Were atoms real?

The idea of leaky abstractions seems relevant here. This is the observation from engineering that when layers of models are built on top of each other, consequences of the lower-level models tend to appear even when the higher layers are meant to abstract them away.

Asking whether a model is "real" seems akin to asking whether its abstraction will ever leak, and if it does, whether the places where lower layers show through are correctly labelled and explained within the model. Atomic chemistry is "real" in that, when it does break down (extreme energies, rare particles, etc), it's for reasons that can be explained in atomic chemistry's own vocabulary. On the other hand, psychology, for example, tends to break down for reasons that can't be explained, or can only be explained in terms of biology.

Under this definition, if the universe is a simulation, then it is real if and only if that simulation runs to completion without information about the simulator's universe leaking into our universe.

It's an interesting question, and probably the right way to ask it, but I've noticed three errors or omissions that would make me very happy if they were fixed. I'll start with the minor nitpicks.

• Lorenz thought his transformed time wasn't real because he was preserving the aether, which defined a particularly "real" time. Before Einstein's interpretation of the photoelectric effect the aether made a lot of sense, which seems like useful context.

• Hydrogen monoxide isn't something early chemists would have measured - maybe they measured hydrogen peroxide, though. Other examples for the law of multiple proportions would be carbon dioxide and carbon monoxide.

• The Copernican model was not more accurate than the Ptolemaic model. Its inaccuracy was its major problem, in fact. The main reason it held on was that it, in its simplicity, felt more "real" - what you report was only thought later. Kepler's model, on the other hand, kicked butt and took names, which may be what you were thinking of.

Very small children understand "real" to be "what's inside" -- what's hidden, essential. Sometimes literally inside: ask toddlers "If you took a dog, and gave it the bones and insides of a cat, would it still be a dog?" they say "no," but "If you took a dog and made it look like a cat on the outside, would it still be a dog?" they say "yes." (I'm getting this from Paul Bloom's "How Pleasure Works.") Young children are essentialist about gender as well -- they assume more differences between the sexes than actually exist, not fewer.

What psychological evidence I've seen suggests that we're in some way wired to see categories as real. "Natural kinds." To think that there's a real difference "out there" between dog and not-dog, not just a useful bookkeeping convention. I'm inclined to believe that Anna's reasoning about "atoms are real" and Eliezer's reasoning about categories actually make more sense than essentialism -- but I suspect that this kind of question-dissolving is not the standard, evolution-provided brain pathway.

This might be a situation where a word ("real") that served some useful purpose in certain contexts has been unwittingly taken out of that context, resulting in a meaningless question that can be dissolved by understanding the original context.

This seems to be the method that Wittgenstein uses to dissolve questions in Philosophical Investigations.

Half the more "philosophical" posts on here seem like they're trying to reinvent the wheel. This issue has been discussed a lot by philosophers and there's already an extensive literature on it. Check out http://plato.stanford.edu/entries/scientific-realism/ for starters. Nothing wrong with talking about things that have already talked about, of course, but it would probably be good at least to acknowledge that this is a well-established area of thought, with a known name, with a lot of sophisticated thinking already underway, rather than having the mindset that Less Wrong is single-handedly inventing Western philosophy from scratch.

This is essentially the debate between scientific realists and anti-realists in philosophy of science. Realists hold that unobservable entities postulated by scientific theories are still "real"; anti-realists hold that these entities are not real. One of the big problems for anti-realists, as you pointed out with your first example, is that "what is observable" changes over time (e.g. we can now "see" atoms in ways that would have startled physicists in the 1860's). However, the anti-realists do have one interesting argument in their favor: many theories that were empirically successful for a long period of time turned out to postulate unobservable entities that didn't actually exist. For example: ether, which made claims that were useful as prediction tools but didn't truly reflect reality. (This argument comes from Bas Van Fraassen, a leading anti-realist.)

Hopefully this historical context is helpful. The point I am trying to make is this: your question is one of those "great unsolved problems in philosophy."

There's a famous quote by Ian Hacking regarding electrons - "If you can spray them, they're real".

In "disguised query" terms, this corresponds to "can X be reliably used to effect changes on the rest of what I consider 'real' already?"

We know that relativistic time dilation is real, for instance, because you have to take it into account to build GPS devices that work as expected, and these are as real as they come - you use them to drive your car somewhere.

The MWI people like to cite Real Patterns by Daniel Dennett. I also wonder what LWers think of structural realism.

