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.