Is Arrow of Time Reversable?

[Sunstone]

Of course it is. ALL physical laws are ultimately subject to that problem.

Yeah, that's what I thought, Poly, but I second guess myself a lot these days -- I'm getting old and prone to mistakes.

 

[wellwisher]

The second law states that the entropy of the universe increases with time. Therefore if you were to travel back in time, the machines and the energy required, will cause the entropy to increase, since perpetual motion is not allowed. When we reach the past, the past will have changed due to the increase in entropy. This means that the past is not exactly the past, but part of a new future. Time will not go backwards but rather we will deflect the time vector, which continues to move forward.

The main source of confusion about time, is connected to the clock. Clocks cycle; noon to midnight to noon. Clocks represent time, but in a way that is similar to a cycling energy wave. However, time does not behave like an energy wave, since time moves one direction. Traditional clocks misrepresent the nature of time, which then create the illusion of time cycling and reversing. The concept of time dilation, in relativity, is based on clocks which misrepresent the nature of time. Measuring time, with a device that simulates energy, is like measuring temperature with a telescope. This can create confusion during interface.

It is possible to design an entropy based clock so the measuring device; clock, actually parallels the nature of time. One example of an entropy clock is the dead fish clock. We catch a fish, and place it on the counter. We tell time by the fish odor, as it decay. Like time, we cannot un-stink the dead fish. It only decays in one direction, and then we need to replace it with another fresh dead fish.

Interestingly, if we refrigerate the dead fish clock, we can slow down the time that is represents. If we make the room warmer we can speed up the entropy clock's time. Relativity of time, via the entropy clock, has a connection to thermal energy, whereas the relativity of time for cyclic energy clocks has a connection to motion and mass.

Entropy needs energy to increase. If there is no energy, the entropy will stay constant and time will appear to stop; no change of state. If we add energy, the entropy can increases as fast as it can absorb energy. The entropy clock is easier to test for relativity, than is the energy clock. This means this form of relativity is more universal.

If you compare a human to a rock, the rock appears frozen in time, while the human appears part of time. This has to do with entropy. The entropy of the rock remains constant, due to the stability of its crystalline nature. Its entropy only changes very little with time. This entropy clock is designed to run slow; change of state. The human body is full of entropy change and this entropy clock is designed to run faster, at the same thermal conditions as the rock. Water helps to keep things fluid, instead of solid, speeding up time within this entropy clock. This is a different way to look at time, using an entropy based clock.

 

[sealchan]

That's fascinating Sealchan! Could you elaborate on your reasoning for seeing time as a "brain distortion" or perhaps "cognitive bias"? I would enjoy learning as much as I can about this.

I think about how important metaphors are to how we form an understanding of our reality. The imperfection of metaphors, that is their limited scope (the way they only partially apply to any reality they are used to describe) seems to me to show up how the human brain contributes to our perception of reality. This is basically the view of Lakoff and Johnson Metaphors We Live By. Metaphors are a cognitive tool which have always helped us to build out a "hardened" language of concepts which are treated as "perfect" references to the reality they point to.

As an example, my view about how imperfect metaphors (time is a flowing river) become perfect concepts (time is a fundamental aspect of the Universe) can be seen metaphorically in the process of an artist painting and then selling the paintings he or she produces. The artist is inspired by some vague, but compelling, intuition to lay down paint on the canvas. As the paint is applied the artist is attempting to capture the meaning of that intuition. At times the artist "discovers" some useful color, shape, represented object, etc and feels that some strong connection has been made. Finally a painting is completed. The artist more or less likes it and maybe doesn't even fully understand it. The next day the artist tries again.

One day the artist brings all of his or her paintings to a gallery for a show. Various art collectors view the paintings. Then there is an auction. One painting stands above all the rest in the series the artist created in order to capture that strong but vague intuition. Apparently it registers as significant for his audience.

Just so do metaphors paint in details of our vaguer notions that concrete language seems to fail. The person who discovers the metaphor feels its significance and may even use it publicly from time to time. If it manages to catch on (let's say becomes a meme) then it may be seen as a deep and critical insight. The painting, in this case, is of a flowing river, but the various images and elements of the painting have convinced his audience that Time itself has been captured. So the while the painting was labelled by the artist "The Flow" every commonly has come to call it the Time Painting.

