(In an earlier blog, "The Eternal Return" it says that the eternal return is Friedrich Nietzsche's deepest concept. I wanted to state that it was not actually his own concept, and people have believed this concept throughout history. Also, the eternal return is the one thing in life I completely believe, and that is the overall meaning of this page.)
Eternal return From Wikipedia, the free encyclopedia (Redirected from Eternal Return) For other uses of the term, see Eternal return (disambiguation).
Eternal return (also known as "eternal recurrence") is a concept which posits that the universe has been recurring, and will continue to recur in a self-similar form an infinite number of times. The concept has roots in ancient Egypt, and was subsequently taken up by the Pythagoreans and Stoics. In the Hebrew Scriptures, the notion is supported in the book of Ecclesiastes. With the decline of antiquity and the spread of Christianity, the concept fell into disuse, though Friedrich Nietzsche briefly resurrected it.
In addition, the philosophical concept of eternal recurrence was addressed by Arthur Schopenhauer. It is a purely physical concept, involving no "reincarnation", but the return of beings in the same bodies. Time is viewed as being not linear but cyclical.
The basic premise is that the universe is limited in extent and contains a finite amount of matter, while time is viewed as being infinite. The universe has no starting or ending state, while the matter comprising it is constantly changing its state. The number of possible changes is finite, and so sooner or later the same state will recur.
Physicists such as Stephen Hawking and J. Richard Gott have proposed models by which the (or a) universe could undergo time travel, provided the balance between mass and energy created the appropriate cosmological geometry. More philosophical concepts from physics, such as Hawking's "arrow of time", for example, discuss cosmology as proceeding up to a certain point, whereafter it undergoes a time reversal (which, as a consequence of T-symmetry, is thought to bring about a chaotic state due to thermodynamic entropy).
The oscillatory universe model in physics could be provided as an example of how the universe cycles through the same events infinitely.
Indian religions The concept of cyclical patterns is very prominent in Indian religions, including Hinduism and Buddhism among others. The Wheel of life represents an endless cycle of birth, life, and death from which one seeks liberation. In Tantric Buddhism, a wheel of time concept known as the Kalachakra expresses the idea of an endless cycle of existence and knowledge. A notable new religious movement called the Brahma Kumaris World Spiritual University teaches that this "eternal return" happens once every exactly 5,000 years in an identically repeating cycle ending with a total annihilation of humanity via an imminent and desirable Nuclear Holocaust, civil war and natural disaster information which is generally hidden from non-members.
Classical antiquity
Scarab on a fresco. In ancient Egypt, the scarab (or dung beetle) was viewed as a sign of eternal renewal and reemergence of life, a reminder of the life to come. (See also "Atum" and "Ma'at.")
The Bible appears to make reference to the idea of recurrence in Ecclesiastes 1:9: That which has been is that which will be, And that which has been done is that which will be done. So there is nothing new under the sun.
The ancient Mayans and Aztecs also took a cyclical view of time.
In ancient Greece, the concept of eternal return was connected with Empedocles, Zeno of Citium, and Stoicism.
Renaissance
The symbol of the Ouroboros, the snake or dragon devouring its own tail, is the alchemical symbol par excellence of eternal recurrence. The alchemist-physicians of the Renaissance and Reformation were aware of the idea of eternal recurrence; an attempt to describe eternal recurrence was made by the physician-philosopher Sir Thomas Browne in his Religio Medici of 1643:
And in this sense, I say, the world was before the Creation, and at an end before it had a beginning; and thus was I dead before I was alive, though my grave be England, my dying place was Paradise, and Eve miscarried of me before she conceived of Cain. (R.M.Part 1:59)
[edit] Friedrich Nietzsche The concept of "eternal recurrence" is central to the writings of Friedrich Nietzsche. As Heidegger pointed out,[citation needed] Nietzsche never speaks about the reality of "eternal recurrence" itself, but about the "thought of eternal recurrence". The thought of eternal recurrence appears in a few of his works, in particular §285 and §341 of The Gay Science and then in Thus Spoke Zarathustra. It is also noted in a posthumous fragment. The origin of this thought is dated by Nietzsche himself, via posthumous fragments, to August 1881, at Sils-Maria. In Ecce Homo (1888), he wrote that the thought of the eternal return as the "fundamental conception" of Thus Spoke Zarathustra.
Several authors have pointed out other occurrences of this hypothesis in contemporary thought. Rudolf Steiner, who revised the first catalogue of Nietzsche's personal library in January 1896, pointed out that Nietzsche would have read something similar in Eugen Dühring's Courses on philosophy (1875), which Nietzsche readily criticized. Lou Andreas-Salomé pointed out that Nietzsche referred to ancient cyclical conceptions of time, in particular by the Pythagoreans, in the Untimely Meditations. Henri Lichtenberger and Charles Andler have pinpointed three works contemporary to Nietzsche which carried on the same hypothesis: J.G. Vogt, Die Kraft. Eine real-monistische Weltanschauung (1878), Auguste Blanqui, L'éternité par les astres (1872) and Gustave Le Bon, L'homme et les sociétés (1881). However, Gustave Le Bon is not quoted anywhere in Nietzsche's manuscripts; and Auguste Blanqui was named only in 1883. Vogt's work, on the other hand, was read by Nietzsche during this summer of 1881 in Sils-Maria. Blanqui is mentioned by Albert Lange in his Geschichte des Materialismus (History of Materialism), a book closely read by Nietzsche.
Walter Kaufmann suggests that Nietzsche may have encountered this idea in the works of Heinrich Heine, who once wrote:
Time is infinite, but the things in time, the concrete bodies, are finite. They may indeed disperse into the smallest particles; but these particles, the atoms, have their determinate numbers, and the numbers of the configurations which, all of themselves, are formed out of them is also determinate. Now, however long a time may pass, according to the eternal laws governing the combinations of this eternal play of repetition, all configurations which have previously existed on this earth must yet meet, attract, repulse, kiss, and corrupt each other again...
Nietzsche calls the idea "horrifying and paralyzing", and says that its burden is the "heaviest weight" ("das schwerste Gewicht") imaginable. The wish for the eternal return of all events would mark the ultimate affirmation of life:
What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more' ... Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus? Or have you once experienced a tremendous moment when you would have answered him: 'You are a god and never have I heard anything more divine.' [The Gay Science, §341]
To comprehend eternal recurrence in his thought, and to not merely come to peace with it but to embrace it, requires amor fati, "love of fate".
My formula for human greatness is amor fati: that one wants to have nothing different, not forward, not backward, not in all eternity. Not merely to bear the necessary, still less to conceal it--all idealism is mendaciousness before the necessary--but to love it.
In Carl Jung's seminar on Thus Spoke Zarathustra Jung claims that the dwarf states the idea of the Eternal Return before Zarathustra finishes his argument of the Eternal Return when the dwarf says, "'Everything straight lies,' murmured the dwarf disdainfully. 'All truth is crooked, time itself is a circle.'"
The translation of Nietzsche's eternal return is from the German ewige Wiederkunft. The German word ewige also means perpetual. Though always translated as eternal it is worth noting this potential dual meaning.
Poincaré recurrence theorem Related to the concept of eternal return is the Poincaré recurrence theorem in mathematics. It states that a system having a finite amount of energy and confined to a finite spatial volume will, after a sufficiently long time, return to an arbitrarily small neighborhood of its initial state. It should be noted that "a sufficiently long time" could be much longer than the predicted lifetime of the universe (see 10^19 seconds).
Arguments against eternal return Nietzsche scholar Walter Kaufmann has described an argument originally put forward by Georg Simmel, which refutes the claim that a finite number of states must repeat within an infinite amount of time:
Even if there were exceedingly few things in a finite space in an infinite time, they would not have to repeat in the same configurations. Suppose there were three wheels of equal size, rotating on the same axis, one point marked on the circumference of each wheel, and these three points lined up in one straight line. If the second wheel rotated twice as fast as the first, and if the speed of the third wheel was 1/π of the speed of the first, the initial line-up would never recur.
However, Nietzsche begins from the premise that nothing is eternal and invariable (for otherwise we consider it a separate world). Therefore even the speed of the wheels would have to fluctuate. And because we assume that space is fully discrete ("quantum"), then speed – as the number of such "space quantums" made in a measure of time – would also have to be discrete, and thus we also have a finite number of velocities.
NASA Achieves Breakthrough In Black Hole Simulation (04.18.06) NASA scientists have reached a breakthrough in computer modeling that allows them to simulate what gravitational waves from merging black holes look like. The three-dimensional simulations, the largest astrophysical calculations ever performed on a NASA supercomputer, provide the foundation to explore the universe in an entirely new way.
According to Einstein's math, when two massive black holes merge, all of space jiggles like a bowl of Jell-O as gravitational waves race out from the collision at light speed.
Previous simulations had been plagued by computer crashes. The necessary equations, based on Einstein's theory of general relativity, were far too complex. But scientists at NASA's Goddard Space Flight Center in Greenbelt, Md., have found a method to translate Einstein's math in a way that computers can understand.
"These mergers are by far the most powerful events occurring in the universe, with each one generating more energy than all of the stars in the universe combined. Now we have realistic simulations to guide gravitational wave detectors coming online," said Joan Centrella, head of the Gravitational Astrophysics Laboratory at Goddard.
