When we observe that awareness and consciousness slowly emerge when babies’ brains are developing as they are growing up, it is obvious that there is a close connection between consciousness and the brain. The fact is, that although we don’t understand yet how consciousness is working in the brain, that we know awareness is a brain function, mediated by the chemical and electrical processes in the brain. This slowly developing awareness shows us that consciousness is not a phenomenon that is a function of a supernatural “spirit” in another presumed realm, but rather a part of growing up. We can get confirmation of that reality again if we observe Alzheimer’s patients who lose their awareness slowly when their brain deteriorates. Reality is observable, there is no awareness or consciousness after the brain is dead.
Some theists will argue that the content of your brain is energy and that since energy, according to the second law of thermodynamics cannot be destroyed and therefore this energy can emerge in another realm and one’s awareness will be resurrected there. They confuse energy with the data contained in that energy. Although energy cannot be destroyed, the data contained in that energy is. Just like the data in a computer can be destroyed without destroying the computer.
That the spirit develops in parallel with your brain in a non-material way is a distortion of what spirit originally meant. In many religions spirit is closely related to breath, indicating that there is a connection that might be a belief that goes back to the time before the human race spread out throughout the world. A baby receives its individual “spirit“ when it takes its first breath and one returns this spirit to the Great Spirit when dying (one’s last breath). Many religions refer to breath as a spirit. It is the life force, we cannot do without, or death follows in minutes if one is deprived of it. The bible is full of references about “spirit”, meaning the breath we need to keep living. The first one is in Genesis where God blows breath into Adam’s nose to make him come alive.
By observing that consciousness and awareness are brain functions and are totally dependent on a functioning brain, we can conclude that when the brain dies, awareness dies and therefore the existence of hell or heaven becomes a moot point because we cannot be aware of it. Anything else is unwarranted speculation because of the absence of any real evidence.