Podcast: Listener Questions Answered

[Fraser]

We finally get organized enough deal with several listener questions: isn’t dark matter just regular stuff we can’t see? how can parts of the Universe be expanding faster than the speed of light? ...

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[aformalevent]

thank you for your wonderful podcast and merry christmas.

but, you (everyone i've ever heard discuss it) didn't actually discount all the possible forms of normal matter in the dark matter discussion.

imagine a (very) cold pluto to neptune (i realize this is a huge range) sized world not contained in a star system. would we see this directly through light? no... would we detect it through it's gravitational lensing? no... if there were thousands of trillions of these scattered in a 'halo' around a galaxy like the oort cloud around our solar system, would we detect this 'unobservable' mass? yes.

One of the arguments i've seen for foreign dark matter is that we can detect how it interacts when two galaxies collide, we have shown that the unobserved mass in each galaxy passes through the other galaxy, implying that it is not gas (since gas could have friction with each other) and thus must be some foreign form of matter since we cannot see it. but this is assuming that we can see all mass this is regular and not gas. which we can't.

again, the galaxy disk argument where the further you are from the centre of the galaxy the more dark matter there is, wouldn't that conform to the simpler and thus (go occams razor) more correct theory of large highly distanced clumps of regular matter in a 'galactic oort cloud'?

I still just can't buy the foreign dark matter arguments, i hope i am convinced one day. I find it easy to belive that there is foreign matter in the universe, but to assume that all the mass we cannot observe is not made of regular lowest teer quarks (and thus protons, electrons, and neutrons) seems incredibly unscientific to me.

Given the huge amount of research and effort going into this theory i'd like to believe that it is credible, and that i simply don't understand, but i keep thinking this and string theory are never going to be proven.