The simulations were performed on the Columbia supercomputer at NASA's Ames Research Center near Mountain View, Calif. This work appears in the March 26 issue of Physical Review Letters and will appear in an upcoming issue of Physical Review D. The lead author is John Baker of Goddard.
Similar to ripples on a pond, gravitational waves are ripples in space and time, a four-dimensional concept that Einstein called spacetime. They haven't yet been directly detected.
Gravitational waves hardly interact with matter and thus can penetrate the dust and gas that blocks our view of black holes and other objects. They offer a new window to explore the universe and provide a precise test for Einstein's theory of general relativity. The National Science Foundation's ground-based Laser Interferometer Gravitational-Wave Observatory and the proposed Laser Interferometer Space Antenna, a joint NASA - European Space Agency project, hope to detect these subtle waves, which would alter the shape of a human from head to toe by far less than the width of an atom.
Black hole mergers produce copious gravitational waves, sometimes for years, as the black holes approach each other and collide. Black holes are regions where gravity is so extreme that nothing, not even light, can escape their pull. They alter spacetime. Therein lies the difficulty in creating black hole models: space and time shift, density becomes infinite and time can come to a standstill. Such variables cause computer simulations to crash.
These massive, colliding objects produce gravitational waves of differing wavelengths and strengths, depending on the masses involved. The Goddard team has perfected the simulation of merging, equal-mass, non-spinning black holes starting at various positions corresponding to the last two to five orbits before their merger.
With each simulation run, regardless of the starting point, the black holes orbited stably and produced identical waveforms during the collision and its aftermath. This unprecedented combination of stability and reproducibility assured the scientists that the simulations were true to Einstein's equations. The team has since moved on to simulating mergers of non-equal-mass black holes.
Einstein's theory of general relativity employs a type of mathematics called tensor calculus, which cannot be turned into computer instructions easily. The equations need to be translated, which greatly expands them. The simplest tensor calculus equations require thousands of lines of computer code. The expansions, called formulations, can be written in many ways. Through mathematical intuition, the Goddard team found the appropriate formulations that led to suitable simulations.
Progress also has been made independently by several groups, including researchers at the Center for Gravitational Wave Astronomy at the University of Texas, Brownsville, which is supported by the NASA Minority University Research and Education Program.
Aug. 2, 2007 20:05 | Updated Aug. 3, 2007 7:51 By JUDY SIEGEL-ITZKOVICH
Could all our blunders be reversed, our failings eliminated? Perhaps so, if an Israeli scientist's research is to be believed. With the help of Prof. Amos Ori, we might just be able to go back and stop the screw-ups from happening in the first place.
Ori, a physicist from the Technion-Israel Institute of Technology in Haifa, has come up with what he says are practical solutions to overcome the hindrances that experts have long regarded as stopping us from traveling back in time.
In a paper published in the latest issue of the Physical Review journal, the scientist offers a theoretical model, based on mathematical equations describing conditions that, if established, could help lead to the development of a time machine of sorts. But rather than building an actual device, Ori explains that "the machine is space-time itself."
Time travel research is based on bending space-time so far that the time lines actually warp back on themselves to form a loop.
"We know that bending does happen all the time, but we want the bending to be strong enough and to take a special form where the lines of time make closed loops," explains Ori. "We are trying to find out if it is possible to manipulate space-time to develop in such a way."
While the possibility of time travel has never been ruled out, scientists have identified a number of physical challenges, including a perceived need for some form of exotic matter to create the necessary warp and get the wheels of time to turn back. Such matter is predicted by the quantum field theory to exist, although only in quantities too small for the construction of an actual time machine.
But Ori puts forth a different approach eliminating the need for exotic matter.
"If the proper initial conditions were achieved, the time machine would evolve on its own without any further intervention," he asserts. "It can be likened to shooting a ship with a cannon. Once the cannon is aimed properly and fired, the cannonball hits the ship on its own, driven solely by the laws of physics. The machine is space time itself. If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time."
But don't pack your bags and get ready to go dinosaur-hunting yet. "We, however," he cautions, "could not return to previous ages because our predecessors did not create this infrastructure for us."
The details of Ori's research are so complicated as to be baffling: In a 2004 paper, Ori outlined a set of conditions that would allow for the creation of a time loop without the need for exotic matter. According to that theory, the time loop would form as a donut-shaped vacuum, inside which time would curve back on itself, so that a person traveling around the loop might be able to go further back in time with each lap. A sphere containing a non-exotic - but unidentified - matter would in turn surround the loop.
"Science had long predicted that if a sufficiently large star collapsed at the end of its life, all the matter left in the star would be crushed into an infinitely small point with infinite gravity and infinite density -- a singularity. Hawking realised that the Universe was, in effect, a black hole in reverse.
Instead of matter being crushed into a singularity, the Universe began when a singularity expanded to form everything we see around us today, from stars to planets to people. Hawking realised that to come to a complete understanding of the Universe he would have to unravel the mysteries of the black hole."
Giant black hole observed at the center of galaxy RXJ 12 42-11 (650 million lightyear's from earth) tearing apart a neighbouring star. Video date- 17 02 2004.
Black Holes, Neutron Stars, White Dwarfs, Space and Time. A journey of simulations of Black Holes, Neutron Stars, White Dwarfs and Space and Time. Though, it is only a simulation, nothing more.
The simulacrum is never that which conceals the truth--it is the truth which conceals that there is none.
It has always astounded me that our clocks and time are based on days, hours, minutes, seconds... Who exactly figured this out, "the base unit of time in the International System of Units that is equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom", and when?? And how did they know way back then about this? Amazing really.
Function: noun Etymology: Middle English secounde, from Medieval Latin secunda, from Latin, feminine of secundus second; from its being the second sexagesimal division of a unit, as a minute is the first 1 a: the 60th part of a minute of angular measure b: the 60th part of a minute of time : 1/86,400 part of the mean solar day; specifically: the base unit of time in the International System of Units that is equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom
Metatron (Hebrew ?????? or ???????), is the name of an angel in Judaism and some branches of Christianity. There are no references to him in the Jewish Tanakh (Old Testament), the Christian Scriptures (New Testament) or any Islamic source. There is no consensus as to his genesis or the role that he plays in the hierarchy of Heaven and Hell.
Origins The Talmud has a section in which it claims that Elisha ben Abuyah, also called Aher ("another", as he was an apostate), entered Paradise and saw Metatron sitting down (an action that in heaven is permissible only to God Himself). Elishah ben Abuyah therefore looked to Metatron as a deity and said heretically, "There are indeed two powers in heaven!" The rabbis explain that Metatron was allowed to sit because of his function as the Heavenly Scribe, writing down the deeds of Israel (Babylonian Talmud, Hagiga 15a).
"... the Talmud states, it was proved to Elisha that Metatron could not be a second deity by the fact that Metatron received 60 'strokes with fiery rods' to demonstrate that Metatron was not a god, but an angel, and could be punished." -[1]
In opposition to this apology, Metatron is identified with the term "lesser YHVH", which is the Lesser Tetragrammaton, in a Talmudic version as cited by the Karaite scholar Kirkisani. The word 'Metatron' is numerically equivalent to Shaddai (God) in Hebrew gematria; therefore he is said to have a "Name like his Master." It should be noted, however, that Kirkisani may have misrepresented the Talmud in order to embarrass his Rabbanite opponents with evidence of dualism. On the other hand, extra-talmudic mystical texts do speak of a "lesser YHVH," apparently deriving the concept from Exodus 23:21, which mentions an angel of whom God says "My name [understood as YHVH, the usual divine proper name] is in him."
The Babylonian Talmud mentions Metatron in two other places: Sanhedrin 38b and Avodah Zarah 3b. Yevamot 16b describes in the amoraic period the duties of 'prince of the world' being transferred from Michael to Metatron.
Metatron is also mentioned in the Pseudepigrapha, most prominently in the Hebrew/Merkabah Book of Enoch, also called 3 Enoch or Sefer Hekhalot (Book of [the Heavenly] Palaces). The book describes the link between Enoch son of Jared (great grandfather of Noah) and his transformation into the angel Metatron. His grand title "the lesser YHVH" resurfaces here. Metatron says, "He [the Holy One]… called me, 'The lesser YHVH' in the presence of his whole household in the height, as it is written, 'My name is in him.'" (12:5, Alexander's translation). The narrator of this book, supposedly Rabbi Ishmael, tells how Metatron guided him through Heaven and explained its wonders. Here Metatron is described in two ways: as a primordial angel (9:2–13:2) and as the transformation of Enoch after he was assumed into Heaven.[2][3]
"Enoch walked with God; then he was no more, because God took him away." —Genesis 5:24 NIV.
"This Enoch, whose flesh was turned to flame, his veins to fire, his eye-lashes to flashes of lightning, his eye-balls to flaming torches, and whom God placed on a throne next to the throne of glory, received after this heavenly transformation the name Metatron." - Gershom G. Scholem, Major Trends in Jewish Mysticism (1941/1961) p. 67. Extract of 3 Enoch.
While this identification of Metatron with Enoch is not to be found in the Talmud itself, the connection is assumed by some of the earliest kabbalists. There also seem to be two Metatrons, one spelled with six letters (??????), and one spelled with seven (???????). The former may be the transformed Enoch, Prince of the Countenance within the divine palace; the latter, the Primordial Metatron, an emanation of the "Cause of Causes," specifically the tenth and last emanation, identified with the earthly Divine Presence.
