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Scientists understand gravity quite well when it comes to two objects, but add a third, and you have chaos. -a system impossible to explain with our simplest equations. But you also have a way to test the limits of Einstein's gravitational theory.
You are probably aware of the fact that there are many unanswered questions about our universe – like what is dark energy, what is dark matter, and why Can not a theory of unified physics explain both the largest and the smallest objects in the universe? A recurring theme of experiments exploring these problems is that they test Einstein's theory of general relativity. You look at the extremes of the theory, hoping that there are places where the real world does not agree with that. But no matter what a fact, the theory has not failed yet.
"Testing general relativity is important right now," said Anne Archibald, a physicist at the University of Amsterdam, in Gizmodo. "We are testing it in a way that has been difficult until now."
Researchers are testing something called the principle of equivalence. You can define mass in two ways: how an object behaves in a gravitational field, and how it behaves when you try to push it, also called its inertial mass. General relativity says that they are the same. If you were in space, accelerating upward in an elevator, the force that your inertial mass feels could be precisely imitated by the feeling of standing on a planet with good gravity.
But are both really the same? Scientists have performed tests comparing Earth, Moon and Sun, and a recent experiment has even involved the planet Mercury. Until now, Einstein's theory has not been proven false.
A new article published in Nature instead uses observations from a three-body system called PSR J0337 + 1715. This system consists of a rotating neutron star firing a beam of light (called pulsar) and a white dwarf that orbit every 1.6 days of Earth, both orbiting another white dwarf every 327 terrestrial days.
They used 800 observations of the system over six years, using the Westerbork Synthesis Radio Telescope in the Netherlands, the Robert C. Byrd Green Bank Telescope in West Virginia, and the William E. Gordon telescope at the l. Arecibo Observatory in Puerto Rico
How would you test the principle of equivalence? Well, you have two objects: one is a white dwarf star, whose mass is mainly composed of matter. Then there is the pulsar. The pulsar needs a lot of gravitational energy to hold it together – and, by the famous Einstein E = mc 2 gravity formula makes the pulsar even heavier, because the 39, energy and mass are equivalent. In fact, a significant fraction of the mass of the pulsar, perhaps 10 to 20%, can come from the gravity that holds it together. If general relativity is false, then the neutron star will behave differently from its neighboring white dwarf companion in reaction to the gravity of the distant white dwarf.
The researchers were able to measure this behavior based on the pulsating behavior of the rotating neutron star. Observations revealed that the white dwarf and the pulsar seemed to behave in exactly the same way in response to the gravity of the other white dwarf. General relativity wins again.
The modeling of three-body systems like these is difficult. As Ingrid Stairs, author and physicist at the University of British Columbia, told Gizmodo, "When you have a third body, there is no solution that is just an equation on a sheet of paper. You may have read the science fiction book. The Three Bodies Problem, which describes how unpredictable these systems are through the prism of an alien species that is trying to survive on a planet orbiting a planet. Archibald was particularly excited by the simulations she used to model the problem, using what she thought was rather basic physics.
These types of tests are important to rule out other theories of gravity that resemble general relativity but differ for the physical domains yet to be explored. A physicist not involved in the study, Clifford Will of the University of Florida, Gainesville, wrote that this research has made the validity of some of these alternative theories "much weaker" – but that's not the case. they were not completely excluded, according to Commentary on Nature . Deviations from general relativity should still be very minimal, says Archibald.
I also asked Archibald and Stairs if they had read Liu Cixin's The Three Body Problem . The stairs did not, and Archibald is halfway there. "One of the book's themes is fundamental physics … if you do the same experiment in two places, the physics does not depend on where." It's this universal basic physics that you can to acquire with meticulous experimentation [Liu] asks, what happens if physics does not work this way? "I am testing this on a fundamental level."
[Nature]
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