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Have you experienced déjà vu?
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It's that shadowy feeling you get when a situation seems familiar.
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A scene in a restaurant plays out exactly as you remember.
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The world moves like a ballet you've choreographed, but the sequence can't be based on a past experience because you've never eaten here before.
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This is the first time you've had clams.
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So, what's going on?
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Unfortunately, there isn't one single explanation for déjà vu.
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The experience is brief and occurs without notice, making it nearly impossible for scientists to record and study it.
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Scientists can't simply sit around and wait for it to happen to them ⏤ this could take years!
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It has no physical manifestations, and in studies, it's described by the subject as a sensation or feeling.
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Because of this lack of hard evidence, there's been a surplus of speculation over the years.
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Since Emile Boirac introduced déjà vu as a French term meaning "already seen", more than 40 theories attempt to explain this phenomenon.
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Still, recent advancements in neuroimaging and cognitive psychology narrow down the field of prospects.
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Let's walk through three of today's more prevalent theories using the same restaurant setting for each.
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First up is dual processing.
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We'll need an action.
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Let's go with a waiter dropping a tray of dishes.
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As the scene unfolds, your brain's hemispheres process a flurry of information: the waiter's flailing arms, his cry for help, the smell of pasta.
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Within milliseconds, this information zips through pathways and is processed into a single moment.
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Most of the time, everything is recorded in-sync.
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However, this theory asserts that déjà vu occurs when there's a slight delay in information from one of these pathways.
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The difference in arrival times causes the brain to interpret the late information as a separate event.
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When it plays over the already-recorded moment, it feels as if it's happened before because, in a sense, it has.
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Our next theory deals with a confusion of the past rather than a mistake in the present.
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This is the hologram theory, and we'll use that tablecloth to examine it.
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As you scan its squares, a distant memory swims up from deep within your brain.
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According to the theory, this is because memories are stored in the form of holograms, and in holograms, you only need one fragment to see the whole picture.
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Your brain has identified the tablecloth with one from the past, maybe from your grandmother's house.
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However, instead of remembering that you've seen this pattern at your grandmother's, your brain has summoned up the old memory without identifying it.
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This leaves you stuck with familiarity, but no recollection.
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Although you've never been in this restaurant, you've seen that tablecloth, but are just failing to identify it.
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Now, look at this fork.
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Are you paying attention?
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Our last theory is divided attention, and it states that déjà vu occurs when our brain subliminally takes in an environment while we're distracted by one particular object.
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When our attention returns, we feel as if we've been here before.
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For example, just now, you focused on the fork and didn't observe the tablecloth or the falling waiter.
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Although your brain has been recording everything in your peripheral vision, it's been doing so below conscious awareness.
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When you finally pull yourself away from the fork, you think you've been here before, because you have, you just weren't paying attention.
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While all three of these theories share the common features of déjà vu, none of them propose to be the conclusive source of the phenomenon.
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Still, while we wait for researchers and inventers to come up with new ways to capture this fleeting moment, we can study the moment ourselves.
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After all, most studies of déjà vu are based on first-hand accounts, so why can't one be yours?
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The next time you get déjà vu, take a moment to think about it.
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Have you been distracted?
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Is there a familiar object somewhere?
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Is your brain just acting slow?
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Or is it something else?
