A report on Time

The flow of sand in an hourglass can be used to measure the passage of time. It also concretely represents the present as being between the past and the future.
Horizontal sundial in Taganrog
An old kitchen clock
A contemporary quartz watch, 2007
Chip-scale atomic clocks, such as this one unveiled in 2004, are expected to greatly improve GPS location.
Scale of time in Jain texts shown logarithmically
Time's mortal aspect is personified in this bronze statue by Charles van der Stappen.
Two-dimensional space depicted in three-dimensional spacetime. The past and future light cones are absolute, the "present" is a relative concept different for observers in relative motion.
Relativity of simultaneity: Event B is simultaneous with A in the green reference frame, but it occurred before in the blue frame, and occurs later in the red frame.
Views of spacetime along the world line of a rapidly accelerating observer in a relativistic universe. The events ("dots") that pass the two diagonal lines in the bottom half of the image (the past light cone of the observer in the origin) are the events visible to the observer.
Philosopher and psychologist William James

Continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future.

- Time
The flow of sand in an hourglass can be used to measure the passage of time. It also concretely represents the present as being between the past and the future.

62 related topics with Alpha

Overall
A right-handed three-dimensional Cartesian coordinate system used to indicate positions in space.

Space

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Boundless three-dimensional extent in which objects and events have relative position and direction.

Boundless three-dimensional extent in which objects and events have relative position and direction.

A right-handed three-dimensional Cartesian coordinate system used to indicate positions in space.
Gottfried Leibniz
Isaac Newton
Immanuel Kant
Spherical geometry is similar to elliptical geometry. On a sphere (the surface of a ball) there are no parallel lines.
Carl Friedrich Gauss
Henri Poincaré
Albert Einstein

In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime.

The Ghost of Christmas Yet to Come shows Scrooge his future in Dickens' A Christmas Carol.

Future

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The Ghost of Christmas Yet to Come shows Scrooge his future in Dickens' A Christmas Carol.
A visualization of the future light cone (at the top), the present, and the past light cone in 2D space.
Project of an orbital colony Stanford torus, painted by Donald E. Davis
Print (c. 1902) by Albert Robida showing a futuristic view of air travel over Paris in the year 2000 as people leave the opera.

The future is the time after the past and present.

Figure 1-1. Each location in spacetime is marked by four numbers defined by a frame of reference: the position in space, and the time (which can be visualized as the reading of a clock located at each position in space). The 'observer' synchronizes the clocks according to their own reference frame.

Spacetime

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Figure 1-1. Each location in spacetime is marked by four numbers defined by a frame of reference: the position in space, and the time (which can be visualized as the reading of a clock located at each position in space). The 'observer' synchronizes the clocks according to their own reference frame.
Figure 1–4. Hand-colored transparency presented by Minkowski in his 1908 Raum und Zeit lecture
Figure 2-2. Galilean diagram of two frames of reference in standard configuration
Figure 2–3. (a) Galilean diagram of two frames of reference in standard configuration, (b) spacetime diagram of two frames of reference, (c) spacetime diagram showing the path of a reflected light pulse
Figure 2–4. The light cone centered on an event divides the rest of spacetime into the future, the past, and "elsewhere"
Figure 2–5. Light cone in 2D space plus a time dimension
Figure 2–6. Animation illustrating relativity of simultaneity
Figure 2–7. (a) Families of invariant hyperbolae, (b) Hyperboloids of two sheets and one sheet
Figure 2–8. The invariant hyperbola comprises the points that can be reached from the origin in a fixed proper time by clocks traveling at different speeds
Figure 2–9. In this spacetime diagram, the 1 m length of the moving rod, as measured in the primed frame, is the foreshortened distance OC when projected onto the unprimed frame.
Figure 2-11. Spacetime explanation of the twin paradox
Figure 3–2. Relativistic composition of velocities
Figure 3-3. Spacetime diagrams illustrating time dilation and length contraction
Figure 3–5. Derivation of Lorentz Transformation
Figure 3–7. Transverse Doppler effect scenarios
Figure 3–8. Relativistic spacetime momentum vector
Figure 3–9. Energy and momentum of light in different inertial frames
Figure 3-10. Relativistic conservation of momentum
Figure 4–2. Plot of the three basic Hyperbolic functions: hyperbolic sine ([[:File:Hyperbolic Sine.svg|sinh]]), hyperbolic cosine ([[:File:Hyperbolic Cosine.svg|cosh]]) and hyperbolic tangent ([[:File:Hyperbolic Tangent.svg|tanh]]). Sinh is red, cosh is blue and tanh is green.
Figure 4-4. Dewan–Beran–Bell spaceship paradox
Figure 4–5. The curved lines represent the world lines of two observers A and B who accelerate in the same direction with the same constant magnitude acceleration. At A' and B', the observers stop accelerating. The dashed lines are lines of simultaneity for either observer before acceleration begins and after acceleration stops.
Figure 4–6. Accelerated relativistic observer with horizon. Another well-drawn illustration of the same topic may be viewed [[:File:ConstantAcceleration02.jpg|here]].
Figure 5–1. Tidal effects.
Figure 5–2. Equivalence principle
Figure 5–3. Einstein's argument suggesting gravitational redshift
Figure 5-5. Contravariant components of the stress–energy tensor
Figure 5–7. Origin of gravitomagnetism
Figure 5–9. (A) Cavendish experiment, (B) Kreuzer experiment
Figure 5-11. Gravity Probe B confirmed the existence of gravitomagnetism

