How does the standard model reflect inertial energy ? The following puzzles me- I am reliably informed that the entire milky way is moving through space towards a nearby galaxy cluster at a heady speed of 1000 Klm per second. I assume this scenario is repeated all across the Universe with billions of galaxies all moving in relation to each other, much like atoms in a gas ? Now in order to produce this motion it must have taken a huge amount of energy ? I don't have the maths skills to work out how much energy it would take to accelerate something as heavy as the milky way to 1000 Klm a second, but I'm guessing it's a pretty huge number ? Point being, that if the laws of thermodynamics are universally true then the energy MUST still be there somewhere. Mustn't it ? It's not like it can 'go outside' the Universe ? So if this vast amount of energy is still there in the form of inertial or potential energy, and energy (on a Universal scale) is the same as mass.. where is it in the standard model ? If anybody can give a 'plain english' answer I'd be most grateful, because it's something that has puzzled me for a while. Thanks.