We have all experienced déjà vu at some point in our life. Déjà vu is a French term that means “already seen” and is basically the feeling that the situation you are currently experiencing has occurred before. For example, you may be on holiday in Europe, walking through a cathedral when you suddenly feel as if you have already been there. Or you may be having coffee with your friends when you suddenly feel as if this exact situation has happened before – you’ve been in the same coffee shop with the same friends discussing the same topic before.

It is a strange phenomenon that no one can explain. It has been noted that as much as 70% of our population has experienced déjà vu at some point or another. The feeling is most common in young people, usually those who are between 15-25 years old.

The strange phenomenon was first studied by the French scientist Emile Boirac. In fact, it was Boirac who coined the term “déjà vu”. A couple of variations to déjà vu exist, including déjà senti (already felt), déjà vécu (already experienced) and déjà visite (already visited). However, these terms are not as popular as déjà vu.

Over the years, countless different theories have been proposed in order to try and explain the weird sensation of déjà vu that we sometimes feel. Below we have collected 15 of the most interesting theories!

A Glitch In Reality

Some people believe that time is only an illusion. According to them, there is no past, present or future. Many of these people also believe in the Glitch Theory, which suggests that déjà vu occurs when there’s a fleeting breakdown in our reality.

When we experience déjà vu, we feel as if we have experienced that moment before. According to the Glitch Theory, déjà vu is a tiny break we get from the illusion of time. Since there is no past, present or future and everything is happening at the same time, when we experience déjà vu we are simply experiencing a greater level of consciousness – we are living more than one experience at the same time.

Two Separate Universes Are In Sync

Some people believe that infinite parallel universes exist and that each universe has a completely different version of us living in it. These people claim that déjà vu is simply different, separate universes syncing together for a short period of time. So, according to the proponents of this theory, whatever it is you’re doing when you’re experiencing déjà vu is exactly what another version of you is doing in a parallel universe.

Basically - déjà vu is caused by you performing the same action in two different universes. That same action creates an alignment between the two parallel universes and gives you an eerie feeling that the moment has happened before.

Minor Seizures

Research in epilepsy has concluded that there is a strong link between déjà vu and the seizures that occur in people that have a specific type of epilepsy, known as medial temporal lobe epilepsy. This type of epilepsy influences a small region of the brain known as the hippocampus.

The hippocampus is important in assisting with the storage of short-term and long-term memories. According to a recent report from the medical journal Neuropsychologia, people that suffer from medial temporal lobe epilepsy “consistently experience déjà vu at the onset of their seizures”.

As a result, some researchers believe that déjà vu happens when our neural misfires and causes neurons to transmit signals randomly. People then experience an unfounded sense of remembered familiarity.

Tuning Fork Phenomenon

Some people explain déjà vu with the Tuning Fork Phenomenon. In fact, The Spiritual Research Foundation claims that as many as 50% of déjà vu moments are caused by this bizarre phenomenon. So what is the Tuning Fork Phenomenon?

The Tuning Fork Phenomenon suggests that absolutely everything in our universe radiates frequencies. Human frequencies, for example, are made of gross, mental, intellectual, and subtle-ego bodies. According to the Tuning Fork Theory, these frequencies produce an aura.

Most human frequencies are completely unique. However, sometimes two frequencies can sync up. When this happens, the feelings and experiences of a few people become entangled and they experience déjà vu.

Living The Same Life Over And Over Again

Some people believe that when we die we are reborn. However, instead of living a new life, we end up living the exact same life that we left behind when we died. According to this theory, we will continue living the exact same life until we get it right, whatever that may mean. So, those that believe this theory claim that déjà vu is just us accidentally remembering our past from exactly the same life.

However, a lot of people seem to dislike the concept of living your life over and over again until you get it “right”. For example, one Reddit user says – “What is “right”? If you mean in terms of morality that depends on if you believe in a universal morality or some sort of ethical behavior that transcends our subjective morality as individuals.”

Reincarnation

Many people believe in reincarnation, i.e. that we lived as someone else in a previous life. According to this theory, when we are reborn, all our memories of our previous life are wiped out and we start fresh.

Those who believe in reincarnation claim that once we are reborn, we get a set of signals that reflect states of consciousness. It is believed that memories created on one level of consciousness can’t ever be retrieved on another level of consciousness. When déjà vu occurs, it is a signal from our previous life. We only get the signal when it occurs in an abnormal level of consciousness. It is said that we transition from one consciousness to another when we recognize a certain smell, sound or image.

Recently, the Twitter user @ScatesJoseph posted an interesting theory on déjà vu – “What if when we die the light at the end of the tunnel is the light to another hospital room, there we are born and the only reason you come out crying is because you remember everything from your past life and you’re crying at the fact that you died and lost everything, as you grow you start to forget your past life and focus on the life you have now, but patches of memory stay behind and that memory causes déjà vu.”

Familiarity-Based Recognition

Our brain can shift between two types of recognition: recollection-based recognition and familiarity-based recognition. Recollection-based recognition occurs when we can remember exactly when a current situation has occurred before (for example you see a familiar man you saw on the bus now shopping at a shop). Familiarity-based recognition occurs when we feel like the same situation has happened before but we can’t remember when exactly (for example, you see a familiar man at a shop but you don’t know where you saw him before). Déjà vu is believed to be an example of familiarity-based recognition.

