Where Time Comes From

[pokerfan]

The time that ends up on your smartphone—and that synchronizes GPS, military operations, financial transactions, and internet communications—originates in a set of atomic clocks on the grounds of the U.S. Naval Observatory. Dr. Demetrios Matsakis, Chief Scientist for USNO's Time Services, gives a tour.

http://www.theatlantic.com/video/index/358609/where-time-comes-from/

[ret5hd]

1. I enjoyed his quiet passion and enjoyment of his job.

[caraher]

2. I thought it came from the Time Transmitter on the Greenwich Marillion

Or at least that's what Philomena Cunk seemed to suggest

[progressoid]

4. "with the present running right up through my middle bits"

[Jim__]

3. JILA Strontium Atomic Clock Sets New Records in Both Precision and Stability

An experimental clock that is based on strontium rather than cesium. A description of the clock - there is also a 50 second video:

Heralding a new age of terrific timekeeping, a research group led by a National Institute of Standards and Technology (NIST) physicist has unveiled an experimental strontium atomic clock that has set new world records for both precision and stability—key metrics for the performance of a clock.

The clock is in a laboratory at JILA, a joint institute of NIST and the University of Colorado Boulder.

Described in a new paper in Nature,* the JILA strontium lattice clock is about 50 percent more precise than the record holder of the past few years, NIST’s quantum logic clock.** Precision refers to how closely the clock approaches the true resonant frequency at which its reference atoms oscillate between two electronic energy levels. The new strontium clock is so precise it would neither gain nor lose one second in about 5 billion years, if it could operate that long. (This time period is longer than the age of the Earth, an estimated 4.5 billion years old.)

...

In JILA’s world-leading clock, a few thousand atoms of strontium are held in a column of about 100 pancake-shaped traps called an optical lattice formed by intense laser light. JILA scientists detect strontium’s “ticks” (430 trillion per second) by bathing the atoms in very stable red laser light at the exact frequency that prompts the switch between energy levels.

...

In the video in the OP, he talks about relativistic problems creeping in when the clock is about 1 meter high and the clock adds about 2 decimal places to the precision due to the differential effects of gravity. It looks like the pancakes in the strontium clock are arranged vertically. I wonder if that addresses the problems with the differences in gravity.

[caraher]

5. The gravity problem is fundamental to time itself

In the video in the OP, he talks about relativistic problems creeping in when the clock is about 1 meter high and the clock adds about 2 decimal places to the precision due to the differential effects of gravity. It looks like the pancakes in the strontium clock are arranged vertically. I wonder if that addresses the problems with the differences in gravity.

I assume you're referring to the video of the strontium clock... those "pancakes" are tiny, separated by something like a wavelength of the light used to make the trap (so roughly a micron between "pancakes&quot . They may be arranged vertically but they don't have to be. So on one hand, that clock may have some advantages from the compact size of the trap - changes in height will be much smaller than a meter or so, which might reduce any errors that might arise from different proper times in different parts of the apparatus.

But I took his real point to be that we're approaching the point where the difference in the rate of passage of time, because of "gravitational redshift," becomes significant relative to the precision of our best clocks over small distances like a meter. At that stage, while further technical improvements in clock stability and precision could be made, those advances are of little clear practical importance because "time itself" is defined to a precision limited by the strength uniformity of the gravitational field where you wish to measure the passage of time. It's a bit like trying to measure the circumference of the Earth to the nearest foot... Earth is only approximately spherical, and the exact number you should get varies a lot, for instance, with whether you're going around the equator or the poles. One foot precision would be meaningless because the thing you seek to measure doesn't have a well-defined circumference to that precision.

[Jim__]

6. Thanks for your response.

I know that gravity affects time. I'll have to think about the implications a little bit more.