When the space is expanding at an accelerating rate and the galaxies, at the edge of the visible Universe, are entering into invisible universe even at greater speed than the speed of light, so is not it obvious that at some distant time all the galaxies would be so distant, scattered and worn out and the energy density of the Universe would be so thin and cold so that new stars cannot form and the galaxies would lose their mass, ultimately galaxies would no longer be gravitationally bound but surrender to the dark energy and dark energy would rule, further expansion dilute the baryonic Universe so thin so that the Universe would face a freezing state and gravity would exist only with the black holes existing then, so what can happen after that needs further thoughts.
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Dark energy was first revealed observationally by examining the light from ultra-distant signals like supernovae. With measurements of both distance and redshift, scientists concluded that the Universe couldn't just be made of matter and radiation, but needed a new form of energy that would change the fate of our Universe. Here's why, more than 20 years later, it's still the biggest unsolved problem of them all.
The effective mass of dark energy is <0 and its gravitating mass is more than matter mass that results a strong effect at large scale as such, the cosmological expansion accelerate.
Antigravity exerted by dark energy affects a cosmic structure strongly at large scale. The dark energy background produces antigravity which is stronger than the matter gravity in the present Universe as a whole. This makes the cosmological expansion accelerated.
The cosmic antigravity can be stronger than gravity globally and also locally in the scale between 3.26 lightyear and 3.262×107 lightyear. The local weakfield dynamical effects of dark energy adequately described in term of Newtonian mechanics, and its effective gravitating density is negative, producing antigravity.
Gravity dominates at distances, while antigravity is stronger than gravity, therefore, a gravitationally bound system with its mass can exist only inside the zero gravity sphere of its radius [circumference of a sphere where, (antigravity - gravity = 0)], while dark energy is effective in the outer region of the domination of gravitating mass and practically have no effect within the strong domination of gravitating mass.
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The ultimate fate of an expanding universe depends on the matter density ΩM and the dark energy density ΩΛ (Ref. the Image "Friedmann universes" below)
Theories about the end of the universe:
• Big Freeze or Heat Death
• Big Rip
• Big Crunch
• Big Bounce
• Big Slurp
• Cosmic uncertainty
Friedmann's universe
