Posted on 12/07/2018 12:39:21 PM PST by ETL
Making lemonade from lemons, two teams of physicists have used data from misguided satellites to put Albert Einstein’s theory of gravity, the general theory of relativity, to an unexpected test.
The opportunistic experiment confirms to unprecedented precision a key prediction of the theory—that time ticks slower near a massive body like Earth than it does farther away.
As Einstein explained, gravity arises because massive bodies warp space-time. Free-falling objects follow the straightest possible paths in that curved space-time, which to us appear as the parabolic arc of a thrown ball or the circular or elliptical orbit of a satellite.
As part of that warping, time should tick more slowly near a massive body than it does farther away. That bizarre effect was first confirmed to low precision in 1959 in an experiment on Earth and in 1976 by Gravity Probe A, a 2-hour rocket-born experiment that compared the ticking of an atomic clock on the rocket with another on the ground.
In 2014, scientists got another chance to test the effect when two of the 26 satellites now in Europe’s Galileo global navigation system, like the one pictured above, were accidentally launched into elliptical orbits instead of circular ones. The satellites now rise and fall by 8500 kilometers on every 13-hour orbit, which should cause their ticking to speed up and slow down by about one part in 10 billion over the course of each orbit. Now, two teams of physicists have tracked the variations and have shown, to five times better precision than before, that they match the predictions of general relativity, they report 4 December in Physical Review Letters. That’s not bad, considering the satellites weren’t designed to do the experiment. However, another experiment set to be launched to the space station in 2020 aims to search for similar deviations with five times greater precision still.
The botched launch of two global-positioning satellites four years ago has proven to be a real gift to physicists.
Scientists have used the Galileo 5 and Galileo 6 spacecraft to measure "gravitational time dilation" more precisely than ever before, two new studies reported.
Gravitational time dilation, also known as gravitational redshift, is a key prediction of the theory of general relativity, which Albert Einstein published a century ago. Gravitational fields slow the passage of time; the closer a clock is to a massive object, the more slowly its hands will move, as seen by an outside observer.
[What Is Einstein's Theory of General Relativity?]
Time dilation also occurs due to motion, as predicted by Einstein's 1905 theory of special relativity: The faster you go, the more slowly clocks tick (again, as seen by an outside observer).
Time dilation isn't just theoretical; global-positioning satellites have to take it into effect to provide accurate readings to users here on Earth. And scientists have measured the phenomenon precisely in the field, most famously in 1976 with the Gravity Probe-A experiment. Back then, researchers launched an atomic clock to an altitude of about 6,200 miles (10,000 kilometers), then compared its ticking to that of a similar instrument here on Earth. The results confirmed the predictions of general relativity, to within 0.007 percent.
The Gravity Probe-A measurement was the gold standard for four decades — until Galileo 5 and 6 came along. The duo launched atop a Russian Soyuz rocket in 2014 to join Europe's Galileo satellite-navigation network, but things didn't go according to plan.
The Soyuz delivered the satellites to incorrect orbits, which were too elliptical for Galileo 5 and 6 to do sat-nav work. (During the close-approach phase of these orbits, the spacecraft were unable to keep the entire Earth in view, which they needed to do to "center" their signal beams.)
The satellites' handlers managed to raise and circularize the pair's orbits over time. But the paths of Galileo 5 and 6 are still elliptical; both satellites climb and fall about 5,280 miles (8,500 km) twice per day, European Space Agency (ESA) officials said.
This characteristic isn't great for navigation work; Galileo team members are still evaluating whether the two satellites can join the proper constellation. But the situation is tailor-made for a time-dilation measurement, especially since Galileo 5 and 6 both have precise atomic clocks of their own, which remain stable to within 1 second every 3 million years.
"The fact that the Galileo satellites carry passive hydrogen-maser clocks was essential for the attainable accuracy of these tests," Sven Hermann, of the University of Bremen's ZARM Center of Applied Space Technology and Microgravity in Germany, said in an ESA statement.
Hermann led one of the two new studies; the other was helmed by Pacôme Delva, at the Paris Sciences & Letters-PSL University and Sorbonne University in France. The two research teams measured how fast the clocks on Galileo 5 and 6 were ticking at various points in their elliptical orbits — at both the near-Earth and more-distant positions — over the span of about three years.
And the researchers managed a roughly five-fold improvement in precision over Gravity Probe-A's work.
"It is hugely satisfying for ESA to see that our original expectation[s] that such results might be theoretically possible have now been borne out in practical terms, providing the first reported improvement of the gravitational redshift test for more than 40 years," Javier Ventura-Traveset, head of ESA's Galileo Navigation Science Office, said in the same statement.
"These extraordinary results have been made possible thanks to the unique features of the Galileo satellites, notably the very high stabilities of their onboard atomic clocks; the accuracies attainable in their orbit determination; and the presence of laser-retroreflectors, which allow for the performance of independent and very precise orbit measurements from the ground, key to disentangle clock and orbit errors," he added.
Both studies were published yesterday (Dec. 4) in the journal Physical Review Letters.
https://www.space.com/42641-einstein-gravitational-time-dilation-galileo-probes.html
Is time and aging the same thing?
Time dilation does affect aging.
