The Problem with Quantum Mechanics and General Relativity:

The quantum realm is rife with enigmas -- inexplicable things that leave us puzzled. Unsurprisingly, since we have the (modest) ambition of obtaining a complete mathematical picture of the entire universe, it seems like there are many properties of particle physics that are completely removed from our existence on Earth. However, that previous sentence is a bit of a paradox, because the quantum world is utterly ingrained into our surroundings. For starters, it can be seen emanating from the sun, as photons of electromagnetism bounce off of everyday objects, before arriving near our retinas. It can also be seen in the form of waves slamming into the shorelines, with the molecules of water slowly eroding large rocks into tiny pebbles of sand. These tiny grains, in turn, accumulate by the trillions, eventually forming the beaches we all love.

In short, we know that the realm of the very small is intricately related to our everyday experiences, and that our level of existence is only a tiny piece of a much larger puzzle. To progress as a species, it is imperative that we have a comprehensive understanding of the world around us.

However, we have had a hard time uniting the physics of the very small with the physics of the very large – Quantum Mechanics and General Relativity. To learn all about this problem, see:
http://www.fromquarkstoquasars.com/the-problem-with-quantum-mechanics-and-general-relativity/

Image source:
CERN