Physics and the Immortality of the Soul

[Cross-posted at Scientific American Blogs. Thanks to Bora Z. for the invitation.]

The topic of “Life after death” raises disreputable connotations of past-life regression and haunted houses, but there are a large number of people in the world who believe in some form of persistence of the individual soul after life ends. Clearly this is an important question, one of the most important ones we can possibly think of in terms of relevance to human life. If science has something to say about, we should all be interested in hearing.

Adam Frank thinks that science has nothing to say about it. He advocates being “firmly agnostic” on the question. (His coblogger Alva Noë resolutely disagrees.) I have an enormous respect for Adam; he’s a smart guy and a careful thinker. When we disagree it’s with the kind of respectful dialogue that should be a model for disagreeing with non-crazy people. But here he couldn’t be more wrong.

Adam claims that “simply is no controlled, experimental[ly] verifiable information” regarding life after death. By these standards, there is no controlled, experimentally verifiable information regarding whether the Moon is made of green cheese. Sure, we can take spectra of light reflecting from the Moon, and even send astronauts up there and bring samples back for analysis. But that’s only scratching the surface, as it were. What if the Moon is almost all green cheese, but is covered with a layer of dust a few meters thick? Can you really say that you know this isn’t true? Until you have actually examined every single cubic centimeter of the Moon’s interior, you don’t really have experimentally verifiable information, do you? So maybe agnosticism on the green-cheese issue is warranted. (Come up with all the information we actually do have about the Moon; I promise you I can fit it into the green-cheese hypothesis.)

Obviously this is completely crazy. Our conviction that green cheese makes up a negligible fraction of the Moon’s interior comes not from direct observation, but from the gross incompatibility of that idea with other things we think we know. Given what we do understand about rocks and planets and dairy products and the Solar System, it’s absurd to imagine that the Moon is made of green cheese. We know better.

We also know better for life after death, although people are much more reluctant to admit it. Admittedly, “direct” evidence one way or the other is hard to come by — all we have are a few legends and sketchy claims from unreliable witnesses with near-death experiences, plus a bucketload of wishful thinking. But surely it’s okay to take account of indirect evidence — namely, compatibility of the idea that some form of our individual soul survives death with other things we know about how the world works.

Claims that some form of consciousness persists after our bodies die and decay into their constituent atoms face one huge, insuperable obstacle: the laws of physics underlying everyday life are completely understood, and there’s no way within those laws to allow for the information stored in our brains to persist after we die. If you claim that some form of soul persists beyond death, what particles is that soul made of? What forces are holding it together? How does it interact with ordinary matter?

Everything we know about quantum field theory (QFT) says that there aren’t any sensible answers to these questions. Of course, everything we know about quantum field theory could be wrong. Also, the Moon could be made of green cheese.

Among advocates for life after death, nobody even tries to sit down and do the hard work of explaining how the basic physics of atoms and electrons would have to be altered in order for this to be true. If we tried, the fundamental absurdity of the task would quickly become evident.

Even if you don’t believe that human beings are “simply” collections of atoms evolving and interacting according to rules laid down in the Standard Model of particle physics, most people would grudgingly admit that atoms are part of who we are. If it’s really nothing but atoms and the known forces, there is clearly no way for the soul to survive death. Believing in life after death, to put it mildly, requires physics beyond the Standard Model. Most importantly, we need some way for that “new physics” to interact with the atoms that we do have.

Very roughly speaking, when most people think about an immaterial soul that persists after death, they have in mind some sort of blob of spirit energy that takes up residence near our brain, and drives around our body like a soccer mom driving an SUV. The questions are these: what form does that spirit energy take, and how does it interact with our ordinary atoms? Not only is new physics required, but dramatically new physics. Within QFT, there can’t be a new collection of “spirit particles” and “spirit forces” that interact with our regular atoms, because we would have detected them in existing experiments. Ockham’s razor is not on your side here, since you have to posit a completely new realm of reality obeying very different rules than the ones we know.

But let’s say you do that. How is the spirit energy supposed to interact with us? Here is the equation that tells us how electrons behave in the everyday world:

i\gamma^\mu \partial_\mu \psi_e - m \psi_e = ie\gamma^\mu A_\mu  \psi_e - \gamma^\mu\omega_\mu \psi_e .

