Imagine walking through an endless series of rooms. As soon as you step through a doorway the door is forever locked behind you. There is however a new door that opens up in front of you that takes you to the next room. Each room is different, some are bedrooms, others offices, kitchens, storerooms and so on. Moving through each room we can experience it while we are there, but once we leave it is only a memory never again accessible physically to us. As we reach the next door we are unaware to what room it will lead to just as the future is unknown to us.
Everybody understands time in their everyday lives and we all quantify time into set agreed upon standards such as second, minute and hour and also into longer periods such as day, year, century, etc. Much like how other things are measured such as distance, volume or weight we agree upon a quantifiable standard for time. Most of us also know that time is also something that we feel progress at different speeds depending on the individual or situation. Some moments seem to drag on for an eternity while in other circumstances they can seem to flash by in an instant. Time while having a measurable standard is also subjectively felt by the individual.
In general though everyone agrees that time flows in one direction, the arrow of time moving from the past through the present into the future. The past is already completed and done with and the present is where we currently are at any given time and the future is still an unknown with a multitude of possibilities. Things such as chance and circumstance can come into play making the future harder and harder to predict the further along we think about it.
Much like the first dimension of a simple line, we view time in the same manner. As we move through that line we can only see the single point that is the now or present. Even the past second that has passed us by cannot be relived in the same manner. As time flows we are pulled along. From one room to the next and the next the flow of time never ceases and never reverses, it simply moves forward into eternity.
This is the most accepted view of time, that time is a single fixed point moving along a singular dimension, that the past and future does not exist and only the present does. Commonly known as presentism in philosophy and the A-series of time in physics. The main issue that arises from the idea of the A-series is when relativity comes into play. Two objects moving at different speeds would be in different ‘presents’ as time would move differently for them. So what happens now for both objects could be very different. The present for one could be either the past or future for the other depending on speed.
“Time is an illusion.”
― Albert Einstein
The B-series of time points to the idea that there is no past, present or future. That all of time already exists. Much like the rooms, each location, each moment is already there and all we need to do is move forward to the next one.
The idea of time as tenseless, without the idea of past, present and future has been gaining some traction in the physics community as it tends to solve some of the issues that occur when using the A-series model.
When it comes to philosophy and religion the ideas of destiny, fate, predestination and so forth all fall within the ideas of B-series time. That the next room you you enter is already there and so is the next and next and all you need to do is reach the next room. In A-series of time the next room does not exist until you open the door and the past room ceases to exist once you close the door.
In either case whether you believe in the A-series or B-series everyone recognizes that we are currently in the present so make the best of it.