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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

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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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 Wolf-

Rayet 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).

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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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