As I think of Time, all I can come up with is that it passes. It is irreversible and just only moves forward. Why do we need time though: to measure or calculate a duration that has been taken to do something. We use seconds, minutes, hours, days etc. to measure time in our daily lives. The definition that I just mentioned for Time may be sufficient to understand it in the context of daily lives but to really understand it we will have dig back in time and understand a bit of history as to how, when and why we came up with this term Time and what it is in the context of Science. Physics is the branch of Science which deals with stuff related to matter, dimensions, time etc. so we must look time in the context of Physics. So, there are two aspects that we’ll try to figure out: one is, how man invented or discovered time; second, what was the basis that lead to what we call seconds, minutes, hours, days, months, years etc.
History of Time
Time as we know today can be divided into two parts, calendar and clock. The calendar part is measured in years, months, days and the clock part are measured in hours, minutes and seconds. Following is the basis of each of these measures:
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- Year – A year can be defined as the duration it takes Earth to rotate around Sun and reach back to the same point. It is approximately 365 days.
- Month – Back in the old ages, people used to follow moon to define segments of time. Time taken to complete each full moon was considered a month. Each year there are approximately 12.3 segments (full moons). The names of the months are a different story in itself and it is mostly related to Romans.
- Day – The time it takes for Earth to completely rotate on its axis. The calendar part was easier to figure out, though things get a bit trickier in the clock part of time.
- Hour – It goes back to 1500 B.C. when Egyptians divided the day into 12 parts (the duodecimal number system with base 12). There are multiple theories behind this number 12; one of the theories is it was based on the number of times a full moon is completed in a year; another one is related to the stars that would appear at night which they used to call “Decamps”. But due to differences in duration of nights in winter and summers, Hipparchus, a Greek Astronomer came up with the idea of dividing a day into 24 parts, 12 for daylight and 12 for night.
- Minutes – Back in the days, the Greek astronomers used to follow a number system called Sexagesimal which they inherited from Sumerians back in 2000 B.C. This was the reason behind dividing an hour into 60 parts called minutes.
- Seconds – Minutes, for the same reason was further divided into 60 parts and was called second minute which led to the word seconds as we call it today. But this time was all based on the astronomical basis. In 1967, the calculation of a second was redefined according to the 9,192,631,770 energy transitions of a Cesium atom. This redefinition which occurred in the modern era of atomic time keeping and what we know today as UTC (Universal Time Coordinated).
Further Scientific Theories about Time
Relativity of Time:
Albert Einstein discovered that the time is relative rather than absolute. It is relative to the observer’s velocity when he/she is observing time.
Time Dilation:
Time Dilation was predicted by several authors in the turn of 20th century. Time in the explanation of special relativity, the “slowing down” of a clock as figured out by a person who is in relative movement with respect to that clock. Time dilation is the time elapsed measured by two clocks, either having relative velocities or by a gravitational potential difference between their locations. The theory of relativity is confirmed by experiments. Time expanding has also been the subject of science fiction works, as it technically provides the means for forward time travel. Theoretically, time dilation would make it possible for passengers in a fast-moving vehicle to advance further into the future in a short period of their own time. The explanation of relativity has been over and over again proven true by experiment and they are of important thing to think about. Time has also been the subject of science fiction works, as it technically provides the means for forward time travel
Velocity Time Dilation:
Special relativity indicates that, for an observer in an inertial frame of reference, a clock that is moving relative to him will be measured to tick slower than a clock that is at rest in his frame of reference. This case is sometimes called special relativistic time dilation. The faster the relative velocity, the greater the time dilation between one another, with the rate of time reaching zero as one approaches the speed of light (299,792,458 m/s). This causes mass-less particles that travel at the speed of light to be unaffected by the passage of time.
Probably time would make it possible for passengers in a fast-moving vehicle to advance further into the future in a short period of their own time. For example, one year of travel might go along with up to ten years on Earth. In fact, a constant 1 g speed increasing speed would permit humans to travel through the whole universe in one human lifetime. Simple Interference of Velocity Time Dilation: Time dilation can be inferred from the observed constancy of the speed of light in all reference frames dictated by the second postulate of special relativity.
This constancy of the speed of light means that, counter to intuition, speeds of material objects and light are not additive. It is not possible to make the speed of light appear greater by moving towards or away from the light source. Consider then, a simple clock consisting of two mirrors A and B, between which a light pulse is bouncing. The separation of the mirrors is L and the clock ticks once each time the light pulse hits either of the mirrors.
A-Theory and B-Theory:
One of central debates in the way of thinking of time is between the A-theorists and B-theorists. The A-theory of time is typically associated with the idea that the present is metaphysically privileged or singled out in some way from past and future times. Furthermore, there is real flow of time as past events move back (or away) further and further into the past and future events move closer and closer to the present.
The B-theory of time in contrast, denies that the present is knowledge based over past and future times. Just as there is nothing knowledge based special about, the B-theorists who try to come up with explanations maintains that there is nothing knowledge based special about the present moment.
Newton's Linear Time:
In this section the similarities listed below the treat time as a limit which serves as an index to the behavior of the physical system because, Newton treat a linear flow of time (what he called mathematical time), time could be believed to be linearly different guideline.
Summary
A brief summary on time is, it has a great impact on our relationship and location within our universe and gravity. Time is a measure of the period of the time (or space) between two events. Time is cultural construct within by which an event can be connected with a series of numbers. Time is inversely proportional to gravity. The more the gravity will be, the slow the time will be.