norbertus t1_j1gmtwa wrote
Reply to comment by bendvis in Did you know it will still take 46 billion years to cross the universe at the speed of light? 65 mph = 4.8 * 10^17 years! by NotAndroid545
The speed of light represents a limit for how fast local interactions can be propagated in space-time, or, how quickly an inertial body can traverse a reference frame.
Einstein's relativity is still within the classical Newtonian framework governed by locality, causality, and determinism, but Einstein's major insight was that Newtonian "absolute space" does not exist.
https://plato.stanford.edu/entries/newton-stm/
In relativity, it does not matter if space is expanding when we are trying to reason about things like how fast a distance can be traversed. In relativity, speeds are not additive and subtractive the way speed works in the grade school math problem about two boats on a river.
https://www.onlinemath4all.com/boats-and-streams.html
Einstein formulated general relativity in the wake of a major failed experiment, probably the most important failed experiment of the last 150 years.
The Michelson-Morley experiment was trying to measure the speed of light relative to the rotation of the earth by measuring its differential at a given point on the earth rotating either into or away from light streaming out from the sun
https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
It turns out there is no difference in the measurable speed of light, which paved the way for relativity.
As it turns out, relativity is what makes GPS work
https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html
And 1905 was the magic year Einstein invented relativity and quantum mechanics (by defining "the quanta")
https://en.wikipedia.org/wiki/Annus_mirabilis_papers
edit: typo
bendvis t1_j1go9t0 wrote
I mean… I appreciate the long-winded explanation of how light moves through space, but none of it covers how space itself expands and how that can make distant objects move away from us at faster than light.
Again, the galaxies are not moving through space faster than light, but the distance between us and them is growing faster than light-speed because of the expansion of space.
They are effectively moving away faster than light. If you magically took off toward one today at light speed, you’d never reach it.
norbertus t1_j1gojn0 wrote
>long-winded explanation
A joke on the "Aether wind?"
> but the distance between us and them is growing
Missed that, you're quite right there, space itself is expanding.
belugwhal t1_j1gpwkb wrote
>As it turns out, relativity is what makes GPS work
Err...I think you mean relativity must be taken into account for GPS to work. If relativity wasn't a thing, GPS would still work (it would just be easier).
norbertus t1_j1gr1b7 wrote
>relativity must be taken into account for GPS to work. If relativity wasn't a thing, GPS would still work
That statement is logically inconsistent.
The paper I cited above
https://www.astronomy.ohio-state.edu/pogge.1/Ast162/Unit5/gps.html
describes the role of relativistic "time dilation" in the functioning of the GPS coordinate system
https://en.wikipedia.org/wiki/Time_dilation
relative speed and the relative strength of a gravitational field each affect the local measurement of "time."
In the case of a GPS satellite, which is out in space and farther from us (its users -- and the earth as a gravitational well) and moving faster relative to us (because they need to stay in orbit and constantly fall over the horizon while we are stationary on the ground), these relativistic effects work at cross-purposes.
GPS uses not triangulation to determine a location, but tri-lateration with a fourth satellite to account for timing delays due to relativity.
The paper I cited notes " If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day"
belugwhal t1_j1gtk7j wrote
Umm.. what I said agrees with this. Dude... You wrote all that for nothing. Maybe reread my comment.
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