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Further reading: [The possible fate of the universe in the future is doomed? 】

We are doomed!

No matter how hard we try to survive and reproduce, it will all be in vain. We have the power to solve climate change, dispose of our nuclear weapons, and prevent the emergence of murderous artificial intelligence, but the day of our demise will eventually come.

It's all about the laws of physics. Because our home – the Earth, the solar system, and the entire universe – has a finite lifespan, everything will be destroyed. The universe can be destroyed in a great explosion, or it can be destroyed in a great tear. But based on current observations, the universe is more likely to head for a depressing dark age – where any celestial body, any atom, will cease to exist, and the universe will eventually become empty, dark and cold. Nothing will happen in the universe except for the speeding of elementary particles and the occasional collision of particles to produce a faint light.

Is this true?

Let's first understand what the fate of the universe would be like if no intelligent life tried to intervene.

The end of the earth

Let's start with the Earth. The Earth is about 4.6 billion years old, which is about the same age as the Sun and other celestial bodies in the solar system. The sun is the source of almost all the light and heat we need in our lives, and it is in middle age. This seems to indicate that there are more than 4 billion years of life left on Earth to live happily.

But that's not the case.

As the sun gradually consumes its own hydrogen fuel, it gets hotter and hotter, and eventually this warming trend threatens life on Earth. In the future, the average temperature of the Earth will increase by a few degrees Celsius every 1,000 years. In hundreds of millions of years, ocean surface temperatures near the equator will approach 80°C, and large parts of the planet will be uninhabitable. While life will do everything it can to adapt to this upheaval, the worst is yet to come.

In a billion years, our planet will be a hot, humid hell, with scorching hurricanes blowing on the oceans and deserts for most of the landmass. Viewed from space, Earth is no longer a pretty blue planet, but a pale yellow planet – bare rocks near the equator glow yellow, and the sky is filled with yellow dust. By 1.2 billion A.D., the Earth will be the same as the ancient Earth of the past, with no animals, no plants, and only some heat-tolerant bacteria living in the hot pools. Eventually, the remaining oceans will boil. In about 5 billion years, the Sun will expand into a red giant, swallowing Mercury and Venus and extending to the Earth's surface. At that time, all the rocks of the earth will glow red. And that's when the story of life on Earth comes to an end.

The demise of the stars

And what about stars? Without stars, energy cannot be provided, and life cannot be sustained. But sadly, every star has a finite lifespan.

Large stars can live from tens of millions to billions of years, and smaller stars can live more than trillions of years. Although new generations of stars will continue to be born, eventually all the raw materials for the formation of new stars in the universe will be exhausted. The last group of stars will be low-mass stars, known as red dwarfs, one of the most common stars in the universe, which accounts for about 85% of the entire universe. Red dwarfs have extremely long lifespans, with some lasting up to around 20 trillion years, more than 2,000 times the lifespan of the Sun. Planets orbiting red dwarfs may have conditions suitable for life and allow life to exist long enough.

But even red dwarfs have a lifespan. In about 200 trillion years, the last red dwarf star will also dim. Since then, all stars in the universe, including red dwarfs, have died, leaving behind only fainter remnants – white dwarfs, neutron stars, or black holes. The universe is almost cold and dark, and even if life survived, it was difficult to face the days without sunlight.

The end of the universe

If the stars are gone, what about the universe? In this regard, we are faced with an unknown territory, and we are not entirely sure what will happen, but we can speculate.

One view is that the universe should have enough matter (including dark matter) and energy to slow down the expansion of the universe through gravity until it stops, and then the universe will contract in turn, like the inversion of the Big Bang. This ending is called the "Great Squeeze".

In addition to the outcome of the Great Squeeze, there is also an opinion that the dark energy that is currently accelerating the expansion of the universe may one day become more powerful. Some scientists have analyzed that the more powerful dark energy (known as ghost energy) will completely tear the entire universe apart, atom by atom. This catastrophic outcome is called the "Great Tear".

However, current observations show that it is very likely that the universe in the future will not be squeezed or torn apart, and that the universe will simply expand forever. The end of this universe seems mild, but it is also a bad one: the future universe will be an extremely pessimistic, boring and boring place. With the death of the last red dwarf, any star in the universe will cease to exist. And another, fainter celestial body, the brown dwarf, a planet slightly larger than Jupiter but not with enough material to be a star, will become the master of the universe. The heat inside them can sustain some intelligent civilizations for tens of billions of years. Left behind are the remnants of the death of stars – white dwarfs, neutron stars and black holes. At that time, searching the vastness of space, the brightest object was no more than the brightness of a 40-watt incandescent light bulb.

