I was watching a video on Youtube by Brian Greene, "the illusion of time."http://www.youtube.com/watch?v=j-u1aaltiq4

In that video, he introduces to me the idea of a "brane," or a slice of the universe at specific points in time. And then, he talks about an alien that is tens of billions of lightyears away from Earth. At that distance, he says that even the slowest movements can angle his brane, or slice of time, such that he is angling it towards the Earth's past (if the alien is moving away from us) or future (if the alien moves towards us).

So I got to wondering. What if you had a wormhole here on Earth, and walked through it to appear somewhere tens of billions of lightyears away from Earth. Depending on your speed of crossing through it, would you appear further into their past/future (depending on which direction you cross)?

And, if you had another wormhole there connecting back to the Earth, wouldn't you be able to travel back into Earth's past? Which would violate causality?

I know lots of people don't like the idea of wormholes, but it doesn't seem to have been scientifically ruled out. So, my question is, despite the fact that wormholes seem to possibly violate causality, why can't it be ruled out? Why is it still a theoretical possibility?

As a side question, if the past, present, and future exist at the same time -- what does that even mean?

(If anyone could edit my post, that would be great. My internet is giving me a horrible screen to work with. I have totally no ability to see my own tags -- look at this interface: https://dl.dropbox.com/u/106018191/phystackex.png)

(The image above is going to take a while to upload because of the slow internet, possibly a few hours at worst.)

  • 1
    $\begingroup$ Possible duplicate: Tachyonic antitelephone vs messaging through a wormhole $\endgroup$ Commented Feb 26, 2013 at 12:24
  • $\begingroup$ "Depending on your speed of crossing through it, would you appear further into their past/future (depending on which direction you cross)?" Further into their past/future than what? $\endgroup$
    – WillO
    Commented Jul 24, 2015 at 19:15

1 Answer 1


I am not sure that the alien can "aim" at our past, nor that we can "aim" at the future because I see time as a construct. We see two or more events occur in 3-space and we measure some interval between them. That is true. But, I have yet to hear anyone describe "naked time" (that is just time without allusion to some other event that defines it.)

As such, IMHO, time seems to be a measurement of entropy, or a comparison of two events rather than something you can pass through in forward or reverse. An alien may indeed see what we call our past, in exactly the same way that we see a supernova long after the blast wave has dissipated, and the dust has settled.... There is an interval between when the light leaves its point of origin and when it arrives here. It makes no sense to say that we are actually viewing "the past". It makes more sense to say that it is just our turn to see the picture. Looking back therefore, we would see the alien some billions of years from now as he WAS viewing us, we and he will always see the other's past but this is a function of distance not of some traversable "time line".

How does this factor in with wormholes? Simple. Lets say we find a way to fold space, or even tunnel through it then the person on the other end will still see our location as it "was" (although considerably closer to our actual moment than before ) and we will see things as they were in the same interval. We,and he will always,therefore "see the past" and leaping through the hole will only bring us to our shared present. Wormholes, then would just be shortcut through space and NOT the "time-machines" our sci-fi tout them to be.

But thats just my opinion on the matter


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