What Is Time? A Simple Explanation

Updated on November 26, 2019

Time is familiar to everyone, yet it's difficult to define and understand. Science, philosophy, religion, and the arts have different definitions of fourth dimension, simply the system of measuring it is relatively consistent.

Clocks are based on seconds, minutes, and hours. While the footing for these units has changed throughout history, they trace their roots back to aboriginal Sumeria. The mod international unit of time, the second, is defined past the electronic transition of the cesium atom. Merely what, exactly, is time?

Scientific Definition

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Physicists define time as the progression of events from the past to the present into the hereafter. Basically, if a system is unchanging, information technology is timeless. Fourth dimension can be considered to be the fourth dimension of reality, used to describe events in three-dimensional infinite. It is not something we can see, touch, or taste, but we tin can measure its passage.

The Pointer of Time

Post-it notes reading past, now, and future

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Physics equations work equally well whether time is moving forward into the futurity (positive time) or backward into the past (negative time.) However, time in the natural world has ane direction, called the arrow of time. The question of why time is irreversible is one of the biggest unresolved questions in science.

Ane caption is that the natural world follows the laws of thermodynamics. The second law of thermodynamics states that within an isolated system, the entropy of the system remains abiding or increases. If the universe is considered to be an isolated arrangement, its entropy (degree of disorder) tin can never decrease. In other words, the universe cannot return to exactly the same state in which it was at an earlier point. Time cannot move backward.

Time Dilation

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In classical mechanics, fourth dimension is the same everywhere. Synchronized clocks remain in agreement. Yet we know from Einstein'south special and general relativity that fourth dimension is relative. It depends on the frame of reference of an observer. This can result in time dilation, where the time between events becomes longer (dilated) the closer i travels to the speed of low-cal. Moving clocks run more slowly than stationary clocks, with the consequence condign more pronounced as the moving clock approaches lite speed. Clocks in jets or in orbit record time more than slowly than those on Earth, muon particles disuse more slowly when falling, and the Michelson-Morley experiment confirmed length contraction and time dilation.

Fourth dimension Travel

Globes stretching in space

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Time travel means moving forward or backward to different points in time, much like you might move betwixt different points in space. Jumping forward in time occurs in nature. Astronauts on the International Infinite Station jump forward in fourth dimension when they render to Earth because of its slower motility relative to the station.

The thought of traveling back in fourth dimension, however, poses problems. One effect is causality or cause and outcome. Moving dorsum in time could cause a temporal paradox. The "granddad paradox" is a classic example. According to the paradox, if you travel back in time and kill your granddad before your mother or father was born, yous could prevent your own nascency. Many physicists believe time travel to the past is impossible, but at that place are solutions to a temporal paradox, such as traveling between parallel universes or branch points.

Time Perception

Young and old hands

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The homo brain is equipped to track time. The suprachiasmatic nuclei of the encephalon is the region responsible for daily or circadian rhythms. Simply neurotransmitters and drugs touch time perceptions. Chemicals that excite neurons and then they fire more quickly than normal speed upward time, while decreased neuron firing slows downwards fourth dimension perception. Basically, when time seems to speed up, the brain distinguishes more events within an interval. In this respect, time truly does seem to fly when one is having fun.

Time seems to ho-hum downward during emergencies or danger. Scientists at Baylor Higher of Medicine in Houston say the brain doesn't actually speed upwards, but the amygdala becomes more active. The amygdala is the region of the brain that makes memories. As more memories form, time seems fatigued out.

The aforementioned miracle explains why older people seem to perceive time as moving faster than when they were younger. Psychologists believe the encephalon forms more than memories of new experiences than that of familiar ones. Since fewer new memories are built later in life, time seems to laissez passer more quickly.

The Beginning and Stop of Time

Time in a never-ending spiral

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As far as the universe is concerned, time had a start. The starting point was xiii.799 billion years ago when the Big Bang occurred. We can mensurate cosmic background radiation as microwaves from the Big Blindside, merely in that location isn't any radiation with earlier origins. One statement for the origin of time is that if information technology extended backward infinitely, the nighttime sky would exist filled with light from older stars.

Volition time cease? The answer to this question is unknown. If the universe expands forever, time would continue. If a new Large Bang occurs, our fourth dimension line would end and a new one would begin. In particle physics experiments, random particles arise from a vacuum, so it doesn't seem probable the universe would become static or timeless. Just time will tell.

Fundamental Points

  • Fourth dimension is the progression of events from the past into the future.
  • Time moves only in ane direction. It's possible to movement forward in time, but not backward.
  • Scientists believe memory germination is the ground for human perception of fourth dimension.

Sources

  • Carter, Rita. The Man Brain Book. Dorling Kindersley Publishing, 2009, London.
  • Richards, Eastward. G. Mapping Time: The Calendar and its History. Oxford University Printing, 1998, Oxford.
  • Schwartz, Herman Chiliad. Introduction to Special Relativity, McGraw-Hill Book Company, 1968, New York.