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Your use of the word "past" is very confusing, yes a very fast spaceship can be used to travel to the future, no you can't travel into the past, that's all ther

Your use of the word "past" is very confusing, yes a very fast spaceship can be used to travel to the future, no you can't travel into the past, that's all there is to say in short.

tsimionescu 4y ago
Well, yes, but that means that my past and yours still exists as a real place that others can visit, in some sense. That's why I gave the example. Of course, that visitation has already happened in our past. But the same person can also know things we havent experienced yet, but whose consequences we will experience in our future.
- deleted 4y ago
  [deleted]
- kgwgk 4y ago
  That’s not how it works. No one can visit your future first and your past later, whatever that means. Otherwise they could just stay with you in your past and wait until their past self joins the party later. [edit: Maybe you were not saying that in this comment. But other comments of yours are wrong so I can’t tell what are you saying, really.]
  - tsimionescu 4y ago
    I was confused, you're right. The only thing that can be said about someone who experiences my past and later meets with me is that we might disagree about the order that far away events happened, but we will both agree that those events are in the past.
    - kgwgk 4y ago
      I think that you can disagree as long as those two events have « space-like » separation. As you say, they could be events that happened in the past and are in your past light-cone. (As long as they happened far enough from each other - or close enough in time.) But one of the events could be your meeting now and here and the other event could be elsewhere. You may disagree on whether that event has happened already or not. Without having any direct confirmation yet, of course. But you may determine later that it was before and after your meeting at t=0.
- the_other 4y ago
  > Well, yes, but that means that my past and yours still exists as a real place that others can visit, in some sense. That's why I gave the example. Of course, that visitation has already happened in our past. If the other person can travel to "my past", can their point of departure be said to be "in my present"? Does this fulfil the math? At T[0][theirs] and T[0][ours], they decide to travel very fast towards us. At T[42][theirs], they meet us, but it's T[-23][ours] At T[42][ours], we remember meeting them It bends my head out of shape, which is fun... but is it "right"? And is it even possible to say T[0][theirs] === T[0][ours]? Is it all better modelled by using T-theirs[0] and T-ours[0]... and some rule like "T-theirs[n] can never = T-ours[n]" ?
  - deleted 4y ago
    [deleted]
  - tsimionescu 4y ago
    No I had made some errors when claiming that. Their time of departure will always appear, both to us and to them, to have been further back in time than their point of arrival. We will disagree on how much farther in the past, but we will agree that it is in the past. For example, if they are moving at almost the speed of light, and zipping past us, to them it may seem that they left their planet a few seconds ago, and only traveled a few meters; but to us and to their friends back home, it may seem like it took them 1 million years and they moved almost 1 million light-years. We will also disagree on the order of some events, but only those that have already happened from both our perspectives.

Your use of the word "past" is very confusing, yes a very fast spaceship can be used to travel to the future, no you can't travel into the past, that's all there is to say in short.

tsimionescu 4y ago

Well, yes, but that means that my past and yours still exists as a real place that others can visit, in some sense. That's why I gave the example. Of course, that visitation has already happened in our past. But the same person can also know things we havent experienced yet, but whose consequences we will experience in our future.

deleted 4y ago
[deleted]
kgwgk 4y ago
That’s not how it works. No one can visit your future first and your past later, whatever that means. Otherwise they could just stay with you in your past and wait until their past self joins the party later. [edit: Maybe you were not saying that in this comment. But other comments of yours are wrong so I can’t tell what are you saying, really.]
- tsimionescu 4y ago
  I was confused, you're right. The only thing that can be said about someone who experiences my past and later meets with me is that we might disagree about the order that far away events happened, but we will both agree that those events are in the past.
  - kgwgk 4y ago
    I think that you can disagree as long as those two events have « space-like » separation. As you say, they could be events that happened in the past and are in your past light-cone. (As long as they happened far enough from each other - or close enough in time.) But one of the events could be your meeting now and here and the other event could be elsewhere. You may disagree on whether that event has happened already or not. Without having any direct confirmation yet, of course. But you may determine later that it was before and after your meeting at t=0.
the_other 4y ago
> Well, yes, but that means that my past and yours still exists as a real place that others can visit, in some sense. That's why I gave the example. Of course, that visitation has already happened in our past. If the other person can travel to "my past", can their point of departure be said to be "in my present"? Does this fulfil the math? At T[0][theirs] and T[0][ours], they decide to travel very fast towards us. At T[42][theirs], they meet us, but it's T[-23][ours] At T[42][ours], we remember meeting them It bends my head out of shape, which is fun... but is it "right"? And is it even possible to say T[0][theirs] === T[0][ours]? Is it all better modelled by using T-theirs[0] and T-ours[0]... and some rule like "T-theirs[n] can never = T-ours[n]" ?
- deleted 4y ago
  [deleted]
- tsimionescu 4y ago
  No I had made some errors when claiming that. Their time of departure will always appear, both to us and to them, to have been further back in time than their point of arrival. We will disagree on how much farther in the past, but we will agree that it is in the past. For example, if they are moving at almost the speed of light, and zipping past us, to them it may seem that they left their planet a few seconds ago, and only traveled a few meters; but to us and to their friends back home, it may seem like it took them 1 million years and they moved almost 1 million light-years. We will also disagree on the order of some events, but only those that have already happened from both our perspectives.