Humans have the alarming capacity to tune out the bigger picture. We grow so preoccupied with occurrences on our own planet that we tend to forget that we are on a small rock spinning around a sun, which in turn is spinning around a galaxy that hurtles through the universe at a stupefying rate of 1.3 million miles per hour; that’s 361 miles per second. Our solar system is of a negligible size compared to the universe, which is accelerating in its expansion at 41 miles per second. Objects in the night sky that are now visible to the naked eye will one day be so far away from us that the rate of expansion exceeds the speed of light, and we will potentially never catch sight of them again. The fact that the universe is essentially pulling itself apart begs the question - is there an end to it all? Will the universe finally meet an end?
The answer, in short, is yes, although scientists are not quite sure how yet. The best explanation we have right now is a concept known as ‘heat death.’ The term brings about infernal imagery, but the outcome is quite the opposite. The universe will spread its energy so thin that it will quite literally freeze itself to death. Even if the human race does survive the end of our solar system, there is no way that we will ever be able to survive the final state of the universe, but what exactly will happen to the universe?
The universe’s existence can be divided into eras. The birth of the universe triggered what is known as the primordial (or inflationary) era. Atoms had yet to form, and the universe was a thick soup of particles, to the point where it was opaque and light could not yet pass through it. As soon as the first atoms formed, a neutral medium was created that allowed for waves to travel through it, hence the beginning of transparency. However, since there were no stars, the universe remained pitch-black and plunged into an epoch which has been dubbed the “dark ages.” The dark ages took place 380,000 years after the Big Bang, and atoms began to coalesce. Matter began to accumulate in great clouds, where the pressure was so high that stars began to form within the first stellar nurseries. The universe was slowly being illuminated, which brought us to the next era, known as the “stelliferous era,” where we are now.
What will the stelliferous era bring us? Around 6 billion years from now, the Milky Way and the Andromeda will collide, creating an elliptical supergalaxy. Galaxies within our area (known as the Local Group) will all coalesce together once their orbits decay, forming an even larger supergalaxy. Assuming that universal expansion continues accelerating, all galaxies beyond our Local Supercluster will be beyond the cosmic horizon for us, and their light beyond this point will never reach us again. Events that transpire within our supergalaxy will not affect the rest of the universe, as expansion has rendered it into its own system. Star formation will slow, as matter density within the universe diminishes, and the luminosity of galaxies will abate. Eventually, light from galaxies beyond the cosmic horizon will be so redshifted that even gamma rays that they emit will have wavelengths longer than the observable universe itself; thus begins the “degenerate era.”
The degenerate era begins 100 trillion years from now and spans for 10 duodecillion years. Stars will stop forming; there is only so much hydrogen in the universe and we will run out. Large stars tend to burn fuel at a faster rate than lower-mass stars, so the last stars left will be low-mass red dwarfs, weighing around 0.08 solar masses. Once these stars finally burn out after around 13 trillion years, nuclear fission will stop entirely. Only ‘degenerate remnants’ will remain, which are the byproducts of a dead star, such as white dwarfs, black dwarves, and brown dwarves, and even these bodies will cool and dim.
After this point, the universe will be pitch-black, with a few instances where light may be observed; two white dwarves may merge, and if their masses are large enough to bypass the Chandrasekhar limit, then a type 1A supernova will illuminate the universe for a few weeks. If the masses of the two white dwarves are not large enough, a carbon star may form, with a life of only 1 million years as the moment stars fuse atoms to form anything heavier than iron, they begin to destruct.
Nonetheless, planets will soon be flung out of orbit due to decaying orbits, which occurs because of gravitational radiation. Eventually, these planets will slip into the numerous black holes that will pepper the universe. A process called gravitational relaxation will cause 90%-99% of objects in a galaxy to be flung out of its orbit. Heavy nuclei will decay until there is nothing but hydrogen nucleons left. This also will not last; the final baryons will decay into photons and leptons.
This brings us to the penultimate era of the universe: the black hole era. Nothing will remain except black holes, which will slowly dissolve into Hawking radiation. As the black hole decays, its temperature will rise, causing it to possess some type of luminosity for a short period of time. Once it reaches the end of its decay, it will begin to push out particles with mass, such as the electron and proton. Once the final black holes decay, we will plunge into the “dark era,” occurring 1 googol years from now. Only photons, neutrinos, positrons, and electrons will remain, flying past each other and rarely encountering one another as the universe will still be expanding. Essentially, it is the end.
It is theorized that the Big Bang stemmed from virtual particle interactions, which begs the question of whether there may be something beyond our universe on a larger scale. Unfortunately, we may never know. Although we don’t realize it, the universe existing in the condition we have now is rare, even rarer than the possibility of life in a star’s habitable zone. If the universe had even the slightest observable curvature, it would have collapsed by now. We are the products of the entropic principle; the very atoms that our bodies consist are the aftermath of star death. The subatomic particles that compose us have been around since the beginning of time itself.
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