In essence, it's proof of one of the key elements we understand about the Universe - and validation of one of the greatest predictions made by the most famous scientist in history, Albert Einstein.
The breakthrough: that what are called "gravitational waves" really do exist.
As one physicist put it: a new era of science has begun.
So what are gravitational waves?
Gravitational waves are ripples, comparable to sound, that travel through space at the speed of light.
We've always assumed they're there - but now we've finally been able to observe them.
Back in 1915, Einstein proposed that space-time, which makes up our universe, is a four-dimensional fabric that can be pushed or pulled as objects move through it.
Consider dropping a bowling ball on a trampoline and watching its contortions, or the waves that spread through the water as you run your hand through a still pool.
Having captured these waves, we can now see how the universe works in an entirely new way, just as we can observe the surface of a pond stirred by ripples.
Just what will we be able to "see" now?
Big, big things.
Think colliding black holes, merging neutron stars, or gargantuan collisions of galaxies.
Where ripples have been made, we can trace them back to the event that created them.
Because waves are neither scattered nor absorbed by the material they pass through - like the pond surface - they let us peer right into the heart of some of the most extreme environments in the Universe, like black holes and neutron star.
Humans can now conduct fundamental physics experiments under conditions that can never be copied in a lab on Earth.
As Australian physicist Professor Matthew Bailes summed it up: "The thought that we can witness black holes merging at close to the speed of light, and in less than a minute releasing thousands of times as much energy as the Sun does in its billion year lifetime, is the stuff of science fiction, and yet, reality."
So how did Albert Einstein figure out that these "waves" existed 100 years ago?
Because he was Albert Einstein, obviously.
Discovery validates Kiwi's decades-old work
The breakthrough will be all the more special for Kiwi scientist Professor Roy Kerr, who found the solution of Einstein's equations which describes rotating black holes.
Physicists have concluded that the detected gravitational waves were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole.
This collision of two black holes had been predicted by Professor Kerr but never observed.
Professor Kerr, Professor Emeritus of Canterbury University, had to struggle to be listened to by astronomers on announcing his result in a 10-minute conference talk in 1963.
Reacting to this morning's announcement, he said: "This observation is the product of one of the most outstanding collaborations of science and technology ever."
"It not only required unbelievable technological advances to be able to measure the incredibly small gravitational vibrations but also several decades of theoretical work needed to calculate the theoretical signals that have now been observed.
"From the frequency of the signal it is clear that this is not two neutron stars colliding but is a pair of fairly heavy black holes. Spinning black holes exist."
