There are geographical places such as the countries, cities and towns, not the past or future. You cannot escape the present. It is a universal law, which the whole universe and its contents must abide by. — Corvus

I could say that I am "here" at my current location (or "geographical place"), whereas earlier I was at a different location and later I might be at a location different to both of these. While I am at each location, I can sensibly say that I am "here" at each location. This is no different to being at the "present" at different times. I always find myself "here" no matter the place and at the "present" no matter the time. Although you can neither escape "here" nor "the present", this does not entail that you cannot depart from or arrive at different places or times.

If one looks at a kind of causation chain that has taken one from birth to the present, at each temporal step a host of causes converges to form the next step, not an easy thing to grasp. Stanislaw Lem had an Ergodic theory of history in which going back in time and performing an act wouldn't necessarily cause a radically different present. The fact that so many aspects of causation go into effect for a moment might mean that they "average out" and any one might have very little effect compared to the others.

The Grandfather paradox might not be completely binding. Give it some thought.

If one looks at a kind of causation chain that has taken one from birth to the present, at each temporal step a host of causes converges to form the next step, not an easy thing to grasp. Stanislaw Lem had an Ergodic theory of history in which going back in time and performing an act wouldn't necessarily cause a radically different present. The fact that so many aspects of causation go into effect for a moment might mean that they "average out" and any one might have very little effect compared to the others.

The Grandfather paradox might not be completely binding. Give it some thought. — jgill

On my view, there is simply no paradox. The timeline branches off into two parallel timelines once time travel first occurs. The Grandfather "paradox", supposedly, is one of contradiction.

The Wikipedia article on time travel states:

If one were able to go back in time, inconsistencies and contradictions would ensue if the time traveler were to change anything; there is a contradiction if the past becomes different from the way it is. The paradox is commonly described with a person who travels to the past and kills their own grandfather, prevents the existence of their father or mother, and therefore their own existence.

The SEP article on time travel states:

The idea is that backwards time travel is impossible because if it occurred, time travellers would attempt to do things such as kill their younger selves (or their grandfathers etc.). We know that doing these things—indeed, changing the past in any way—is impossible.

Let's say Bob travels back in time to 1990 with a plan to kill his younger self. When he arrives, there will be two versions of Bob in 1990: young Bob who is not a time-traveller and old Bob who is a time-traveller. According to the Grandfather paradox, if Bob were to kill his younger self, then he would no longer exist. But why? There were two version of Bob in 1990 and only one of them was killed. Why would older, time-traveller Bob suddenly vanish into thin air?

I understand that young Bob can now no longer grow up to build a time machine, but so what? He already did that. And now he continues to live out his existence as old Bob from 1990 onwards because that is the logical sequence of events following the time travel event. The time travel event creates a second timeline (from 1990 onwards) in which young Bob no longer goes on to build a time machine, but on the first timeline he did build a time machine and went back and killed young Bob.

According to what I've read, there cannot even be two Bobs in 1990 because that causes a contradiction (e.g. Bob is in two places at once). But of course there must be two Bobs in 1990 if Bob is to time travel at all. They're not both the same version of Bob obviously (one is a time traveller), so it seems wrong to say that there is any contradiction.

I think there may be differences between alternate histories (like Lem's theory) and alternate timelines. But I'm too tired to cogitate. :yawn:

I could say that I am "here" at my current location (or "geographical place"), whereas earlier I was at a different location and later I might be at a location different to both of these. While I am at each location, I can sensibly say that I am "here" at each location. This is no different to being at the "present" at different times. I always find myself "here" no matter the place and at the "present" no matter the time. Although you can neither escape "here" nor "the present", this does not entail that you cannot depart from or arrive at different places or times. — Luke

When you say "I am here." in the each different locations, you are not saying anything about the physical geographical locations themselves, but you are stating that YOU are in a location.
Anyhow, it wouldn't be a concept such as happiness, hopes, past or future, you would be in physically.

And no matter how far back or forward, you imagine to have gone to, it would be always the present, because everything happens in present. You cannot escape from it.

Another problem with time travel would be, that EVEN IF you might have gone to the past or future, but the rest of the universe will still stay at the present. There is no point of you going back to 100 years back, if the rest of the universe stays at the present. It is just physical, metaphysical, logical and QM impossibility to wake up all the deads from the graves, and rebuild all the castles which had been demolished, and reinstate all the past monarchies and governments into the power .... etc.

