Cosmology deals with the big questions about the universe, the same questions that keep
philosophers up at night. How did the universe begin? Has it always expanded? Will the Universe
Ever End? As the last years of the 20th century drew
to a close, the astrophysical community was shocked to learn that the universe might be
collapsing. Science has known for a long time that distant
galaxies always move away from us, with the farther ones moving the fastest. The universe
is expanding. With all the matter in the cosmos, gravity
should slow down that expansion but it appears the expansion of the universe is actually
speeding up. Galaxies would be destroyed, the solar system
would become unbound, and eventually, the atoms of all planets would be ripped apart
by the rapid expansion of space. Ultimately, our universe would explode into a singularity
of literally infinite energy. Scientists have been trying for decades to
link mainstream physics' understanding of viscosity with cosmic viscosity, which indicates
the universe's resistance to accelerating expansion.
On large scales, the universe is modeled as a fluid, and the driving force behind the
Big Rip (if it occurs) could be the universe's cosmic viscosity.
Physics suggests that finding infinity indicates that we are missing a piece of the puzzle. No
matter how large the Big Rip gets, an improved theory might show that the expansion rate
of the universe won't reach infinity. If this so-called Big Rip is in our future,
it will take another 22 billion years for it to arrive.
Dark energy is a cosmological constant, a kind of uniform energy that exists throughout
the universe. If the cosmological constant is dominant in the universe, it would keep
expanding forever. The universe will continue to accelerate if the cosmological constant
remains dominant. Although it might not sound like much, it's
a bleak way to go. The cosmological constant will continue to
accelerate the expansion of the universe. This means that all the galaxies outside our
immediate neighborhood will be too far away to be visible in a few trillion years. Their
light will not reach us. Entropy will also continue to change.
The process of star formation itself will end in 100 trillion years after all the matter
necessary to fuel it has been consumed. In the end, black holes will evaporate, matter
itself will decay into radiation, and the universe will be a cold, lifeless place for
all eternity. This is called the Big Freeze. There's always a chance that dark energy won't
matter. We don't know what dark energy is, so we can't predict how it will behave in
the future. There are scenarios in which our universe
is all that exists. But what if there is more out there, and our universe is but a small
part of a multiverse? Can these other universes affect the outcome of our own?
The universe would exist in a state known as a false vacuum. In this state, we believe
that we exist in the most stable state, but it's still possible for it to suddenly change
states. It might be like a bubble boiling in water, just one of many with a unique set
of laws and constants. In the end, these bubbles may run into each
other, and from our vantage point, it would be as if our universe collided with another
universe. It would be as bad as it sounds. As everything in our universe changes to a
completely different state as a result of such a collision, our universe would end immediately.
There is the possibility of combining the two universes or creating something entirely
new. We would have no warning, and we could not stop it.
We could, however, find out whether a false vacuum existed in our universe in the very
distant past to determine whether such a collision is likely to happen again.
The size of such a prehistoric false vacuum would be much smaller than our universe, but
it could still leave behind a hint that something curious happened a long time ago.
It is very difficult to predict how the universe will end based on local measurements alone.
Even though we don't know for sure, anything is possible in a world of infinite possibilities.
With the advent of dark energy, some of the previous contenders for our ultimate fate
are now much less likely. The Big Crunch is one of the classic scenarios
of the end of the world. What if the expansion of the universe doesn't last forever? Due
to the gravitational pull of all the matter in the universe, the universe may stop growing
at some point. It would then begin to collapse back into itself.
In the end, the universe would reach a tiny singularity, a dark reflection of the Big
Bang. There was even speculation that a Big Crunch
could produce a Big Bounce right afterward, bringing the creation of a new universe into
being. Perhaps our universe is just one iteration of an infinite series of Big Bangs, Crunches,
and Bounces. Intelligent beings might find a way to cheat
a Big Freeze-like scenario in the distant future. The end times would require the beings
to store a finite amount of energy in the universe. They would then use half of this
energy to power their thoughts. After this, the beings would enter a stasis
state, in which no energy would be consumed. A certain point would come when half of the
remaining energy would be released, due to an as yet unknown technology created by the
beings, allowing them to think once more. They would have effectively come back to life,
unaware of the intrusion into their minds. Eventually, they'd exhaust all their energy
and return to stasis, but with more energy in reserve.
This cycle could continue indefinitely, and from their perspective, the universe would
never end. Through this energy rationing, the beings' thinking sessions might slow over
time, but there could be an infinite number of them.
Eventually, the parts of the universe that are currently in contact will be isolated
from each other, and the energy stored in these areas will become unavailable.
Therefore, some theorists have speculated that our descendants could transfer information
to new baby universes via wormholes or black holes.