Post Reply Time Travel Explanation
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Posted 9/8/11
First of all, let me start off with this: time travel is theoretically possible. There is no absolute law of physics that prevents it. However, there are numerous problems and pitfalls.

To begin with, most current theories deal only with sending information. Some think that physical travel is impossible others think it is too complex and dangerous at this point. Sending information would alter the world in the way depicted in the series, depending on the actions taken with based on it. This is why it has been proposed that travel to the past may be impossible (but not the future). Some believe that the universe has a self correction method because the ramifications of altering the past are dire to say the least.

Lets start with the "world lines" mentioned in the series. This is an expression of the many worlds theory based on quantum mechanics. In it's most distilled form, this theory says that every decision at every level creates a new universe for each possible outcome. Think about it this way:

This is what is known as divergence or, as it is referenced in the series, divergence number. And divergence only increases as causality moves forward (Causality: action X causes result X and in that order. I am using causality here because causality is incontrovertible where as time is a construct to describe the world. In addition, it makes more sense because it is actions and results that cause divergence, not 'time'.) As you can see, if you take all of the choices, no matter how insignificant, into account, the number of universes or worlds quickly approaches infinity. Now, what the show is saying by "moving world lines" is that by sending information into the past, we can affect the outcome of a situation in the past and therefore any and all universes spawned from that point. This alters the number of possible outcomes and therefore the divergence. Lets go back to out example:

We again encounter situation 1 with outcomes A, B, C, and D. But we have sent information in the past to tell ourselves that A is the outcome we want. Therefore A now has the highest probability and will form the basis for most if not all universes from that point on. This reduces the divergence by narrowing the number of possible universes by as much as 3/4 and, shifting and deleting all universes that do not conform to that constraint. Furthermore, only one universe has to send information back to affect all of the others. You could have millions of spawned universes and if one sends information back, all of the millions of spawned universes are "shifted" to conform.

In addition, what the show says about memory alteration is most likely true. Since memories are caused by experiences; if those experiences are altered then so are the memories. Now as to answer the question of why the protagonist retains his memories. He is the "traveler". He (or his information) is the one actually moving. It is like being at the center of a storm. You can see all of the rain and wind but, you are not affected by it.

Back to time travel in general. As you can see, this 'many worlds theory' becomes quite messy, quite quickly. So messy in fact, most physicists dismiss it as nonsense. The predominate theory of quantum mechanics is one based on probabilities and the fact that things at the sub-atomic level are not truly physical objects. That would require an entire text book to explain (I know, I have two!) but the take away is that the many worlds theory is pretty much thought of as 'junk science'. As one of my professors put it: if many worlds exist, then you shouldn't be afraid to get shot because even if the you in this world dies, there is at least one you in a world that didn't.

On to black holes. A Kerr black hole is a rotating ultra dense unit of matter. It is so dense that in fact it has collapsed in on itself and the resulting gravity does not let even light escape. There are other types of black holes as well but they are essentially all massive gravity wells. To give you a picture of the density, take the entire Earth as it is now and collapse it down to the size of the tip of a ball point pen. That is a black hole. Black holes, or singularities as they are properly known, have been long associated with time travel in both science and popular culture. Einstein, who proposed the existence of singularities but dismissed them as nonsense because of the "messiness" of them, even suggested a possible link with time travel (But that is impossible because black holes don't exist, right? Wrong.) Essentially singularities bend space and time to beyond the breaking point and scientists have no idea what happens there. There are a few theories but none are proven or have gained experimental traction yet. So, do black holes exist? Yes. Can they be used for time travel? Maybe, perhaps probably.

On one note, the characters use of a black hole to compress data is likely nonsense. In the standard four dimensions (three directions and time) black holes are information sinks. Anything that goes in doesn't come out and therefore can not be compressed. This does not hold true in higher dimensions necessarily but, that is irrelevant because only the four dimensions are useful to humans directly.

For completeness, let me say that the basic information on the Large Hadron Collider is mostly correct. It was built mainly for one purpose; to find the Higgs boson, theoretically the basis of matter having mass. Wikipedia has a good article on the LHC and the Higgs so I will that there. And yes CERN is real. And yes, the translators made a mistake. It is CERN, not SERN. It is Europe's main laboratory for research of all kinds but it is most famous for it's nuclear physics research.

I am going to leave this post here. I could say a lot more but I think this more than enough to bend almost anyone's brain. I will be monitoring this thread for the foreseeable future so, post any questions you have and I will post back as soon as I can. Hope this helps for anyone that was curious.
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Posted 9/9/11
I'm going to start by getting this out of the way: They didn't translate CERN wrong, it was written as SERN as part of the running gag where everything is a real brand except slightly changed. Mew tube springs to mind. (Coincidentally, this is a carryover from Chaos;head, which I highly recommend to everyone)

Anyway, while everything you say is correct, I want to explain the relationship between memory and divergence in terms that I understand a little better on the off chance that someone else on here is of my same frame of mind.

When universes diverge, I think of memories never having existed in the first place, rather than being modified. For example, you are in universe 2, witch diverged from universe 1 into 2, and 2A. You travel to 2A by sending D-Mail back to 1 and once you reach there you have entered an environment where the memories of 2 never existed in the first place, so you (and the rest of the universe) remember the events of 2A rather than 2 even though you experienced 2 (though you might still remember 2, or even remember 2 and NOT remember 2A, witch is how everyone's favorite mad scientist reacts)

I started thinking like this in response to the question of how exactly peoples memories got changed.
43584 cr points
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Posted 9/14/11
I think the recurrence of other characters memories may be able to be chalked up to information leakage. In your explanation, you assume a total dissolution of the other world lines. However, we have a traveler with knowledge of that universe in the new one. This creates an information cross over. I am not aware of any way to predict what would happen in this situation because you now have more information in the universe than when it was created. This is a major problem because it is a basic tenet of physics that information can not be lost or gained. There is a certain amount of information in the universe since it's inception. However, with this in mind, perhaps constant exposure to the traveler could have a carry over or ghosting effect on others. It may not be memories but, perhaps just some fuzzy images like trying recall a dream. I can't say for sure but, I guess it is possible.

As for SERN vs CERN, I am aware of the running joke but, as CERN figures in so heavily into the plot, I did not consider it a part of the joke. It is kinda like making a Knight Rider anime and calling the car Knit. Perhaps it is just my taste but, I feel that was kinda a poor choice.
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