To us, time is the clock ticking, the passage from morning to afternoon to evening to night, and the passage from days to weeks to months to years to decades to centuries. However, this is not time itself. It is just how we measure the passage of time and how we call some measured intervals of time.
Time is more complex than the answer you get when you ask `what time is it now?’ or `what date is it today?’.
Defining and explaining time is such a difficult problem that it has not been fully explained by any scientist.
Albert Einstein’s general and special relativity theories have made it possible to understand some aspects of the complex nature of time.
What Is Time?
Webster’s New World College Dictionary defines time as a period or interval between two events or during which something exists, happens or acts.
Plato defined time as a moving image of reality.
The passage of time is connected to the concept of space. In the theory of general relativity, time is regarded as a fourth dimension in equal footing with the three dimensions of space. The four dimensions are together referred to as space-time continuum.
Time is real. It has many facets. It is represented through change.
One unique quality of time is that it is measured by motion and becomes evident through motion.
Time is elusive. We can measure it but we cannot see or sense it.
What Is the Origin of Time?
According to the general theory of relativity, the universe, space and time were created during the big bang that occurred about 13.7 billion years ago. Before the big bang, all matter was packed into an extremely tiny dot. There was no universe, space or time.
Our universe cannot exist without time and time cannot exist without the universe. The universe and time are like two sides of the same coin.
Heavenly bodies that tell us about the passing of time- the sun, Earth and Moon– are part of the universe created during the big bang.
The Passage of Time
To us, time flows in a smooth and perpetual motion. Scientists have considered two possibilities on the passage of time. One possibility is that time flows smoothly and continuously. The second one is that it moves in discrete steps only that we have not been able to observe it moving from one frame to another.
The Arrow of Time
Our perception is that time flows from the past through the present and into the future. Although there is no law of physics stating this is so, the arrow of time gives time a definite and consistent direction and enables us to place events in their order of occurrence.
The past is different from the future. Causes precede effects. We are going into the future but going back to the past would be tricky. We have no memory of future events. We can only remember past events.
Is Time Constant?
There is no constant universal time. Time is relative.
According to Einstein’s theory of relativity, the faster an object moves, the slower time runs until time comes to a stop at the speed of light. This is referred to as the time dilation effect.
Apart from speed, time is also affected by gravity. At powerful gravitational fields such as those at the event horizon of black holes, time slows down.
Why Are There Time Zones?
We all want the sun to be at its highest point in the sky at midday. This would not happen if there was only one time zone as the Earth rotates 15 degrees every hour. That is why there are different time zones.
Time zones are created by dividing the world into 24 slices, each 15 degrees. Time is set separately for each zone. People in a given zone set their time the same way. There is a one hour difference from one zone to the next.
All time zones are measured from a starting point centered at England’s Greenwich Observatory. This point is known as Greenwich Meridian or Prime Meridian. Time here is referred to as Greenwich Mean Time or Universal Time.
How We Measure Time
When we measure time, we measure the interval between events using units we have chosen for the purpose.
1 Picosecond is one millionth of a second. It is the shortest amount of time that can be measured accurately as of the present.
24 hours makes up one day. This is the period it takes for the planet Earth to complete one rotation on its own axis.
365.24 days equals one year, the amount of time it takes for Earth to orbit the sun.
4.5 billion years is the estimated age of our planet.
10-15 billion years is the suspected age of the universe since the Big Bang.
Is Time Travel Possible?
Time travel is a subject that fascinates scientists and ordinary people alike. We do travel through time every day. We move forward into the future at the rate of one hour per hour. But can we travel faster or slower than this speed in order to travel into the future or past?
Time travel into the future is theoretically possible though manipulating cosmic phenomenon such as wormholes and black holes. However, it has not been achieved and cannot be done with the current technology. What is problematic is time travel into the past although research is ongoing.
Will Time Ever End and How Will It End?
According to the general theory of relativity, development of space could lead to the collapse of the universe. All matter would shrink into a tiny dot reversing the Big Bang. This would end the concept of time as we know it.