The 2nd Law of Thermodynamics

The 2^nd Law of Thermodynamics says that entropy only increases in a closed system.  In very simple terms, nature tends towards equilibrium which results in going from order to disorder.  The disorder cannot be reversed unless you have both an outside force and a specific mechanism to restore that order.  If you are missing either one of these, the direction of heading toward disorder cannot be reversed.  Some believe this is where the arrow of time comes from. 

 

Here’s an example of the 2^nd Law of Thermodynamics in action.  Take a glass of water and put a drop of blue dye in it.  The blue dye is concentrated and starts in a more orderly state.  Once it hits the water, it begins to diffuse through the water until it is equally and uniformly dispersed throughout the glass.  The blue dye has gone from a more ordered state to a more disordered state.  The solution has reached equilibrium.  This is the natural tendency.  To get the blue dye back to a more orderly state, an outside force is needed (heat) and a mechanism to restore the order (distillation/evaporation). 

Another thing to note is that it’s the difference in state that allows the change to take place; the blue dye vs the clear water.  This difference in state that can cause change can be referred to as a driving force.  Once the equilibrium has been reached, the color cannot become darker or lighter without either adding more dye or more water.  A driving force must be applied to bring about a change.  Another example would be having water at 50 degrees and wanting to heat it.  In order to do this, you need to add a heat source of a higher temperature, such as putting a pot on a stove.  The heat transfers from the burner to the pot/water until equilibrium is reached, where the heat entering the system and leaving the system are the same and the temperature cannot increase anymore.

 

For our universe, the drop of blue dye represents the singularity of the Big Bang (crudely, since the singularity wasn’t a pellet of energy).  It was the minimum entropy or maximally ordered state.  The entropy value has been calculated. 

The expansion of our universe is like the diffusion of the dye in the water.  The difference is the water was contained in a glass, where our universe continues to expand. 

As this expansion continues, our universe will go more and more to an equilibrium state and the energy will equalize to the point of being ineffective.  There will not be a driving force to bring about a change in state and we will enter the Heat Death state.  The stars will burn out and all life will cease.

What does this mean? 

One of the implications is that the universe had a finite beginning.  If our universe did not have a finite beginning, we should have entered the Heat Death state an infinite time ago.  A beginning of the universe requires an outside cause to bring about the change in state.   

 

Maybe we are one of many universes spawned by the multi-verse which reset the entropy.  The 2^nd Law of Thermodynamics would apply to the multi-verse as well, so the multi-verse should have entered the Heat Death state an infinite time ago.  One of the ironies of the multi-verse (there are many) is that the same laws of physics that describe our universe had to pre-exist for the formation of our universe, but that’s a different post for another day.