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The protagonist is a scientist attempting time travel. A project has been completed to construct an enormous rod in space. When the rod is spun up to near light speed, a space ship will be able to dive near it and travel back in time. The scientist reflects on the idea that time travel seems to violate laws of nature. As the space ship begins its maneuver, the Sun goes supernova, destroying the solar system (and the rod) thereby preventing a paradox from occurring.

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    FWIW, this device is called a Tipler cylinder. "[...] results have shown that a Tipler cylinder could only allow time travel if its length were infinite or with the existence of negative energy. [...] Niven's story borrows its title from Tipler's paper". BTW, if we can make exotic matter with negative energy, i.e., negative mass, we could also use it to stabilize wormholes and warp drives.
    – PM 2Ring
    Commented Jun 22, 2020 at 8:22
  • what i liked the most about the Guy Pearce-starring Time Machine is the way the universe prevented paradox by, in various ways, having the death of his fiance always result. It was as if the universe were creative, coming up with different stories, all with the same ending -- sort of seeing the mind of the Creator. (Besides that there was much I did not like about the Time Machine with Guy Pearce. Much.)
    – releseabe
    Commented Jun 22, 2020 at 9:56

1 Answer 1

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"Rotating Cylinders and the Possibility of Global Causality Violation", a short story by Larry Niven.

A project has been completed to construct an enormous rod in space. When the rod is spun up to near light speed, a space ship will be able to dive near it and travel back in time.

"Take a massive cylinder," Quifting said patiently, "and put a rapid spin on it. I can plot a curve for a spacecraft that will bring it around the cylinder and back to its starting point in space and time."

As the space ship begins its maneuver, the Sun goes supernova, destroying the solar system (and the rod) thereby preventing a paradox from occurring.

Violet-white light blazed through the windows behind the mathematician making of him a sharp-edged black shadow. Quifting ran forward and smashed into the holograph wall. His eyes were shut tight, his clothes were afire. "What is it?" he screamed. "What's happening?"

"I imagine the sun has gone nova," said the emperor.

The wall went black.

A dulcet voice spoke. "Director Chilbreez on the line."

"Never mind." There was no point now in telling the director how to get an enemy to build a time machine. The universe protected its cause-and-effect basis with humorless ferocity. Director Chilbreez was doomed; and perhaps Quifting had ended the war after all. The emperor went to the window. A churning aurora blazed bright as day, and grew brighter still.

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    Note that the sun goes nova, not supernova. Sol is too small to supernova, and Niven is too good of an author to make a mistake like that. (Yes he makes other mistakes, as everyone does, but he always researched his topics well). Commented Jun 22, 2020 at 16:57
  • @PaulSinclair Lacking a binary companion, Sol can't go nova either.
    – Schwern
    Commented Jun 22, 2020 at 17:22
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    @PaulSinclair Sol-like stars don't "go nova" either, and while Sol is mentioned, it's not stated that Sol is the star in question. In fact, it's mentioned as the site of a previous attempt, that was resolved without any astronomical events. Commented Jun 22, 2020 at 17:39

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