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Duke University
The Future of our Universe
Sam Pease
Math 89S: Mathematics of the Universe
Professor Hubert Bray
September 2016
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Humans of the future will look out into quite a different universe from the one we see
today. Assuming that our species is in it for the long run there are many cosmological events
that our distant descendants will observe along with many things that will only occur long
after we have any chance of being alive. We often think of the universe on a larger scale to
be static and unchanging because on the timespan of our short human live it is, but in the
long run the universe will go through much changing before finally winding down to an end.
There are multiple eras and phases that it will go through all marked by distinct features and
qualities. But, unfortunately, according to current scientific views all things do eventually
come to an end. Life on earth will find an end as conditions become survivable and the
greater universe as a whole will eventually degenerate into a lifeless place very different
from the vibrant structures we see today.
In the future there are many beautiful views that humanity will be able to see from
earth. Within the next 10 thousand years the red supergiant star Antares will likely have
exploded in a supernova. (Hockey, T.; Trimble, V.) This explosion will be visible from the
earth during the day even with competition from the sun. It would have a brightness similar
to that of a full moon, making our nights much more brightly lit and remaining visible into
the days. But it is unclear whether it is possible to have spectacular views with a naked eye
without posing dangerous side effects to life on earth. The most dangerous effects from a
supernova would be the depletion of earth’s ozone layer from high energy electromagnetic
radiation directed at earth. It has been approximated that about fifty percent of earth’s ozone
would be depleted if the supernova were at a distance of 10 parsecs and only 10 percent at a
distance of 30 parsecs (Ellis & Schramm). This means that Antares, with a distance of 190
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parsecs will not fry earth when going supernova. Similarly, in the next million years the red
supergiant star Betelgeuse is also expected to go supernova, also without disastrous effects
(European Southern Observatory). However, sometime in the next 300 thousand years WolfRayet star WR 104 is expected to explode in a supernova and it has been suggested that it
may produce a gamma ray burst that could pose a threat to life on Earth should its poles be
aligned 12° or lower towards Earth. It is not currently known if the poles are aligned towards
earth or not so, as of right now it is unclear if this is a potentially large problem to be faced
(Peter Tuthill, John Monnier, Nicholas Lawrance, William Danchi, Stan Owocki, Kenneth
Gayley). But even if this doesn’t cause problems for humanity Anne Minard approximates
that sometime within 500 million to 600 million years a supernova or gamma ray burst will
occur close enough to cause serious damage to our ozone, cause acid rain, and initiate global
cooling. This is what may have been the cause for the Ordovician–Silurian extinction event
which was the second largest mass extinction event on earth that killed 70% of marine life
that lived during the Ordovician period (488-443 million years ago).
An artist’s impression of a plume
Betelgeuse from the European
Southern Observatory on left and
“Betelgeuse explosion footage as
seen from Earth” from the YouTube
channel reyk javik pictured below
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We don’t often think about how imperfect and fallible our timekeeping systems are,
but in the next 50 thousand years the length of the day used for astronomical timekeeping
will reaches about 86,401 SI seconds, due to lunar tides decelerating the Earth's rotation.
Under the present-day timekeeping system, a leap second will need to be added to the clock
every day (Finkleman, David; Allen, Steve; Seago, John; Seaman, Rob; Seidelmann, P.
Kenneth). Tidal acceleration is where two orbiting bodies gravitational effect on each other is
to decelerate each body’s rotation. This can happen from a conservation of energy standpoint
because the rotation energy is transferred into potential energy as the bodies are pushed into
a more distant orbit. The most studied system of this type is the Earth-Moon system and the
effects are very visible as the moon’s rotation is the same length as its orbit, causing the same
face to be directed toward us at all times. In 50 billion years, if the sun has not engulfed the
Earth-Moon system it will become tide locked, with each body showing one face to the other
(Murray, C.D. & Dermott). While this end scenario of tidal acceleration is unlikely to
actually happen we will see effects of the process. In 600 million years, tidal acceleration
will have pushed the Moon’s orbit far enough from Earth that total solar eclipses are no
longer possible (NASA). As the moon drifts farther and farther away from us its apparent
size will decrease and at some point it will no longer be able to block out the sun from our
view. This is brought upon quicker by the fact that the sun is steadily growing.
After 100 thousand years many of our constellations will no longer be recognizable.
Stars are moving in different directions independently of each other and their apparent
motion across the sky is called their proper motion. Some stars appear “fixed” but they are in
fact moving relative to the sun. So the fact that stars are not moving the same direction
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means that constellations will stretch with their constituent stars separating as time moves on
(Kuhn). In approximately 1.4 million years the star Gliese 710 will pass close enough to our
solar system to possibly have an effect on us (Bobylev). It has a high chance, P=.86, of
penetrating the Oort cloud, and a nonzero possibility, P=1x10^4, of passing close enough to
have a significant effect on Kuiper belt objects. The Oort Cloud is an extended shell of icy
objects that exist in the outermost reaches of the solar system. It is spherical in shape and
reaches from about 0.8lightyears to 3.2lightyears away from the sun. It is thought to be the
origin of most of the long-period comets that we’ve observed. A nearby star passing into the
Oort cloud would perturb the icy bodies there and increase the likelihood of comet impacts in
the inner solar system. The Kuiper belt in the space between Neptune and the Oort cloud and
is the home to short period comets and many larger objects such as dwarf planets. This
would further increase the amount of comet impacts in the inner solar system.
