You know how the sound of things moving from you changes? Towards you the pitch is higher, away from you it is lower. The same happens with light. We know how some things should look like, so if they are more toward red or blue, we know their speed relative to us. Blue = towards us = “we will collide” (you also do not collide with every car with a siren where you hear that effect).
Comment on Uh oh lol
unknownuserunknownlocation@kbin.earth 3 months ago
ELI5?
Eheran@lemmy.world 3 months ago
unknownuserunknownlocation@kbin.earth 3 months ago
Great explanation, thanks!
ThermonuclearEgg@hexbear.net 3 months ago
Just like how a siren changes pitch when it’s coming from a vehicle passing by due to the Doppler effect, the same thing happens to moving light sources due to relativistic effects.
Usually astronomical objects are redshifting because the universe is expanding and are thus receding away from Earth’s frame of reference. Most of them are forever unreachable even if we could travel at the speed of light.
Something blueshifting means it’s coming closer from Earth’s frame of reference. In some cases, this could result in the galaxy colliding with ours.
IrateAnteater@sh.itjust.works 3 months ago
If something is red shifting, it’s accelerating away from you. If something is blue shifting, it’s accelerating towards you. An entire galaxy accelerating towards you is somewhat concerning.
OrganicMustard@lemmy.world 3 months ago
Redshift comes from relative velocity (and other effects), not acceleration. Andromeda’s light is blueshifted as it’s moving towards us, but it’s not accelerating.
Cethin@lemmy.zip 3 months ago
I was going to argue with this too, but the meme says blueshifting, not blueshifted. They’re right, but mostly because the meme is probably written poorly. Maybe they meant it’s accelerating toward us though. Idk.
yaroto98@lemmy.world 3 months ago
On top of that, we’ve found that basically everything is redshifting as the universe expands. So to see a blueshifting galaxy would mean something potentially unnatural.
wewbull@feddit.uk 3 months ago
Right, but I don’t get why this thread is full of people talking about collisions. Even if it was moving at the speed of light (it’s not) it’s still billions of years away.
It would just prove our theory of universe inflation to be incorrect.