
Einstein's Messengers
The Universe Has Three Dimensions of Space and One Dimension of Time
The Universe Has Three Dimensions of Space and One Dimension of Time
Einstein's Messengers (National Science Foundation)

Ripples in the fabric of spacetime from monumental
collisions between black holes, and how scientists are trying to measure
them with lasers and mirrors. From LIGO and the National Science
Foundation.
In physics, spacetime (or space–time; or space/time) is any mathematical model that combines space and time into a single continuum.
Spacetime is usually interpreted with space being threedimensional and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions.
According to certain Euclidean space perceptions, the universe has three dimensions of space and one dimension of time.
By combining space and time into a single manifold, physicists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.
In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer.
In relativistic contexts, however, time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer and also on the strength of intense gravitational fields, which can slow the passage of time.
The first reference to spacetime as a mathematical concept was in 1754 by Jean le Rond d'Alembert in the article Dimension in Encyclopedie. Another early venture was by Joseph Louis Lagrange in his Theory of Analytic Functions (1797, 1813). He said, "One may view mechanics as a geometry of four dimensions, and mechanical analysis as an extension of geometric analysis".
New Discovery about the Fabric of SpaceTime
Scientists have turned up rare evidence that spacetime is smooth as
Einstein predicted, while pushing closer to a complete theory of
gravity.
From NASA Goddard Space Flight Center, Fermi Gamma Ray Space
Telescope.
After discovering quaternions, William Rowan Hamilton commented,
"Time is said to have only one dimension, and space to have three dimensions. ...
The mathematical quaternion partakes of both these elements; in technical language it may be said to be 'time plus space', or 'space plus time': and in this sense it has, or at least involves a reference to, four dimensions.
And how the One of Time, of Space the Three, Might in the Chain of Symbols girdled be."
Hamilton's biquaternions, which have algebraic properties sufficient to model spacetime and its symmetry, were in play for more than a halfcentury before formal relativity. For instance, William Kingdon Clifford noted their relevance.
What Lies Beyond Our Own SpaceTime Continuum
Mystery of Time  Time Lapse & Stop Motion Photography Video
The
ideas of Time & Space are explored. Scientists use a "time
microscope" or a camera running at 3000 frames per second to help
explain time.
This film gives a glimpse of what lies beyond our own spacetime
continuum. The elemental concepts of the theory of relativity are
demonstrated.
A science film about time and space. The marvels of
science provide the visible evidence of a Divine plan of creation.
Another important antecedent to spacetime
was the work of Clerk Maxwell as he used partial differential equations
to develop electrodynamics with the four parameters.
Lorentz discovered
some invariances of Maxwell's equations late in the 19th century which
were to become the basis of Einstein's theory of special relativity.
Fiction
authors were also on the game as mentioned above. It has always been
the case that time and space are measured using real numbers, and the
suggestion that the dimensions of space and time are comparable could
have been raised by the first people to have formalized physics, but
ultimately, the contradictions between Maxwell's laws and Galilean
relativity had to come to a head with the realization of the import of
finitude of the speed of light.
While spacetime can be viewed as a consequence of Albert Einstein's 1905
theory of special relativity, it was first explicitly proposed
mathematically by one of his teachers, the mathematician Hermann
Minkowski, in a 1908 essay building on and extending Einstein's work.
His
concept of Minkowski space is the earliest treatment of space and time
as two aspects of a unified whole, the essence of special relativity.
The idea of Minkowski space also led to special relativity being viewed
in a more geometrical way, this geometric viewpoint of spacetime being
important in general relativity too.
The Extraordinary Genius of Albert Einstein
The speed of light, usually denoted by c, is a physical constant important in many areas of physics.
Light and all other forms of electromagnetic radiation always travel at this speed in empty space (vacuum), regardless of the motion of the source or the inertial frame of reference of the observer.
Its value is exactly 299,792,458 meters per second (approximately 186,282 miles per second).
In the theory of relativity, c interrelates space and time, and appears in the famous equation of mass–energy equivalence E = mc2.
It is the speed of all massless particles and associated fields in vacuum, and it is predicted by the current theory to be the gravitational waves and an upper bound on the speed at which energy, matter, and information can travel.
The speed at which light propagates through transparent materials, such as glass or air, is less than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (n = c / v).
For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s; the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s slower than c.In most practical cases, light can be thought of as moving instantaneously, but for long distances and very sensitive measurements the finite speed of light has noticeable effects.
In communicating with distant space probes, it can take minutes to hours for the message to get from Earth to the satellite and back. The light we see from stars left them many years ago, allowing us to study the history of the universe by looking at distant objects.
The finite speed of light also limits the theoretical maximum speed of computers, since information must be sent within the computer chips and from chip to chip. Finally, the speed of light can be used with time of flight measurements to measure large distances to high precision.
Ole Rømer first demonstrated in 1676 that light traveled at a finite speed (as opposed to instantaneously) by studying the apparent motion of Jupiter's moon Io.
In 1905, Albert Einstein postulated that the speed of light in vacuum was independent of the source or inertial frame of reference, and explored the consequences of that postulate by deriving the theory of special relativity and showing that the parameter c had relevance outside of the context of light and electromagnetism.
After centuries of increasingly precise measurements, in 1975 the speed of light was known to be 299,792,458 m/s with a relative measurement uncertainty of 4 parts per billion. In 1983, the meter was redefined in the International System of Units (SI) as the distance traveled by light in vacuum in 1⁄299,792,458 of a second.
As a result, the numerical value of c in meters per second is now fixed exactly by the definition of the meter.

