How can dark energy be a repulsive force when expanding the universe...?

Question

but is an attracting force when it is holding our galaxy together?

I believe scientists think our galaxy is 2% matter, 23% dark matter and 75% dark energy

Answer 1

You are confusing dark ENERGY with dark MATTER. Dark MATTER is matter with gravity that we cannot see. Dark ENERGY is an unknown force assumed to be causing the acceleration of the expansion of the universe.

Answer 2

Camp's right. Dark energy is the hypothesized, mysterious energy that seems to be causing the acceleration of the expansion of the universe, like a permanent repulsive force. We have never witnessed or proven the existence of dark energy, scientists are just using the theory that there is this unexplained "dark energy" that is causing the clear accelerating expansion.

Dark matter, however, is defined as all matter that does not emit light (thus that it is very difficult for us to discover outside our own solar system). In fact, your computer is dark matter, as well as your chair, your car, you, Earth, and all other planets. Other forms of dark matter include asteroids, white dwarfs, brown dwarfs (all of these so far are MACHOs: MAssive Compact Halo Objects... see link below for description), and WIMPs (Weakly-Interacting Massive Particles), which are things like neutrinos, and matter that only interacts with gravitational force and the weak force.

We have proven the existence of dark matter by measuring the orbital velocities of stars around the center of their respective galaxies... the stars on the outer edges are orbiting too fast if the only mass in the galaxy were the stars that we can see, therefore there must be a lot of dark matter in every galaxy (I believe your ratio holds true) that holds galaxies together.

Hope that helps.

Answer 3

I think you got it backwards