Transcript 13. Time and the past and future histories of the universe

Time and the Past and
Future Histories of the
Universe
Michael Bass, Professor Emeritus
CREOL, The College of Optics and
Photonics
University of Central Florida
Orlando, FL 32816
© M. Bass
What is time?
We never seem to have enough of it.
 It seems to run faster than ever.
 We can’t take time to smell the roses.
 It seems to fly when your having fun.



It seems to drag when your not.
We have a psychological sense of
time because the world only makes
sense if time is what we think it is.
© M. Bass
Concepts of time

Cyclic –





The seasons are cyclic.
The tides are cyclic.
The moon goes through cycles.
The planets seem to move in cycles.
If you look around you would think that time
may be cyclic.


In fact the cycles could be extended to the
cycle of birth, life, and death and other life
cycles.
Might make you feel comfortable.
© M. Bass
Concepts of time

Linear –



There is a past, present and future.
While things seem to repeat there are
differences.
Causality – You would expect that there is
an order to how things happen.
• This means that events follow one another in
proper order.
• The sound of a drum never comes before it is
struck.
© M. Bass
How do we determine it?



We can not and do not measure it directly!!!
We measure time by counting changes in
something.
 How many swings of a pendulum.
 How many vibrations of a quartz crystal.
 How many oscillations of a certain atom.
 How many days since the sun passed over a
certain stone at Stonehenge.
 How many days between full moons.
The units are different but the result is the same:
 We count changes and call it a measure of time.
© M. Bass
Some great moments in time
(From “The Story of Time”, Royal Astronomical Observatory-Greenwich, UK)

28000 BC – marks carved on a bone seem to represent the moon’s course over 2.5
months.


4236 BC – Egyptian calendar showing that the star Sirius rose next to the sun every
365 days
3500 BC – Egyptians use obelisk as a sundial

3114 BC – Current Great Cycle of the Maya calendar begins. It lasts 5126 years.
and the world did not end
on Dec. 21, 2012 !!!

1400 BC – first water clocks. This is critical break from
measuring time by astronomy to measuring it by a mechanical device.
© M. Bass
More great moments in time







45 BC – The Julian calendar begins. A purely solar
calendar fixing the year at 365 days with a leap day
added every 4 years.
1277 AD - Roger Bacon calculates that the Julian
calendar year is 11 minutes longer than the solar year
and tells Pope Clement that it must be fixed.
1300-1400 AD – First records of mechanical clocks with
pendulums and bells in church towers.
1500-1510 AD – Peter Henlein in Nuremburg invents the
spring powered clock .
~1550 AD Nicolas Copernig (Coppernicus) revises the
calendar by assuming the earth goes around the sun –
starts a revolution.
1556 AD – Christian Huygens makes a pendulum clock
with error less than one minute per day.
1582 AD – Pope Gregory XIII reforms the Julian calendar.
It becomes the current Gregorian calendar
© M. Bass
More modern great
moments in time





1660 AD – Isaac Newton defines the fundamental
laws of mechanics on the basis of time – more
specifically on how things change with time. He
postulates an absolute universal time!
1761 AD – John Harrison builds a marine
chronometer with error less than 1/5th of a second
per day. Makes measurement of longitude
possible while at sea.
1884 AD – The demands for readable railroad
schedules requires adoption of Standard Time and
time zones.
1905 AD – Albert Einstein shows that time is
affected by motion and in 1914 AD by gravity.
1949 AD – China adopts the Gregorian calendar.
© M. Bass
Modern and future moments
in time
In a nanosecond light







1957 AD – Electric wrist watches are
marketed.
1967 AD – First quartz crystal
watches are marketed. These are
secondary time standards. The
primary is at NIST and the Naval
Observatory.
1970s AD – Measurement of
picoseconds.
1980s AD – Measurement of
femtoseconds.
1990s AD – Consideration of
measurment of attoseconds.
2012 AD – Current Maya great cycle
will end
4909 AD – Gregorian calendar will be
one day ahead of the solar calendar.
travels 30 cm (about
one foot).
In a picosecond light
travels 0.3 mm. (about
as close as you can
hold your thumb and
forefinger without
touching).
In a femtosecond light
travels 300 nm (about
300 atoms in a lattice).
In an attosecond light
travels 0.3 nm about
the size of an atom).
© M. Bass
The arrow of time

Today we think of time as somehow flowing
from past to present to future.


