How gravitational waves open hidden corners of the universe to human eyes

Didn’t you feel it?

The mass of the eight suns disappeared on May 21, 2019. In a world like ours, where mass and energy are conserved, mass cannot disappear without consequences: thus, with the merger of two distant black holes, the entire universe shook. A powerful gravitational shock wave rippled outwards from the merger, expanding for billions of years before passing through Earth. On that day, every cell in your body expanded and compressed in four quick successions, as did the atoms of everything else on Earth and in our solar system.

You might not have noticed, but scientists did: Three gravitational-wave observatories strategically located around the planet — observatories that look not like traditional optical telescopes but rather long beam darkroom lasers — watched their lasers vibrate just enough to spot this black hole. merger.

That humans can measure such distant events in the universe with relative accuracy is one of the marvels of modern science. This particular merger occurred about 16 billion light-years away from us, or 17 percent of the width of the known universe. Until recently, such apparently distant astronomical events were a mystery to astronomers. It is only because of the advent of gravitational wave astronomy, a very new field in observational astronomy, that our eyes on the universe have widened.

Gravitational waves are ripples in the fabric of space and time produced when two black holes collide with each other. Famed physicist Albert Einstein first theorized about the existence of gravitational waves in 1916, and after discovering it a century later, astronomers applied that knowledge to achieve the previously unimaginable, such as observing a black hole devouring a neutron star. Science headlines regularly recount how gravitational waves allow scientists to do new things like peer inside neutron stars and discover the most wobbly black hole ever discovered.

after what exactly We are Gravitational waves? Could the newfound human ability to observe them be as game-changing as the headlines suggest? To what extent is the excitation on gravitational waves intrinsic, and to what extent is it merely noise?

To answer the first question — what are gravitational waves — it helps to first understand gravity itself.

As Montana State University physics professor Dr. Neil Cornish explained to Salon, Einstein’s general theory of relativity was “rather radical in its rewriting of gravity” because it replaced the idea of ​​gravity as a type of force with gravity as simply space and time.

Cornish noted that “there is no gravitational force in Einstein’s theory”. “It’s just that we live in space-time that is curved and shaped with matter and energy in it.” Because black holes are the collapsed remnants of former stars, they are massive, and when they collide with each other they produce measurable gravitational waves.

“As they orbited, they were like a hammer banging on a drum,” Levine recalled to Salon.

But gravitational waves weren’t definitively detected until 2015, at the Laser Interferometer Gravitational-Wave Observatory (LIGO)—two facilities located in Washington state and Louisiana that, together, can measure the direction and strength of gravitational waves passing through Earth. The two facilities were opened in 2002, and have been in operation for years without finding any results; It was only in 2015 that engineers improved their resolution enough to detect the tiny perturbations at the atomic level that define gravitational waves. The year 2015 saw the confirmation of what Albert Einstein predicted a century ago.

The confirmation of Einstein’s theory was a milestone in the history of modern science — and according to Barnard Physicist and Astronomer Jana Levine, the major moment of discovery in 2015 was “extremely cinematic.”

Levine recalls to Salon about the binary black hole merger that led to the confirmed gravitational waves: “The drum is space-time, and they created ripples and sounds, technically speaking, the same way an electric guitar plays sound or a drum plays sounds, but in the shape of space and time before they coalesce, merge and subside.”

She added that “there are a lot of impressive things about this phenomenon,” among which is that it emits the greatest amount of energy discovered by man since the Big Bang itself. However, traveling all those years at the speed of light, only to arrive at Earth at the perfect moment to be detected in 2015 “to be recorded by this instrument that has been innovating over a hundred years” was, to say the least, “brilliant”.

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Cornish also used music to illustrate gravitational waves.

“When you’re producing sound waves with a guitar, cello, or violin, the distance between the peaks on the sound waves is roughly the same size based on the object that’s producing them,” Cornish explained. “In the same way that you can tell just by listening, you know, is that a guitar or is that a drum or a tuba? The same goes for these collisions” between black holes and other cosmic bodies, all of which produce different types of gravitational waves.

However, how much can this really change our knowledge of science?

“I love this kind of question. It’s tough,” Dr. Rana X Adhikari, a professor of physics at Caltech, told Salon via email. Adhikari said that when it comes to assessing the usefulness of gravitational waves for future scientific endeavors, it’s easier to describe quality rather than quantity.

“The kind of information you get from gravity is very different from what you get from other types of astronomy.”

“I can tell you a little bit more qualitative,” Adhikari told Salon. “The kind of information you get from gravity is very different from what you get from other types of astronomy.”

By analogy, Adhikari compared it to the relationship between light and sound. While we can process different colors with our eyes, a person singing while wearing a yellow shirt will look the same as someone singing while wearing a blue shirt. You need a different instrument to measure vocals. In the same sense, “gravity tells us about things that light is obscured, like black holes. The same goes for neutron stars. These are really exciting things, because we’ve never really studied what’s inside them. Gravity is probably the only probe we have going into the heart of a neutron star to tell us what’s going on.” is happening “.

Cornish also told Salon that our ability to detect gravitational waves would be very useful to current and future astronomers.

“We’re already able to extract very detailed information because the motion of mass is directly reflected in these oscillations that we capture in these gravitational ripples,” Cornish explained. Rather than simply inferring, gravitational waves allow for direct measurements. “This is how we can confidently say, ‘Well, we detected a black hole of this mass because the actual size of the black hole changes the wavelengths, and inversely the frequency of that wave. So a bigger black hole, just as a bigger instrument plays a lower pitch, we can extract a great deal of information from these signals.”

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