So a little lesson in the wonders of thermodynamics….Obviously you are hard-core, because your eyes have not glazed over and you are still reading.
To put it simply, it helps to mathematically explain why a system will change from ordered to disordered over time. The theory introduced the property known as entropy, which is used to explain the ‘amount’ of order.
The theory unfolded in the 1800s when scientists were trying to understand the maths around fluid dynamics – specifically to help engineers improve the efficiency of steam exchangers (such as old steam trains!) However, it has found application in physics and helps explain why ultimately everything (including the universe) will move from a state of order (low entropy) to disorder (high entropy).
My explanation is no where near as elegant as that of Professor Brian Cox. For a succinct explanation (using a sandcastle!) watch this 2 minute video, taken from one of my all time favourite top 3 documentaries ever – The Wonders of the Universe