Interesting article from National Public Radio:
New Clock May End Time As We Know It
"My own personal opinion is that time is a human construct," says Tom O'Brian. O'Brian has thought a lot about this over the years. He is America's official timekeeper at the National Institute of Standards and Technology in Boulder, Colorado.
To him, days, hours, minutes and seconds are a way for humanity to "put some order in this very fascinating and complex universe around us."
We bring that order using clocks, and O'Brian oversees America's master clock. It's one of the most accurate clocks on the planet: an atomic clock that uses oscillations in the element cesium to count out 0.0000000000000001 second at a time. If the clock had been started 300 million years ago, before the age of dinosaurs began, it would still be keeping time — down to the second. But the crazy thing is, despite knowing the time better than almost anyone on Earth, O'Brian can't explain time.
"We can measure time much better than the weight of something or an electrical current," he says, "but what time really is, is a question that I can't answer for you."
Some more:
The New Clock
At the nearby University of Colorado Boulder is a clock even more precise than the one O'Brian watches over. The basement lab that holds it is pure chaos: Wires hang from the ceilings and sprawl across lab tables. Binder clips keep the lines bunched together.
In fact, this knot of wires and lasers actually is the clock. It's spread out on a giant table, parts of it wrapped in what appears to be tinfoil. Tinfoil?
"That's research grade tinfoil," says Travis Nicholson, a graduate student here at the JILA, a joint institute between NIST and CU-Boulder. Nicholson and his fellow graduate students run the clock day to day. Most of their time is spent fixing misbehaving lasers and dealing with the rats' nest of wires. ("I think half of them go nowhere," says graduate student Sara Campbell.)
Sounds like my electronics bench... More:
Time Undone
Right now, on the top of Mount Everest, time is passing just a little bit faster than it is in Death Valley. That's because speed at which time passes depends on the strength of gravity. Einstein himself discovered this dependence as part of his theory of relativity, and it is a very real effect.
The relative nature of time isn't just something seen in the extreme. If you take a clock off the floor, and hang it on the wall, Ye says, "the time will speed up by about one part in 1016."
That is a sliver of a second. But this isn't some effect of gravity on the clock's machinery. Time itself is flowing more quickly on the wall than on the floor. These differences didn't really matter until now. But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, "and you will start to see that difference."
This new clock can sense the pace of time speeding up as it moves inch by inch away from the earth's core.
That's a problem, because to actually use time, you need different clocks to agree on the time. Think about it: If I say, 'let's meet at 3:30,' we use our watches. But imagine a world in which your watch starts to tick faster, because you're working on the floor above me. Your 3:30 happens earlier than mine, and we miss our appointment.
Fascinating. And in 20 years, we will be able to buy these clocks for $74.92 in WalMart. A fun time to be alive.
For a great story on relativistic time-keeping, check out Tom's story at Leapsecond:
Summary
In September 2005 the kids and I took several very accurate cesium atomic clocks from home and parked 5400 feet up Mt Rainier (the volcano near Seattle) for a full two days. The goal was to see if the clocks actually gained time, even if billionths of a second, as predicted by Einstein's general theory of relativity. Does gravity really alter time and can this weird phenomenon be detected with a family road trip experiment?
The outcome was that yes, there was a distinct and measurable difference between the clocks that spent two days a mile high and the clocks in his lab close to sea level.
