For any object to exist, it must be distinguishable from its environment. This distinguishing mechanism is called a ‘boundary-mechanism‘. The full system* that this mechanism contains within it is called a ‘boundary‘.
* Any system contained within a boundary-mechanism will always consist of a bunch of sub-boundaries. Each sub-boundary, too, will be defined by its own distinguishing mechanism and sub-sub-boundaries (…ad infinitum). It’s recursion of distinguishing mechanisms all the way down.
The terminology around ‘boundaries’ is simply a tool/framework for further exploration.
Most investigations into ‘objects’ or ‘systems’ focus only on what happens internally within the object/system. But nothing exists in isolation, and most ‘objects’ interact with their environment (consisting of other ‘objects’).
By shining a light on the distinguishing mechanisms that separates objects from environments, we are better able to understand & explore the foundational elements of these interactions. This helps us gain unique insights into the way reality itself is structured.
Every ‘object’ or ‘system’ or ‘thing’ will have a separation-forming mechanism. But not all such mechanisms will be physical.
Many different types of boundaries (with unique mechanisms for separation) exist in our world. Some are based on ideas (e.g., religion and religious narratives), but a lot of them are based on density gradients (e.g., galaxy and the density of occurence of mass, where your table ends etc.).
The important thing is that there should be a mechanism that allows for separation. There are very few constraints on how that mechanism ought to look like.
You are partly right. Naming things such as “humans”, “cats” or “mountains” is an exercise in labelling. And labelling is mostly done by humans.
But this does not mean that boundaries don’t exist. Even without a label, some fundamental changes do occur in our reality. Consider a ‘table’ in your room – it has a certain uniform-ish molecular composition (made up lignin molecules); however, at some point in space, the density of lignin molecules will go towards zero. These will be the non-table parts of your room, including the air that surrounds the table.
Regardless of what you want to call a table or not, the fact that there was a change in the density of lignin molecules is undeniable. Independent of naming conventions and/or labelling.
You are partly right. Both statements are true: (1) boundaries exist and (2) yet, they have an ‘unreal’, illusionary quality to them.
The best way to think about it is comparing macro physics to quantum mechanics. The laptop (or phone or tablet) that you’re reading this answer on has both: a definite physical location and definite velocity that can be calculated. That is undeniable.
Yet, zoom in enough and it will be composed of quantum particles for whom those statements are not true. In fact, many of these quantum particles will be not even be localized in space – they are more akin to probability distribution fields of electromagnetic charges.
So our reality incorporates both – macro and quantum worlds. And while they may seem at odds at first, they work together to create the reality around us. And this is why most people would agree that we need to study both the quantum world and the macro world. One is not more ‘real’ than the other – both are complementary aspects of reality. If you find this thought interesting, you can explore the concept of hidden truths in Maya and the art of reality maintenance.
One can (presumably) make the exact same argument for the study of separation and oneness.
A formal study into ‘boundaries’ is still in its infancy. Therefore, there isn’t too much peer-reviewed evidence to support some of the hypotheses detailed in the book.
However, the book attempts to use peer-reviewed research from many disciplines (physics, sociology, biology, chemistry) to put forth a theory that optimizes for three things:
Having said that, there is no guarantee that any framework will accurately reproduce the truth. This is as true of a study of boundaries as it is of any science.
To better understand frameworks (or methods of making sense of the world) and investigate the concept at a meta-level, refer to the Book Chapter 5 (Emergence of frameworks).