The given time symmetrical Feynman diagrams drawn with respect to space-time coordinates
Why does it move forward when many laws in physics are time-symmetric in the sense, it doesn’t depend on whether it is t or –t?
An interesting example from PBS Spacetime’s YouTube video narrates a similar instance of formation of a proton from pion and positron and provided proton decay is possible, the process is reversible and time-symmetric. This also contains the details of the past and future inside it: the memory and deterministic tendencies. While there exists a forward and backward direction for space- why is time irreversible?
Remaining as one of the unsolved problems in physics, we could humbly beat around the bush to get a gist of the situation. The evolution of the cosmos has a great deal to do with the concept of time and its direction. The universe originated from a compact state that is the Big Bang, which most likely saw the beginning of time.
The direction of time can be explained on the basis of the second law of Thermodynamics and the irreversible urge of the universe to race toward disorder and chaos: the tendency to go to a high entropy state. So, since the Big Bang, a perfectly low state of entropy, time had the tendency to move forward to randomness like it does today.
This is speculative and poses more questions than it answers. But this is a possibility and a very good one at that. Considering Big Bang was a low entropy state and time moves forward to high entropy, does there exist a probability that time reversal from the state of the big bang is possible with respect to our perspective if there was a higher entropy state in the reverse direction; a mirror universe with us in their deepest past? The question has already been asked.We will have to wait for answers.
You come across many theories, speculations and stories in the quest to know why time moves forward: quantum entanglement, parallel universes and what not. Whether or not you reach the end of the tunnel, the journey is surely worth it!
Cover image credits: www.researchgate.net
The Arrow of Time and How to Reverse It