Nov 25, 2022 07:51 PM
(This post was last modified: Nov 26, 2022 01:58 AM by C C.)
https://aeon.co/essays/why-doesn-t-physi...ow-of-time
EXCERPTS (Gene Tracy): . . . The flow of time is certainly one of the most immediate aspects of our waking experience. It is essential to how we see ourselves and to how we think we should live our lives. Our memories help fix who we are; other thoughts reach forward to what we might become. Surely our modern scientific sense of time, as it grows ever more sophisticated, should provide meaningful insights here.
Yet today’s physicists rarely debate what time is and why we experience it the way we do, remembering the past but never the future...
[...] To declare that question outside the pale of physical theory doesn’t make it meaningless. The flow of time could still be real as part of our internal experience, just real in a different way from a proton or a galaxy.
Is our experience of time’s flow akin to watching a live play, where things occur in the moment but not before or after, a flickering in and out of existence around the ‘now’? Or, is it like watching a movie, where all eternity is already in the can, and we are watching a discrete sequence of static image, fooled by our limited perceptual apparatus into thinking the action flows smoothly?
The Newtonian and Einsteinian world theories offer little guidance. They are both eternalised ‘block’ universes, in which time is a dimension not unlike space, so everything exists all at once. Einstein’s equations allow different observers to disagree about the duration of time intervals, but the spacetime continuum itself [...] is an invariant stage upon which the drama of the world takes place.
In quantum mechanics, as in Newton’s mechanics and Einstein’s relativistic theories, the laws of physics that govern the microscopic world look the same going forward or backward in time. Even the innovative speculations of theorists such as Sean Carroll at Caltech in Pasadena – who conceives of time as an emergent phenomenon that arises out of a more primordial, timeless state – concern themselves more with what time does than what time feels like. Time’s flow appears nowhere in current theories of physics.
[...] How did that come to pass? Isn’t science supposed to test itself against the ground of experience? This disconnect might help to explain why so many students not only don’t ‘get’ physics, but are positively repulsed by it. Where are they in the world picture drawn by physicists? Where is life, and where is death? Where is the flow of time?
[...] Current cognitive science says that our memories are a kind of story that our brain creates, formed from the clay of sensory input, sorted into patterns based upon our past life experience, guided by predilections we have inherited in our DNA...
[...] Consider our experience of ‘now’. This seems at first to be a simple thing, a well-defined point in time. We certainly seem to anticipate a particular now coming at us from the future, and then receding from us into the past. Our experience of the ‘now’ is built out of a mix of recent memories and our current sense perceptions, what we see, hear, feel, taste and smell. Those sensory perceptions are not instantaneous, but signals from stimulated nerve endings...
[...] We usually don’t sense this mingling of near past and near future because our brain works quickly enough to obscure the process, but there are moments when it struggles to keep up...
[...] It’s possible that our experience of the flow of time is like our experience of colour. A physicist would say that colour does not exist as an inherent property of the world. Light has a variety of wavelengths, but they have no inherent property of ‘colour’...
[...] So the flow of time might be a story our brain creates, trying to make sense of chaos. In a 2013 paper, the physicists Leonard Mlodinow of Caltech and Todd Brun of the University of Southern California go even further and argue that any physical thing that has the characteristics of a memory will tend to align itself with the thermodynamic arrow of time, which in turn is defined by the behaviour of extremely large numbers of particles.
According to this theory, it is no puzzle that we remember the past but not the future, even though the microscopic laws of nature are the same going forward or backward in time, and the past and future both exist. The nature of large systems is to progress toward increasing entropy – a measure of disorder, commonly experienced as the tendency of hot or cold objects to come into equilibrium with their surroundings. Increasing entropy means that a memory of the past is dynamically stable, whereas a memory of the future is unstable.
In this interpretation, we are unable to see the future not because it is impossible to do so, but because it is as unlikely as seeing a broken window heal itself, or as a tepid cup of tea taking energy from the atoms of the surrounding room and spontaneously beginning to boil. It is statistically extremely, extremely unlikely...
[...] Lee Smolin at the Perimeter Institute in Ontario argues that scientists must change tack, accepting the flow of time as real and building the church of a new physics upon that rock.
The British physicist Julian Barbour takes an opposite stance; going beyond Newton and Einstein, in The End of Time (1999) he proposes that time itself is an illusion. Instead, the Universe consists of a collection of static moments, like a pile of unsorted photographs tossed into a shoebox. Each photo contains a snapshot of the world entire, a unique configuration of all things: planets, galaxies, bumblebees, people. Barbour gives the collection of all possible moments an evocative name: The Heap.
Because each instant in The Heap is a moment of the entire world, it contains references to all other moments, so the shoebox also contains an implied web of connections, branching threads of mutual association. Following a single thread, one would experience an apparent flow of time. Most threads would follow isolated paths that are without sense or meaning, but a very few threads and their neighbours follow paths that are mutually coherent. We might say that such paths tell a story, or that they include a sensible memory of the past at each step. The family of threads that are mutually coherent is robust, whereas the isolated and incoherent threads are fragile, with brittle associations providing no neighbouring reinforcement... (MORE - missing details)
RELATED (scivillage): Is Time Real? David Eagleman interview.
