Jan 29, 2020 07:02 PM
(This post was last modified: Jan 29, 2020 07:20 PM by C C.)
Fine-tuning versus naturalness
https://www.symmetrymagazine.org/article...aturalness
EXCERPT: When physicists saw the Higgs boson for the first time in 2012, they observed its mass to be very small [...] The measurement became a prime example of an issue that dogs particle physicists and astrophysicists today: the problem of fine-tuning versus naturalness. ... To understand what’s fishy about the observable Higgs mass being so low, first you must know that it is actually the sum of two inputs [...see article for details...] many particle physicists aren’t comfortable with this situation. There’s no known underlying reason for these almost exact cancellations, and insisting that “it is the way it is” is unsatisfying.
Observable parameters that don’t seem to naturally emerge from a theory, but instead must be deliberately manipulated to fit, are called “finely tuned.” [...] The opposite of fine-tuning is naturalness. “It’s sort of two sides of the same coin,” says theorist Stefania Gori ... “We say a theory is natural when you can write down this theory with parameters that are all basically of the same order.”
So how much fine-tuning should we allow in our theories? “This is one of the fundamental debates that may decide the future of particle physics,” says experimentalist Lawrence Lee Jr. ... [...] “From an experimental point of view, the fine-tuning problem is really useful in a sense of guiding what we should investigate,” says Joseph Haley ... Sometimes, he explains, a parameter may appear to be fine-tuned (like the Higgs mass) until experiments reveal a hidden, underlying issue—some additional piece of the equation we didn’t know about before. “Once we have a more complete theory, it’s like, ‘Oh, it had to be that value all along, it just wasn't clear why.’”
Lee, also an experimentalist, says his research is strongly motivated by the fine-tuning problem. “In general, what we want from our theories—and in some way, our universe—is that nothing seems too contrived,” he says. However, not all physicists see situations that are described as fine-tuning as a problem. For them, there doesn’t need to be a reason that, say, two parameters have nearly equal, opposite values that result in a cancellation. After all, coincidences happen.
[...] Other physicists say it would be nice to get rid of apparent fine-tuning, but doing so isn’t necessarily the main drive in their research... (MORE - details)
You might feel like time's flying, but dinosaurs had 23-hour days
https://www.abc.net.au/news/science/2020...s/11886448
EXCERPT: The length of an Earth day has been increasing slowly throughout most of the Earth's 4.5-billion-year history, says Rosemary Mardling, an astrophysicist at Monash University, and it all has to do with the Moon. [...] Back when the Moon was formed, the length of an Earth day was a very brief two to three hours, and a much closer Moon was orbiting the Earth every five hours.
So how did the Moon slow us down? It has to do with gravitational force and the transfer of angular momentum. "If someone was sitting on a chair that could spin and you tried to slow them down with your hand, they would slow down a little bit and you'd be flipped around a bit. You'd get some angular momentum." [...] Much like the hand interrupting the spinning chair, the gravitational pull of the Moon exerts a force on the Earth that transfers angular momentum from the spin of the Earth into the orbit of the Moon.
"In doing so, the Earth slows down a little bit and the Moon moves away from the Earth," says Dr Mardling. We can measure the speed of the Moon's retreat — reflective panels on the Moon allow for fine calibrations that show that it's currently moving away one to two centimetres a year. We also know that the spin of the Earth is slowing. "The spin down rate is very slow," says Dr Mardling, "It's about two milliseconds per century."
