Dec 10, 2024 07:30 PM
https://aeon.co/essays/scientists-are-no...ith-a-bang
EXCERPTS: . . . The 20th century changed everything. Lemaître’s hypothesis, initially met with scepticism, suggested that the Universe had a fiery origin – one that might be discoverable. Today, many of us still believe this story. [...] The question of our Universe’s birth seems settled. And yet, despite how the Big Bang is portrayed in popular culture, many physicists and philosophers of physics have long doubted whether science can truly tell us that time began. In recent decades, powerful results developed by scientifically minded philosophers appear to show that science may never show us that time began. The beginning of time, once imagined as igniting in a sudden burst of fireworks, is no longer an indisputable scientific fact.
[...] In the three years after Einstein proposed special relativity, the German physicist and mathematician Hermann Minkowski began to realise that the theory did more than simply reveal the interdependence of space and time. Instead, Minkowski showed that Einstein had mathematically woven time and space into a previously unimaginable four-dimensional object: spacetime. With this new understanding, the pieces were falling into place for an entirely new view of the Universe’s birth.
Though we perceive the world as three-dimensional, Minkowski showed that special relativity makes more sense when the world is understood as four-dimensional. Different people can have differing perspectives of the same object, like a house, which can be unified into one three-dimensional description of height, length and width.
Similarly, in four-dimensional spacetime, observers experience varying perceptions of simultaneity, length and duration that can be integrated into a unified structure. Four-dimensional spacetime consolidates all reference frames – based on the measurements of rulers and clocks – into a single, unified structure that is independent of any single frame of reference.
This is the profound insight Minkowski garnered from Einstein’s special relativity. But though special relativity deepened our understanding of the Universe, it could not address the beginning of time on its own. A new theory of gravity was needed.
[...] Through general relativity, moments and their contents become fully intertwined.
According to Einstein’s new theory, spacetime affects matter, and matter affects spacetime. Just as an otherwise invisible magnetic field can be revealed by sprinkling iron filings around a magnet, the structure of spacetime can be revealed by observing how matter moves through spacetime. This insight suggested that physics might, at last, tell us something about the beginning of time.
[...] This means that matter and spacetime are intertwined. And, given this intertwining, moments of time can be distinguished by their contents: each moment, then, is unique due to its special configuration of matter and energy. And by tracking changes in the configuration of matter and energy – by tracking changes in the curvature of spacetime – perhaps some moment could be distinguished as a moment of creation? The Universe, then, might subsequently include a record of its own birth.
Einstein completed general relativity in 1916, ushering in an entirely new way of thinking about time. By the 1920s, the beginning of time stopped being a question reserved only for theologians or philosophers. The origin of the Universe now appeared to be a question with scientific answers.
[...] As the 20th century progressed, questions began to emerge about the Big Bang. Was it truly the Universe’s origin? The observable Universe may once have expanded from a hot, dense state, but that doesn’t necessarily mean the entire Universe did so, or that there was nothing before the hot, dense state.
[...] three physicists – Arvind Borde, Alan Guth and Alexander Vilenkin – showed that any path along which spacetime is expanding (on average) cannot extend infinitely into the past...
[...] According to these results, no region of the Universe could have been expanding forever, but perhaps it was doing something else before it began to expand? Recently, the mathematics of Borde, Guth and Vilenkin has been challenged by Joseph Lesnefsky, Damien Easson and Paul Davies. In their view, once we do the mathematics properly, we can see that the Universe could have been expanding forever.
In recent decades, more physicists have started to think that the ‘cataclysm’ will be replaced with something else in a future theory. And even more radical arguments are now emerging that question our established ideas about the Big Bang – ideas that have been missed in popular accounts of the Universe. These arguments address spacetime’s global structure, and they strongly suggest that no theorem and no amount of data will ever allow us to know whether spacetime originated in some past cataclysm.
[...] Can an observer determine the overall properties of spacetime only from data available within their own past light cone? The question hinges on whether there is a single point from which all of spacetime can be seen.
