The concept of time continues to amaze and befuddle us.
Here, for example, is one interesting fact: did you know that time travels faster just above the earth than it does on the surface of the planet?
In the 20th century, Albert Einstein had said that time can be understood to flow like a river; in some places it moves faster than others. He also likened it to the fabric of space. Earlier this year, British cosmologist Stephen Hawking provided tantalizing proof of time's fluidity. In a newspaper article, he cited as evidence what happens daily to the Global Positioning System (GPS) satellite network in orbit around the earth. The system that so many of us now rely on for accurate navigation requires the constant adjustment of its computer clocks.
Hawking writes, "Inside each spacecraft is a very precise clock. But despite being so accurate, they all gain around a third of a billionth of a second every day. The system has to correct for the drift, otherwise that tiny difference would upset the whole system, causing every GPS device on Earth to go out by about six miles a day." (Six miles per day!) Imagine what this drift, left unchecked, would do to aviation safety.
Hawking explained that the reason the clocks need adjustment is that the earth's gravity acts like a drag on the flow of time, and actually slows it down compared to the flow of time in space.
For more on Hawking's thoughts about time, including the possibilities of time travel, see Stephen Hawking's Time Machine, which was a summary posted on discovery.com
Link: Research on the frontiers of physics leads to interesting theories about time travel