Why the Concept of "Natural Afterlife" Is Nonsense (2)

If you ask a serious, decently informed person if s/he believes a perpetual motion machine is feasible, the person will likely respond: "Of course not! It's nonsense!" This shows the person may at least have had some basic exposure (maybe in high school physics) to the 2nd law of thermodynamics.  In a more advanced course, i.e. Calculus Physics taken in first year university, two statements express the 2nd law. They are:

(I) The Kelvin -Planck statement:

It is impossible to construct a heat engine, operating in a cycle, which produces no other effect than absorption of thermal energy from a hot reservoir and the performance of an equal amount of work.


II): The Clausius statement:

It is impossible to construct a cyclical machine that produces no other effect than to transfer heat continuously from one body to another at higher temperature.

These are often generalized in another form to read:

“The entropy (degree of disorder of a system) increases in all natural processes”


Thus, for example, gasoline once burnt in your car engine cannot be captured from the exhaust gases and used over again.. Also, any energy process will also have a large part of any energy produced coming off as unusable waste energy. There is no way, or any process that can deliver 100% usable energy.

In terms of biological -organic systems it means that death is the highest entropy state. This means that once one is dead he remains dead.  There are no "Lazarus-type" resurrections.  Once one's life is extinguished it remains so. In other words, if one adheres to the laws of the natural world there can be no personal afterlives, i.e. peculiar to the individual which are contingent on a lower entropic state (e.g. dream ideation or experience) that pre-existed the person's demise.

However, the supernaturalist doesn't adhere to physical- natural laws, so of course, he is at liberty to invent "afterlives" - even eternal, or "timeless ones".  No biggie. He can even invent "heaven" and "hell" plus "purgatory" - if he happens to be Catholic.

The point is, that unless one is a supernaturalist, he cannot invoke a timeless state contingent on a "dream state" condition that had to involve a particular energy regime associated with synapses in the brain. In other words, a "natural afterlife" which demands indefinite preservation of a synaptic state pre-brain death,  must be as much nonsense as perpetual motion machines.

Let's delve into this further.

According to Bryon Ehlmann,  a proponent of this "theory":

The natural afterlife is timeless. Again, it is the final moment of your NDE. It is like a paused movie scene and the feelings and memories you have at the exact point at which the movie was unknowingly paused. Since it is timeless, no further events happen within the dream. You, however, are never aware of this and that your dream was not just “paused,” but actually stopped since you too were “stopped.”


Now consider: He at once invokes the presumption this "natural afterlife" is timeless. But what must happen in terms of the 2nd law, i.e. to be "timeless"? The answer is that the entropy of the dream- sustained system - whatever it is-  must be zero. However, the natural afterlife proponents decline and indeed reject nonlocal consciousness (e.g. of the Stuart Hameroff or Bohmian type), which means they are hoist on their own petards.  This means they are left with explaining a "dream state" system they invented that has arrived from a higher entropy state to a lower one, something completely disallowed for closed systems. (Wherein the entropy must always increase, unless it can avail itself of external energy, i.e.  green plants in terms of sunlight).

Consider that in the instants preceding actual death, and possibly with an NDE in train, successive brain states evolve leading to one final state:

{s₁, s₂, s₃, s₄……………s_n}   ®  Ã

Entanglement and increased entropy of neuronal states is dictated by:

 

ENT (Ã) = -Tr à ln Ã

Where Tr denotes the trace  (of diagonal elements)  of the  corresponding density matrix.

This means, using our model from the previous blog post, that synaptic function must begin to slow, i.e. as neural transmission and efficiency begins to recede. The person is headed toward a maximum entropic state as are the specific portions of the brain which create the ideations, dreams, thoughts a person has.

The entropy then will be the total aggregate of accessible states:

ENT(Ã) = ln Ã

Conservation of probability requires:

¶P/ ¶t = ¶ / ¶t (Tr(Ã)) = 0

In other words, the process must be one for which any change in the defined state  Ã   tends to zero , given there can be NO further entropy change. However, the natural afterlife bunch are asserting there is a change from what would be maximum entropy (at death) to a defined zero entropy ("timeless") state, post death, i.e. in their NED (never ending dream scenario). Hence, they are postulating a major contradiction of the 2nd law of thermodynamics.

