It's that shadowy feeling you get when a situation seems familiar.

A scene in a restaurant plays out exactly as you remember.

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.

This is the first time you've had clams.

So, what's going on?

Unfortunately, there isn't one single explanation for déjà vu.

The experience is brief and occurs without notice, making it nearly impossible for scientists to record and study it.

Scientists can't simply sit around and wait for it to happen to them ⏤ this could take years!

It has no physical manifestations, and in studies, it's described by the subject as a sensation or feeling.

Because of this lack of hard evidence, there's been a surplus of speculation over the years.

Since Emile Boirac introduced déjà vu as a French term meaning "already seen", more than 40 theories attempt to explain this phenomenon.

Still, recent advancements in neuroimaging and cognitive psychology narrow down the field of prospects.

Let's walk through three of today's more prevalent theories using the same restaurant setting for each.

First up is dual processing.

We'll need an action.

Let's go with a waiter dropping a tray of dishes.

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.

Within milliseconds, this information zips through pathways and is processed into a single moment.

Most of the time, everything is recorded in-sync.

However, this theory asserts that déjà vu occurs when there's a slight delay in information from one of these pathways.

The difference in arrival times causes the brain to interpret the late information as a separate event.

When it plays over the already-recorded moment, it feels as if it's happened before because, in a sense, it has.

Our next theory deals with a confusion of the past rather than a mistake in the present.

This is the hologram theory, and we'll use that tablecloth to examine it.

As you scan its squares, a distant memory swims up from deep within your brain.

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.

Your brain has identified the tablecloth with one from the past, maybe from your grandmother's house.

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.

This leaves you stuck with familiarity, but no recollection.

Although you've never been in this restaurant, you've seen that tablecloth, but are just failing to identify it.

Now, look at this fork.

Are you paying attention?

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.

When our attention returns, we feel as if we've been here before.

For example, just now, you focused on the fork and didn't observe the tablecloth or the falling waiter.

Although your brain has been recording everything in your peripheral vision, it's been doing so below conscious awareness.

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.

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.

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.

After all, most studies of déjà vu are based on first-hand accounts, so why can't one be yours?

The next time you get déjà vu, take a moment to think about it.

Have you been distracted?

Is there a familiar object somewhere?

Is your brain just acting slow?

Or is it something else?