In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold.

The present is a moment in time discernible as intermediate between past and future.

Present

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The present is a moment in time discernible as intermediate between past and future.
A visualisation of the present (dark blue plane) and past and future light cones in 2D space.

The present (or here and now) is the time that is associated with the events perceived directly and in the first time, not as a recollection (perceived more than once) or a speculation (predicted, hypothesis, uncertain).

Everything is in the Past (Vassily Maximov, 1889).

Past

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Set of all events that occurred before a given point in time.

Set of all events that occurred before a given point in time.

Everything is in the Past (Vassily Maximov, 1889).
Thoughts of the Past (John Roddam Spencer Stanhope, 1859)

The concept of the past is derived from the linear fashion in which human observers experience time, and is accessed through memory and recollection.

In this diagram, time passes from left to right, so at any given time, the universe is represented by a disk-shaped "slice" of the diagram

Universe

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In this diagram, time passes from left to right, so at any given time, the universe is represented by a disk-shaped "slice" of the diagram
Television signals broadcast from Earth will never reach the edges of this image.
Astronomers have discovered stars in the Milky Way galaxy that are almost 13.6 billion years old.
The three possible options for the shape of the universe
The formation of clusters and large-scale filaments in the cold dark matter model with dark energy. The frames show the evolution of structures in a 43 million parsecs (or 140 million light-years) box from redshift of 30 to the present epoch (upper left z=30 to lower right z=0).
A map of the superclusters and voids nearest to Earth
Comparison of the contents of the universe today to 380,000 years after the Big Bang as measured with 5 year WMAP data (from 2008). (Due to rounding errors, the sum of these numbers is not 100%). This reflects the 2008 limits of WMAP's ability to define dark matter and dark energy.
Standard model of elementary particles: the 12 fundamental fermions and 4 fundamental bosons. Brown loops indicate which bosons (red) couple to which fermions (purple and green). Columns are three generations of matter (fermions) and one of forces (bosons). In the first three columns, two rows contain quarks and two leptons. The top two rows' columns contain up (u) and down (d) quarks, charm (c) and strange (s) quarks, top (t) and bottom (b) quarks, and photon (γ) and gluon (g), respectively. The bottom two rows' columns contain electron neutrino (νe) and electron (e), muon neutrino (νμ) and muon (μ), tau neutrino (ντ) and tau (τ), and the Z0 and W± carriers of the weak force. Mass, charge, and spin are listed for each particle.
3rd century BCE calculations by Aristarchus on the relative sizes of, from left to right, the Sun, Earth, and Moon, from a 10th-century AD Greek copy.
Flammarion engraving, Paris 1888
Model of the Copernican Universe by Thomas Digges in 1576, with the amendment that the stars are no longer confined to a sphere, but spread uniformly throughout the space surrounding the planets.

The universe (universus) is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy.

Portrait by Johann Gottlieb Becker, 1768

Immanuel Kant

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German philosopher and one of the central Enlightenment thinkers.

German philosopher and one of the central Enlightenment thinkers.

Portrait by Johann Gottlieb Becker, 1768
Kant's house in Königsberg
Portrait of philosopher David Hume
Engraving of Immanuel Kant
Kant with friends, including Christian Jakob Kraus, Johann Georg Hamann, Theodor Gottlieb von Hippel and Karl Gottfried Hagen
Kant's tomb in Kaliningrad, Russia
Immanuel Kant by Carle Vernet (1758–1836)
Kant statue in the School of Philosophy and Human Sciences (FAFICH) in the Federal University of Minas Gerais (UFMG), Belo Horizonte, Brazil
Immanuel Kant
In his Metaphysics, Immanuel Kant introduced the categorical imperative: "Act only according to that maxim whereby you can, at the same time, will that it should become a universal law."
5 DM 1974 D silver coin commemorating the 250th birthday of Immanuel Kant in Königsberg
Statue of Immanuel Kant in Kaliningrad (Königsberg), Russia. Replica by of the original by Christian Daniel Rauch lost in 1945.
West German postage stamp, 1974, commemorating the 250th anniversary of Kant's birth

In his doctrine of transcendental idealism, Kant argued that space and time are mere "forms of intuition" which structure all experience, and therefore that while "things-in-themselves" exist and contribute to experience, they are nonetheless distinct from the objects of experience.