If one agrees that the synaptic cleft dimension (see last post) is scaled to allow application of the Heisenberg Uncertainty Principle (as Physicist Henry Stapp has shown, i.e. in his 'Mind, Matter and Quantum Mechanics') then it is feasible to obtain a rough estimate of the final energy state potential just before death. I.e. let us imagine the last workable synapse firing to generate an ideation. For this estimate we will allow a   2τ time indeterminacy or:

2 τ = 2 x (10^-34) s

Then using:

ΔE Δ t ³  h/2π

the calculated energy change (‘indeterminacy in energy’) is:

ΔE » (h/2π)/  Δ t

Or:

ΔE »  1.05 x 10^-34 J-s/ (2 x (10^-34) s) » 0.5 J

So one half joule is available - which means for the end state to be sustained this energy must also be sustained, e.g. in the alleged "timeless" state. This is roughly equal to the energy given off by a half-watt bulb (say in a small flashlight) for one second..

 

It is also useful to estimate how much information - as bits-  this amount of energy corresponds to. We already know that one bit has 0.693 kT of energy (in joules) where k is the Boltzmann constant and T is the ambient temperature. Then the number of bits would be:

N(bits) = (0.5 J) / (0.693kT)

 

Taking k = 1.38 x 10^-23 J/K and T = 300 K (about typical room temperature), one obtains:

N(bits) = (0.5J) /  [(0.693 x 1.38 x 10^-23 J/K) ( 300 K)]

N(bits) = 1.74 x 10²⁰

This would be the total number of bits in the final ideation (dream state)  that would need to be sustained in the timeless state. (The only assumption made is that any given 'frozen'  dream image contains information, it cannot be content or information free, or it doesn't exist - especially to the person allegedly experiencing it.) Thus persistence of the dream image/content  cannot be done without energy, any more than a paused TV image can be sustained without electrical energy. But where is it coming from? The natural afterlifers reject non-local consciousness as even remotely possible, indeed they dismiss consciousness entirely! This leads one to believe they are making the error first identified by Prof. Daniel N. Robinson (op. cit., p. 6):

 

"The claim 'I am conscious of the rabbit in the garden' is different from the claim 'I know there is a rabbit in the garden'.  There is a difference between being conscious of and being conscious. The former is always subject to error. Being conscious or aware is to be the possible subject of an experience, the self."

He also expands on the  notion of self-reference, and takes to task those who believe it to be merely an epiphenomenon of the brain, by way of the 'Mary' problem. 

A bit of digression here: Central to discriminating opposing Materialist models of mind are qualia. The term refers to subjective properties perceived in the material world, including colors, shapes and sounds (music). Arguably, none of these have objective existence but are tied to our neural processing and mode of consciousness. The qualia problem is often also called the Mary problem since it presents a hypothetical character (“Mary”) who inhabits a black and white world, but knows everything about colors in physics terms. Still, though she knows what color signifies – a particular wavelength in the electromagnetic spectrum – she has never experienced it.  The qualia problem helps to distinguish between what many call monistic physicalism and what I refer to as quantum physicalism. Monistic physicalism in its most rudimentary form can be summarized by Victor Stenger’s comment[1]:

 

It does not matter whether you are trying to measure a particle property or a wave property. You always measure particles. Here is the point that most people fail to understand: Quantum mechanics is just a statistical theory like statistical mechanics, fundamentally reducible to particle behavior

 

And the biggest contradiction to Stenger’s interpretation is[2]:
 

Although Y is a real field it does not show up immediately in the results of a ‘single measurement’, but only in the statistics of many such results. It is the de Broglie –Bohm variable X that shows up immediately each time.
 

In Stenger’s monistic physicalism, reality is structured around locality (predicated on particles), and quantum wave mechanics and its inherent potentiality never enters the field Y  to the extent of overturning particle dominance. In this way, emergence and holism are kept at bay. Conversely, J.S. Bell’s awareness of the hidden variable X enables quantum waves to supersede particles and in turn, demands the brain is treated as a quantum mechanical device.

 

 

On account of the latter position, physicist Henry Stapp has correctly noted[3]:
 

Brain processes involve chemical processes which must, in principle, be treated quantum mechanically. In particular, the transmission process occurring at a synaptic junction is apparently triggered by the capture of a small number of calcium ions at an appropriate release site. In a quantum mechanical treatment, the locations of these calcium ions must be treated quantum mechanically
 

 All of this means, again, that the only "natural afterlife" plausibly (albeit improbably) on offer or even remotely feasible based on physical laws, is the one described in the previous post to do with de Broglie waves.

