Conservation of energy?

Since we invented the notion of 'energy', perhaps we defined it in such a way that it had to be conserved. Potential energy (for example the energy possessed by something by virtue of its height) is just an invention to keep energy constant.

When is now?

If we imagine time on a 'normal' scale like a ruler, it stretches from 'zero' (the Big Bang) to 'the present' - which is some sliding point on the scale. This is very much like the visual metaphor used in a sound-editing program.
Alternatively we can visualise the present as a zero-point - the past recedes away from us and the future stretches out before us to infinity.
Perhaps we are mislead by this scalar metaphor for time. If we plotted time on a log scale, we would not have to allocate zero to either the Big Bang or the present (since log-scales do not have a zero). 'The present moment' would then be a more flexible concept defined by how small an interval we chose to examine.
In any case, our own perception lags behind the 'actual' occurrence of an event. So when does an event actually occur? Is this a sensible question to ask?