Can someone explain the dark matter hypothesis?

Coincidentally, I watched “The Theory of Everything” yesterday, a wonderfully acted bioflick about Stephen Hawking. It motivated me to start reading his book, ”“A Brief History of Time,” which covers dark matter and many other time-space ideas. I have an extra copy, if you’d like me to send it to you.

There are observed galaxy rotation curves, and theoretical rotation curve. The discrepancy is hypothesized as being caused by dark matter which is present but not observable.

“Dark matter” is not one hypothesis but many. You’re correct that according to our current understanding of gravity, there’s too little visible mass to account for the observed motion of galaxies. This means that either our current understanding of gravitation is flawed (which is a competing hypothesis and, IMHO, the most likely answer), or the vast bulk of matter which exists is not visible to us. Many hypotheses have been suggested to account for this missing mass, including: brown dwarf stars (stars which burn so dimly that you could actually walk around on their surface), micro-black holes, dust, exotic particles, and strangelets.

There’s also the observation that the galaxies are moving away from one another and accelerating as they do so in defiance of gravity which should be braking the diffusion. The only explanation consistent with Newton’s enshrinement is that some unseen matter is outpulling the mutual attraction of the galaxies toward one another.

@stanleybmanly, I believe that dark energy not dark matter is the current hypothesis to explain the expansion of the universe.

@Pachy, thank you for your offer. I will send a message to you with my address.

They made it up to account for what would have otherwise made everything else we know to be true, proven to be fundamentally wrong. Convenient, eh?