According to Johann Andreas Eisenmenger, Metatron transmits the daily orders of God to the angels Gabriel and Sammael. Metatron is often identified as being the twin brother to Sandalphon, who is said to have been the prophet Elijah.
The Zohar calls Metatron "the Youth" a title previously used in 3 Enoch, where it appears to mean "servant".[3] It identifies him as the angel that led the people of Israel through the wilderness after their exodus from Egypt, and describes him as a heavenly priest.
VM Samael Aun Weor identifies Metatron as the Prophet Enoch, the Angel who provided humanity with the 22 Hebrew letters and the original Tarot, stating that the Angel lives in the superior worlds in the region Aziluth (The Initiatic Path in the Arcana of Tarot and Kabbalah).
Etymology There are numerous possible etymologies for the name Metatron; this section lists a few.[4] It should be noted, however, that some scholars such as Philip Alexander believe that if the name Metatron originated in Hekhalot-Merkabah texts (such as 3 Enoch) then it may be a made up word like the magic words Adiriron and Dapdapiron.[5]
Hugo Odeberg,[6], Adolf Jellinek[7] and Marcus Jastrow[8] suggest the name may originate from either "keeper of the watch" ???? or the noun "to guard, to protect" ??? an early derivation of this can be seen in Shimmusha Rabbah. Where Enoch is clothed in light and is the guardian of the souls ascending to heaven. Odeberg also suggests that the name Metatron might be taken from the Persian name Mithras.[6] He lays out a number of parallels between Mithras and Metatron based on their positions in heaven and duties.
Metatron seems to be made up of two Greek words, after and throne, µet? ??ó???, taken together as "one who serves behind the throne" or "one who occupies the throne next to the throne of glory". This has been disputed due to the word ??ó??? not being used in place of the Hebrew word for throne. The two words do not appear in any known text, leading to the belief of Gershom Scholem in particular to dismiss this idea[9] with the words "this widely repeated etymology.... has no merit."[10].
The word s???????? (synthronos) used as "co-occupant of the divine throne"[11] however like the above etymology it is not found in any source materials.[6] It is supported by Saul Lieberman and Peter Schäfer who give further reasons why this might be a viable etymology.[12][13]
The Latin word Metator (messenger, guide, leader, measurer) had been suggested by Eleazar ben Judah of Worms (c. 1165 - c. 1230), Rabbi Moshe ben Nachman, and brought to light again by Hugo Odeberg.[6] When transliterated into the Hebrew language, we get ?????? or ??????. Gershom Scholem argues that there is no data to justify the conversion of metator to metatron.[10] Philip Alexander also suggests this as a possible origin of Metatron, stating that the word Metator also occurs in Greek as mitator–a word for an officer in the Roman army who acted as a forerunner. Using this etymology, Alexander suggests the name may have come about as a description of "the angel of the Lord who led the Israelites through the wilderness: acting like a Roman army metator guiding the Israelites on their way".[14][15] Another possible interpretation is that of Enoch as a metator showing them "how they could escape from the wilderness of this world into the promised land of heaven". Because we see this as a word in Hebrew, Jewish Aramaic, and Greek, Alexander believes this gives even more strength to this etymology.
Other ideas are µet???a "a measure".[16] Charles Mopsik believes that the name Metatron may be related to the sentence from Genesis 5:24 "Enoch walked with God then he was no more, because God took him."[17] The Greek version of the Hebrew word "to take" is µetete?? (it was transferred).[citation needed] ??? meaning RON is a standard addition to ?????? metatron and other angelic names in the Jewish faith. So Mopsik believes if we concentrate on ??? MTT he believes it appears to be a transliteration from the Greek µetete??.
In the entry entitled "Paradigmata" in his study, "'The Written' as the Vocation of Conceiving Jewishly", John W McGinley gives an accounting of how this name functions in the Bavli's version of "four entered pardes."[18] This account maintains that "Ishmael ben Elisha" is a Rebbinically sanctioned cognomen for Elisha ben Abbuyah (the "Akher" of the Bavli's account). This hypothesis explains why the generators of the "chambers" portion of the Heikhalot literature make "Ishmael ben Elisha" the major protagonist of their writings even though this Rabbi Ishmael was not directly mentioned in the Bavli's account (in the Gemara to tractate Khaggigah) of "The Work of the Chariot."
Metatron's Cube
Metatron's CubeThe Fruit of Life (a component of the Flower of Life) has thirteen circles. If each circle's centre is considered a "node", and each node is connected to each other node with a single line, a total of seventy-eight lines are created. Within this cube, many other shapes can be found, including two-dimensionally flattened versions of the five platonic solids.
In early kabbalist scriptures, Metatron supposedly forms the cube from his soul. This cube can later be seen in Christian art, where it appears on his chest or floating behind him. Metatron's cube is also considered a holy glyph, and was often drawn around an object or person to ward off demons and satanic powers. This idea is also present in alchemy, in which the cube was favoured as a containment circle or creation circle.
The simplest means of constructing Metatron's Cube is to begin with a cube flattened along a diagonal that passes through its centre, such that it becomes a 2D figure, equivalent to a regular hexagon divided via its own diagonals into six equilateral triangles. The vertices of this 2D figure are then connected with additional lines. Several steps later, the full Metatron's Cube figure is formed.[19] The cube resembles the fourth dimensional analog of the cube, or the Tesseract.
Strange Phenomena Observed in Our Universe "A mathematician confided
That a mobius strip is one sided
And you'll get quite a laugh
if you cut it in half;
it's one two-sided piece when divided!"
Cut or tear a lengthwise strip from a sheet of paper. Curl it in on itself and tape it, and you have a link in a paper chain. Twist it a hundred and eighty degrees before taping it (forming a sort of twisted 8), and you have created a Mobius strip--a bizzare mathematical obscurity which has been charming and befuddling scientists, philosophers, mathematicians (and bored people with tape and scissors) for many ages.
What's the reason for all this hubbub? The answer is deceptively simple: as the geometry professors put it, the strip has but one side. Want proof? Run your finger along the "outside" of the Mobius strip, and you will pretty soon discover that the "outside"; has become the "inside," and in no time at all the "inside" becomes "outside" again, and your finger has traveled the entire area of the once double sided band! Common sense dictates that paper is aways two-sided, but unfortunately for common sense, there is no way to logically distinguish two sides to this twisted strip. Logician's conclusion? Outside and inside do not exist for Mobius strips at all!
Thinkers of all sorts have had fun pondering the implications of such an unusual strip. A daring two-dimensional traveler embedded in a Mobius strip would not only have to abandon the concepts of "in" and "out" but also left and right. For instance, a flat, left-handed, one-sided adventurer embedded in a Mobius strip would flip and become right handed, and left handed again, after traveling the length of the strip. His heart would also "flip" over to and back from the right side of his body. If our three-dimensional universe's space were Mobius shaped, traveling around the universe could make the same things happen to us!
"Yes," says the skeptic. "But our universe's space-time is not shaped like a mobius strip. (Actually, according to current belief, it is shaped like a flat sheet, a saddle, or even perhaps a balloon.) Where are the practical applications to all this nonsense?"
The answer lies neither in quantum physics nor General Relativity, but in the quirky gray matter between called SuperString Theory. Feynman diagrams containing the Mobius strip phenomena have been used to plausibly explain the geometry of what theoretical physicists call "colliding open strings." If SuperString Theory lives up to its promise, the concept of a Mobius strip may help to bridge the theories of quantum physics and general relativity and lead to a unified theory of the macro and micropscopic universes.
Nope, Mobius strips don't follow common sense--but then again, neither do the mysteriously contracting rulers and lengthening seconds indicated by Einstein's General Relativity. And they're not nearly as strange as the electrons of quantum theory which apparently "choose" their location depending upon whether or not they are being watched by a human observer.
SuperString Theory, if successfully completed, may find some sort of sense in the paradoxes posed by quantum physics and General Relativity, and (supposedly) make the physical universe understandable to us all with only a single equation. All this, thanks to the Mobius strip.
The Eternal Return is for Nietzsche the most weighty thought. It is a difficult thought, hard to grasp and conceptualize. In Nietzsche's mind the Eternal Return was a horrifying thought, almost paralyzing. Here is a selection from The Gay Science:
The greatest weight. -- What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence--even this spider and this moonlight between the trees, and even this moment and I myself. The eternal hourglass of existence is turned upside down again and again, and you with it, speck of dust!' Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus? Or have you once experienced a tremendous moment when you would have answered him: 'You are a god and never have I heard anything more divine.' If this thought gained possession of you, it would change, you as you are or perhaps crush you.
Plato argued that time is constant - it's life that's the illusion. Galileo shrugged over the philosophy of time and figured out how to plot it on a graph so he could get on with the important physics. Albert Einstein said that time is just another dimension, a fourth one to go along with the up-down, side-side, forward-back we move through every day. Our understanding of time, Einstein said, is based on its relationship to our environment. Weirdly, the faster you travel, the slower time moves. The most radical interpretation of his theory: Past, present, and future are merely figments of our imagination, constructs built by our brains so that everything doesn't seem to happen at once.
Einstein's conception of unified spacetime works better on graph paper than in the real world. Time isn't like those other dimensions - for one thing, we move only one way within it. "What's needed is not to make the notion of time and general relativity work or to go back to the notion of absolute time, but to invent something radically new," says Lee Smolin, a physicist at the Perimeter Institute in Waterloo, Ontario.
