Today, an American team of scientists have announced the results from an ongoing experiment, LIGO (Laser Inferometer Gravitational Wave Observatory). This is a big, big deal, so you may or may not have read about this in the popular media. To fully appreciate the significance of the announcements, a few things need to be understood about gravity.
In my previous article on gravity, I explained that the universe can be imagined to be made of a fabric called ‘spacetime’. Objects with mass distort this fabric, which in turn causes objects with mass to attract one another (This is much better explained in my previous article). In this context, gravitational waves are ripples, or waves, in the spacetime fabric – equivalent to the waves we see on the surface of a pond when the water is disturbed. What I’m describing here is Einstein’s famous Theory of General Relativity.
The reason we know that this is a valid description of reality is because there is experimental proof for almost all of the astounding predictions this theory makes- Time dilation/length contraction, gravitational lensing, and gravitational redshifting of light – just to name a few. One of the reasons for all the hype about these gravitational waves is that they are the last prediction Albert Einstein made, using his famous General Relativity Theory, that is yet to be confirmed – until today.
The ability to detect and measure gravitational waves would bring about a novel way for cosmologists to probe the universe and potentially offer insight into questions about the Big Bang, and the shape of the universe. If we imagine the universe to be a body of water, then the big bang can be imagined to be a huge rock thrown into this pool, a very long time ago. In this analogy gravitational waves are the waves seen on the surface of that pool of water, after the rock has entered the water. By studying these waves we can gain information about the shape of the pool, as well as determine when the rock was thrown in the water.
However, gravitational waves are not only produced during the big bang, but indeed every time an object with mass accelerates through the fabric of spacetime (which happens all the time since moving in a circle is a type of acceleration).
Here, another analogy is valid: in the same way that an accelerating charge emits energy in the form of photons (light), so too does an accelerating object with mass emit gravitational waves. This implies that even the earth gives off gravitational waves as it orbits the sun, radiating away energy in the form of gravitational waves which causes the orbit to become smaller and smaller.
This is true, but there is no need to panic since the distance between the earth and the sun is so vast, and the rate of energy dissipation is so small that it would take longer than the lifetime of our universe to see this orbit decay. So we’re all good for now. However, the decay of orbits has already been observed in cases where neutron stars or black holes orbit one another, creating huge ripples in spacetime which are large enough to detect.
In summary; the detection of gravitational waves brings about a new era for astronomy and cosmology – one that does not rely on telescopes to detect photons of various energies, but one which uses gravitational waves to study phenomena. This will most likely lead to many new and groundbreaking insights, as we essentially have access to a whole new sense with which to experience the universe, with a different set of constraints. Gravitational waves are the final piece in the General Relativity puzzle, yet just one more piece in the near infinite puzzle for a better understanding of the universe.