 

Bryon Ehlmann writes:

 

  The natural afterlife is relative. Others know that you are dead and that your brain is no longer functioning and that your last dream—what would have been an NDE had you recovered—has ended, but you do not. For you, the NDE becomes an NED.

 

But this really says nothing, not anything a physicist can hang his hat on, i.e. in terms of energies available, entropy, neural thresholds etc. So whether the 'natural afterlife is relative" is roughly like whether one million angels can dance on the end of a pin, or one thousand.  Others "know you are dead" - ok, fine, but if they have sense they will have an EEG attached at the last instant to see if any mercurial action potential causes wave spikes that might indicate a final dream state. (Better yet, keep the EEG attached over time to see if any tiny wave forms re-appear  - after all a 0.5 J end state in stasis ought to be detectable electrically!)

 

Bottom line: a dream state or dream, final or not, must have energy to support it as I showed. It can't persist indefinitely in a metaphysical vacuum, following death,  no matter how many words (or clever analogies)  the natural afterlife crew churns out.  (See A.J. Ayers'  Language, Truth and Logic).  Those interested in seeing Ehlmann's detailed responses to an earlier blog post of mine on the after life can go to this link.

 

http://possibilities-and-phenomena.quora.com/The-Natural-Afterlife-vs-a-Quantum-based-de-Broglie-Wave-Afterlife

 

 

Then make your own decision!

--------------------------------------
Addendum:
 

 Ehlmann's comment in his link response,  that:

"The deBroglie wave afterlife is described using phrases such as “de Broglie waves,” “essential energy associated with the microtubules disperses out from the brain and becomes ‘entangled’ in a larger, undifferentiated whole,” “quantum coherence,” and “quantum wave states are stored in a multitude of microtubules” as well as by numerous mathematical equations. The complexity is enough to make one’s head spin!"


Is really irrelevant. He mixes up the use of precise language (which any serious person ought to strive to employ to avoid ambiguity), with constructs that others have invoked. Thus, the terms "de Broglie waves", "quantum coherence" and "entanglement" are all well known within the context (QM) in which they apply. Their use doesn't make for 'complexity' but rather exactitude in referencing and distinguishing elements of a hypothesis related to the underpinning physical theory - something Elhmann would do well to attend to more.

"Undifferentiated whole",  likewise, is merely another term (synonym) for quantum nonlocality - which again is basic to discussing anything to do with quantum mechanics. Since de Broglie waves encompass quantum mechanics, it is natural for this term to appear. That doesn't mean the basis is "complex", only that the person approaching it from a more generic (anecdotal) perspective hasn't adequately done his homework.

Where the complexity actually arises is in the use of "micro-tubules" (an added structure of the brain inside neurons) but which is really due to Hameroff and Penrose, not me. Technically, the de Broglie wave hypothesis requires no special additional structures since these decay anyway at the time of death - the only thing really left are wave forms, i.e. the  de Broglie  waves themselves.  NO unheard of violations of natural law are required here, unlike the violations of the entropy law by the NED team.

Ehlmann maintains he is a "skeptic" and he:  "will wait until (my)  theory of de Broglie waves is published in a peer-reviewed scientific journal".  Of course,  this is ridiculous. I make no claim to having a "theory" that is in any way significant enough to qualify to be published in a journal. I only offer the de Broglie wave hypothesis as a scientifically plausible, albeit improbable, explanation for a possible afterlife scenario.  I offered it as part of two blog posts-   because I maintain the 'natural afterlife' proposition of Ehlmann et al isn't plausible at all.

Let me also again clarify that my own POV is that death means the end of whatever had previously existed, including ALL formerly conscious states, ideations and any residual derivatives of them.  That means I implicitly accept the scientific world view of entropy as defining the "arrow of time" (at least in the classical realm) and that death means one has reached a maximum entropy condition. This maximum entropy automatically rules out any "timeless state" embodying any kind of ideation, or "dream" - since such state would have entropy zero.  Others can go along with the natural afterlife if it makes them feel better, but I believe they will only be fooling themselves.
 