Title page of the 1781 edition

Critique of Pure Reason

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Book by the German philosopher Immanuel Kant, in which the author seeks to determine the limits and scope of metaphysics.

Book by the German philosopher Immanuel Kant, in which the author seeks to determine the limits and scope of metaphysics.

Title page of the 1781 edition
Immanuel Kant, lecturing to Russian officers—by I. Soyockina / V. Gracov, the Kant Museum, Kaliningrad
Outline of Kant's division of the science of logic into special logic, general logic, and the pure and applied forms of general logic.
A diagram of Immanuel Kant's system of thought

While Kant claimed that phenomena depend upon the conditions of sensibility, space and time, and on the synthesizing activity of the mind manifested in the rule-based structuring of perceptions into a world of objects, this thesis is not equivalent to mind-dependence in the sense of Berkeley's idealism.

The Shepherd Gate Clock at the Royal Observatory, Greenwich

Clock

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The Shepherd Gate Clock at the Royal Observatory, Greenwich
Clock face of the Elizabeth Tower in London, also known as Big Ben
Digital clock radio
Clock on the Beaux Arts façade of the Gare d'Orsay from Paris
24-hour clock face in Florence
Simple horizontal sundial
The flow of sand in an hourglass can be used to keep track of elapsed time
A water clock for goldbeating goldleaf in Mandalay (Myanmar)
A scale model of Su Song's Astronomical Clock Tower, built in 11th-century Kaifeng, China. It was driven by a large waterwheel, chain drive, and escapement mechanism
An elephant clock in a manuscript by Al-Jazari (1206 AD) from The Book of Knowledge of Ingenious Mechanical Devices
A 17th-century weight-driven clock
Richard of Wallingford pointing to a clock, his gift to St Albans Abbey
16th-century clock machine Convent of Christ, Tomar, Portugal
Lantern clock, German,
The Dutch polymath and horologist Christiaan Huygens, the inventor of first precision timekeeping devices (pendulum clock and spiral-hairspring watch)
Opened-up pocket watch
Early French electromagnetic clock
Picture of a quartz crystal resonator, used as the timekeeping component in quartz watches and clocks, with the case removed. It is formed in the shape of a tuning fork. Most such quartz clock crystals vibrate at a frequency of 32,768 Hz
Balance wheel, the oscillator in a mechanical mantel clock.
The Shepherd Gate Clock receives its timing signal from within the Royal Observatory, Greenwich.
Synchronous electric clock, around 1940. By 1940 the synchronous clock became the most common type of clock in the U.S.
A modern quartz clock with a 24-hour face
A linear clock at London's Piccadilly Circus tube station. The 24 hour band moves across the static map, keeping pace with the apparent movement of the sun above ground, and a pointer fixed on London points to the current time.
Software word clock
Many cities and towns traditionally have public clocks in a prominent location, such as a town square or city center. This one is on display at the center of the town of Robbins, North Carolina
A Napoleon III mantel clock, from the third quarter of the 19th century, in the Museu de Belles Arts de València from Spain
A monumental conical pendulum clock by Eugène Farcot, 1867. Drexel University, Philadelphia, USA
One mechanical clock (was useful for sailing purposes)
Mechanical digital clock (with rolling numbers)
Matthew Norman carriage clock with winding key
Decorated William Gilbert mantel clock
Digital clock displaying time by controlling valves on the fountain
Simplistic digital clock radio
Diagram of a mechanical digital display of a flip clock

A clock or a timepiece is a device used to measure and indicate time.

From left to right: the square, the cube and the tesseract. The two-dimensional (2D) square is bounded by one-dimensional (1D) lines; the three-dimensional (3D) cube by two-dimensional areas; and the four-dimensional (4D) tesseract by three-dimensional volumes. For display on a two-dimensional surface such as a screen, the 3D cube and 4D tesseract require projection.

Dimension

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[[File:Dimension levels.svg|thumb | 236px | The first four spatial dimensions, represented in a two-dimensional picture. 1. Two points can be connected to create a line segment.

[[File:Dimension levels.svg|thumb | 236px | The first four spatial dimensions, represented in a two-dimensional picture. 1. Two points can be connected to create a line segment.

From left to right: the square, the cube and the tesseract. The two-dimensional (2D) square is bounded by one-dimensional (1D) lines; the three-dimensional (3D) cube by two-dimensional areas; and the four-dimensional (4D) tesseract by three-dimensional volumes. For display on a two-dimensional surface such as a screen, the 3D cube and 4D tesseract require projection.

In classical mechanics, space and time are different categories and refer to absolute space and time.