How does one scientifically disprove something?

In the article titled Buddhism Without the Hocus-Pocus in the The Chronicle of Higher Education (January 13, 2012, page B4, unfortunately behind a subscription wall) by Owen Flanagan, a professor of philosophy at Duke University, that I wrote about yesterday, the author quotes the Dalai Lama as saying that if science disproves rebirth, then Buddhists should give it up.

On the surface, this looks like a refreshingly undogmatic attitude for a religious leader towards one of the central tenets of his religion. One cannot imagine the leaders of other religions saying such things. A pope who said that if the resurrection of Jesus was to be disproved then Christians should give it up would likely be promptly depoped or unpoped or whatever the word is. A prominent Muslim imam who even hinted that it might be possible that the Koran was not the divine and inerrant word of god directly handed down would likely suffer an even worse fate.

But while I applaud the Dalai Lama’s statement as a welcome affirmation of the primacy of scientific knowledge over religious dogma, I cannot help but suspect that he is being a little disingenuous here and not being as committed to empiricism as it might first seem. The key is the word ‘disprove’. How does one scientifically ‘disprove’ something?

One can disprove something if one can exhaustively investigate all the possible options that it can have and show that they do not exist. For example, I can prove that unicorns do not exist in my office by looking everywhere in it, under desks, in file drawers, in closets, etc. and not finding it, and that should convince pretty much anyone that the existence of unicorns in my office has been disproved.

But it becomes harder to disprove the existence of unicorns anywhere on the Earth because it is impossible to examine all the possible places that unicorns could possibly be living in. This is why the legends of the Yeti or Bigfoot or the Loch Ness monster are so durable and seemingly impervious to disproof. And it gets even worse if we were to allow for habitable life on other planets in distant galaxies. Then disproving the existence of unicorns becomes impossible.

But even within my office, the existence of unicorns cannot be disproved if advocates are allowed to advance auxiliary hypotheses as needed. Unicornists could claim that unicorns are so tiny that they cannot be seen by the naked eye or that they appear only when it is totally dark or if there is no observer in the room and so on. No proposition, however preposterous, can be disproved if one allows the proponents to advance such ad-hoc stratagems.

But while it is a well-known feature of science that no theory can be definitively disproven, yet the historical landscape of science is strewn with the corpses of dead theories, such as phlogiston, ether, polywater, N-rays, and so on. How could that happen?

This is because in science, a theory must have some mechanism that drives it, be connected to existing accepted theories, and make predictions that are testable, even if such tests may be hard to carry out. That empirical foundation is non-negotiable. Then, as I said in my New Humanist article, a scientific theory is declared dead if none of its predictions are confirmed and if the theory becomes unnecessary as an explanatory device for any observed phenomena.

It becomes clear then that the question of ‘disproof’ of a theory only becomes meaningful when its proponents are willing to specify in advance what its mechanism consists of so that it makes firm predictions that can be tested, and if they agree that in the event that the prediction is contradicted then they must reject the theory and that they are not allowed to advance untestable ad-hoc hypotheses that have no purpose other than to salvage the theory.

Using that yardstick, the theory of tiny/unobservable unicorns in my room can be considered ‘disproved’ because it does not meet those minimal considerations.

So what about disproving rebirth? As far as science is concerned, rebirth has already been disproved because there have been no empirically sound verifications that it has occurred and it is an unnecessary explanatory concept. There is absolutely no phenomenon that requires rebirth for its explanation. Science has disproven rebirth as far as it possibly can.

The Dalai Lama seems like a smart person. I think that he knows all this but is merely playing on popular misunderstandings of the word ‘prove’ and ‘disprove’ to salvage belief in a central doctrine of Buddhism while appearing to be accepting of science. What I would like someone to ask him is what kinds of observations or experimental results he would consider a disproof of rebirth.


  1. says

    I quoted this at Pharyngula way back in 2008 [!] – seems relevant:

    In the Q&A subsequent to his 1985 Gifford lectures (now in The Varieties of Scientific Experience, Carl Sagan participated in the following exchange:

    “Questioner: …Talking about proofs for the existence of God, I’d like to put it in perspective that there’s no completely satisfactory proof that everyone in this room exists. I don’t know if you know of one. I think it comes down in the end to belief of one sort or another that people in this room exist, and putting the proofs about God’s existence in that context, we’re demanding a lot more in proving God’s existence than we are in proving our own existence.

    CS: But the burden…the burden of proof is on those who claim that God exists. Or do you think not?

    Questioner: I think you say that. I don’t think that, in fact.

    CS: You think the burden of proof is on those who say that God does not exist?

    Questioner: An equal burden of proof, I would say. I don’t see why it should be put to those who say He exists.

