time

=Time=

toc Read here about the concept of time, and aspects of this complex concept that relate to comprehending scale. Time is considered a physical property that can be measured and depicted in a scalometer.

=Overview= Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects.

=Units of Time=

Seconds
Time is measured in SI Units in seconds.

The second is an SI base unit. It is defined as 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 caesium-133 atom.

There is a theoretical minimum time, being Planck time (tp). One Planck time is the time it would take a photon travelling at the speed of light to cross a distance equal to one Planck length. Theoretically, this is the smallest time measurement that will ever be possible,[3] roughly 10−43 seconds. Within the framework of the laws of physics as we understand them today, for times less than one Planck time apart, we can neither measure nor detect any change. As of May 2010, the smallest time interval that was directly measured was on the order of 12 attoseconds (12 × 10^−18 seconds), about 10^24 times larger than the Planck time.

= Samples of Scalometers= Sample scalometers are shown below.

Frequency
Frequency is measured in SI Units in hertz, being the reciprocal of seconds (1/s, or s^-1).

Discussion of the minimum unit of time
William G. Unruh is a professor in the department of physics and astronomy at the University of British Columbia. He wrote in @http://www.scientificamerican.com/article.cfm?id=is-time-quantized-in-othe:

> "There is certainly no experimental evidence that time--or space for that matter--is quantized, so the question becomes one of whether there exists a theory in which time is quantized. Although researchers have considered some theories in which there is a strict quantization of time (meaning that all times are an integer multiple of some smallest unit), none that I know of has ever been seriously regarded as a viable theory of reality--at least, not by more people that the original proponent of the theory.

> "One could, however, ask the question in a slightly different way. By putting together G (Newton's constant of gravity), h (Planck's constant) and c (the velocity of light), one can derive a minimum meaningful amount of time, about 10^-44 second. At this temporal scale, one would expect quantum effects to dominate gravity and hence, because Einstein's theory links gravity and time, to dominate the ordinary notion of time. In other words, for time intervals smaller than this one, the whole notion of 'time' would be expected to lose its meaning.

> "The biggest obstacle to answering the question definitively is that there exists no really believable theory to describe this regime where quantum mechanics and gravity come together. Over the past 10 years, a branch of theoretical physics called string theory has held forth the greatest hope, but it is as yet far from a state where one could use it to describe the nature of time in such a brief interval."

=Instruments That Measure Time= Atomic clocks set the standard of time measurement.

In this public domain image, NIST shows the increasing accuracy of atomic clocks over the years

=Ordering Time= Methods for displaying time values are discussed.

Timeline
A timeline is a list of events in chronological order. A timeline is often used to discuss scales of time.

Duration Scale
A duration scale is an ordering of time intervals from shortest to longest.

=Operational Measurement Of Time Is Logarithmic=

The experience of time today is based on the counting of crystal oscillations. An oscillation is by definition repeated opposing acceleration of a substance. That is generally mapped to a sine function, though other exponential functions may fit better. Thus the origin of time itself as a repeating behavior is exponential.

=Proportional Nature of time=

Glashow adopted logarithmic time, marking nine stages of logarithmic development: fertilized egg, free blastocyst, attached blastocyst, embryo, fetus, infant, child, teenager, adult. These stages occupy equal areas of a timeline when a human life is rendered logarithmically. Von Baeyer quotes him as saying, “a month is an eternity to a six-year-old child, but it passes in a twinkling to a pensioner.”

=Links=

See Chronoception for a discussion of the reception or construction of time information in people.