Scientists will soon test Einstein’s theory of general relativity by measuring time distortion.
According to new research published on June 22 in the journal Astronomy of Nature, the newly proposed method turns the edge of space and time into a vast cosmic lab to investigate whether general relativity can identify dark matter – a mysterious, invisible form of matter that can only be inferred by its gravitational influence on visible matter of the universe and energy — as well as the accelerating expansion of the universe due to dark energy. The method is ready to be tested in future surveys of the deep universe, according to the study’s authors.
Related: The expanding universe may be a mirage, a new theoretical study suggests
General relativity states that gravity is the result of mass warping the fabric of space and time, which Einstein combined into a four-dimensional entity called space-time. According to relativity, time passes more slowly near a massive object than in a mass-less vacuum. This change over time is called time distortion.
Since its introduction in 1915, general relativity has been tested extensively and has become ours best description of gravity on massive scales. But scientists aren’t yet sure if this can explain the invisible dark matter and dark energy, which together make up about 95% of the energy and matter in the universe.
“The time distortion predicted by general relativity is measured precisely at small distances,” Camille Bonvin, lead study author and an associate professor at the University of Geneva, told Live Science via email. “It has been measured for planes flying around the Earth, for stars in our galaxy, and also for clusters of galaxies. We propose a way to measure time distortion at great distances.
The method proposes testing time distortion by measuring redshift, the change in the frequency of light emitted by an object as it moves away from us. Bonvin says the difference here is that this method measures the redshift caused by light attempting to climb out of a gravitational well, a “dent” in space-time created by a massive object.
“This ascent changes the frequency of light because time passes at different rates in and out of the gravitational well,” he said. “As a consequence, the color of the light is changed; it is redshifted. … By measuring the gravitational redshift, we get a measure of time distortion.”
Time to test general relativity
Time distortion suggests that time is not absolute in our universe but rather passes at different rates depending on the gravitational field. This idea is not exclusive to general relativity.
“Time distortion exists in all modern theories of gravity,” Bonvin said. “However, the amplitude of time distortion – how much the presence of a massive object slows down time – varies from theory to theory.”
In general relativity, the distortions of time and space are predicted to be the same; in other theories of gravity, this is not always the case. That means that by measuring the distortion of time and comparing it to the distortion of space, physicists can test the validity of general relativity.
The team’s new method could also test another leading theory of the cosmos: Euler’s formula, which astronomers use to calculate the motion of galaxies. In particular, the team’s proposed measurement of time warping could prove whether dark matter is compliant Euler’s equationas assumed by earlier studies of time warping.
“We have never observed a particle of dark matter directly. We have only felt its presence gravitationally,” said Bonvin. “As a consequence, we do not know whether dark matter obeys the Euler equation. It may be that dark matter is affected by additional forces or interactions in our universe besides gravity. If this is the case, dark matter does not obey the Euler equation. “
The team’s method could be used by future missions, including the European Space Agency’s Euclid telescope, scheduled to launch in July, and the Dark Energy Spectroscopic Instrument, which is three years into its five-year survey of the universe.
“It is possible to measure time distortion in the data delivered by these surveys,” Bonvin said. “This is very interesting because, for the first time, we will be able to compare the distortion of time in space, to test whether general relativity is valid, and we will also be able to compare the distortion of time to the speed of galaxies, to see if Euler’s equation is correct. At a new scale, we can test two fundamental laws.”
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