Apr 21, 2021 07:46 AM
(This post was last modified: Apr 21, 2021 05:35 PM by C C.)
One idea to explain dark matter – ultralight bosons – fails the test
https://www.jioforme.com/one-idea-to-exp...st/359035/
INTRO: Dark matter continues to resist our best efforts to pin it down. While dark matter remains a dominant theory of cosmology, and there is lots of evidence to support a universe filled with cold dark matter, every search for dark matter particles yields nothing. A new study continues that tradition, ruling out a range of dark matter candidates... (MORE)
The many faces of liquid gallium
https://physicstoday.scitation.org/do/10...420a/full/
INTRO: The periodic table hosts five metals that are liquid near room temperature. Although all are good conductors, working with them can be problematic. Francium is radioactive and has a half-life of just 22 minutes; rubidium and cesium are exceptionally reactive and prone to exploding or catching fire; and the most well-known, mercury, is famously toxic. That leaves just one liquid metal, gallium, for safe experimentation.
On page 30 of Physics Today’s April 2021 issue, Michael Dickey of North Carolina State University notes that Ga’s propensity to form a surface oxide layer when exposed to oxygen has largely impeded its practical application. The layer prevents Ga from flowing freely and impedes electrochemical reactions. But as he goes on to explain, that layer can be viewed as an asset. Rather than thinking of Ga as a substitute for Hg, he and his research group have explored Ga’s inherent benefits. The videos below highlight just a few of their experimental discoveries... (MORE - details, videos)
'Brazil nut puzzle' cracked by researchers
https://www.livescience.com/brazil-nut-p...acked.html
EXCERPTS: One of physics' nuttiest problems has been cracked (for Brazil nuts, anyway): granular convection. [...] The secret, they say, is in the larger nuts' orientation. "Critically, the orientation of the Brazil nut is key to its upward movement," lead study author Parmesh Gajjar ... "The Brazil nuts initially start horizontal but do not start to rise until they have first rotated sufficiently towards the vertical axis." Smaller nuts jostle against the sides of bigger ones, making it increasingly likely that the big ones will turn.
Once the Brazil nuts point upward — after about 50 packet shakes, according to the study — more space is freed for smaller nuts to fall down their sides with successive shakes. The subsequent downward flow of smaller nuts forces the bigger ones up. So, by the time a typical packet of mixed nuts arrives on grocery store shelves, it has been jostled enough to have all of its bigger contents right at the top.
The finding has applications beyond nuts, though. The results could prove helpful in a wide range of industries... (MORE - details)
The many worlds fantasy
https://iai.tv/articles/the-many-worlds-...-auid-1793
EXCERPTS: . . . Quantum mechanics doesn’t itself have any prescription for the “collapse of the wave function” – it has to be added by hand in an ad hoc fashion, as first done by the Hungarian mathematical physicist John von Neumann in the 1930s. That’s awkward and unsatisfactory – sure, the maths works okay, but we’re none the wiser about what actually happens in the real world to convert smooth quantum probability waves into unique observations. The Many Worlds interpretation was proposed by Hugh Everett in his doctoral dissertation at Princeton in 1957 as a way to avoid this problem. What if, Everett said, there simply is no wave function collapse that selects one possible outcome from all the possibilities? What if, instead, they all occur – but in alternative realities? In this view, as the photon reaches the double slits, it passes through one slit in one universe and the other slit in the other.
