Understanding Time
madness asked excellent probing questions at the top of this thread. Let’s see how they can be answered.
Before considering the arrow of time let’s be a little more basic and clarify our understanding of time. When we see the sun at sunrise, noon, and sunset, we remember not only those observations but also the order in which they were made. Each long term or short-term memory is ‘tagged’ with its sequential position in a string of memories. Our notions of the past, present, and future are based on our recognition of memory sequences. That is the source of our concept of time.
We are not the only animals that recall memory sequences. Animals that hunt often base their present actions on the action they anticipate of their prey. To distinguish between present and future requires some understanding of time.
In a few sentences I will use the term ‘abstraction.’ so let’s be clear about what I mean by that term. An abstraction expresses a quality or characteristic apart from any specific object or instance. For example, there are red apples, red sunsets, and red light. Red is an abstraction. Red does not have existence independent of the things it characterizes. There is no such thing as red itself.
Time is an abstraction we make from the motion of things. We cannot conceive of time without conceiving of things that move, such as the rhythmic beating of our hearts, the motion of the sun across the sky, the swinging of a pendulum, the oscillations of a quartz crystal, and the alternating electromagnetic field of a photon. We do not sense time; we sense things and observe and remember their changes. Therefore, time without things can have no meaning for us. Just as there is no such thing as red itself, there is no such thing as time itself.
Since there is no such thing as time itself, it is meaningless to consider time to have physical existence. Time, therefore, cannot have physical properties; it cannot spin, dilate, shrink, or flow. When we say that time flows, we are speaking metaphorically as if time were similar to the water flowing in a river. But water is a real thing, time is not.
The idea of going forward or backward in time presumes that the time traveler would be spared the effects of the travel, that he could even go to times before and after his own existence. I guess he would don a cloak that shields him from time.
The notion of time running backwards implies that
all motions would be reversed and that all history would retrace its steps backward. It’s not possible. There are too many things that prohibit the reversal of time. Water can’t change its direction through a check valve. Electrons cannot change their direction through a diode or transistor.
The Earth would have to change its direction of rotation in order to make sundials tell time backwards. If it changed its direction instantaneously there wouldn’t be a human-built structure left standing and there would be horrific flooding. Instead of people getting younger they would be killed; that wouldn’t be a backward replay of history. And if it changed direction slowly, there would be terrible destruction as equatorial oceans moved towards the poles during the reversal. That, too, would not be a backward replay of history. The notion of time reversal, of history running backward, is self-contradictory.
As I said, it’s not possible. It’s as funny as a man jumping up upside down from a swimming pool and landing feet first on a diving board. Just because we’ve seen films run backward or wished we could take back some words we’ve said doesn’t make time running backwards possible, let alone a good idea The idea of the reversal of time, of going back in time, is fantasy.
If the arrow of time is stationary like a traffic sign, it can point only toward the future. If the arrow of time flies, it flew from the past to the present and now flies toward the future. The past no longer exists. The future does not yet exist. We are forever stuck in the present, observing the past, and anticipating the future.
Now let’s answer the questions posed in the opening of this thread.
1) How do we know that time flows at all?
Time can flow metaphorically but not physically. In the same way that time is an abstraction from the motions of things, the flow of time is an abstraction from the continuity of the motions of things. The continuity of things and their motions is based on our concept of object persistence, a concept formed during infancy.
Is there any scientific way to distinguish between time flowing or not?
If science deals with reality and not metaphors, there is no way for science to probe that question.
2} Does it make any sense at all to ask why time flows in the direction it does?
That question is equivalent to asking why
all things move. I don’t think it makes sense to ask that kind of question.
What would be strange is if time suddenly changed direction. But even then, would we even notice?
The question is pointless since irreversible processes preclude time reversal. Think of light and heat going back to a lamp to create ac electricity. Think of the check valve and diode.
Basically, i have no idea what physicists mean when they ask why time has an arrow
Physicists who ask that question are incorrectly taking metaphoric descriptions of time literally. The direction of time is implicit in Newton’s first law: “Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon”. The notion of continuity of motion is implicit in his (now archaic) use of the word ‘perseveres’ and his use of the term ‘uniform motion.’