What we talk about when we talk about gravitational waves.
By now you’ve all read the headline: gravitational waves detected at LIGO! Major breakthrough in physics! Einstein confirmed! Scientists just heard the faint sound of two black holes colliding and it’s important! Science science science waves gravity Stephen Hawking SCIENCE!
So let’s get down to business and cut right through the crap peddling and click baiting. Is this a big deal? Yes. Is anyone telling you why? No, because it’s hard to explain in one headline. Predictably, half the world is getting this as a takeaway: EINSTEIN PROVEN RIGHT! (has there really been any doubt since Dyson’s confirmation in 1919?). LIGO is not about Einstein. I spent 6 months of my life researching and investigating LIGO; I then had the privilege to see it in person when I traveled to Nowhere, Washington and spent a pretty chunk of Discovery Channel money to tell their story when no one gave a crap. From this experience I can tell you, with one singular word, exactly why the current LIGO results are bigger than the Higgs Boson and bigger than Einstein.
That word is LISA. LISA is going to change everything.
To understand LISA and LIGO, you need to think about the concept of a telescope from a scientist’s perspective. Suppose you want to study the planet Jupiter. There is nothing in our technological arsenal that is capable of safely sending a human observer to the Jovian sphere, so instead, we use telescopes to parse out the intimate details of this distant world. Our telescopes catch the dim light reflecting off Jupiter, and then magnify it to the point where we can literally watch the weather change. Neat! The laws of physics then clearly state that the bigger your telescope, the more distant stuff you can see. After Edwin Hubble built the world’s largest telescope (at the time) he discovered that the little blurry things were actually distant galaxies, billions of light years away in space and time. Scientists have since built Space born telescopes like COBE, WMAP and PLANCK that are so sensitive, they can see light coming from the very horizon of the Universe. In essence, they can look back in time to the very beginning of everything! Everyone thought that we were about to learn exactly how our Universe suddenly just came to be 13.8 billion years ago.
Except, the Universe decided to play hardball.
For the first 400,000 years of our Universe’s existence, light (“electromagnetic radiation”) was trapped inside matter. Because light (“electromagnetic radiation”) could not travel freely, there is thus a solid wall at the 400,000 years year mark that no telescope can ever see past. Think of it like this: whenever you look at a distant star, you are seeing that star as it was millions, perhaps billions, of years ago – this is so, because it has taken the light (“electromagnetic radiation”) from that star many years to reach you. Ok, so instead of looking at a distant star, now take a look at an empty patch of space in the night sky – your telescope is looking as far back in time as the Universe will allow. In this case, it detects light (“electromagnetic radiation”) that originated 400,000 years after the big bang. Without the ability to observe any light (“electromagnetic radiation”) older than 400,000 years after the big bang, we are literally in the dark as to what happened when our Universe was born.
But what if there was another form of radiation that we could observe?
There is! Electromagnetic radiation (“light”) not the only form of energetic radiation that can transmit information; as it turns out, objects with mass can also emit GRAVITATIONAL RADIATION. It works like this: if I move an object with electric charge back and forth, it will induce a electromagnetic wave that propagates outwards at the speed of light. If I move an object that has mass, it too will induce a gravitational wave that moves radially outward at the speed of light. But here’s the key difference between gravitational waves and light waves: human beings evolved to detect and process electromagnetic radiation (vision) with our eyeballs because electromagnetic waves are quite large and energetic! Unfortunately, gravitational radiation is so puny that if our Sun were to suddenly explode, we would barely feel the resulting gravitational wave. (Of course, we would also be flung off into the cold expanse of deep space fated to freeze to death, but that’s beside the point.)
LIGO was a simple proof-of-concept experiment to prove that gravitational waves could be directly detected with a large enough machine and a large enough gravitational even (say, the collision of two black holes many light years away.) LIGO is that machine – it works by firing two laser beams into mirrors to form an “L” shape, each leg being exactly 4 kilometers long. The lasers start at the bottom left and corner of the L, fire outwards, reflect, then converge back at the starting point. If sufficiently strong gravitational radiation happens to pass through Earth, it will stretch and squash the space-time we live in such that the lasers in the L shape will distort by a distance smaller than an atom, and the alarm bells will sound. Simple enough. And yet when LIGO was built, nobody knew if gravitational radiation really existed… even though Einstein predicted it and since 1919, nobody has ever really doubted that Eintstein was wrong. We had indirect evidence of gravitational radiation, but nothing concrete. And so, LIGO was proposed as a billion-dollar proof of obscure science concept – much to the chagrin of 90s era congressional republicans who saw the whole affair as wasteful government spending. Kip Thorn (The “Interstellar Dude”) championed the project, the NSF gave the finger to congress, and LIGO survived. LISA didn’t.
Over a billion dollars later, the pricey LIGO had only heard crickets… and the occasional truck that rumbled down the road a few miles away from the experiment. NASA abandons LISA and sells whatever could be salvaged to the Europeans.
And so, a woman enters this story who embodies the very definition human fortitude. Her name is Nergis Malvalvola and she was raised in Pakistan. Today, she is a professor at MIT and CalTech, a Macarthur Fellow, and one of the world’s most respected experimental physicists. She has dedicated her life to perfecting LIGO, and spent decade after decade refining every detail of this billion-dollar project. While she will undoubtedly scold me for this statement, I nevertheless feel obligated to mention that she is a gay woman who obliterated the thick glass ceiling of boys-club physics and deserves to be cherished as a hero to all outsiders who dream of contributing to endeavors greater than themselves. Back to the story: Nergis blazed a trail and led the charge to upgrade the experiment’s sensitivity. She, and her numerous colleagues, collaborated to invent a groundbreaking technique to increase the detector’s sensitivity from resolving the width of an atom, to resolving the width of a tiny, tiny, tiny, tiny, sub atomic particle. This major upgrade just paid off, because you all just read the headline. The damn thing finally worked!
Thanks to the brilliance of Nergis and her colleagues, LIGO has now directly observed gravitational waves. Specifically, the gravitational wave radiation from a distant black hole colliding with another black hole. If an electromagnetic radiation based telescope were to resolve this event, it would have to have a mirror larger than orbit of the Earth around the Sun! That is the sheer power of LIGO – humanity’s first gravitational wave telescope! With this successful proof of concept, the time has come to put in LIGO in space, and jack up it’s power to 11.
LISA stands for the Laser Interferometer Space Antenna. LISA is LIGO, but in space. She works off the same principles, but without having to worry about the curvature of the Earth, her lasers can fire much longer distances to form a gargantuan “L” shape. Remember how light is bounded until 400,000 years after the big bang? Gravity isn’t. In fact, nearly every reputable cosmological model we have predicts testable gravitational radiation artifacts in the earliest moments of the big bang. In other words, we now have the technology to literally look back in time to the very beginning of everything and watch our Universe birth itself. Think about that for a moment.
TL;DR –
LIGO just proved that LISA is worth the billions it will cost to put her into space.
When LISA goes up (or whatever she’s called by then), she will see farther back in time than any other telescope in the history of mankind. Which means…
…In our lifetimes, we will almost assuredly learn the exact physics of how the Universe (as we know it) came to be.
So yeah, LIGO’s a big deal.
Announcement of the Discovery of Gravity Waves
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