Inverse-Square Law

[Rev. Green]

Gravity obeys the inverse-square law at ordinary distances. To make it obey the same law at large distances we invent dark matter, and to keep it on track at vast distances we invent dark energy. Electro-magnetism obeys the inverse-square law at ordinary distances. What happens at large distances? Does elecro-magnetism naturally deviate slightly from the law, and do we need "uncharged magnetism" or some such hocus-pocus to keep it on track?

[jim360]

I'm not sure the premise of the question is entirely an accurate portrayal of the situation. But, in any case, so far as I am aware, there's been no need as yet to introduce "dark photons", or the like, to explain as yet nonexistent observations of weirdness in EM.

There may, on the other hand, be soon a need to do so over *short* distances, as there are some signs of anomalies in the behaviour of muons (the electron's bigger brother).

[ToraToraTora]

No.

[ToraToraTora]

^^That was the short answer!

As jim says i think the premise of the question is flawed, yes dark matter/energy are devices to make the maths fit the observation but the "distance" assumption is flawed there is no defined distance that we start having to use DM/DE it's just that locally the amounts are tiny as to render them unnecessary they tend to become noticeable on a galactic scale. EM has no such issues and thus does not need us to create any "hocus pocus" to make the maths fit the observations, distance has no relevance.

[jim360]

That's not quite what I had in mind, TTT. Dark Energy is anyway weird because it acts in the opposite sense to matter, pushing out rather than pulling in. In terms of the inverse square law, Dark Energy would actually serve to break it if anything.

But really what I mean is that neither DM nor DE are "fudges" in the way that I think was implied. Their effects and even their overall concentrations can be very precisely measured, eg by looking at the Cosmic Microwave Background. In the meantime, at large scales the relevant equations are those of General Relativity, which in itself "breaks" the inverse square law, albeit not by much.

[ToraToraTora]

I see jim, yes I too struggle with dark energy, I find dark matter a much simpler concept to grasp. Would agree though that dark matter is what we call the mass that must be there to hold galaxies together?

[jim360]

Yes, that seems to be one of its "jobs", so to speak. Galaxies spin too fast to be held together under their own observable mass (which *does* link to the inverse square law), so we postulate that something else must be there. Since it has been independently observed in other ways, eg with the CMB as I mentioned, it's about more than just that, though, which is essentially the point I was trying to make.

[Old_Geezer]

Dark matter is hardly invented. I see no patent. It's hypothesised since more matter is necessary to explain how the galaxies hang together and rotate as they do. As for dark energy, that's been hypothesised because the expansion of the universe is accelerating and there must be an energy source to account for it.

[jim360]

// Dark matter is hardly invented. I see no patent. //

Like many things in science, it was gifted to humanity free of charge :)

[mibn2cweus]

The cost of knowledge is paid in understanding.