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Starting at from 600 million years from now our aging sun will start to become a
problem for life on earth. If humanity has survived wiping itself out and many other natural
disasters it will definitely have to have figured out a way to get off earth before the sun
engulfs the planet. As the sun ages it increases in luminosity (10% in the next billion years,
which is an increase in average global temperature to 116 degrees Fahrenheit) it not only
increases surface temperatures but it also increases the amount of water vapor, a greenhouse
gas, in the atmosphere, further raising temperatures. Higher temperatures lead to increased
weathering of silicate rocks, drawing down more carbon from the atmosphere. Carbon is
normally recycled though plate tectonics; however, increasing water loss eventually stops
plate tectonics due to greater friction between the plates. Lower atmospheric carbon levels
begin to kill off higher order plants which will then lower the oxygen content of the
atmosphere to zero over several million years. This of course ends most large multicellular
life on earth. Microbial photosynthesis is still able to continue for a further 100 million years
even with extreme CO2 fluctuations. But eventually life, reduced to small isolated colonies
in isolated microenvironments, will die out as temperatures continue to rise as high as 300
degrees Fahrenheit on average by 2.8 billion years from now (O'Malley-James, Jack T.).
Life’s chances of survival are not helped by the fact that if the earths inner core continues
growing at the rate that it currently is then the molten outer core will freeze. The implication
of this is that earth will lose its protective magnetic field and the ozone layer will be buffeted
away by solar radiation (Waszek, Lauren; Irving, Jessica; Deuss, Arwen). And it is predicted
that the water vapor in the atmosphere will have risen to 40% in 3.5 to 4.5 billion years from
now. This combined with the 35%-40% increase in luminosity from the sun will make the
earth comparable to a modern day Venus with surface temperatures of 2420 degrees
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Fahrenheit, capable of melting rock (Guinan, E. F.; Ribas, I.). And then the end of earth lies
when it is consumed by our dying sun. In about 5 billion years from now our sun will have
run out of hydrogen in its core and begun to transition to become a red giant. Then the earth
will finally be consumed the growing sun in about 7.59 billion years (Schroder, K. P.;
Connon Smith, Robert).
All the while that this is happening in our solar system much is changing on a larger
scale around us. In 4 billion years from now our own milky way galaxy will have collided
with our neighboring Andromeda galaxy, creating a new combined galaxy known as
Milkdromeda. While the galaxies are colliding, due to the fact that they are mostly empty
space with stars scattered throughout there are not likely to be any collisions between stars,
so this will not be a specific downfall for our solar system (NASA). After this collision the
rest our local group of galaxies wont converge until 450billion years from now (University of
Arizona). But by this point the galaxies in our local group will be the only thing visible in the
night sky to us. After 100 billion years all stars outside of our local group will be outside of
our event horizon. As the universe’s expansion continues to accelerate due to dark energy
distant stars will be moving away so fast that all light coming from them will be redshifted to
the point where they are undetectable. It is at this point that we are no longer cable of
receiving information from outside our local group that we live in (Ethan Siegel). And then
by 150 billion years from now the cosmic microwave background will cool from its current
temperature of ~2.7 K to 0.3 K making it essentially undetectable with current technology
(Chown, Marcus).
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If this picture of our future didn’t already seem bleak enough it only gets worse. 100
trillion years from now the Stelliferous era will end and the Degenerate era will begin. The
Stelliferous era is marked by most of the energy generated in the universe arising from
nuclear processes in conventional stellar evolution. But this point in time marks the end of
normal star formation so the degenerate era begins which is an era where most of the mass of
the universe is tied up in degenerate stellar objects. Theses degenerate stellar objects are
remnants of stars such as brown dwarfs, white dwarfs, and neutron stars. Most of the energy
produced in this time comes from proton decay and particle annihilation. All remaining stars
formed from before that point will have exhausted their fuel by the 120 trillion year mark.
The longest lived low mass red dwarfs will have expended their 10-20trillion year lifespans
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and only brown dwarf stars and stellar remnants such as white dwarfs, neutron stars, and
black holes remain. Occasionally brown dwarfs will collide to form a red dwarf, so the
universe will not be completely dark. There will be on average 100 stars burning in the milky
way at this point opposed to our current 100 billion. There will also be the occasion
supernova created from collisions of stellar remnants. By 10^19 to 10^20 years 90-99% of
brown dwarfs and stellar remnants will have been ejected from our galaxy. When two of
such objects pass near each other they have the ability to sling-shot the lower mass object out
of the galaxy. Then in 10^30 years all remaining objects in all galaxies will have fallen into
the supermassive black hole at galaxies’ centers. This means that the entire universe will
only consist of solitary objects (Adams, Fred C.; Laughlin, Gregory).
Then in 3x10^43 years the black hole era will begin. If the proton half-life takes the
longest expected value, then all nucleons will have decayed by this point. This means that all
matter will have decayed and black holes are the only celestial objects in the universe. But
the black holes will too decay, through hawking radiation, like everything else in the
universe. By the year 1.7×10^106 all black holes will have decayed and the universe will
only be populated by subatomic particles. This marks the beginning of the dark era (Adams,
Fred C.; Laughlin, Gregory). And then the universe is likely to reach its final energy state in
10^10^120 years, which is when the universe is in thermodynamic equilibrium, or maximum
entropy, which means that no work can be done. And this is the likely end of the universe
(Linde, Andrei.).
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