Isn’t the rate of expansion in the universe increasing, and at an uneven rate at that? Meaning it could just as easily be an as of yet unknown natural phenomenon?
The expansion is supposed to be happening everywhere at the same time, not just at the edges.
For example, tomorrow there should be more space between the Sol and Alpha Centauri systems than there was yesterday.
Our present understanding suggests that ‘normal’ universal expansion should not (in and of itself) result in anything moving towards us.
Yep. Space is expanding everywhere at once, but the effect is minuscule at the scales we’re used to. And even at galactic scales the “speed” of expansion might seem like a lot to us, but it still isn’t enough to overcome the motion of objects. I looked up some rough numbers to give you an idea:
The rate of expansion of space is 73 km/s/Mpc. So for every 3.26 million light-years between you and a distant galaxy, the space between you and that galaxy is expanding by 73 kilometers per second.
Andromeda’s blue shift indicates it’s headed towards us at 110 km/s. And in my non-expert head I’m thinking that blueshifted light must have already been redshifted by the millions of years traveling through space to reach us. So the galaxy’s speed through space towards us when the light was emitted was considerably higher.
Andromeda is 2.5 Million light-years away, btw. So the cumulative distance of space between here and there is expanding at something like 73 km/s/Mpc * 2.5 Mly * 1Mpc/3.26Mly = 57 km/s.
But when talking about relativistic distances and speeds, basic terms regarding time and location don’t always make sense.
Yes, but not because of universal expansion really, they’re just headed in a direction that is going to intersect at some point, likely combining the two galaxies together. This’ll be so far in the future we’ll all be long dead though, on top of it being unlikely that anything is going to even come close to our solar system
It’s not just that, but it is unlikely that any star in our galaxy will collide with any star in Andromeda.
I think it’s easy to think of galaxies as individual things, like these nodes in the universe where all the stuff is stored. But galaxies are incredibly vast and incredibly empty.
The part that stuck with me is that if you made the Milky Way the size of the United States, our gigantic sun holding 99.86% of the matter in the solar system would be microscopic – the size of a red blood cell. And iirc, the planet earth would be all the way down to the size of a virus.
Isn’t the rate of expansion in the universe increasing, and at an uneven rate at that? Meaning it could just as easily be an as of yet unknown natural phenomenon?
The expansion is supposed to be happening everywhere at the same time, not just at the edges.
For example, tomorrow there should be more space between the Sol and Alpha Centauri systems than there was yesterday.
Our present understanding suggests that ‘normal’ universal expansion should not (in and of itself) result in anything moving towards us.
Aren’t the milky way and andromeda on a collision course with each other?
Milky way and Andromeda are close enough that expansion is too small to overpower gravity
Our local group is racing toward The Great Attractor but will never reach it as expansion is pulling it away faster than we’re falling toward it
Yep. Space is expanding everywhere at once, but the effect is minuscule at the scales we’re used to. And even at galactic scales the “speed” of expansion might seem like a lot to us, but it still isn’t enough to overcome the motion of objects. I looked up some rough numbers to give you an idea:
The rate of expansion of space is 73 km/s/Mpc. So for every 3.26 million light-years between you and a distant galaxy, the space between you and that galaxy is expanding by 73 kilometers per second.
Andromeda’s blue shift indicates it’s headed towards us at 110 km/s. And in my non-expert head I’m thinking that blueshifted light must have already been redshifted by the millions of years traveling through space to reach us. So the galaxy’s speed through space towards us when the light was emitted was considerably higher.
Andromeda is 2.5 Million light-years away, btw. So the cumulative distance of space between here and there is expanding at something like 73 km/s/Mpc * 2.5 Mly * 1Mpc/3.26Mly = 57 km/s.
But when talking about relativistic distances and speeds, basic terms regarding time and location don’t always make sense.
Yes, but not because of universal expansion really, they’re just headed in a direction that is going to intersect at some point, likely combining the two galaxies together. This’ll be so far in the future we’ll all be long dead though, on top of it being unlikely that anything is going to even come close to our solar system
That’s the other part I find fascinating; these two galaxies are gonna intersect, but our solar system probably won’t hit anything. That’s so gnar.
It’s not just that, but it is unlikely that any star in our galaxy will collide with any star in Andromeda.
I think it’s easy to think of galaxies as individual things, like these nodes in the universe where all the stuff is stored. But galaxies are incredibly vast and incredibly empty.
I love the video this guy did on the subject: https://www.youtube.com/watch?v=VsRmyY3Db1Y
The part that stuck with me is that if you made the Milky Way the size of the United States, our gigantic sun holding 99.86% of the matter in the solar system would be microscopic – the size of a red blood cell. And iirc, the planet earth would be all the way down to the size of a virus.
Galaxies are gravitationally bound, they do not expand in the same way as the universe.
Fair enough, I should have been thinking bigger.
Expansion red-shifts light.