- To say that two people ‘look alike’ is to make a statement not just about others, but also about oneself. Because face space is psychological, each person has her own, reﬂecting her face-recognition abilities as well as learned visual expertise. When environments and predilections vary, face spaces diverge. So perceived similarity1 in appearance always reﬂects both the observer and the observed. This expanded notion of resemblance complicates the concept of a doppelgänger, dead ringer or twin stranger. To the prosopagnosic or novice, lookalikes abound. To the super-recogniser or expert, no two people look the same.
- And so, does someone out there look exactly like you? It depends on what exactly you mean. Whatever our revised deﬁnition of similitude2, it must respect the interdependency between the observer and the observed. One possible revision – let’s call it ‘identical0’ – is that two people can be said to be identical in appearance if and only if no person could ever learn to tell them apart, even with a lifetime of exposure. Because this deﬁnition is so stringent that it rules out identical twins, who likely look as similar3 as two people ever could, it’s unlikely that you have any identical0 twin strangers.
- Expanding that deﬁnition somewhat, we might say that two people are ‘identical1’ in appearance if no untrained observer could reliably tell them apart. The extraordinary capabilities of the best face-recognisers suggest that you’re unlikely to ﬁnd someone similar4 enough in appearance to fool them. Relaxing it even further, we might say that two people are ‘identical2’ in appearance if the average untrained person can’t reliably tell them apart. Here, the idea of a doppelgänger is at least plausible.
- Estimates of the number of humans who ever lived on Earth put the number at 100 billion or so. This means that for every stranger you’ve brieﬂy mistaken for a friend, or every celebrity for another, there are tens, hundreds, perhaps even thousands more people who, if you met them, you’d think looked even more similar5. Somewhere out there, perhaps in another place and time, there’s a person whose appearance is so similar6 to yours that the average untrained person couldn’t tell you apart – your identical twin stranger.
- Jordan Suchow is a cognitive scientist studying vision, learning, memory and technology at the University of California, Berkeley.
For the full text, see Aeon: Suchow - Haven’t we met before?.
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