Suppose there is a physical theory that predicts that the observable physical laws differ when applied to the observer himself rather than to the other people, for any given observer.

Would existence of such theory invalidate the applicability of scientific method?

I am referring to a paper by Thomas Breuer where he has proven that an observer in quantum mechanics cannot measure certain parameters about himself or a system that includes himself, even if he can measure similar parameters of other people. This means his own wavefunction appears differently to him, a phenomenon which Breuer called "subjective decoherence".

So my question is whether this result disproves usefulness, credibility or validity of scientific method?

  • 1
    I'm a bit confused by this question. If a person cannot measure certain parameters about herself, how can these parameters be said to have an 'appearance' to him at all? And in any case, there's no cut-and-dry way of saying when a physical system constitutes an "observer" or not, and when you get into interpretations powerful enough to evaporate that concern (e.g. Many Worlds) you have theories that don't invalidate the scientific method but simply predict its weakness.
    – anon
    Sep 21, 2011 at 21:17
  • 1. "If a person cannot measure certain parameters about herself, how can these parameters be said to have an 'appearance' to him at all?" - from the linked page it follows that the person simply will not able to distinguish between two quantum states. This manifests as an excess decoherence of a wavefunction. 2. Many-Worlds is not ego-asymmetric. It is an interpretation that was invented to combat ego-asymmetricity, inevitable in other interpretations.
    – Anixx
    Sep 22, 2011 at 0:29
  • And as Many-Worlds is a theory where the scientists are cloned, it is unclear how one can apply scientific method at all inside such interpretation (see my another question: philosophy.stackexchange.com/questions/1275/… ) I am not sure scientific method is applicable where scientists are cloned (together with their instruments), selected, and then questioned after selection. This is simply a setting which is incompatible with scientific method, and it is essential to Many-Worlds.
    – Anixx
    Sep 22, 2011 at 0:31
  • 1
    1) I'm not sure if "his own wavefunction appears differently to him" effectively communicates this situation. It's like how I can't see the back of my own fleshy eyeballs (attempting to do so would destroy my ability to see), while I can see the back of other people's eyeballs by taking them out and looking at them. This doesn't literally mean my eyes 'appear' differently to me, as they have no appearance to me at all. 2) True, that's good point, and that's what makes the question worthwhile.
    – anon
    Sep 22, 2011 at 0:39

3 Answers 3


So my question is whether this result disproves usefulness, credibility or validity of scientific method?

It would problematize the scientific method only for those cases where results are not repeatable through controlled observation.

Most (if not all) mysterious quantum effects disappear at the level of everyday objects, so the odds of these kinds of things actually causing a practical problem for science as it is routinely practiced are vanishingly small.

  • I agree with this assessment if to speak about present-day applications of quantum mechanics. But this is a question of principle as new applications that explore this phenomenon can arise.
    – Anixx
    Sep 15, 2011 at 14:14
  • 4
    And "mysterious quantum effects" are repeatable under controlled observation, so it's not problematic even then!
    – Rex Kerr
    Sep 15, 2011 at 14:15
  • I also would know about impact of such theories in principle, without direct connection with quantum mechanics.
    – Anixx
    Sep 15, 2011 at 14:16
  • 2
    @Anixx: The "new applications" you refer to are largely (if not completely) imaginary at this point. There's no evidence to suggest that we are anywhere close to being able to use any kind of "mysterious quantum effect" at the level of everyday, phenomenal objects. Personally, I find there to be enough interesting questions in philosophy in this world; there's no need to bring science fiction into the mix. Sep 15, 2011 at 14:19
  • 1
    Based on Breuer's paper, we can conclude that it may be possible to construct a device that will cause subjective decoherence with regard to certain quantum measurements. There's no reason to believe that this has any effect at the macroscopic level, and even if it did, such a device would not have any bearing on the general validity of science; rather, it would only problematize information gathered on that specific, artificially constructed device. In other words, this is a thought experiment which bears little relationship to the actual workings of the world, or the workings of science. Sep 15, 2011 at 18:48

So my question is whether this result disproves usefulness, credibility or validity of scientific method?

At the worst, it only means that the scientific method is in some need of revision.

Understand that what we call the scientific method is, even at the present, in no way the provably-best method that we can use. Like eating, breathing, not tormenting prides of hungry lions, and logical argumentation, it is just one of an increasingly elaborate suite of "best practices" that we have settled upon for achieving certain objectives; in this case, being able to reliably predict or even control certain pieces of the universe about us.

If you want to be skeptical of the "validity" of the scientific method, you don't have to wait for an exotic experiment to come about to vindicate your doubts. But at the same time, the existence of an exotic experiment doesn't invalidate all of the past successes of the scientific process. What it would indicate — as with all scientific revolutions — is that reality is more subtle than we previously thought, and that our methodology is in some need of revision. It's not clear in advance what this revision would look like, but whatever the new methods are, there should also be a good explanation in retrospect — as was true with, for instance, Newtonian mechanics — why it worked so well for so long, if it was wrong. And we can expect that the answer will be that it wasn't very wrong, just somewhat wrong, and that the degree of wrongness only became apparent in newly discovered and somewhat exotic circumstances.

Science as it is practiced now may not be science as it is practiced a thousand years in the future: but we may regard it as being part of the same continuous tradition if it remains concerned with somehow going very carefully and precisely about finding out how the world works. It might be running up a blind alley a thousand years hence, or we might currently be doing so now; but science is not about being right (which we cannot verify), but by doing our methodical best to be the least wrong that we can manage.


It is no problem at all: once you have discovered that you can't measure things, you ask other people to do the measurements for you. This happens all the time. Maybe you don't have the right camera, or you don't have a particle accelerator, or you use a CCD camera instead of your eye to capture some photons.

Also, those phenomena for which a human-sized observer is entangled with observables of other systems are extraordinarily limited, given how big human observers are. So this particular theoretical point is of no interest physically.

  • The question is whether a measurement by other people will be relevant if the theory predicts its difference from a measurement conducted on(by) you.
    – Anixx
    Sep 15, 2011 at 17:43
  • @Anixx - Depends on what you're trying to explain, doesn't it? Anyway, I fail to see the difference between this case and any other case where you need to share data in order to get a coherent picture of a phenomenon.
    – Rex Kerr
    Sep 15, 2011 at 17:49
  • Look. If theory predicts there is one special person, measuring characteristics of other people to determine the characteristics of the special one is quite useless...
    – Anixx
    Sep 15, 2011 at 18:02
  • @Anixx - Such a case might be hard to deal with, but there's no evidence of one special person. So it's a moot point. (You can still set up experiments for them and ask them to report back to you, however.)
    – Rex Kerr
    Sep 15, 2011 at 19:17
  • "but there's no evidence of one special person." - this is not the case, at least of to consider the theory.
    – Anixx
    Sep 15, 2011 at 19:22

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