Time

Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions.

Time has long been an important subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields without circularity has consistently eluded scholars. Nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems.

Time in physics is operationally defined as "what a clock reads".

The physical nature of time is addressed by general relativity with respect to events in space-time. Examples of events are the collision of two particles, the explosion of a supernova, or the arrival of a rocket ship. Every event can be assigned four numbers representing its time and position (the event's coordinates). However, the numerical values are different for different observers. In general relativity, the question of what time it is now only has meaning relative to a particular observer. Distance and time are intimately related and the time required for light to travel a specific distance is the same for all observers, as first publicly demonstrated by Michelson and Morley. General relativity does not address the nature of time for extremely small intervals where quantum mechanics holds. At this time, there is no generally accepted theory of quantum general relativity.

Time is one of the seven fundamental physical quantities in both the International System of Units (SI) and International System of Quantities. The SI base unit of time is the second. Time is used to define other quantities – such as velocity – so defining time in terms of such quantities would result in circularity of definition. An operational definition of time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as the second, is highly useful in the conduct of both advanced experiments and everyday affairs of life. To describe observations of an event, a location (position in space) and time are typically noted.

The operational definition of time does not address what the fundamental nature of it is. It does not address why events can happen forward and backward in space, whereas events only happen in the forward progress of time. Investigations into the relationship between space and time led physicists to define the spacetime continuum. General relativity is the primary framework for understanding how spacetime works. Through advances in both theoretical and experimental investigations of space-time, it has been shown that time can be distorted and dilated, particularly at the edges of black holes.

Temporal measurement has occupied scientists and technologists, and was a prime motivation in navigation and astronomy. Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the international unit of time, the second, is defined by measuring the electronic transition frequency of caesium atoms (see below). Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human life spans.

There are many systems for determining what time it is, including the Global Positioning System, other satellite systems, Coordinated Universal Time and mean solar time. In general, the numbers obtained from different time systems differ from one another.

Source: Time (wikipedia.org)

Google Earth time-lapse feature winds clock back 37 years

Google Earth has launched a time-lapse feature that lets users wind back the clock and see how the world has changed over several decades. The feature uses millions of satellite images from the past 37 years to let people scroll through time.

Ethiopia: The country where a year lasts 13 months

Ethiopians are marking the start of a new year, with feasting in many homes despite the difficulties caused by rising prices and the war and hunger crisis raging in the north. Find out more about Ethiopia's unique calendar and cultural heritage.

The Government and iPhones don't recognise it, but this stretch of desert has its own time zone

With urban legends like the Nullarbor Nymph, it's not too hard for tourists travelling the famous Australian east-west highway to get confused. But it's the three clocks at the Border Village roadhouse on the South and Western Australian borders that get the oddest looks.

The benefits of embracing 'deep time' in a year like 2020

For much of 2020, the world has been trapped in the short-term: glued to 24-hour news cycles, pandemic announcements, or social media culture wars. With the virus and politics drawing almost all attention, it has been difficult to imagine next year – let alone further ahead.

The psychology behind 'revenge bedtime procrastination'

Emma Rao spent almost three years on China’s notorious ‘996 schedule’: working from nine in the morning to nine in the evening, six days a week. Rao, who is originally from Nanjing, moved to financial hub Shanghai about five years ago to work for a multinational pharmaceutical company.

Time complexity

In computer science, the time complexity is the computational complexity that describes the amount of computer time it takes to run an algorithm.

John Cage musical work changes chord for first time in seven years

Fans have flocked to a church in Germany to hear a chord change in a musical composition that lasts for 639 years. It is the first change in the piece, As Slow As Possible, in seven years.

Why time seems to be going faster while we are in lockdown

As parts of the world begin to ease their lockdowns, some people are looking back and finding the time in isolation seems to have gone surprisingly fast.

Be more punctual, Ecuadorians are urged

Fire sirens will sound and church bells ring out at midday around Ecuador to mark the launch of the government's campaign to eradicate sloppy timekeeping - a vice which it says is hampering the country's economy.

Cells' internal clocks revealed

Scientists have found that each cell of the body has an internal "clock", which can be affected by various genes. Research in the Proceedings of the National Academy of Sciences shows that skin cells can be used to measure the speed of a person's body clock.

Cell discovery clues to body clock and beating jet lag

New discoveries into how the body clock works could provide clues to help combat jet lag, research suggests. The cells had been thought to be inactive during the day - but their research found the opposite was true.

Changes to the world's time scale debated

Time, as we know it, could soon be in for a radical change. This week, scientists at the Royal Society are discussing whether we need to come up with a new definition of the world's time scale: Coordinated Universal Time (UTC).

Circadian rhythm

A circadian rhythm (/sərˈkeɪdiən/), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours.

Fish living in dark caves still feel the rhythm of life

Most animals have an internal body clock, or circadian rhythm, that lasts around 24 hours and is modified by the light-dark cycle of a day.

Lunar clock to be built for 2012

Scientists and artists plan to build a 40m-wide lunar clock by the River Thames by 2012. The aim is to create a new London landmark close to the proposed Olympic stadium as a monument to a more natural way of marking time.

Why having fun makes time speed

Scientists have come up with a theory for why time flies when you are having fun - and drags when you are bored. Scans have shown that patterns of activity in the brain change depending on how we focus on a task.

Imaginary time

Imaginary time is a mathematical representation of time which appears in some approaches to special relativity and quantum mechanics. It finds uses in connecting quantum mechanics with statistical mechanics and in certain cosmological theories.

Free Will and Quantum Clones: How Your Choices Today Affect the Universe at its Origin

The late philosopher Robert Nozick, talking about the deep question of why there is something rather than nothing, quipped: "Someone who proposes a non-strange answer shows he didn't understand the question.

Hints of 'time before Big Bang'

A team of physicists has claimed that our view of the early Universe may contain the signature of a time before the Big Bang. The discovery comes from studying the cosmic microwave background (CMB), light emitted when the Universe was just 400,000 years old.

The food that could last 2,000 years

On 8 September 1941, Nazi forces surrounded Leningrad from the west and south, and through Finland to the north. A thin strip of land across Lake Ladoga kept the residents in touch with the rest of Russia, but heavy shelling made it impossible to evacuate the population.

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