This seems like a pretty good idea. It suggests that the "reality" of a theory is point on a continuum, not a binary property. For example, under this interpretation, I'd say Newtonian physics is pretty real, but Relativistic physics is even more real than Newton's physics.

By the mid sixteen century, it was clear to the astronomers at the University of Wittenburg that Copernicus’s model was useful. It was easier to use, and more theoretically elegant, than Ptolemaic epicycles.

Copernicus's model still had epicycles. He improved on the Ptolemaic model by dropping the equant.

Are atoms real? Whatever the answer to that question is imagine if it were exchanged, that is suppose that magically the reality of atoms became unreal or the reality of atoms became real, would the world be in any way different as a result? I think the clear answer is no, therefore regardless of what the status of atoms may ultimately be, the question "Are atoms real?" is not real because real things make a difference and unreal things do not.

John K Clark

This is an extremely thought-provoking article that I haven't been able to get off my mind, so thanks.

I think we can all agree that reality (the 'territory') as a whole is real, but this is nigh-tautological. The question of whether a particular concept is a true part of reality (e.g. atoms) is more interesting but not as straightforward.

jsalvatier suggests that 'the "reality" of a theory is point on a continuum, not a binary property', and it seems there's something to this. My gut response to the question of 'are atoms real?' was 'of course! we've got photos and everything!'. But what is a photo other than the result of a scientific experiment that gives us strong evidence in favour of the theory? Going back to the everyday definition of 'real', we consider something to be real when there's so much evidence that we can't imagine any alternative. 'I'll believe it when I see it with my own eyes' some say. But our eyes are just partial evidence, not a final arbiter of reality on their own. Others believe Uri Geller's powers to be real because he can perform his tricks in plain sight, in front of a camera. Eliezer has claimed that "A peer-reviewed, journal-published, replicated report is worth far more than what you see with your own eyes.". So my gut response was wrong. All we have is evidence, and some theories have more of it than others.

So, if the theory of atoms was supplanted by a superior alternative, would atoms no longer be real? It doesn't seem right that something that happens in our mind should affect the world out there. "Reality is that which, when you stop believing in it, doesn't go away". So all we can confidently say is our probability estimate that a certain aspect of our map is complete (a.k.a. 'atoms are real, 99%'). Which is not as satisfying and of course, given that our definitions can change over time, this may get more murky as the definition of an atom is refined to be in line with incoming observations and new theories. For instance, while we know the original definition of atom (indivisible) to be false, we consider that it's coiner was in fact right in some sense.

Altogether I think the problem is that while 'atoms' are concepts that appear in our theories, and therefore maps, 'real' is a word that refers to the territory. So I guess the question could be restated as 'Is the map (atoms) the territory (real)?'. At this point perhaps it could be claimed that with perfect processing of perfect information, the map does become the territory but I don't think it's worth kicking this dead horse any further.

When I hear "Are atoms real?" I imagine zooming in on some object until I can see an atom. Could they just be asking if, given the technology required to magnify/compress/measure some form of sensory input about something, it would make some kind of intuitive sense to a human brain?

Like, if you could stand above the solar system and look down on it, the Copernican model would say it makes more sense to hover over the Sun and imagine everything rotating around you than to hover over the Earth and imagine everything rotating around you while pirouetting .

Similarly, if I could put "drops of something" in the luminaferous aether and watch it eddy and swirl, I'd be convinced its real. That something doesn't exist, but that's only evidence of its non-reality.

If something "really" happened, I would expect that, if I had a time machine that didn't cause paradoxes and whatnot, I could go back in time and watch it.

Though, this version of "real" doesn't really account for questions about more abstract things, like "Is this love for real?" or "Is free will real?". (Though, free will is a disguised query for something else, but digressing...)

Another way to state your conclusion is that the "is it real?" question reduces to the question of whether a model yields a Level 1 or Level 2 understanding [/self-promotion]. Indeed, those concerns where part of what motivated me to create the hierarchy.

The atomic theory seems to me very different to me than the others, which seem more like the motivating example. The atomic hypothesis also seems much easier. In particular, I think everyone was in agreement about what it would mean for atoms to be real or not, whereas in the other examples I think that there was no such agreement.