_______________________________________
When Einstein finalized his theory of gravity and curved spacetime in November 1915, ending a quest which he began with his 1905 special relativity, he had little concern for practical or observable consequences. He was unimpressed when measurements of the bending of starlight in 1919 confirmed his theory.
Even today, general relativity plays its main role in the astronomical domain, with its black holes, gravity waves and cosmic big bangs, or in the domain of the ultra-small, where theorists look to unify general relativity with the other interactions, using exotic concepts such as strings and branes.
But GPS is an exception. Built at a cost of over $10 billion mainly for military navigation, GPS has rapidly transformed itself into a thriving commercial industry. The system is based on an array of 24 satellites orbiting the earth, each carrying a precise atomic clock.
Using a hand-held GPS receiver which detects radio emissions from any of the satellites which happen to be overhead, users of even moderately priced devices can determine latitude, longitude and altitude to an accuracy which can currently reach 15 meters, and local time to 50 billionths of a second. Apart from the obvious military uses, GPS is finding applications in airplane navigation, oil exploration, wilderness recreation, bridge construction, sailing, and interstate trucking, to name just a few. Even Hollywood has met GPS, recently pitting James Bond in “Tomorrow Never Dies” against an evil genius who was inserting deliberate errors into the GPS system and sending British ships into harm’s way.
But in a relativistic world, things are not simple. The satellite clocks are moving at 14,000 km/hr in orbits that circle the Earth twice per day, much faster than clocks on the surface of the Earth, and Einstein’s theory of special relativity says that rapidly moving clocks tick more slowly, by about seven microseconds (millionths of a second) per day.
Also, the orbiting clocks are 20,000 km above the Earth, and experience gravity that is four times weaker than that on the ground. Einstein’s general relativity theory says that gravity curves space and time, resulting in a tendency for the orbiting clocks to tick slightly faster, by about 45 microseconds per day. The net result is that time on a GPS satellite clock advances faster than a clock on the ground by about 38 microseconds per day.
To determine its location, the GPS receiver uses the time at which each signal from a satellite was emitted, as determined by the on-board atomic clock and encoded into the signal, together the with speed of light, to calculate the distance between itself and the satellites it communicated with. The orbit of each satellite is known accurately. Given enough satellites, it is a simple problem in Euclidean geometry to compute the receiver’s precise location, both in space and time. To achieve a navigation accuracy of 15 meters, time throughout the GPS system must be known to an accuracy of 50 nanoseconds, which simply corresponds to the time required for light to travel 15 meters.
But at 38 microseconds per day, the relativistic offset in the rates of the satellite clocks is so large that, if left uncompensated, it would cause navigational errors that accumulate faster than 10 km per day! GPS accounts for relativity by electronically adjusting the rates of the satellite clocks, and by building mathematical corrections into the computer chips which solve for the user’s location. Without the proper application of relativity, GPS would fail in its navigational functions within about 2 minutes.
So the next time your plane approaches an airport in bad weather, and you just happen to be wondering “what good is basic physics?”, think about Einstein and the GPS tracker in the cockpit, helping the pilots guide you to a safe landing.
Clifford M. Will is James S. McDonnell Professor of Physics at Washington University in St. Louis, and is the author of Was Einstein Right? In 1986 he chaired a study for the Air Force to find out if they were handling relativity properly in GPS. They were.
“Relativity”
The only time my relatives worry about is Happy Hour.
So... gravity slows down time.
I wonder if the clocks on the Sun are set an hour behind ?
Yes, according to Einstein, the effects of gravity are "equivalent" to acceleration.
So it's not only high rates of motion that cause time to slow down, but also strong gravitational fields.
A windowless elevator accelerating through empty space in the absence of gravity (left) is indistinguishable from one at rest in the presence of gravity (right).
https://www.cfa.harvard.edu/~ejchaisson/cosmic_evolution/docs/fr_1/fr_1_part1.html
What would really help in evaluating all this information is a better explanation of how gravity works.
If a planet for instance bends space/time, then it would be logical to assume that doing so generated some kind of ‘energy’. That energy could be the actual force that ‘attracts’ other bodies. If we knew exactly what part of the EMS that energy was, then maybe we could apply an opposite charge to an object the size of... well an aircraft... it would then essentially be Zero gravity.
I bet that previous civilizations knew what the frequency was and how to offset it. It would explain quite a few things.
I thought that the GPS satellites were configured to accommodate time dilation. So what’s all the fuss about this experiment?
Another thought.
Maybe the reason that time appears to slow down when an atomic clock, or any electronic clock, is under less gravity is because gravity may have an on affect the orbits of the various components of atoms.
.
Its about the shape and density of local space being altered gravitationally.
Time has a different density in zero-gravity conditions.
I guess it was just a further demonstration.
Density?
Time doesn't slow down under less gravity, it speeds up, at least in relation to a clock in a zero gravity field.
The whole idea behind a theory is to test it.
So live in high altitudes you’ll live longer.
Simply put, according to Relativity theory, a clock in motion runs more slowly than a stationary clock at your side. Likewise, a clock in a strong gravitational field runs slower than a clock in a less strong or zero gravitational field.
Lol! Or along the equator. Centrifugal force!
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.