<p>There are really two type of &quot;dark matter&quot; in the universe and two &quot;dark matter problems&quot;.</p>
<p>The first problem is that most of the &quot;normal matter&quot; in the universe is dark and difficult to find (a.k.a. <a href="https://en.wikipedia.org/wiki/Missing_baryon_problem" rel="noreferrer">the missing baryon problem</a>). This dark matter could consist of gas between galaxies (most likely) or in the form of objects that have a very high mass to luminosity ratio (planets, brown dwarfs, cold white dwarfs, black holes, golf balls, bricks etc.).</p>
<p>This type of &quot;dark matter&quot; <em>does</em> interact with light normally (although black holes don't emit light), but it doesn't emit enough light to make it easy to find. About 10-20 years ago, it was still a bit of a mystery that most of the &quot;normal matter&quot; in the universe couldn't be identified, but now it is generally thought to be a solved problem, thanks to the discovery of the &quot;<a href="https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic_medium" rel="noreferrer">warm-hot intergalctic medium</a>&quot;.</p>
<p>The second dark matter problem is a bit more tricky. We know that a significant part (&gt;90%) of the gravitating matter in the universe is dark - in that we cannot see it. There isn't enough of the &quot;normal dark matter&quot; (i.e. the planets, brown dwarfs etc. that were referred to above) to explain the difference. Therefore the hypothesis is made that most (80%) of this material is an additional form of &quot;non-baryonic&quot; dark matter which <em>does not interact with light at all</em> (or very, very weakly). This is now conventionally what is referred to generically as dark matter and it is an unsolved problem.</p>
<p>This non-baryonic dark matter <em>does</em> interact gravitationally in much the same way as normal matter. What it is, is still the result of theoretical speculation. <em>Some</em> of the candidates are massive particles called <a href="https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic_medium" rel="noreferrer">WIMPS</a> (weakly interacting massive particle), which are expected to have some additional interactions via the weak nuclear force. Another possibility is the <a href="https://en.wikipedia.org/wiki/Axion" rel="noreferrer">axion</a>, which may interact with light (very weakly) under some circumstances.
A further possibility would be <em>primordial</em> black holes; these would interact with light in the sense of absorbing everything incident upon them, but would be otherwise invisible.</p>

CC BY-SA 4.0
2021-07-19T14:04:49.983Z
Isn't the "first type" known as the "Missing baryon problem"? https://en.wikipedia.org/wiki/Missing_baryon_problem
Daddy Kropotkin
CC BY-SA 4.0
2021-07-19T14:21:36.397Z
@DaddyKropotkin yes. I've put that link in.
ProfRob
CC BY-SA 4.0
2021-07-19T12:53:17.123Z
2021-07-19T14:21:09.883Z
2021-07-19T14:21:09.883Z
ProfRob
<p>Does dark matter not interact with light, or does it not interact with anything in the universe?  What do they talk about in the scientific community the most?</p>

CC BY-SA 4.0
2021-07-19T14:56:08.633Z
Might be helpful: https://astronomy.com/news/2020/06/half-the-matter-in-the-cosmos-was-missing-but-astronomers-found-it
Daddy Kropotkin
<observational-astronomy>
Is it known in the scientific community that dark matter does not interact with light?
Red bel
# Is it known in the scientific community that dark matter does not interact with light?

(Asked by: username_0 on 2021-07-19)

Does dark matter not interact with light, or does it not interact with anything in the universe? What do they talk about in the scientific community the most?

**Tags:** observational-astronomy
> **Comments:**
> **username_1**: Might be helpful: https://astronomy.com/news/2020/06/half-the-matter-in-the-cosmos-was-missing-but-astronomers-found-it  

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## 1 answers

### Answer by username_2 on 2021-07-19. Score: 6

There are really two type of "dark matter" in the universe and two "dark matter problems".

The first problem is that most of the "normal matter" in the universe is dark and difficult to find (a.k.a. [the missing baryon problem](https://en.wikipedia.org/wiki/Missing_baryon_problem)). This dark matter could consist of gas between galaxies (most likely) or in the form of objects that have a very high mass to luminosity ratio (planets, brown dwarfs, cold white dwarfs, black holes, golf balls, bricks etc.).

This type of "dark matter" *does* interact with light normally (although black holes don't emit light), but it doesn't emit enough light to make it easy to find. About 10-20 years ago, it was still a bit of a mystery that most of the "normal matter" in the universe couldn't be identified, but now it is generally thought to be a solved problem, thanks to the discovery of the "[warm-hot intergalctic medium](https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic_medium)".

The second dark matter problem is a bit more tricky. We know that a significant part (>90%) of the gravitating matter in the universe is dark - in that we cannot see it. There isn't enough of the "normal dark matter" (i.e. the planets, brown dwarfs etc. that were referred to above) to explain the difference. Therefore the hypothesis is made that most (80%) of this material is an additional form of "non-baryonic" dark matter which *does not interact with light at all* (or very, very weakly). This is now conventionally what is referred to generically as dark matter and it is an unsolved problem.

This non-baryonic dark matter *does* interact gravitationally in much the same way as normal matter. What it is, is still the result of theoretical speculation. *Some* of the candidates are massive particles called [WIMPS](https://en.wikipedia.org/wiki/Warm%E2%80%93hot_intergalactic_medium) (weakly interacting massive particle), which are expected to have some additional interactions via the weak nuclear force. Another possibility is the [axion](https://en.wikipedia.org/wiki/Axion), which may interact with light (very weakly) under some circumstances.
A further possibility would be *primordial* black holes; these would interact with light in the sense of absorbing everything incident upon them, but would be otherwise invisible.

> **Comments:**
> **username_1**: Isn't the "first type" known as the "Missing baryon problem"? https://en.wikipedia.org/wiki/Missing_baryon_problem  
> **username_2**: @DaddyKropotkin yes. I've put that link in.  

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