That's an article worth reading. We have frequently discussed MOND versus dark matter on this and other threads.
We are told in the article that the Cassini probe allowed us to precisely track Saturn’s orbit, but found no anomaly of the kind predicted by MOND.
The article concludes: "MOND, as presently formulated, cannot be considered a viable alternative to dark matter any more".
However, we are reminded that the standard dark matter model of cosmology isn’t perfect - there are things it struggles to explain, from the universe’s expansion rate to giant cosmic structures.
As the man in the KCRA 3 video said, now is a good time to familiarise yourself with the nearby stars to Corona Borealis.
This is a widefield and slightly distorted view of the sky around the constellation taken in the UK:
At the top is the pole star, Polaris, always due North and as high as your latitude in degrees in the Northern Hemisphere.
To its right is Ursa Major, aka The Big Bear, The Big Dipper or the Plough:
I mentioned earlier that you can follow the handle of The Big Dipper (which is almost overhead ATM) round to Arcturus, which has risen in the East at sunset currently. Vega is rising too at sunset, and is to the left of Arcturus in the UK.
Corona Borealis is 2/3 of the way toward Arcturus from Vega, and Alpha and the crescent shape is easy to see in a clear sky. A recent long exposure photo looking South-East in early evening.
Best, Steve.
MOND has been thoroughly rejected as as explanation for dark matter. WIMPs are still limping along but a research group is still in place (I think you posted a photo of them about a year ago Galu).
Sean Carrol makes the point that where gravity is strong, you don’t need dark matter to explain how ordinary matter behaves, but only in regions where gravity is weak (but not too weak). So dark matter is associated with ordinary matter as if there is an additional component that couples to matter or gravity.
Very nice PBS video explaining how the source of gravity is the warpage of time around an object. Interestingly, Matt Dowd references two other videos explaining gravity in a similar way.
https://www.pbs.org/video/how-does-gravity-affect-light-zx47ji/?continuousplayautoplay=true
One of the videos referenced was discussed on phys.org and rejected as an explanation. I suspect the respondent (a physicist) believes it’s a particle based explanation. Matt Dowd says Einstein did not need quantum mechanics to explain gravity, but what does need to be explained is the precise mechanism that causes time to dilate in that case. Einstein’s field equations explain the behaviour of matter and light in a gravity field with great precision, but like Maxwell’s EM through a vacuum, not the deep underlying mechanism. It seems strange that in the case of gravity, particle physicists are looking for a graviton, while relativists are looking at time as the first step to an underlying theory. Until we get an understanding of the deep underlying mechanisms of both of these phenomena, my guess is a cogent explanation for both DE and DM will elude us.
https://www.pbs.org/video/how-does-gravity-affect-light-zx47ji/?continuousplayautoplay=true
One of the videos referenced was discussed on phys.org and rejected as an explanation. I suspect the respondent (a physicist) believes it’s a particle based explanation. Matt Dowd says Einstein did not need quantum mechanics to explain gravity, but what does need to be explained is the precise mechanism that causes time to dilate in that case. Einstein’s field equations explain the behaviour of matter and light in a gravity field with great precision, but like Maxwell’s EM through a vacuum, not the deep underlying mechanism. It seems strange that in the case of gravity, particle physicists are looking for a graviton, while relativists are looking at time as the first step to an underlying theory. Until we get an understanding of the deep underlying mechanisms of both of these phenomena, my guess is a cogent explanation for both DE and DM will elude us.
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I shall watch that video today. I like PBS programmes in general on Sky TV, but they are mostly not available outside the US for everyone AFAIK.
This is a huge series on SpaceTime from Matt O'Dowd on YouTube:
https://www.youtube.com/@pbsspacetime/videos
Here Ad-free and directly linked:
This one looks up our street too, as a commenter at YouTube mentions. Surely a child of ten at diyaudio.com knows what a DFT is?
My own notion is that time flows at a rate for a particle determined by its absolute gravitational potential and its velocity. It would be interesting to draw some of the possible potential wells for Black Holes and the Earth relative to radius.
We shall see.
This is a huge series on SpaceTime from Matt O'Dowd on YouTube:
https://www.youtube.com/@pbsspacetime/videos
Here Ad-free and directly linked:
This one looks up our street too, as a commenter at YouTube mentions. Surely a child of ten at diyaudio.com knows what a DFT is?
My own notion is that time flows at a rate for a particle determined by its absolute gravitational potential and its velocity. It would be interesting to draw some of the possible potential wells for Black Holes and the Earth relative to radius.
We shall see.
For the record, that should read, "MOND has been thoroughly rejected as an alternative to the standard dark matter model of cosmology".
I believe you are referring to the DARWIN Project: https://darwin.physik.uzh.ch/
DARWIN is a proposed dark matter WIMP detector employing a massive underground vat of supercooled Xenon.
'For the record, that should read, "MOND has been thoroughly rejected as an alternative to the standard dark matter model of cosmology".'