The only way to plausibly think about time travel would be thinking the possibility of the existence of so many different possible worlds which are running at different times. And if you proved their existence, then you would have to find out how to get there from the actual world to one of the possible worlds of different times - say 100 years back or 2000 years back or 200 years forward. But are there such possible worlds in real existence? QMly oh yeah why not, Logically yes, Metaphysically maybe, Physically Nope.

When you say "I am here." in the each different locations, you are not saying anything about the locations themselves, but you are stating that YOU are in a location. — Corvus

Likewise when I say "I am at the present time" or when you talk about the present: you are not specifying anything about the times themselves, but you are stating that YOU (or we) are at a particular time.

And no matter how far back or forward, you imagine to have gone to, it would be always the present, because everything happens in present. You cannot escape from it. — Corvus

Right, I agree. But how does this help your argument against time travel? I'm happy to refer to earlier and later times instead of past and future times if you'd prefer.

Another problem with time travel would be, that you might have gone to the past or future, but the rest of the universe will still stay at the present. There is no point of you going back to 100 years back, if the rest of the universe stays at the present. — Corvus

Why not? That's what time travel is.

It is just physical, metaphysical, logical and QM impossibility to wake up all the deads from the graves, and rebuild all the castles which had been demolished, and reinstate all the past monarchies and governments into the power .... etc. — Corvus

This is not what time travel is. A time traveller does not bring (objects and events from) other times into our present time. Rather, a time traveller leaves our present time to arrive at other times.

This is not what time travel is. A time traveller does not bring (objects and events from) other times into our present time. Rather, a time traveller leaves our present time to arrive at other times. — Luke

The whole point of time travel is about going to the place at the time of the past or future with the historical or futuristic people in real flesh in the reality at the time.

What would be a point time traveling to Königsberg of 1776, and on your arrival at the place, you see the modern military bases with the nuclear arms all over the place instead of Immanuel Kant taking his daily walks around the town centre?

What would be the point of traveling 2200 years back to the ancient Greece, if you met up with a bunch of Chinese tourists with mobile phones taking selfies in front of the relics, instead of seeing Plato and Socrates talking to his students in the Lycīum?

The whole point of time travel is about going to the place at the time of the past or future with the historical or futuristic people in real flesh in the reality at the time. — Corvus

I agree. I don't understand this argument:

It is just physical, metaphysical, logical and QM impossibility to wake up all the deads from the graves, and rebuild all the castles which had been demolished, and reinstate all the past monarchies and governments into the power .... etc. — Corvus

Time travel has nothing to do with waking the dead or rebuilding demolished castles.

Time travel has nothing to do with waking the dead or rebuilding demolished castles. — Luke

Well, Kant has been dead for over 200 years. How else could you meet him, if you are going back to his time. Someone has to wake him up from the grave, and reinstate him as the professor of the university, and make the universe as it was in 1776. :nerd:

Well, Kant has been dead for over 200 years. How else could you meet him, if you are going back to his time. Someone has to wake him up from the grave, and reinstate him as the professor of the university, and make the universe as it was in 1776. :nerd: — Corvus

Kant is alive in his time. I'd be going back to his time.

Kant is alive is in his time. I'd be going back to his time. — Luke

:chin: :roll: :yawn:

Someone has to wake him up from the grave, and reinstate him as the professor of the university, and make the universe as it was in 1776. — Corvus

There is no need to "make the universe as it was in 1776" or to raise Kant from the dead. If I travel to 1776, then that was a time when Kant was alive.

Your argument is like saying that in order to travel to Greece, you need to recreate Greece at your current location. What really happens is that you travel to Greece, you don't bring Greece to you at your current location. Similiarly, with time travel, you travel to another time, you don't bring the other time to you. Therefore, there is no need to "recreate" the other time in our time, or to "make the universe as it was in 1776" in our time in 2024. You are travelling to another time, not recreating it here and now. Kant was alive in 1776 so if you were to travel to 1776 then it would not be possible to raise Kant from the dead, because he would not be dead.

If I travel to 1776, then that was a time when Kant was alive. — Luke

Your premise "If I travel to 1776" is an impossibility from the reality of 2024, and therefore it is false. Your conclusion is true in that 1776 was the time Kant was alive.

Even if your conclusion was true, but because your conclusion was drawn from the false premise, your proposition is invalid.

Your premise "If I travel to 1776" is an impossibility from the reality of 2024, and therefore it is false. — Corvus

Why do you say it's impossible? It is possible that someone will invent the technology for time travel in 2024.

