April 27, 2008

• A Journey through Time and Space

  I saw The Forbidden Kingdom last night.  It was a fun movie.  And despite it being basically a pure action movie, it also got me thinking about something deeper.  Namely, the nature of time and the universe itself.  Not to give anything away, but the movie shares something in common with Back to the Future: the present is only possible because of events that the main character changed in the past.

  [warning: the following may hurt your brain, proceed at your own risk]

  Now, the most common theory of time travel you hear about is that the time traveller is actually traveling into an alternate universe.  Thus, a paradox wouldn’t arise if you, say, travelled back into the past and caused the death of your ancestors.  You would be able to change the future through your actions, even in a way that would prevent you from being born in that future, because you would actually have been born into a different future (in the universe you started from).  The problem with this idea is that there is no real explanation of how time travel would actually work.  How would you make that jump to an alternate universe?  But there is another way. 

  What if the passage of time were an illusion?  Physicists consider time to be a dimension just like the three axes of the spatial dimensions (hence the notion of spacetime).  It is possible that when the universe began, all of time began with it.  The past, present, and future would all exist simultaneously.  Our perception that time only moves forward could be just an illusion, because that is all our minds are capable of perceiving.

  This idea is comforting in one sense, because it bestows upon us a sort of immortality.  Even after we die, even if the universe collapses back upon itself, our entire lives will still exist as a timeless pattern through four dimensions.  But this idea is discomforting in another sense… it implies a lack of free will.  There really is no need to worry about that, however.  Whether we really have free will or not doesn’t change anything in our lives.  Wether we were pre-destined to make a decision or “chose” to make it, we wouldn’t be able to tell the difference.

  So what does this all have to do with time travel?  Well, consider the universe.  It exists in three dimensions.  As a three-dimensional region, it has a shape to it.  The general shape could be a sphere, or it could be something more complex.  To see where I’m going with this, consider a flat (i.e. two-dimensional) piece of paper.  Of course, a piece of paper isn’t really two-dimensional since no matter how thin it is, it is still made up of three-dimensional partices, but bear with me. 

  If you were to draw two dots on opposite end of the paper, the shortest path between them would be a line running across the length of it.  However, if you took the paper and curved it back on itself in the third dimension, you could make the two dots touch.  Although the shortest path in the context of the two-dimensional surface of the paper is still that long line, the shortest path when considering this new third dimension is now reduced to zero. 

  If you were a two-dimensional being living within the surface of the paper, you would be unaware of this new path.  You wouldn’t be able to see into the third dimension, just as we are unable to see into the fourth dimension (i.e. time).  We only perceive our three-dimensional surroundings in the context of one point in time, wherever (or whenever, you could say) we happen to be.  Similarly, the 2-d being would only perceive its two-dimensional surroundings wherever it happens to be in 3-d space. 

  Now, if our 2-d being was somehow able to move past the “edges” of its 2-d universe, it would be able to travel between the faraway spots on the paper instantaneously.  Taking this idea to the third dimension, we have the concept of a wormhole.  If our 3-d space curves back onto itself in the fourth dimension, there can be two points in space that meet and thus could be instantaneously travelled between if we could only break through that “edge.”  Physicists believe that the incredible mass and density of black holes might create such large curvatures in space-time that a wormhole may be formed.

  Now, finally, we can see how all of this applies to time travel.  We can go one step further, and consider that four-dimensional space-time may curve back onto itself in the fifth dimension, if such a dimension exists.  Voilà!  We now have a wormhole through space and time (e.g. ‘the gate of no gate’ from The Forbidden Kingdom).

  edit: I recommend this cool animation as a way of visualizing higher dimensions.  It goes over ten dimensions, which interestingly coincides with the predictions of competing string theory models that there are either 10, 11, or 26 total dimensions.  Of course, string theory is still highly speculative at this point, as are the animation’s ideas about higher dimensions.

  • 12:49 am
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