Dont’ worry about the details; it’s the fact that the equation exists that matters, not its particular form. It’s the Dirac equation — the two terms on the left are roughly the velocity of the electron and its inertia — coupled to electromagnetism and gravity, the two terms on the right.

As far as every experiment ever done is concerned, this equation is the correct description of how electrons behave at everyday energies. It’s not a complete description; we haven’t included the weak nuclear force, or couplings to hypothetical particles like the Higgs boson. But that’s okay, since those are only important at high energies and/or short distances, very far from the regime of relevance to the human brain.

If you believe in an immaterial soul that interacts with our bodies, you need to believe that this equation is not right, even at everyday energies. There needs to be a new term (at minimum) on the right, representing how the soul interacts with electrons. (If that term doesn’t exist, electrons will just go on their way as if there weren’t any soul at all, and then what’s the point?) So any respectable scientist who took this idea seriously would be asking — what form does that interaction take? Is it local in spacetime? Does the soul respect gauge invariance and Lorentz invariance? Does the soul have a Hamiltonian? Do the interactions preserve unitarity and conservation of information?

Nobody ever asks these questions out loud, possibly because of how silly they sound. Once you start asking them, the choice you are faced with becomes clear: either overthrow everything we think we have learned about modern physics, or distrust the stew of religious accounts/unreliable testimony/wishful thinking that makes people believe in the possibility of life after death. It’s not a difficult decision, as scientific theory-choice goes.

We don’t choose theories in a vacuum. We are allowed — indeed, required — to ask how claims about how the world works fit in with other things we know about how the world works. I’ve been talking here like a particle physicist, but there’s an analogous line of reasoning that would come from evolutionary biology. Presumably amino acids and proteins don’t have souls that persist after death. What about viruses or bacteria? Where upon the chain of evolution from our monocellular ancestors to today did organisms stop being described purely as atoms interacting through gravity and electromagnetism, and develop an immaterial immortal soul?

There’s no reason to be agnostic about ideas that are dramatically incompatible with everything we know about modern science. Once we get over any reluctance to face reality on this issue, we can get down to the much more interesting questions of how human beings and consciousness really work.

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198 Responses to Physics and the Immortality of the Soul

  1. BlakeG says:

    Given that few of those who believe in an afterlife are naturalists, this blog post is arguably an uninteresting waste of time (as others have suggested). I always think its a trajedy when I see a good scientist making this kind of move. In truth, “Science says xyz” simply means “[ASSUMING philosophical naturalism is true], our best evidence suggests xyz is true”. It’s consequently naive TO say to someone who ISN’T a philosophical naturalist “Science says xyz, therefore […] our best evidence suggests xyz is true”, without givin an argument for philosophical naturalism. It’s like a Christian saying “The Bible says xyz, therefore xyz is the case” without giving an argument for Biblical authority.

    In short: Of course if naturalism is true then there is no life after death. Why did you take a whole post to explain this? Why didn’t you tackle the interesting and philosophically controversial question: “Is naturalism true”?

  2. BlakeG says:


  3. Hubertus Bigend says:

    The last time I looked, no one had the foggiest notion of what consciousness is, yet it is discussed above as though its attributes are known. How can one say that the mind does or does not die along with the body when we don’t know what the mind is. The soul (should one exist) as the vehicle for life after death is even more obscure. At least we interact with each other using our minds (through the agency of the body). The soul is simply posited to exist (with no supporting evidence whatsoever); it takes no active part in our time alive, and it does not seem to influence the body or mind in any way – in short, it adds nothing! It is simply concocted as a raison d’être for religion.

  4. I’m continually amazed at the convolutions people will go through in order to hold on to the idea that they have “an immortal soul” – I didn’t expect those people to be any relevant proportion of your (responsive) readers, though. How depressing.

    Excellent article, Sean, and a lovely proof. We also have an excellent understanding of how thoughts, ideas, etc, are generated – *physically* within the brain. How they stop cold when we die.

    The term ‘supernatural’ implies it exists totally outside the natural, physical world, and there’s absolutely zero evidence for it – it’s just a rather silly “what if there is something we cannot see or know in ANY way?”. What’s the point of believing in something which, by definition, is outside our realm of experience? It’s utterly irrational.

