A 24-satellite GPS constellation. Here, the number of satellites in view from a given point on the Earth's surface changes with time. Gif: Wikipedia
By comparing two times—the time a signal was transmitted by one of those satellites in space with the time it was received by your GPS receiver on Earth—your phone can calculate how far away each satellite is. By doing this with multiple satellites, your GPS is able to triangulate its location on Earth and to compute the time. The more satellites in view—the minimum is four at any given time—the more your GPS receiver can average out errors like random measurement noise and atmospheric delays.Getting precise location depends upon getting precise time. If one GPS satellite is off by a billionth of a second, your GPS receiver will be a foot off. If the satellite's clock were off by one full second, your location on Google Maps would appear to be about two-thirds of the way to the Moon. If you've ever been told by your phone that you're in the middle of a river when you're standing at a subway station, you may have been the victim of these errors.There are many other reasons for accurate time, but we civilians can't know them all. The Master Clock also keeps time for a host of other military operations: flying drones, aiming missiles, establishing secure communications, and other secret things. That is to say, not all time is created equal: the more critical you are to America's national security (say, you're a Navy SEAL, or a drone missile), the more accurately you might need to know the time or your location.
IF ONE GPS SATELLITE WERE OFF BY ONE FULL SECOND YOUR LOCATION ON GOOGLE MAPS WOULD APPEAR TO BE ABOUT 2/3 OF THE WAY TO THE MOON
"From the onset of locating a threat, to placing a weapon on target, and subsequently evaluating the success of this engagement, all are impacted by the precision of time," John G. Grimes, the Navy's Chief Information Officer, said in 2008. And this is precisely why Europe, Russia, and China have for years been assembling GPS-like systems of their own—Galileo, GLONASS and Beidou, respectively—which are said to be cheaper than GPS and don't rely on increasingly suspect American technology.For now, however, GPS, with its Master Clock-defined time, is central to time telling even in Moscow and Beijing. Many people worldwide get their time from GPS satellite signals. If, somehow, GPS time dissemination stopped working, "a lot of things would break down," from cell phones to financial markets, Matsakis said.
Conversely, in the event that the Master Clock (and an Alternate Master Clock, which is located in Boulder, Colorado), were destroyed in, say, a terrorist attack, GPS could serve as a backup system. "Especially in the context of nuclear war: if a whole bunch of cities get destroyed, at least GPS would work for awhile."Still, without the Master Clock to calibrate them, the clocks on the GPS satellites would gradually drift, per the law of special relativity. "If the Master Clock broke for 24 hours, the world would probably be okay. But I wouldn't do that for a week."
There have been some [attacks]… we think about it all the time.
Generally, Dept. of Defense servers are kept protected inside a secure network known as NIPRNET. To provide time to the world, the Naval Observatory's NTP servers live outside that boundary. At approximately 11pm EST, as the attacks continued, the Navy Cyber Defense Operations Command ordered USNO to take its NTP servers offline. For 3 million clients, time, as the Master Clock knows it, stopped. "This is the first time in 17 years that we have ceased NTP operations," Schmidt wrote that night.The Observatory's network admins restored the server the following day, but not before actively denying requests to specific IPs within China, a process that "requires considerable horsepower." The decision, Schmidt wrote, wasn't easy. "When it comes to making a choice between staying online and denying USNO NTP to China, we must unfortunately make the more secure choice.""The DOD is very aware of the dangers," Matsakis told me. The Master Clock itself "has never really been attacked," he said, "but we think about it all the time."
A Brief History of (Disseminating) TimeSecurity fears help illustrate why the ability to keep time is only as good as its ability to disseminate it to the world; like time and space, time keeping and time dissemination are inextricably connected. For decades, the Observatory's time signal was a "time ball" that sat atop its telescope's dome—cutting edge technology for 1845. By dropping the ball every day precisely at noon, the inhabitants of Washington could set their timepieces, while ships in the Potomac River could set their clocks before putting to sea. A re-creation of that ball still sits atop the Observatory's main building, next to one of its telescopes.In 1865, the Observatory began broadcasting a time signal via telegraph lines to the Navy Department, and eventually, via Western Union lines, to railroads across the nation. It was the railroad lobby who by 1885 would succeed in standardizing US time into time zones; up until then, the time depended on the city you were in: New York was five minutes ahead of Philadelphia, which was seven minutes ahead of Washington.
Between the Master Clock's contribution to Universal time—it makes up about 1/3 of the average—and the dominance of GPS, the U.S. has become the world's dominant timekeeper
Time wars: Greenwich driftLike the mechanism of our modern clocks, which echo that of the pendulum clocks first developed in the 10th century, the definition of a second is also a sort of hand-me-down.It was around 1000 AD when the Persian scholar al-Biruni began using seconds—a word derived from the second division by 60 of an hour—to measure the times of new moons. Based on the solar definition of a second—1/86,400 of each day—the Paris-based group called the International Bureau of Weights and Measures (BIPM), which is itself part of the U.N, came up with a standard based on the more stable measurements of atomic physics: when the electrons of an undisturbed cesium atom transition from one energy level to the next, they are known to emit radiation that oscillates 9,192,631,770 times per second. The time that takes, the BIPM determined, was closest to the previous definition of a second: "the fraction 1/31,556,925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time."
