Modern science says that there is no ‘flow of time’. Everything exists at every moment simultaneously. There is no ‘now’ that travels at 1 second per second along the time dimension, changing the future into the past. The concept of ‘now’ is purely an illusion generated by our brains. There is however an ‘arrow of time’ which points from the past (the big bang) to the future.
The ‘arrow of time‘ is generated by the second law of thermodynamics. This law states that in general ‘entropy increases’. Entropy is a state of disorder or a lack of structure. This ‘law’ is really just a statistical correlation of the fact that molecules like to zip around at random (brownian motion). If you place a perfectly spherical bubble of gas molecules inside a large empty box (a state of low entropy), pretty soon the gas will be evenly distributed throughout the box (a state of high entropy). The chances of the molecules forming themselves back into a nice sphere are almost zero. In the same way, it is easy to smash a cup by dropping it off a table, but it is almost impossible for a cup to spontaneously form out of it’s shards. On the large scale, we imagine the arrow of time points from a time of low entropy (the big bang, when everything was very ordered into a tiny point) to a time of high entropy (the ‘heat death’ of the universe when all matter is equally spread out in a formless void). In this way we can think of the universe as a wind-up toy that begins with a high degree of order and winds down to a low degree of order.
When the human mind views a video tape, it is easy to tell if it’s being played forwards or backwards. This is because our brains have evolved to perceive the arrow of time in order to survive. Evolution gave us an organ (the brain) that is specifically designed to ‘surf the arrow of time’. Our brain can predict the future by observing the past. For example if we see a coconut in mid-air above us, we know to jump out of the way, because it’s coming our way fast. This example also shows how the human brain is finely tuned to perceive the effects of gravity around us. The reality of two invisible forces, time and gravity are built into our brains at a very deep level. The better our brains perceived time, the more successful we became. Long term planning is a one of our greatest abilities.
In the early 20th century, science combined the concepts of space and time into ‘space-time’. To the 3 dimensions of space we added a fourth dimension of time. Forms in the spatial dimensions change, and that is what constitutes our idea of time. In reality nobody really understands time or why the illusion of time moving is so hard to shake. The passage of time is intrinsically linked to our own consciousness, another black hole of human understanding.
Space has 3 dimensions. What if time also has multiple dimensions? Possibly the reason why time seems so mysterious, is because we are only perceiving a tiny slice of it. We can only imagine moving forwards and backwards in time. What would a side-to-side motion in time represent? Moving between different parallel universes? Creatures that did operate in multi-dimensional time would seem to us to be completely nonsensical and magical. In the same way that an earthworm can only perceive the presence or absence of light, maybe our ‘time sensing organ’ is very primitive. Maybe there is a whole ‘time universe’ out there that we can only begin to imagine.