Cosmologic philosophy: general relativity proven again (Introduction)

by David Turell , Wednesday, June 27, 2018, 23:13 (2127 days ago) @ David Turell

Using gravitational lensing with two galaxies in line with us:

https://www.scientificamerican.com/article/einsteins-greatest-theory-validated-on-a-gal...

"... it is no secret general relativity is in some respects incomplete, and perhaps even fundamentally flawed: It cannot, for instance, explain conditions inside a black hole or during the first instants of the big bang. The theory also has a complicated relationship with a fundamental tenet of modern astronomy and cosmology—the notion that the universe is suffused with dark matter, a mysterious, invisible substance that only interacts with normal matter through gravity.

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" Similarly, in 1998 cosmologists found evidence the universe is expanding faster than expected, driven by an even more mysterious dark energy. In 2011 that research netted a Nobel Prize, but its validity hinges on general relativity being the correct description of gravity at cosmological scales.

"For their test, Collett and his collaborators focused on two galaxies in a coincidental celestial alignment, with one directly in front of the other along an Earthbound observer’s line of sight. In keeping with general relativity, the “foreground” galaxy’s great bulk warps the surrounding fabric of spacetime, forming a “gravitational lens” that distorts and magnifies the far-distant background galaxy’s light. Precisely measure those distortions, and you gain a good sense of how much mass the foreground galaxy should contain according to general relativity.

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"Those measurements required marshaling the combined power of the world’s two most advanced optical instruments—NASA’s Hubble Space Telescope in low Earth orbit and the European Southern Observatory’s Very Large Telescope (VLT) in the Chilean Andes. Collett’s team used Hubble to measure the foreground galaxy’s mass via gravitational lensing and the VLT to measure its mass via the speeds of stars twirling around its edges. After carefully analyzing and comparing the data, they found a striking agreement between these independent mass measurements. With an error margin of just 9 percent, the experiment’s findings are the most precise measurement of general relativity beyond our solar system to date. The results also indirectly support the theory’s validity in the face of dark matter, dark energy and other cosmological curveballs.

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"The real value of this new result, he says, comes from its unprecedented scale and precision, which are of relevance regardless of what one’s preferred theory might be. McGaugh should know—he is one of the more open-minded researchers when it comes to alternatives to dark matter and general relativity’s description of gravity. He studies a class of dim, diffuse galaxies that appear to defy some tenets of those theories. “This is another test that any theory you want to build has to satisfy,” he says.

"For now, says Tommaso Treu, an expert in gravitational lensing at the University of California, Los Angeles, who is unaffiliated with Collett’s study, any scientists struggling to overturn the unfinished revolution that Einstein began in 1915 must remember that dismissing a time-tested, century-old theory would be an extraordinary achievement requiring equally extraordinary evidence. “Everyone would love to prove Einstein wrong,” Treu says. “There is no better way to be famous.'”

Comment: As the article notes there are aspects of the theory that still don't fit, but it remains generally applicable.