> Well, I don't think I understand entropy - even after Wikipedia. Okay, here's a commonly used explanation. Entropy and time are bound together -- as time pas

> Well, I don't think I understand entropy - even after Wikipedia. Okay, here's a commonly used explanation. Entropy and time are bound together -- as time passes, overall entropy increases (with local violations like us). This is one idea about why time "moves" in the direction it does -- if time were to reverse, we could tell because some classic entropy results would run in reverse, violating common sense. Imagine that there's a room, and in one corner of the room there's a perfume bottle. At time zero, the cork is removed from the perfume bottle. Because of entropy, the tendency of isolated systems to move from order to disorder, the perfume disperses through the room. Ask yourself what the probability is for the perfume to spontaneously recombine in the bottle, versus the probability that it will disperse through the room. That probability differential is a measure of entropy. > So is there somewhere in universe some energy that is not available to do anything at all? Sure -- any isolated system can eventually get to a point where no useful work can be performed. Imagine an engine without any temperature differentials anywhere, or any way to acquire a temperature differential from an external source. Such an engine cannot do useful work. A steam engine requires a heat source and a heat sink. Without a temperature differential, the engine cannot function. Same with a gas engine. > Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ? But without tapping an external energy source, the energy in an isolated system won't concentrate itself or spontaneously create a temperature differential suitable for exploitation. In an isolated system, the level of disorder always increases over time. > If so how did it get to that state? Simple physics. For two masses having a temperature difference, one with temperature "a", the other "b", and a temperature conductivity of "k", they will eventually reach the same temperature this way: Δ = (b-a) e^(-t k) Δ (delta) = temperature difference at time t a = temperature a b = temperature b t = time k = energy transfer coefficient The above refers to an isolated system with an initial temperature difference. As time passes, that difference declines.