How do we know how much visible matter exists?

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Discussion Overview

The discussion revolves around the methods used to infer the existence and quantity of visible matter in the universe, particularly in the context of dark matter. Participants explore the definitions and implications of baryonic matter versus dark matter, as well as the challenges in accounting for all forms of matter that may not be easily observable.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the common understanding of "visible matter," suggesting it includes various forms of matter that may not be bright, such as dust, gas, and other non-luminous objects.
  • Another participant introduces the concept of baryonic dark matter and provides links to external resources for further reading.
  • A different participant clarifies that the original question pertains to baryonic matter, not dark matter, and emphasizes the importance of definitions in the discussion.
  • Further clarification is provided regarding the definitions of dark matter, noting that it typically refers to matter that does not interact electromagnetically but can be inferred from gravitational effects.
  • One participant expresses gratitude for the diverse responses, indicating that the discussion has provided multiple perspectives and additional reading material.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and implications of baryonic versus dark matter, indicating that multiple competing views remain regarding how to classify and quantify visible matter.

Contextual Notes

The discussion highlights the complexity of defining "dark matter" and "visible matter," with participants noting that definitions can influence the interpretation of the question. There are also unresolved aspects regarding the completeness of the definitions and the types of matter that may exist but are not accounted for in current models.

Xezlec
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In discussions of how we infer the existence of dark matter, it always feels like people gloss over how exactly we know how much "visible matter" exists. I am led to believe that "visible matter" refers to any matter which can interact with things like photons, but doesn't that include things that might not be bright and flamey like stars? How can we tell there isn't just way more dirt, dust, gas, rock, rogue planets, space squirrels, icky black crud, and floating black velvet paintings of Elvis out there than what is close to stars and thereby illuminated?
 
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Math Is Hard said:
No, I think the question is about plain old baryonic matter. Not dark. It's a good question.

It depends on how you define "dark matter". The proposed explanations from Xezlec are within the definitions on baryonic dark matter, (MACHO). The deifinition made by wiki article on Dark Matter "dark matter is hypothetical matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter." which already in the definition out rules the possibility of baryonic (in this context non leptonic, neutrino background are referred to as baryonic dark matter even thoug neutrinos are leptons)- and strong interacting dark matter.

The best definition of dark matter would be matter that can't be observed by telescopes due to their EM interactions but must exist due to its gravitational interaction. With this definition; both WIMPs, MACHOs, 'baryonic' and SIMPs (strongly interacting dark matter) are possible.
 
Thanks, everyone! That answers my question six ways from Sunday, and gives me more to read about too.
 

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