    I suppose if we keep explaining this long enough, it will eventually sink in. Thanks for writing it.

  5. Lord says:

    Supernatural = Multiverse

  6. KWK says:

    BlakeG and LM,MI seem to have hit the nail on the head. Or to put it another way: we are all Bayesian creatures, and the conclusions stated here regarding the (non-)existence of the soul add approximately zero information beyond what can be easily determined from one’s choice of priors. So the much more interesting issue–to me, at least–would be a detailed evaluation of the process one might use to construct a naturalistic or supernaturalistic prior (aka “worldview”).

    The most obvious way *not* to pursue such an undertaking, though, is to make the fatuous claim, “Now that we’ve discovered X, supernaturalism is clearly bogus.” (where X = fire, or electrons, or evolution, or …). While any reasonable priors–including, yes, some supernaturalistic ones–are amenable to revision or even overthrow given new data, a lot of data are just plain orthogonal to the truth of falsity of such priors. The laws of physics fit rather neatly within a Christian worldview, for example, whereas “here’s the body of Jesus” would be rather more akin to finding fossil rabbits in the Precambrian in terms of its significant impact on any supernaturalist worldview.

  7. math says:

    Hey! Which of the terms is the interaction term with the information in my brain? Surely that is real, but I can’t determine which of the terms it is. Also, what is the particle responsible for transmitting math, surely it is gauge invariant. Hey does math propagate at the speed of light? I just want to know when the rest of the universe will discover the dirac equation since it has only been around for about 70-80 years. Surely the rest of the universe doesn’t know it yet?

  8. DaveH says:

    There are many people who waver on the fringes of reason wrt souls and life-after-death, for the simple reason that they haven’t thought it through. I think there is some value in reminding people that these concepts are not in accord with how we observe the world actually working.

    Sean is making the case that science has something to say about such claims. I don’t think much of a philosophical case need be made for naturalism. The epistemological justification of naturalism IS its empirical efficacy (and the lack of a coherent rival).

  9. They call me 'Mad' says:

    “there’s no way within those laws to allow for the information stored in our brains to persist after we die”

    I think they’re called books.

    If souls are no more than information and memories, personalities and preferences, then the children we once were are already dead. Who remembers their own birth? Whatever happened to that happy three year old, excited to explore this shining world? Was there life… after?

    Teachers and mothers, friends and lovers, the memories we share, that we pass on. I sit by the fire and read Newton’s own words, as if he were speaking within my mind. His thoughts, mine. Is it he? A fragment? A fading echo? What puts the fire in the equations? Whence comes this light of perception, illuminating the walls of our inner cave? Computation and calculation in endless dark; fearful numbers and data churning, circulating, repeating… meaning. Memes swim through the darkness, and flash as they leap from one black pool to another, up the glittering waterfalls. Alliances form and shift, cooperate, congregate and disperse, inherited, passed down as treasured heirlooms, in rooms that collapse and decay as the occupants move forever on. Room to room to room, an ever-lasting, ever-changing party.

    I forget yesterday. Nothing much happened, I’m sure. I got up, had breakfast, read the paper… and died. What I was that day as evanescent as the morning mist. I shall not mourn myself. I did not have much of a life, and left nothing to show for it. Time passing, and passing time, the humdrum ticking of the clock. Another day, another death, hidden where nobody noticed.

    But what if I had taken some other path, into the what might have been? Possibilities stacked like the pages of a book, the many worlds, the many me’s, striding abreast ‘tween parallel mirrors, sitting companionably together by the glowing fires, an infinity of us spreading out like ripples across the multiverse? Do my shadows know what I think? Do they yet live? Am I the last to die? Is each one too thinking that they are… all alone?

  10. The moon is green cheese idea is silly. We had determined the moon was not made of any kind of cheese long before the first robotic missions landed there.

    Calculations of the moon’s mass and gravity proved it was a rocky object with no hollow core or material other than rock and maybe metallic elements.

    So yes, we can prove that the moon is not made of green cheese. That argument is not valid and it’s embarrassing that an otherwise intelligent individual would even suggest it. His credibility was not done any favors by that.

