"When I asked if a time machine would ever be invented, Baba Gyani Triviani said - sure, haven't you heard of that old joke? They call it a clock"
My friend recently asked me about time machines and if I believed in it. I didn't pay much thought to it, and said that I hadn't thought much about it. Later, when she posted a status update on Facebook, I began to think. Of course, you may have seen or heard identical arguments elsewhere, so I am not claiming any originality here.
First of all, Artistick proves that a time machine wouldn't work because... Click here to read
The universe is considered to be running on some weird supernatural technology: So, there will be references and analogies to code here and there
Case 1: [Single Universe]
We are all in a particular time frame. If I go to the past and make some modifications, those changes must affect the future. Say, if I go to the past, and kill a man. Then, in the future of that past, which could be the present, that man or his children should not exist. Then, how will others get affected by his disappearance? If that man was talking to a woman (in the present) precisely at the instant I kill him in the past (there will, of course, be a master clock synchronising time frames - electronics engineers will know better) will he disappear in the present? If he does, then will the woman have memories of that man? Or should no memories exist about that man with anyone? He should also disappear from all photos, records, etc.
For this to happen, the whole world should be updated in an atomic process. All photos, records, memories of people should be updated in one shot. All changes made by this person should be undone. This is fairly complex - If that person was, say a mason who laid some bricks in a building. Then will those bricks get selectively removed? If he was a programmer, software would crash. If he was a driver, will those people be returned to places where they started the journey? If yes, then the things that those people did at the destinations will also get undone, because they would not have made that trip at all, since the driver was also non existent.
The simplest way to solve this problem is to roll back the universe by the number of years by which the person made the time travel to kill that man... This would mean that every time a time travel is made, all changes after the interval of travel is lost forever. So, if a person goes back by 5 years, everything that happened in the past 5 years gets undone. This also means that most likely, only one time travel can be made, since the time machine will be lost as well (not necessarily, but likely).
This would have another problem - if he goes back in time in a time machine to a period before the time machine was created, will the time machine continue to exist? If not, then he will be stuck in the past forever, and there will be two of him there. Therefore, I don't think this situation can exist.
Case 2: [Multiple Universe - Or Time Frames]
Again, take a similar example of going to past and killing a man. Now, we have seen in case 1 that it is fairly complex to do such complex operations (roling back universe). So, we can simplify this by creating multiple time frames. In this case, when I go to the past, I am leaving current time frame to a different time frame. Killing a person there, will eliminate that person in that time frame. Thereafter, the future of that time frame will carry on, as if that person never existed. However, he will continue to exist in this time frame. Now this will take us to two situations
Case 2a: [Multiple Time Frames already Exist]
This means that there are an infinite number of time frames existing, where each time frame is offset from another time frame by a fixed period of time. Therefore, the time machine can be made to point to any of these time frames. It is similar to having an array of time frames. Clearly, the resources required to run such a system is huge!! This has an added overhead of constantly updating time frame pointers... (need to rethink this whole thing again - little complex). Thus, I doubt if this situation can exist as well.
Case 2b: [Time Frames get created on run time]
This means that initially only one time frame exists. But an archive of events (every event ever) is maintained in one repository from time zero. When a time machine is used to go back in time, a clone of the universe is created, and we go back to a period - And the information for that time frame can be pulled out from the "History Repository". Thereafter, any changes made there, will affect events in that time frame. Here, it is akin to creating objects as and when we require them. The limiting factor would be amount of resources available to sustain such enviroments. Will there ever be an out-of-memory exception? Also, note that in none of these cases can a time frame be erased. So, memory is never being freed.
Thus, to conclude, multiple time frames either exist infinitely (less probable) or cannot be destroyed and will persist forever (which means only a limited number of time trips can be made - limiting factor would be amount of resources or memory)
Please note: Killing a person merely indicates an event in this discussion. You can replace it by any other event of your choice
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