But can we define energy more than this..? No. we can define energy only by its effects. Then why we are defining all the effects to just one cause called energy..? Why can't it be multiple causes..? Because we see this transformation of one effect from another, we say all of these are attributed to one cause. This assumption or understanding of us (as one cause called energy) also works mathematically perfect.
One way to look at it is 'Energy' is the observer which we cannot fathom, which is just a witness to all the transformations happening. The effects of energy such as momentum are the 'observed', which keep getting transformed from one form into another. But then these two cannot be separated at all..
We can say we are a bundle of energy, when we view it from the perspective of energy. We can say we are the effect of energy when we view it from the perspective of the effect. That can become a-dvaitic or non-duality.
We can say finite is part of the infinite, when looking at it from infinite side. We can say finite can never become infinite when looking at it from finite side. That can become dvaitic or duality.
I see this infinite undefinable property of Energy.as Shiva or a puruSa, who remains just observer or sAksi. The momentum associated with energy or the effects of energy as shakti or prakrti, the observed evolute.
There are five puruSas say brhadharanyaka upanishad.
Watch Shiva thandava stotram in tamil here