---

[1] Stenger, God and the Folly of Faith, 155

[2] Bell,: Foundations of Physics, (12,) .989

[3] Stapp, H. op. cit., p. 152

 

 

Why the Concept of a "Natural Afterlife" is Nonsense (1)

It appears that unknown to many of us (atheists), a new "theory" of an afterlife has surfaced that proposes there can be a personal  "natural afterlife".  Leaving out for the moment the overtones of oxymoron, let's examine it in more detail.

The basic claim is that this phenomenon doesn't depend on the NDE or 'near death experience' and indeed, it is exactly when one lacks the NDE that the emergence into a natural afterlife can occur- since consciousness is left behind.  In other words, the extraordinary claim is made that a final "dream state" can transform into an eternal state of afterlife, independent of consciousness.

One of the primary advocates of the natural afterlife thesis, Bryon Ehlmann, claims:

Ironically, the plausibility of experiencing the natural afterlife after death depends not on the persistence of any consciousness but on its total demise. That is, it depends on not knowing that we have died, that NDE events have ended, and that time is marching on without us.

This is an astounding claim given the fact neuroscience shows that no dream state of any kind is possible without a consciousness- forming structure, i.e. brain. (See e.g. 'The Evolution of Consciousness' by Robert Ornstein). To assert a "perpetual dream state" can be incepted at what is terminal, physical death, meaning the brain must perish too, is therefore nonsense.

What makes dreams possible at all? We look here at the fundamental unit of neural dynamics:




We are looking at an electro-chemical signal (action potentials in (B) ) which are conveyed to the receptor neurons in the region of the temporal lobes. The waveform really represents changes in permeability, we note that when an axon is in its resting state it maintains a constant potential difference, or ‘resting membrane potential’ of –70 mV. When it is excited, it rises to a peak voltage of around 40 mV. This is sketched as the wave pulse peak in (B) with the ‘baseline’ value of (-70 mV) included for reference. One could say that (A) portrays the axon segment shown in a kind of equilibrium condition, or one conducive to a dream state. Only levels of partial consciousness are available in these states.  Generally, a full peak voltage of 40mV is associated with some level of consciousness.

Now, we go to the driver of consciousness localized at the site of the synaptic cleft or terminal.


In the diagram, we focus on Axon 1 and note that when the action potential arrives at the terminal it’s depolarized. This depolarization enables Calcium ions (Ca+2) already within the terminal to diffuse out into the mediating space. These ions follow a concentration gradient, unlike the case of the Na+ ions in the sodium pump. As the ions migrate, then diffuse to the post-synaptic cell (at Axon 2), they leave a channel in their wake that allows quantal releases of neurotransmitter (shown as a solid dot). These, like the Ca+2 ions diffuse across to the post-synaptic cell(s).

One neurotransmitter is acetylcholine. If the transmission of this or any similar chemical is rapid firing will occur, if not it won’t. Note also that Axon 2 must have a way of eliminating neurotransmitters almost as soon as they arrive. For acetylcholine, the enzyme cholinesterase acts to break it down into choline and acetate. In these inactive forms the neuron is spared being in a state of maximal and continuous excitation that would otherwise destroy it.

Generalizing the electrical cable analogy, the synapses act as switches in the system, the ‘on’ or ‘off’ positions denoted by information, in the form of chemical messages, to cross the synaptic cleft and trigger firing of the post-synaptic neuron(s) or not. Most probably there are bundles of similar neurons linked together by their respective connections, to perform critical functions. One might refer to the neuronal super-assembly or 'super-circuit’ within which considerations such as networks, and optimization of paths as well as 'adjacency and order' take precedence. Again, this is almost absurdly oversimplified since there really are no neurons that have only one connection to another. Indeed, we expect the typical neuron to have something like 10,000 connections to others.

What happens if this entire neural dynamic is terminated? We can begin to grasp the effects by first noting from the above diagrams that all waves of polarization and de-polarization cease. Hence, all synaptic activity ceases. There is no more firing of neurons, nor is there any movement of neurotransmitters across axons. BUT....these neurotransmitters are also responsible for dream states. They are also responsible for persistence of dream states!

Consider the electric cable analogy described above. What happens at death, or brain death? Well, the putative electrical signal cable is cut. What happens if an electrical cable to your home is cut? Well the service is terminated...there is no energy "leakage' or  residue that continues after cutting because this would violate the physical laws we know. The electrical energy cannot continue to propagate into your home devoid of the cable within which it's carried. In the same way, all the brain's potential energy terminates at death, there are no 'residuals' left to continue anywhere. Hence, there can be no natural afterlife.

