Time Travel by Brian Clegg

Author:Brian Clegg
Language: eng
Format: epub
Publisher: Johns Hopkins University Press
Published: 2021-09-15T00:00:00+00:00

Pre-65 million years before present

Seeing dinosaurs in the wild

Circa AD 30

The crucifixion of Jesus

22 November 1963

Assassination of John F. Kennedy

9 November 1989

Fall of the Berlin Wall

11 September 2001

Attack on the Twin Towers, New York

The idea of time-travelling tourists continues to provide entertainment, if not practical visitations. In February 2012, a blue plaque, similar to those put up by the UK’s heritage industry, appeared on a building in Golden Square in London. It read ‘Jacob von Hogflume, 1864–1909, Inventor of time travel, lived here in 2189’. Though the logic of the wording is a little misguided, it’s a shame that the plaque, devised by Dave Askwith and Alex Normanton, didn’t last long before being taken down.

In reality, there’s a fundamental reason – one that Stephen Hawking should have realized in the first place (he later retracted his question). A time machine based on general relativity provides a gateway to a location where time slows down, taking us into the past – but such a gateway can never reach a point further in the past than when the time machine was first set up. There is no mechanism to travel earlier than when that link into the past was constructed. This means that if we want to echo science fiction and travel to see distant historical events or visit the dinosaurs, we have to hope some alien civilization started a time machine operating a long time ago – an unlikely prospect at best.

Such limitations apply to both data and people travelling through time, but there are extra ways information can move into the past that aren’t available to human beings.

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