Trip the Gravitational Wave Fantastic
By Corey Gray
A long time ago in a galaxy far, far away….
Two black holes spun toward each other at speeds approaching the speed of light.
Imagine what it would have been like to witness this dance of strong gravity. Each of these objects had the mass of about thirty of our suns, but they were squeezed down to the diameter of the San Francisco Bay Area. Their gravitational effects were so strong, light was powerless to escape their grasp. But there’s more. These objects actually warped space and time around them! They were spheres of utter darkness surrounded by an aura of bent space. That alone creates a visual worthy of science fiction.
With two of these bruisers in the same vicinity, the spatial oddness goes up a notch. Each object curved space around them, but now they were spinning toward each other. As they spiraled through spacetime, they caused ripples in space like waves on a pond. These ripples are gravitational waves, and they grew as the black holes got closer to each other with every round trip. The very fabric of space churned until both of these black holes smashed into each other and generated a cataclysmic release of gravitational wave energy equal to three of our suns. These ripples in space began their journey through our universe and carried with them information from the merger of the two black holes from which they were generated.
For all intents and purposes, this could have been the end of this particular story.
Meanwhile, a Little Closer
At the same time, on the other side of the universe, 1 billion light years away, a tiny blue dot in space bubbled with simple life. Basic multicellular organisms on our planet were unaware of the existence of black holes or gravitational waves, but they would eventually evolve into an audience … much, much later.
So, two parallel journeys had begun: the gravitational waves from our binary black hole merger and the evolution of life on our little, blue planet. Those little organisms from a billion years ago gave way to plants and other creatures. Fast forward a few hundred million years, and our planet exploded with larger creatures such as insects and reptiles. Another few hundred million years and dinosaurs roamed the earth followed by mammals. Move yet a few more million years, and the first homo sapiens made their first footprints in the soil. As we approached the present day, modern humans evolved, cultures developed, and cities were born.
Meanwhile, the gravitational -wave signal also evolved in time as it traveled through the universe at the speed of light. The signal passed through countless planets, stars, and galaxies. After each hundred million years, this signal, which was once violently large, became smaller and smaller. After traveling a billion years it was but a tiny whisper by the time Earth appeared in its crosshairs.
Is Anybody Listening?
On March 14, 1879, a new mind came into existence on Earth: Albert Einstein. In 1915, Einstein inaugurated a new era in astrophysics with his general theory of relativity, and from this work came the concept of gravitational waves. The journeys of life on Earth and the gravitational waves from a pair of black holes were on a collision course.
In 1915, gravitational waves had been traveling within the Milky Way for thousands of years. But the detection of gravitational waves would prove to be elusive in Einstein’s lifetime because of both limited technology and lack of knowledge of possible sources. Gravitational waves would be the one remaining loose end from a theory which would be elegantly proven right in many ways.
In the following decades, astronomy would introduce humanity to super-dense objects such as neutron stars and mysterious players known as black holes. Additionally, the technological advances of the twentieth century laid the groundwork for forging a renewed hunt for gravitational waves. The final ingredients needed were passion, vision, and a little bit of luck. This is where the founders of LIGO (Laser Interferometer Gravitational-Wave Observatory) entered Einstein’s story.
A young member of MIT’s faculty, Dr. Rainier (Rai) Weiss wrote the seminal paper describing how an interferometer could be used to detect gravitational waves; this document would ultimately provide the groundwork for LIGO. Rai was joined by theoretical physicist Dr. Kip Thorne from Caltech. You might recognize him from his work on the film Interstellar. Dr. Thorne would lay out the types of events Rai’s detector would be capable of detecting. Rounding out the trio was a creative physicist from Scotland, Dr. Ron Drever, who helped develop the technological advances that made LIGO a viable gravitational -wave hunter.
The game plan was to build a large-scale experiment. Simply put, this machine would monitor the distance between two masses to an unprecedented precision: we’re talking being able to detect distance changes 1,000 times smaller than the width of a proton!
This sensitivity is needed because the signals we would be looking for would be extremely tiny. Gravitational waves are not sound waves, but similar to how we listen to sound with our ears, the masses of LIGO’s detectors are like our eardrums. When a gravitational wave passes through the earth, it causes LIGO’s masses to vibrate, and these vibrations are observed with light that is then converted to an electrical signal. LIGO’s masses are like a vibrating eardrum that sends an electrical signal to our brain.
Simple enough, right?
The Native MacGyver Tackles Gravitational Waves
Making a gravitational wave detector would be a feat in physics and engineering. It would involve generations of scientists and decades of work.
In the 1990s, after a couple of decades of preparation, LIGO was finally approved for funding and construction preparations. During this time, I was beginning my college years. I had no idea where my studies would eventually take me, but the sciences pulled me. My first role model was my father, who was a self-made electrical engineer. I must also admit my formative years included lots of sci-fi and, of course, MacGyver. I wanted to be a Native MacGyver: hence the physics path.