Others, including famed astrophysicist Stephen Hawking, note that time is defined by entropy. That is, the universe, in its current expanding direction, is becoming more and more disordered- entropy is increasing and always has been since the inception of the universe, as is time. Thus, time can represented as a measure of entropy in the universe.
Somebody is going to get it right eventually. It'll just take time.
Erin Biba, San Francisco-based writer
"In this moment there is nothing that comes to be. In this moment there is nothing that ceases to be. Thus there is no birth-and-death to be brought to an end. Thus the absolute peace in this present moment. Though it is at this moment, there is no limit to this moment, and herein lies eternal delight."
Zen Master Seung Sahn elaborated on this topic in his excellent book The Compass of Zen (p. 143):
"Everyone thinks that this is extremely difficult teaching, something beyond their reach or experience. How can things appear and disappear, and yet there is, originally, even in this constantly moving world, no appearing and disappearing? A student once asked me, 'The Mahaparinirvana-sutra seems very confusing. Everything is always moving. And yet everything is not moving? I don't understand this Buddhism . . .' But there is a very easy way to understand this: Sometime you go to a movie. You see an action movie about a good man and a bad man--lots of fighting, cars moving very fast, and explosions all over the place. Everything is always moving very quickly. Our daily lives have this quality: everything is constantly moving, coming and going, nonstop. It seems like there is no stillness-place. But this movie is really only a very long strip of film. In one second, there are something like fourteen frames. Each frame is a separate piece of action. But in each frame, nothing is moving. Everything is completely still. Each frame, one by one, is a complete picture. In each frame, nothing ever comes or goes, or appears or disappears. Each frame is complete stillness. The film projector moves the frames very quickly, and all of these frames run past the lens very fast, so the action on-screen seems to happen nonstop. There is no break in the movement of things. But actually when you take this strip of film and hold it up to the light with your hands, there is nothing moving at all. Each frame is complete. Each moment is completely not-moving action.
"Our minds and the whole universe are like that. This world is impermanent. Everything is always changing, changing, changing, moving, moving, moving, nonstop. Even one second of our lives seems full of so much movement and change in this world that we see. But your mind--right now--is like a lens whose shutter speed is one divided by infinite time. We call that moment-mind. If you attain that mind, then this whole world's movement stops. From moment to moment you can see this world completely stop. Stop. Stop. Stop. Stop. Stop. Like the film, you perceive every frame--this moment--which is infinitely still and complete. In the frame, nothing is moving. There is no time, and nothing appears or disappears in that box. But this movie projector--your thinking mind--is always moving, around and around and around, so you experience this world as constantly moving and you constantly experience change, which is impermanence. You lose moment-mind by following your conceptual thinking, believing that it is real."
"This is not unchanging, yet it is not moving. It has never been void; there is no question of inside or outside, no separation of absolute and relative. Realize that this is your own original face: even if it appears as ordinary or holy, even if it divides into objective and subjective experiences, all comes and goes completely within it, all arises and vanishes herein. It is like the water of the ocean making waves; though they rise again and again, never is any water added. It is also like waves dying away; though they die out and vanish, not a drop is lost."
--Zen Master Keizan, Transmission of Light
"The life of a sentient being is a long dream. Existence only appears to be real. When one finally awakens, or attains Buddhahood, existence is seen for what it is--a sequence of illusions. Until that time, people will remain obsessed by the body, mind, and external phenomena, not realizing that they are illusory. You will live in a dream, thinking that it is reality. . . .
"Sentient beings mistakenly view their moment-to-moment illusory existence as a continuous, connected lifetime. Because they are unaware that their life is unreal, they do not attempt to wake up."
--Ch'an Master Sheng-yen, Complete Enlightenment, pp. 108-109
"If you are attached to your thinking, then everything has name and form. This is the world of opposites. But name and form are always changing, changing, changing. Because of this, everything is impermanent. Everything is like a dream, is like dew, is like a bubble or a flash of lightning. Nothing stays but is always in a process of change. Rather than being some constant, fixed reality, this whole universe constantly appears and disappears. But there is a way to experience the true nature of this constantly changing universe. Simply do not become attached to any outside world. Don't become attached to names and forms. If you keep that point, then your mind is not moving. You attain that names and forms are fundamentally empty. This whole universe is completely empty. You are completely empty. Nothing ever comes or goes. Nothing ever appears or disappears. When you keep this mind, you soon attain your true self."
--Zen Master Seung Sahn, The Compass of Zen, pp. 127-129
"It is like a cinema-show. There is the light on the screen and the shadows flitting across it impress the audience as the enactment of some piece. If in the same play an audience also is shown on the screen as part of the performance, the seer and the seen will then both be on the screen. Apply it to yourself. You are the screen, the Self has created the ego, the ego has its accretions of thoughts which are displayed as the world, the trees and the plants. . . . In reality, all these are nothing but the Self. If you see the Self, the same will be found to be all, everywhere and always. Nothing but the Self exists."
--Sri Ramana Maharshi
"To talk about the world as being made by God tomorrow or yesterday, would be talking nonsense. God makes the world and all things in this present now."
--Meister Eckhart
"Waking up from the dream means realizing that nothing ever happened. With Enlightenment there is no history. It has been burned out of existence. Time itself has been destroyed."
--Andrew Cohen
"It is like an image reflected in a mirror, it is seen but it is not real; the One Mind is seen as a duality by the ignorant when it is reflected in the mirror constructed by their memory. . . . The existence of the entire universe is due to memory that has been accumulated since the beginningless past but wrongly interpreted."
--The Lankavatara Sutra
"Just understand that things do not originate of themselves. All of them come into existence from your own single mental impulse of imagination mistakenly clinging to appearances.
"If you know that mind and objects fundamentally do not contact each other, you will be set free on the spot. Everything is in a state of quiescence right where it is; this very place is the site of enlightenment."
--Zen Master Pai-chang
"There is nothing to overcome and nothing to prepare for¾you cannot prepare for where you already are.
"If you believe that some process in time will gradually release you from the illusion of samsara, then you are in a very secure position. But if you realize that the idea of time is the illusion of samsara then the whole business is finished up very quickly. As long as there is any investment in the future, you are a hundred billion miles away from home."
--Andrew Cohen, Enlightenment is a Secret
"There is only now. Everything we call the 'past' is absolutely nothing but present memory. Everything we call the 'future' is absolutely nothing but fantasy and commentary, that is, present memory rearranged. If we continue to pretend that there is some other time or place to be, besides right here, right now, we are cruelly and pathologically deluding ourselves."
--Scott Morrison, There Is Only Now
"Beginningless time and the present moment are the same. . . . You have only to understand that time has no real existence."
--Zen Master Huang Po
"Eternity is not, and cannot, be found tomorrow--it is not found in five minutes--it is not found in two seconds. It is always already Now. The present is the only reality. There is no other."
--Ken Wilber, No Boundary
"All temporal succession coincides in one and the same Eternal Now. So there is nothing past or future."
--Nicolas de Cusa
"If you want to know what eternity means, it is no further than this very moment. If you fail to catch it in this present moment, you will not get it, however many times you are reborn in hundreds of thousands of eons."
--Zen Master Seppo
"You examine the face of heaven and earth, but you have not come to know the one who is in your presence, and you do not know how to examine the present moment."
--Jesus Christ, The Gospel of Thomas, saying 91
"The idea of time is only in your mind. It is not in the Self. There is no time for the Self. Time arises as an idea after the ego arises. But you are the Self beyond time and space; you exist even in the absence of time and space."
--Sri Ramana Maharshi
Time
Time has been studied by philosophers and scientists for 2,500 years, and thanks to this attention it is much better understood today. Nevertheless, many issues remain to be resolved. Here is a short list of the most important ones—what time actually is; whether time exists when nothing is changing; what kinds of time travel are possible; why the time dimension has an arrow but a space dimension does not; whether the future and past are real; how to analyze the metaphor of time's flow; whether the future will be infinite; whether there was time before the Big Bang; whether tensed or tenseless concepts are semantically basic; what is the proper formalism or logic that captures the special role that time plays in reasoning; and what are the neural mechanisms that account for our experience of time. Some of these issues will be resolved by scientific advances alone, but others require philosophical analysis. Philosophers of time are deeply divided on the question on what sort of ontological differences there are among the present, past and future. There are three competing theories. Presentists argue that necessarily only present objects and present experiences are real; and we conscious beings recognize this in the special "vividness" of our present experience. According to the growing-universe theory, the past and present are both real, but the future is not. The more popular theory is that there are no significant ontological differences among present, past and future. This view is called "eternalism" or "the block universe theory."
