Jan 29, 2023 03:12 AM
(This post was last modified: Jan 29, 2023 03:14 AM by C C.)
How Quantum Physicists ‘Flipped Time’ (and How They Didn’t)
https://www.quantamagazine.org/how-quant...-20230127/
EXCERPT: . . . In a paper published in 2013, Giulio Chiribella, a physicist now at the University of Hong Kong, and co-authors proposed a circuit that would put events into a superposition of temporal orders, going a step beyond the superposition of locations in space. Four years later, Rubino and her colleagues directly experimentally demonstrated the idea. They sent a photon down a superposition of two paths: one in which it experienced event A and then event B, and another where it experienced B then A. In some sense, each event seemed to cause the other, a phenomenon that came to be called indefinite causality.
Not content to mess merely with the order of events while time marched onward, Chiribella and a colleague, Zixuan Liu, next took aim at the marching direction, or arrow, of time itself. They sought a quantum apparatus in which time entered a superposition of flowing from the past to the future and vice versa — an indefinite arrow of time.
[...] Whatever their philosophical inclinations, physicists hope that the ability to design quantum circuits that flow two ways at once might enable new devices for quantum computing, communication and metrology... (MORE - missing details)
String theory was supposed to explain all of physics. What went wrong?
https://arstechnica.com/science/2023/01/...verything/
EXCERPTS: String theory began over 50 years ago as a way to understand the strong nuclear force. Since then, it’s grown to become a theory of everything, capable of explaining the nature of every particle, every force, every fundamental constant, and the existence of the Universe itself. But despite decades of work, it has failed to deliver on its promise.
What went wrong, and where do we go from here?
[....] It’s been almost half a century since physicists first realized that string theory could potentially provide a theory of everything. Despite decades of work involving hundreds of scientists over several (academic) generations and countless papers, conferences, and workshops, string theory hasn't quite lived up to that potential.
One of the biggest issues involves the way that strings interact with each other. A major pain in the asymptote when it comes to quantum theory is the infinite variety of ways that particles can interact. It’s easy enough to write down the fundamental governing equations that describe an interaction, but the math tends to blow up when we actually try to use it...
[...] The earliest versions of string theory needed 26 spatial dimensions, but after supersymmetry and some dimensional layoffs, theorists were able to slim that number down to “only” 10...
Now, the Universe doesn’t have 10 spatial dimensions, at least on large scales, because we would have noticed them by now. So all the extra dimensions have to be tiny and curled up on themselves. When you wave your arm in front of you, you’re traversing these tiny dimensions countless times, but they’re so small (typically at the Planck scale) that you don’t notice them.
The extra dimensions give the strings enough vibrational options to explain all of physics...
[...] It gets worse. By the early 1990s, string theorists had developed not one, not two, but five different versions of string theory. The variations were based on how a fundamental string was treated...
[...] After 50 years of work on a theory of everything, we’re left with approximate theories that seem so tantalizingly close to explaining all of physics… and yet always out of reach... We don’t have a string theory, so we can’t test it. But it might be possible to perform experiments on string theory-adjacent ideas, and there’s been some progress on that front... (MORE - missing details)
https://www.quantamagazine.org/how-quant...-20230127/
EXCERPT: . . . In a paper published in 2013, Giulio Chiribella, a physicist now at the University of Hong Kong, and co-authors proposed a circuit that would put events into a superposition of temporal orders, going a step beyond the superposition of locations in space. Four years later, Rubino and her colleagues directly experimentally demonstrated the idea. They sent a photon down a superposition of two paths: one in which it experienced event A and then event B, and another where it experienced B then A. In some sense, each event seemed to cause the other, a phenomenon that came to be called indefinite causality.
Not content to mess merely with the order of events while time marched onward, Chiribella and a colleague, Zixuan Liu, next took aim at the marching direction, or arrow, of time itself. They sought a quantum apparatus in which time entered a superposition of flowing from the past to the future and vice versa — an indefinite arrow of time.
[...] Whatever their philosophical inclinations, physicists hope that the ability to design quantum circuits that flow two ways at once might enable new devices for quantum computing, communication and metrology... (MORE - missing details)
String theory was supposed to explain all of physics. What went wrong?
https://arstechnica.com/science/2023/01/...verything/
EXCERPTS: String theory began over 50 years ago as a way to understand the strong nuclear force. Since then, it’s grown to become a theory of everything, capable of explaining the nature of every particle, every force, every fundamental constant, and the existence of the Universe itself. But despite decades of work, it has failed to deliver on its promise.
What went wrong, and where do we go from here?
[....] It’s been almost half a century since physicists first realized that string theory could potentially provide a theory of everything. Despite decades of work involving hundreds of scientists over several (academic) generations and countless papers, conferences, and workshops, string theory hasn't quite lived up to that potential.
One of the biggest issues involves the way that strings interact with each other. A major pain in the asymptote when it comes to quantum theory is the infinite variety of ways that particles can interact. It’s easy enough to write down the fundamental governing equations that describe an interaction, but the math tends to blow up when we actually try to use it...
[...] The earliest versions of string theory needed 26 spatial dimensions, but after supersymmetry and some dimensional layoffs, theorists were able to slim that number down to “only” 10...
Now, the Universe doesn’t have 10 spatial dimensions, at least on large scales, because we would have noticed them by now. So all the extra dimensions have to be tiny and curled up on themselves. When you wave your arm in front of you, you’re traversing these tiny dimensions countless times, but they’re so small (typically at the Planck scale) that you don’t notice them.
The extra dimensions give the strings enough vibrational options to explain all of physics...
[...] It gets worse. By the early 1990s, string theorists had developed not one, not two, but five different versions of string theory. The variations were based on how a fundamental string was treated...
[...] After 50 years of work on a theory of everything, we’re left with approximate theories that seem so tantalizingly close to explaining all of physics… and yet always out of reach... We don’t have a string theory, so we can’t test it. But it might be possible to perform experiments on string theory-adjacent ideas, and there’s been some progress on that front... (MORE - missing details)