Let me modify that, there can be a rudimentary natural afterlife if one subscribes to the notion of real de Broglie waves, as postulated by the Stochastic Interpretation of Quantum Mechanics. Real, physical de Broglie waves, by the way, were originally detected in the Davisson-Germer experiment. The experiment revealed wave patterns from which the de Broglie wavelength  could be computed. The experimental set up is shown below:


This  experiment consisted of firing an electron beam from an electron gun directed to a piece of nickel crystal at normal incidence. An accident occurred in which air entered the chamber, producing an oxide film on the nickel surface. To remove the oxide, Davisson and Germer heated the specimen in a high temperature oven, not knowing that this affected the formerly polycrystalline structure of the nickel to form large single crystal areas with crystal planes continuous over the width of the electron beam. To make a long story short, when the experiment re-commenced  the electrons were scattered by atoms which originated from crystal planes inside the nickel crystal, leaving patterns from which the de Broglie wavelength could be calculated according to:


This astounding result showed that matter can appear as waves, just as light can.

The point of all this is that de Broglie waves represent the wave mirror image of matter. When matter degenerates or corrodes, and according to conservation of mass-energy, de Broglie waves will survive. The issue is whether these waves can encompass consciousness and it isn't a stretch or excess speculation to believe they can. Look at the molecules of Ca++ crossing the synaptic cleft for example. If rudimentary consciousness is tied to the de Broglie wave of such ions,  then those associated waves ought to be able (theoretically) to survive physical death.

This is not "overly complex" as Bryon Ehlmann claims, nor is it unrealistic. We know de Broglie waves exist - they've been proven by experiment. We also know that they can be tied to consciousness, as David Bohm has shown in his assorted papers, e.g. . Bohm, D. and Hiley, B.J.: Foundations of Physics, Vol. 12, No. 10, p. 1001.

Thus, if the preceding template is accepted, then it is feasible that de Broglie waves could provide the basis for a rudimentary, impersonal, wave-based consciousness (nonlocal) that continues after death. This is indeed much simpler than supposing one magically falls into a perpetual dream based on the last image or neurotransmission one experienced before death.

To summarize: At death, these de Broglie waves are enfolded in such a way as to act like very finely scaled Electromagnetic waves. The waves also exhibit a similar form to propagating electro-magnetic waves, e.g.  with an electrical component E(x, t) = E ₀ exp [i(kx – wt]) (j) . However, the consciousness that results is nonlocal rather than individual or personal- because the expelled waves mix with all other released waves, from all other deceased individuals. (Nonlocal consciousness has also been invoked to explain phenomena such as telekinesis, such as disclosed in the experiments of R. Jahn at Princeton).

One more comment from Ehlmann is worth considering in this installment:

If while conscious, one can fall asleep while watching a movie and not realize it until waking up, chances seem excellent that while unconscious, one can die while in a dream and never realize it

But he mixes two different conditions, one for a living human and one that pertains to a dead one, i.e. in a so-called "dead man's dream" .  The use of the term "unconscious" is also problematical, as a number of authors- researchers (e.g. Daniel N. Robinson, Robert Ornstein, David Bohm, Henry Stapp et al) have argued that there is no genuine state of being un-conscious. What is described as such is merely a much lower  level of consciousness,  below the critical threshold of self-awareness.

 If I fall asleep while watching TV it basically signals a change in the polarization- depolarization wave thresholds (Fig.1), and a diminished self-awareness. In this state, or actually varied states, I may be aware of a clock ticking in the background but not aware of myself experiencing the clock ticking. . Also, as Prof. Daniel N. Robinson has noted (Consciousness and its Implications) it is just as feasible - given the physical dynamics - for "interior brain events to unfailingly arouse one from sleep to consciousness even without a sound." Again, this indicates variable thresholds of consciousness are operative, as opposed to an absolute absence of such.. The conscious state is then dictated  and defined by fluctuating levels of neurotransmitter activity.