EXCERPTS (Gene Tracy): . . . The flow of time is certainly one of the most immediate aspects of our waking experience. It is essential to how we see ourselves and to how we think we should live our lives. Our memories help fix who we are; other thoughts reach forward to what we might become. Surely our modern scientific sense of time, as it grows ever more sophisticated, should provide meaningful insights here.
Yet today’s physicists rarely debate what time is and why we experience it the way we do, remembering the past but never the future...
[...] To declare that question outside the pale of physical theory doesn’t make it meaningless. The flow of time could still be real as part of our internal experience, just real in a different way from a proton or a galaxy.
Is our experience of time’s flow akin to watching a live play, where things occur in the moment but not before or after, a flickering in and out of existence around the ‘now’? Or, is it like watching a movie, where all eternity is already in the can, and we are watching a discrete sequence of static image, fooled by our limited perceptual apparatus into thinking the action flows smoothly?
The Newtonian and Einsteinian world theories offer little guidance. They are both eternalised ‘block’ universes, in which time is a dimension not unlike space, so everything exists all at once. Einstein’s equations allow different observers to disagree about the duration of time intervals, but the spacetime continuum itself [...] is an invariant stage upon which the drama of the world takes place.
In quantum mechanics, as in Newton’s mechanics and Einstein’s relativistic theories, the laws of physics that govern the microscopic world look the same going forward or backward in time. Even the innovative speculations of theorists such as Sean Carroll at Caltech in Pasadena – who conceives of time as an emergent phenomenon that arises out of a more primordial, timeless state – concern themselves more with what time does than what time feels like. Time’s flow appears nowhere in current theories of physics.
[...] How did that come to pass? Isn’t science supposed to test itself against the ground of experience? This disconnect might help to explain why so many students not only don’t ‘get’ physics, but are positively repulsed by it. Where are they in the world picture drawn by physicists? Where is life, and where is death? Where is the flow of time?
[...] Current cognitive science says that our memories are a kind of story that our brain creates, formed from the clay of sensory input, sorted into patterns based upon our past life experience, guided by predilections we have inherited in our DNA...
[...] Consider our experience of ‘now’. This seems at first to be a simple thing, a well-defined point in time. We certainly seem to anticipate a particular now coming at us from the future, and then receding from us into the past. Our experience of the ‘now’ is built out of a mix of recent memories and our current sense perceptions, what we see, hear, feel, taste and smell. Those sensory perceptions are not instantaneous, but signals from stimulated nerve endings...
[...] We usually don’t sense this mingling of near past and near future because our brain works quickly enough to obscure the process, but there are moments when it struggles to keep up...
[...] It’s possible that our experience of the flow of time is like our experience of colour. A physicist would say that colour does not exist as an inherent property of the world. Light has a variety of wavelengths, but they have no inherent property of ‘colour’...
[...] So the flow of time might be a story our brain creates, trying to make sense of chaos. In a 2013 paper, the physicists Leonard Mlodinow of Caltech and Todd Brun of the University of Southern California go even further and argue that any physical thing that has the characteristics of a memory will tend to align itself with the thermodynamic arrow of time, which in turn is defined by the behaviour of extremely large numbers of particles.
According to this theory, it is no puzzle that we remember the past but not the future, even though the microscopic laws of nature are the same going forward or backward in time, and the past and future both exist. The nature of large systems is to progress toward increasing entropy – a measure of disorder, commonly experienced as the tendency of hot or cold objects to come into equilibrium with their surroundings. Increasing entropy means that a memory of the past is dynamically stable, whereas a memory of the future is unstable.
In this interpretation, we are unable to see the future not because it is impossible to do so, but because it is as unlikely as seeing a broken window heal itself, or as a tepid cup of tea taking energy from the atoms of the surrounding room and spontaneously beginning to boil. It is statistically extremely, extremely unlikely...
[...] Lee Smolin at the Perimeter Institute in Ontario argues that scientists must change tack, accepting the flow of time as real and building the church of a new physics upon that rock.
The British physicist Julian Barbour takes an opposite stance; going beyond Newton and Einstein, in The End of Time (1999) he proposes that time itself is an illusion. Instead, the Universe consists of a collection of static moments, like a pile of unsorted photographs tossed into a shoebox. Each photo contains a snapshot of the world entire, a unique configuration of all things: planets, galaxies, bumblebees, people. Barbour gives the collection of all possible moments an evocative name: The Heap.
Because each instant in The Heap is a moment of the entire world, it contains references to all other moments, so the shoebox also contains an implied web of connections, branching threads of mutual association. Following a single thread, one would experience an apparent flow of time. Most threads would follow isolated paths that are without sense or meaning, but a very few threads and their neighbours follow paths that are mutually coherent. We might say that such paths tell a story, or that they include a sensible memory of the past at each step. The family of threads that are mutually coherent is robust, whereas the isolated and incoherent threads are fragile, with brittle associations providing no neighbouring reinforcement... (MORE - missing details)
RELATED (scivillage): Is Time Real? David Eagleman interview.
