TIME TIME Defined 2 time Function verb Inflected

TIME

TIME : Defined… • 2 time Function: verb Inflected Form(s): timed; tim·ing transitive senses 1 a : to arrange or set the time of : SCHEDULE b : to regulate (a watch) to keep correct time 2 : to set the tempo, speed, or duration of … • 3 : to cause to keep time with something 4 : to determine or record the time, duration, or rate of <time a horse> 5 : to dispose : to keep or beat time From Webster’s Dictionary

WHAT IS TIME? • • • • Is time real? Is time psychological? Is time an illusion? Has time existed forever? If time had a beginning, why and how did it start? Does time really move? Where is time going? Does time go only in one direction? Does time ever come back? Does time have cycles? Does time come in quanta, like energy? Will time ever end? Can time stop?

“TIME IS THE MOVING IMAGE OF ETERNITY. IT IS AS IF WE WERE FLOATING ON A RIVER, CARRIED BY THE CURRENT PAST THE MANIFOLD OF EVENTS WHICH ARE SPREAD OUT TIMELESSLY ON THE BANK. ” PLATO

“TIME GLIDES BY WITH CONSTANT MOVEMENT, NOT UNLIKE A STREAM. FOR NEITHER CAN A STREAM STAY ITS COURSE, NOR CAN THE FLEETING HOUR. ” OVID

SAINT AUGUSTINE ‘CONFESSIONS’ (5 TH CENTURY) “HOW, THEN, CAN THESE TWO KINDS OF TIME, THE PAST AND THE FUTURE BE, WHEN THE PAST NO LONGER IS AND THE FUTURE AS YET DOES NOT EXIST ? ”

The Arrow of Time “RUINE HATH TAUGHT ME THUS TO RUMINATE: THAT TIME WILL COME AND TAKE MY LOVE AWAY. THIS THOUGHT IS AS A DEATH WHICH CANNOT CHOOSE BUT WEEP TO HAVE THAT WHICH IT FEARS TO LOSE. ” William Shakespeare Sonnet 64, 11 – 14

“THE MOVING FINGER WRITES; AND HAVING WRIT, MOVES ON: NOR ALL YOUR PIETY NOR WIT SHALL LURE IT BACK TO CANCEL HALF A LINE, NOR ALL YOUR TEARS WASH OUT A WORD OF IT. ” Omar Khayyám translated: E. Fitzgerald

“With Earth’s first Clay They did the Last Man’s knead, And then of the Last Harvest sow’d the Seed: Yea, the first Morning of Creation wrote What the Last Dawn of Reckoning shall read. ” Omar Khayyám translated: E. Fitzgerald

“TIME WILL RUN BACK, AND FETCH THE AGE OF GOLD” John Milton

“TIME GOES, YOU SAY? AH NO! ALAS, TIME STAYS, WE GO” Austin Dobson Collected Poems 1905

“FOR WHEN I WAS A BABE AND WEPT AND SLEPT, TIME CREPT; WHEN I WAS A BOY AND LAUGHED AND TALKED, TIME WALKED; THEN WHEN THE YEARS SAW ME A MAN, TIME RAN BUT AS I OLDER GREW, TIME FLEW. ” Henry Twells

“ GATHER YE ROSEBUDS WHILE YE MAY, OLD TIME IS STILL A-FLYING “ Robert Herrick 17 th Century Poet

“Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external. ” Isaac Newton

“I NEVER WORRY ABOUT THE FUTURE IT COMES SOON ENOUGH” A. Einstein

THE ARROW OF TIME WHY DOES TIME NEVER GO BACKWARD? The answer apparently lies not in the laws of nature, which hardly distinguish between past and future, but in the conditions prevailing in the early universe.

CAN TIME STOP?

Past and Future We think we can change and influence the future (OR CAN WE? ) Can we change the past (under suitable circumstances)?

THE PAST EXISTS ONLY AS A RECORD IN THE PRESENT

WHY DO WE REMEMBER THE PAST AND NOT THE FUTURE?

