Neutrinos – and other ‘hot’ dark matter proposals – are generally considered to be ruled out due to being incompatible with the observations on galaxy formation.
Similarly, black holes are ruled out by (gravitational) microlensing data – there’s not enough of 'em to account for the missing mass.
For a charitable interpretation, he could have had something like gravitational waves in mind, though the bunched-up rubber sheet is a seriously warped analogy…
The thing that frustrates me about multiple universes is that I appear to be stuck in the one universe in which all of my posts are stupid. Dang.
Yes; here’s an article I found that mentions observations of this.
Does it cheer you to consider that your posts might be stupid in an infinite number of universes? 
“Stupid? I am not merely stupid! I am -” <dramatically flings arms wide> - “- OMNISTUPID!!”
Thanks. A further point of confusion:
Weak interaction is responsible for radioactive decay.
So doesn’t that suggest that dark matter rich areas should be discernible from sparse areas? Though I suppose they have nothing to decay into, they still change type. Is there no entropy involved in that?
However, they are still useful as an counter to the OP’s objection. It may be crazy to have a type of matter that can pass through light-years of lead without detection. Nevertheless, it does exist in the form of neutrinos. Imagining a type of dark matter which is just like a neutrino except cooler and more massive isn’t a stretch.
No need to feel frustrated.
You can always take comfort in the thought that somewhere in the Multiverse, there’s a multiverse with Your name on it, in which the multidimensional strings within your consciousness resonate with certainty, in the answers that this version of your Self so desperately seek.
Grasshopper.
Okay, I get it. P=mv , but v=d/t , and it is the t in the v that dilates, resulting in a non-linear value for P.
Since gravity has not reconciled with QM, its laws have not really been fully modeled. I asked the question more or less for that reason: not is there conservation of gravity in spacetime, but if there were, what effect would it have on galactic math? What kind of realistic conservation curve might be sufficient to account for the observed discrepancy? (And I used a fluid analogy because the 2D rubber sheet image is only for visualizing planar paths.)
It is interesting to imagine that we live in an invisible sea of dark matter, and not altogether beyond the pale, given that the matter we can observe is more empty space than actual stuff. It would be a bit disconcerting to conclude that the aether of ancient times does in fact exist.
That idea is contrary to the whole idea of quantum multiverses. EVERY time RaftPeople (or you, Der Trihs) makes a post, the universe (that is, the universe in which the post is made) bifurcates into two universes: One in which the post is stupid, and one in which the same post is not-stupid.
But how can the same post be stupid in one universe but not-stupid in another? The difference can only be in the surrounding universe: In one, the entire surrounding universe is such that the post in stupid in that context, and in the other, the entire surrounding universe is different in (gross or subtle) ways that make the post non-stupid.
So take heart, RaftPeople, Der Trihs and all other sometimes-stupid posters! Somewhere among the multiverses there is a smart post for every stupid post, and a stupid post for every smart post! If you find yourself making stupid posts, RaftPeople, just wait patiently and your smart-post-time will come. Someday you will make a post, and the universe will cleave in twain, and you will find yourself in the side of your smart post! (But of course, there will still be the other one of you finding yourself making yet another stupid post.)
So post on, and rest assured that, in the multiplicity of universes, smartness of posts is conserved! There is no OMNISTUPID! (But, of course, in some universe where Der Trihs wrote that, there is an OMNISTUPID.)
I know this is an SR side comment, but since I’m just learning to think about dark matter, I hiccuped all the harder at this, which I thought I had down, sort of.
The mass of some freshly-smashed elementary particle is measured by the energy at which it can be nudged onto the stage and show itself, right? Mass and energy relate absolutely, as it were. Say it takes 15Gv for one particle to show up, to move it from non-separateness to uniqueness, to, well, particularity. That’s its “rest mass,” once we realize (account for, subtract) the fact that “it” had been traveling at such a speed, or “it” would be a 15-Gver standing still relative to you?
Perhaps we could give an ::SR:: header within this thread to clear up this perennial weed.
But yes, this would create a nearly uncountable number of new universes every nano second. That isn’t an issue though, there’s no limit or lack of “space” in the theoretical multiverse.
infinite universe - you are right, but I don’t think that contradicts what anyone else says.
dark matter - the usual forms of matter are already accounted for. This doesn’t mean there has to be actual matter that is weird and new, it just means our observation show us a universe that acts like it has X amount of matter we can’t account for (there is dark energy too). There are several different theories about it.
Personally, I wonder if a steady state universe is still feasible. It would still create an observable universe that appears to be flying apart from a start date, if every time the space was stretched apart enough, new space was created in some regions.
You need to put this on a t-shirt.
The main reason the steady state universe was abandoned was that there was nothing in it that would generate the Cosmic Microwave Background Radiation. And it was not only new space being created by expansion but also new matter to fill that space. Otherwise there wouldn’t have been anything observable to us that wasn’t gravitationally bound (i.e. nothing outside the local cluster and possibly supercluster, assuming there is one). Or at least nothing as close as other galactic clusters currently are.
I wonder something about the many-worlds interpretation. If two universes happened to be in identical states, do they collapse back into a single universe?
This needs to be on a t-shirt. The number of “scientific” discussions I’ve had where the other person tried to use this argument certainly feels infinite.
Too many letters, not quite snappy enough. How about a nice mathematical equation that sums it up? Oh, wait… math’s has its limitations after all.
Did a quadratic equation beat you up and take your lunch money once or something? You seem to have it in for math.
You mean there’s a universe out there in the infinite and infinitely multiplying multiverse, in which I am actually Cecil? Awesome!
Too bad I’m not there. OH, wait, I am. Just not “me” me.
Ow. I sprained my brain.
An important note, by the way: The Many Worlds interpretation of quantum mechanics is not a scientific fact, nor a theory, nor really even a hypothesis. What it is (and this is all that it is) is one possible description of a universe which is mathematically consistent with the laws of quantum mechanics as we’ve observed them. There are quite a few different interpretations of quantum mechanics, all of them exactly equivalent in terms of what observations they predict, and not all of them require Many Worlds. They do, unfortunately, all contain some feature or another that seems counterintuitive, but it’s not always the same counterintuitive feature, so you do at least have some freedom to pick and choose how to sprain your brain.
I think you misunderstand the meaning of “infinite number”. If there is an infinite number of permutations of every possibility reflected in manifestations of the multiverse (various universes), then there is not a universe in which you are Cecil, but an infinite number of them. One is not a fraction of infinity, the only fraction of infinity is infinity.