# Whats in the space between any 2 galaxies?

## Main Question or Discussion Point

like is there any gravitational potential in the space between 2 galaxies due to galaxies mass.?how large is this gravitational potential is it significant..If possible please provide me a link where i can learn more about it..thanks in advance

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bcrowell
Staff Emeritus
Gold Member
In Newtonian mechanics, the gravitational potential can be anything you want it to be, since it's arbitrary up to an additive constant. It isn't a physical substance that exists in the space between two galaxies. If you want to estimate it relative to its value within a galaxy, just plug in to the usual equation, approximating the galaxy as a sphere.

In general relativity, there is not any way of defining a gravitational potential that applies to cosmological spacetimes. That means that if you try to generalize this to discuss things happening on cosmological scales, it won't work. The Newtonian approximation only works for your original question because you were describing something within a cluster of galaxies, which is much smaller than the Hubble scale.

In Newtonian mechanics, the gravitational potential can be anything you want it to be, since it's arbitrary up to an additive constant. It isn't a physical substance that exists in the space between two galaxies. If you want to estimate it relative to its value within a galaxy, just plug in to the usual equation, approximating the galaxy as a sphere.

In general relativity, there is not any way of defining a gravitational potential that applies to cosmological spacetimes. That means that if you try to generalize this to discuss things happening on cosmological scales, it won't work. The Newtonian approximation only works for your original question because you were describing something within a cluster of galaxies, which is much smaller than the Hubble scale.
I think this is a simple way to put the question in..Has anyone observed a gravitational effect of 1 galaxy on the other(if yes,this proves that force of gravity had been passed in the medium between)If no,it means force of gravity doesn't exist..Isn't it a simpler way of presenting question.?

mfb
Mentor
The existence of galaxy clusters itself is evidence that galaxies attract each other - otherwise, we would expect a nearly uniform distribution of galaxies everywhere. Galaxies (or parts of them) moving around other galaxies can be seen, too.

(if yes,this proves that force of gravity had been passed in the medium between)
That "medium" is an extremely good vacuum, even better than the vacuum inside the galaxies.

The existence of galaxy clusters itself is evidence that galaxies attract each other - otherwise, we would expect a nearly uniform distribution of galaxies everywhere. Galaxies (or parts of them) moving around other galaxies can be seen, too.
Since clusters of galaxies exist,ie gravitational attraction between any 2 galaxies have been recorded,are the velocities of both galaxies in match with there mutual gravitational pull without need of any dark matter concept????

As mentioned the medium between galaxies is perfect vacuum,Can we distinguish this vacuum with space,ie Is this vacuum(similar to spacetime) capable of being wrapped due to presence of Gravitational field flowing through it?

mfb
Mentor
are the velocities of both galaxies in match with there mutual gravitational pull without need of any dark matter concept????
No.

As mentioned the medium between galaxies is perfect vacuum
Not perfect, but extremely good.

Can we distinguish this vacuum with space,ie Is this vacuum(similar to spacetime) capable of being wrapped due to presence of Gravitational field flowing through it?
Vacuum is space with no matter at that place. I don't understand the question.