WHY DO WE REMEMBER THE PAST AND NOT THE FUTURE? INDEED, WE “REMEMBER” THE FUTURE WHEN WE MAKE “PREDICTIONS”!

Cosmological Theories The Big Bang Theory The Universe exploded some 13. 7 billion years ago from a very compact, very hot, high density state, and it is still expanding.

Direction of Time ? Historical Arrow of Time • Evolution of the Universe • Formation of galaxies, stars; biology – [Generation of order or information – simpler to more complex]

Cosmic Evolution of Matter Big Bang, galaxies, stars, heavy elements, planets, earth, life Evolution of Life Bacteria, algae, multicell organisms, fish, reptiles mammals, man Evolution of Intelligence and Technology Nomadic Life, fire, language, settlements, agriculture, writing, art, industry and technology, conquest of space

BIG BANG OBSERVATIONAL SUPPORT • The universe is expanding (Hubble’s Law). • There is a blackbody 2. 7 K background remnant radiation from the “primordial fireball”. • There are small fluctuations in the background radiation indicating the seeds of clusters of galaxies. • The He and D abundances fit the predicted values derived from a hot Big Bang. • The ages of the oldest stars agree with the age of the expanding universe. • The observed overall isotropy and homogeneity of the universe is consistent with the Big Bang.

THE ARROW OF TIME “Creation” Big Bang … Oldest Elements …… Oldest Galaxies ……… Our Galaxy ………… Oldest Stars …………… The Sun ……………… The Earth ………………… 4. 5 x 109 years

Thermodynamic Arrow of Time • Paradoxically the arrow of time can be defined with the opposite processes!! • Processes which destroy information and generate disorder (ENTROPY) – Melting an ice cube in hot tea – Evaporating a bottle of perfume

ENTROPY A measure of ORDER or DISORDER A measure of INFORMATION or CHAOS From LOW ENTROPY to HIGH ENTROPY HISTORICAL ARROW OF TIME: From high entropy to low entropy THERMODYNAMIC ARROW OF TIME: From low entropy to high entropy

COSMIC ENTROPY • At the hot Big Bang the universe within its horizon was very smooth, and the ENTROPY was at a MINIMUM state. (That is the total INFORMATION at the Big Bang was at a MAXIMUM ). • The Universe expanded and the temperature decreased, and the NET ENTROPY INCREASED, OR THE NET INFORMATION DECREASED.

ENTROPY FLUCTUATIONS • During the Big Bang expansion FLUCTUATIONS began to grow and some parts of the Universe decreased in entropy and increased in information (such as the formation of galaxies, stars, and life). But the NET ENTROPY for these systems, integrated over a period of time, also increased, - and eventually all INFORMATION will change into CHAOS (for an open Universe). • Fluctuations into lower Entropy may be due to Gravity

The Paradox of Irreversibility • Historical Arrow of Time – Thermodynamic Arrow of Time Both define preferred directions in time, which seem irreversible. WHY? ? • Why the ice cube in hot tea does not get colder and the tea hotter? ? • Why the molecules of perfume in the room do not gather together in the bottle?

Order out of Chaos!! • The laws of physics say nothing that these processes cannot happen. • The laws of physics are time-symmetrical (every detailed action could occur in reverse). • It seems that the concept of the passage of time is not needed in the laws of physics.

Universal Arrow of Time • Big Bang • • Temperature T=Tmax Entropy S=Smin Relative Order Information Total expansion to infinity Expansion to zero velocity and collapse T=Tmin S=Smax Disorder Chaos

THE ARROW OF TIME ASYMMETRY? • • The second law of thermodynamics The expansion of the universe Radiation expanding away from its source The process of measurement in quantum mechanics (the collapse of the wave function) • The decay of the neutral K meson (K°) (is asymmetric in time)

Causality and the Arrow of Time • IF A CAUSES B, THEN B DOES NOT CAUSE A • IF A CAUSES B, THEN A IS EARILER THAN B THIS IS THE TIME ASYMMETRY OF CAUSATION

? TIME ? • Make a movie of randomly moving molecules of a gas in an enclosure. • Play the movie forwards and backwards… • It would look pretty much the same, and we could not tell which way time is flowing!!!

