Was Einstein right? Galileo to test Theory of Relativity

10 Nov 2015

Albert Einstein, via public domain

Albert Einstein’s most famous work, the General Theory of Relativity, is being put to the test by two Galileo satellites, due to an accident in their flight patterns.

E=Mc2, or so we’re told. Well, why not put it to the test? That’s what the ESA is thinking, anyway, after two of its satellites finally broke free of their, relatively speaking, house arrest.

The fifth and sixth satellites were sent up to space last year, but their orbits were all wrong, rendering them pretty useless.

So ESA scientists spent the last year putting into place “a demanding set of manoeuvres” to align their erratic orbits into a more circular pattern, with the results making them the perfect foils for the Theory of Relativity.

This is despite the fact that 5 and 6 are still not entirely ready for full operational use because they aren’t yet into a full circular route, climbing and falling 8,500km, twice a day.

ESA Galileo Einstein

The original (red) and corrected (blue) orbits of the fifth and sixth Galileo satellites, along with that of the first four satellites (green) – via ESA

Albert Einstein’s General Theory of Relativity

This shifting to and from Earth is key to Einstein’s theory, in which he predicted that time would pass more slowly close to a massive object.

This was verified experimentally, most significantly in 1976 when a hydrogen maser atomic clock on Gravity Probe A was launched 10,000km into space, confirming the prediction to within 140 parts in a million.

Atomic clocks on navigation satellites have to take into account that they run faster in orbit than on the ground – a few tenths of a microsecond per day, which would give us navigation errors of around 10km per day.

“Now, for the first time since Gravity Probe A, we have the opportunity to improve the precision and confirm Einstein’s theory to a higher degree,” ESA’s senior satnav adviser Javier Ventura-Traveset said.


Passive hydrogen maser atomic clock of the type flown on Galileo, accurate to one second in three million years – via ESA

Accuracy is key

This new effort takes advantage of the passive hydrogen maser atomic clock aboard each Galileo, the elongated orbits creating varying time dilation, and the continuous monitoring thanks to the global network of ground stations.

“Moreover, while the Gravity Probe A experiment involved a single orbit of Earth, we will be able to monitor hundreds of orbits over the course of a year,” explained Ventura-Traveset.

“This opens up the prospect of gradually refining our measurements by identifying and removing systematic errors. Eliminating those errors is actually one of the big challenges.

“For that we count on the support of Europe’s best experts plus precise tracking from the International Global Navigation Satellite System.”

Gordon Hunt was a journalist with Silicon Republic