Did you feel it?
May 21, 2019 is the Mass of Eight Sun tanning disappeared. In a universe like ours, where mass and energy be preserved, mass cannot vanish without consequence: and so it went, as two distant ones black holes put together, the whole universe trembled. A powerful one gravitational shock wave expanded outward after the merger and expanded for billions of years before passing through the Earth. On that day, every cell in your body was stretched and compressed in four rapid successions, just like the atoms of everything else on Earth and in our solar system.
You may not have noticed, but scientists did: Three gravitational-wave observatories strategically placed over the planet — observatories that don’t resemble traditional optical telescopes, but rather long laser beams in dark rooms — saw their lasers shake just enough to see this black hole. detect fusion.
That humans can measure such distant events in the universe with relative precision is one of the marvels of modern science. This particular merger occurred about 16 billion light-years from us, or 17 percent of the width of the known universe. Until recently, such phenomenally distant astronomical events have typically been a mystery to astronomers. It is only because of the advent of gravitational wave astronomy, a whole new field of observational astronomy, that our view of the universe has broadened.
Gravity waves are ripples in the fabric of space and time that form after two black holes collide. Acclaimed physicist Albert Einstein first theorized about the existence of gravitational waves in 1916, and after being discovered a century later, astronomers have applied this knowledge to achieve the previously unthinkable, such as observing a black hole devouring a neutron star. Science news headlines regularly talk about how gravitational waves enable scientists to do new things, such as look in neutron stars and discover the most shaky black hole ever detected.
But what exactly to be gravitational waves? Could humanity’s newfound ability to observe them really be as game-changer as the headlines suggest? And to what extent is the excitement about gravitational waves substantive, and to what extent is it mere hype?
To answer the first question – what are gravitational waves – it is helpful to first understand gravity itself.
Like dr. Montana State University physics professor Neil Cornish explained to Salon, Einstein’s general theory of relativity was “quite radical in rewriting gravity” because it replaced the idea of gravity as a kind of force with gravity as simply space and time.
“There is no gravity in Einstein’s theory,” Cornish noted. “It’s just that we live in a time-space that is curved and shaped by the matter and energy in it.” Because black holes are the collapsed remnants of former stars, they are huge and when they collide they produce measurable gravitational waves.
“As they orbited the Earth, they were like hammers beating a drum,” Levin recalled to Salon.
But gravitational waves weren’t finally detected until 2015 at the Laser Interferometer Gravitational-Wave Observatory (LIGO) — two facilities in Washington and Louisiana that together can measure the direction and strength of gravitational waves passing through the Earth. The two facilities opened in 2002 and have operated unsuccessfully for years; it wasn’t until 2015 that engineers were able to fine-tune their precision enough to detect the tiny atomic-level perturbations that define gravitational waves. 2015 marked the confirmation of what was predicted a century earlier by Albert Einstein.
The confirmation of Einstein’s theory was a milestone in the history of modern science – and according to Barnard College physics and astronomy Dr. Janna Levin’s big moment of discovery in 2015 was “very cinematic”.
“As they orbited the Earth, they were like hammers beating a drum,” Levin recalled in Salon about the merger of binary black holes that produced the confirmed gravitational waves. “The drum is space-time, and they created ripples and sounds, technically they sound the same way an electric guitar plays sounds or a drum plays sounds, but in the form of space-time right before they merged, merged and into came to rest.”
She added that “there are a lot of impressive things about this phenomenon,” including that it radiated the most energy detected by humans since the Big Bang itself. But to travel at the speed of light all these years, only to arrive at Earth at the perfect moment to be detected in 2015 “to be recorded by this instrument devised in the space of a hundred years” was, to say the least, “fascinating”.
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Cornish also used music to illustrate gravitational waves.
“If you produce sound waves with a guitar, a cello or a violin, the distance between the peaks on the sound waves is about the same size based on the object producing it,” Cornish explains. “The same way you can tell just by listening, you know, is this a guitar or is this a drum or a tuba? The same goes for these collisions” between black holes and other cosmic objects, all of which produce different types of gravitational waves .
But to what extent can this really change our understanding of science?
“I like that kind of question. It’s tough,” Dr. Rana X. Adhikari, a professor of physics at the California Institute of Technology, emailed Salon. Adhikari said that when it comes to assessing the utility of gravitational waves for future scientific endeavors, it’s easier to describe quality than quantity.
“The kind of information you get from gravity is just very different from what you get with other types of astronomy.”
“However, I can tell you something more qualitative,” Adhikari told Salon. “The kind of information you get from gravity is just very different from what you get with other kinds of astronomy.”
In comparison, Adhikari likened it to the relationship between light and sound. Although we can process different colors with our eyes, someone singing while wearing a yellow shirt sounds the same as someone singing while wearing a blue shirt. You need another instrument to measure the vocals. Along the same lines, “gravity tells us about things that are obscured by light, like black holes. The same goes for neutron stars. Those are really interesting things, because we’ve never studied the insides of those. Gravity is probably our only probe going into the heart comes from a neutron star to tell us what’s happening.”
Cornish also told Salon that our ability to detect gravitational waves will indeed be very useful to current and future astronomers.
“We’re actually able to extract very detailed information because the motion of the mass is directly reflected in these oscillations that we pick up in these ripples of gravity,” Cornish explains. Rather than just distracting, gravitational waves enable direct measurements. “So we can confidently say, ‘Okay, we detected a black hole of this mass because the actual size of the black hole changes the wavelengths, and vice versa, the frequency of that wave. So a bigger black hole, just like a bigger instrument plays a lower pitch, we can extract a lot of information from these signals.”