Electromagnetic forces can't act across such large distances simply because of the inverse square law. Gravity is weak at short ranges but is immensely stronger at greater ranges. There was a simple possibility that was raised about this dark matter issue some time back - the possibility that not all dead stars end up as black holes and evaporate. Smaller stars might fizzle into brown dwarfs, and some stars may even have failed to ignite at birth.

As such, there's a possibility of the Universe being littered with plenty of matter that do not actively radiate visible, IR or UV radiation, hence we do not pick them up on our telescopes and yet they exert gravitational effects.

Yes, gravity also obeys the inverse square law if we view it from classical mechanics. In quantum mechanics and M-theory, this is not necessarily the case. There's a possibility for gravity to actually be a very strong force but much of it leaks into the bulk beyond our brane.

Both are governed by inverse square law, but gravity's effects are weaker at extremely short ranges than it does at longer ranges although gravity waves fall off according to the inverse square law. Much further out, gravity likewise weakens. All forces have their ranges.

Similarly, the strong nuclear force and electroweak force are both present within an atom, and yet why are their ranges so different? You can hardly detect the strong force beyond the atomic nuclei and within the nuclei it's way stronger than the electroweak force, and yet the electroweak force ends up extending macroscopically into electromagnetism.

How do you explain these ranges based on inverse square law alone?

This post has been edited by jswong: Apr 21 2010, 02:44 AM