Time and the Past and Future Histories of the UniverseMichael Bass, Professor EmeritusCREOL, The College of Optics and PhotonicsUniversity of Central FloridaOrlando, FL 32816

© M. Bass

© 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.

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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.

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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.

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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.

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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.

1400 BC – first water clocks. This is critical break from measuring time by astronomy to measuring it by a mechanical device.

and the world did not end on Dec. 21, 2012 !!!

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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

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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

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.

In a nanosecond light 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. This is a very Judeo-Christian idea.

All the fundamental laws of physics (e.g.: Newton’s Laws, Quantum Mechanics, Electromagnetics, …) are time reversal invariant. 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?

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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.

Planck length,

Planck time,

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© 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

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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.

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© 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.