Nearly a century ago to the date, physicist Albert Einstein theorized the existence of spacetime-rippling gravitational waves but lacked the necessary technology to back up his argument with real, raw data. Well, today this all changes as a team of scientists at the Laser Interferometer Gravitational-wave Observatory (LIGO) confirmed the direct detection of a series of ripples created by gravitational waves. Furthermore, the scientists didn’t only detect the ripples but were able to confirm the actual source of the waves themselves — the product of an enormous collision between two massive black holes some 1.3 billion years ago. If there was ever an opportunity to say “mind blown,” that time is unequivocally right now.
Back around 1915 and 1916, Einstein shattered the then-known about rules of our universe, positing that space wasn’t as static as the scientific community had been led to believe. Rather, the German physicist stated that the geometry of the universe is constantly bent and twisted by its surrounding energy and matter. Essentially, this theory existed as part of the bedrock for his work on general relativity which explains how observed gravitational attraction between masses is the result of the warping of spacetime by these very masses. Today, Einstein’s work on general relativity remains one of the vital pillars of information in astrophysics.
Despite his advancements with general relativity, Einstein severely lacked the means to look for gravitational waves and even deemed them nearly impossible to detect. Today, however, researchers from Caltech and MIT operate the twin detector LIGO device which boasts the capability to detect minuscule vibrations from passing gravitational waves. Back in September of 2015, the LIGO device caught the glimpse of an energy signal 50 times greater than all of the universe’s stars combined (!) and exceeded the “five-sigma” standard of statistical significance. For five months, the LIGO team dissected the signal by converting it to audio and listening to the two massive black holes collide.
“We’re actually hearing them go thump in the night,” says MIT assistant professor of physics, Matthew Evans. “We’re getting a signal which arrives at Earth, and we can put it on a speaker, and we can hear these black holes go, “Whoop.” There’s a very visceral connection to this observation. You’re really listening to these things which before were somehow fantastic.”
Co-founded in 1992 by physicists Kip Thorne (with whom Christopher Nolan famously consulted for Interstellar), Ronald Drever of Caltech, and MIT’s Rainer Weiss, the LIGO experiment was created solely for the purpose of detecting gravitational waves. During its first eight years in existence (2002-2010), it failed to detect even one gravitational wave, causing the experiment to undergo a temporary hiatus for the installation of improved detectors. After a five-year, $200 million revamp primarily funded by the National Science Foundation (NSF) — which actually cost $620 million — the new and improved LIGO facilities were up and running in Livingston, Louisiana, and Hanford, Washington.
Concerning the instrument itself, each LIGO site boasts an L-shaped interferometer which measures roughly 4 kilometers in length and utilizes a split beam laser light which runs up and down each arm. As the lasers travel the arms, they bounce around among a series of precisely placed mirrors while consistently monitoring the exact length it travels between each mirror. If, and in this case, when, a gravitational wave passes through the instrument, the distance the lasers travel between the mirrors will change in a manner so small it’s nearly unnoticeable.
“You can almost visualize it as if you dropped a rock on the surface of a pond, and the ripple goes out,” says MIT’s Curtis and Kathleen Marble Professor of Astrophysics, Nergis Malvalvala. “[It’s] something that distorts the space-time around it, and that distortion propagates outward and reaches us on Earth, hundreds of millions of light years later.”
After running computer simulations of the waves, it was determined the energy came from objects measuring roughly 29 and 36 times as massive as the sun. Before the otherworldly collision, the two objects were spiraling a mere 130 miles from each other before eventually merging — aka crashing into each other. According to LIGO member Bruce Allen, only black holes are capable of containing so much mass in such a confined space and further added, “before you could argue in principle whether or not black holes exist; now you can’t.”
Though LIGO scientists are able to report the severity of the collision created an invisible explosion capable of making an atomic bomb explosion look like a mere spark, it spent the better part of five months making sure the initial reading was, in fact, real. As word slowly trickled out of a detected gravitational signal, the scientists worked day and night to determine whether it was genuine or not. Possible alternatives on the table ranged from the lab’s own false signals (or “blind injections”) to a full-blown, man-made hoax. These possibilities were soon ruled out after the team realized it was not actually running any blind injection tests and that a fabricated signal was highly unlikely.
“We thought it was going to be a huge challenge to prove to ourselves and others that the first few signals that we saw were not just flukes and random noises,” says MIT LIGO laboratory director David Shoemaker. “But nature was just unbelievably kind in delivering to us a signal that’s very large, extremely easy to understand, and absolutely, magnificently in alignment with Einstein’s theory.”
Now that the team has effectively proven the existence of gravitational waves, the very fabric of astrophysics, general relativity, and the entire universe begs to be viewed in a different way. As Science Mag notes, Johns Hopkins University physicist Marc Kamionkowski acknowledges that these findings opens the door for scientists to study general relativity in extreme conditions — i.e., instances where the gravitational field of a body accounts for nearly all of its mass. MIT also admits that the gravitational field’s detected by the LIGO device are but the tip of the iceberg in terms of the fundamental physics of our universe.
“This really opens up a whole new area for astrophysicists,” adds Matthew Evans. “We always look to the sky with telescopes and look for electromagnetic radiation like light, radio waves, or X-rays. Now gravitational waves are a completely new way in which we can get to know the universe around us.”
Moving forward, the LIGO team intends to continue to sift through data gathered during the recent observational run which ended last month — the first such run using the equipment’s upgraded sensors. As it searches for other gravitational wave signals in the abundance of data, the lab said it is also preparing to begin recording data this July. Evidenced by comments made by David Shoemaker, the lab has no intention of resting on its gravitational wave laurels.
“In a few years, when this is fully commissioned, we should be seeing events from a whole variety of objects: black holes, neutron stars, supernova, as well as things we haven’t imagined yet, on the frequency of once a day or once a week, depending on how many surprises are out there,” Shoemaker says. “That’s our dream, and so far we don’t have any reason to know that that’s not true.”
A complete summation of the team’s findings published in the Physical Review Letters on February 11 which further explains the way in which the LIGO detectors sensed the gravitational waves. It’s an understatement to call the results revolutionary, as the discovery drastically alters even the most basic understanding of our universe. What an absolutely fascinating time to be alive, huh?
