In or around 1974 an American physicist named Frank Tipler wrote that, based on what is understood about the relationship between time and the spacial dimensions, there was a method–in theory at least–for constructing a time machine.
Tipler said that if one constructed a cylinder out of the “stuff” of which black holes are constructed, and spun it very fast, the material would not collapse in on itself and form a singularity. Some physicists dispute this. Tipler also thought that one would not be crushed by entering the space in the center of the cylinder; I guess this would work on the same principal as the idea that a person at the center of the earth should be weightless as the mass–and, therefore, the gravitational pull–acting on him or her would be equal on all sides.
In any case, Tipler said that if such a whirling cylinder was constructed and the device spun at sufficient speed, it would contort or “tip” the four dimensional geomerty of the space which it occupied. (I am probably not explaining this very well, but then, I’m not a physicist.)
Suppose you take an ordinary cube and draw arrows along its sides, marking some as “height”, others as “length”, and others as “width”. If you then tip the cube on its side, two of the dimensions “switch places”; for instance, the arrow which is being “height” may now be pointing in the direction in which the “length” arrow was pointing a moment before.
In a somewhat analogous fashion, in Tipler’s model, time would “switch places” with one of the three spacial dimensions. This would mean that if one moved forward or backward inside the cylinder, it would mean you were moving through time. Once the cylinder stopped spinning and the four dimensions were restored to their normal orientation, the person who had moved about inside the cylinder would find he or she had moved forward or backward in time.
Which direction in the cylinder would be the future, and which would be the past? In H.G. Well’s novel The Time Machine the anonymous inventer says that he can make the parts of his machine rotate in either of two directions, but he won’t know which way pushes the machine forward in time and which pushes it backwards until he actually tries it out. It would seem to be the same for Tipler’s hypothetical time machine.
I have read that one limitation on the Tipler design is that it could not put a person farther into the past than when the cylinder was first built. This has to do with the idea that the cylinder itself does not travel in time except in the ordinary sense that everything and everybody “go” from their past existence to their future through the eternal present.
To address the question in the original OP, how would distance within the cylinder relate to time? Would moving one foot forward move a person a second ahead in the future, or a month, or a thousand years? Until the device is actually built and tested, no one seems to know.
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