What is the fate of our universe? What will happen to the most mystic creation in the long run? These all are the challenging questions that Physics has been facing from the day, the universe is originated from Big Bang. We may never be truly certain about the future of the universe but science has begun to paint a stunning amazing picture of how the future might unfold. And what about the future of life in the universe? Well, we know that the time span of universe is beyond one’s imagination and the existence of life in the universe just a very very small fraction (tends to zero almost) to that time scale. The vision of the future will inevitably evolve as we probe for more hints. But one thing is clear:- ‘The Universe Has Just Only Begun’. So, let’s take a journey to the end of time.
THE ANTHROPOCENE ERA
The Holocene will end one day. What we are doing right now and in the next few years will profoundly affect the next few thousand years. The conditions that modern humans have ever known so far, will be changing and changing fast. Things will have started moving on this planet. Sea level will rise drastically, Sahara will become tropical, supervolcano eruption will occur, new island chain will appear and many things will happen that one can hardly imagine. New supercontinents will form due to the huge impact of asteroids with the earth.
FATE OF SUN AND OTHER STARS
As the sun will begin to turn out of fuel one day, it won’t simply fade away to nothing. Its core will collapse and the extra heat, that it will generate will cause its outer layer to expand-sun will explode into a supernova and it will die. After the supernovae explosion, the sun by slowly cooling in the freezing temperature of deep space will become a white dwarf – a hot, dense, shrunken stellar corpse. The fate of the sun is the same as for all the other stars. One day they all must eventually die and the cosmos will be plunged into an eternal night. As all the stars will eventually run out of fuel, the temperature of the universe drops, and the stars, one by one in the night sky, will turn off and there will no more new stars created. And so the universe will end not with a Bang but with the whimper, and not in a fire, but ice.
THE DEGENERATE ERA
Now before going to the next stage, lets discuss something more about the white dwarf, neutron star and black holes and their differences. After the death of the stars, their fate depends on their mass. And here comes the concept of two forces – gravitational force and electron degenerate pressure. The gravitational force is responsible for the star to collapse where the degenerate electron pressure balances it by resisting the collapse through thermal pressure. Scientist Subrahmanyan Chandrasekhar had introduced a limit to that the mass of a star, named as Chandrasekhar Limit (C.L.) which can tell us the fate of the stars. The currently accepted value of Chandrasekhar Limit is about 1.4 times the mass of sun (2.765 x 1030 kg). White dwarfs resist gravitational collapse through the electron degeneracy pressure. The C.L. is the mass above which electron degeneracy pressure in the star’s core is insufficient to balance the stars’ gravitational self attraction.
Consequently, a white dwarf with a mass higher than the limit is subjected to further
gravitational collapse, evolving into a different type of stellar remnants, such as a neutron star or a black hole. Those with masses up to the limit remains stable as white dwarfs. The mass of the star that will give rise to a black hole is much higher than that which leads to the formation of white dwarfs and neutron stars.
With the death of the last star in the universe, the age of starlight will come to an end. The universe will become a cosmic cemetery, strewn with remnants of dead stars. With no fuel left to burn, a white dwarf’s faint glow comes from the last residual heat from its extinguished furnace. Looking at it from where the earth is now, it will only generate the same amount of light as the full moon on a clear night. The faint glow of white dwarfs will provide the only illumination in a dark and empty void littered with dead stars and black holes. Over time, gravity will eject the dead stars and planets from their galaxies, sending them out into the freezing void. Some brown dwarfs may collide by chance and form accidentally new stars in this time zone. Colliding Neutron stars puncture the darkness of the universe with ultra-bright supernovae. But in time, even the white dwarfs will fade and die. White dwarfs will become so cold that they will barely emit any more heat and light and a black dwarf will be the final fate of those last stars. Black dwarfs are dark, dense, decaying balls of degenerate matter. Their constituent atoms are so severely crushed in it that the black dwarfs are million times denser than our sun. Stars take so long to reach this point that we believe that there are currently no black dwarfs in the universe.
The black holes will start to swallow the stray matters of the universe. The rotational energy of the black holes will become the last reliable source of energy for any exotic future civilizations. Even if our life dies out, one could imagine at some time, arbitrarily far in the future, a fluctuation will occur which will allow intelligent life to exist again in the universe, for a little while.
EXPANSION OF SPACETIME
As the expansion of the universe will accelerate, it will begin to spread matter apart faster than the speed of light. By that point, distant galaxies and stars will be receding so quickly that their light will become undetectable. The secrets of this vast cosmos will be locked away forever.
