What Are The Greatest Long-Term Threats That Humanity Faces?

The end of the mammals and biosphere, the death of stars and the annihilation of matter are the four astrophysical predictions which can wipe out.

The future is an open book. Granted, we might not be successful in predicting rainfall levels for the coming week, but we can certainly predict an apocalyptic or astronomical event that will take place a few billion years from now. How is that possible? Astrophysical predictions are mysterious, but they have been meticulously calculated and theorized by physicists and star scholars since time immemorial.

Astrophysical predictions, What Are The Greatest Long-Term Threats That Humanity Faces?, Science ABC, Science ABC

A 10-day (or longer) forecast is right only about half the time. (Photo Credit: Sasenki/ Shutterstock)

It’s feasible for us to predict the future of the whole Solar System, and of the galaxies beyond, those moving in the ever-expanding void of space. These predictions can be called “physical eschatology”, a discipline coined by astronomer Martin Rees for using astrophysics to glean insight to the future of our universe.

The first questions that might come to mind are: What will be the future of humans? What will be the most significant challenges that humanity will face? We cannot yet say how we will overcome them, or whether we may have help from extra-terrestrials (possibly our future allies). However, one thing we can say for certain is that threats to our existence are coming.

Let’s take a look at a string of predictions or threats that have the capacity to wipe out the existence of humans from this universe.

Crystal ball in hands of God. Endless space. 3D rendering - Illustration( Bruce Rolff)S

Physical eschatology, a discipline of theology, is applied to the long-term predictions of the state of Universe. (Photo Credit: Bruce Rolff/ Shutterstock)

Surviving the end of our mammalian life-span

In a few tens of thousands of years, a race will begin to survive through to the end of our current interglacial period: the long-interrupted Ice Age in which we are living. It is pointless to ponder over this, since all of our ancestors have survived the previous ice ages. Furthermore, with our modern-day technology, we might end up cosily sleeping in our warm beds with plenty of bio-engineered food to fill our bellies for the next thousand years.

Frozen city in icy landscape - Image(Jagoush)s

With the advent of a new ice age, most of the mammalian population will perish, cities will freeze, and humans will have to depend solely on technology for their survival. (Photo Credit: Jagoush/ Shutterstock)

The archetypal lifespan of a mammalian species is approximately one million years. However, you soon might be struggling among a nuclear age, bioengineered pandemics and the climatic deterioration that we have bought upon ourselves. Basically, before natural extinction can faze us out, we will have wiped ourselves out, or at least tried our best. From nuclear war to pandemics, humanity has many risks it needs to address urgently: the natural extinction rate is a much smaller threat than the danger we pose to ourselves.

The Earth has never remained in the same state; over the years, the planet has experienced temperatures much higher than the current one, when palm trees and alligators enjoyed a lush life in the Arctic. There have been eras when the Earth was no more complex than a “popsicle snowball”. Then there is always the chance of meteor impacts, super-volcanos, gamma-ray bursts, or the emerging imminent ecological disruptions that have led to natural mass extinctions over the past 100 million years. We might be scientifically advanced enough to predict them, but surviving them is a different ballgame altogether. 

Surviving the end of our biosphere

Our Sun’s increased brightness (10%, at most) will be catastrophic for the Earth’s biosphere within a few billion years.

The increased heat will lead to the weathering of rocks at exponential rates, leading to the initiation of chemical reactions that will remove significant amounts of carbon dioxide from our atmosphere. Soon enough, plant life will starve due to a lack of food produced by photosynthesis, as there is not CO2 to fuel the process. Also, the overheating will be exacerbated by the evaporating ocean water in the atmosphere. By this point in the future, humanity will have to be advanced by colonizing on a massive level, not on our dwindling globe, but on planets far away. One approach to this is by geo-engineering reflective aerosols and solar shades, shielding Earth’s atmosphere from the “scorching stellar fire”.


The green cover would be wiped from the face of our planet; artificial oxygen and bioengineered food would be the means of survival. (Photo Credit: Pixabay)

The ultimate solution would be “self-sustaining habitats”. All of this might seem a bit absurd in this current era of technology, but we’re talking about an epoch billion of years from now, where the possibilities are endless. Mars might host the best cafeteria in the solar system and Jupiter might have the most prominent theme park of the supergiants. Hopefully, humans live long enough to ride those rollercoasters!

Surviving the end of stars

Our universe has already reached a peak in its star formation, and in the next few billion years, it will experience the birth of the “peak star”. After all the luminous and short-life stars have burned out of fuel, all that will remain will be a long-lived population of red dwarves. They might shine for trillions of years, but with no new stars being added in the remnant galaxies, in 10-100 trillion years or so, even the red dwarfs will sputter out, and the Universe will lose its last rays of hope. 

Our very own star, in around 5 billion years, will start to swell more rapidly (due to the accumulated helium heating its core), turning into a humongous red giant. The surface temperature will be lower than earlier, but the total irradiance (owing to its enormous surface) will increase exponentially. This is the point in space-time where Earth will be no more, swallowed entirely by the expanding Red Giant. Soon after (maybe a billion years or so), our Red Giant will have expelled much of its atmosphere as a planetary nebula and finally become a tiny white dwarf.

Vector illustration with stages of star life cycle from birth to the death. Fully editable, made of gradient meshes. - Vector( Marusya Chaika)s

(Photo Credit: Marusya Chaika/ Shutterstock)

Among all of this expansion and chaos, where are we? Perhaps we’ve migrated to some distant solar system! To survive, humans would require energy sources other than the starlight we now enjoy. Without any neutron stars and supernovas around, nuclear fission would be a thing of past (eons earlier). Fusing hydrogen from brown dwarfs, tapping into the energy of rotating black holes by super-radiant scattering, or dumping matter (undeniably garbage) into black holes and gathering the released energy are some of the possible sources. However, all of this would require technology that is tremendously more advanced than interactive home speakers. Fortunately, a billion years from now, if humanity somehow still exists, it’s entirely possible that we will achieve all this.

The End Game: Death of Matter

The matter we know of (based on our current knowledge of the Universe) is based on atoms, composed of protons, electrons and neutrons. Protons and electrons are usually considered to be perfectly stable (whereas neutrons are stabilized by protons). However, existing on their own, they decay with a half-life of a few hundred seconds.

Astronaut in multiverse Some elements provided courtesy of NASA 3D Render - Illustration( Bruce Rolff)s

If the multiverse theory holds, we might end up escaping the death of our current Universe. Otherwise, it’s all over for us. (Photo Credit: Bruce Rolff/ Shutterstock)

However, protons aren’t truly stable when scaled over an enormously large time span. Proton decay has, therefore, not been observed thus far, despite meticulous research. This gives us some hint that it takes a trillion years to happen.

This decay will be “our last act”. Whatever is left of the Universe—after the departure of stars—will gradually turn into radiation and the plasma of free electrons and positrons lurking around in space, unable to form habitable systems. The last of the icy black dwarfs will turn into helium and hydrogen crystals, evaporating silently into the stillness. Civilizations, however advanced, would have long ago perished in this last stage of life. The only entities left would be the radiation and black holes in an otherwise lonely, barren Universe.

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About the Author

Dev is an undergraduate (Bachelor of Science) from St. Xavier’s College (India). He watches a lot of anime and documentaries on the universe and wildlife. He spends most of his time engaging in sports and exercise. He has represented his state at the National Volleyball tournament, in India. Along with that, he has a flair for sketching, photography and would be glad to take up gardening as a career.

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