In about 100 billion years, brown dwarfs will also die, and although there are still white dwarfs, neutron stars, and dead planets in the universe, the particles that make up white dwarfs, neutron stars, and planets also have a lifespan – neutrons decay into protons, and protons decay as well. Although the decay period of protons is extremely long, if the half-life of protons is about 1041 years, then white dwarfs, neutron stars, and planets will disintegrate after about 3×1043 years and become more basic particles, leaving only black holes, and the universe will enter the age of black holes.

Black holes will be the last sentinels in the universe, but even black holes are not immortal. Through Hawking radiation, they lose mass and eventually disappear in an explosion – the last burst of visible light in the universe. Eventually, after about 1.7×10106 years, any black holes will evaporate and the universe will enter a "dark age", when the universe will be free of atoms. The rest will be photons, as well as a few other elementary particles, traveling through the vast expanse of space. Other than that, nothing will happen again.

Find a new place to live

So, what else can we do? Should life accept this sad fate? Can we postpone — perhaps indefinitely — this fate of perdition? It sounds like a lot of difficulty, but if we do nothing, then we will face a certain fate.

First of all, we can avoid perishing due to the change of the sun. As the Sun warms, we can move farther away from the Sun, such as immigrating to Mars, or going to the moons of Jupiter or Saturn. For example, about 3 billion years from now, Saturn's moon Titan (Titan) may be a mild-climate, watery paradise with a thick atmosphere that can withstand any lethal radiation.

If we have a great attachment to the Earth, we can move it to a new orbit farther away. We can push an asteroid or comet very close to the Earth, creating a gravitational pull that allows the Earth to escape the sun's scorching clutches.

But what we have won is only 100 million years. After the death of the sun, our future successors, whether they are still human beings, a replacement species, or artificial intelligence, will need a new energy celestial body. But even red and brown dwarfs do not exist permanently. At that point, our successors will have to find new ways to obtain energy to sustain their civilization.

But if the expansion of the universe continues to accelerate, then over time, the vast amount of matter and energy that we are able to utilize in interstellar space will eventually leave us at speeds faster than the speed of light, and we will never be able to exploit them. At that time, the range of resources available to humans in the future will be extremely limited. So what to do?

There is a way to obtain energy efficiently. In 1960, Freeman Dyson, a physicist at Princeton University in the United States, believed that advanced intelligent civilizations might build a huge spherical structure that envelops stars to capture and preserve most or all of the star's energy output. This type of structure is called a "Dyson sphere". Even during the black hole period of the universe, intelligent life could build similar Dyson spheres to collect the energy released by black holes, such as Hawking radiation, a type of radiation produced by virtual particles in a vacuum in the event horizon of a black hole, which is a very weak radiation: the Hawking radiation produced by a slightly larger black hole is equivalent to the radiation produced by an object whose temperature is only a little higher than absolute zero. But in the dark future, we must use everything we can to make use of it.

However, as mentioned earlier, the black hole will eventually disappear due to Hawking radiation, and there will be no energy available for intelligent life. So after that, can intelligent life still have any hope of survival?

Escape from this universe

Some scientists believe that when our universe is no longer suitable for any life, we can move to a new universe. Humanity in the future will have to make this long-term escape plan before the Dark Ages come. Moving to a new universe will be our only hope.

Scientists believe that since the birth of the universe is a natural event, then it must follow certain laws of physics, and a sufficiently advanced intelligent civilization will have the ability to create a new universe according to these laws. Moreover, mainstream cosmologists believe that there is more than one universe, and that the Big Bang is only a part of the larger space-time that is happening, which means that there are many, many universes like us, and when our universe perishes, we can create a wormhole to reach another universe.

This is not an easy task. It takes a huge amount of energy to create a new universe or to create a wormhole or other tunnels to reach another universe. This energy may be equivalent to the energy produced by a particle collider the size of the solar system, or equivalent to the energy of an entire star or even a black hole. This amount of energy may consume most of the energy of an advanced intelligent civilization, and it will take thousands or even tens of thousands of years of work to accomplish this task, and the technology used will be incredibly complex and huge. This will be the greatest engineering project in the universe.

Of course, there are other possibilities. A few years ago, when Switzerland's Large Hadron Collider was about to be opened, some skeptics believed that it would inadvertently or trigger a "phase transition," a change in the structure of space-time similar to ice turning into water, propagating from Earth at the speed of light, changing the structure of the entire universe itself, and eventually bringing the universe back to its youth rather than going to the Dark Ages. However, it is clear that the energy of the Large Hadron Collider is not high enough. Perhaps in the future, advanced intelligent civilizations will produce more powerful particle accelerators to trigger phase transitions in the universe, so as to lead the future of the universe to another path.

Of course, the plan is not really to save the universe, but to save life in the universe. Finding a way to keep life on the path of eternity is the ultimate goal that any intelligent life should pursue.

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