Einstein's theory of relativity, critical for GPS, seen in distant stars | Hacker News Reader

Einstein's theory of relativity, critical for GPS, seen in distant stars

phys.org

44 pointsdnetesn11 comments

What a stupid headline.

I was just about to comment the same thing. It is the worst!

Or maybe not: How does this connect with General Relativity and GPS? As predicted by Einstein's theory, clocks under the force of gravity run at a slower rate than clocks viewed from a distant region experiencing weaker gravity. This means that clocks on Earth observed from orbiting satellites run at a slower rate. To have the high precision needed for GPS, this effect needs to be taken into account or there will be small differences in time that would add up quickly, calculating inaccurate positions.

This is one of the few cases where I went from thinking the headline was clickbait to thinking it was an excellent way to draw a connection between high-level science and aspects of the world that lay people can easily connect with. It would be nice if the author used the section you quoted for something like a "see TL;DR below", but anyone who fully reads the article should get the connection at least.

I was already aware of why GPS is usually mentioned in context of GR (it is like one of the few cases where we need to make GR corrections), but still think it's a dumb headline. Time changing due to gravity is sort of the foundational insight of GR. It's true that GPS needs to take into account GR effects... that is essentially where the connection between GPS and these stars starts and ends.

GR is all around us.

> GR is all around us.

...and it's critical for GPS accuracy, right?

You're being needlessly contrarían, and generating noise in an otherwise interesting discussion.

TLDR: Gravitational redshift was detected by Chandra from a close orbiting star and neutron star system. The x-ray emissions were frequency shifted more than the relative motion would account for, so the shift was attributed to gravitational effects.

Ahh finally we can have GPS around other stars.

Off-topic, but has anyone ever taken the time to dive into:

http://alternativephysics.org/book/GPSmythology.htm

...which claims that the "standard" account of GPS needing relativistic adjustments is not correct. If nothing else, the author seems to have perfected the "crank" writing form.

I agree that it looks like crank writing.

The enthusiasm shown for labelling their work as "alternative physics" is a clear tell.

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