The possibilities for dark matter have shrunk
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The possibilities for dark matter have shrunk
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Re: The possibilities for dark matter have shrunk
#2LZ Dark Matter experiment page: https://lz.lbl.gov/
Way better press release with lots of cool pictures: https://newscenter.lbl.gov/2024/08/26/lz-experiment-sets-new...
Re: The possibilities for dark matter have shrunk
#3LZ Dark Matter experiment page: https://lz.lbl.gov/ Way better press release with lots of cool pictures: https://newscenter.lbl.gov/2024/08/26/lz-experiment-sets-new...
Agree. What a bad article. URL should be changed.
Re: The possibilities for dark matter have shrunk
#4By the way, apart from the fact that dark matter predictions have been contradicted by increasingly sensitive experiments over and over and over, there is another inconvenient piece of observational evidence: An analysis of stellar velocities at the edge of the Milky Way, published last year [1] shows that they are "Keplerian", i.e. following classical behavior without the influence of any purported dark matter. So either the Milky Way is anomalously dark matter deficient (how very convenient :), or maybe the discrepancy that dark matter was invented to explain will simply disappear when more accurate astronomical data including the fainter stars becomes available.
[1] https://www.scientificamerican.com/article/the-milky-way-may...
Re: The possibilities for dark matter have shrunk
#5I’m betting on primordial black holes for at least some of it. If you consider early universe densities their formation seems almost certain.
Most models predict that they exist but the unknowns are around how common they are and their mass ranges and therefore whether they could account for most or all dark matter.
There’s a little bit of speculation that “planet nine” is a PBH. I really hope for that one. It would give us actual access to a black hole within probe range, which could allow us to “complete physics.” Could also be a gateway to the universe through gravity assist, letting us yeet interstellar probes out at incredible velocities.
Re: The possibilities for dark matter have shrunk
#6I’m betting on primordial black holes for at least some of it. If you consider early universe densities their formation seems almost certain. Most models predict that they exist but the unknowns are around how common they are and their mass ranges and therefore whether they could account for most or all dark matter. There’s a little bit of speculation that “planet nine” is a PBH. I really hope for that one. It would…
Assuming P9 is further out from the sun than the other planets... It would be orbiting slower than the rest, and will probably give you a smaller gravity assist than the rest. Gravity assist can only change your velocity by up to your relative velocity (because it's just a flyby orbit as far as the assister is concerned - speed in equals speed out).
Re: The possibilities for dark matter have shrunk
#7By the way, apart from the fact that dark matter predictions have been contradicted by increasingly sensitive experiments over and over and over, there is another inconvenient piece of observational evidence: An analysis of stellar velocities at the edge of the Milky Way, published last year [1] shows that they are "Keplerian", i.e. following classical behavior without the influence of any purported dark matter. So e…
We've also seen instances where visible "clumping" in a galactic disc correspond to differences in the rotation curves, which dark matter can't really explain. But this is still a topic of much debate.
However, there's lots of good evidence for dark matter besides rotation curves of galaxies. For instance, models of galactic formation work a lot better with it than without it (without dark matter, as galaxies coalesce, they get hot and the pressure keeps the gas apart and makes star formation really hard).
We also see the Bullet Cluster, where two galaxies collided/passed through each other. The gas and dust has been slowed down from collisions, but the dark matter has passed right through. We know this from the gravitational lensing. The lensing happens around the mass of the galaxy, but with the bullet cluster, the lens is off to the side where there is no normal matter, because the dark matter kept going when the regular matter slowed down.
In other words, we have some really good evidence for dark matter, but there's a few things going on here and there we can't explain.
Re: The possibilities for dark matter have shrunk
#8I’m betting on primordial black holes for at least some of it. If you consider early universe densities their formation seems almost certain. Most models predict that they exist but the unknowns are around how common they are and their mass ranges and therefore whether they could account for most or all dark matter. There’s a little bit of speculation that “planet nine” is a PBH. I really hope for that one. It would…
Assuming P9 is further out from the sun than the other planets... It would be orbiting slower than the rest, and will probably give you a smaller gravity assist than the rest. Gravity assist can only change your velocity by up to your relative velocity (because it's just a flyby orbit as far as the assister is concerned - speed in equals speed out).
Hmm... you could probably still do a powered flyby though:
https://en.wikipedia.org/wiki/Oberth_effect
This is different from a normal gravity assist. Close to a black hole the gravitational field would be quite strong, making this potentially very powerful.
Re: The possibilities for dark matter have shrunk
#9There is no dark matter in theories of superfluid quantum gravity.
Dirac later went to Dirac sea. Gödel had already proposed dust solutions, which are fluidic.
PBS Spacetime has a video out now on whether gravity is actually random. I don't know whether it addresses theories of superfluid quantum gravity.
>>> "Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity." (2015) https://hal.science/hal-01248015/
Re: The possibilities for dark matter have shrunk
#10Earlier quoted context omitted.
Assuming P9 is further out from the sun than the other planets... It would be orbiting slower than the rest, and will probably give you a smaller gravity assist than the rest. Gravity assist can only change your velocity by up to your relative velocity (because it's just a flyby orbit as far as the assister is concerned - speed in equals speed out).
Hmm... you could probably still do a powered flyby though: https://en.wikipedia.org/wiki/Oberth_effect This is different from a normal gravity assist. Close to a black hole the gravitational field would be quite strong, making this potentially very powerful.
I love this human can-do attitude. Screw black hole radiation, distortion of space time fabric at its core, just lets use it as a mega slingshot!