7 May 2004

I very much appreciated Freeman J. Dyson's practical, down-to-earth approach in reviewing Brian Greene's new book, The Fabric of the Cosmos: Space, Time, and the Texture of Reality (NYRB, 2/13/04). However, there is one point at which he, too, like the author, indulges in fantasy. Concerning the chapter, "Teleporters and Time Machines," Mr. Dyson debunks the notion of using a "portal" in "hyperspace" to travel into the past on the basis that it would require more than the total energy of the sun to hold such a portal open. Well and good, but he does not dispute the idea itself that "you can walk through the tunnel to emerge in your own past." As someone who has spent more than 15 years reassembling the documents of one man's past in order to write his biography (the spy, Walter G. Krivitsky), I am very much aware that some things may remain from the past, but the past itself is gone.

The word itself means that all things pass, not that they sit together somewhere in a protected location. Everything in every moment changes, whether in the microcosm of atomic particles or in the macrocosm of human history. To go back to a moment in time would require all the changes to reverse: exhaust from cars to return to the proper tail pipes and convert itself back into gas, rain to fly up to the clouds and the departed to arise from the dead. There is no scientific reason to believe in any such thing.

If the theorists of time travel propose another dimension, a parallel universe where every change in our dimension is duplicated, fixed step by step and preserved like a videotape ready for replay, they do not explain how a portal in hyperspace will insert us into the desired frame and then get the thing going. Obviously the whole thing is imaginary, and the physicists who write about it have less credibility than the writers of science fiction. I wish Mr. Dyson, a very sensible physicist, had said so.

Gary Kern
Grand Terrace, CA

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