Say something was to happen in the universe, so minuscule that no one notices it, and it has no effect on history whatsoever. Is it correct to say that it never happened, because when we say something is 'real', we just mean 'it had consequences that can still be witnessed'?

Of course, I'm aware that this cannot happen in real life, because anything, no matter how small, has some effect on the universe. However, it is an interesting thing to think about, given that what we deem 'real' is just a series of evidence for things.

  • For this naive form of the question the answer is a trivial no, that something happened can be verified indirectly, without observation. Nothing alive could observe the Big Bang, for example, but it happened. In a more sophisticated form, the answer is the main point of disagreement between realists, who believe in "verification transcendent truths", and anti-realists, who do not, see SEP, Challenges to Metaphysical Realism.
    – Conifold
    Oct 19 '20 at 21:12
  • Who is the observer? Oct 20 '20 at 4:29
  • @Conifold -- metaphysical realism is is simply an assumption, an irrational belief, leap of faith <== a position known otherwise as Cartesian doubt. The question, therefore, is not about the irrational nature of "metaphysical realism". The question is a) why we want to believe in it anyway, and b) what exactly are its tenets, what statements we want to believe to be true.
    – silkfire
    Oct 20 '20 at 17:34
  • "anything has some effect" You make a definition. What about Planck-scale 'quantum foam', evidenced by the Casimir effect? What about the clouds of probabilities known to affect fundamental particles, like mass through the Higgs interaction? The other side of the scales is, conservation of information, & 2nd law of thermo-d, where information spreads out not concentrates, in a closed system, on average - if, & when it doesn't, 'time's arrow' goes backwards. The 'size' of our smallest probes, photons fundamentally limits certainty = uncertainty principle.
    – CriglCragl
    Oct 21 '20 at 1:24

This question is a longstanding one in both traditional philosophy and quantum physics.

The necessity for something to be observed before it exists entails the existence of some observer. A famous Bishop Berkeley once used this argument as proof of the existence of God, the ultimate observer.

Mathematicians talk of "discovering" a new theorem. That term implies that the theorem existed in some sense before it was discovered. This contrasts with say Otto's "invention" of the four-stroke piston engine cycle, which did not exist until he invented it. But where do the idea of the four-stroke, or the mathematics of its operating cycle, lie? Where do discovery and invention divide? We see two philosophically opposed positions embedded in the English language.

Quantum physics is stuffed with counter-intuitive weirdnesses which have been demonstrated over and over again in the laboratory. One such phenomenon is the inaccessibility of any quantum wave to direct observation; either it will remain unobserved or it will "collapse" into a localised particle. The standard interpretation of all this weirdness is known as the Copenhagen interpretation. It holds that only observations exist and nothing therefore exists until it is observed; the wave describes only what you are likely to observe when you do so. (because of this the interpretation is sometimes summarised as "shut up and calculate"). The more extreme examples of this position demand a conscious observer before anything can be said to exist, while more moderate positions suggest that "observation" includes interactions with other quanta - reducing Berkeley's God to whatever arbitrary blob of stuff has gotten in the way this time.

Recent experiments in some areas have developed a technique of partial sampling or partial detection, in which individual quanta are not fully observed but, as it were, touched for some incomplete information about them. The statistical aggregation of many such partial measurements yields firm results without collapsing the wave function. (These experiments include such joys as sending the mass of an electron down one path and its spin down another, combining them back together at the finishing line.) While this weakens some aspects of the Copenhagen position, such as the impenetrability of the wave function, it does not affect the strong position of demanding an observer to do so.

Others of course feel that the whole observer business is a load of sophistry and there has to be some underlying reality independent of all such nonsense. Copenhagen is just a cover for our ignorance and, given time, we will learn to further invade the wave function's privacy.

So, certainly for now, the answer to the question is a matter of opinion. It may or may not become clearer as science advances.

  • Thank you for such a comprehensive answer! I believe all of it has to do with the fact that humans can only study what they observe, and thus whatever we can't observe, we can't study (if that makes sense). This whole question is redundant in my opinion, because there cannot be a definite answer to it (for example - we can't comment about something that doesn't exist, because if we were to do so, it would start to exist). Still, fabulous answer!
    – akshat
    Oct 20 '20 at 16:54
  • Ultimately, all we observe directly are our own subjective experiences. Everything else is inferred from that by our busy little brains. So there are useful questions over how far we should push those inferences; an independent reality, other people, quantum waves, where does it all end? Oct 20 '20 at 18:00
  • @akshat By your definition, there was nothing real before humans appeared. Even quantum mechanics isn't that weird. Here's a related question about the physics: physics.stackexchange.com/questions/453410/…
    – D. Halsey
    Oct 20 '20 at 23:05
  • 1
    @D.Halsey Hence Bishop Berkeley's famous view, noted in my answer. Oct 21 '20 at 10:01

In short, no! It is often a good idea not to have models of reality that contain inert objects, but knowing about something and its having an independent reality are, at the end of the day, different questions.

  • 1
    I think it boils down to what your definition of 'real' is. For all we know, real are only the things that have been experienced in some way by humanity. Sure, maybe somewhere something might exist; but if it (or the consequences of its existence) is/are not observed by anyone or anything EVER, then it lacks all the characteristics of a 'real' thing, and is, for all intents and purposes, not real.
    – akshat
    Oct 19 '20 at 15:26
  • It is possible in science, that something can be held as a theorem and not be observed per say, but the effects of its existence being observed in a set of things observable. Oct 19 '20 at 15:59
  • @akshat Read 1984. Whether or not the past exists is a major question posed by the book. What you ask sounds similar.
    – kutschkem
    Oct 20 '20 at 13:23

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