[...] Since the dinosaurs lived during the Mesozoic era, from 250 million years ago to 65 million years ago, day length would have been longer than this — probably closer to 23 hours. At that time, the Moon would have been closer to the Earth too. [...] The Moon and Earth's celestial dance will take billions of years to end. "This process finishes when the length of the day is the same as the length of the [lunar] month," says Dr Mardling, who once worked this out to be around 45 (current Earth) days. This means that the Moon will take 45 days to orbit the Earth and the Earth will take 45 days to complete a rotation that currently takes 24 hours... (MORE - details)
https://www.symmetrymagazine.org/article...aturalness
EXCERPT: When physicists saw the Higgs boson for the first time in 2012, they observed its mass to be very small [...] The measurement became a prime example of an issue that dogs particle physicists and astrophysicists today: the problem of fine-tuning versus naturalness. ... To understand what’s fishy about the observable Higgs mass being so low, first you must know that it is actually the sum of two inputs [...see article for details...] many particle physicists aren’t comfortable with this situation. There’s no known underlying reason for these almost exact cancellations, and insisting that “it is the way it is” is unsatisfying.
Observable parameters that don’t seem to naturally emerge from a theory, but instead must be deliberately manipulated to fit, are called “finely tuned.” [...] The opposite of fine-tuning is naturalness. “It’s sort of two sides of the same coin,” says theorist Stefania Gori ... “We say a theory is natural when you can write down this theory with parameters that are all basically of the same order.”
So how much fine-tuning should we allow in our theories? “This is one of the fundamental debates that may decide the future of particle physics,” says experimentalist Lawrence Lee Jr. ... [...] “From an experimental point of view, the fine-tuning problem is really useful in a sense of guiding what we should investigate,” says Joseph Haley ... Sometimes, he explains, a parameter may appear to be fine-tuned (like the Higgs mass) until experiments reveal a hidden, underlying issue—some additional piece of the equation we didn’t know about before. “Once we have a more complete theory, it’s like, ‘Oh, it had to be that value all along, it just wasn't clear why.’”
Lee, also an experimentalist, says his research is strongly motivated by the fine-tuning problem. “In general, what we want from our theories—and in some way, our universe—is that nothing seems too contrived,” he says. However, not all physicists see situations that are described as fine-tuning as a problem. For them, there doesn’t need to be a reason that, say, two parameters have nearly equal, opposite values that result in a cancellation. After all, coincidences happen.
[...] Other physicists say it would be nice to get rid of apparent fine-tuning, but doing so isn’t necessarily the main drive in their research... (MORE - details)
You might feel like time's flying, but dinosaurs had 23-hour days
https://www.abc.net.au/news/science/2020...s/11886448
EXCERPT: The length of an Earth day has been increasing slowly throughout most of the Earth's 4.5-billion-year history, says Rosemary Mardling, an astrophysicist at Monash University, and it all has to do with the Moon. [...] Back when the Moon was formed, the length of an Earth day was a very brief two to three hours, and a much closer Moon was orbiting the Earth every five hours.
So how did the Moon slow us down? It has to do with gravitational force and the transfer of angular momentum. "If someone was sitting on a chair that could spin and you tried to slow them down with your hand, they would slow down a little bit and you'd be flipped around a bit. You'd get some angular momentum." [...] Much like the hand interrupting the spinning chair, the gravitational pull of the Moon exerts a force on the Earth that transfers angular momentum from the spin of the Earth into the orbit of the Moon.
"In doing so, the Earth slows down a little bit and the Moon moves away from the Earth," says Dr Mardling. We can measure the speed of the Moon's retreat — reflective panels on the Moon allow for fine calibrations that show that it's currently moving away one to two centimetres a year. We also know that the spin of the Earth is slowing. "The spin down rate is very slow," says Dr Mardling, "It's about two milliseconds per century."
[...] Since the dinosaurs lived during the Mesozoic era, from 250 million years ago to 65 million years ago, day length would have been longer than this — probably closer to 23 hours. At that time, the Moon would have been closer to the Earth too. [...] The Moon and Earth's celestial dance will take billions of years to end. "This process finishes when the length of the day is the same as the length of the [lunar] month," says Dr Mardling, who once worked this out to be around 45 (current Earth) days. This means that the Moon will take 45 days to orbit the Earth and the Earth will take 45 days to complete a rotation that currently takes 24 hours... (MORE - details)