We observe 3 dimensions on everyday basis: Height, Width and Depth. Time is considered to be the fourth dimension.
That’s not all. According to M-theory, there are 11 dimensions in space-time. We are not able to observe those extra dimensions, but those extra dimensions play an important role in unifying the theory of relativity and quantum mechanics.
Scientists believe that M-theory, or String theory, is the brightest chance for us to unify these theories.
Last years, the aLIGO detectors provided proof of gravitational waves. Why was it extremely difficult to detect such a basic thing as gravitational waves? It is because gravity is the weakest force of all.
Now scientists believe that could be due to extra dimensions. All other forces like electromagnetic, nuclear, etc are observed in the dimensions we know.
aLIGO is due to get an upgrade in form of additional machines, by late 2018 or early 2019. Then, it will be easier to detect the pattern of gravitational waves. It could even be possible to measure the wave activity absent from our known dimensions.
Gravitational waves have just started unraveling tip of the iceberg of the cosmic secrets. Hold your breath! You are living in exciting times!