It’s sort of how if you hold a slinky on one end hanging down, then drop the slinky, bottom will not start falling until the top reaches it. In a sense, bottom will be hanging onto nothing. But of course that nothing is tension from the top of the slinky.
Comment on 8 Minutes
synapse1278@lemmy.world 1 month ago
If I understand that right, gravity also moves in space at the speed of light, therefore Earth will keep on orbiting for 8min around nothing?
abfarid@startrek.website 1 month ago
Tyfud@lemmy.world 5 weeks ago
That was an intuitive way to think about it, thank you.
DogWater@lemmy.world 1 month ago
That is correct as weird as it sounds
BigBenis@lemmy.world 1 month ago
The sun could be gone but its influence would remain. Kinda like getting out of a pool and looking back to see the waves on the surface that you caused.
vithigar@lemmy.ca 1 month ago
Kind of. The concept of simultaneity breaks down at distances where the speed of light matters. If we base our on what we currently observe and call “now” on the Sun the eight minute old state we currently observe then what does “now” on earth look like from the point of view of the Sun at that same moment? You can’t reconcile a single “now” for observers in both locations.
An alternative take which is also consistent with observable physics is that the speed of light is infinite but it’s causality itself that propagates at c.
Thinking in those terms also makes a number of relativistic effects more intuitive. You need infinite energy to reach the speed of light simply because it’s infinitely fast. Time dilates when moving because you’re encountering approaching causality earlier than you otherwise would have. Time “stops” for anything traveling at the speed of light because at infinite speed it just experiences literally everything in its line of travel at once and the concept of “after” becomes meaningless, encountering all future oncoming causality in a single instant.
This was a bit of a tangent but it’s something that has fascinated me for a long time.
Liz@midwest.social 1 month ago
I’m trying to understand how that reference frame works when you just just bounce a photon off a mirror and time how long it takes to come back? Like, light must have a non-infinite speed to the stationary observer, or it wouldn’t take time to traverse the distance.
FiskFisk33@startrek.website 5 weeks ago
thats the thing, thats from your reference frame. From the photons perspective time stands still and everything happens at once
vithigar@lemmy.ca 5 weeks ago
The observable effect is the same either way. If light is infinitely fast and causality propagates at c then it’s still going to take (distance to the mirror / c) for the fact that you turned on the light to reach the mirror, and that same amount of time for the fact that the light reflected to propagate back to you.
Liz@midwest.social 5 weeks ago
Those two things don’t square. If you’re moving relative to the mirror when your fire the photon, it would hit in a different place than if you were stationary. The photon can’t be moving infinitely fast in your reference frame for that to happen.
curiousaur@reddthat.com 5 weeks ago
Information can only travel at the speed of light.
tetris11@lemmy.ml 5 weeks ago
Yes, but bad news travels much faster, and the sun disappearing would be very bad news to at least some people.
insufferableninja@lemdro.id 5 weeks ago
bad gas travels fast in a small town