Short story could be from 1960-1980s. In English.

Scientists are frantically working in a lab trying to develop a impenetrable force field. They have created one that does not use much power, but it is weak. (it might stop a fist from going through, but a bullet will go through.)

When you add more power to make it stronger, (i.e. able to stop a bullet) in a few minutes, it becomes unstable, and explosively fails. destroying anything near (maybe the room too) And the Math and equations say it is a fixed limit, so it will never work.

There is some sort of back story, aliens on a very high G world (like Jupiter), living under tremendous pressure, have been discovered, however they are very hostile. Fortunately, neither they nor humanity have any materials or alloys strong enough, that would allow them to leave their planet, due to the need to maintain internal pressure at the surface pressure as they rise in the atmosphere. i.e. their space ships would pop like balloons.

The scientists and leaders and diplomats are happy that the aliens would not be able to use force shields to escape their planet.

Meanwhile, someone else has been working on a force field (Engineer type?) and we are witnessing a discussion between him and someone else as they fly around in a spaceship who's exterior wall IS a force field.

How did he do it? He cranked the power up way high, so the field is so strong that nothing can penetrate it, Although light will pass through. But at that power level, the field will only last about .00001 second ( 1/100,000th of a second) So he has a relay operating at a millionth of a second, turning the power off and on, so the field does not have time to become unstable.

There was some punch line or pun as the last line. (Very Asimovian, So it might have been an Asimov story) but I dont remember what it was.

  • 2
    Hostile aliens with force fields on Jupiter sounds a lot like Asimov's "Victory Unintentional," though most of the rest, especially strobing the shield, doesn't fit. Perhaps a minor conflation?
    – DavidW
    Aug 29, 2022 at 11:25
  • 1
    I believe Victory Unintentional is the sequel to the title in the answer given. It's amusing. Aug 29, 2022 at 11:33

1 Answer 1


This is almost certainly Not Final!, a short story by Isaac Asimov.

The story follows your memory very accurately. It was thought that Earth would be safe from invasion from the inhabitants of Jupiter, but this new discovery, pulsing force-field on and off very rapidly means that force-field hulls would become practical.

From the wikipedia summary:

The ending line, "I imagine he'll be rather pleased" [with the applicability of the new technology], is ironic since the reader knows that this is precisely the reverse of what we know Orloff's (and the rest of the human race's) reaction to the news will be, since this implies that the Jovians will eventually be able to overcome the technical difficulties and emerge from their planet to wage war on humanity.

Per Wikipedia, this story was originally published in 1941. The 1942 story Victory Unintentional was a sequel to this story.

  • Yes, I thought it was an Asimov story, because of that unremembered final punch line or pun.
    – NJohnny
    Aug 30, 2022 at 0:06
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    The Wikipedia article says "Earth colonists on Ganymede, the largest satellite of Jupiter, have discovered the existence of intelligent life on the planet's surface." What does the story think the "surface" is? Aug 30, 2022 at 14:33
  • @AndyLester You can find out more about the surface, and its inhabitants, in the sequel "Victory Unintentional" Aug 30, 2022 at 19:30
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    One of the long standing problems with science fiction is that the underlying science keeps changing.
    – Zeiss Ikon
    Aug 31, 2022 at 15:48
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    @ZeissIkon, Asimov has an even better example: "Everest was successfully climbed in May 1953, and the story (although written in April 1953) did not appear in print until December of that year, meaning Asimov predicted Everest would never be conquered seven months after it was." — Everest (short story) - Wikipedia Aug 31, 2022 at 23:43

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