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Comment by creata | Hacker News Reader

I've always wondered - if special and general relativity weren't known, could the GPS engineers have just measured the error and empirically accounted for it? I don't know relativity or GPS or engineering well enough to answer.

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Yes, the clock slippage is a constant factor, entirely predictable. If made public it would probably have catalyzed the discovery of special relativity soon afterwards, but then people would’ve been super confused because its predictions still wouldn’t match the observations and indeed would widen the discrepancy rather than narrowing it!

Yeah, absolutely. You'd be surprised how much high-precision engineering absolutely relies on "this but you have to mill a tiny amount off the end because if you do the maths it comes out ever so slightly too big, and then adjust on test".

It's possible, but it seems more likely that the first tests would have shown "weird timing errors we couldnt diagnose" and then the project never got a follow up.

For something so militarily useful? When the Soviet Union was still seen as a threat to the US? When it was already so expensive anyway? I guess it's possible, but it's hard to believe they'd just give up like that.

The problem with "it's hard to believe" is that this is an area where I'm not even sure how to effectively estimate the counterposition, I've seen things that I thought were interesting get cancelled or have no follow up all the time, and it makes sense, no idea if it will matter, or even work, and even if it does, how much will it cost to realise any value?

Who knows how often really impactful tech is gated behind some non-obvious thing which we never follow up on.

I mean Douglas Engelbart basically bet his entire career behind the Mother of All Demos[0], if it had flopped, modern computing as we know it would be fundamentally different, same with Hiroo Kinoshita and Extreme Ultraviolet Lithography[1][2], we just would have had Moore's law falling off a cliff.

-[0]: [The Mother of All Demos, presented by Douglas Engelbart (1968)](https://www.youtube.com/watch?v=yJDv-zdhzMY)

-[1]: https://spie.org/news/photonics-focus/mayjune-2023/developin...

-[2]: [The Closest Thing We Have to Alien Technology by Veritasium](https://www.youtube.com/watch?v=MiUHjLxm3V0)

A modern-time retrograde of Mercury.

Of course, the good-old-fashioned retrograde of Mercury would still be a real puzzler in that timeline, too.

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