In 1977, the philosopher David Malament argued that, without an all-seeing point, no observer could fully determine the global structure of their spacetime. Only from an all-seeing point could enough information be gathered to definitively know whether the Universe has a wide variety of global properties, including an origin.
In 2009, the philosopher J B Manchak demonstrated that Malament was right. Building on Malament’s proposal, Manchak showed that it is impossible to determine the overall structure of any spacetime without an all-seeing point. From any specific point within a spacetime, observers can never be certain of the global nature of their spacetime. Furthermore, all observations fit multiple possibilities – the data you have gathered from your specific past light cone can be explained by several different, even mutually exclusive, models of spacetime....
[...] So, should we expect the unobserved parts of the Universe to behave like the parts we have observed, and could that help us infer our Universe’s global properties? To make such a projection, we need a lawlike pattern. However, most lawlike patterns are defined solely by local properties. Manchak has shown that no lawlike pattern based solely on local properties would help us to determine our spacetime’s global characteristics.
What about lawlike patterns that are not written in terms of local properties? The only known non-local lawlike patterns involve quantum entanglement – strange correlations in measured properties between widely separated particles. To determine whether two particles are entangled, we need to bring measured results together at a single point. However, this can’t happen faster than light, which means we can’t directly measure instantaneous changes taking place between the particles: we have no way of really knowing whether a particle in a terrestrial laboratory is entangled with one on the other side of the Universe. Quantum entanglement cannot help us discover spacetime’s global properties either. The problem remains: as the Malament-Manchek theorem suggests, spacetime’s global features remain unknowable.
This theorem has been well received by philosophers of physics during the past decade. It is often cited, but seldom rejected. Most philosophers of physics now think the matter has been settled: no amount of data can sufficiently determine spacetime’s global properties. It is likely that there are no theorems strong enough to determine whether our Universe began in a past cataclysm. The Malament-Manchak theorem shows that we can’t know how time began – or even if it began.
[...] In the end, whether time had a beginning is a cosmological riddle. Despite dramatic scientific developments, no theorem or observation seems powerful enough to tell us whether the Universe emerged from ‘bright but very rapid fireworks’ or has always existed... (MORE - missing details)
EXCERPTS: . . . The 20th century changed everything. Lemaître’s hypothesis, initially met with scepticism, suggested that the Universe had a fiery origin – one that might be discoverable. Today, many of us still believe this story. [...] The question of our Universe’s birth seems settled. And yet, despite how the Big Bang is portrayed in popular culture, many physicists and philosophers of physics have long doubted whether science can truly tell us that time began. In recent decades, powerful results developed by scientifically minded philosophers appear to show that science may never show us that time began. The beginning of time, once imagined as igniting in a sudden burst of fireworks, is no longer an indisputable scientific fact.
[...] In the three years after Einstein proposed special relativity, the German physicist and mathematician Hermann Minkowski began to realise that the theory did more than simply reveal the interdependence of space and time. Instead, Minkowski showed that Einstein had mathematically woven time and space into a previously unimaginable four-dimensional object: spacetime. With this new understanding, the pieces were falling into place for an entirely new view of the Universe’s birth.
Though we perceive the world as three-dimensional, Minkowski showed that special relativity makes more sense when the world is understood as four-dimensional. Different people can have differing perspectives of the same object, like a house, which can be unified into one three-dimensional description of height, length and width.
Similarly, in four-dimensional spacetime, observers experience varying perceptions of simultaneity, length and duration that can be integrated into a unified structure. Four-dimensional spacetime consolidates all reference frames – based on the measurements of rulers and clocks – into a single, unified structure that is independent of any single frame of reference.
This is the profound insight Minkowski garnered from Einstein’s special relativity. But though special relativity deepened our understanding of the Universe, it could not address the beginning of time on its own. A new theory of gravity was needed.
[...] Through general relativity, moments and their contents become fully intertwined.
According to Einstein’s new theory, spacetime affects matter, and matter affects spacetime. Just as an otherwise invisible magnetic field can be revealed by sprinkling iron filings around a magnet, the structure of spacetime can be revealed by observing how matter moves through spacetime. This insight suggested that physics might, at last, tell us something about the beginning of time.