I attended a small college on the beautiful northern California coast: Humboldt State University. In addition to my studies, I would also connect with other Native students on campus. They would be my second family. I would eventually graduate with Bachelor of Science degrees in physics and applied mathematics.
Ultimately, I took my talents to south-central Washington state’s high desert and joined the LIGO team as an operations specialist in March of 1998. At this time, LIGO was but a shell. There were a few buildings and a massive empty vacuum system. I joined a team of many and our task was to fill this vacuum system with the metal and glass that would make a gravitational -wave detector. This was our focus: building and running a machine that would make Einstein proud.
I have to admit, with this focus, came a lack of foresight. I can’t speak for everyone, but my world for 18 years was building stuff, working shifts to collect data, public outreach, and eventually becoming a supervisor for our team of operators. The bigger picture of actually detecting gravitational waves and doing cool new astrophysics was there, but it was in a dark corner of my mind, buried under cobwebs.
Never Bet Against Einstein
In the early morning hour of 4:50, Central Standard Time, in the year 2015, on September 14th, LIGO’s Louisiana detector detected a strong gravitational-wave signal. Seven milliseconds later, LIGO’s Washington detector observed the same signal at 2:50 a.m., Pacific Standard Time. The signal was quick, under a half-second on each machine, but the detection was made. And, just like that, the signal we named GW150914 had passed through the earth and was quickly and quietly continuing its trip through our universe.
But, its mark had been made and, more importantly, recorded. GW150914 was now ready to change physics, open an entirely new field of astronomy, and change our world.
Never bet against Einstein.
A Universal App
To make a detection, you need more than LIGO’s two detectors. Our machines produce tons of data. The job of sifting through all this data is the task of LIGO’s powerful computing and search tools. A gravitational -wave signal will be small and most likely buried within the data. Luckily, from general relativity, we have a good idea of the types of events LIGO can detect, and they include events such as black-hole binary mergers, neutron-star binary mergers, black-hole-neutron-star binary mergers, and supernovas. With these types of examples, we have literally tons of possibilities because there can be all sorts of mass options to consider. Our search tools take all these scenarios and make templates out of them. These templates are then used by our fast computers to see if there are any matches in the data.
Basically, LIGO and its search tools are similar to you and your smartphone. If you are like me, your favorite apps on your phone are the song recognition ones, such as Shazaam. For these apps, every song is unique, and because of this, every song is labeled with a unique digital fingerprint. So, when you use the app, the phone’s microphone grabs data in the form of sound. Millions of digital song templates are then compared with the data you recorded. When a match is made, your phone outputs a result such as Punk Rock Girl by The Dead Milkmen, or whatever song you are trying to figure out. When our search tools trigger on a possible event, they output results, and an email is sent to LIGO scientists. So, if you’re at a club and hear a song you like, you use the app and have your phone try to recognize the song. LIGO, with its two detectors, sort of does the same thing, but instead of trying to identify a song from the loud speakers, our detectors are trying to identify gravitational waves from the other side of the universe!
“A Very Interesting Event…” Indeed
Thus, on September 14th, a couple of minutes after our entire planet was sloshing in the wake of gravitational waves, an automated email was sent. One of the first people who saw this email was on the other side of the world in Germany, and this scientist sent out the historic email with the subject line “Very interesting event …”
The night before the event, I was the operator on shift just before the gravitational waves were detected by our machine. I handed the reins of the detector to the operator at midnight for the beginning of her shift. GW150914 was passing through the earth, and both of our machines, about the time I was laying my head on my pillow to sleep.
Later that morning, after waking, my morning ritual was to open my laptop, see how our detectors did overnight, and read emails. Our interferometers are like living breathing beasts — beasts that are our babies because we have spent so much time with them. They have good days and bad days. In a perfect world, our machines would be collecting data 24/7, but unfortunately, these sensitive machines are finicky and on a noisy earth. Earthquakes, storms at sea, wind storms, and hurricanes are examples of seismic noise each of our machines must battle every day. Because of this, our machines cannot collect data all the time. Some times our Washington machine will be purring along collecting data, but Louisiana will be down, and vice versa. We must have double coincidence (both machines observing and collecting data) to make a detection — if only one machine records an event, it won’t count. So all of us are obsessed with seeing how our machines are doing. It’s a juggling act, and you want BOTH machines in the air, not down on the ground.
So when I woke up on September 15th, after checking both machine’s activity overnight, I checked my email. As I wiped the sleep from my eyes, certain emails definitely woke me up. I obviously didn’t believe any of them at first. It had to be a test! By the time I made it to work, the mood at the observatory was electric. The excitement was controlled but palpable. After a few days, I cornered various coworkers in the hallway, and it was becoming apparent this could actually be a reality! I can’t speak for all, but I’ve been floating on cloud-9 since September 2015. When you think about this astrophysical event, and the way we detected it, it truly is mind-blowing. A huge violent event a billion years ago, traveled through much of our universe, made it to earth, and wiggled human-made machinery which many of us had a hand in building.
