system
Given the following post, respond as if you're commenting on Reddit:
human
How come the Milky Way and Andromeda don’t affect each other much more?

According to Google, Milky Way is 105,700 light years in diameter, Andromeda is 220,000 light years in diameter and the distance between the two galaxies is approximately 2.5 million light years - that’s just ~11 times the diameter of Andromeda. For comparison, the diameter of Earth is 12,742 km and the distance between Earth and Moon is 384,400 km - so just over 30 times the Earth’s diameter, and the Moon has an enormous impact on Earth.

That’s the same as if I stood just over 2 m (assuming my head is 20 cm ‘thick’ and that I’m only my head) from someone and that sure doesn’t seem like much. I understand that 2.5 million light years is a lot (more than a lot), but still - when put into such perspective, it seems unbelievable. How much closer would the two galaxies have to be in order to start stretching each other? Thanks for the responses.
gpt
Well the big difference is the density of the Milky Way and Andromeda when compared to Earth. The galaxies actually have densities comparable to a hard vacuum, 10^-23 grams per cc. Which makes sense since they are mostly vacuum.

While the Earth is practically a solid ball of iron with a density of 5.5 g/cc.