At the beginning of this century concept of "absolute time" was believed and thought two precise clocks would measure same , but later time was proved to relative to person or observer. When gravity and quantum mechanics were unified, concept of "imaginary time" was introduced where forward and backward directions in time are one and the same, but as in contradiction to real time these are very different. But why is this difference? This difference is what we notice as past and future. If we travel in forward path its future and backward is past.
Lets take an example, Imagine a glass cup falling from a table and broken into pieces . If we make a video of this and play it backwards ! what happens ? the broken pieces gather into single cup!! this is rather impossible in real time , the only reason for this is " Entropy never decrease" . If it decreases it'll break the second law of thermodynamics. Murphy's law also states " Things always tend to go wrong" . So what is entropy? Entropy is the disorderliness of a system. An example to explain this is consider your room which you didn't clean for many days .what happens? it'll go dirty, everything will be in disordered state, this disorder with respect to time is entropy. If you apply your energy and clean the room then you spent your energy to bring a system from disorder to order. Hence totally in the universe entropy goes on increasing with time.
The arrow of time is divided into three types,
1) Thermodynamic arrow of time - the direction of time where we consider entropy is increasing wrt time.
2) Psychological arrow of time- direction where we feel time is passing.
3) Cosmological arrow of time- Direction where universe is expanding.
In the universe there are more disordered states than the ordered once. This is same as cube which we play, where only one state which forms exact picture and other states do not. Universe started in high ordered state and entropy is increasing with time. If this is not true then universe should end up in state of high order that means entropy should decrease with time, which is not real as per observations we made with a glass cup on the table. And if it were to be true anyhow people in that universe would feel time to be running backwards ( psychological time). So one could remember his future rather than his past !!. And could predicts the stock exchange tomorrow's prices!
So , why we remember past ,why not future? This is because we have memory of things which are happened and the happened things increased entropy of universe. And while remembering the past we spent our energy, our brain may have trillion pieces of information, but it has spent energy in form of sweat or convection to store there. We can assume human memory to be somewhat like computer's memory, where in computer has two states 1 and 0. Before store of memory , the memory units will be state if disorder when memory is stored , the disorder is converted to order , with the spent of energy as heat, which is radiated by computer's cooling fan.So when computer records an item in memory the entropy of universe still increased.
All the three above mentioned arrow of time points in same direction . Neither of them could point other direction if so pointed, then it'll be more or less fiction movies where in they remember future. There is a concept in black holes called 'worm hole' through which we can go to past and kill our grand father, which makes a question for our existence where the person is trapped behind the event horizon ,but recent evidences show this is not possible. So we must say all the arrows point in same direction and entropy is increasing and universe is exapnding and we remember past not the future !!
So , why we remember past ,why not future? This is because we have memory of things which are happened and the happened things increased entropy of universe. And while remembering the past we spent our energy, our brain may have trillion pieces of information, but it has spent energy in form of sweat or convection to store there. We can assume human memory to be somewhat like computer's memory, where in computer has two states 1 and 0. Before store of memory , the memory units will be state if disorder when memory is stored , the disorder is converted to order , with the spent of energy as heat, which is radiated by computer's cooling fan.So when computer records an item in memory the entropy of universe still increased.
All the three above mentioned arrow of time points in same direction . Neither of them could point other direction if so pointed, then it'll be more or less fiction movies where in they remember future. There is a concept in black holes called 'worm hole' through which we can go to past and kill our grand father, which makes a question for our existence where the person is trapped behind the event horizon ,but recent evidences show this is not possible. So we must say all the arrows point in same direction and entropy is increasing and universe is exapnding and we remember past not the future !!
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