Time

Physical time or clock time is public time, the time that clocks are designed to measure. Biological time, by contrast, is indicated by an organism's various internal clocks or cyclic processes such as its heartbeats and repeated breathing and its sleep/wake cycle (circadian rhythm). It is also indicated by signs of aging. Psychological time is different from both physical time and biological time. Psychological time is private time. It is also called "subjective time" and "phenomenological time," and it is best understood not as a kind of time but rather as awareness of physical time. Psychological time is the time of the manifest image. Physical time is the time of the scientific image.

There is no experimental evidence that the character of physical time is affected in any way by the presence or absence of mental awareness or the presence or absence of any biological phenomenon. For that reason, physical time is called "objective time."

When a physicist defines "speed" to be the rate of change of position with respect to time, the term “time” in that definition refers to physical time. Physical time is more fundamental than psychological time for helping us understand our shared experiences in the world, and so it is more useful for doing physical science, but psychological time is vitally important for understanding many mental experiences, as is biological time for understanding biological phenomena.

We don't need to look at a clock to detect time's existence. We mentally encounter time by seeing a leaf fall. But if we close our eyes, we still can encounter time by imagining a leaf fall. What all these encounters with time have in common is that we are having more and more experiences and accumulating more and more memories of those experiences. The leading explanation of why psychological time exists is accumulation of memories.

Psychological time's rate of passage is a fascinating phenomenon to study.  At the end of viewing an engrossing television program, we think, “Where did the time go? It sped by.” When we are hungry and having to wait until we can leave work and go to lunch, we think, “Why is everything taking so long?” When you are younger, you lay down richer memories because everything is new. When you are older, you lay down much less rich memories because you've seen it all before. That is why older people report that a decade goes by so much more quickly than it does for younger people.

Do things seem to move more slowly when you are terrified? "Yes," most people would say. "No," says neuroscientist David Eagleman, "it's a retrospective trick of memory." The terrifying event does seem to move more slowly when you think about it later, but not when it is occurring. "Anytime you have richer memories, things seem to have lasted longer." Because memories of the terrifying event are "laid down so much more densely," he says, it seems to you upon playback (namely upon your remembering) that your terrifying event lasted longer than it really did according to the clock time.

A major philosophical problem is to explain the origin and character of our temporal experiences. Philosophers and cognitive scientists continue to investigate, but so far do not agree on, either how we experience temporal phenomena or how we are conscious that we do. A pessimistic physicist, Julian Barbour, says, "I do not believe that science...will ever explain why we experience instants...." 

With the notable exception of Husserl, most philosophers say our ability to imagine other times is a necessary ingredient in our having any consciousness at all. We make use of our ability to imagine other times when we experience a difference between our present perceptions and our present memories of past perceptions. Somehow the difference between the two gets interpreted by us as evidence that the world we are experiencing is changing through time with some events succeeding other events. Locke said our train of ideas produces our idea that events succeed each other in time, but he offered no details on how this train does the producing.

Physical time or clock time is public time, the time that clocks are designed to measure. Biological time, by contrast, is indicated by an organism's various internal clocks or cyclic processes such as its heartbeats and repeated breathing and its sleep/wake cycle (circadian rhythm). It is also indicated by signs of aging. Psychological time is different from both physical time and biological time. Psychological time is private time. It is also called "subjective time" and "phenomenological time," and it is best understood not as a kind of time but rather as awareness of physical time. Psychological time is the time of the manifest image. Physical time is the time of the scientific image.

There is no experimental evidence that the character of physical time is affected in any way by the presence or absence of mental awareness or the presence or absence of any biological phenomenon. For that reason, physical time is called "objective time."

When a physicist defines "speed" to be the rate of change of position with respect to time, the term “time” in that definition refers to physical time. Physical time is more fundamental than psychological time for helping us understand our shared experiences in the world, and so it is more useful for doing physical science, but psychological time is vitally important for understanding many mental experiences, as is biological time for understanding biological phenomena.

We don't need to look at a clock to detect time's existence. We mentally encounter time by seeing a leaf fall. But if we close our eyes, we still can encounter time by imagining a leaf fall. What all these encounters with time have in common is that we are having more and more experiences and accumulating more and more memories of those experiences. The leading explanation of why psychological time exists is accumulation of memories.

Psychological time's rate of passage is a fascinating phenomenon to study.  At the end of viewing an engrossing television program, we think, “Where did the time go? It sped by.” When we are hungry and having to wait until we can leave work and go to lunch, we think, “Why is everything taking so long?” When you are younger, you lay down richer memories because everything is new. When you are older, you lay down much less rich memories because you've seen it all before. That is why older people report that a decade goes by so much more quickly than it does for younger people.

Do things seem to move more slowly when you are terrified? "Yes," most people would say. "No," says neuroscientist David Eagleman, "it's a retrospective trick of memory." The terrifying event does seem to move more slowly when you think about it later, but not when it is occurring. "Anytime you have richer memories, things seem to have lasted longer." Because memories of the terrifying event are "laid down so much more densely," he says, it seems to you upon playback (namely upon your remembering) that your terrifying event lasted longer than it really did according to the clock time.

A major philosophical problem is to explain the origin and character of our temporal experiences. Philosophers and cognitive scientists continue to investigate, but so far do not agree on, either how we experience temporal phenomena or how we are conscious that we do. A pessimistic physicist, Julian Barbour, says, "I do not believe that science...will ever explain why we experience instants...." (Barbour 1999, p. 255)

With the notable exception of Husserl, most philosophers say our ability to imagine other times is a necessary ingredient in our having any consciousness at all. We make use of our ability to imagine other times when we experience a difference between our present perceptions and our present memories of past perceptions. Somehow the difference between the two gets interpreted by us as evidence that the world we are experiencing is changing through time with some events succeeding other events. Locke said our train of ideas produces our idea that events succeed each other in time, but he offered no details on how this train does the producing.