What is Time?

From a mundane perspective time is a constant, universal and unremitting occurrences throughout the universe. An indicator of past, present and future, recording events in history in chronological orders to references. Classical perception of time began with Galilean invariance of time with the assumption that time and space are completely seperable. Time remains invariant between difference frame of references while in motion. In 1583 he discovered that pendulum’s harmonic constant motion can be used in timing the motion of a swaying lamp in harmonic motion. The first mathematical interpretation of time began with Newton’s motion of objects influenced under gravity, a treatment of time began: linear time, conceived as universal clock. 

 

Albert Einstein’s 1905 theory on Special relativity challenged fundamental understanding of Absolute Time. His theory pivoting on frame of reference as a means to measure time, speed of time and most important thing, an intertwined concept of space and time changed the very definition and understanding of time forever. If an observer A at location A measures time “A Time” and observer B measuring same time from location B as “Time B” then observer B would measure it differently. The difference is markedly pronounced when speed of frame of references between Observer A and Observer B is close to speed of light. 

 

Time Dilation

In classical physics time pervases across universe remaining unchanged. Einstein’s relativistic theory changes the basic notion that time can be different depending on location (frame of reference of observer). This results in time events becoming longer (dilated) the closer one travels to speed of light. As a result moving clocks runs slower than stationary clocks as speed approaches speed of light.

We know a day as when sun rises in the east and sets in the west. In times perspective one earth solar day is equal to 24 hours (in exact terms 23 hours 56 minutes 4.09053 seconds). Similarly in Mars a solar day is apparent interval of successive returns of sun as seen by an observer. One day in Mars equals 1.02749125 earth days. 

This results in one Martian year being equal to 1.88 earth years. 

 

Time Travel

GPS satellite’s orbit earth at a speed of 8,700 miles per hour (14,000 km per hour). This slows down clocks in GPS as the faster one travels, the slower one experiences time. When satellites orbit at 20,200 Km (12,550 miles) above earth's surface GPS clocks speeds up by a slightly larger fraction of time. Satellites traveling at high earth orbit runs faster as earth’s gravity is much weaker. So GPS clocks experience time differently than what’s on earth’s clocks.  

According to NASA, time travel is possible, just not in the way you might expect. Albert Einstein’s theory of relativity says time and motion are relative to each other, and nothing can go faster than the speed of light , which is 186,000 miles per second. Time travel happens through what’s called “time dilation.”

Time dilation is how one’s perception of time is different to another, depending on their motion or where they are. Hence, time travel involves curving spacetime. 

Space and time are not absolute values, and what makes this all more complex is that curving of spacetime is required before time travel.

Wormholes and warp drives are tools that are used to create this curvature.  The matter needed to achieve curving spacetime via a wormhole is exotic matter, which hasn’t been done successfully. 

 

To prove time travel is not possible Stephen Hawking theorized a Champagne party with GPS specific location. 

The anecdote of Stephen Hawking's champagne party for time travellers where Hawking had a GPS-specific location for the party. He didn’t send out invites until the party had already happened so only people that could travel to the past would be able to attend. No one showed up and Hawking referred to this event as "experimental evidence" that time travel wasn't possible.

The Beginning and End of Time

Universe came into being at a time and the starting point was 13.8 billion years ago. This measurement is purely based on Cosmic Wave Radiation as there isn’t earlier radiation available to counter that for the time being. 

Will universe end? The answer is unknown. As our planet speeds through milky way through ever expansive universe science is limited by it’s technology, methods, scientific postulations, thesis, to answer this question. 

But one can be sure that if time is abstract there is no start or end of time and the literal quantity that signifies time is only measured in one frame of reference.