Which Statements about Cold and Hot Dark Matter are Incorrect?

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Discussion Overview

The discussion revolves around identifying incorrect statements regarding Cold Dark Matter (CDM) and Hot Dark Matter (HDM) within the context of a practice problem for a final exam. Participants explore the properties and implications of CDM and HDM, including their characteristics and effects on structure formation in the universe.

Discussion Character

  • Homework-related
  • Debate/contested
  • Exploratory

Main Points Raised

  • Some participants propose that statements a) and e) about CDM being true are valid, while b) and d) are considered false.
  • One participant asserts that option c) is true, arguing that HDM leads to more suppression of small scale fluctuations compared to CDM.
  • Another participant references an article suggesting that CDM particles may not be as cold as previously thought, indicating a potential challenge to the assumption that they travel much slower than the speed of light.

Areas of Agreement / Disagreement

Participants express uncertainty about the truth of statement c), with differing opinions on the implications of CDM and HDM. There is no consensus on which statements are definitively incorrect.

Contextual Notes

Some statements rely on specific definitions of cold and hot dark matter, and the discussion includes references to observational data that may influence the understanding of dark matter properties.

kingwinner
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I will be writing my final exam tomorrow evening, and I am currently stuck on the following practice problem. It would be very nice if someone could help me out and I will remain eternally grateful for your help!

1) (Multiple Choice) Which of the following statement(s) about Cold Dark Matter (CDM) is (are) incorrect:
a) CDM particles travel at a speed much lower than c
b) neutrinos are a candidate for CDM
c) simulation models using CDM produce smaller scale structures than those using Hot Dark Matter
d) CDM is likely baryonic
e) CDM particles should be more massive than HOT Dark Matter particles

Well, I believe that a and e are true, b and d are false, but I am totally unsure about c...is it true or false and why? Does anyone know?

Thank you!:smile:
 
Astronomy news on Phys.org
Does anyone know whether c is true or false?

Thanks!
 
The option c is true because the more free-streaming (as for HDM) the more suppression of small scale fluctuations. You can read about it here.
 
a) is my guess. There was an article about this about a year ago:
http://news.bbc.co.uk/2/hi/science/nature/4679220.stm
an excerpt:

". . .The speed is a big surprise. Current theory had predicted dark matter particles would be extremely cold, moving at a few millimetres per second; but these observations prove the particles must actually be quite warm (in cosmic terms) at 10,000 degrees. . . ."

Still, much less than 'c' by any measure.
 
What is Cold and Hot Dark Energy?
 

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