Cesiums. Strontiums. Rubidiums. Ytterbiums.People are constantly working on making better clocks, and many promising designs have worked well in test mode. In 2011, a cesium clock in Britain was presented as the world's most accurate long-term time keeper, after scientists determined that the clock would only lose or gain less than a second in 138 million years. And yet, these clocks are already outdated. While clocks that use cesium atoms are known to be reliable over long periods of time, they're not as accurate in the short term as timepieces that make use of other elements like hydrogen, mercury, and calcium, and a relatively new mechanism called, poetically, a "fountain."In this apparatus, a laser traps and cools atoms until they are so cold that their random motions essentially cease. Then they're launched straight up into a microwave cavity, where their natural resonance frequency can be measured. In April, the National Institute of Standards and Technology (NIST) in Boulder debuted a new cesium fountain clock, the NIST-F2, which is designed to not gain or lose 1 second in 300 million years. (See video showing how it works below.)
"We can see requirements ten years down the road that are going to need better clocks," Matsakis said, specifically "space-related" technologies and more accurate GPS. "That's the reason the Navy funds us to build better clocks."
In February, the Naval Observatory in Colorado upgraded the Master Clock with several brand new fountain clocks that use the element rubidium. (Counting the oscillations of rubidium could boost the timing reference for GPS by 10-fold, from 1 to 2 nanoseconds down to 300 picoseconds.) The clock is so delicate that installing it required an "airsled hover lifter"—essentially, a hovercraft—in order to ensure that it didn't come into contact with the floor or the walls.The Master Clock now relies on up to four rubidium fountains, which, Matsakis said makes it, for now at least, "the most precise continuously-operating system ever constructed to measure anything."Increasing precision is increasingly costly. A good cesium clock can now be purchased for as little as $75,000, a maser can cost around $250,000, and a rubidium fountain simply cannot be bought. Its parts can cost as much as $600,000, but that doesn't include the salaries of the half-dozen PhDs who've worked for a decade developing these fountains. In total, the Observatory runs on less than $20 million a year, a modest budget for the Department of Defense. (The Observatory is also allocated funds by NASA, the Air Force, and other agencies for special projects that are performed at cost.)
For now at least, the Master Clock is the most precise continuously-operating system ever constructed to measure anything.
There is a display of historical clocks at the Observatory, and when he walks past it, Matsakis is able to put the costs of his newest clocks in perspective. "We have a Cummins clock from the mid-1800s in there. It says that in today's dollars, it cost just as much as a maser does today. We have over a hundred clocks now. In the Song dynasty the Emperor used a water clock. It had a staff about as large as my department just to maintain it."Researchers are also developing atomic clocks that require even fewer people and take up much less space. The most accurate cesium clocks are the size of a compact car and draw about a kilowatt of power; now there are efforts to get atomic clocks down to the size of a computer chip, enabling GPS devices far more accurate than what we use today.
Wait a second: what is time?At some point, the big question about time came up. What is it?"Once I had this definition of time, that it's a coordinate that you can measure the evolution of in a closed system," Matsakis said. "Now, I think of time as something that, stripped down to its essence, is a measure of interactions," an idea based on Einstein's theory of relativity, which pins time and space to the relative motion of objects. "It's an intriguing thought: if you don't have interactions, time is irrelevant."He offers an example that begins at the end of time. "One way that time could stop is if the universe could reach a cold death. If our universe expands forever, and the suns die out, and they become black holes which evaporate over eons, what's left is a rarefied gas, a cold gas that's uniform across the universe. With everything the same, how can you have time? There'd be nothing to measure time. Time would stop, and not with a bang. It would just peter out."The relative interactions that govern the movement of time explain why events in the universe don't easily fit along a timeline. "Imagine that people witness Al Capone robbing a bank in 1930," he said. "Then, a supernova a thousand light-years away is observed somewhere on Earth in 1987. Did the star explode first, or was the bank robbery first? It depends on the observer."In an email later, I mentioned Nietsche's proposal of eternal return. Matsakis shot back: "It is very hard to define fundamental things. I haven't tried to define 'place.' Socrates spent years trying to define justice. Maybe they were right about him corrupting the youth."It was Aristotle's contemporaries who first mastered the calculation of the passage of time, or chronos, and it was they who also recognized another kind of time, kairos—the moments that define our pleasures and our pains and our deepest feelings and thoughts.In other words, the kind of time that can't be metered by any clock.Tensions linger between this sense of "time," which Henri Bergson would later describe as "duration," and the tick-tocks of "the time" overseen by the timekeepers. Now more than ever before, argues Douglas Rushkoff in Present Shock, distractions keep the latter version of time in a kind of tug of war with the former."We spent centuries thinking of hours and seconds as portions of the day," Rushkoff told David Pescovitz last year, "But a digital second is less a part of a greater minute, and more an absolute duration, hanging there like the number flap on an old digital clock." The rush of the present and its seemingly infinite, hyperlinked possibilities means "a diminishment of everything that isn't happening right now—and the onslaught of everything that supposedly is."But according to time, not everything is happening at once, as Wheeler joked. Could the Master Clock, I wondered, with its steady, orderly pace, remind us that the world isn't moving any faster?But not even this ticking will be the same in the future. With new clocks, the way that time is counted will change. And in time, the definitions of time will change too, if not the questions that endlessly circle it."What I tell people is, I can't tell you what time is," Matsakis said, "but I can tell you what a second is."At least for now.See also:
A Short History of Long-Term Thinking, for Our Fifty Thousand Year Time Capsule
If We Want Anyone to Remember Humanity, We Need to Talk About Time Capsules
"Where Time Comes From": The Atlantic Video
Chasing the Elusive Arrow of Time with Computer Algorithms