  11. SMOTH says:

    Thanks for mentioning that amino acids, viruses and bacteria are not often thought of as having souls! I’ve always used examples such as this to back up my assertions when on this subject. Do ants go to heaven? Dogs? monkeys? rocks? People with brain damage? My way of thinking doesn’t require any math or science, only common sense. Does anyone reading this remember the 1800’s? of course not! That’s because you didn’t exist yet. After we die is absolutely no different. How could it be any other way? There is absolutely nothing but hearsay to indicate anything else. I believe that we should spend out lives being good and being useful, not worrying about death or any sort of fiction that happens after we die. After all, immortality would be so boring! You’re only here for a brief flash, make it count.

  12. bad Jim says:

    I suspect that the overwhelming majority of those who believe in a soul also believe in a non-physical mind and vice versa. Such beliefs are based on emotion and tradition and not upon physical evidence.

    Those who hold out for some sort of yet-to-be discovered phenomenon are ignoring the fact that brain activity involves large numbers of molecular interactions and energies that are orders of magnitude larger than quantum events. Any sort of spirit or non-physical mind
    would need to expend measurable amounts of energy to affect the functioning of the brain, and there’s no way for it to do so, nor evidence that it does.

  13. R says:


  14. Baby Bones says:

    Although I’m not a proponent of life after death, there are a couple of non-religious ideas that point to the possibility of a non-mechanical explanation for consciousness and existence. I think we live in a world where new behaviors emerge that bear no relation to the underlying phenomena. For instance, a typical place in the universe is a vacuum near absolute zero, whereas Earth is very non-typical by comparison. It would be very difficult to predict the existence of Earth were the only samples of universal stuff available for analysis the typical stuff. Similarly, I doubt if anyone able to ignore their own liveness would be able to suppose that life could emerge from non-living matter that shows such a strong tendency towards thermal equilibrium.

    To make a distinction between the rise of human intelligence and all life that came before it is false but I think it is fair to say that our awareness operates on a completely different “level” than say a bacterium, so the hypothesis that I would entertain is that there is actually such a level and it cannot bear a relation to the parts that make it up.

    I’m not saying that all aspects of intelligence lie at this level but one or more do. Call that level a soul, or a will, or self-awareness. I’m not supposing that it is immortal but I’m not requiring that it plays by any rules of the physical universe either.

    And there is no need to stop at the level of intelligence. If we could imagine an intelligent anthill that gained an interest in human behavior and decided to emulate it, we would have a problem in locating its intelligence. Our intelligence is apparently inside our body and mostly inside our brain, but an intelligent anthill would not make that conclusion. Furthermore, the anthill intelligence would see a city as its peer, for its intelligence in the “air” just like its intelligence is, and it would attempt to communicate with a city-being made up of many human-ant agents.

  15. paul kramarchyk says:

    Sean, science please. Talk about science. Not medieval superstition. When someone of your stature talks about souls and god it brings the end of time crackpots out of hiding . And it scares me how many there are. Stop scaring me.
    Thank you.

  16. Well written.

    I have had similar thoughts in the past, but without the physics background I found that I was never able to articulate it properly. It seems to me that many of the detractors in the comments are actually saying that intelligence is a non-measurable concept outside of known physics. Why? biochemistry and physics explain everything quite nicely and completely.

  17. The discussion demonstrates convincingly that quantum theory of consciousness is desperately needed to get rid of these Moon as green cheese arguments.

    First of all, we still do not understand the relationship of the essentially geometric time of physicists to the experienced time. As western pragmatists we just identify these times although even child realizes that they are totally different things (reversibility contra irreversibility for instance if someone in the audience has not realized it yet). The lack of this understanding has fatal consequences for quantum measurement theory so that the only thing we are able to is the primitive reaction “Shut up and calculate!”. We cannot even imagine answering “What after biological death?” or what happens to consciousness after biological death before we have clarified the relationship between these two times.

    Secondly, we do not even know whether consciousness is a property of physical system or represents totally different level of existence.

    Thirdly, most of matter and energy is dark and it is now becoming clear that the standard beliefs about what dark matter as extremely weakly interacting particles are simply wrong. The most recent experiments suggests that dark matter candidates are electromagnetically charged (PAMELA and Fermi, DAMA contra Xenon100). We are completely confused: how on earth matter can be invisible and electromagnetically charged at the same time? What goes wrong in our basic assumptions?

