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B Time Dilation, Interstellar Travel, and "The Forever War"

  1. Mar 4, 2017 #1
    Dear community,
    I have no formal education in physics, but I think I have understood some of the basic concepts and ideas in SRT. I am currently trying to find a solution to a problem that came up during my reading of Joe Haldeman's "The Forever War", a Sci-Fi novel that deals with the impact of time dilation on intertsellar travel. A summary can be found here: http://www.tor.com/2012/01/17/future-shock-the-forever-war-by-joe-haldeman/.

    Most people talking about Haldeman's novel focus on the impact of time dilation on returning soldiers: In order to reach the frontline and come back after the battle, they need to cover great distances at velocities close to c. The clocks on earth and the soldier's clocks are heavily de-synchronized due to time-dilation and the veterans return to a society that is barely recognizable for them, with all their families and friends dead.

    So far, so good. However, Haldeman mentions also a second consequence of time-dilation, but I am unsure if this consequence is legitimate. Here is the problem: We normally think of war as a process during which events occur sequentially and in which both parties evolve in reaction to each other. For instance, party A invents a new strategy/weapon and, as a reaction, party B develops a counter-strategy/adequate defensive weapon. Yet, Haldeman seems to imply that this conception of the sequentiality of events in the process of war is also undermined by time-dilation. Take, for instance, the following passage of Haldeman's book:

    "And as with any engagement, because of time dilation, there was no way to tell what sort of weaponry they [the aliens] would have. They might have never heard of the stasis field. Or they might be able to say a magic word and make us disappear."

    The point seems to be that, prior to an encounter with aliens, there is no way to know how sophisticated their weapons will be due to time-dilation. However, my problem is that I don't really see why time dilation should be relevant here: Assume that we have one common measure of time, for instance from the perspective of Planet Earth. A new technology, say the stasis field, is invented in the year t1. The aliens develop a counter weapon at some later point in time, t2. Now imagine a group of soldiers euqipped the stasis field that engages in a fight with aliens at some later point in time t3. Now, if this group of human soldiers wants to determine whether the aliens will be equipped with the counter-weapon against the stasis field, the only relevant piece of information is whether the aliens have left their base before or after t2. Time-dilation seems to be completely irrelevant here, because it only concerns how much objective time has passed for the aliens on their spaceship during their journey with velocities close to c. But time dilation doesn't mess up the order of events t1, t2 and t3, right? Or am I missing something here? Does the relativity of simultaneity play a role here?

    Many thanks for your help,
  2. jcsd
  3. Mar 4, 2017 #2


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    The way I read it, all that was meant was that information about anything takes time to travel. So you just don't know what tech will the Taurans have by the time you get there. Every piece of intel you get is always going to be outdated. Time dilation doesn't have anything to do with it, apart from messing with one's intuitions.
  4. Mar 4, 2017 #3


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    Also, if you're going to strike a base you don't know when the base last got upgraded. Since it takes you hundreds of years to reach your objective you may find that the base was closer to the bad guys' home than yours, and got upgraded with tech that's only fifty years old compared to your two hundred year old stuff.

    I don't think that's an effect of time dilation so much as the size of the battlefield. Time dilation just lets you survive the journey.
  5. Mar 4, 2017 #4
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