Current theories predict that the atoms themselves will begin to decay, destroying all remaining matter in the universe. A proton, one of the fundamental building blocks of atomic matter, what makes us up, can just spontaneously fall apart (hypothetical statement of Grand Unified Theory). Any material that will evade the pull of a black hole eventually will die away as its protons will disintegrate. As the proton decay is still unproven, this chapter of the future could look very different in light of new discoveries.
The matter in the black dwarfs, the last matter in the universe will eventually evaporate
away and be carried off into the void as radiation, leaving absolutely nothing behind.
THE BLACK HOLE ERA
With the black dwarfs gone, there won’t be a single atom of matter left in the universe. All that will remain of our once-rich cosmos will be particles of light and black holes – and the Black Hole era will begin. No planets or stars or lingering stellar remnants, for life to cling to. Yet even then, time will only begin to tick. On the scale of a human lifetime, the universe has just emerged from the womb of cold, dark, empty – this is how the cosmos will spend most of its life. Our universe gives life only a brief moment to shine – a haven in time, safe from its fiery birth and cold death. The arrow of time creates a bright window in the universe’s adolescence during which life is possible in
the universe. But it’s a window that doesn’t stay open for long. As a fraction of the lifespan of the universe, as measured from the beginning to the evaporation of the last black hole – life, as we know it, is only possible for a very very very small fraction of time. Black holes will eventually become the fundamental building blocks of the universe. A galaxy will basically be a supermassive black hole in the center with smaller black holes orbiting it. Zombie galaxies filled with black holes will continue to evolve. They will eat each other and get bigger, and maybe they will fall into the supermassive black hole, and it will get even bigger. The universe will still be an exciting and
In this far-flung age, black hole mergers will become the main event in the universe. Some will grow to enormous sizes, probably trillions of times the mass of our sun. When they merge, they will send out strong, powerful gravity waves that will resonate throughout the universe. Black holes can bang on space-time like mallets on a drum. When two black holes are going around each other, and crossing thousands of kilometres in a fraction of a second, they leave behind in their wake a ringing of space, an actual wave on space-time. Those are the gravitational waves and are literally the sounds of the space ringing. And they will travel out from these black holes at the speed of light as they ring down and coalesce into one – spinning and quite black hole.
Scientists used to think that black holes were immortal. But even these will die one day. On the timescale of unimaginable length (quadrillions of years into the future), black holes will begin to evaporate away at an increasing rate through Hawking Radiation until they vanish in a gigantic explosion. Quantum Mechanics has allowed particles and radiation to escape from the ultimate prison, a black hole. Black holes will begin to evaporate away, erasing the last large-scale structures in the universe. As they die, they will light up the darkness one by one. As the black holes will slowly die off, the universe will continue to expand driven by the mysterious force we don’t yet understand, the Dark Energy.
The latest evidence shows that the expansion of universe is not slowing down, but it is speeding up out of control. And the universe, we think, will die in ice trillions upon trillions of years from now. Dark energy, unlike matter or radiation, does not dilute away as the universe expands. This has crucial implications for what the universe is going to do in the future. So, what will be the future of the universe? Well, if the Dark Energy remains dominant and repulsive, the universe will expand forever – faster and faster and faster with time, a runaway universe. If the energy continues to be there, the universe will become cold, dark and empty. That’s the future as it might be. We don’t
know as we don’t yet understand the nature of Dark Energy. And so we don’t know about the future, and we don’t even understand our origins, and that is why this subject is so interesting to everyone.
Discovering the true nature of Dark Energy could change our vision of the future dramatically. If it somehow weakens over time, the universe could collapse under gravity – which will be a big crunch to the existing theories for the universe. Physicists increasingly suspect that there may be multiple universes beyond our own, each with their own unique laws of physics. Some would harbour the right conditions for life. Others could collapse or be ripped apart. Others still could be far more exotic than anything we could imagine. New pieces to this puzzle are out there
somewhere, waiting to be found in future. There are ideas, whereby what actually is the end of our universe, could in some sense, lead to the beginning of a new one. Some speculate that there may be a way to escape our universe before entropy erases everything. There is a theory which tells us that if you have an atom smasher, that can constrict the tremendous amount of energy at a single point, you can perhaps open up a gateway – a ‘Baby Universe’. So, an evolution may take place among universes, in the multiverse, if intelligent life in any universe will create a baby universe and proliferate child universes. If there is no way to escape the universe, entropy will march on, destroying the last remaining supermassive black holes. As the last one explodes and dies, it bathes the universe in light one last time, and the universe will sink into hibernation for the rest of its life.
Source: Wikipedia and Facebook page ‘Physics Now’.
Source of Figures: Internet
By Dwaipayan Dubey, IISER Kolkata.