[...] This means that matter and spacetime are intertwined. And, given this intertwining, moments of time can be distinguished by their contents: each moment, then, is unique due to its special configuration of matter and energy. And by tracking changes in the configuration of matter and energy – by tracking changes in the curvature of spacetime – perhaps some moment could be distinguished as a moment of creation? The Universe, then, might subsequently include a record of its own birth.
Einstein completed general relativity in 1916, ushering in an entirely new way of thinking about time. By the 1920s, the beginning of time stopped being a question reserved only for theologians or philosophers. The origin of the Universe now appeared to be a question with scientific answers.
[...] As the 20th century progressed, questions began to emerge about the Big Bang. Was it truly the Universe’s origin? The observable Universe may once have expanded from a hot, dense state, but that doesn’t necessarily mean the entire Universe did so, or that there was nothing before the hot, dense state.
[...] three physicists – Arvind Borde, Alan Guth and Alexander Vilenkin – showed that any path along which spacetime is expanding (on average) cannot extend infinitely into the past...
[...] According to these results, no region of the Universe could have been expanding forever, but perhaps it was doing something else before it began to expand? Recently, the mathematics of Borde, Guth and Vilenkin has been challenged by Joseph Lesnefsky, Damien Easson and Paul Davies. In their view, once we do the mathematics properly, we can see that the Universe could have been expanding forever.
In recent decades, more physicists have started to think that the ‘cataclysm’ will be replaced with something else in a future theory. And even more radical arguments are now emerging that question our established ideas about the Big Bang – ideas that have been missed in popular accounts of the Universe. These arguments address spacetime’s global structure, and they strongly suggest that no theorem and no amount of data will ever allow us to know whether spacetime originated in some past cataclysm.
[...] Can an observer determine the overall properties of spacetime only from data available within their own past light cone? The question hinges on whether there is a single point from which all of spacetime can be seen.
In 1977, the philosopher David Malament argued that, without an all-seeing point, no observer could fully determine the global structure of their spacetime. Only from an all-seeing point could enough information be gathered to definitively know whether the Universe has a wide variety of global properties, including an origin.
In 2009, the philosopher J B Manchak demonstrated that Malament was right. Building on Malament’s proposal, Manchak showed that it is impossible to determine the overall structure of any spacetime without an all-seeing point. From any specific point within a spacetime, observers can never be certain of the global nature of their spacetime. Furthermore, all observations fit multiple possibilities – the data you have gathered from your specific past light cone can be explained by several different, even mutually exclusive, models of spacetime....
[...] So, should we expect the unobserved parts of the Universe to behave like the parts we have observed, and could that help us infer our Universe’s global properties? To make such a projection, we need a lawlike pattern. However, most lawlike patterns are defined solely by local properties. Manchak has shown that no lawlike pattern based solely on local properties would help us to determine our spacetime’s global characteristics.
What about lawlike patterns that are not written in terms of local properties? The only known non-local lawlike patterns involve quantum entanglement – strange correlations in measured properties between widely separated particles. To determine whether two particles are entangled, we need to bring measured results together at a single point. However, this can’t happen faster than light, which means we can’t directly measure instantaneous changes taking place between the particles: we have no way of really knowing whether a particle in a terrestrial laboratory is entangled with one on the other side of the Universe. Quantum entanglement cannot help us discover spacetime’s global properties either. The problem remains: as the Malament-Manchek theorem suggests, spacetime’s global features remain unknowable.
This theorem has been well received by philosophers of physics during the past decade. It is often cited, but seldom rejected. Most philosophers of physics now think the matter has been settled: no amount of data can sufficiently determine spacetime’s global properties. It is likely that there are no theorems strong enough to determine whether our Universe began in a past cataclysm. The Malament-Manchak theorem shows that we can’t know how time began – or even if it began.
[...] In the end, whether time had a beginning is a cosmological riddle. Despite dramatic scientific developments, no theorem or observation seems powerful enough to tell us whether the Universe emerged from ‘bright but very rapid fireworks’ or has always existed... (MORE - missing details)