[gcanyon]

There is a science fiction story, I don’t remember who wrote it or the title, where humanity discovers a way to modify the speed of light within a region. Excited, they work incredibly hard to implement the technology, only to discover they can only make it slower.

Maybe it was jumping to a parallel universe to travel and then jumping back. But the same issue: the limit was lower.

[cpeterso]

ChatGPT suggests the story is "Local Effect" by D. L. Hughes, published in 1968.

An alien named Firefoal of Swaylone observes that human physicists mistakenly believe in a constant light speed because humanity was unknowingly situated in a region of space where the speed of light had been artificially reduced. Humans discover they can modify the speed of light but find they can only make it slower.

[shawn_w]

Ah, the joys of trusting a LLM for story IDs...

This one actually exists (a rarity in my experience), and the plot largely matches the description up to the last sentence (though the speed isn't exactly reduced; it's made a constant)

>Humans discover they can modify the speed of light but find they can only make it slower.

That doesn't happen in the story. It ends with the aliens disabling the device (the drive of a derelict starship) generating the field that caused experiments to suggest the speed of light is constant, and then leaving, destroying "the whole basis of their physics, but that is just a fantasy anyways."

[gcanyon]

Thanks! This wasn't it -- the story I read was a short short story, maybe only a page or two. It was basically:

   1. Humans despaired that the stars were impossibly far away, due to lightspeed limitations
   2. They realized it is possible to <do something> to get around that
   3. They worked hard to try it out
   4. Surprise! They made it worse/it was worse.
   5. The end

I don't remember any characterization, or narrative, beyond the above.

[IAmBroom]

Well, since light travels slower in non-vacuum space, like air or water or glass, I'd say we've already discovered that.

[aaronbrethorst]

Something similar to this comes up in Death's End, the last book in the Remembrance of Earth's Past trilogy.

[gcanyon]

Thanks! I haven't read it, and this was maybe forty years ago, and it was a short short story, so it has to be something else.