Why do you say it's impossible? It is possible that someone will invent the technology for time travel in 2024. — Luke

In what sense is it possible, or under what ground is it possible?

In what sense is it possible, or under what ground is it possible? — Corvus

I already answered that. It's possible that someone could invent the technology for time travel.

You said it was impossible and that my premise was false. The onus is on you to explain why it's impossible.

I already answered that. It's possible that someone could invent the technology for time travel.

You said it was impossible and that my premise was false. The onus is on you to explain why it's impossible. — Luke

I thought it was obvious. Your statement has too many unclear terms. When it says someone could invent, who is someone? Does he exist in the real world? What is his name? Where is he from? What does he do?

The technology, which technology is it? What is the technology based on? How does it work?

And time travel? What do you mean by time travel? Does time exist? In what form does it exist? Travel? what do you mean by travel? Are you physically going somewhere? Where is the destination?

So, you statement is made up with the terms which doesn't have clear meanings. Therefore your statement is not true, and the negation of the statement is true. Because the negation of the statement is true, your statement is false. How is that? :smile:

For you to refute my argument, you must clarify all the unclear terms in your statement with concrete clarity in meanings, and we can start again thereat.

So, you statement is made up with the terms which doesn't have clear meanings. Therefore your statement is not true, and the negation of the statement is true. — Corvus

Non sequitur. If it's an unclear statement, how does it follow that it's not true?

How is that? — Corvus

Very poor. You've offered zero support for your assertion that time travel "is an impossibility from the reality of 2024".

Non sequitur. If it's an unclear statement, how does it follow that it's not true? — Luke

It is not true, because its negation is true.

Very poor. You've offered zero support for your assertion that time travel "is an impossibility from the reality of 2024". — Luke

Support is not our goal of argument. The goal of the argument is finding out which statement is true. It seems clear that yours is not true.

P.S. : You have not managed to clarify any of the unclear terms in your statement, which are the base of the invalidity, and entailing the ground for its falsity.

It is not true, because its negation is true. — Corvus

You said it wasn't clear what the statement or its terms mean. How do you know it's not true if you don't know what it means?

You said it wasn't clear what the statement or its terms mean. How do you know it's not true if you don't know what it means? — Luke

I knew the negation of the statement was clearer, and it gave the ground for the truth, which entailed the falsity of your statement.

I knew the negation of the statement was clearer, and it gave the ground for the truth, which entailed the falsity of your statement. — Corvus

Absolute nonsense. Goodbye.

Absolute nonsense. Goodbye. — Luke

That's a poor argument and conclusion. Good day. :)
I will reconsider your statement for its truth, if you come back with the clarifications for all the mysterious terms you used in it.

Your statement is a typical case for a logical form itself cannot verify the truth / falsity of statements. You must investigate the contents i.e. concepts and ideas in the statements or propositions for its clarity and soundness for the fitness as qualifying the elements for legitimate truth bearers.

If you are using unclear, mysterious or false terms or ideas in statements or propositions, it should be pointed out, and the whole claim must be classed as invalid, unsound or false before checking out the logical forms or structures.

And time travel? What do you mean by time travel? Does time exist? In what form does it exist? Travel? what do you mean by travel? Are you physically going somewhere? Where is the destination? — Corvus

1. Travelling to another point in time from the one you started from.
2. That precedes the rest so will leave aside.
3. Doesn’t matter. Time might not exist but the concept of another point in history remains. Problems remain to be solved but it’s not as if a normal person can’t grok this concept easily.
4. Travel means point A to point B or further. The actual medium is dependent on the medium through which you’re travelling. In this case it may well be zero(seen Event Horizon?). But who knows.
5. ………1776. I didn’t get any impression there was a geographical element to the travel discussed.

Unsure why you’re having so much trouble. I don’t personally think this is going to happen. But your impossibility claim seems more to be you having trouble with holding a few different things together in the idea (location, medium, dimensionality etc..
But hey I could be wrong. I just had no issue understanding the argument.

Time is a concept in mind. Travel means physical motion describing going from physical location A to B. How do you travel in the concept to another physical location, unless travel means something else such as an extremely odd imagination? Or time means some other object such as a town or city called Time?

Time is a concept in mind. — Corvus

If you’re a Kantian or similar about time. Not everyone is. Beside this, time as a concept describes a pattern which actual does obtain among material and bodies. Just move through the pattern of materials.

