If a particle really only interacted with gravity, would it pass through matter? AFAIK "touching" things is electron repulsion...
Looking at it from a quantum field perspective, pretty much. If the only interactions are through gravity then the underlying field's evolution can't be influenced by anything else, I have no real idea what the implications of that would be because we don't have a QFT for gravity.
Mmm. Burrito.
This is a funny comic, but it really does disturb me how certain most theoretical physicists are about the nature of dark matter, despite there not really being any good philosophical reason for us to expect these anomalies to be caused by a particle that interacts non-gravitationally.
Here's the best evidence of difficult to detect matter likely being real. You wouldn't see such a shift in gravity if there aren't matter unaffected by friction
xkcd
A community for a webcomic of romance, sarcasm, math, and language.