    What if this dark matter plays a key role in living systems: what if it is controller of ordinary matter in living systems? What about dark part of the biological body: what happens to it in biological death? And so on….

    We find the primitive beliefs of people of earlier centuries entertaining at best. Perhaps we should avoid demonstrating publicly this moon as green cheese attitude if we want to avoid the same fate: internet is merciless, all will be stored and read by future generations;-).

  18. Darth Dog says:

    Great post. Very clearly explained. Seems straightforward to me.

    But wow. Reading through the comments is something else. Actually makes me wish that some of them had disappeared Saturday in The Rapture.

  19. Andrew S says:

    There is no evidence for life after death, supernatural phenomena, free will, unnecessarily complicated physical theories, or any number of other fantastical things. The reason why many people believe such things anyway is because if they didn’t, then they would probably conclude that existence is the ultimate trap in which they have no power, no control, and no purpose. Thus, natural selection will favor those that believe in these things (even if these beliefs are false) to the extent that such beliefs allow or encourage them to reproduce rather than kill themselves in despair.

    Seen this way, it is not surprising that the majority of people believe in things that we have no evidence for. It’s all evolution’s doing. It is, however, an ironic quirk of fate that natural selection should seek to prevent the majority of the population from knowing or accepting what is (based on the evidence we have) the truth. Promoting false beliefs is evolution’s ultimate defense mechanism.

  20. bad Jim says:

    No more invocations of dark matter, please. As far as we know it has mass but doesn’t otherwise interact with other sorts of matter. In particular, it doesn’t couple to electromagnetic fields, which mediate most of the processes of life forms. At our scale, for all practical purposes, it may as well be purely supernatural. The coriolis effect doesn’t make the water in a tub circulate one way or the other because a tub isn’t that big. Any effect so tiny that we can’t detect it in theory cannot affect us in practice.

    We’re biological organisms. Our brains are made of living cells, whose conductors are membranes moving signals along ion gradients. Our wetware isn’t nearly as fine-featured or fast as the solid-state constructions we’re using to communicate, whose manufacturers have so far found it unnecessary to take dark matter into account.

  21. David Santo Pietro says:

    Give unto science that which belongs to science. Give unto religion that which belongs to religion.

  22. dinvlad says:

    Nice article, Sean! I couldn’t agree more. But the real problem of why all these questions about the existance of soul arise is because of lack of education on modern physics. Unfortunately, people just don’t see what we’re trying to tell them. They don’t think in terms of fundamental interactions, even though those basic science was told to them in high school.
    But I do think the situation will improve over time – not that more people would become physics graduates, but just the physical science (including life sciences) will reach so unthinkable before things (like dramatically extending our lifecycle, and whatnot), so that previous religion-based view would simply become laughed at, just like we now ridicule the ancient view that the Earth is flat.
    We should take our time..

  23. Steve Hall, MD says:

    Guess I’ll go to bed comforted by the fact that the physical laws underlying life are completely understood. Maybe my job will be easier tomorrow.

  24. raghavan Jaganathan says:

    From consciousness and ethics angle, I have seen people with defects in the body functioning normally. This incudes brain defects like stroke, parkinsonism etc .I am yet to see person with defect in the mind without any structural abnormality of the brain( schezophrenia, mania etc) functioning normally. I think consciousnes is more primitve than nucleic acid(DNA & RNA) . Life is an interaction of both. Consciousness without material is possible . But material without consciousness will merely be stone and mud. ( quarks and electrons)

  25. slw says:

    What is the particle for information? If two particles collide, can you tell by observing the collision results that one was part of a rerun of Cheers and the other was the latest Dr Who episode?
    There is an infinite number of ways to carry information in the world around us. Hell, even the exact same signal can be interpreted in an infinite number of ways. It can be very hard to detect there even is a signal at all if you don’t know what to look for, FHSS communications for example.
    No, I don’t think there is an afterlife in the classical religious sense, however the concept of preserving a consciousness after a physical body dies seems well doable. No new physics required, just transfer the information contained in the body to another medium.