It is true that that the debates used the dichotomy "real or just a useful tool" that appeared in the other examples. Yes, what they meant by "real" was "is it useful in a less circumscribed setting," but the setting for the atomic theory was very cleanly circumscribed: the law of multiple proportions. It seemed back then (and seems to me) quite plausible that some other underlying phenomenon could give rise to that law. The discovery of another consequence that seemed much less plausibly explained by (hypothetical) other theories brought about rapid acceptance of the theory. (Quantization of charge would have done well here, but I believe the actual consequence was in explaining isomers and especially stereoisomers, which is a scale-free phenomenon, like ratios, but unlike quantization of charge.)

In the other examples, it was not clear what the competing theories were and whether they were distinguishable. Of course, since there was no particular theory competing with the atomic theory, there was danger of the situation becoming muddier, but that doesn't bother me so much.

This is rather tangential, but it's something about geocentrism that has been bothering me recently. Aristarchus (c 250 BC) and Hipparchus (c 150 BC) computed that the sun has 10x the diameter of the earth and thus the earth should circle the sun. Their contemporaries said: no, heliocentrism implies that the fixed stars are very far away. That's an OK argument against heliocentrism, but did they really engage with the intermediate step? [see update] Ptolemy agreed that the sun was 10 million kilometers away, but did he discuss its size?

And what did later astronomers do? When Kepler and his contemporaries got it right, did they think this a big deal? Did they think it relevant to heliocentrism? This larger distance makes the distance to the fixed stars proportionately larger, but I think the plausible size of the universe should increase superlinearly in observed distances, so discovering that the sun is farther away than you thought should erode the parallax argument against heliocentrism.

ETA: improved measurement of the tides should allow one correctly do Hipparchus's calculation, and multiply the AU by 10. For fixed parallax, the (lower bound) distance to the fixed stars is measured in AU and thus increases proportionately, which is what I meant above. But later astronomers measured stars more accurately than earlier, providing evidence against parallax, and thus against heliocentrism. In fact, no one followed Hipparchus, but instead used astronomical measurements to improve on Aristarchus and Ptolemy. So I don't have much to ask heliocentric Kepler about the discovery that the sun was even bigger (though he had to bite a bigger bullet than Hipparchus of distance to fixed stars). Still, did his predecessors really grapple with the size of the sun?

Added, 2013: the writings of Aristarchus and Hipparchus are lost, so we're not really sure what they did, but they did both conclude that the sun is much bigger than the earth. Aristarchus was heliocentric, but Hipparchus was geocentric. Added, 2014: actually, even the claim that Hipparchus was geocentric is dubious. The claim that their contemporaries were geocentric, let alone that they made a parallax argument, is a complete fabrication for symmetry with the Renaissance arguments. My question about Ptolemy and later remains.

Why can't real-ness just be functionality? People often resist this concept, but it seems sensible to me.

Exploring the function of things, in fact, how we know about the universe - when we talk about what something is, we'll really talking about an aggregate of functions that it has (e.g. we know that if we do something to a part of the universe, something will happen - since the result varies by the part of the universe we're looking at and the conditions under which we perturb it, we can divide the universe into "things.") We can say that atoms (for example) are real because we have observed consequences of our actions that (as far as we can tell) could only happen if something fitting our description of an atom existed.

Thinking of something as "real" in the sense that it seems like a sensible and somewhat self-explanatory entity is just a matter of familiarity, I think. We think of atoms as "real" because we've grown up conceiving of the world in that way (which is only the case, one would hope, because they have been shown to be "real" in the more strict scientific sense I mentioned above.)

Aether not only correctly predicted that light would act as waves, but also incorrectly predicted that the Earth's motion with respect to aether should affect the perceived speed of light.

I don't know anything about old ideas about aether, but I've wondered why it was wrong, and whether the aether-idea is really conclusively wrong or whether someday science could return to that idea.

Does "aether" necessarily mean that the observed speed of light may vary? In particular, what is packed into the word "aether" that demands this?

...I'm wondering if a different "aether" that doesn't require observer-dependent light speeds may be no less weird than current assumptions we have about how light propagates?

It looks like you dropped a word:

Despite this usefulness, there was considerable (debate?) as to whether atoms were “real” or were merely a useful pedagogical device.

Hrm... I'd say atoms are real iff reality (whatever that is) obeys a certain set of (approximate) regularities (that basically amount to the rules for atoms). ie, there's a sense in which they're "actually there"

The atoms are an explanation for a phenomena iff the fact that those particular regularities are largely sufficient to explain the phenomena in question. That is, that one doesn't have to "dig deeper" to still explain things.

(Of course, if atomic theory in general had failed and only explained a single particular thing, that would suggest that the first criteria was violated.)