This controversy raises the issue of tenseless versus tensed theories of time. Eternalism or the block universe theory implies a tenseless theory. The earliest version of this theory implied that tensed terminology is not semantically basic, but could be analyzed away with tenseless terminology. For example, the future-tensed sentence "The Lakers will win the basketball game" might be analyzed as "The Lakers do win at time t, and time t happens after the time of this utterance." The verb phrases "do win" and "happens after" aren't functioning as present tensed phrases. They are tenseless (logically, although not grammatically). The idea behind the analysis is that once all tenseless facts are fixed, all tensed facts are thereby fixed. Later versions of the tenseless theory do not imply that tensed terminology is removable or reducible, but only that the truth conditions of tensed remarks can be handled with tenseless facts. On the other hand, advocates of a tensed theory of time say that tenseless terminology is not semantically basic but should be analyzed in tensed terms, and that tensed facts are needed to make the tensed statements be true. For example, a tensed theory might imply that the world involves irreducible tensed properties such as presentness or now-ness or being-in-the-present, and no adequate account of the present tensed fact that it's now midnight can be given without these tensed properties. So, the philosophical debate is over whether tensed concepts have semantical priority over untensed concepts, and whether tensed facts have ontological priority over untensed facts.
This article explores both what is now known about time and what is controversial and unresolved, by addressing the following questions:
Table of Contents (Clicking on the links below will take you to those parts of this article) 1. What should a philosophical theory of time do? 2. How is time related to mind? 3. What is time? 4. What does science require of time? a. Relatvity and Quantum Mechanics b. The Big Bang c. Is time infinite? d. Atoms of time 5. What kinds of time travel are possible? 6. Is the relational theory of time preferable to the absolute theory? 7. Does time flow? 8. What gives time its direction or "arrow"? a. What needs to be explained? b. Explanations or theories of the arrow c. Multiple arrows d. Reversing time 9. Is only the present real? 10. Are there essentially tensed facts? 11. What is temporal logic, the symbolic logic of time? 12. Supplement of frequently asked questions:
What are proper times, coordinate systems, and Lorentz transformations? What are instants and durations? What is an event?
What is a reference frame? What is an inertial frame?
What is spacetime?
What is a Minkowski diagram? What are the metric and the interval? Does the theory of relativity imply time is partly space?
Is time the fourth dimension?
Is there more than one kind of physical time?
How is time relative to the observer?
What are the relativity and conventionality of simultaneity?
What is the difference between the past and the absolute past?
What is time dilation?
How does gravity affect time?
What happens to time near a black hole?
What is the solution to the twins paradox (clock paradox)?
What is the solution to Zeno's paradoxes?
How do time coordinates get assigned to points of spacetime?
How do dates get assigned to actual events?
What is essential to being a clock?
What is our standard clock?
Why are some standard clocks better than others? What does it mean for a clock to be accurate? 13. References and Further Reading
Should it define "time"? Yes, but it is improper to demand that we define our term "time" as a prelude to saying anything more about time, in large part because as we've learned more about time our definition of time has evolved. What we really want is to build a comprehensive, philosophical theory of time that helps us understand time, say, by helping us solve problems about time. We don't want to start building this theory by adopting a definition of time that prejudices the project from the beginning.
Although there are theories of how to solve a specific problem about time, it is always better to knit together solutions to several problems. Ideally, the goal is to produce a theory of time that will solve in a systematic way the constellation of problems involving time. What are those problems?
One is to clarify the relationship between time and the mind. Does time exist for beings that have no minds? It is easy to confuse time itself with the perception of time.
Another problem is to decide which of our intuitions about time should be retained. Some of these intuitions may reflect deep insights into the nature of time, and others may be faulty ideas inherited from our predecessors. It is not obvious which is which. For one example, if we have the intuition that time flows, but our science implies otherwise, then which view should get priority? Philosophers of time must solve the problem of how to treat our intuitions.
A third problem for a philosophical theory of time is to clarify what physical science presupposes and implies about time. A later section of this article examines this topic. Most all philosophers of time claim that philosophical theories should be consistent with physical science, or, if not, then they must accept the heavy burden of proof to justify the inconsistency.
A philosophical theory of time should describe the relationship between instants and events. Does the instant that we label as "11:01 A.M." for a certain date exist independently of the events that occur then? In other words, can time exist if no event is happening? This question or problem raises the thorny metaphysical issue of absolute vs. relational theories of time.
A theory of time should address the question of time's apparent direction. If the projectionist in the movie theater (cinema) shows a film of cream being added into black coffee but runs the film backwards, we in the audience can immediately tell that events couldn't have occurred this way. We recognize the arrow of time because we know about the one-directional processes in nature. This arrow becomes less and less apparent to us viewers as the film subject gets smaller and smaller and the time interval gets shorter and shorter until finally we are viewing processes that could just as easily go the other way, at which point the arrow of time has disappeared. Philosophers disagree about the explanation of the arrow. Could it be a consequence of the laws of science? The arrow appears to be very basic for understanding nature, yet it is odd that asymmetries in time don't appear in the principal, basic dynamical laws of physics. Could the arrow of time reverse some day? Philosophers wonder what life would be like in some far off corner of the universe if the arrow of time were reversed there. Would people there walk backwards up steps while remembering the future?
Another philosophical problem about time concerns the two questions, "What is the present, and why does it move into the past?" If we know what the present is, then we ought to be able to answer the question, "How long does the present last?" Regarding the "movement" of the present into the past, many philosophers are suspicious of this notion of the flow of time, the march of time. They doubt whether it is a property of time as opposed to being some feature of human perception. Assuming time does flow, is the flow regular? With some theories time, we can make sense of Friday seconds lasting much longer than Thursday seconds, as the flow of Friday time slows to a crawl.
Some philosophers doubt whether the future and past are as real as the present, the feature that is referred to by the word "now." A famous philosophical argument says that, if the future were real, then it would be fixed now, and we would not have the freedom to affect that future. Since we do have that freedom, the future can't be real. Some philosophers consider this to be a clever, but faulty argument.
For a last example of a philosophical issue regarding time, is time a fundamental feature of nature, or does it emerge from more basic features--in analogy to the way the smoothness of water flow emerges from the complicated behavior of the underlying atoms? From what more basic feature does time emerge?
A full theory of time should address this constellation of philosophical issues about time. Narrower theories of time will focus on resolving a few members of this constellation, but the long-range goal is to knit together these theories into a full, systematic, detailed theory of time.
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2. How is time related to mind?
Physical time is public time, the time that clocks are designed to measure. Psychological time is private time. It is best understood as being aware of physical time. Psychological time passes passes swiftly for us while we are enjoying reading a book, but it slows dramatically if we are waiting anxiously for the water to boil on the stove. The slowness is probably due to focusing our attention on shorter intervals of physical time. Some philosophers claim that psychological time is completely transcended in the mental state called "nirvana." Meanwhile, the clock by the stove is measuring physical time and is not affected by anybody's awareness. When a physicist defines speed to be the rate of change of position with respect to time, the term "time" refers to physical time. Physical time is more basic for helping us understand our shared experiences in the world, and so it is more useful than psychological time for doing science. But psychological time is vitally important for understanding many human thought processes. We even have an awareness of the passage of physical time during our sleep, and we awake knowing we've slept for one night, not for one month. But if we've been under a general anesthetic and wake up, we have no sense of how long we've been unconscious. Psychological time stopped.
Psychologists are interested in whether we can speed up our minds relative to physical time. If so, we might become mentally more productive, get more high quality decision making done per fixed amount of physical time, learn more per minute. Several avenues have been explored: using drugs such as cocaine and amphetamines, undergoing extreme experiences such as jumping backwards off a tall tower with bungee cords attached to the legs, and trying different forms of meditation. So far, none of these avenues have led to success productivity-wise.
Any organism's sense of time is subjective, but is the time that is sensed also subjective, a mind-dependent phenomenon? If it were subjective in the way judgments of good food or good music are subjective, then it would be miraculous that everyone can so easily agree on the ordering of public events in time. For example, first, Einstein was born, then he went to school, then he died. Everybody agrees that it happened in this order: birth, school, death. No other order. The agreement on time order for so many phenomena is part of the reason that many philosophers and scientists believe physical time is an objective phenomenon not dependent on being consciously experienced. The other part of the reason time is believed to be objective is that our universe has a large number of different processes that bear consistent time relations, or frequency of occurrence relations, to each other. For example, the frequency of a fixed-length pendulum is a constant multiple of the half life of a specific radioactive uranium isotope; the relationship doesn't change as time goes by (at least not much and not for a long time). The existence of these sorts of relationships makes our system of physical laws much simpler than it otherwise would be, and it makes us more confident that there is something objective we are referring to with the time-variable in those laws.
If there were no minds, would physical time be absent, too? Aristotle raised this metaphysical question when he said, "Whether, if soul (mind) did not exist, time would exist or not, is a question that may fairly be asked; for if there cannot be someone to count there cannot be anything that can be counted..." [Physics, chapter 14]. He doesn't answer his own question because, he says rather profoundly, it depends on whether time is the conscious numbering of movement or instead is just the capability of movement's being numbered were consciousness to exist. Aristotle's distinction foreshadows the modern distinction between psychological time and physical time.
St. Augustine, adopting a subjective view of time, said time is nothing in reality but exists only in the mind's apprehension of that reality. Henry of Ghent and Giles of Rome both said time exists in reality as a mind-independent continuum, but is distinguished into earlier and later parts only by the mind. In the 11th century, the Persian philosopher Avicenna doubted the existence of physical time, arguing that time exists only in the mind due to memory and expectation. In the 13th century, Duns Scotus disagreed with all these philosophers and recognized both physical and psychological time.
At the end of the 18th century, Kant suggested a subtle relationship between time and mind--that our mind structures our perceptions so that we know a priori that time is like a mathematical line. Time is, on this theory, a form of conscious experience.
