Modified Gravity Theory Passes a Critical Test

Re:Modified Gravity Theory Passes a Critical Test by sandworm101 on Wednesday July 29, 2020 @10:53AM (#23987299)

It is not that dark matter has not been observed. It has. It is called "matter" because its gravitational influence has been observed. Therefore at one level we know it exists because something is impacting gravity at large scales, we are just unsure about its other properties. We cannot see it directly but there are lots of things we don't see directly and that doesn't mean we aren't sure they exist. So it isn't a total invention to make the math work. It is a 'best fit' for a gap in our knowledge.

Dark energy is perhaps a different story.

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Re:Modified Gravity Theory Passes a Critical Test by narag on Wednesday July 29, 2020 @11:36AM (#23987817)

IIRC, dark matter is supposed to be a different kind of matter that interacts "less than normal" with ordinary matter.

Or is there a version in which it's ordinary matter, just "hidden" by something or in some exotic "other dimension", black hole or parallel universe thingy?

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Re:Modified Gravity Theory Passes a Critical Test by sandworm101 on Wednesday July 29, 2020 @11:45AM (#23987980)

It is thought to reacted less with normal matter because we aren't seeing it react with normal matter. So one potential explanation is a particle that is so tiny/fast, with no electrical charge, that it is can fly through planets without hitting anything: a "ghost" particle like the neutrino. The term used is WIMP (Weakly Interacting Massive Particle). Are we know is that it has mass, because it influences gravity. That's one possible explanation for dark matter.

Ideas based on extra dimensions are becoming less popular. We have evidence that gravity experiences the same dimensions that light does. Gravity waves from things like neutron stars merging seem to arrive at earth at the same time as light. So it is doubtful that extra dimensions can explain dark matter.

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