Lorentz, not Lorenz.

[5] Thus, to extend this conjecturally toward our original question: when someone asks "Is the physical world 'real'?" they may, in part, be asking whether their predictive models of the physical world will give accurate predictions in a very robust manner, or whether they are merely local approximations. The latter would hold if e.g. the person: is a brain in a vat; is dreaming; or is being simulated and can potentially be affected by entities outside the simulation.

Hmm. Let's say we live in a multiverse where there are infinitely many universes with laws we cannot compute, so our laws are very much local (but not necessarily approximations). Would it make the world as we know it less real? I would not feel that.

On the other hand living in a simulation would feel unreal, though it might be based on a fantasy that you can 'break out' somehow.

Another use of the term is authenticity; e.g. I'd be proud to own a book signed by Churchill, but ashamed if it was a fake. (Physical laws to not dictate either way - it could have been authentic). This last example makes me think that it's going to be hard to disentangle the term from its psychological connotations.

I'm not sure what point you're trying to make, if you're trying to make one.

One other constructive criticism: why don't you consider some non-examples? I mean, theories that gave good predictions, seemed to generalize, and then, didn't?

I can't think of any stellar examples right now, but the lame example of the black swan comes to mind.

Besides the predictive power as a way to measure "realness", I would add persistence. A car in my dream is less real than a car before me when I cross a street in my daily life, in the sense that it persists more in my mind.

Taboo real?

:P

Only anti-realists think hidden questions lurk behind the concept of 'reality' [that's a fair definition of anti-realism]; realists take 'real' as primitive. You feel confused because you want an anti-realist account of "real," despite being a realist yourself . (Or else, you're an anti-realist smart enough to see through the extant anti-realist theories.)

Quine's is a famous example of an anti-realist account. Quine said the concepts denoting existing things (those that are real) are those variables you must quantify over in the best scientific theory of the subject. The problem with that is that "best scientific theory" isn't specifiable except with reference to what's real, although Quine made a noble effort.

When you ask whether atoms are real, the question doesn't concern the best explanatory framework; what's real determines best explanatory framework rather than the other way around—at least that's what realists think. The best theory is the one that best accounts for what's really there; the best theory doesn't doesn't determine what's real. Things may exist even though our best theory says otherwise. To parry the attack, the anti-realist can only retreat to epicycles—say, the best theory in the idealized long run—introducing concepts more problematic.

You know Eliezer argues that atoms are not individually real, right?

How about photons? If they are real can they be particles as well as waves? Feynman (who got a nobel prize for it together with Sin-Itiro Tomonaga and Julian Schwinger (they all thought of it independently)) went for waves. So did he think that for a photon to exist at all it needs to be classified? I think he felt photons were "real" but kind of shady before he nailed them down as waves instead of particles (making them "really real").

The map is not the territory. What you think of when I say "atom" is your map. An atom is the territory. What you think of is just a useful device. This applies to everything. Trees, rocks, etc.

AnnaSalamon,

When scientists debated the real existence of atoms, they were debating exactly that: whether atoms are real. Why must there be something to "unpack" here? [They certainly were not disagreeing about how to apply the reality concept.] The concept of "real," the distinction between real and imaginary, is as basic as it gets. Does it seem to you there must be something more primitive? If so, you haven't said why. Some philosophers, called "anti-realists," contend that reality can be cashed out in terms of concepts more fundamental, but none have succeeded in overcoming the basic objection: something can be real and be contrary to our best theories; what our best theories posit isn't necessarily real. Therefore, reality can't be analyzed further in terms of conformity to or usability in our theories (which is what most posters are trying to do). You intuit—when you report confusion—the failure of not only the current theories but any reductionist theory of the "real." What's really "out there" doesn't depend on what we think about it!

Why would you think the "real" can be "unpacked"? Your premise asserts the universal existence of hidden meamings for words. Elizer defended the strange idea that words inherently elude the assignment of a new, arbitrary meaning. There's supposedly some connection between a word and what it represents that becomes fixed once assigned. The first commenter, Caledonian2, confuted Elizer's position by distinguishing between factors that can interfere with the correct application of a definition and those fixing the definition itself. Elizer's claim that affective factors and the like constrain the meaning of a term was based on evidence showing that extraneous factors may undermine the correct use of the term; the point being that you can substitute concepts if you know how to control for the influence of these factors.

Your premise, that there's "hidden meaning," hasn't been confirmed. As you realize, no one has "unpacked" "real." It's because your premise is false.