and not the blob from Betelgeuze.

 

[untermensche]

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

No, that's YOUR claim about others' claim. That what they have proposed exceeds your ability to understand - that is the "problem", and it's all yours.
Don't throw a tantrum though, if you can help it.

It is the only possibility with this imaginary claim of time travel.

An observer going to the past is moving to a place they have never been.

The past already came and went and they were not in it. They were born long after the past came and went.

You want to claim that an observer can go into the past that came and went without changing that past.

Blindness.

Irrational delusion.

 

[untermensche]

They could have gone to my yesterday. They didn't. Not the guy from Bhutan, not the lady from 22021, and not the blob from Betelgeuze.

What do you mean?

According to you many time travelers in the future can go to your yesterday.

But for some reason you didn't see any of them the first time you lived yesterday.

It is a lie to say that an observer moving to a past they were not a part of before they went is not changing that past.

And impossible for an observer living in their present to somehow miraculously already be part of some past that came and went without them in it.

 

[Treedbear]

...
An observer going to the past is moving to a place they have never been.

The past already came and went and they were not in it. They were born long after the past came and went.
...

Yeah, that could create problems. Like their death would have to occur before their birth.

 

[Elixir]

An observer going to the past is moving to a place they have never been.

Yawn
Everyone is always in a place they have never been.

Irrational delusion.

Projection.

The past already came and went and they were not in it.

Unless they were. You don't know, because you weren't there.

 

[Jokodo]

They could have gone to my yesterday. They didn't. Not the guy from Bhutan, not the lady from 22021, and not the blob from Betelgeuze.

What do you mean?

According to you many time travelers in the future can go to your yesterday.

But for some reason you didn't see any of them the first time you lived yesterday.

Because none do/did. Not everything that is compatible with the laws of physics does happen. We live in a universe of is, not a universe of can. For example, 700,000-odd Bhutanese could have visited me yesterday and none did, or indeed ever. Do we conclude from this that Bhutan is one big open air jail?

It is a lie to say that an observer moving to a past they were not a part of before they went is not changing that past.

It's also a lie to say that any of us are implying such.

And impossible for an observer living in their present to somehow miraculously already be part of some past that came and went without them in it.

But they can be, must be part of a past that came and went with them in it. In the model we are discussing, in 2021 a time traveller from 22021 shows up if and only if a time traveller in 22021 successfully journeys 20,000 years into the past. There is only one version of 2021, ever, which either does or does not contain the person from 22021 in concordance with what happens in 22021.

 

[skepticalbip]

They could have gone to my yesterday. They didn't. Not the guy from Bhutan, not the lady from 22021, and not the blob from Betelgeuze.

What do you mean?

According to you many time travelers in the future can go to your yesterday.

But for some reason you didn't see any of them the first time you lived yesterday.

It is a lie to say that an observer moving to a past they were not a part of before they went is not changing that past.

And impossible for an observer living in their present to somehow miraculously already be part of some past that came and went without them in it.

Someone who believes they live in a 3D universe trying to imagine the "illogical" possible reality of a 4D spacetime universe is like someone who believes they live in a 2D universe imaging the "illogical" possible events in a 3D universe.

 

[Jokodo]

...
An observer going to the past is moving to a place they have never been.

The past already came and went and they were not in it. They were born long after the past came and went.
...

Yeah, that could create problems. Like their death would have to occur before their birth.

How is that a problem? I mean, other than for programmers building datasets of biographical data who will run into bugs in productionbecause they never tested that particular edge case? Unexpected edge cases causing bugs is a quite ordinary occurrence and certainly not evidence about the nature of the universe. Openstreetmap.org shows very "interesting" behaviour when mapping entities that straddle the anti meridian (180° east/west), that's not exactly evidence for a flat earth, is it? I have written code that will fail at the poles and antimeridian (and explained as much in the comments), and that certainly doesn't show that deep down, I don't believe in that ball earth crap - or is it?

 

[skepticalbip]

...
An observer going to the past is moving to a place they have never been.

The past already came and went and they were not in it. They were born long after the past came and went.
...

Yeah, that could create problems. Like their death would have to occur before their birth.

How is that a problem?

If someone is born in Europe then how could they possibly die in South America?

 

[Jokodo]

openstreetmap.org does funny stuff with antimeridian-straddling geographical entities, therefore, the Earth cannot be spherical:



https://www.openstreetmap.org/relation/1116270

(An even better example as it splits a contiguous land mass: https://www.openstreetmap.org/relation/151231:


)

I'm starting to sound like a broken record, but: someone's mistaking the map for the countryside...

 

[untermensche]

How is that a problem?

If someone is born in Europe then how could they possibly die in South America?

They can't die in South America before they were born.

 

[Jokodo]

How is that a problem?

If someone is born in Europe then how could they possibly die in South America?

They can't die in South America before they were born.

Not without time travel.

 

[untermensche]

They could have gone to my yesterday. They didn't. Not the guy from Bhutan, not the lady from 22021, and not the blob from Betelgeuze.

What do you mean?

According to you many time travelers in the future can go to your yesterday.

But for some reason you didn't see any of them the first time you lived yesterday.

It is a lie to say that an observer moving to a past they were not a part of before they went is not changing that past.

And impossible for an observer living in their present to somehow miraculously already be part of some past that came and went without them in it.

Someone who believes they live in a 3D universe trying to imagine the "illogical" possible reality of a 4D spacetime universe is like someone who believes they live in a 2D universe imaging the "illogical" possible events in a 3D universe.

Somebody that lives in a universe where the days of the dinosaurs are gone and they were not there is trying to pass on some irrational garbage that going to those days now would not be changing them.

Only a child would buy it.

 

[untermensche]

They can't die in South America before they were born.

Not without time travel.

In other words no point unless we accept miracles are possible.

 

[Jokodo]

They can't die in South America before they were born.

Not without time travel.

In other words no point unless we accept miracles are possible.

We already have to accept the miracle intercontinental travel for them to die in South America regardless of chronological order.