    CS: But would you say that, no matter what contention is made, that the burden of proving or disproving it falls equally on those who agree and those who disagree?

    Questioner: I would say that.

    CS: Have you thought of the political implications of this?

    Questioner: Well, it’s not a political issue, I don’t think.

    CS: No, but I thought it was a general proposition you were proposing.

    Questioner: If you take a physical proposition, would you say you know that in every case the burden of proof rests to prove one type of case or the other type of case?

    CS: The burden of proof always falls on those on those who make the contention.

    Questioner: Well, all right. Yes. But only in the sense that it’s disproving the other contention.

    CS: No, no. It can be in an area where no one has any other contentions.

    Questioner: Yes, well…

    CS: It is – and it seems to me quite proper. Because otherwise opinions would be launched very casually if those who proposed them did not have the burden of demonstrating their truth. Here is a set of thirty-one proposals that I make, and good-bye. I mean, you would be left with a chaotic circumstance.

    Questioner: Yes, all right. Yes, I see. I see your point. Yes.” (240-2)

  2. Henry Gale says

    I think the first issue is the definition of ‘rebirth.’ Various traditions of Buddhism define it differently. Some schools keep the ‘soul’ in the same realm while others have it going through various realms or even dimensions.

    Some argue there is one consciousness that evolves through many rebirths while others say there is no single consciousness but instead rebirth is like the flame from one candle being passed to another candle.

    That said, there may be proof of rebirth although personally I think the methods are suspect.

    When a high level Buddhist monk dies there is usually some organized effort to find the monk in his/her reincarnated form. Since the person was a monk and presumed to be ‘good’, the search looks for the monk in a human form – a baby.

    This search goes around with some various things some of which were owned by the deceased monk and some that were not. The candidate is given a test where the items are placed in front of them and the child is tested to see if they can identify those items they owned in the previous incarnation.

    If this procedure could be legitimized then perhaps you could identify a rebirth fairly easily.

    The current Dalai Lama is said to have identified several trinkets from his past incarnation:

    Thondup was presented with various relics, including toys, some of which had belonged to the 13th Dalai Lama and some of which had not. It was reported that he had correctly identified all the items owned by the previous Dalai Lama, exclaiming, “That’s mine! That’s mine!”

    Now if that had been done as a double blind experiment….

  3. Henry Gale says

    I guess I should add, I understand that you cannot disprove rebirth exists. But if by using a strict scientific regimen to examine candidates you never find a single reborn monk, then over time the evidence would start to weigh heavy.

    Especially if for hundreds of years reincarnated monks were found pretty easily, and then all of a sudden, you can’t find any.

  4. Cathy W says

    I think I first saw that quote in Carl Sagan’s “Demon Haunted World” – and the Dalai Lama followed it up with a comment that “I don’t think science will be able to disprove reincarnation”. So I think he knows he’s pretty safe there.

    I do appreciate that he’s at least willing to pay lip service to the idea that his religion should be reality-based, in contrast to the Southern Baptist higher-up who basically said that if reality contradicts the Bible, then reality is wrong.

  5. anatman says

    i think the claim that you can’t disprove a theory paints with too broad a brush. how about the bell inequality? it’s experimental confirmation disproved any local hidden variable quantum theory. other classic experiments disproved any theory that said that e.g. photons in a particular experimental configuration had individual identities, so you could not meaningfully talk about ‘photon a’ and ‘photon b’. turing disproved any theory that claimed to solve the halting problem. other examples easily come to mind.

  6. Mano Singham says

    The Bell inequality is a good example. The people who accept that the experiments disproved the possibility of a local hidden variable theory are those who accept quantum mechanics (with all its computational machinery) as the framework in which the phenomenon must be analyzed. But if you are willing to abandon quantum mechanics or some of its auxiliary assumptions, then one could create a ‘theory’ that would explain the results without abandoning locality. I occasionally get papers that claim to do just that.

    The point is that the scientific community as a whole tends to agree on the framework in which the experiments should be analyzed and interpreted. That is what enables it to judge when theories are disproven. Step outside that framework and all bets are off. The continuing debate about whether ‘cold fusion’ is valid or has been disproven is an example of how the framework influences the conclusion.

  7. says

    I thought that the real beauty of Bell’s theorem is that is assumes nothing about quantum mechanics. If there is locality, the probabilities of certain outcomes must follow his inequality. The probabilities do not follow that inequality, hence locality is disproven. The simplicity and elegance of the theorem, and its lack of assumptions, always impressed me.

