The thing that they can't be sure of is, might the consciousness originate outside the body, and simply use a functioning body as a method for expressing itself.

Look at an electric motor, for example. When the motor is running, it is "awake - conscious." When the motor is not running, it is "asleep - unconscious." The electricity is the consciousness. The motor is the body.

Modern science mostly involves things that we can see or otherwise sense, and thereby measure. It involves, mostly 3 dimensional things, because we are 3 dimensional beings. Yet, we daily use and exist inside the fourth dimension, the dimension we call time. But measuring time in various ways is a little more difficult that measuring space (3D). Measuring time involves abstract measurements. What about dimensions greater then the fourth?

Mathematically, we are aware of at least 28 dimensions. We have only "mapped" the first 6 or so completely, mathematically. Another 8 or so have had a large amount of mathematical work done on them. Those remaining, beyond 14, have been mapped mathematically only in small part, because of how complex and abstract they are.

What if the subconscious mind and brain are built to automatically work in a hundred dimensions? What if consciousness is dimension 99? We simply do not know. Current science - even quantum math - is way too limited in the ways we use it to measure things like this. Thus, we may essentially be beings that exist "way out there somewhere," and simply use the body, brain and heart for expression, somewhat like an electric motor is used by electricity to express itself.