End of Universe, Black Holes, Dark Energy, Multiverse

A Journey to the Demise of the Universe!

Govindswaroop Rahangdale

Dec 21, 2020

Humans are not the pinnacle of evolution. Many people may argue how it can get better than this; Darwin made it clear that evolution is constant. This law is also true for our universe, no matter how beautiful or perfect it may look. Instead, unfortunately, the universe might be on the start line of a long decline. On that happy note, let’s embark on a journey towards the futuristic climax to our universe.

There are some problems with making predictions. Firstly, we do not have any telescopes or equipment to “look at the future events,” so we are in a bit of a dark here. Secondly, we do not fully understand our laws of physics, like quantum mechanics or gravity. Therefore, as we go towards the far future, we would get more and more speculative. Lastly, we will go forward in steps of a few billion years and larger.

Our first step will be about five billion years, which will be the merger of two galaxies, our Milky Way and the Andromeda galaxy spitting out gas and stars away along with their solar systems. They will form an amorphous blob of gas and stars, which the scientists call the Milkomeda. The merging will produce huge massive stars glowing bright blue shining across the sky. Living fast and dying young, these stars won’t last for long and die. Of course, by that time, the sun as a red giant would have swallowed the earth. The sun, being a white dwarf at that time, would be peacefully dying off. Our system would either be in the amorphous blob or looking at it from outside.

Let’s move on to about a hundred billion years into the future. Our universe contains something unknown but dominating called dark energy, responsible for the accelerated expansion of the cosmos. The percentage of dark energy (currently about 70%) is always increasing, and in the far future, it will increase to about 100%. At this point, the galaxies will be so apart from each other that the light from other galaxies won’t reach our “blob.” The only thing we see would be the remaining stars of our galaxy. Everything else would be accelerating away from us at a rate that we would never observe anything. Imagine any species living at that time would never realize that the universe is expanding. They would only see some local stars and nothing but inky blackness in the sky. Life has become isolated.

Our next step would be to roughly 10 trillion years. The massive blue stars die after a few million years, the smaller stars die a few billion years later, and the tiny red dwarves live for trillions of years. The leftover “blob” had lost all its gas, and there is no new star formation. All you see is all the stars getting older and redder. Our patch of the universe becomes redder and redder as there are only these red dwarves left. These stars, too, will get older, and our galaxy will fade away continuously.

There will come a time when all the red dwarf stars die, at about 100 trillion years. These red dwarfs end their life by becoming a white dwarf, slowly cooling down to a dead black dwarf without any energy. At this point, there will be billions of these dead hearts of stars floating around, but there will be no more starlight. Energy is now scarce in the universe.

Let’s take a giant leap in our timescale, to about ten nonillion years (1032 years). All neutrons have decayed into protons, and all the protons would have decayed into photons and positrons. All matter decays into energy. All that’s left in the universe is the black holes. Black holes radiate energy in the form of Hawking radiation, evaporating themselves away.

Over an immense timescale, 10100 years, a massive black hole will start to lose enough energy that it starts to shrink very rapidly. The radiation increases more quickly as they shrink. This creates runaway feedback, which drives them down to a point, and they explode, releasing all of their final matter in a burst. Thus, there will be random bursts of energy from all the black holes in the universe. Now, all the matter and all the energy have dissolved into nothingness. The universe reaches a beautifully named state, the heat death of the universe.

For a cheerful ending, not for life but the universe, some theories propose that dark energy would play a particular role after 102000+ years. The dark energy might be able to decay and descend to a lower energy state. As the universe changes its energy state, this release of energy will give a new burst to the expansion of the universe. Just like bubbles form in a fizzy drink at nucleated sites, there will be this change of energy in individual places of this universe, resulting in rapidly expanding patches of the universe. These patches are virtually new universes!

Imagine what if this has already happened and our current universe is born from a previous universe’s death. This cycle of universes goes on endlessly from infinitely in the past to infinitely in the future.

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