How can Andromeda collide with the Milky Way?

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SUMMARY

The discussion clarifies the misconception that all galaxies are moving away from each other, specifically addressing the future collision between the Andromeda Galaxy and the Milky Way. While galaxies billions of light years apart are receding due to the expansion of the universe, Andromeda, located only 2.5 million light years away, is actually moving towards the Milky Way due to its momentum and gravitational attraction. This local interaction contradicts the broader observation of universal expansion, emphasizing the importance of scale in cosmic dynamics.

PREREQUISITES
  • Understanding of cosmic expansion and Hubble's Law
  • Familiarity with gravitational forces between celestial bodies
  • Knowledge of galaxy distances and scales in astronomy
  • Basic concepts of momentum in astrophysics
NEXT STEPS
  • Research the implications of gravitational interactions between galaxies
  • Study the effects of cosmic expansion on local versus distant galaxies
  • Explore the future collision dynamics of Andromeda and the Milky Way
  • Learn about Hubble's Law and its application in modern astronomy
USEFUL FOR

Astronomy enthusiasts, astrophysicists, and students studying cosmic dynamics and galaxy interactions will benefit from this discussion.

Jur van Oerle
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If everything in the universe is moving away from everything else in the universe, how can Andromeda collide in the distant future with the Milky Way?
 
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Jur van Oerle said:
If everything in the universe is moving away from everything else in the universe...
Because this part isn't true. Locally, galaxies interact with each other.
 
So, what exactly do people mean when they say 'everything is moving away from everything else'?
 
Jur van Oerle said:
So, what exactly do people mean when they say 'everything is moving away from everything else'?
You have to keep in mind the scales. Galaxies at distances of billions of light years away are all moving away from each other at significant speeds due to the expansion of space. However the Andromeda Galaxy is only 2.5 million light years away. The magnitude of its speed away from us that is due to the expansion of space is far smaller than the magnitude of its speed toward us due to its existing momentum and gravitational attraction between the Milky Way and Andromeda.

If someone is telling you that everything includes local galaxies in this case, then they don't know what they're talking about.
 
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Alright, that makes sense.
I think it is my own ignorance, when I watch YouTube channels like Vsauce and MinutePhysics that is what I understand from it.
Thanks for clarifying!
 
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