Science has taught us that what we see and touch is not what is really there. - Hans Christian von Baeyer

We don't know what energy is, any more than we know what information is, but as a now robust scientific concept we can describe it in precise mathematical terms, and as a commodity we can measure, market, regulate and tax it.

If you don't understand something, break it apart; reduce it to its components. Since they are simpler than the whole,you have a much better chance of understanding them; and when you have succeeded in doing that, put the whole thing back together again.

Entropy is not about speeds or positions of particles, the way temperature and pressure and volume are, but about our lack of information.