# Gravity and Dark Matter

## Main Question or Discussion Point

Hi,

Many astronomers believe that there is no center to the universe.
So where ever you go, you would approximately see same amount of matter (stars galaxies etc) around you. So we can assume that there wont be net
gravitational effect on any body at all the places in the universe (neglecting local gravitation like the one between Earth and Sun).

1) So why always dark matter is said to be of overcoming gravity when there is no net gravity on any object ?

2) If the universe came from Big Bang then shouldn't it have a boundary ?
Boundary came to my mind because a Bang will always push the matter outwards and my visualization clearly shows a boundary to the expansion of matter from a single point ?

3) Many believe that we are in 3D space on a 4D platform. How can we visualize this ?. I can easily vizualize time as fourth dimension because
gravity wraps space but I cant visualize a directional fourth dimension like

Thanks,
talksabcd

Related Astronomy and Astrophysics News on Phys.org
mathman
1) So why always dark matter is said to be of overcoming gravity when there is no net gravity on any object ?
The stars in each galaxy are revolving around the center of the galaxy. Their speed of revolution is too high to be held in place by the baryonic matter of the galaxy. Dark matter is needed to give enough mass for the stars to stay in orbit and not fly off. Astronomers have also noted the same problem in describing clusters of galaxies.

Now I have realized that I have put 'Dark Matter' instead of 'Dark Energy'.
Its a typo.. It should be Dark energy.

Can someone answer the above questions ?. Please replace Dark Matter with Dark Energy in the above questions listed in the 1st
post of this trail.

Thank You
talksabcd (talks basics)

Last edited:
mathman