> The vast majority of matter in the universe is dark—it is entirely invisible and detected only through its gravitational effects
They state like dark matter is a fact. Isn't it a hypothesis?
> The FRBs shine through the fog of the intergalactic medium, and by precisely measuring how the light slows down, we can weigh that fog, even when it's too faint to see
Light is always light and has always the same speed but its path in a gas is less straightforward than in a vacuum because of the interactions with atoms. It takes longer to get through. Its speed as we can measure it is c divided by the refractive index of the gas, if I'm not wrong.
Yep. And then journalists wonder why people don't like them. How much harder would it be to write "measuring how much longer would it take for the light to get to us" without making people feel gaslit next time they are told speed of light is obviously always the same
1. It is a phenomenon not a hypothesis. Dark matter is a collection of observational facts that indicate an unknown source of gravity.
2. Yes, in any medium lights slows down. This is what refractive index measures.
This has nothing to do with dark matter, it's about the missing baryonic matter. And this result just confirms what most people thought anyway, but it's still rather important because it's a very solid result so we don't need to call it "missing matter" anymore.
This study accounts for missing ordinary matter, not dark matter. The linked article makes this clear in the first paragraph. Sometimes I wonder if the first commenters (and often top commenters) on HN read the article at all or just respond based on the headline, because these comments often seem barely related to the actual article content.
Readit News
They state like dark matter is a fact. Isn't it a hypothesis?
> The FRBs shine through the fog of the intergalactic medium, and by precisely measuring how the light slows down, we can weigh that fog, even when it's too faint to see
Light slows down??
Same thing for light in a liquid or in a solid. Example: speeds of radio waves in networking cables https://en.wikipedia.org/wiki/Velocity_factor#Typical_veloci...
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From the HN guidelines:
"Please don't comment on whether someone read an article."