In the 20th century, the philosopher of science Bas van Fraassen described physical time by saying, "There would be no time were there no beings capable of reason" just as "there would be no food were there no organisms, and no teacups if there were no tea drinkers," and no cultural objects without a culture.
The controversy in metaphysics between idealism and realism is that, for the idealist, nothing exists independently of the mind. If this controversy is settled in favor of idealism, then time, too, would have that subjective feature--physical time as well as psychological time.
Another philosophical issue involving time and mind is how to account for our "feeling" that time passes, that it flows? Philosophers disagree about whether this flow is an objective feature of reality or is, instead, entirely a feature of human perception. In other words, does our mind contribute the flow to time? This is an issue even if it is agreed that time itself is objective. Within the field of cognitive science, one wants to know what are the neural mechanisms that account for our experience of time, but so far very little progress has been made on this fascinating topic.
It has been suggested by some philosophers that Einstein's theory of relativity, when confirmed, showed us that time depends on the observer, and thus that time is subjective, or dependent on the mind. This error is probably caused by Einstein's use of the term "observer." Einstein's theory does imply that the duration of an event isn't absolute but depends on the observer's frame of reference or coordinate system. But what Einstein means by "observer's frame of reference" is merely a perspective or framework from which measurements could be made. The "observer" does not have to be a conscious being or have a mind; it could be a clock on a rock. Einstein's point is that a clock on this rock might measure a different duration than a second clock in a rocket hurtling past the rock. Einstein isn't making a point about mind-dependence.
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3. What is time?
One way to answer the question "What is time?" is to declare that it is what accurate clocks measure. This is correct, but it doesn't tell us enough. We want something "deeper."
The most popular "deep" answer to the question "What is physical time?" is that it is a special system of relations among instantaneous events. It is what underlies our temporal claims that Newton lived before Einstein but at the same time as Leibniz yet a lot longer than anyone who died as a teenager. (The relations are in italics.) This is the answer offered by Adolf Grünbaum who applies the contemporary mathematical theory of continuity to physical processes. How do we tell whether this is the correct answer to our question? To be convinced, we need to be told what the relevant terms mean, such as "certain system of relations." In addition, we need to be presented with a theory of time implying that time is this system of relations; and we need to be shown how that theory adequately addresses the many features that are required for a successful theory of time. This article won't carry out this task.
A different answer to the question "What is time?" is that time is the form of becoming. To assess this answer, which is from Alfred North Whitehead, we need to be told what the term "form of becoming" means; we need to be presented with a detailed theory of time implying that time is the form of becoming; and we need to investigate how it addresses those many features required for a successful theory of time. The metaphysical attitude being used here in assessing whether Grünbaum's and Whitehead's answers are correct is the attitude that fruitful problem solving is a guide to what exists. It is the same attitude that declares zero to exist because zero is so useful for solving the numerical equation x + b = c in the special case when the two numbers b and c happen to be equal, and because having solutions to these sorts of equations is indispensable to the best scientific theories.
If physical time, psychological time, and biological time are three different kinds of time, then three answers are required to the question "What is time?" and some commentary is required regarding their relationships, such as whether one is the most fundamental. Many philosophers of science argue that physical time is the most fundamental of the three even though psychological time is discovered first by each of us as we grow out of our childhood, and even though psychological time was discovered first as we human beings evolved from our animal ancestors. The remainder of this article focuses more on physical time than psychological or biological time.
Another answer to "What is time?" is that time is whatever the time variable t is denoting in the best-confirmed and most fundamental theories of current science. Nearly all philosophers would complain that this answer is just saying the time variable ranges over times. The answer is methodologically suspect, they say, because the nature of physical time can be revealed only with a philosophical theory of time that addresses the many philosophical issues that scientists don't concern themselves with.
Some philosophers, notably Zeno and McTaggart, answer the question, "What is time?" by replying that it is nothing because it doesn't exist. In a similar vein, the early 20th century English philosopher F. H. Bradley argues, "Time, like space, has most evidently proved not to be real, but a contradictory appearance....The problem of change defies solution." However, most philosophers agree that time does exist. They just can't agree on what it is.
Whatever time is, it is not "time." One has four letters; the other does not. Nevertheless, it might help us understand time if we improved our understanding of the sense and reference of the word "time." Should the proper answer to the question "What is time?" produce a definition of the word as a means of capturing its sense? Definitely not--if the definition must be some analysis that provides a simple paraphrase in all its occurrences. There are just too many varied occurrences of the word: time out, behind the times, in the nick of time, and so forth.
But how about a definition that is more realistic? Might it be helpful to explore the grammar of the term "time" in either ordinary language or the physics literature? Most philosophers today would agree with A. N. Prior who remarked that, "there are genuine metaphysical problems, but I think you have to talk about grammar at least a little bit in order to solve most of them." However, do we learn enough about what time is when we learn about the grammatical intricacies of the word? Ordinary-language philosophers are especially interested in time talk, in what Wittgenstein called the "language game" of discourse about time. Wittgenstein's expectation is that by drawing attention to ordinary ways of speaking about time we will dissolve rather than answer our philosophical question. But most philosophers of time are unsatisfied with this approach and have the goal of uncovering important features about time itself.
That was Aristotle's goal when he provided an early, careful answer to our question, "What is time?" by declaring that "time is the measure of change" [Physics, chapter 12], but he emphasizes "that time is not change [itself]" because a change "may be faster or slower, but not time..." [Physics, chapter 10]. For example, a specific change such as the descent of a leaf can be faster or slower, but time itself can't be faster or slower. Aristotle advocates what is now referred to as the relational theory of time because he believed that "there is no time apart from change...." [Physics, chapter 11]. Aristotle was clear that time is not discrete but "is continuous.... In respect of size there is no minimum; for every line is divided ad infinitum. Hence it is so with time" [Physics, chapter 11].
René Descartes had a very different answer to "What is time?" He argued that a material body has the property of spatial extension but no inherent capacity for temporal endurance, and that God by his continual action sustains (or re-creates) the body at each successive instant.
In the 17th century, the English physicist Isaac Barrow rejected Aristotle's linkage between time and change. Barrow said time is something which exists independently of motion or change and which existed even before God created the matter in the universe. Barrow's student, Isaac Newton, agreed that the relational theory of time is incorrect. Newton argued very specifically that time and space are an infinitely large container for all events, and that the container exists with or without the events. He added that space and time are not material substances, but are like substances in not being dependent on matter or motions or anything else except God.
Gottfried Leibniz objected. He argued that time is not an entity existing independently of actual events. He insisted that Newton had underemphasized the fact that time necessarily involves an ordering of any pair of non-simultaneous events. This is why time "needs" events, so to speak. Leibniz added that this overall order is time.
In the 18th century, Immanuel Kant said time and space are forms that the mind projects upon the external things-in-themselves. He spoke of our mind structuring our perceptions so that space always has a Euclidean geometry, and time has the structure of the mathematical line. Kant's idea that time is a form of apprehending phenomena is probably best taken as suggesting that we have no direct perception of time but only the ability to experience things and events in time. Some historians distinguish perceptual space from physical space and say that Kant was right about perceptual space. It's difficult, though, to get a clear concept of perceptual space. If physical space and perceptual space are the same thing, then Kant is claiming we know a priori that physical space is Euclidean. With the discovery of non-Euclidean geometries in the 1820s, and with increased doubt about the reliability of Kant's method of transcendental proof, the view that truths about space and time are apriori truths began to lose favor.
In 1924, Hans Reichenbach defined time order in terms of possible cause. Event A happens before event B if A could have caused B but B couldn't have caused A. This was the first causal theory of time, that was originally suggested by Leibniz who said, "If of two elements which are not simultaneous one comprehends the cause of the other, then the former is considered as preceding, the latter as succeeding." The usefulness of the causal theory depends on a clarification of the notorious notions of causality and possibility without producing a circular explanation that presupposes an understanding of time order. Reichenbach's idea was that causal order can be explained in terms of the "fork asymmetry". The asymmetry is due to the fact that outgoing processes from a common center tend to be correlated with one another, but incoming processes to a common center are uncorrelated. [Do you remember tossing a rock into a still pond? Imagine what the initial conditions at the edge of a pond must be like to produce correlated, incoming, concentric water waves that would expel the rock and leave the water surface smooth.] Some philosophers argue that temporal asymmetry, but not temporal priority, can be analyzed in terms of causation. But even if Reichenbach were correct that temporal priority can be analyzed in terms of causation, the question remains whether time itself can be analyzed in those terms.
The usefulness of the causal theory also depends on a refutation of David Hume's view that causation is simply a matter of constant conjunction [that is, always being together]. For Hume, there is nothing metaphysically deep about causes preceding their effects; it's just a matter of convention that we use the terms "cause" and "effect" to distinguish the earlier and later members of a pair of events which are related by constant conjunction.
During history, a variety of answers have been given to the question of whether time is like a line or, instead, like a circle. The concept of linear time first appeared in the writings of the Hebrews and the Zoroastrian Iranians. The Roman writer Seneca also advocated linear time. Plato and and most other Greeks and Romans believed time to be motion and believed cosmic motion was cyclical, but this wasn't envisioned as requiring any detailed endless repetition such as the multiple rebirths of Socrates. However, the Pythagoreans and some Stoic philosophers did adopt this drastic position.
