What would be an example of something with no rest-mass that can result in an observable gravitational effect? Or are you saying that is what we might be looking for?
Can a hypothetical "flock" of photons cause a gravitational effect?
I guess my question is an attempt to get some insight into why it is assumed that there is "missing matter" causing the observed effects rather than saying that there is unexplained spatial distortion which might be due to matter. mathman's answer was a reasonable answer. Is that the answer...
Very roughly put, my limited understanding is that dark matter is postulated because of effects seen in the geometry of space similar to those created by matter.
Is it necessarily true that there is some form of matter causing that spatial distortion? Couldn't it be postulated that there are...
The eyes respond to light, the brain processes it and then constructs our sense of objects. We sense patterns of brightness and color. A blind person given sight cannot perceive or recognize a coke bottle until he touches it. It just a pattern of intensity and color, not an object. (read...