I think that the metaphors that work are those that draw from intimately common bodily experience and usefully and meaningfully allow us to capture something of the ineffable in our existence. They give us a handle on something important but also something that is difficult to understand.

Recently we have come also to understand that "time is a dimension". Given our intense familiarity with a world as grid and buildings as having floors we know that by moving along the north-south and east-west axis and then taking the stairs up or down, we can arrive anywhere on the planet. Time, then, is usefully also seen as another "dimension" as we seek to arrive at the corner of Einstein and Newton and take the elevator to the fourth floor and arrive there at 4pm. We remember significant events in our life as taking place at certain locations and at certain times. We can think of our lives as significantly revolving around the literal path through time and space that our bodies have travelled to get to where it has currently arrived.

If we set aside the notion of time as a flow and also of time as a dimension, how might we describe time that avoids any metaphoric reference? I suspect it is not possible. We might then add that for us time is a mystery and a myth even as it is also a practical concept with continual value and utility.

 

[sealchan]

Well, you are incorrect that it is *only* the second law that is temporally asymmetrical. It turns out that the weak nuclear force is also. Furthermore, the weak force is one of the (presumed) fundamental forces and so this is a more fundamental thing than the second law.

The problem with the weak force is, well, that it is weak. It shows up in some types of radioactive decay, is of very short reach, and doesn't seem to otherwise be relevant to, say, the direction of time in the second law. So this time direction *seems* to not be necessarily the one we are interested in.

It is useful, perhaps, to realize that the second law is a *statistical* law. In a sense, it only applies to 'large' collections. We have actually seen violations of it in small samples (involving a dozen or fewer molecules).

Another aspect of this is that the second law can be restated as 'the direction of the arrow of time is that of higher probability'.

For example, if you have a roomful of air, it is incredibly unlikely that all of the molecules will be on one side of the room and none on the other. it is much more likely that about the same number of molecules will be on one side as the other. Hence, the direction of increased probability is to have the air expand from half the room into the rest of the room. That is the direction of entropy increase.

Now, a reasonable question is why the arrow of probability increase should be the same at all locations. Why is it that the direction of time *here* is the same as the direction of time *there*?

And, as I noted above, we can find *small* areas where the direction of entropy increase *is* opposite that of the larger universe. But why the overwhelmingly dominant direction is consistent is a mystery as far as I can see.

This could be the illusion of the gradient and of the comfortable way we have of understanding a system as resulting in an averaging out of localized possibilities. Of course if we stand on top of a hill and drop a large beach ball on a breezy day we know that the beach ball will find its way down the gradient of the hill in one direction or another. We favor the view that the gas flows out and equally fills the volume of a chamber just as we know that ball will come to rest at the bottom of the hill. What we ignore, often, is the crazy paths that sometimes happen as the ball takes its journey to its assured final resting place. We can draw a circle around the base of our hill and know with some certainty that the ball will cross the line of that circle. But we forget how little we can predict at what point of that circle the ball will cross it. The circle, so to speak, does a trick and provides us certainty in exchange for a well-defined ambiguity which we consider is of little value.

So I would say that time itself doesn't exist as a causal "thing" such that one can say that here or there the "arrow points". This is mistaking an emergent quality of a system as a fundamental property of that system. It is fundamental to the community of knowers who have linguistically re-presented that experience of reality in terms of gradients and vectors that we understand the constraints of that system and that we can quantify the state of that system in a way that an equation can usefully describe. The trick, then, is to realize that in spite of a mathematical description of our physical universe having great efficacy, value and usefulness, it is also arbitrary, inconsistent and misleading in those rarified circumstances we find ourselves in when we actually observe beyond the customarily ignored boundaries of the lab and the rarified conditions in which these equations are seen to match the experience. Our technology, our machines do as much or even more to constrain physical behavior, to narrow down possible input, as they do to take advantage of some property of our reality to obtain some desired goal.