The Constants of Nature by John Barrow

Author:John Barrow [Barrow, John D.]
Language: eng
Format: epub
ISBN: 978-0-307-55535-9
Publisher: Knopf Doubleday Publishing Group
Published: 2002-04-29T04:00:00+00:00

Figure 8.9 (a) A stack of slices of space taken at different times; (b) a block of spacetime made from all the slices of space. This block could be sliced up in many ways that differ from the slicing chosen in (a).

Figure 8.10 March in a straight line and it is clear who is in front of whom. March in a circle and everyone is in front and behind everyone else.

If this type of backward time travel is an escape from the thermodynamic end of the Universe and our Universe appears to be heading for just such a thermodynamic erasure of all possibilities for processing information then maybe super-advanced beings in our future are already travelling backwards into the benign cosmic environment that the present-day universe affords. Many arguments have been put forward to argue against the arrival of tourists from the future but they have a rather anthropocentric purpose in mind. It has been argued that the great events in Earth's history (events around Bethlehem in 4 BC, the Crucifixion, the death of Socrates, and so on) would become magnets for backward time travellers, creating a huge cumulative audience that was evidently not present. But there is no reason why escapees from the heat death of the Universe should visit us, let alone cause crowd control problems at critical points in our history.

My favourite argument44 against backward time travel is a financial one. It appeals to the fact that interest rates in the money markets are non-zero to argue that neither forward nor backward time travellers are taking advantage of their position to make a killing on the financial markets. If they were able to invest in the past on the basis of knowing where markets would increase in the future then the long-term result would be to drive interest rates to zero. Again, it is easy to avoid allowing this argument to rule out time travellers escaping the heat death of the Universe. One suspects, however, that financial investments might be the least of their concerns.

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