Correct Galu! I was just testing you there and you've passed with flying colours
I like Matt O'Dowd's stuff. I found the PBS video online after reading some stuff on phys.org re time dilation - so I think you will get some of the PBS shows just by searching. He does go down the rabbit hole on string theory and QM when he discusses it - but then again who doesn't
Correct Galu! I was just testing you there and you've passed with flying colours
I like Matt O'Dowd's stuff. I found the PBS video online after reading some stuff on phys.org re time dilation - so I think you will get some of the PBS shows just by searching. He does go down the rabbit hole on string theory and QM when he discusses it - but then again who doesn't
There are number of gravitation TD calculators on the web that use the standard dt' = dt*sqrt[(1-(2*m*G)/(r*c^2)] equation. For the Milky Way, the TD from the centre to the periphery (50k LY) comes out at ~9.4us. I used a mass of 6^43 kg.
Thanks to a team at the University of Oxford, Einstein has been proved correct regarding a key prediction about black holes.
Einstein’s theory predicts that sufficiently close to a black hole it is impossible for particles to safely follow circular orbits, instead they rapidly plunge toward the black hole at close to the speed of light.
X-ray emission data from within the innermost stable circular orbits of nearby black holes has given the first observational proof that a 'plunging region' not only exists around a black hole, but exerts some of the strongest gravitational forces yet identified in our galaxy.
https://www.physics.ox.ac.uk/news/first-proof-black-hole-plunging-regions
Quote: "Einstein’s theory predicted that this final plunge would exist, but this is the first time we have been able to demonstrate it happening. Think of it like a river turning into a waterfall – hitherto, we have been looking at the river. This is our first sight of the waterfall. We believe this represents an exciting new development in the study of black holes, allowing us to investigate this final area around them. Only then can we fully understand the gravitational force. This final plunge of plasma happens at the very edge of a black hole and shows matter responding to gravity in its strongest possible form."
Einstein’s theory predicts that sufficiently close to a black hole it is impossible for particles to safely follow circular orbits, instead they rapidly plunge toward the black hole at close to the speed of light.
X-ray emission data from within the innermost stable circular orbits of nearby black holes has given the first observational proof that a 'plunging region' not only exists around a black hole, but exerts some of the strongest gravitational forces yet identified in our galaxy.
https://www.physics.ox.ac.uk/news/first-proof-black-hole-plunging-regions
Quote: "Einstein’s theory predicted that this final plunge would exist, but this is the first time we have been able to demonstrate it happening. Think of it like a river turning into a waterfall – hitherto, we have been looking at the river. This is our first sight of the waterfall. We believe this represents an exciting new development in the study of black holes, allowing us to investigate this final area around them. Only then can we fully understand the gravitational force. This final plunge of plasma happens at the very edge of a black hole and shows matter responding to gravity in its strongest possible form."
I wasn't expecting Einstein to be proved wrong, as it goes. But it's a deep subject:
https://profoundphysics.com/black-hole-orbits/
The website is infested with irritating ads, so I present a summary:
OK, we must modify Newton's Laws with an inverse cube r factor in General Relativity.
This diagram is inaccurate AFAIK, because the effective potentials (which include kinetic energy) at large r approach each other for the Newtonian and Einsteinian cases.
But certainly suggest complexity with General Relativity.
This I knew for the Schwarzschild case. Believe me, it turns into a nightmare of mathematics for spinning and charged Black Holes.
Now I must get back to the video about calculating the Universe with the DFT (Discrete Fourier Transform) and Schrodinger's Equation.
Surely an FFT (Fast Fourier Transform) is better, but I am a bit rusty on the subject,
https://profoundphysics.com/black-hole-orbits/
The website is infested with irritating ads, so I present a summary:
OK, we must modify Newton's Laws with an inverse cube r factor in General Relativity.
This diagram is inaccurate AFAIK, because the effective potentials (which include kinetic energy) at large r approach each other for the Newtonian and Einsteinian cases.
But certainly suggest complexity with General Relativity.
This I knew for the Schwarzschild case. Believe me, it turns into a nightmare of mathematics for spinning and charged Black Holes.
Now I must get back to the video about calculating the Universe with the DFT (Discrete Fourier Transform) and Schrodinger's Equation.
Surely an FFT (Fast Fourier Transform) is better, but I am a bit rusty on the subject,
That's not a summary, it's a lengthy cut and paste!
Summary: a brief statement or account of the main points of something.
@Galu, I have noticed a recent tendency from you to nitpick alleged faults in posts. @Bonsai is doubtless aware of it too.
This hardly endears you to your fellow toilers in the Gravity vinyard...
I say outrageous things very often, but the Moderators are well aware of my place on the Autistic Spectrum and turn a blind eye mostly.
I do wonder if the balance of your mind is disturbed?
I think a Rabies Test is indicated. Do tell us how you get on, because I am deeply interested in Medical Matters after recent personal travails.
This hardly endears you to your fellow toilers in the Gravity vinyard...
I say outrageous things very often, but the Moderators are well aware of my place on the Autistic Spectrum and turn a blind eye mostly.
I do wonder if the balance of your mind is disturbed?
I think a Rabies Test is indicated. Do tell us how you get on, because I am deeply interested in Medical Matters after recent personal travails.