Rhishav Narayan Choudhury

Wrapped up in our individual bubble of time and space, we tend to forget that the ground upon which we stand is but a colossal rock hurtling across the vast expanse of space at hundreds of thousands of kilometres an hour, yet trapped in the immensity of the Sun’s gravitational web. On the universal clock of the cosmos, Earth’s future is rather bleak and her time short, but the future of life need not be. The last star in our universe will die out in about one hundred trillion years and so life has plenty of time to prosper

“Men shut their doors

against a setting sun”

— William Shakespeare,

English playwright and poet

A recent Reuter’s poll found that one in seven people believe in the Mayan prophecy that the world will come to an end on December 21of this year. Although there is absolutely no rational scientific evidence to support such a doomsday prediction happening any time soon, there is a plethora of scientific understanding that such a cataclysmic event will ultimately occur. The fate of Earth lies in the hands of the Sun, our creator, worshipped as Surya riding across the sky in his horse-drawn chariot or as Ra gliding through the heavens in his solar boat. The giant ball of gas that our planet orbits around at an average distance of 150 million kilometres is the source of all life on Earth; it is because of this magnificent orb of energy that we possess the ability to marvel at its very splendour. To unlock the key to understanding ourselves and the immense infinity beyond, we must comprehend the stars above.

So how did the twinkling lights that we see scattered across our sky on a clear night come to be? About 100 million years after the big bang and cosmic inflation began, i.e. approximately 13.7 billion years ago; the first stars were born in their respective galaxies within interstellar clouds of gas and dust as gravity began to amplify differences in the components of space.  Such stellar nurseries, sprinkled throughout our very galaxy, the Milky Way, gave birth to hundreds of billions of stars and will eventually produce tens of billions more. Ultimately, however, the raw material for new stars is being used up; even though massive stars die in supernova explosions and return some material into space and although galaxies can accrete fresh gas from intergalactic space, the new material cannot replenish all the gas that stars have consumed. Thus, it is estimated that star formation will continue to decrease with time, and that one hundred trillion years from now stars will form at only about one-hundredth of their current rate.

Life will, however, follow a different trajectory. Eventually — after about a trillion years — heavy elements such as carbon, oxygen and nitrogen that largely make up planets and in turn life will constitute a significant fraction of stars’ masses and shorten their life. These elements should be more conducive for the birth of planets along with stars, and so favour the prospects of life in the universe. Astronomers have already discovered more than 700 Jupiter-like gas giants beyond our solar system, and although space-based telescopes are just beginning to detect them, Earth-like planets most definitely are out there. In the far future, the universe should be filled with worlds like ours that are composed almost entirely of heavier elements. As time goes on, the increasing relative abundance of these heavier elements should produce planets more hospitable to life. Thus, however full or empty of life the cosmos may be today, it should be filled with more abundant and varied forms of life in the future.

Even after hundreds of billions of years have elapsed and even star formation has slowed to near standstill, enormous numbers of stars will continue to shine. Most stars have low masses and extremely long lifecycles, and the relation between their mass and lifetime is inversely related. High-mass stars are so luminous that they burn themselves out quickly and explode after a few million years. Stars with significantly less mass on the other hand can exist for hundreds of billions of years or even longer, they consume their fuel so slowly that even on their measly supply can fuel their nuclear core for eons of time. These types of stars die in a distinct way as well, with sun-like stars becoming red giants before revealing its core white dwarf. Those with large masses collapse into themselves forming either a neutron star or a black hole that causes the star’s outer layers into space in one of the most beautiful yet destructive cosmological happenings, a supernova, while the so-called runts of the star family never generate the nuclear reaction to produce such phenomena and eventually become “harmless” helium white dwarf. The latter has yet to be observed due to the length of time required for a star to reach such a phase.  

So when is our time up, or at least Earth’s? Approximately five billion years from now, the sun will balloon into a red giant star and swallow the inner solar system including our home before slowly fading into darkness. Our galaxy, the Milky Way, fifteen billion years will be confronted by the onrushing arrival of the neighbouring Andromeda system and these two galaxies will either collide or begin to orbit their common centre of mass in what will be a chaotic restructuring of our galactic surroundings. There is also a possibility of planets in our solar system falling out of orbital sync, which has a multitude of possible repercussions. Either way, if our descendants are still around on this planet or in this galaxy when such an event occurs, they will in all likelihood be completely obliterated unless they can migrate out of here or alter the workings of nature. The possibility of life being able to traverse such cosmic distances or moulding the universe for their own purposes remains solely within the realms of our imaginations and science fiction for now.         

Wrapped up in our individual bubble of time and space, we tend to forget that the ground upon which we stand is but a colossal rock hurtling across the vast expanse of space at hundreds of thousands of kilometres an hour, yet trapped in the immensity of the Sun’s gravitational web. On the universal clock of the cosmos, Earth’s future is rather bleak and her time short, but the future of life need not be. The last star in our universe will die out in about one hundred trillion years and so life has plenty of time to prosper. This world will eventually end, but life can march on, in another time in a different place.

(The writer, who hails from Guwahati, is a freelance contributor studying in the US)