Universe is totality of everything that exists that include time, space, matter , dark matter , vacuum, physical matter , energy etc. When we think of future of universe , which is continuously increasing , the theory called Big Freeze comes in . The present knowledge and observation on universe indicates that the universe will expand continuously forever.
The continuous expansion of universe will result in its cooling many years. In such cool environments, life cannot survive . The totality of this is called as big freeze.
The future of universe seems to be bleak. The rate of space between the galaxies or the galaxies cluster will increase if cosmological constant accelerates universe expansion. With the time, the gas supply that is required for formation of star will be completed exhausted. This will result in last star formation after around 1 * 10^13 years , thus the star will stop to shine and the left behind generally known as stellar remnants will slowly disappear due to the decay of their photons. This will further left behind black holes which also disappear with time due to emission of hawking radiation . The totality of this all will result in uniform temperature all over the universe.
The indefinite expansion of universe does not determine spatial curvature. Therefore it can be open or flat or closed . Even if closed, present dark energy will counteract the force of gravitation between the matter. If the dark energy is absent then also, open and flat universe will continue to expand forever . This is another miracle of the universe.
The microwave anisotropy probe of Wilkinson indicates the shape of universe to be spatially flat and also has large amount of dark energy . If so , the rate of expansion will accelerates continuously . While observing distant supernovae, it has been confirmed that the universe is expanding continuously. The doubling of the universe size at a constant rate , the expansion will become exponential .
There are various studies carried out to know more on the expansion of the universe and its future . Recently , Fred Adams and G. Laughlin had divided the future as well as the past of expanding universe into five different era. Primordial era is the first era. This is the time when stars did not formed and also time after big bang . Stelliferous era , is the second era. This is the present day and includes all galaxies and stars that we see. The times were star formation takes place with the collision of clouds of gases. The third will be degenerate era , in this the stars will be burnt out , and in which only stellar remnant will be present . This will also include black holes and neutron stars. Next era will be black hole era, in which the white dwarfs , small astronomical object and neutron stars will be destroyed due to proton decay. In this era only black holes will remain. The final and fifth era will be dark era . In dark era , black holes will also disappear , and only dilute gas of leptons and photons will remain.
In future the universe will be continuously expanded. But if it recon tract, the universe will contract finally into hot dense state. The timelines for various eras will be e.g., for stelliferous era from 1 million years to 100 trillion years after the big bang. Degenerate era will be from 100 trillion to 10 40 years. Black hole era 1040 to 10^100 years . Dark era from 10^100 years and beyond. And many such phenomenon's can take place ahead in the future of universe.
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