A few hundred years ago, the word “moment” used to mean a precise amount of time, just like a minute equals 60 seconds.
Nowadays, we just use it to describe a very short period of time, but without any hard definition. This leaves room for some ambiguity, so here are a few ways to measure how long a moment is:
In medieval times, a moment was 90 seconds
For a long time, humans have divided the day into 24 hours. However, the hour itself was divided into 40 moments, rather than 60 minutes as we have today.
This state of affairs continued well into 16th Century, with clocks often dividing an hour into halves or quarters.
Once clocks and other time keeping technologies began to be more advanced and precise, the 60 minute hour replaced the 40 moment hour because it offered more division possibilities.
Thus, 60 minutes could be divided by: 2,3,4,5,6,10 and 12 whereas 40 moments could only be divided by 2,4,5 and 10.
It’s a small thing, but over the long run convenience trumps all.
If a moment is as long as a thought, then it’s ~150 milliseconds
In this case, we define a thought as the mental idea you get when you experience a certain stimuli.
For instance, it takes a runner roughly 150 milliseconds to process the sound of a starting gun, into a conscious “RUN!” signal.
One psychological hypothesis states that our mind’s stream of consciousness is like a movie reel, meaning it is composed of individual thoughts very tightly connected and flowing in quick succession.
Thus, if a moment is as long as a thought, then it’s safe to say it clocks in at +/- 100 milliseconds give or take depending on the circumstances.
If a moment is a memory, then how long is a moment?
Sometimes we use the word moment in contexts such as “that was a beautiful moment” or “an unforgettable moment”.
In this context, “moment” is something much more tangible, that includes a certain time, location and emotion. A memory, basically.
Now, a single memory can recall events that last a few seconds, such as passing by an interesting building or even hour long episodes, like first dates, important job interviews etc.
The next step is to then look at how these memories are formed.
In the movie Memento, the main character suffers from severe anterograde amnesia, meaning he cannot form long term memories. Because of this, he has to rely exclusively on his short term memory.
However, short term memory can only store information for a period of 20-30 seconds. After this period, the information is sent over to higher level mental processes for long term retention.
The main character in Memento lost this capacity. Thus, from the perspective of his short term memory brain, a moment was at most 30 seconds long.
If a moment is as long as the present, how long is the present?
Sometimes, the word “moment” can mean an exact, single point in time. In this context, a good analogy is to view a moment more like a still photo, rather than a video.
So if a moment is only a single point in time, how long can this single point in time be?
You could say it’s a second. But a huge amount of stuff can happen in one second. For instance, just 1 second after the Big Bang, the Universe had expanded to a radius of a few tens of light years across.
You could say that the present is only as long as a human thought, which would bring us back to the figure of 100 milliseconds.
For science’s sake, let’s say that the present moment is equal to the shortest possible measurable time unit in physics.
That would be Plank time. They are used to measure how long it takes light to travel across 1 Plank length, which also happens to be the smallest possible unit of distance for anything in the Universe.
So how long is a Plank time? Well that would be 5.39 × 10 −44 seconds.
The number probably doesn’t mean much, so here’s another way of looking at it: there are more Plank times in one second then there are seconds in the 13.7 billion years that have passed since the Big Bang.
To put it even more into numbers, there are 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000 Plank times into a single second.
So as far as physics is concerned, the present moment is pretty short.
How long is a moment, when it can be your last?
If you’ve ever lived through a life threatening or dangerous experience, you’ll know the sensation of time seemingly grinding to a halt and moving in slow motion.
This happens because during emergencies your amygdala will encode more information and detail into your memories.
Out of all our organs, our brain is by far the most energy consuming. By some estimates, the brain consumes 20% of your body’s energy while accounting for just ~2% of the weight.
To reduce this energy consumption, our brain is very selective with what information it remembers and which it discards.
In times of emergency however, it memorizes almost every bit of information available. This then creates denser memories, and the events in these memories seem to last far longer than normal, mundane day to day life episodes.
How long a moment is, depends on how old you are
Interestingly, time also seems to flow differently depending on how old you are, and the mechanism is very similar to the one mentioned above.
During childhood, each and every experience is likely to be brand new. As a result, a child’s brain works overtime to encode as much information as possible into the brain.
This creates a form of hyper awareness, where the child is conscious of everything that happens.
As we get older and experience more things, our brain starts to create patterns out of all the experiences. These patterns act like shortcuts of sort, and eliminate the necessity to memorize stuff we don’t need.
Case in point: compare the first kiss you ever had with a regular kiss in a serious relationship. Both are kisses, but during your first kiss your brain was hyper aware of every sensation and busily writing it into your memory.
For regular kisses however, your brain uses the mental shortcut and doesn’t write it down to memory.
How long is a moment for an animal or insect?
Have you ever noticed how difficult it can be to swat a fly or a mosquito? They seem to have surprising reflexes, as if they your hand is coming at them from a mile away.
This is because animals have evolved to have very different perceptions of time, depending on their circumstances.
As an example, insects live in a slow motion world since their environment is filled with predators such as birds, mammals and other insects. Their slow motion perception of time allows to observe threats much faster, and take evasive measures quicker.
However, large animals with few or no predators (think giant blue whale) don’t need to waste their energy on fast reflexes, so they live their life as if on fast forward. They can afford to lose some detail about their environment because nothing can hurt them anyway.
To put in movie terms, a film requires at least 20 frames per second so that the human eye can perceive the images as a single, uninterrupted flow.
Dogs on the other hand need at least 70 frames per second. Anything lower than that and they will see the movie as just a sequence of stuttering images.
How long is a moment when in a dream?
Dreams can often be very eventful and span events that should last hours, days or even years. Obviously, the laws of physics don’t allow you to live years in a few hour period. This means there must be some sort of mental trickery involved to make it seem like a moment in a dream is much longer than a moment in real life.
With the help of lucid dreamers, people who can control their dreams, scientists have discovered that time perception during dreams is surprisingly close to reality. In one experiment, it appeared that subjects perceived time as flowing 50% slower than during real time.
However, different studies have suggested that dream time flows at a roughly 1:1 ratio, or maybe a tine bit slower than real time.
Overall, the science is still uncertain but it does seem to point that dream time flows more slowly than real time, we just don’t know by how much.
How long is a moment in general relativity?
One of the more startling implications of general relativity is that time flows differently depending on how fast an object is.
For instance, viewed from Earth a space ship that travels towards Alpha Centauri (4.3 light years away) at 99.9% the speed of light would take around 4 years to complete.
However, for occupants inside the ship the whole journey would last just 65 days, or just over two months.
By using a simple calculation, a 90 second moment on the near light speed spaceship would last around ~2000 seconds here on Earth.
This phenomenon is called time dilation, and these figures can vary greatly depending on how fast the ship is, and also it’s acceleration. If you would like to play around with the figures you can check this calculator site.