If i am correct it is conventional thought to state that the universe as a whole is a closed system. The laws of thermodynamics, to me, clearly suggests that this is the case. But i wonder if the universe can be both closed and yet open or should I say infinite and yet finite simultaneously. The reasoning that occured to me and wished to share and explore could be best described using a simple mathematical model as follows: 1+10+1=12 1+[10000-9990]+1 = 12 The notion is that within a simple equation we can add infinite complexity yet retain the same outcome in this case being the value 12. so maybe it is worth asking what is the difference between 10+2 = 12 and 12 = 12. Possibly you will think this is more about philosophy and possibly you are essentially correct. However when working with "energy over time" equations the need to keep the universe a closed one yet allow for seemingly infinite values to be a part of a finite value appears to be very important. This extends to the example of a hydro electric station and how teh energy created by the flow of water generates energy. The questioned occured to me that the water has a potential energy and even though a hydro station capitalises on that potential the potential of the water remains constant regardless of how it's potential is used by the station. To clarify what I mean we can assume that the water is going to go to the sea regardless of whether it is diverted for a small time or not. The water retains it's potential regardless of the energy taken from it's decent to sea level. so in a stream of water we take a certain amount of energy from that flow but the flow retains it's potential. so the equation is like 100 + [10000-9900]= 100 meaning that energy has been generated with out any impact on the overall value of the original value. When thinking of a tidal generator using the out and inflow of sea water it is worth considering that the energy is happening whether we use it or not however energy can be achieved without diminishing the source of that energy as that energy is being expended regarless of whether we utilise it or not..... I do appologise if I have made a confusing mess of what I am attempting to describe here, and I look forward to any contributions that may help clarify the terminology needed.