With circular time, you can be assured that after your death you will be reborn. The future will become the past. If time is like this, then the question arises as to whether there would be an endless number of times when each state of the world reoccurred, or whether, accepting Leibniz's Principle of the Identity of Indiscernibles, each supposedly repeating state of the world would occur just once because each state would be not be discernible from the repeated state.
Islamic and Christian theologians adopted the Greek common sense idea that time is linear and the Jewish-Zoroastrian idea that the universe was created at a definite moment in the past. Augustine emphasized that human experience is a one-way journey from Genesis to Judgment, regardless of any recurring patterns or cycles in nature. In the Medieval period, Thomas Aquinas agreed. Nevertheless, it was not until 1602 that the concept of linear time was more clearly formulated--by the English philosopher Francis Bacon. In 1687, Newton advocated linear time when he represented time mathematically by using a line rather than a circle. The concept of linear time was promoted by Barrow, Leibniz, Locke and Kant. In 19th century Europe, the idea of linear time became dominant in both science and philosophy. However, in the twentieth century, Gödel and others discovered solutions to the equations of Einstein's general theory of relativity that allowed closed loops of proper time. These causal loops or closed curves in spacetime allow you to go forward continuously in time until you arrive back into your past. You might even meet your younger self. If so, some definitions of "person" will need to be revised to allow for this. The logic of the term "time" that is embedded in our time talk does not rule out a nonlinear structure for time, but there is no reason to believe (physical) time is actually like this or that anything has gone back in time.
Is time an emergent entity? Sound emerges from molecules in the sense that, although a single molecule can have no sound, a very large group of molecules can make a sound. Does time emerge from more basic entities? There are two opposing camps on this issue. One says that both space and time emerge from some micro-substrate, although there is no agreed upon theory of what the substrate is. The second camp says that space emerges but time does not. In 2004, after winning the Nobel Prize in physics, David Gross expressed the views of this second camp:
Everyone in string theory is convinced...that spacetime is doomed. But we don't know what it's replaced by. We have enormous amount of evidence that space is doomed. We even have examples, mathematically well-defined examples, where space is an emergent concept.... But in my opinion the tough problem that has not yet been faced up to at all is, "How do we imagine a dynamical theory of physics in which time is emergent?" ...All the examples we have do not have an emergent time. They have emergent space but not time. It is very hard for me to imagine a formulation of physics without time as a primary concept because physics is typically thought of as predicting the future given the past. We have unitary time evolution. How could we have a theory of physics where we start with something in which time is never mentioned?
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4. What does science require of time? a. Relativity and Quantum Mechanics
The general theory of relativity and quantum mechanics are the two most fundamental theories of physics, and the Big Bang theory is the leading theory of cosmology. According to relativity and quantum mechanics, spacetime is, loosely speaking, a collection of points called "spacetime locations" where the universe's physical events occur. Spacetime is four-dimensional and a continuum, and time is a distinguished, one-dimensional sub-space of this continuum. Any interval of time--any duration--must be a linear continuum of instants in which one event follows another from past to present to future. So, a duration has a structure like an interval of real numbers. General relativity theory allows the geometry of space to change with time as the distribution of matter-energy changes.
This first response to the question "What does science require of time?" is too simple. There are complications. There is an important difference between the universe's cosmic time and a clock's proper time; and there is an important difference between proper time and a reference frame's coordinate time. Most spacetimes can not have coordinate systems. Our theory of cosmology, which is some version of the Big Bang theory, places additional requirements on time, as we shall see in the next section. Some physicists are advocating revision of the classical Big Bang theory in order to allow for the "multiverse," in which there are multiple Big Bangs in parallel universes, so that there is time before our Big Bang. Also, all physicists believe that relativity and quantum mechanics are logically inconsistent and need to be replaced by a theory of quantum gravity. A theory of quantum gravity is likely to have radical implications for our understanding of time, such as time and space losing their discreteness and even their separate identities on the very smallest scale.
Aristotle, Leibniz, Newton, and everyone else before Einstein, believed there was a frame-independent duration between two events. For example, if the time interval between two lightning flashes is 100 seconds on someone's accurate clock, then the interval also is 100 seconds on your accurate clock, even if you are flying by at an incredible speed. Einstein rejected this piece of common sense in his 1905 special theory of relativity when he declared that the time interval between two events depends on the observer's reference frame. As Einstein expressed it, "Every reference-body has its own particular time; unless we are told the reference-body to which the statement of time refers, there is no meaning in a statement of the time of an event." Each reference frame, or reference-body, divides spacetime differently into its time part and its space part.
In 1908, the mathematician Hermann Minkowski had an original idea in metaphysics regarding space and time. He was the first person to realize that spacetime is more fundamental than time or space alone. As he put it, "Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality." The metaphysical assumption behind Minkowski's remark is that what is "independently real" is what does not vary from one reference frame to another. It's their "union," what we now call "spacetime," that doesn't vary. It follows that the division of events into the past ones, the present ones, and the future ones is also not "independently real". However, space and time are not completely equivalent even in relativity because time is a "distinguished" sub-space of the 4-d spacetime continuum. Being distinguished implies that time isn't just another 4th dimension of physical space; it's a special dimension unlike the space dimensions, even when we confine our attention to a single reference frame.
A coordinate system is a way of representing space and time using numbers to represent spacetime points. Science confidently assigns numbers to times because, in any reference frame, the happens-before order-relation on events is faithfully reflected in the less-than order-relation on the time numbers (dates) that we assign to events. In the fundamental theories such as relativity and quantum mechanics, the values of the time variable t are real numbers, not merely rational numbers. Each number designates an instant of time, and time is a linear continuum of these instants, similar to the mathematician's line segment. Therefore, if these fundamental theories are correct, physical time is one-dimensional rather than two-dimensional, and continuous rather than discrete. These features don't require time to be linear, however, because a segment of a circle is also a linear continuum, but there is no evidence for circular time, that is, for causal loops or worldlines that are closed curves in spacetime.
What about instants? A duration is an ordered set of instants, not a whole or sum of instants. That is, instants are members of durations, not parts of them. Any duration is infinitely divisible, and it endlessly divides into more intervals; it never divides into instants. The parts of durations are just more durations. The instant is not part of the duration; instead, the singleton set of an instant is a subset of the duration. Instants are like real numbers in that they are boundaries of durations. They are locations in time, but they are "in" time as members are in sets, not as parts are in wholes.
Regarding the number of instants in a duration, time's being a linear continuum implies the instants are so densely packed that between any two there is a third, so that no instant has a next instant. In fact, time's being a linear continuum implies that there is a nondenumerable infinity of instants between any two instants. There is little doubt that the actual temporal structure of events can be embedded in the real numbers, but how about the converse? That is, to what extent is it known that the real numbers can be adequately embedded into the structure of the instants? The problem is that, although time is not quantized in quantum theory, for times shorter than about 10-43 seconds, the so-called Planck time, science has no experimental grounds for the claim that between any two events there is a third. Instead, the justification is that the assumption of continuity is convenient and useful, and that there are no better theories available.
Because of quantum mechanical considerations, physicists agree that the general theory of relativity must fail for durations shorter than the Planck time, but they don't know just how it fails. Most importantly here, there is no agreement among physicists as to whether the continuum feature of time will be adopted in the future theory of quantum gravity that will be created to take account of both gravitational and quantum phenomena. The string theory of quantum gravity predicts that time is continuous, but an alternative to string theory, loop quantum gravity, does not.
Relativity theory challenges a great many of our intuitive beliefs about time. The theory is inconsistent with the common belief that the temporal order in which two events occur is independent of the observer's point of reference. For events occurring at the same place, relativity theory implies the order is absolute (independent of the frame), but for distant events occurring close enough in time to be in each other's absolute elsewhere, event A can occur before event B in one reference frame, but after B in another frame, and simultaneously with B in yet another frame.
Science impacts our understanding of time in many other fundamental ways. Relativity theory implies there is time dilation between one frame and another. For example, the faster a clock moves, the slower it runs, relative to stationary clocks. Time dilation shows itself when a speeding twin returns to find that his (or her) Earth-bound twin has aged more rapidly. This surprising dilation result has caused some philosophers to question the consistency of relativity theory, arguing that, if motion is relative, then from the perspective of the speeding twin, the speeding twin should, instead, be the one who aged more rapidly. This argument is called the twins paradox. Experts now are agreed that the mistake is within the argument for the paradox, not within relativity theory. As is shown in more detail in the Supplement of Frequently Asked Questions, the argument fails to notice the radically different relationships that each twin has to the rest of the universe as a whole.
There are two kinds of time dilation. Special relativity's time dilation involves speed; general relativity's involves acceleration and gravitational fields. Two ideally synchronized clocks need not stay in synchrony if they undergo different accelerations or different gravitational forces. We've already mentioned the clock that is taken to the wine cellar. This gravitational time dilation would be especially apparent if one of the two clocks were to fall into a black hole. A black hole can form when a star exhausts its nuclear fuel and contracts so compactly that the gravitational force prevents anything from escaping the hole, even light itself. The envelope of no return surrounding the black hole is its event horizon. As a clock falls toward a black hole, time slows on approach to the event horizon, and it completely stops at the horizon (not just at the center of the hole)--relative to time on a clock that remains safely back on Earth.