However, because the converse is not true for a dead man, i.e. there is no rousing from that 'sleep' - then it is ridiculous to claim one "can die in a dream without realizing it".  The very attribute of "realization" implies self-awareness or a high level of CONSCIOUS thought, which the dead man is incapable of. Thus, asserting a man  dies in a dream "without realizing it" makes no sense at all. Of course he won't realize it because he lacks self-awareness, the highest conscious state!  Also,  once dead, being roused is not the same as being roused from a lower conscious state, i.e. while dozing in front of a TV.  The point is that no dream is possible once you're dead because an information content is needed. (See next blog post).

Obviously, information content can't persist because all  neurotransmitter flow has ceased (in true death, not as in the NDE, which isn't true death).  A maximal entropy condition is attained, also indicating no lower entropy (information) can ensue.  The synaptic cleft no longer functions, i.e. in allowing or enabling Ca++ passage, so there is nothing there. To claim that one can retain a dream image or final dream state - the last image embedded on death- is therefore preposterous. Where is it? There's no soul, no brain, so where? Floating in the ether?

There are no final dreams, (or dream)  a dead man can have. Nor is there anything he can take with him - no mental ideation or state- to a supposed eternity. (Okay, preserving a "timeless"  state)

It is either the de Broglie option, or none at all!  Take your pick! Again, the simplest hypothesis is that no afterlife exists, period. When you die it's curtains, nothingness. The next simplest hypothesis is the de Broglie nonlocal wave state enabling a rudimentary consciousness, though I'm not even sure such entity makes sense given our current language limitations.  The point is that the natural afterlife based on a fixed, never-ending dream makes no sense at all. It contravenes every physical law we know, yet its adherents propose that physical laws, limitations are inapplicable. This is the very definition of pseudo-science.

If the natural afterlife proponents want us to take them seriously they will have to do two things:

1) Indicate the basis for falsification of their hypothesis.

2) Propose an experiment to test the validity of their claim, or failing that - state clearly the necessary and sufficient conditions for a natural afterlife to occur.

More to come.

Near Death Experiences: All in the Brain?

The archetypical milieu was described first by Raymond A. Moody in his blockbuster book, 'Life After Life'.  Somehow you ended up semi-  "croaked", and you find yourself floating up and out of your physical body. Then, you glide toward a "tunnel" and lo and behold, a searing white light envelops your field of vision. It then proceeds to enfold you with its love, or if you've not been a very good boy or girl - say spreading hate - you're required to first give a review of your life.

Bullshit or believable? It probably depends on where you stand in the faith-religious belief spectrum. Believers then are more likely to consider NDEs (near death experiences) have some validity while Materialists- Physicalists- Atheists think it's all tricks of the brain - performed while the person is in a vulnerable brain state, open to hallucinatory phantasmagorias.

Now, a new study reveals that rather than a partial ascent into an afterlife, the NDEs may merely be a bunch of neurons running loco in your brain. Constrain the discharges, and you out the NDE as easy as pulling the plug.  According to the lead researcher, neurologist Jimo Borjigin:

"A lot of people believed that what they saw was heaven, but science has given a convincing alternative."

What did science find? Neuroscientists at the University of Michigan recorded electro-encephalograph signals in nine anesthetized rats after inducing cardiac arrest. Within the first 30 seconds after the hearts had stopped, all the mammals exhibited a surge in brain activity that had features associated with consciousness and visual activation. The recorded bursts of activity even exceeded levels associated with the normal, awake state.

In other words, the little beasties are having the rodent version of an NDE. According to the senior author, anesthesiologist George Mashour:

"On a fundamental level this makes us think of the dying brain"

As in humans, species Homo Sapiens.

The study was published online Monday in The Proceedings of the National Academy of Sciences. Of course, religious types and many others will object on the basis that such a study is too "ratomorphic". They will argue that it is dangerous to over extrapolate EEG records from rats to humans. After all, rats have a much more primitive cerebral cortex.

Even co-authors Borjigin and Mashour hesitate to make a direct connection between the rat "NDEs" and the human variety.  They note the links are merely speculative and "provide a framework for human study."

