'Dark fluid' with negative mass could dominate the universe

Post by antidesitter » Wed, Dec 05, 2018, 7:09 PM UTC

zamalek wrote: post #16

duality wrote: post #13

Earlier quoted context omitted.

"Every other force besides gravity is polarised, so why not also gravity?" Gravity is mediated by a spin-2 gauge boson, the graviton, whereas the other known fundamental forces are mediated by vector (spin-1) bosons. There is an exercise in Peskin & Schroeder (I believe) working out the lack of a gravitation "repulsion" resulting from this difference. That being said, I think this kind of phenomenology is excellent a…

> raises lots of interesting questions Exactly. What I liked about MOND was that it basically amounted to "we don't know." The populist notion that dark matter is conclusively matter, and dark energy is energy seems a bold claim for such a young species. Crazy theories like non-universal constants are probably crazy, but they do explore unconventional lines of thought. One of those, most likely an unknown unknown, ma…

Post by tzakrajs » Wed, Dec 05, 2018, 7:12 PM UTC

RobertoG wrote: post #58

I'm confused. From the article: "This is explained by the Hubble-Lemaître Law, the observation that more distant galaxies are moving away at a faster rate." If we observe an accelerating universe how can be that galaxies in the past move away at a faster rate?

Post by raverbashing » Wed, Dec 05, 2018, 7:15 PM UTC

duality wrote: post #56

raverbashing wrote: post #19

Earlier quoted context omitted.

Given there have been no detections of individual gravitons, saying it's a spin-2 gauge boson is speculation at best (though it might be what the model predicts)

If it weren't, general relativity would be wrong as well and we know that (in its domain of applicability) it's a highly accurate model. GR models gravity as fluctuations in the metric tensor of spacetime, which is a symmetric rank-2 tensor. This is all you need to know to conclude that a graviton (a quantize fluctation of that tensor) must be spin-2. https://en.wikipedia.org/wiki/Graviton mentions "[I]t can be shown…

Post by mirceal » Wed, Dec 05, 2018, 7:22 PM UTC

Post by guscost » Wed, Dec 05, 2018, 7:24 PM UTC

acqq wrote: post #35

zamalek wrote: post #16

Earlier quoted context omitted.

> raises lots of interesting questions Exactly. What I liked about MOND was that it basically amounted to "we don't know." The populist notion that dark matter is conclusively matter, and dark energy is energy seems a bold claim for such a young species. Crazy theories like non-universal constants are probably crazy, but they do explore unconventional lines of thought. One of those, most likely an unknown unknown, ma…

“What’s most impressive is that the predictions of dark matter were first made in the 1970s and 1980s, and were observationally confirmed later. This is not a case of tweaking the model to fit the data; this is a case of the best kind of science you hope for: where you make predictions, make the observations, and what you see validates and confirms the predictions you had made. And yet, even 35 years later, there are…