For some reason, humans are fascinated by how the world will end. Every major religion has a story about how they believe the end will unfold. Some believe that when this world ends, another will be reborn from the ashes. Others hold that the end of this world will be the end of the world as it is currently known but not the destruction of all life. Still others hold that the end of the world will end all physical life but that souls and spirits will remain. 

Religions have their various views of how Armageddon will appear, and innumerable filmmakers have seen their vision of the apocalypse played out on screen. What about scientists, though? What does science say the end of the world will look like?

End of Humanity

When dealing with the end of the world, most people are only really concerned about the end of humanity. The Earth might keep turning, but if humans are gone, humanity, understandably, sees the world as ended.

Humans could be wiped out in any number of ways, just like any other species on the planet. The human race could fall if there was an outbreak of a disease that medicine simply could not cure. According to biologists, such an illness that was actually capable of killing off all seven billion humans before modern medicine could treat it or to which humans could naturally become immune would likely have a long incubation time, the period of time where a person is infected but the disease is not harming them yet. It would also need to kill swiftly once symptoms began to show. A fast killer would keep medicine or the natural immune system from being able to intervene in time while a long incubation period would allow the infected to pass the disease on to others long before they were aware that they were carrying it.

An extinction level event could wipe out humanity, just as it killed off the dinosaurs, but humans are unique in that humanity could also end up killing off itself. Nuclear war, biological weapons gone out of control, robots or artificial intelligence rising up against humans and other manmade disasters could easily spell the end for humanity while allowing other species to survive. Not much would survive a true nuclear winter, but the cockroaches would be thrilled to find that what remained of humanity’s cupboards were no longer defended by shoes and cans of Raid.

End of Earth

Sometimes people mean the end of humanity when they reference the end of the world, but other times they mean it more literally. Whether anyone wants to contemplate it or not, eventually the Earth itself will cease to exist. Humanity’s end is uncertain, but how the Blue Planet will die is almost guaranteed.

The Sun is essentially a giant hydrogen bomb. Its energy and light are produced by hydrogen atoms combining to become helium. In roughly five billion years, the Sun will run out of hydrogen, and the nuclear fusion that powers the solar system will come to an end. As this occurs, the Sun will cool and swell into a red giant. It will consume Mercury and Venus and burn Earth’s atmosphere and water away. Then, the gravity of the sun will tear the planet apart. Earth will be killed by the star that made life possible in the first place.

Though it is unlikely, there is the chance that Earth would die in a different manner. When the Sun begins to fail, the orbits of the planets will be thrown out of alignment. This could mean that Earth is destroyed in a collision with Mars or Venus instead of the Sun. A breakdown in orbits also allows for the extremely remote possibility of Earth being tossed far enough away from the Sun to survive its expansion. In that event, however, Earth would be uninhabitable for any form of life as it would be too cold unless the planet became a wandering celestial body and somehow found a new star to orbit. That scenario, however, is extremely unlikely. Earth has a better chance of being swallowed by one of the wandering black holes that inhabit the universe.

End of the Milky Way

Humans will eventually die, Earth will eventually die and eventually even the Milky Way will be no more. The end of the galaxy, at least, will not be quite as final as the destruction of Earth. About a billion years before the Sun dies, the Milky Way will collide with its nearest galactic neighbor, the Andromeda Galaxy. The two spiral galaxies will warp each other out of shape and shuffle their stars and solar systems more or less at random. The energy released could trigger the birth of large number of new stars and rearrange existing solar systems as the two black holes in the centers of the galaxies merge. The resulting galaxy will likely be either a disk or an elliptical galaxy instead of the familiar spiral shape. 

End of the Universe

Scientists believe that eventually even the universe will end. How precisely that will happen is a matter of debate, but scientists have come up with three main theories as to how the entire universe will die.

The first theory is called the Big Crunch. Essentially, the Big Crunch theory states that one day the expansion of the universe will reverse. Matter will solely become compressed until the universe returns to its state prior to the Big Bang and reforms the Cosmic Egg. From here, some people theorize that another Big Bang will occur and a new universe will form. That universe then will expand, eventually reach its full size, collapse in a Big Crunch, form a Cosmic Egg and repeat the entire cycle. 

The second major theory is that of the Big Rip. The Big Rip is the exact opposite of the Big Crunch. In the Big Rip theory, the universe will continue expanding forever. Eventually, this expansion will become so great that molecules, atoms and even subatomic particles are torn apart. The very fabric of space-time will be shredded and all semblance of existence will cease.

The third major theory of the end of the universe is called the Big Freeze or, more ominously, heat death. Like with the Big Rip theory, the Big Freeze theory states that the universe will continue to expand forever. Eventually, it will become so large that particles can no longer interact with each other. The expansion of the universe will become faster than the speed of light, and the maximum entropy of the universe will have been reached. No more heat transfer or work can be complete from a physics standpoint, and the universe ends quietly and meekly.

How things will end has been a question that has spurred almost as much human interest as the question of how things began. Some endings are better understood or more likely than others, but only one thing is certain. Eventually, all things will end. The question is simply what sort of new beginning follows.