what are the consequences of time travel

[sushi]

what are the consequences of time travel?

do you believe in the grandfather paradox, in which you assassinate your grandfather to erase your existence in the presetn

is time deterministic (only one time) or is there multiple timelines

is it possible to kill hitler and have another entire different future, or future will end up just the same. or maybe hitler cant be killed and one cant change anything by going back to the past.

 

[The Grey Man]

The thing about paradoxes is that it is impossible to believe in them because they are self-contradictory. If you killed your grandfather before he could beget your father, then your father was never born and therefore did not beget you, so you were never born either: unless never having been born is somehow compatible with killing one's grandfather, this is contradictory. The only way to avoid the contradiction is to make one of the terms equivocal so that, for example, there is one 'grandfather' who begot your father and another whom you prevented from doing so. This assumption, of course, implies interaction between alternate timelines.

 

[Rook]

entropy reigns. a broken eggshell mended not can be.

 

[sushi]

so you can move back to the past but not change the past, that seems counterintuitive.

 

[Rook]

the pure amount of energy required for time travel boggles the mind. basically, from one present moment to another, you reverse everything.

Even for a single second in the entire universe the math, the pure behemothian scope of it is incalculable. It's like... reversing Hiroshima, every wave that ever lapped at a shore, every grain of sand that ever shifted in all deserts, every star that was formed and destroyed.

I can't even start to imagine what energy input would be needed for such a feat, even if it is possible.

 

[Ex-User (9086)]

First we need to talk methods of time travel. You could say that none exist and that means you don't read enough sci-fi.

Rook mentioned energy, yeah that's one plausible way to do that, you need the power equivalent of the whole universe, or a huge chunk of it to reverse time, it may be easier to create a whole new universe at that point, one where you don't need to time travel to save your loved one, ahh the drama of it. Needing the whole universe assumes you're relying on theory that doesn't even account for time travel. You could get away with reversing part of the universe using part of the energy, optimizations to be made for sure.

Stuff other than energy can be used for time travel, too much to summarize.

You can also think about the nature of the universe that you are altering. If the universe is truly infinite, or if you can make it infinite and populated with matter, then your time-travel would be a movement between identical parts of the statistically distributed phase space of all possible arrangements of particles per given volume of space, located conveniently far apart. If space is really big and has comparable distribution of stuff in it, like unimaginably big, not even infinite, it's bound to repeat even if it's not deterministic.

Then we would have to consider the realms of impossibility, the degrees of impossibility of the approach you want to use. Some time-travel methods are only slightly impossible, that is; they would be possible if there was one more type of matter, or a different physical constant, a small change to what we know is available. Some methods are downright ridiculous and not actionable, still good for thought experiments.

If time travel is at all possible, then the universe will make itself right, it won't just explode, your time travel ain't that cool. I'd say that if the universe is time-travel compatible then your action of changing the past will make you lose the future you would have if you haven't time travelled, which would reshape the universe to be compatible with the change. A lot depends on whether time is a dimension.

You might think that doing something and going back in time to reverse it cancels out, but it doesn't. You've now created a situation where you stop yourself from going back and continue in an altered universe than the one you started in. If you sum the information in the universe before your first time-travel attempt and after it, the information content increases, you're not the same, things are not the same.

Entire books worth of speculation can be written on the topic, google is your friend.

There's tons of physics that we don't know. Watch this cool episode that approaches a theoretical description of some slightly impossible form of time-travel.

Spoiler

 

[BurnedOut]

The automatic existence of multiple timelines which is unavoidable given how time travel creates time traveling. Time traveling is an easy concept to understand if an assumption is made that each timeline is an independent one. This is similar to the philosophy of functional programming where all the copies are preserved in the process but the one you obtain is the one you observe.

Then there are several speculations on the 'nature' of time itself. One of the prevalent one which is most prominently seen in 12 Monkeys and The Flash is that time is sentient and disallows making any timeline mutable but in that process, time is rendered mutable to a certain extent in order to facilitate time travel itself. In 12 Monkeys, time can be destroyed which again brings us back to the assumption that time should be immutable but it is not after the existence of time travel. Additionally, 12 Monkeys adds the concept of 'determinism' to time travel in order to preserve the order of time travel but the existence of multiple timelines allows the creation of a time-independent entity and the same can be found in The Flash.

While science's stated paradoxes disapprove time travel, fiction often tends to render time as being sentient or malleable in order to forward their plot. However, all of the paradoxes can be found in 12 Monkeys. The Flash tends to circumvent these by theorizing the existence of tachyons and black matter and suchlike which can be somehow harnessed by Team Flash. 12 Monkeys also circumvents the paradoxes partially by inventing concepts of time-independent bodies and suchlike but it is left to the viewer to conclude if 12 Monkeys ultimately adhered to the time-traveling laws apparent.

 

[sushi]

i think reverse time is possible, entropy decrease

its just so far unattainable with current technology. Time can go both directions. Events can happen and unhappen. Eggs can crack and uncrack.

 

[BurnedOut]

How is it entropy if it can be decreased?

 

[scorpiomover]

what are the consequences of time travel?

1.1) Lots of bereaved parents going back in time, trying to save their children from dying.

Lots of people trying to going back in time, trying to save their lover.

Even if the effort is futile, plenty of people are so upset about the loss of a child or a partner, that they act extremely irrationally for a long while, desperately trying to preserve the memory of their loved on.

So even if you tell them that they can't bring them back, they'll still try.

1.2) Neo-nazis going back in time to ensure Hitler wins the war.

1.3) Chinese going back in time to stop the Hundred Years of Shame.

2.1) When people go back, they stand in line for a coffee, which makes the person who was supposed to be getting their coffee then, late, which causes cascading effects which changes history.

Because of 1.1, 1.2 and 1.3, history keeps changing. You never know, because your history is continually being rewritten as if it was always meant to be this way.

Or, going back in time and changing things, has no effect on history. You never know, because time-travel ends up with the same history as if there was no time travel.

3.1) The invention of a government agency in every country, tasked with preerving the timeline.

Different governments of different countries want to preserve a different version of events. So they keep fighting over the timeline.

We end up with Time Wars, like those that destroyed the Daleks and the Time Lords.

But again, we don't know, not unless we are inducted into a Time Agency, because whatever changes happen, ripple from the past, making it seem as if things were this way all along.

do you believe in the grandfather paradox, in which you assassinate your grandfather to erase your existence in the presetn

These sorts of paradoxes are a problem in the present as well, as the Twin Paradox applies to Einstein's theory of relativity. So there has to be a solution.

is time deterministic (only one time) or is there multiple timelines

I think time goes in spirals. So: both.

is it possible to kill hitler and have another entire different future, or future will end up just the same. or maybe hitler cant be killed and one cant change anything by going back to the past.

Don't know. Be interesting to try. Care to help build a TARDIS?

 

[onesteptwostep]

Personally I think it's impossible to travel to the future. The past? Maybe, but will we be able to go back to the traveler's present time? Im not sure..

 

[BurnedOut]

Personally I think it's impossible to travel to the future.

One of the key things about time travel is that the future, past and the present are breached.

"Time travel creates time travel." (12 Monkeys)

 

[sushi]

when cause happens , universe becoming direction


the reverse can be true
when universe happen cause becomes

the two are interchangable, that is why i believe time is reversable

tree falls down (cause happens), it breaks and hit someone (becoming)

i dont know what the reverse is, but the process, cause and direction seem reversible.

 

[scorpiomover]

"Time travel creates time travel." (12 Monkeys)

Time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel causes time travel
Seems like it's a never-ending story.