Sorry to bother you all with another-of-its-kind (most probably unsatisfactory) analogy that I came up with myself (error detection sirens should be blaring now) to better understand "energy" in cosmological expansion, but I just can't rest until I find out how (in)accurate it is from you all. I mean seriously, no personal theory here, just an analogy to simplify certain concepts. Here it is: Think of what happens inside a balloon as you heat it. That's right, just like why we can't say what caused the balloon to start expanding in the balloon analogy ( a poor guy blowing his lungs out from 13.8 billion years for no apparent reason), I'll be leaving the cause of "heating" aside for the moment. The number of air molecules inside the balloon stays constant. Let's attribute this to the cosmological constant. As the balloon heats up, it increases in volume, and the particles move away from each other more and more. Let the volume of the balloon represent energy content, and the volume between the particles denote dark energy. When the balloon is relatively small in volume (I mean really small), the total volume mostly comprises of the volume of the particles themselves, but as the balloon grows in size, the interspaces between the particles become bigger contributers to the total volume, and their ownership rights to the balloon volume increase continually with time. What this incoherent analogy attempted to explain in a simpler way: -The invariance of the cosmological constant -The increase in energy content of the universe - The increase in dark energy content of the universe What this analogy does not wish to address (no, it just won't ): -Any link with the actual volume of the universe -Reference to any geometric center of the universe - The shape or boundary of the universe - What's outside the balloon - Whether the guy blowing the balloon will run out of gas I'm positively sure you'll be sighing with pity by the time you start reading this thinking how wrong I am, so if I didn't give your eyes an unsightly mess, I hope that I gave you a good laugh :) EDIT: This analogy is not a direct comparison of quantities. Temperature, pressure, etc and other quantities of the balloon on which no comparisons have been made (to the real world) are NOT being represented by their respective counterparts in the universe, so they have no significance here. Please don't extrapolate this analogy to explain things not mentioned here.