Fri Dec 7, 2018, 10:22 AM

How a mistake has led to a greater understanding of Einstinian Time Dialation

Clocks on a pair of Galileo satellites have given physicists the first refinement of gravitational redshift since 1976.

The experiment was only possible because in 2014, a launch went ever-so-slightly wrong: two Galileo satellites known as Doresa and Milena were launched into elliptical orbits, rather than circular orbits.

The elliptical orbit had a semi-major axis of 26,200km inclined at 49.8 degrees – and that eccentricity gave a team of boffins from five countries an idea for an experiment - since the satellites' orbits take them in and out of Earth's gravity just a little, they should be able to measure how gravity affects time on the two birds.

Thus was born the ESA's GREAT experiment (Galileo's gravitational Redshift Experiment with eccentric sATellites – the ESA has an announcement here).

As the American Physical Society noted: "The resulting modulation of the gravitational redshift of the onboard atomic clocks allows the redshift determination with high accuracy."

Working in two independent teams – one led by Sven Herrmann in Germany, the other led by Pacôme Delva in France – they measured how the frequencies of the satellites' hydrogen maser master clocks changed at various distances from Earth.

Einstein predicted that clocks would slow down slightly in the presence of a gravitational field. The APS (which published the research in Physical Review Letters) said that this "redshift" of a clock's frequency results from relativity's equivalence principle.

In 1976, scientists tested this by hoisting a clock 10,000km high on a rocket, and comparing its frequency shift to one on earth, in an experiment called the Gravity Probe A.

By combining the Galileo satellites' experience of time with laser-ranging (to reduce uncertainty about the satellites' orbit), the experiment "showed that general relativity could predict the clock's frequency shift with a precision of 0.007 per cent".

Working with three years of data, the two groups "improved constraints on general relativity violations by up to a factor of 5.6, providing the first improvement of redshift tests in over 40 years".

1 replies, 108 views

Reply to this thread

Back to top Alert abuse

Always highlight: 10 newest replies | Replies posted after I mark a forum
Replies to this discussion thread
Arrow 1 replies Author Time Post
Reply How a mistake has led to a greater understanding of Einstinian Time Dialation (Original post)
Currentsitguy Dec 7 OP
JaimeBondoJr Dec 7 #1

Response to Currentsitguy (Original post)

Fri Dec 7, 2018, 10:34 AM

1. I remember hearing one of the old-time drag racers, Kenny Bernstein, talking about time dilation...

He said in one pass down the track he could figure out next year's team budget.

Reply to this post

Back to top Alert abuse Link here Permalink