By Benjamin Vermette
Gravitational waves were discovered! On September 14, 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) turned up the volume on their detector to hear the sounds of deep space.
It is a major breakthrough – it was even called a “revolution in physics”. Einstein predicted these waves in his general relativity theory a century ago.
To officialise the discovery, an announcement was made on February 11 through a press conference in Washington DC as well as a published paper in Physical Review Letters. It was followed worldwide by scientists and media.
“Ladies and gentlemen, we have detected gravitational waves,” said David Reitze, the executive director at the LIGO laboratory, at the press conference. “We did it!”
But what exactly are gravitational waves?
In 1915, brilliant physicist Albert Einstein published a paper on general relativity.
As I explained in one of my previous articles, the theory of general relativity describes gravity.
In a way, it’s not true that two objects attract each other; the objects bend the space around them, causing a change in their paths. What you need to understand is that empty space is something, like a fabric. Envision it like a bowling ball on a mattress, the bowling ball being a massive celestial object like the Sun or a black hole, and the mattress being the fabric of space (and time). Of course the bowling ball bends the mattress, causing any object, for instance a golf ball, to curve when it passes near the bowling ball.
Is there a special and mysterious force of attraction between the golf ball and the bowling ball? No!
The same happens when the moon orbits the Earth, or the Earth goes around the Sun, or the International Space Station revolves around us. They are like the golf ball going around the bowling ball: they follow their natural motion, or what is called in science their ‘geodesic’, because of the curved space-time.
So, empty space shares qualities with a fabric; it is able to bend, compress and dilate, giving birth to all kinds of physical events.
As David St-Jacques, Canadian astronaut puts it: “If things like massive black holes on the other edge of the Universe were to collide with each other, that would be such a dramatic and massive event that it would send ripples through space-time itself.”
As he explained, it was similar to people in North America asking: “Hm. Could we sense it if a cliff were to collapse on a European coast? Would the waves reach us?”
Waves obtained due to the energy liberated from the cliff collapse move through both water and air (the sound that is generated in the air by this energy occurs in the form of sound waves).
The same goes for when two black holes collide; the energy liberated from this event transforms into waves, which interact with the fabric of space, spreading beyond the point of the collision.
It’s just like the waves of a cliff collapse, but in the emptiness of space (kind of).
“[Albert Einstein] realized that if space is flexible enough to warp, then it should also be able to ripple, to vibrate, to undulate. “And it’s these ripples we call gravitational waves,” said physicist Brian Greene.
So how did LIGO discover those?
1.3 billion light-years away from Earth, two enormous black holes collided, and they caused observable gravitational waves.
The two black holes originally had masses of 29 and 36 solar masses (the mass of the Sun). “After they merged they created a single black hole with a mass of 62 times that of the Sun. You may notice those masses don’t add up right; there’s 3 solar masses missing. That mass didn’t just disappear! It was converted into energy: the energy of the gravitational waves themselves,” wrote Phil Plait, American astronomer, for Slate.
And that’s a lot of energy, enough to distort and bend your body when it passes through you. Only by a tiny, little-bitty amount, but still!
The video above demonstrates the effect (exaggerated) of gravitational waves passing through Earth.
The LIGO facilities were arranged in such a way that two long cylinders, each measuring precisely the same length, are perpendicular to each other.
In those long tubes two lasers are shining, being reflected at both ends and those being of the same length, it makes the lasers “come back” at exactly the same time, cancelling each other out.
The only way for the lasers to not come back at the same time, is if the tubes change in length. But how can you do that? Just ask… gravitational waves!
If a gravitational wave passes through Earth, and subsequently through a LIGO facility, the tubes will change in length by a fraction of an atom (!), one being longer and the other being shorter. This way, the lasers won’t come back at the same time, and won’t cancel each other out!
This video will teach you about this in more detail.
But what does it means, anyway?
In the end, this is what gravitational waves are to the human ear: faint little chirps. This linked soundcloud account features this subtle noise.
So, how do these faint little chirps influence us, and the future of physics?
The detection of gravitational waves opens up a whole new sphere of astronomy.
Gravitational waves have always been passing through Earth. In the past, physicists have been deaf concerning gravity waves, but now, being able to detect and measure them opens up a whole new way of seeing (or hearing, if you prefer) the universe.
But physicists, astronomers and scientists are not the only group to which the detection of gravitational waves is relevant.
Imagine a world where findings in physics had not been applied, so no more cell phones, computers, and GPSs would exist.
In such a world, physics wouldn’t be irrelevant. I think humankind would still try to develop physics, to understand the universe, and to feed our sense of wonder, because curiosity and imagination is part of us. This is what we have been exploiting since our ancestors started walking on two feet, exploring Africa.
We want to know, we ask questions, we try to understand the world we live in, not only physically, but socially and economically too. Wonder is built into us, just like curiosity.
This is exactly what physics provides to humans. They nourish wonder and satisfy curiosity. We know the universe has more complexity than we can currently comprehend, so what better way to dream, wonder and imagine than to understand it?
If theoretical physics such as cosmology seem irrelevant to you and you have no motivation for understanding your environment or learning something, just do it for the sake of it; the grave will provide plenty of time for not-knowing.
If this doesn’t satisfy you, just think that the dinosaurs didn’t have the right resources to predict and prevent their own extinction. But we do. Thanks to science.