Transcript HW 6 section 1 - Physics @ IUPUI

Goal: To understand the fate of the
most relevant things to us in the
universe.
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Objectives:
1) To learn about the end of Life on Earth
2) To learn about the future fate of Earth
3) To learn about the fate of Our galaxy
4) To learn about the fate of The Local
Group
• 5) To learn about The end of stars
• 6) To learn about The end of matter
End of Life on Earth
• We will ignore the possibility that mankind
destroys itself in a way that kills everything on
the earth.
• We will also ignore the possibility that some
really large object or other unpredictable
astronomical even destroys all life.
• So, we are just looking at life on earth in general
assuming that nothing unplanned happens.
The sun gets brighter
• Slowly over time the sun gets brighter.
• The sun is 30% brighter now than it was 4
billion years ago.
• Eventually this will become a problem for
life on Earth.
• Once the temperatures on Earth get over
140 degrees life will perish.
Mitochondrial DNA
• Mitochondrial DNA needs to split for there to be
reproduction.
• However Mitochondrial DNA won’t split for
temperatures > 140 degrees F.
• So, once temperatures get above that (due to a
brighter sun) then you cannot have reproduction.
You might still have life surviving for a time, but if
it cannot reproduce it is doomed to extinction.
• However, it will be 1-2 billion years before this
can happen.
Other issues
• The other issues involve water.
• The first is that water is slowly leaving
Earth.
• A very small amount gets to the upper
atmosphere where it is broken down by
solar UV rays into Hydrogen and Oxygen.
• They Hydrogen then escapes.
• In 2 billion years the earth will loose its
water.
Last issue
• If the Earth were to warm up too much the water vapor
content would increase.
• Water vapor is a greenhouse gas (the most prevalent)
and a 3 C rise in temperature gives a 20% rise in water
vapor levels.
• This heats the earth more.
• At some point the oceans would release the Carbon
Dioxide that they carry and the earth would experience a
“runaway” greenhouse effect and become as hot as
Venus.
• Assuming we don’t do it to ourselves it will take about 12 billion years for this to happen.
For last 3 billion years of Earth’s life
• Earth will be a lifeless planet.
• Eventually the sun will turn into a red giant (5
billion years from now).
• The earth will be baked and the surface will be
melted (temperatures will increase by a factor of
30!).
• The sun will grow 100 million miles in radius.
• The earth may or may not be eaten by the sun
(depending on how much mass the sun looses
the earth may be able to get far enough away to
survive).
6 billion years from now
• The sun will shed its outer layers and
become a white dwarf the with time cools
to a black dwarf.
• If the earth did not get eaten then the earth
might actually escape from the sun (if the
sun looses enough mass) or the earth will
just go into a higher orbit.
• Either way the earth will now freeze and
stay frozen until its final end.
Our galaxy
• Our galaxy – as we know it – probably has a
much shorter time to live than our planet.
• In 2-3 billion years our galaxy will probably
collide and then merge with Andromeda.
• The merger time may take a billion years, or if
Andromeda just grazes us we may all do
another pass.
• When the merger is finished there will be a new
galaxy (begin naming contest now! And please
don’t let us astronomers call it the Andromeda
Way galaxy…).
• This won’t affect us though.
Our Local Group
• Our local group is speeding towards the
Virgo cluster at 600 km/s (or 0.005 light
years/year).
• Since Virgo is 50 million light years away
our Local Group will merge with the Virgo
cluster in about 25 billion years (give or
take 5 billion).
• So, in 20-25 billion years we will be in the
Virgo Cluster – thus ending our Local
Group.
End of stars
• Eventually all of the dust and gas in our
universe will be used up.
• Once this happens you can no longer
make stars.
• This will take 100 trillion years – after
which the only main sequence stars in
existence will be brown dwarfs.
In 100 trillion years
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All that will be left:
Black Holes
Neutron Stars (Quark Stars)
White Dwarfs
Planets/moons ect
Brown Dwarfs
1 quadrillion years
• In 1 quadrillion years all the planets will
have been stripped from what remains of
the dead stars (white dwarfs, ect).
• This will be done very slowly over time via
gravitational perturbations of passing
objects.
• The planets will here forth wonder alone in
the heavens until the end of their days.
1019 years
• Because of gravitational interactions of passing
stars in this time span most of the stars of every
galaxy are expected to be tossed out of their
galaxies.
• Note this is 10 million trillions or 10 quintillion
years.
• In 100 quintillion years whatever has not
escaped falls into the central black hole due to
gravitational radiation – so galaxies are no more.
1036 years
• This is 1000 decitillion years.
• This is the estimated half life of a proton.
• So, after this it is expected that half of the
protons in the universe will have decayed!
• All of the protons decay by 1040 years.
• After that the only things left are photons
and black holes!
• This is the ultimate fate of the earth.
Black Holes
• As was mentioned, the space just above the
black hole can radiate Hawking Radiation.
• When the temperature of the universe falls to
extremely low levels then the black hole can
loose energy.
• The smallest black holes die first (at about 1040
to 10100 years from now), but the giant ones in
the cores of galaxies can last for 10150 years!
Photon age
• The entire universe is now photons.
• These photons will get lower and lower in
energy with time as the universe expands (and
at an ever increasing rate).
• At this point the universe is at its lowest energy
level and any life that survived the rest could not
survive anymore (no energy to tap into).
• And the universe just dies…
• We have no idea what will happen to space or
time after this point.
Big Rip
• Since the expansion of the universe will
continue to accelerate that means that
clusters of galaxies will get smaller
(tougher to keep them together).
• If the acceleration is fairly constant there is
not much of an affect on the outcome of
the universe.
• However, if that acceleration increases it is
possible to have a Big Rip.
What is a Big Rip
• A Big Rip is the universe being pulled
apart (even the atoms) by the expansion
of the universe.
• First clusters would fling apart, then
galaxies, then stars and planets, ect.
• Furthermore this would mean that the
observable universe would shrink greatly
with time.
How long do we have?
• Well, the soonest is 20 billion years from
now although it is likely to be much further
away than that.
Conclusion
• Nothing is forever, not even our galaxy.
• Everything has an end it seems – perhaps
even our universe itself.
• However that all a very long time away.
• The greater concern is that we don’t wipe
ourselves out in the next 100-200 years so
that we can actually worry about this
events billions of years in the future.