End of Everything
The topic seems a bit scary, but the whole thing becomes more and more interesting and adsorbing with every passing sentence. A voyage through time that will unravel the deep secrets of how and when will the life, the earth, the sun, the galaxy and the matter will END. Let us embark upon this journey to envision the End of Everything.
A teacher is valued because of the students and a speaker because of the audience. What would a speaker do without audience? Can the same logic be applied to the Universe that we live in? Would there be any importance of this Universe without the existence of Life at all? In a sense, Universe would not have existed without Life, as there would be nothing to sense the existence of the Universe. This is a highly debatable topic, but worth giving a thought.
Among all the species on Earth, humans are the one who are blessed with highest degree of intelligence and hence power. But, even so, we usually have a very short term view of the things. We are concerned about the end of month, end of college/school year or life after marriage and retirement. Even if we consider 80 years as an average lifespan of humans - that much, is all that we usually envision. Now, lets think big and look forward - millions and trillions years into the future - and see how the grand structures of the Universe Ends.
The End - Humans - 10,000 years
As per the widely accepted theory of Human Evolution it is believed that Humans originated about 2,00,000 years ago. Since then, Humans have progressed "wildly" inhabiting every nook and corner of the Earth and beyond - in space. It is also believed that the more we progress, the more we near the end of ours and several other species on the Earth.
Vast majority of every species that has ever lived on Earth has been already wiped off. There is no concrete reason to say that humans will be able to survive for extensively longer period. There are several man-made and natural disasters that could wipe us out. An asteroid strike, global warming, an epidemic over a vast geographical area, supernova explosion nearby or just one outburst of coronal mass ejection from the Sun could in principle wipe us out.
There's no way to know, but there's a calculation that can help. It's called the Doomsday Argument, developed in 1983 by astrophysicist Brandon Carter. According to Carter, if you assume that half of the humans who will ever live have already been born; you get approximately 60 billion people. If you assume that another 60 billion are yet to be born, our high population levels only give us another 9,000 years or so. Or more precisely, there's a 95% chance that humanity will have ended by the year 11,000. There are other calculations, but they give similar amounts, ranging from a few thousand to a few million years.
The End - Life - 500 million years to 5 billion years
The life on Earth as we know is mainly because of the Sun. Ironically, life giver shall also be life taker. The Sun is slowly heating up. In as soon as 500 million years, the temperature on Earth will rise to the point that most of the world will be a desert. The water from the face of the earth would have boiled away. The hardest of creatures will find it difficult to survive with no place to hide from the scorching heat of the Sun. Only the organisms that live deep underground will survive, as they have already for billions of years.
The End - Earth - 6 billion years to 7.5 billion years
The Sun is slowly heating up and will eventually use up all its Hydrogen fuel in about 5 billion years. That will be the final stage of its life. The Sun will turn into a red giant ball consuming each of the inner planets: first Mercury, then Venus, and finally encompassing even the orbit of the Earth. As the Sun expands and encompass the orbit of the Earth, there will be tremendous friction to the orbiting Earth - resulting in a drastic slow down in its orbital velocity, eventually spiraling down into the Sun. One other scenario is that as the Sun expands; the orbit of the Earth will be pushed farther, keeping it away from the outer boundary of the Sun. Even then, the Earth will be scorched to a cinder, and effectively destroyed 5 billion years from now.
The End - Sun - 1 trillion years
As the Sun becomes a red giant, it has just started its journey of its End. With the end of its hydrogen fuel, the Sun will have to switch to helium as its fuel, then carbon and finally oxygen. The Sun's gravitational force is just enough to use Oxygen as fuel, nothing more than it. So once, Oxygen is also used up, it can no further use other heavier elements present and hence the fusion process shall shut down, turning itself into a white dwarf star. It will still retain most of its mass, but have a size no larger than the Earth's diameter. For a few thousand years, it shall remain yellow hot with the leftover heat of fusion, and will cool down over time. Eventually, its temperature will match the background temperature of the Universe and will become a cold black dwarf - a chunk of floating matter in the darkness of the space.
As of yet we have not detected black dwarfs, hinting that Universe is not very old for the stars to have gone to that stage. But give another trillion years and the Sun should finally become a black dwarf along with billions of other stars in ours and other galaxies.
The End Solar System Trillion years and beyond
Once the Sun ends its life resulting in a white dwarf and latter on a black dwarf, the planets not consumed during the Sun's red giant stage would continue to orbit around the dead Sun for eons. The Earth might be in the group of the other planets.
The End Cosmology Trillions of years from now
The Universe is expanding, and the rate of expansion if accelerating. Hence, Universe is in a accelerated stage of expansion. Expansion of the Universe basically means that the galaxies are moving away from each other. The inter-galactic space is increasing. This has been happening since the first moment of the Big Bang that took place roughly 13-14 billion years ago. Two to three trillion years from now, not a single galaxy would be visible to any other galaxy in the Universe. All would have drifted so far from each other that light would take enormous time to reach and by the time light travels, galaxies would have drifted more. Life, if any, would not see anything beyond their own galaxy, but only the stars of the galaxy they reside in.
The End Stars 100 trillion years
We can see stars forming in the nebulas spread everywhere in our Milky Way. There is still enough gas and dust remaining to create whole new generations of stars. But we also know of galaxies where there is no star formation taking place, as the galaxies have grown old. The fate of all the stars depends upon its size. But, eventually, every star will one day use all the fuel and fade to white to black dwarf. So, in 100 trillion years from now, every star in the Universe will be a black dwarf.
The End Regular Matter 10 raise to 30 years
So now we have a Universe with no stars, only cold black dwarfs wandering in the absolutely dark deep space. There will also be neutron stars and black holes left over form the time when there were stars in the Universe. Chunks of matter and black dwarfs will merge to become black holes and these black holes will be consumed by even larger black holes. In future, it might happen that all matter will exist in a few, truly massive black holes.
As per the current physics theories, protons are unstable over a longer period of time. They just can't last forever. Any matter that wasn't consumed will start to decay. The protons will turn into radiation leaving electrons, positrons, neutrinos and radiation to spread out into the space. Decaying process of protons might take place in about 1030 years.
The End Black Holes 10 raise to 100 years
Black holes were thought to be one-way streets. Matter that goes in, cannot come out. But, as per renowned physicist and mathematician Stephen Hawking, black holes can evaporate. It is not much and not fast, but black holes can release a tiny amount of radiation back into space. As it release radiation, black holes losses its mass and eventually losses all its mass.
Ultimately, all that we see, experience and comprehend will evaporate into space in the form of radiation. The temperature of the entire Universe will reach a final temperature just above absolute zero. Expansion of the Universe might still be going on, pushing the photons and elementary particles away from each other until they are effectively cut off from each other. No future gravity will bring them together.
Perhaps the future of the Universe is cold and dark. It's not happy and exiting to know this but it will help us to appreciate the colorful Universe and age we live in today.