Gravitational Waves
Our universe is complex and our knowledge of it is limited. It is very hard to keep track of various breakthroughs and connect the dots. Moreover, as we focus on narrow pursuits, we often tend to lose our path in fundamental sciences. We become five-year-olds in fundamental sciences. Reddit's "Explain like I am Five" is one of the first things I look for whenever the world comes across a major scientific breakthrough.
When the existence of gravitational waves was proven on Feb 11, 2016, the question on everyone's mind was "what are gravitational waves", "why is it a big deal?", "Should I even care?". Well, honestly, many of us and our children can live for 100s of years without caring, but generations beyond those, assuming humanity survives, will find Feb 11 2016, discovery to be useful. Such breakthroughs are not new, just a few hundred years ago, we did not believe that earth was spherical.
So, what are gravitational waves?
When you consider the space as matter, and when bodies like stars and sun move that matter, they produce waves on that surface. Using instruments it is confirmed that these waves exists and we actually "listened" to them for real!
To follow along in simple terms, this is the excerpt of the conversation on Reddit.
A user loljetfuel explained the concept like.
Since I actually tried to explain this to a pair of 5-year-olds today, I figure why not share :) You know how when you throw a rock in a pool, there are ripples? And how if we throw bigger rocks in, they make bigger ripples? Well, a long time ago, a really smart guy named Einstein said that stars and planets and stuff should make ripples in space, and he used some really cool math to explain why he thought that. Lots of people checked the math and agree that he was right. But we've never been able to see those ripples before. Now some people built a really sensitive measuring thing that uses lasers to see them, and they just proved that their device works by seeing ripples from a really big splash. So now we know how to see them and we can get better at it, which will help us learn more about space.
The scientist from LIGO, dwarfboy1717 further supported this answer stating:
LIGO scientist here! Great explanation! I'll add:
If Einstein is right (hint: HE IS), gravitational waves would travel outward from (for instance) two black holes circling each other just like the ripples in a pond. When they come to Earth and pass through the detectors, a signal can tell us not only that the gravitational wave has been found, but it can also tell us lots of information about the gravitational wave! As you track what the gravitational waves look like over a (very) short amount of time, you can tell what kind of event caused them, like if it was two black holes colliding or a violent supernova... along with other details, like what the mass of these stars/black holes would have been! This discovery has ushered in an awesome new era of astronomy. BEFORE we started detecting gravitational waves, looking out at the universe was like watching an orchestra without any sound! As our detectors start making regular observations of this stuff, it will be like turning on our ears to the symphony of the cosmos!
Big Deal!. It's wonderful we are able to share this news in a way that every one of us can understand and relate to!
Further Reading
Read the discussion on reddit here.
Watching
Watch the video Allan Adams, theoretical physicist from MIT, explaining the significance of gravitational waves.