This is why the recent study is perhaps better taken in context with an earlier book by Dr. Kevin Nelson: The Spiritual Doorway in the Brain: A Neurologist's Search for the God Experience.
Nelson is one of the world's leading researchers in the biology of near-death and other related experiences, and his book takes the reader from investigations of MRI (magnetic imaging resonance) studies of the brain to historical anecdotes and philosophical inquiry. Three decades of research led Dr. Nelson to a unique and unexpected conclusion about near-death experiences -- rather than arising from parts of the brain that are unique to higher cognitive functions, they actually involve the oldest, most primitive parts of our brain, and might also relate to having dreams while still awake. (What we call "lucid dreaming")

Note here that if the "oldest most primitive parts of the brain" are involved, there may well be continuity between the rat experiences and the human ones, because of course it is precisely those "most primitive regions" we share the most with rodents.

Two of the NDE aspects that came under scrutiny in Nelson's book are: the tunnel which people traverse, and the white light.

Regarding the tunnel, in his words:

"The tunnel is easy to explain. Much of the near-death experience is caused by low blood flow to the brain and to the head. When this happens, the eye fails before the brain fails. The outside field of vision goes first, but the center is preserved until the very end, so you develop a tunnel-like sensation. This sensation is also common in people who are about to faint."

As for the white light which beckons:

"As for the light, when your eye loses blood flow, light might become all that you're capable of seeing. Another reason for the light is the REM system, which is the "rapid eye movement" state of sleep. When the eye and the retina shut down, the remaining control system for vision is the REM system -- this is why you can see things when you're dreaming, and this type of vision might be activated during a near-death experience and cause a person to see light"

In other words, there is a totally physical explanation for both effects. No supernaturalist hokum need be invoked.

Another key aspect of the NDE is the "OBE" or out of body experience, and Nelson makes clear one can experience OBEs outside of the NDEs. In one experiment, scientists actually induced fainting episodes in the test subjects, and many of them had an out-of-body experience while they fainted, which also commonly occurs during real near-death experiences. So in fact, many individuals know what it's like to have a near-death experience.

In regard to some people who don't see a white light but rather a kind of "hell" or experience very distraught emotions in a dark place, Nelson explains that not everybody sees light, not everybody has a sense of euphoria -- some people actually have an unpleasant emotional response during the near-death experience. What generally happens here is the pleasure system of the brain is engaged. This happens with spiritual experiences in general. When the Russian novelist Dostoevsky faced execution and lived to tell about it, he related a story of ecstasy and spiritual awakening. The dopamine reward system seems to be activated when a person believes they are near death, and the REM system, counterintuitively, is also activated. Experiments have shown that if you destroy parts of the brain that support REM sleep, you also take away the effectiveness of the dopamine reward system. Many pieces of the puzzle are missing, but we know there's a connection.

In respect of whether the NDE really shows a person coming back from the dead, Nelson is adamant:

"Returning from death is not something that people do. When a person drowns in ice water, the brain cells shut down and stop functioning, but they don't die. But when a person's heart stops, their brain cells burst after about five minutes. When the cells burst, they're dead and don't come back. If the cells are frozen instead, they don't burst, and when they warm up, they start functioning again."

In other words, when you're gone, you're gone.

What about any God connection?

Nelson is clear and succinct:

"You don't need to know how the brain is working in order to dismiss God, and knowing how the brain works doesn't prove or disprove a God. These are separate questions. Does evolution prove that God doesn't exist? I don't think so. Does it make it easier to explain consciousness in a Godless universe? Yes, but you can also conclude that there is no God without knowing anything about evolution or how the brain works"

For now, one only needs to process that NDEs are no evidence that one can return from the dead, or that one even gleans some objective experience about it. Even the Bible agrees that there is nothing after death, for example Job (6:18) teaches that there is no existence after death; men "go to nothing, and perish," and "he that goeth down to the grave shall come up no more." (7:9). Meanwhile, The Book of Ecclesiastes (3:19-20) says men are like beasts; "as one dieth, so dieth the other," that man "hath no pre-eminence above a beast"; "all go into one place; all are of the dust, and all turn to dust again."

Readers may also wish to consult this Scientific American article:

http://www.scientificamerican.com/article.cfm?id=why-near-death-experience-isnt-proof-heaven

The article on why so many seem to latch onto supernatural explanations:

"The reason people turn to supernatural explanations is that the mind abhors a vacuum of explanation. Because we do not yet have a fully natural explanation for mind and consciousness, people turn to supernatural explanations to fill the void. "

However, that doesn't make the supernatural plausible, and it is always preferable to find a physical explanation - even if only a tenuous hypothesis is available - than to jump onto the supernatural bandwagon.