General Relativity theory may have even more profound implications for time. In 1948, the logician Kurt Gödel discovered radical solutions to Einstein's equations, solutions in which there are closed timelike curves, so that as one progresses forward in time along one of these curves one arrives back at one's starting point. Gödel drew the conclusion that in such a universe, there cannot be "an objective lapse of time." So, "whether or not an objective lapse of time exists," that is, whether time really exists, depends "on the particular way in which matter and its motion are arranged in the world." If matter is distributed so that there is Gödelian spacetime, then the universe has no time. Reinforcing this conclusion, Stephen Hawking showed in 1969 that only if a general relativistic spacetime fails to have closed timelike curves can it admit of a partition into spacelike 3-d slices.
In Einstein's relativity theory, the focus is on proper time rather than a global, coordinate time. Proper time along a worldline in 4-d spacetime is the time elapsed by an object having that worldline, as shown on an ideal clock having the same worldline. According to the relationalist, what it is that is being measured when we measure proper time? If the object being measured never changes, then we aren't measuring change in the object. The standard answer is that we are measuring the advancing phase of the quantum wave function, an esoteric kind of change.
b. The Big Bang In 1922, the Russian physicist Alexander Friedmann predicted from general relativity that the universe should be expanding. In 1927, the Belgian physicist Georges Lemaitre suggested that galaxy movement could best be accounted for by this expansion. And in 1929, the American astronomer Edwin Hubble made careful observations of clusters of galaxies and confirmed that the universe is undergoing a universal expansion. Atoms are not expanding; our solar system is not expanding; even the cluster of galaxies to which the Milky Way belongs is not expanding. But most every galaxy cluster is moving away from the others. It's as if the clusters are exploding away from each other, and in the future they will be very much farther away from each other. Now, consider the past instead of the future. At any earlier moment the universe was more compact. Projecting to earlier and earlier times, and assuming that gravitation is the main force at work, the astronomers now conclude that 13.7 billion years ago (plus or minus 1%) the universe was in a state of nearly zero size and infinite density. Because all substances cool when they expand, physicists believe the universe itself must have been cooling down over the last 13.7 billion years, and so it begin expanding when it was extremely hot. The Big Bang theory is a theory of how our universe evolved, how it expanded and cooled from this beginning. This beginning process is called the "Big Bang." As far as we knew back in the 20th century, the entire universe was created in the Big Bang, and time itself came into existence "at that time." So, asking what happened before the Big Bang was like asking what on Earth is north of the North Pole. At least that's the best response to this question assuming the classical theory of the Big Bang of the 20th century. With the appearance of the new theories of quantum gravity and the multiverse in the 21st century, the question has been resurrected as legitimate.
In the literature in both physics and philosophy, descriptions of the Big Bang often assume that a first event is also a first instant of time and that spacetime did not exist outside the Big Bang. This intimate linking of a first event with a first time is a philosophical move, not something demanded by the science. It is not even clear that it's correct to call the Big Bang an event. The Big Bang "event" is a singularity without space coordinates, but events normally must have space coordinates. One response to this problem is to alter the definition of "event" to allow the Big Bang to be an event. Another response, from James Hartle and Stephen Hawking, is to consider the past cosmic time-interval to be open rather than closed at t = 0. Looking back to the Big Bang is then like following the positive real numbers back to ever smaller positive numbers without ever reaching a smallest positive one. If Hartle and Hawking are correct that time is actually like this, then the universe had no beginning event, but it has a finite amount of past time, and the term "the Big Bang" refers not to any single event. But in order to simplify the discussion ahead, this article will speak of "the" Big Bang event as if it were a single event. The Big Bang theory in some form or other is accepted by the vast majority of astronomers, but it is not as firmly accepted as is the theory of relativity.
There are serious difficulties in defending the Big Bang theory's implications about the universe's beginning and the universe's future. Classical Big Bang theory is based on the assumption that the universal expansion of clusters of galaxies can be projected all the way back. Yet physicists agree that the projection must fail in the Planck era, that is, for all times less than 10-43 seconds after "the" Big Bang. Therefore, current science cannot speak with confidence about the nature of time within the Planck era. If a theory of quantum gravity does get confirmed, it should provide information about the Planck era, and it may even allow physicists to answer the question, "What caused the Big Bang?" The scientifically radical, but theologically popular, answer, "God caused the Big Bang, but He, himself, does not exist in time" is a cryptic answer because it is not based on a well-justified and detailed theory of who God is, how He caused the Big Bang, and how He can exist but not be in time. It is also difficult to understand St. Augustine's remark that "time itself was made by God." On the other hand, for a person of faith, belief in God as creator is usually stronger than belief in any scientific hypothesis or in any epistemological desire for a scientific justification of the remark about God or in the importance of satisfying any philosopher's demand for clarification.
Careful cosmological observations near the end of the 20th century and beginning of the 21st have now convinced astrophysicists that the volume of space is not finite, but is infinite and by-and-large flat. Its large scale geometry is Euclidean, not Riemannian nor hyperbolic. Since 2000, many cosmologists have come to believe the Big Bang wasn't the beginning after all, and the universe was infinite even when our Big Bang was initiating. This has fueled theories of the multiverse. The multiverse contains other universes much like our universe, except that they are very far away from ours. Although the theory hasn't been tested, the key idea here is that if spacetime is infinite, then everything that is possible is actual somewhere. Since there are different possible initial values at the time of our Big Bang, there must be different kinds of Big Bangs that have taken place elsewhere at different times [before and after our Big Bang]. These other Big Bangs have created "parallel" universes. Ascending another level up the hierarchy of multiverses, if there are different possible values for the physical constants and for the kinds of elementary particles in our universe, then there must be parallel universes far from us which have all those possible values. To ascend yet again, if, according to quantum mechanics, at any instant in a universe, there are alternative possibilities for what event occurs next, then there must be parallel universes in which all those possibilities are actualities, though these universes won't be far away, but will be truly parallel in the sense of being off in their own space. Finally, progressing again up the hierarchy of speculation about multiverses, if there are various logically possible alternatives for the laws of physics, then every such logically possible universe is an actual universe, and we have something very similar to the modal realism of the Princeton philosopher David Lewis. [See Tegmark 2003.] In some of these universes there is no time dimension.
c. Is time infinite?
There are three ways to interpret the question of whether physical time is infinite: (a) Was there an infinite amount of time in the universe's past? (b) Is time infinitely divisible? (c) Will there be an infinite amount of time in the future?
(a) Was there an infinite amount of time in the past? By invoking the radical notion that God is "outside of time," St. Augustine declared, "Time itself being part of God's creation, there was simply no before!" So, for theological reasons, Augustine declared time had a finite past. After advances in astronomy in the late 19th and early 20th centuries, the question of the age of the universe became a scientific question. With the acceptance of the classical Big Bang theory, the amount of past time was judged to be less than 14 billion years because this is when the Big Bang began. The assumption is that time does not exist independently of the spacetime relations exhibited by physical events. Recently, however, the classical Big Bang theory has been challenged. There could be an infinite amount of time in the past according to some proposed, but as yet untested, theories of quantum gravity based on the assumptions that general relativity theory fails to hold for infinitesimal volumes. These theories imply that the beginning of the Big Bang was actually an expansion from a pre-existing physical state. There was never a singularity. In that case our Big Bang could be just one bang among other bangs throughout an infinite past of the multiverse. For a discussion of these theories requiring an infinite past time, see Veneziano, 2004.
(b) Is time infinitely divisible? Yes, because general relativity and quantum mechanics require time to be a continuum. But the answer is no if these theories are eventually replaced by a relativistic quantum mechanics that quantizes time. "Although there have been suggestions that spacetime may have a discrete structure," Stephen Hawking said in 1996, "I see no reason to abandon the continuum theories that have been so successful."
(c) Will there be an infinite amount of time in the future? Probably. According to the classical theory of the Big Bang, the answer depends on whether events will keep occurring. The best estimate from the cosmologists these days is that the expansion of the universe is accelerating and will continue forever. There always will be the events of galaxies getting farther apart, and so time will have an infinite duration in the future, even though gravity will continue to compact much of the matter into black holes.
There have been interesting speculations on how conscious life could continue forever, despite the fact that the available energy for life will decrease as the universe expands, and despite the fact that any life swept up into a black hole will reach the center of the hole in a finite time at which point death will be certain. For an introduction to these speculations, see Krauss and Starkman, 2002.
Back to Table of Contents d. Atoms of time
In the classical theories of relativity and quantum mechanics, time is not quantized, but is a continuum having the character described above. However, if certain, as yet untested, theories attempting to unify relativity and quantum mechanics are correct--such as the theory of loop quantum gravity--then time will come in discrete pieces or atoms lasting about 10-43 second. There will be a shortest duration for any possible event, and time will be "digital" rather than "analog."
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5. What kinds of time travel are possible?
The term "time travel" is a metaphor because the ordinary term "travel" implies change in spatial location, but the term "time travel" implies change in "temporal location." There are many phenomena that have been taken by some people to be time travel [crossing a time zone, being frozen, remembering past events] but which are not now under serious consideration by philosophers of time, so this section does not focus on them. Using the term "time travel" in the sense that is of interest today to philosophers of time, there is travel to the past and travel to the future.
a. Travel to the future
According to relativity theory, there are two ways to travel into another person's future. First, in the twins paradox, a person speeding away from their twin who remains on Earth will, upon reunion, be younger than their two who stayed back on Earth. The speeding twin will