“Unusual Film” How can we make a film where a hen becomes smaller? Chick crawls into a shell egg? ? By running film backwards? (No, that’s cheating).

“Unusual Film” How can we make a film where a hen becomes smaller? Chick crawls into a shell By running film backwards? egg? ? (No, that’s cheating). Get 10000 eggs in an incubator – 1 st frame of old hen While clock is running forwards! 2 nd frame a hen born a little after that, and so on to the hatching egg [Statistically backward running of time] for people Principle of Indistinguishability for hens for electrons!!

Special Theory of Relativity • The physical world has FOUR dimensions 3 of space x, y, z 1 of time t “SPACE – TIME” • A point in this 4 -dimensional system is called an EVENT. • One can think of ALL events PAST and FUTURE in the Universe by their x, y, z, t, coordinates.

Special Theory of Relativity • The physical world has FOUR dimensions 3 of space x, y, z 1 of time t “SPACE – TIME” • A point in this 4 -dimensional system is called an EVENT. • One can think of ALL events PAST and FUTURE in the Universe by their x, y, z, t, coordinates. A 4 -dimensional map Of everything in all of time In such a “space-time” there is no “movement of time”. The objective world simply is, it does not happen!!

The special theory of relativity leads to a picture in which “potentialities becoming actualities” is either highly subjective or meaningless.

THE TWIN PARADOX From: THE SPECIAL THEORY OF RELATIVITY

From: THE GENERAL THEORY OF RELATIVITY The rate of time passage is note the same from one place to another. Rate depends on the strength of gravity

To a distant observer time on the surface of a black hole appears to have stopped!!

Speculation Cosmic Time Travel • Violating Causality? – What would happen if someone went back in time and killed his grandmother when she was a baby? • Black holes have a singularity • Wormholes have two mouths and a connecting tunnel • Time Travel – A traveler falling into one mouth of a wormhole and down the throat might emerge from the second mouth only a few moments later, but halfway across the universe!

How to build a timehole. First, build a wormhole whose mouths are less than an hour apart by spaceship. At noon on time-travel day, accelerate one of the mouths to near light speed for one hour. A clock outside that mouth now reads 1 P. M. , while clocks inside the wormhole and outside the stationary mouth have barely budged off noon. If a spaceship plunges into the mouth that moved, it can speed through the wormhole in an instant, emerge from the other mouth just after noon, and return to the other mouth the long way around, in time to see itself going in.

The Mother and Baby Paradox From: THE GENERAL THEORY OF RELATIVITY (GTR) The mother becomes younger than her baby, while time is going in one direction, but with different rates !

The Big Bang from a singularity Singularities are places where the curvature of space-time is infinite and the concepts of space and time cease to have their normal meaning.

• GTR – time and mass/energy are related. • Rate of time passage is slow near large masses, while in vast empty spaces time would go very fast compared to ours. • The whole concept of time passage seems to be entirely due to the fact that there are masses in the universe.

Space-time • If time had no boundary then it ceases to be well defined at the Big Bang. • Just like the DIRECTION of north is not well defined at the north pole. • Asking what happened before the Big Bang is asking for a point say 1 km north of the north pole!

Space-time • What was before the Big Bang? • Did space-time exist? • Did space-time begin at the Big Bang? (with zero space and zero time).

Possible Cosmological Model The Oscillating Universe R(t) Rmax d Expan Con tract ? TIME Can you tell which way? • Or is it that in one cycle: • Time runs forwards during the expansion • Time runs backwards during the contraction ? ? ? ? ?

Time • Is it a handicap in our attempt to understand the nature of the physical world that we try and interpret all things in our subjective terms of a flowing time? • A deeper understanding of physical laws could remove our prejudices on the concept of the flow of time.

“Or say that the end precedes the beginning, And the end and the beginning were always there Before the beginning and after the end And all is always now. ” T. S. Eliot

To everything there is a season, and a time to every purpose under the heaven. Ecclesiastes Time is defined to make motion look simple. Albert Einstein Time is nature’s way to prevent everything from happening all at once. A Bathroom Wall