What actually is a Wall of Force?
Well, the thing to note is that it is an evocation, not a conjuration. Very different.
A conjurer creates matter having certain properties by knotting the aether into a particular “shape”. A spray of something an acidic, a ball of burning stuff. It will exist for a period of time, usually, and then unravel.
Evocation is quite different, and goes back to Plato’s ideal forms.
What is the nature of fire? Well, the nature of fire is to burn. An evoker “evokes” – “manifests”, if you prefer – this inner nature of fire, without recourse to any gross matter on which the burniness subsists, and so creates a spherical region of sheer burniness – burniness in and of itself. (The concussion and sound are consequences of this, rather than being things in themselves.) Thus, a Fireball. Likewise, a Cone of Cold is a cone of sheer freeziness; and a Sound Burst a burst of loudness.
Now, what is the nature of solid matter, qua being solid matter? As the mage Pauli explains, the nature of solid matter is that it excludes other solid matter from the volume it occupies, and exerts force on other solid matter that tries to do so. Why can you not press your hand through a brick wall? Because the brick wall pushes back on your hand, in order to keep it out.
That is what a Wall of Force is – a volume in which is evoked sheer solidity, solidity in and of itself. Such walls need to be thin because they need to displace the air previously occupying the space. Even a Bigby’s Hand (showing my years – we no longer call the spell that, for legal reasons) is only a thin membrane in the approximate shape of a hand. Of course, these ideal forms can only be manifested briefly on Prime – often instantaneously – as Prime is not the place where these forms reside (they normally reside in the same place that fictional objects do). Maintaining an evocation for longer than an instant is always more advanced magic.
Assignment: 200 words. Summarise pp 453-460, “on the nature of fictional objects”.
Additional Credit: explain why a Disintegrate unfailingly dispels a Wall of Force.