It’s a life-changing notion. Being a part of a huge project such as LIGO, and also to be around for this first detection filled me with awe. When thinking of the arc of history, it is humbling. Our project is rooted in the writings of Albert Einstein. We are connected to one of the world’s monumental achievements: the general theory of relativity. Many generations are a part of this discovery, and we are all connected. It truly is an honor to play a small part in this piece of scientific history. I have caught myself daydreaming about thoughts such as this. But this was only the beginning. A completely new field of astronomy has been launched. Gravitational -wave astronomy is so much different than our current astronomical fields. It truly is exciting to see what the future of this field has in store for humanity. Obviously, this is the sort of announcement you scream from a mountaintop.
But we had to hold our tongue!
The Verification Frenzy
We had the data in the can, but we had to make absolutely sure it was real. We had to be beyond 100% sure. You only get to make a First Announcement once. All 1,000+ members of the LIGO Scientific Collaboration (LSC), had to keep one of the biggest scientific discoveries in decades a secret!
Almost immediately, the LSC was whipped into action. Scientists at the observatories locked everything down. We froze our machines and kept running them for a few weeks in the same configuration as that September 14th morning to collect background data. In parallel, scientists went through thousands of other signals. We had to make sure this event couldn’t be mistaken for anything else. Every day, items were checked off our list, and with every check, we were becoming more closely connected to history.
Once we were nearing the end of weeks of ruling out tons of possibilities, the task of writing The Paper also began. It filled one with pride to see a huge group come together for a common goal. It was gratifying to read early drafts of the paper. It was like poetry. The plots were like art. GW150914 was monumental. It was a huge signal. I mean, you could actually see the event by eye in the data! This had once been theoretical, but now we had actual data! And, oh yeah, we directly detected gravitational waves for the first time — on the 100-year anniversary of Einstein’s theory of general relativity! That happened.
We kept working though. We still had months of data to collect. We had several papers to write. We also had to prepare for The Announcement.
The Big Reveal
I joined our Education and Public Outreach (EPO) Group a couple of months before the announcement, and a unique opportunity came up. This was an international event, and with that, we wanted to share our news in as many languages as possible. I instantly jumped on this. I am a member of the Siksika Nation (Northern Blackfoot), and I am not a fluent speaker, but my mother, Sharon Yellowfly, is. So, a few days before the announcement, I gave a draft of the press release to my mother to translate into Siksika. I am not sure a breakthrough scientific press release has ever been translated into a Native American language, but I thought it was an opportunity I couldn’t pass up.
I wanted other Native speakers to read this, and I wanted Native youth to see that someone like them was part of a huge scientific discovery like this.
On Thursday, February 11, 2016, LIGO made the announcement of the direct observation of gravitational waves from the merger of two black holes. We could not be happier with the overall reaction to the news. Over the following weeks we saw amazing examples of LIGO love. Fans have used gravitational waves in fashion, art, comics, and even music! We were trending on Facebook.
Humanity now has a completely new path of thought and reality with this confirmation of Einstein’s ideas about gravitational waves. Who knows how many young minds were influenced by this huge new discovery and where it will take us next!
Just the Beginning
This is only the beginning. LIGO will continue to make more observations, and with each detection, we will learn something new. LIGO will also be joined by several other land-based detectors in the near future, and in the coming years the window to gravitational wave astronomy will keep opening as completely different types of detectors come online. There is one at the South Pole looking for signals from the Big Bang, and there is another detector which will be launched into space. Now is the time for gravitational -wave astronomy to fulfill Einstein’s legacy.
Addendum: Another Detection
As I was writing this article, I had to be a little sneaky and not completely forthright with the SACNAS editors. The reason: a second official detection was announced!
On the evening of December 25, 2015, both LIGO detectors recorded a second gravitational -wave signal. Once again, it was another binary black hole merger. This time, the merging black holes were quite a bit smaller. This time, the gravitational -wave data was a bit buried in the noise of our data. However, this time we recorded more of the signal before the merger. In other words, this second detection was noticeably different and gives us new information about black-hole mergers.
Detecting this second signal was huge, but it did get a little ignored because much of our focus was on the announcement for GW150914. However, once February 11th passed, all focus went to this other detection, GW151226, known as the Boxing Day event. It was detected in Louisiana and Washington on the evening of Christmas, but since our detectors are in different time zones, we use Universal Time (UTC) as our time standard, and this is why we call this one the Boxing Day Event.
Currently we are in the middle of commissioning and upgrading our machines, but we plan to get back to collecting data and observing later in 2016.
About the Author:
Corey Gray (Siksika Nation) is the lead operator at the LIGO Hanford Observatory. Corey was hired as an operator for LIGO in 1998 shortly after obtaining BS degrees in physics and applied mathematics from Humboldt State University.