[...] That the MWI advertises itself as an antidote to the sleight-of-hand of wave function collapse is a red herring too. For the whole concept is now redundant: a careful consideration of what happens when we make a measurement on a quantum system reveals that “collapse” is no longer a useful concept. There is now, in contrast, a fairly good picture of how the possibilities inherent in a quantum system gradually tip one way or another through the interactions with its environment that ultimately cause decoherence and give rise to definite, classical outcomes. Many Worlders seem keen to cling to this obsolete straw man of collapse, but quantum physics is moving on. That’s not to say we can explain all of its puzzles – but it now seems unlikely that the intriguing, inventive and bold suggestion of proliferating universes will help very much. It’s time to take another road... (MORE - details)
https://www.jioforme.com/one-idea-to-exp...st/359035/
INTRO: Dark matter continues to resist our best efforts to pin it down. While dark matter remains a dominant theory of cosmology, and there is lots of evidence to support a universe filled with cold dark matter, every search for dark matter particles yields nothing. A new study continues that tradition, ruling out a range of dark matter candidates... (MORE)
The many faces of liquid gallium
https://physicstoday.scitation.org/do/10...420a/full/
INTRO: The periodic table hosts five metals that are liquid near room temperature. Although all are good conductors, working with them can be problematic. Francium is radioactive and has a half-life of just 22 minutes; rubidium and cesium are exceptionally reactive and prone to exploding or catching fire; and the most well-known, mercury, is famously toxic. That leaves just one liquid metal, gallium, for safe experimentation.
On page 30 of Physics Today’s April 2021 issue, Michael Dickey of North Carolina State University notes that Ga’s propensity to form a surface oxide layer when exposed to oxygen has largely impeded its practical application. The layer prevents Ga from flowing freely and impedes electrochemical reactions. But as he goes on to explain, that layer can be viewed as an asset. Rather than thinking of Ga as a substitute for Hg, he and his research group have explored Ga’s inherent benefits. The videos below highlight just a few of their experimental discoveries... (MORE - details, videos)
'Brazil nut puzzle' cracked by researchers
https://www.livescience.com/brazil-nut-p...acked.html
EXCERPTS: One of physics' nuttiest problems has been cracked (for Brazil nuts, anyway): granular convection. [...] The secret, they say, is in the larger nuts' orientation. "Critically, the orientation of the Brazil nut is key to its upward movement," lead study author Parmesh Gajjar ... "The Brazil nuts initially start horizontal but do not start to rise until they have first rotated sufficiently towards the vertical axis." Smaller nuts jostle against the sides of bigger ones, making it increasingly likely that the big ones will turn.
Once the Brazil nuts point upward — after about 50 packet shakes, according to the study — more space is freed for smaller nuts to fall down their sides with successive shakes. The subsequent downward flow of smaller nuts forces the bigger ones up. So, by the time a typical packet of mixed nuts arrives on grocery store shelves, it has been jostled enough to have all of its bigger contents right at the top.
The finding has applications beyond nuts, though. The results could prove helpful in a wide range of industries... (MORE - details)
The many worlds fantasy
https://iai.tv/articles/the-many-worlds-...-auid-1793
EXCERPTS: . . . Quantum mechanics doesn’t itself have any prescription for the “collapse of the wave function” – it has to be added by hand in an ad hoc fashion, as first done by the Hungarian mathematical physicist John von Neumann in the 1930s. That’s awkward and unsatisfactory – sure, the maths works okay, but we’re none the wiser about what actually happens in the real world to convert smooth quantum probability waves into unique observations. The Many Worlds interpretation was proposed by Hugh Everett in his doctoral dissertation at Princeton in 1957 as a way to avoid this problem. What if, Everett said, there simply is no wave function collapse that selects one possible outcome from all the possibilities? What if, instead, they all occur – but in alternative realities? In this view, as the photon reaches the double slits, it passes through one slit in one universe and the other slit in the other.
[...] That the MWI advertises itself as an antidote to the sleight-of-hand of wave function collapse is a red herring too. For the whole concept is now redundant: a careful consideration of what happens when we make a measurement on a quantum system reveals that “collapse” is no longer a useful concept. There is now, in contrast, a fairly good picture of how the possibilities inherent in a quantum system gradually tip one way or another through the interactions with its environment that ultimately cause decoherence and give rise to definite, classical outcomes. Many Worlders seem keen to cling to this obsolete straw man of collapse, but quantum physics is moving on. That’s not to say we can explain all of its puzzles – but it now seems unlikely that the intriguing, inventive and bold suggestion of proliferating universes will help very much. It’s time to take another road... (MORE - details)