B Andromeda Collision VS Expansion

AI Thread Summary
The discussion centers on the apparent contradiction between the Milky Way's impending collision with Andromeda and the universe's overall expansion. While Andromeda is indeed on a collision course with the Milky Way, the universe's expansion means that galaxies farther away are moving apart from us. On smaller scales, such as the distance to Andromeda, local gravitational forces can dominate over the expansion, allowing galaxies to move towards each other. The timeline for intergalactic travel remains speculative and uncertain, as interstellar travel itself poses significant challenges. Overall, the conversation highlights the complexities of cosmic dynamics and the limitations of predicting future travel capabilities.
newrd
Messages
11
Reaction score
1
Hi Folks,
I've read that by the time mankind is ready for intergalactic travel, our nearest galactic neighbour will be too far to even travel to. But I've also read that Andromeda is on a collision course with the Milky Way. Which is correct? And if the universe is expanding and everything is moving apart, how come we're not moving away from Andromeda?
Thanks!
 
Space news on Phys.org
newrd said:
I've read that by the time mankind is ready for intergalactic travel, our nearest galactic neighbour will be too far to even travel to.
Where did you read that? Quoting sources helps us help you - if you've got something wrong, we can see if it's because you've misunderstood something, or if the author of what you read misrepresented something.

I tend to suspect whatever you were reading was a bit fanciful. "When we'll be ready for intergalactic travel" simply isn't something we can know. But anyway, nearby galaxies aren't moving that fast on the kind of time scale we're likely to be around.
newrd said:
But I've also read that Andromeda is on a collision course with the Milky Way.
Andromeda is certainly coming towards us.
newrd said:
And if the universe is expanding and everything is moving apart, how come we're not moving away from Andromeda?
On small scales (less than a hundred million light years), plenty of stuff is moving in all directions relative to us. It's only beyond that kind of distance that you see the overall picture of "everything moving away from us". This is, basically, because the "speed" with which things recede from us grows with distance. At low distances, random velocities of the galaxies can be larger than the average expansion motion.
 
  • Like
Likes newrd
newrd said:
Hi Folks,
I've read that by the time mankind is ready for intergalactic travel, our nearest galactic neighbour will be too far to even travel to. But I've also read that Andromeda is on a collision course with the Milky Way. Which is correct? And if the universe is expanding and everything is moving apart, how come we're not moving away from Andromeda?
Thanks!
Honestly, there's just no possible way to make any statement about when intergalactic travel may or may not happen.

Interstellar travel looks to be so unimaginably difficult that it might well be impossible. We have no idea when interstellar travel might happen (if ever), let alone intergalactic travel. You just can't put a timeline on something when you have no idea how it can ever occur.
 
Thanks guys, Ibix your answer that its on a small scale explained it perfectly, cheers!
 

Thread 'Matter density right after the decoupling'

https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
View full post »

Thread 'Rutgers finds a transparent Einstein Cross - apparently a dark matter "halo".'

The formal paper is here. The Rutgers University news has published a story about an image being closely examined at their New Brunswick campus. Here is an excerpt: Computer modeling of the gravitational lens by Keeton and Eid showed that the four visible foreground galaxies causing the gravitational bending couldn’t explain the details of the five-image pattern. Only with the addition of a large, invisible mass, in this case, a dark matter halo, could the model match the observations...
View full post »

Thread 'Big Bang and Infinite Universe'

Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
View full post »

Similar threads

I Collision between the Milky Way and Andromeda and Redshift
Replies
6
Views
2K
I Andromeda vs. Milky Way galaxies
Replies
30
Views
4K
B Galaxy Collisions & Expansion: What's Going On?
Replies
3
Views
1K
I Collision of Milky Way and Andromeda....?
Replies
17
Views
4K
I Interstellar Travel vs Universe Expansion: Is Andromeda Reachable?
Replies
1
Views
1K
B Trying to understand the Andromeda-Milky Way collision
Replies
9
Views
3K
I Inflationary vs deflationary phase of Big Bang
Replies
10
Views
3K
I How Does Space Expansion Affect the Velocity of Galaxies?
2
Replies
65
Views
6K
Will the Milky Way and Andromeda Collide Despite the Expanding Universe?
Replies
2
Views
2K
I How can Andromeda collide with the Milky Way?
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top