All the fundamental laws of physics (e.g.:
Newton’s Laws, Quantum Mechanics,
Electromagnetics, …) are time reversal
invariant.



This is a very Judeo-Christian idea.
For the mathematically inclined – they are all
second order in time so that replacing t with – t
doesn’t change anything.
The laws don’t care about the arrow of time.
Why then is there an arrow of time?
© M. Bass
Entropy, Probability and Time





Entropy is a thermodynamic quantity giving a measure
of irreversibility.
It is related to the likelihood that a system exists in a
particular configuration.
Since entropy must increase in a (or remain constant
in a reversible) thermodynamic system, all systems
evolve towards more and more likely configurations.
The future of a system is a more likely configuration
than its past.
Time then must go from past to future, from less likely
to more likely configurations of the universe.
© M. Bass
Planck Time



Planck invented a
set of units based
on the universal
constants (?) of the
universe.
G
35
l


1
.
616
x
10
m
Planck length,
P
3
c
Planck time,
lP
G
 44
tP  

5
.
39
x
10
sec
5
c
c
© M. Bass
Time and the Universe: Where we come from
and where we are going.
(The Future of the Universe, F. C. Adams and G. Laughlin, News of Michigan Physics, Fall 2000)





In the beginning there was nothing, and then the
big bang – between 10-44 and 10-35 seconds the
universe expands from a pinprick to larger than we
can presently see (This is the INFLATION ERA.)
Then there is energy and the expanding universe
cools and matter and antimatter appear. A tiny
imbalance favors matter over antimatter as these
things annihilate each other)
Free quarks appear after about 10-30 seconds.
More cooling and expansion and the quarks
combine into neutrons and protons. There are
photons, electrons, neutrinos and other stuff left
over from the annihilations after less than 1
second. There are nonuniformities that will lead
to galactic clusters, galaxies and other cosmic
structures. This is about 4% of the universe.
Dark matter is about 20% and Dark energy is
the rest of the universe and we don’t know
what either is.
nothing
everything
everything
© M. Bass
Getting started & the present





More cooling and expansion and the
neutrons and protons combine to form H, D,
He and Li. It is still too hot for the electrons
to bind with the nuclei and so the universe
is a plasma. This NUCLEOGENESIS ERA
takes about 3 minutes.
After about 300,000 years the universe
cools enough to allow atoms to form and it
becomes transparent. At this point the light
is free to travel through the universe.
At about 200,000,000 years the first
gigantic stars form. They live a short time,
supernova explosions occur and higher
atomic mass atoms are formed.
Several star forming generations go by and
after about 13 billion years there is us.
WE LIVE IN THE STELLIFEROUS ERA OF
THE UNIVERSE.
+
+
+
- +
- +
+
+
+ +
+
-
© M. Bass
The future







After 1014 years the stars burn out ( By this time we have not existed for
billions of years).
In the DEGENERATE ERA of the universe there are various dwarf stars,
neutron stars, and black holes.
After 1025 years these collide and leave black holes and particles.
After 1040 years the last of the protons decay leaving the universe in the
BLACK HOLE ERA.
After 1065 years solar mass black holes decay via Hawking radiation.
After 10105 years the last black holes decay and the universe is finally in
the DARK ERA where there is nothing but very, very long wavelength
photons.
MAYBE, JUST MAYBE, A NEW UNIVERSE WILL BEGIN FROM A
QUANTUM FLUCTUATION IN THE EMPTYNESS OF THE REMAINS
OF OUR UNIVERSE – AN MAYBE NOT.
© M. Bass
Acceleration
Now we know that Dark Energy is
accelerating the expansion.
 This was totally unexpected but has
been confirmed by observation.
 What is worse it is getting stronger as
time goes on and so in the very far
future
 everything will be torn apart by this
anti-gravity leaving a universe of
quantum foam and nothing else.

© M. Bass
The range of time





We have seen that time is the critical fact of all our
theories about our universe.
We can conceive, even if it is difficult, of time ranging
from 10-43 seconds to times of 10105 years (or if you
wish 10112 seconds).
We are starting to wonder if, for very short times, time
itself must be quantized and we are starting to use
such ideas to formulate theories of how things came
into being and how they will decay away.
Of course, Einstein’s extraordinarily superb theory of
general relativity considers time as continuous and so
we have to resolve this seeming conflict.
It just goes to show you that while we know a great
deal about time and we certainly know how important it
is, we still don’t really understand it.
© M. Bass