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N8CCRG t1_iwyymll wrote

Reply to comment by grrrrreat in Dark Matter as an Intergalactic Heat Source. Spectra from quasars suggest that intergalactic gas may have been heated by a form of dark matter called dark photons. by MistWeaver80

If you're arguing for a modified theory of gravity, lots of people have tried that, and lots of various measurements have set forth extremely good evidence that modified theories of gravity can't fix the problems. Meanwhile dark matter can.

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typicalspecial t1_iwz89py wrote

I wouldn't discount modified gravity entirely. Of course dark matter can fix it, because dark matter is defined as whatever will fix it.

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N8CCRG t1_iwzb3yk wrote

Not true. Dark matter is just defined as matter that we can't see but otherwise behaves like matter, and that fixes all of the various measurements. Meanwhile, modified gravity doesn't. You can make a modification that tries to explain one measurement, but then it fails to fix a separate measurement, and often make problems worse, like the proverbial floorboard that gets hammered down on one end and the other end pops back up.

And that's not my opinion, that's what the actual publications routinely find.

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typicalspecial t1_ix0lyt7 wrote

It behaves like matter in that it influences gravity, and that's about it. Proposed particles get ruled out just as modifications do. Ruling out a modification doesn't invalidate all possible models; ruling out proposed dark matter particles doesn't invalidate dark matter being a particle. We can't definitively say it's matter until we can verify its interaction with anything.

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N8CCRG t1_ix0oxql wrote

That's what defines matter: it interacts via gravity. Other interactions are different for every other type of particle we know about. Some particles interact through some mechanisms and others don't, but they all interact through gravity.

Meanwhile, modifcations have been blanket ruled out, not individually. Dark matter has been measured in so many different ways, we have been able to say that no modified theory of gravity could explain all of those measurements.

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