I see your point about Occam’s razor, it is a brilliant logical tool, but in some cases it does not apply. Dark matter does indeed seem like a cop-out, (the invoking of a giant invisible substance to explain away the faults in our equations) but it is in fact precisely the opposite. It is hard to call something a cop-out when it raises more questions than it actually explains.
The explanation of the motion of galaxies using dark matter is just that- an explanation! Scientists have stated their ignorance when we found that our theories of gravity do not work at large scales. But it seems you’re saying that we need not proceed from that point. That is not the way science works. The theory that a form of matter exists that does not interact with ordinary matter through the electromagnetic force, and therefore is not visible, and is is present at six times the amount of normal matter, was not just thought up. It follows directly from evidence. If what we can observe in the universe behaves as if it existed around dark matter, and other theories that try to adjust our current laws of gravity fail spectacularly, then we are forced to conclude that our universe is one that includes dark matter until evidence comes along that disproves that theory.
To reiterate the point that dark matter is the only current theory that explains the observed data, I have attached a jpg image of a graph that shows the the way large structures are distributed in the observable universe. The red points are the observations made of our universe and the black line is the predictions made by standard cosmology, including normal matter, dark energy, dark matter and general relativity governing them. The dotted blue lines are the predictions made by our classical theories of gravity, and the solid blue lines our best relativistic alterations of gravity without dark matter. I’ll leave it to you to interpret the evidence.
It is true that what is being discussed is still controversial, and new evidence could come around any day that either proves one theory, or overturns everything we thought we understood, leaving us to start from scratch. These are just the best predictions we can make using the available evidence. Because of this, alternate opinions are expected, and should be encouraged; it is what makes science work so well.
To be honest the only issue I hold is with your last statement. If it exists in reality, than science can explain it through a method of repeated observations, hypothesis and experimentation. If it is falsifiable, than science can prove it’s existence. Anything that is not falsifiable, and does not exist physically in a state in which it can be observed, then by definition it cannot be proven to exist. Ergo it does not need to be explained by science, for if there is no evidence for something that cannot actually be proven, then it is completely reasonable to say that it does not exist, and the opposite to assume that it does in face of overwhelming evidence to the contrary.
With many regards,
P.S- I am much to blame for this, my apologies, but I think we should try to move the topic back to the Multi-Universe, as it is a rich idea (and the title of the conversation).