Please read Comparison of smallest thing with that of universe, Speed through the Universe, How are stars formed?, Stars are like factories, Universe has unchanging Laws, We Exist because of Imperfection and  Why we cannot see big bang?  before or in conjunction with this article.

How Will The Universe End?

Four Ways To Destroy The Universe

Let’s talk something about the fate of our universe. There are various theories on this like Big Crunch in which the matter, space and time in the universe collapse into a dimensionless singularity same as it was before the Big Bang. The second theory is Big Rip in which all expansion of the universe will cause all forms of matter to go far from each other and then cause them to rip apart. The third is Big Freeze in which stars are expected to form normally for a trillion more years, but ultimately the supply of gas needed for star formation will be depleted. As existing stars run out of fuel and stop shining, the universe will slowly grow darker. Ultimately black holes will dominate the universe, which themselves will disappear over time as they emit Hawking radiation. Fourth and last major theory regarding universe’s fate is the Big Slurp. It’s a new theory postulated after Higgs bosons discovery in LHC Large Hadron Collider by Cern. In this model, if the Higgs Boson particle weighs in at a certain mass, it could indicate that this space this vacuum of our universe may be inherently unstable, perhaps existing in a perpetual metastable state. This kind of a vacuum metastability event could happen at virtually any moment, anywhere in our universe. The bubble could pop over and start expanding at light-speed until it swallowed us entirely.

Universe Fate Depends On Its Shape

The current consensus of the most scientific community is that the ultimate fate of the universe depends on its overall shape and how much density of matter it has either enough to halt expansion or less than that. Critical density is the average density of matter required for the Universe to just halt its expansion. To date, the critical density is estimated to be approximately six atoms of hydrogen per cubic meter, whereas the average density of ordinary matter that we can see in the Universe is believed to be only 0.2–0.25 atoms per cubic meter.

End of our Universe

We can determine the end of our universe. The fate of the universe is determined by a struggle between the expansion and the pull of gravity. Let me give you a tennis ball example when you throw a ball in the air it goes up and then comes down because of negative, positive energies. In ball’s case, negative energy is gravity which pulls and +ve is kinetic energy which speeds it up. The ball will escape in outer space and will never come back on the ground if +ve energy is greater. So in simple, if the total energy is bigger than zero it escape if it is less than zero it returns. So for the universe, the negative piece is all matter and dark matter, and the positive piece is the speed of expansion which Hubble tells us. So -negative is “Gravity,” and +ve is “Expansion”. Then if G/Expansion>1 universe will collapse and if G/E<1 expand forever. This rate of expansion is expressed by the Hubble Constant, while the strength of gravity depends on the density of the matter in the universe.

Will the Universe Slow Down Or Expand Forever?

Now it’s clear that the contracting force is because of matter and its gravity but you can ask what is the reason for the expansion of the universe as in the case of a ball that we throw towards the sky; it is our own force with which we throw it. Well after Edwin Hubble in 1920 discovered the universe was not static and born in a Big Bang, after that, it was long thought the gravity of matter in the universe was certain to slow the expansion of the universe. Until, in 1998, the Hubble Space Telescope’s observations of very remote supernovas unveiled that a long time ago, the universe was expanding more slowly than it is today. Then the results of the WMAP mission and observations of distant supernova have suggested that the expansion of the universe is actually accelerating, which implies the existence of a form of matter with a strong negative pressure. This strange form of matter with negative pressure is called dark energy and it is a big mystery in science.

Critical Density Vs Dark Energy

Now this energy of empty space (dark energy) vs density of matter chart along with the timeline of the universe shows that they are passing through each other at this point when we human beings are in this universe. Otherwise in the future density of matter will decrease. So that means in future with the energy of empty space objects will move far and far even more than the speed of light. Although nothing can travel more than the speed of light but on an expansion scale as big as this observable universe this is happening even now. That means if we wait long enough the rest of the universe will disappear. This expansion would not only be just for the space between galaxies but the space within them and then a time will come that the galaxies, stars, planets, and matter even the subatomic building blocks that comprise all matter can no longer hold themselves together, at which point they rip apart.