Heat by the way is something physicists can explain and is physical energy. Physical manifestation. You can of course spiritually manifest it too. But more importantly here for the sake of showing a difference let me use the word space.
Physical space is one thing, described and defined by physics and in the three dimentional physical world. They may even go on theoretically to describe other universes and spaces. C'est la vie. But then there is spiritual space. Very important to recognise the difference and how they both fit in Aikido and in what way. Technical. Real. Not physical, not mental.
The point though, is that there is a recognizable effect someone can point to and which reliably demonstrates a quality (heat) or thing (vibrating atoms). There is some kind of mutually accessible experience which offers a definition. If there isn't a shared experience, it's impossible to relate, isn 't it? This is the point to describing the physical experience/result; not in suggesting a seperation of the spiritual and physical, but in finding commonality with which to help verify something about the effect/affector.
Je ne sais pas; c'est la vie.
Here's to shared understanding and positive individual growth for the sake of all.
All my best,