Quote: Original post by IFooBar
So I was watching sound of thunder today (warning, it was horrible, watch at own risk) and now I'm wondering if you could devise an experiment, or algorithm, that could calculate how fast change ripples into the future. Is it instant? (i.e. kill butterfly a billion years ago and kapoot, universe disappears?) or does it take some time to get to the present? Do all the changes happen at once? Or do they come in waves (this is what happened in the movie)? And if they do come in waves, again, how long does it take?

Do you guys know of any research into this kind of stuff?

"Change" in this context is kind of meaningless (which is what I took szecs' comment to mean).

Your question sounds more Hollywood to me than real. What does it mean for "change" to "ripple" into the future? If I go back in time and stop Hitler from being born, the "change" that I have enacted is discrete, in the sense that I have actively taken action to alter the occurrence of a single event. Ensuing events will be different, but have no relationship to an arbitrary collection of other events we feel "would" have happened.

As Hodgman stated, time would continue to progress at one second per second. But at this point there is no "rippling" of change or anything else; the future, which by definition has not yet occurred, cannot be compared to anything as it does not yet exist.

For the purposes of comparison we could say that Timeline A (where Hitler existed) is different from Timeline B (in which he was never born). But from a chronological perspective, after our historical meddling none of the events of Timeline A occur, as the conditions we created require some different set of events to take place. There is no medium through which a ripple could travel-- time is still linear.

I would also ask about what you mean by "present". The present is thet time where you currently find yourself, and as such is relative. If you go back in time from today to 1500 AD, 1500 AD would be the "present" for you. There is no arbitrary time to be reached for your comparisons to be made. If you watch the outcomes of any historical changes you make happen as they occur, then changes will reach the future at one second per second, as above. If you time-jump again to 1,000 years later, then all changes that took place in the interim might be viewed as having reached your new present (2500 AD) "all at once", with additional events taking place at one second per second.

But it's all guesswork. It's pointless to argue the feasability of this or that aspect of time travel, just like there's no point to arguing how artificial gravity works, or warp speed travel. The particulars of time travel are whatever your heart desires them to be-- if there were rules about it that were understood well enough to address your questions, we would have time travel technology. So far all that we can agree on is that a flux capacitor is absolutely required.

Quote: Original post by IFooBar
Interesting. So in spacetime, if an event happened at position a, and we are currently at position b, then |a-b| * c (?) for a ripple to reach the present? (with a and b being vectors (x,y,z,t) and c being the speed of light) But then can you use c in a space that has time as an axis?

I think you've misunderstood the essence of spacetime :). It's precisely that: space-time - meaning that both space and time make up spacetime. Together. The question "can you use c in a space that has time as an axis" is nonsensical. Think of it this way: everything everywhere in spacetime is in constant motion. Always.

Consider:


Representing movement through spacetime

In the above graph everything always moves the length of the orange arrow through spacetime and this motion is always at a constant speed s. The catch is that this speed (think of it as momentum) can be used for either motion through space or time - by increasing your speed in space, you decrease your speed in time and vice versa. Hence, when you're standing perfectly still, you're using all of your spacetime momentum to move through time. According to special relativity (and the formula presented above), movement in spacetime is ony ever possible within the red semicircle.

Quote:
Also, you think maybe you forgot about general relativity? which permits a number of ways to time travel...

General relativity, in conjunction with special relativity, prohibits time travel by imposing the speed of light as a physical barrier. It is quantum mechanics with quantum entanglement and string theory that propose certain hypothetical workarounds for this.

To address your time travel argumentation, accelerating to speeds faster than c would mean flipping the orange arrow across the horizontal axis, which is strictly impossible. Special relativity ensures this and general relativity is dependent on and an extension to special relativity.

"how fast" is asking for speed. Speed is distance divided by time.

Thus, we can conclude that the changes will propagate slower the later you do them (as time is increasing in value). This is the reason why the Enterprise crew will not disappear when the Borg will not have assimilated Earth in 2063. The conclusion that they (the Enterprise) will not be protected by a time bubble into which they will not get by following the sphere is false. The true reason is (will be?) that the 23th century is quite a bit in the future, so the divisor in above equation is large, and therefore changes will propagate more slowly. Thus, the Enterprise crew will have been assimilated, but the changes since the Borg will not have assimilated Earth will not have propagated yet.

However, it has to be taken into account that time is cyclic. So at some point, the divisor will become smaller as you advance in time, and changes will propagate faster the later you initiate them. Also, it has to be taken into account that real time is a lot more cyclic than movie time.

This has been documented in the Back to the Future movies. In the second installment, which was filmed 4 years after the first, Biff will disappear almost instantly (within half a minute of returning) after having changed the past 60 years ago. In the first movie, it takes Marty a week before beginning to fade after the past 30 years ago had been changed. 60/30 = 2, so it should take Biff 3.5 days to disappear. However, since real time cycles about 10,000 times faster than movie time, it will only take him 30 seconds.

The one great mystery remaining to be solved is how great the cartesian distance between "present" and "past" is, which is the one thing that hinders us from calculating exactly how long changes take to propagate in every case.

the most funny thing about all these timeline is that most people obsessed with the past, but not the future. maybe for the fact that we're moving into the future.

i don't want to change the thread from science into religion, but I think there is an overlap with predestination and religion. In islam, there are things you can change (as of now) and there are things meant to be. god has a location where he put this 'things mean to be' but i forgot what it was called, just in the tip of my tongue. anyway, why god create this 'location of future secret' is as much as mystery why bad things happen to good people, fallen angel,etc.

there are time the devil able to 'glimpse' into this location and share some of the tidbit, allowing some people to 'see the future'.


there is this movie featuring nicholas cage about someone who can see 5 minutes into the future. this is always better than being back into the past. i can use it for date conversation, heh, heh.

my opinion, the past is destroyed just like a stephen king novel, i forgot what the name. you can't go back to something already destroyed.

for those who believe in big bang, i called the past as tiny whimper. if big bag from nothingness came our world, tiny whimper is when our world of the past become nothingness.

see, just like the thread reading invention, i loves to think and come up with theories :-)

Quote: Original post by samoth
"how fast" is asking for speed. Speed is distance divided by time.

Indeed, it used to be thought of as such before 1905.

Quote: Original post by samoth
The one great mystery remaining to be solved is how great the cartesian distance between "present" and "past" is, which is the one thing that hinders us from calculating exactly how long changes take to propagate in every case.

Also answered in 1905. See my previous post.

Quote: Original post by FableFox
there is this movie featuring nicholas cage about someone who can see 5 minutes into the future. this is always better than being back into the past. i can use it for date conversation, heh, heh.

2 minutes actually :)

Hawking talks about light-cones in Brief History, IIRC.

IMO, the occurance of an object arriving at some point in the past (and probbaly the future as well) alters its trajectory along a timeline.

So, if you travel into the past and kill a butterfly you are, at that moment you arrived in the past, in the universe where the butterfly was killed and will continue to travel along that 'timeline'. If on the otherhand you were to somehow send someone else back into the past to kill the butterfly for you, there will be no change from your perspective because the person sent will be in the other universe the moment he arrived.

This question seems about as meaningful as asking "how far does it take for over there to get over here."

Quote: Original post by Sneftel
This question seems about as meaningful as asking "how far does it take for over there to get over here."

It takes forty two.

do not worry, Feynman to the Rescue



those ones sums pretty much all we know about time