While I agree with the article, I think of time travel a bit differently these days.

The old idea I have/had looks like this:

- we are just one of the many (very likely infinite) possibility in this universe

- I believe time travel is a possibility, from a philosophical point of view. I believe in moving forward, not backward.

Put it this way: If I didn't write this comment, your previous five seconds would be reading something else. That's a different history of you and definitely a different history of you and everyone else, even if they are not on HN (you and me are part of each other's experience, even if we are completely strangers, just think about the number of likes on a Youtube video, we could have clicked that button on the same video without knowing the existence of each other).

Think about a street performer. The performance was great, quite inspirational. Everyone who passed by or stood there to watch the performance have a different thought. A guy who just lost his job was going to commit sucicde but the music and the performance cheered him up. A high school kid who just got out of school thought the show added joy to his day. A mother with a young child thought the show was an interesting entrainment and she uploaded a video of the performance on FB later that night and many of her friends echoed her afterward.

One event can make big impact on everyone. If you didn't dye your hair so often your chance of getting blood cancer would be much lower and your family wouldn't have to see you die a few years younger. The outcome would be very different.

If we go back to the past, we will create a new past. From a programmer's mouth, we will create a new object, totally distinct, occupy a different chunk of memory. If "possibility" is a computer with unlimited RAM, that's the model we will use.

old_1930 = historyTable(1930_version_1234);
old_current = historyTable(0xlolcat);
new_1930_everyone = deepcopy(new_1930_everyone + old_current.me;
new_1930 = new World(now_everyone);
// new_1930.next = old_1930.next;

This construction makes sense. I copy myself and everyone in 1930. Because the original past we came from didn't have "us" in it. We didn't exist in 1930s. That is, adding an extra atom would mean a different 1930. This means whatever happens next, even if it were just removing that single atom again, doing so will affect everyone. How do you know that single atom didn't make the air module accelerate faster because that atom was hit so much more often?

Note my construction doesn't say much about deleting. If the original "past" object still exists in this unlimited RAM machine, can I delete it? Can I just detach such node from the other linked list and delete from memory?

If only we performed a deepcopy on old_current.me. But remember, we will remain to have a disconnection with reality. We will keep remembering about friends we used to have but no longer exists because when we do a deepcopy we only copy the pointer to the other events in our memory. We can't locate friend Alice and friend Bob in the new past object anymore.

But if we don't do a deepcopy, we will not be able to delete ourselves. That is, we can't delete the original world. People who lived in the old_1930 would continue to experience the old_1931, old_1932, etc.

B U T, we can't just attach nodes this way.

new_1930_everyone = deepcopy(new_1930_everyone + old_current.me;
new_1930 = new World(now_everyone);

If 2014/02/21 7:35:01 - 7:35:02 are the two moments I want to preserve in the future, then we will have the following problem: the deepcopy of me is NOT compatible with the original me from 2014/02/21 7:35:01am AND 7:350:02AM. Because by the time I do a pointer modification, the deeopcopy of me from that new 1930 would have seen a real Hilter, killed a person for the first time. This is true for everyone else who lived through 1930s and 2014 in both the new and original world...

Me != me. Therefore, we cannot go back and simply change pointer and expect to see good things. I might even carry a dust particle from 1930 into 2014.

Anyhow, what I am proposing doesn't really make sense. There are holes and I am too tired to continue. This is what happen when I couldn't sleep for the last 36 hours.