  8. Mano Singham says

    ‘Quantum mechanics’ is not a single thing. It consists of a set of postulates and that relate observable quantities to their mathematical representations. So there are statements about what constitutes a state, an operator, an observable, a measurement, how states are superposed, etc. The entire package is what we call quantum mechanics and is what is used in analyzing experimental data. But there is no logical reason why one is compelled to accept the entire package, except the fact that it is so successful and we don’t know anything else as good, so far at least.

    People can relax any one or more of those elements and replace them with something else to explain away a result they do not like. Scientists will ignore them them because they have effectively left science (let alone quantum mechanics), unless the new theory predicts unexpected things that are verified, in which case they might start looking at it more closely.

  9. says

    But you haven’t addressed my point. Bell’s theorem does not use any of that QM package. It is a simple inequality about probabilities of certain observable events. It can be proven without any knowledge of QM. It really does disprove locality.

    I understand there are some other very subtle general hidden assumptions used in the proof of Bell’s theorem, but none of these are related to QM.

  10. Mano Singham says

    What Bell’s inequality showed was that if locality was added to standard QM, the inequality went in one direction. When the experimental results disagreed, it mean that locality could not be a part of QM, although people still look for loopholes. The proofs of Bell’s theorem use standard results of QM, such as that measurements of an electron’s spin result in either up or down irrespective of the axis along which it is measured, and so forth.

    The implications of Bell’s theorem is that experimental results seem to indicate that (locality plus standard QM) is ruled out.

    Incidentally, some are still not convinced that the experimental results are airtight because they are statistical in nature.

  11. says

    Mano, I am continuing our discussion above about Bell’s Theorem.

    You said “The implications of Bell’s theorem is that experimental results seem to indicate that (locality plus standard QM) is ruled out.” This is not quite right. No experiment is needed to show that locality and QM are inconsistent. Bell’s theorem shows that locality and QM are inconsistent. The role of experiments was merely to confirm that the QM predictions were indeed true. Since Bell had shown that locality is incompatible with QM, this disproved locality.

    Bell’s inequality (which must be valid if locality is true) does not depend at all on any part of the QM package. It can be proven by someone who knows nothing about QM. Bernard D’Espagnat sketched the proof from this very general viewpoint in a nice Scientific American article in 1979.

    Wikipedia’s article on Bell’s theorem is well-done. Check it out. For a physicist like yourself, I’d recommend D’Espagnat’s book on the foundations of QM to help clarify thoughts on this subject.

    I’ll close with a quote from the Wikipedia article: “What is powerful about Bell’s theorem is that it doesn’t refer to any particular physical theory. What makes Bell’s theorem unique and powerful is that it shows that nature violates the most general assumptions behind classical pictures, not just details of some particular models.”


  12. Mano Singham says


    You say, “Since Bell had shown that locality is incompatible with QM, this disproved locality.”

    But incompatibility only means that you have to choose between one or the other. There is no logical reason why you are compelled to abandon locality. You could argue that QM should be abandoned instead.

  13. says

    Bell actually showed much more than just the incompatability of QM and locality. He showed that locality was incompatible with certain observable measurement correlations. These correlations were then observed by the experimental tests, proving that reality is nonlocal. QM has nothing to do with it. QM only provides a shortcut for predicting the observations.

    I think you are still misunderstanding the nature of Bell’s theorem. You said that when Bell’s inequality was shown to be violated, “There is no logical reason why you are compelled to abandon locality. You could argue that QM should be abandoned instead.” No, this is completely wrong. As I said earlier, the derivation of Bell’s inequality has nothing to do with QM. Please read the Wikipedia article or D’Espagnat’s book, or any other treatment of the theorem. Giving up QM does nothing to save locality. Bell’s inequality follows directly from the concept of locality. Its observed violation proves that reality itself is nonlocal. This conclusion would follow even if QM were shown to be false. ANY correct future theory of physics must be nonlocal (unless there are some subtle additional hidden assumptions involved in the proof of Bell’s inequality).

    Bell’s inequality, which follows from locality, is one of the most profound results in all of science. Yet it can be proven by a high school student (no QM needed). Its observed violation means that one of our most deeply held scientific principles is disproven. Amazingly beautiful result!

  14. Robert B. says

    “Reality is nonlocal” is far, far too general a statement. It’s not as though space and distance vanished from physics after Bell published. It would instead be correct to say, “There exist nonlocal phenomena.” And since the only nonlocal phenomena observed so far have been quantum-mechanical in nature, it is very odd to say that “QM has nothing to do with it.” QM is exactly the setting in which non-locality has been observed.