Unless you deny the external world entirely, changes exist. Choose your “point in time” based on the “previous state of affairs” you’re after. No need for dates - but would require a more god-like knowledge of history

It would be recreating the past in the future. — LuckyR

Recreating a piece of some past state. Indeed, this isn't time travel being described.
I can build a new 1928 Studebaker, even giving it the same serial number as one made in that year. Has that car time traveled or is it just a new thing? I satisfied the conditions of the OP by doing so. Is it even a Studebaker if I built it instead of the defunct company?

There's several physics violations made by the OP, mostly that the state of some system can be fully measured (violating Heisenberg uncertainty), counterfactuals, and violations of entropy, the latter of which can be fixed by recreating a finite state, just a system in a box, not everything.

The question for the OP scenario then becomes, how is the thing created in the box you? Suppose you recreate a 'you' while you're still around, outside the box. Clearly the created thing in the box is not you. Nothing has 'traveled' into the future.

That said, yes it has. If you look at the state of Earth in 1990, you'll find me there. Have I time traveled to 1990? It seems I have. The statement presumes there is a 1990 in existence to examine, which pretty much means presentism is abandoned, which says only today exists.

You cannot travel into a place where the destination doesn't exist. We are all nailed into the present until deaths under the universal law. — Corvus

This is what I mean. Corvus seems to assume presentism with this statement. The whole notion of time travel seems to assume otherwise, that there are 'other times' available as valid destinations.

Impossibility of time travel seems to be one of the universally necessary truth. — Corvus

Funny that you will nevertheless travel to tomorrow. I plan to see you there.
People talk about time dilation being time travel. It isn't any different than doing the same thing sitting still. You get to 'the future' either way, assuming you live long enough to get to the target destination.

On a different note, closed time loops are valid solutions to Einstein's field equations. So are tachyons, and nobody has any reason to suspect either actually exists anywhere, but it isn't mathematically impossible. They don't for instance violate things like the grandfather paradox, and don't require branching of timelines.

If you’re a Kantian or similar about time. Not everyone is. Beside this, time as a concept describes a pattern which actual does obtain among material and bodies. Just move through the pattern of materials. — AmadeusD

Yes, my view of time is similar to Kantian time.  It is a concept in mind.  Time doesn't exist in the physical world like space does.

Unless you deny the external world entirely, changes exist. Choose your “point in time” based on the “previous state of affairs” you’re after. No need for dates - but would require a more god-like knowledge of history — AmadeusD

Do you claim that change is the same thing as time?  No, one can deny the existence of time without denying the existence of the world.  They are totally different things altogether.  The world exists physically, but time exists in mind.

I don't think it is me who has difficulties in understanding the issue.  It was Luke who had to prove that his statements were logical.  I had clear arguments against them. 
So what is your own definition of time, and time travel? Can you travel in time physically, or is it in some other way?

This is what I mean. Corvus seems to assume presentism with this statement. The whole notion of time travel seems to assume otherwise, that there are 'other times' available as valid destinations. — noAxioms

If you insist that you can travel into the past or future in your imagination, yeah I would say it might be imaginable within your imagination. I was only pointing out the impossibility of time travel in the physical world.

Funny that you will nevertheless travel to tomorrow. I plan to see you there.
People talk about time dilation being time travel. It isn't any different than doing the same thing sitting still. You get to 'the future' either way, assuming you live long enough to get to the target destination. — noAxioms

Strictly speaking there is no tomorrow in reality. What you call tomorrow is in your imagination as a concept or idea. There is only "Now" for the whole universe and its members. :) So you might say, we are travelling into tomorrow, but in actuality you are awaiting for another "Now" which will be in next 24 hrs of duration.

Time doesn't exist in the physical world like space does. — Corvus

I agree with this, as a Kantian definition. But I do think there must be an actual “something” from which our senses infer a consistent ratio of change from moment to moment. I suppose whatever that medium is, is what I refer to as “time”. Perhaps it’s something not perceptible which is why we’ve evolved “time” as a figure of mentation.

Do you claim that change is the same thing as time? — Corvus

I am leaning toward “no”. Time being immaterial, change being material in some sense or another. The “previous states of affairs” may obtain somehow, though I can’t answer the how.

o what is your own definition of time, and time travel? Can you travel in time physically, or is it in some other way? — Corvus

Unsure precisely but I view it similarly to the Tesseract in Interstellar to use a visual metaphor. All change occurring in tandem - but, and this is the important part - in order of appearance (as such). Appearance “in time” doesn’t necessarily speak of duration. Our position in it requires duration - hence developing the mental faculty for it.

As always, these are vague, young, naive ideas I’m having. I’m not trained or anything yet