why a day has just 24 hours, why we say *this much* span is of 1 sec..?

Question

this is something which we created for our convenience, so does time really exists????
why would it not be same throughout the universe if it really is??

on a planet like jupiter, we'd have a different span for 1 sec and may be more hours in a day (if we use our clock system)

Answer 1

Others have already addressed the question of if time exists or not and why the span of a second changes with relative velocity (or in the presence of super gravity). So instead, let me actually answer your question as it was posed.
To understand why we have 24 hours and why we have 60 seconds you have to look to astronomy (which is not just the study of the heavens but also of the measurements of time).
The two most fundamental time measurments are the day and the year. The day is measured by the rising and setting of the sun. The year is measured by the cycle of the seasons.
The ancients understood this and at some point they determined how many days existed within a year. The actual figure is approximately 365 days (plus a few extra hours).
365 is a difficult number to work with mathematically once you stray away from multiples of 5, so to make things easier, the ancients defined a circle to be 360 degrees so that the earth moves approximately 1 degree per day. They used 360 because it was close to the number of days in a year and also because 360 is easily divisible by 2,3,4,5,6 and is therefore easy to work with mathematically. For the same reason, they decided that 60 would be a good number to work with in subdividing the circle into minutes and seconds.
This same thought process went into dividing the day into time periods. They decided to divide the days 360 degree rotation into 15 degree intervals which they called "hours". And they applied the 60 minute and second subdivision to the hours as well.
Now in the modern era, we can calcualte and measure very precisely, and so the second is actually defined as the amount of time it takes for light to travel 288792458 meters in a vaccum.

Answer 2

Time does really exist. What you are wrestling with is the fact that we humans have defined its passing for our use and convenience. But just because we have defined a certain time period doesn't mean that time doesn't exist. We humans did not create time, but have simply measured it.

Humans need things to be synchronized, so time must be defined and standardized so to be the same for everyone. Even technologically ignorant peoples mark the changing of seasons. One way that early Native Americans talked about time was the passing of a certain number of moons. They had no watch or clock, but they understood the passing of events. The Christian Bible, speaking of 2000+ year old history, talks about the people there speaking of the "third hour" or the "fifth hour", etc.

Time signifies the passing of events. If time didn't exist, you couldn't breathe, light wouldn't come from the sun to the earth, an almost infinite number of things wouldn't happen, because the status of all existing objects would stay the same. Scientists measure and define time this way, relying on objects with extremely stable event histories. It is currently defined based on a certain number of vibrations of a particular atom.

This answerer doesn't know the reason for "24" hours in a day; it is probably based on traditions over many years. As for time being the same throughout the universe, this answerer also does not understand relativity theory, which would apply to that question.

Answer 3

A sec doesn't change depending on where you are at; under the International System of Units, the second is currently 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. This definition refers to a caesium atom at rest at a temperature of 0 K. The funny thing is that time dialates when an object travels faster relative to the objects around it. So is there an underlying medium that can be used as a universal reference?

Answer 4

Days are an astronomical fact.
Hours are just a conventional division of a day into 24 segments we have chosen.
We can take our watch with us and measure time in another planet, but it wouldn't be very practical as that planet will not have the same day duration.
It could be practical to bring our calendar and watch with us only to synchronize our communications with the Earth. Much as we do when we travel to another continent but still want to know what time it is at home.

Answer 5

Our concept of hours and seconds is just our way of taking measurements of the passing of time. Good example is the passing of years on different planets. One Earth year is roughly equal to 365.25 Earth days (24 hr periods), whereas as Mercury's year is equal to roughly 88 Earth days. However, in Mercury days (from sunrise to sunrise) each "year" is about a half a day long because of the slow rotation of the planet. If there was any sort of life on Mercury, this would mean they would celebrate 2 birthdays every day.

Answer 6

Time exists no matter what label you put on it. It is our perception of time that makes the difference. Take the fly as an example. They have extremely fast reflexes because they see time in what we would call slow motion. So, one second for us is an instant, but for a fly it's a much longer period, based on its perception.

Then you could say that time only exists if there is perception of it. Then what is time in an absolute sense? Find someone smarter to explain it. When you get to this point, time is as much a scientific as a philosophical question.

Answer 7

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Answer 8

Actually we don't have a 24hr day,its slightly less. thats why every 4 years we have an extra day, (leapyear)