If the theory is correct, then it means that déjà vu happens when we have a slight memory of something happening before but the memory is not strong enough for us to remember the details.

A Visit From Men In Black

Do you remember the 1997 film Men In Black? In it, one of the men in black, known as Agent Zed, tells the recent recruit – “Your entire image is crafted to have no lasting memory with anyone you encounter. You’re a rumor, recognizable only as déjà vu and dismissed just as quickly.” In the film, men in black use a special device called neuralyzer to wipe the memories of extraterrestrials from human brains.

Thus, while this theory is far-fetched, some people do indeed believe in men in black and that they have the ability to wipe our memories. However, sometimes we still recall snippets of these memories and, you guessed it, this is when we experience déjà vu.

Mix Up Of Senses And Memory

It has been proved that our memory is context-dependent, which means that we will remember information better if we're placed in the environment in which we studied it. This theory thus proposes that various stimuli – sights, sounds or smells — in the environment can easily evoke a distant memory and thus cause déjà vu. In addition, we are more likely to remember something which we constantly think about.

However, proponents of this theory fail to come up with a reason that would explain why déjà vu occurs when the person experiencing it does not recognize any of the stimuli.

Divided Attention

The Divided Attention Theory or the Cell Phone Theory proposes that when we are distracted by something we will unconsciously take in what is around us but we will not register it consciously. Then, when we focus on what we are doing or where we are properly, we will feel as if the surroundings are familiar to us even though they are not.

Dr. Alan Brown tested this theory by showing photographs of different locations to a group of students, planning to ask them which seemed familiar. However, before he showed them the photographs he flashed them on the screen for 10-20 milliseconds.

The brain registered these photos, but the students were not aware that they had seen them. Interestingly, students felt like the photos that they had seen for 10-20 milliseconds before the test were more familiar than those they didn’t see.

The Hologram Theory

The Hologram Theory was proposed by Herman Sno, the world’s leading expert on déjà vu. According to Sno, our memories are basically three-dimensional images. In addition, the whole formation of a memory can be recreated by just one element.

Thus, according to Sno, if one stimulus, such as sound or smell, in your environment reminds us of a moment from the past, then the whole memory can be reconstructed in our head like a hologram, and this is when we experience déjà vu. However, we don’t recognize the memory after déjà vu has passed because the stimulus that triggers déjà vu and the previous memory is often hidden from our consciousness.

Precognitive Dreams

Precognitive dreams are basically dreams that predict the future through a sixth sense. In fact, a lot of people claim that their dreams can predict the future which would suggest that humans have a subconscious sixth sense.

Some people claim that we feel déjà vu because we have dreamed of the moment before in a premonitory dream. For example, you may dream of sitting an exam in an exam hall and then later you actually end up sitting that exact exam in that exact exam hall you dreamed of. Dreaming is not a conscious process and thus we don’t recognize the stimulus (the exam hall), but we still feel that it is familiar.

Brain Fact-Checking Its Own Memory

Recently, scientists have come up with a new explanation for the curious phenomenon of déjà vu. A year ago Dr. Akira O’Connor from the University of St Andrews presented her research at the International Conference on Memory in Budapest. Her research suggests that déjà vu is simply our brain undertaking fact-checking of its own memory system.

O’Connor’s research involved the artificial triggering of déjà vu. This was achieved by giving study participants a series of connected words but omitting the word that links them. For example, one series of words was bed, pillow, dream, and night. The linking word was sleep. When the participants were asked whether they heard any words beginning with “S”, they replied negatively. But when they were later asked what words they heard, most of them thought they heard the word “sleep”, even though they knew they didn’t really. This resulted in them experiencing déjà vu.

Interestingly, it was noticed that during déjà vu, frontal areas of the brain (decision making) were activated, as opposed to areas that are associated with memory. Thus, O’Connor thinks that the frontal regions of our brains monitor our memories looking for errors. When they spot one, they become activated.

Amygdala

The amygdala is a small region in our brain’s medial temporal lobe. There are two of them in our brain. The amygdala is responsible for our fear. So, if you are scared of bugs and you see one, it will be your amygdala that processes your response. If we find ourselves in a seriously dangerous situation then our amygdala may even disorient our brain for a short period of time.

If we consider déjà vu as a brain malfunction, then we can explain it with the amygdala. Let’s say we are in a situation that is very similar to a situation that has occurred before. In that case, our amygdala might end up producing a panic response which will put us in a temporary state of confusion, also known as déjà vu.

Dual Processing

The Dual Processing Theory suggests that sometimes memories are not formed correctly in the brain. The theory is based on how information is stored in our brains, meaning whether it is stored in short-term memory or long-term memory. Basically, déjà vu occurs when two cognitive processes are temporarily out of sync.

In 1963, Robert Efron at the Veterans Hospital in Boston was testing this theory when he realized that the temporal lobe of the brain’s left hemisphere sorted through the incoming information. However, it also turned out that this temporal lobe received this information not once but twice (with only a few milliseconds delay in between). Thus, the first time information arrives through the left hemisphere, and then the second time it arrives through the right hemisphere. If the second transmission of information is slightly delayed, then the brain might consider it a separate memory. This could then cause people to feel as if the event has happened before.