SIOUX CITY -- Like many of his generation, the news of the attack on Pearl Harbor remains vivid in John Hendrix' memory.
Now 92 years old, he remembers Dec. 7, 1941, and can recall his reaction when hearing radio reports about the Japanese attack on the U.S. fleet anchored in Hawaii. He wanted to enlist in the military right then and there and fight back.
"Me and my buddy, we wished we were in the Army. We were 15 years old," Hendrix said.
They were too young to serve at that time, but Hendrix would get his chance soon enough.
Born and raised in Tennessee, Hendrix said he left home at age 17 to work in a shipyard in Georgia to learn how to be a sheet metal mechanic.
"I stayed there at the shipyard until I was drafted," he said. "I knew when I got 18 I'd be drafted. I got a notice from my draft board."
Today marks the 77th anniversary of the attack on Pearl Harbor, an event that drew the United States into World War II. The two waves of Japanese planes that swept over Pearl Harbor and surrounding airfields left 2,343 U.S. servicemen and 68 civilians dead and another 1,143 wounded.
After the attack was over, six U.S. battleships were either sunk or destroyed along with several other ships. Dozens of Navy and Army Air Corps planes were destroyed.
When Hendrix entered the Navy in April 1944, he wasn't bent on revenge for the attacks, but he soon saw some of the rebuilding still taking place more than two years later.
Once Hendrix had completed boot camp, he sailed from Newport News, Virginia, to Pearl Harbor, to await further orders.
"There was still evidence of the attacks," he said of Pearl Harbor's condition when he arrived there. "The Navy was putting in sidewalks and the Army was doing this and that."
After about two weeks, Hendrix was assigned to the USS Kidd, a destroyer named for Rear Adm. Isaac C. Kidd, who died on board the battleship USS Arizona, which exploded and sank to the bottom of Pearl Harbor during the Japanese attack.
The USS Kidd had just returned from fighting in the Pacific Ocean and soon rejoined it.
Hendrix was assigned to one of the ship's 5-inch guns, but at 130 pounds, he wasn't big enough to handle the 80-pound shells, he said. He was reassigned to the chief's quarters, where he served the ship's commanding officers.
"I wore the phones. I knew everything that was going on," he said.
After a stop in Fiji, the USS Kidd sailed to the Philippine Islands, where it took part in the battle of Leyte Gulf, one of the largest naval battles of World War II. Hendrix remembers being on the ship's deck and watching American invasion forces land.
"We sat in the harbor and bombarded the beaches," he said.
Once the battle was over, the USS Kidd escorted American ships to New Guinea to pick up more troops. While returning to the Philippines, the USS Kidd received orders to return to the United States for maintenance. Back in the United States, Hendrix was transferred to land duty and served the remainder of the war at a naval base in Bremerton, Washington, before his discharge in April 1946.
After his discharge, Hendrix went to Odessa, Texas, where he drove trucks. He had a cousin in Sioux City, and moved here in 1964 to be a trucker for Holdcroft Trucking. Hendrix spent 36 years as an over-the-road trucker before retiring.
Now a resident of Holy Spirit Retirement Home in Sioux City, Hendrix easily rattles off the dates of his service and tells stories of his service time.
Like so many others, that service time can be traced back to one date: Dec. 7, 1941.
Scientists have invented a new clock that keeps time more precisely than any that have come before.
The clock is so accurate that it won't gain or lose more than one second in 14 billion years — roughly the age of the cosmos. Its ticking rate is so stable that it varies by only 0.000000000000000032 percent over the course of a single day.
That level of exactitude is not really necessary for those of us who rely on clocks to get us to a doctor's appointment on time, or to know when to meet up with friends.
But keeping time is just the beginning. This new clock is so exact that it could be used to detect dark matter, measure the gravitational waves that ripple across the universe, and determine the exact shape of Earth's gravitational field with unprecedented precision.
Indeed, these hyper-accurate clocks can help scientists better probe the mysteries of the cosmos, experts said.
"It turns out that if you have all these digits of precision for making a measurement, it can give you a microscope onto our very universe," said physicist Andrew Ludlow of the National Institute of Standards and Technology in Boulder, Colo. Ludlow led the work that produced the new clock, which was described last week in the journal Nature.
Since the 1960s, time has been measured by so-called atomic clocks that use the natural oscillations of a cesium atom as a pendulum. Think of it as a watch with a hand that ticks just over 9 billion times per second.
The optical lattice clock Ludlow and his colleagues developed measures the much faster oscillations of a ytterbium atom. Its atomic pendulum swings about 10,000 times faster, at a speed of 500 trillion times per second.
"Cesium is a beautiful atomic system, but we have reached the basic limits of how good it can be," Ludlow said. "Ytterbium can break down time into much finer intervals, enhancing the precision with which you can measure it."
Optical lattice clocks have been around for only 15 years, and they are still in the development stage, Ludlow said. Scientists continue to tinker with them, gradually increasing their accuracy with each new adjustment.
Most of the improvements in the latest iteration are due to a new heat shield that Ludlow's group developed a few years ago. It protects the ytterbium atoms from the effects of heat and electric fields, which can interfere with their natural oscillations.
"We want to be sure that when we are measuring the ticking rate of the atom, we are measuring the rate Mother Nature gave it, and that it is not perturbed or shifted due to an environmental effect," he said.
With so many oscillations, the ytterbium clock can detect shifts in the gravitational field of our planet with unprecedented precision, Ludlow and his coauthors wrote in Nature.
As Einstein's theory of general relativity predicts, time moves differently depending on where you are in a gravity field.
A clock on top of a tall mountain — far from Earth's center — will tick a tiny bit faster than a clock at the base of that same mountain.
It's not a mechanical error. Time actually passes faster at the top of that mountain.
Most clocks aren't accurate enough to register that extremely subtle difference. After all, in 10 years, two clocks that are 1,000 meters apart in altitude will be off by just 31-millionths of a second.
Scientists have already demonstrated that it is possible to measure differences in Earth's gravitational field by comparing the tick rate of two optical lattice clocks in different locations. However, until now those same gravity maps could be made just as accurately using other, cheaper techniques.
The new clock can detect changes in just 1 centimeter of elevation, a measurement far more precise than was previously possible, Ludlow said.
In addition, his team is part of an international collaboration that is using hypersensitive clocks to try to detect dark matter, the mysterious stuff that is thought to be five times more plentiful in the universe than normal matter.
"Very little is known about dark matter, but most theories predict that it would interact with atoms in a way that would impact the ticking rate of our clock," he said.