    In any case, a Many Worlds interpretation of the relevant experiments makes clear that the non-locality is… I wouldn’t say an “illusion,” exactly, but an artifact of a particular frame of reference. (It’s like a centrifugal force term in a rotating-frame Hamiltonian.) A more useful way to look at it: measuring one half of the entangled pair moves the measurer – meaning anything that can be changed by the measurement result, including both the instrument and the scientist – into a part of the universal wave function that changes which outcomes on the other beam that measurer can possibly learn about. According to Many Worlds, every electron everywhere always has both up spin and down spin. All a measurement does is change what measurements are locally possible – these locally-possible measurement sets are the “worlds” of the theory’s name.

  15. P Smith says

    “Rebirth” is as inane as (and similar to) the bunk of “water memory”. And I wouldn’t put it past “rebirthers” and “reincarnationists” to put the two together. What I say below isn’t said to lend credence to such garbage, I say it because that’s probably how they’d present it.

    The thing that makes something alive is nothing more than chemical reactions, and after things die, those reactions cease and the elements in the body are disseminated in the Earth. New life occurs when existing life consumes matter and reproduces. It wouldn’t surprise me to hear the looneytunes claim that the matter we consume and use to reproduce somehow “contains memory of past lives”.

    If they did, I’d have one question for them: For you to have “memory of past lives”, wouldn’t that require cannibalism for you to have consumed the material of other human beings?


  16. says

    Robert, when I said that QM had nothing to do with it, the “it” was the derivation of Bell’s inequality (more specifically, the later derivations by D’Espagnat and others). The derivation of Bell’s inequality do not assume the validity of QM. The derivation assumes local realism and some other subtle things. Bell’s inequality follows from these assumptions. Since this inequality is violated in our world, we have disproven the assumption of [local realism + other more subtle assumptions that are still being elucidated by physicists]. We have NOT disproven [local realism + QM] as Mano wrote. The derivation of Bell’s inequality does not hinge on the validity of QM. This was my point.

    I agree with you, though, that the many-worlds interpretation of the universe changes the meaning of this kind of nonlocality and makes it into a sort of illusion.

  17. Mano Singham says


    Sorry for the delay in responding but my copy of Bell’s paper (On the Einstein-Podolsky-Rosen paradox, J. S. Bell, Physics, vol. 1, 195, 1964) was in my office.

    Bell himself states in his paper that what he is showing is that standard quantum mechanics is incompatible with locality.

    The paradox of Einstein, Podolsky and Rosen was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality. In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics. It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty

    In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote. Moreover, the signal involved must propagate instantaneously, so that such a theory could not be Lorentz invariant.

    Of course, the situation is different if the quantum mechanical predictions are of limited validity. Conceivably they might apply only to experiments in which the settings of the instruments are made sufficiently in advance to allow them to reach some mutual rapport by exchange of signals with velocity less than or equal to that oflight. In that connection, experiments of the type proposed by Bohm and Aharonov, in which the settings are changed during the flight of the particles, are crucial. [My emphasis-MS]

    The phrase “without changing the statistical predictions” refers to the statistical predictions of QM. To argue that experiments are not necessary to rule out locality is to argue that we can arrive at an empirical truth about the world through logic alone.

  18. says

    Mano, thanks for continuing with this. I think it is important to get to the bottom of this, because Bell’s inequality leads to one of the most profound disproofs in all of science. From your response, I think we may be misunderstanding each other. I never argued that “experiments are not necessary to rule out locality” or that “we can arrive at an empirical truth about the world through logic alone.” I think you miss my central point.

    Do you have D’Espagnat, or could you take a look at the Wikipedia article? Bell was careful to say that his inequality would be violated if the statistical PREDICTIONS of QM were true. He did not need the theory itself. His derivation of the inequality (or at least the later derivations by D’Espagnat, who worked with Bell at one point in his career) did not depend on QM.

    One could have measured the observed correlations without any knowledge of QM, and one could have checked to see whether the correlations violated Bell’s inequality. (The values did need to be checked.) QM tells us the correlations would violate Bell’s inequality, but we didn’t need QM. We could have just checked the corrections directly. Even if QM had never been discovered and we only had pre-QM knowledge of photon polarization, we could have made these polarization measurements, and we would still have rejected Bell’s inequality. We would then conclude that local realism (plus a few other subtle assumptions still being debated) must be rejected.
    So my central point is: it was not (QM + local realism) that had to be rejected because of such experiments, as you wrote. It was just local realism that had to be rejected. That makes it a really brilliant and profound disproof of a fundamental concept.

    Now maybe you used “QM” as shorthand for “the correlation values predicted by QM”. That would be ok. But it would be misleading. Bell’s inequality is derived from locality, not (QM + locality), and we could have rejected it (and hence rejected locality) even if QM was unknown to us.

  19. Mano Singham says

    I was using QM as a shorthand for the correlation values predicted by QM because those are the things that Bell’s theorem deals with so we may not be that far apart.

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