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This is how (https://news.ucr.edu/articles/2020/09/28/scientists-precisely-measure-total-amount-matter-universe https://news.ucr.edu/articles/2020/09/28/scienti

This is how (https://news.ucr.edu/articles/2020/09/28/scientists-precisely-measure-total-amount-matter-universe https://news.ucr.edu/articles/2020/09/28/scientists-precisel...): [Dr. Mohamed Abdullah] explained that one well-proven technique for determining the total amount of matter in the universe is to compare the observed number and mass of galaxy clusters per unit volume with predictions from numerical simulations. Because present-day galaxy clusters have formed from matter that has collapsed over billions of years under its own gravity, the number of clusters observed at the present time is very sensitive to cosmological conditions and, in particular, the total amount of matter. That article links to paper, co-authored by Abdullah, Anatoly Klypin, and Gillian Wilson, which concludes that "matter makes up 31.5±1.3% of the total amount of matter and energy in the universe" and "80% of matter is actually dark matter". So 20% of 31.5±1.3% is 6.3±0.26%, which is how much normal matter is in the total amount of matter and energy in the universe. I realize that's different than the 4% number given by the other commenter. This is the latest estimate I could find. Maybe the estimated ratio of dark matter has changed with newer measurements, or maybe the other commenter was working from older estimates.

ncmncm 5y ago
Yes, the number -- 4%, 6%, what have you -- has bounced all over in recent years. Probably 6% is more current than 4%. One of the problems with the standard model of the early universe is that whenever an observation -- e.g. mix of light-element isotopes, expansion rate, simulations -- produces a number different from its predictions, its prediction has been easily adjusted to match.
- xenophonf 5y ago
  One of the problems with the standard model of the early universe is that whenever an observation -- e.g. mix of light-element isotopes, expansion rate, simulations -- produces a number different from its predictions, its prediction has been easily adjusted to match. That's how the scientific method works. You come up with a hypothesis, you test it, you adjust it accordingly, and you re-test it. If you can't come up with tests for it, or if your measurements never match the hypothesis, you throw the hypothesis out. That's why string theory and MOND are getting crapped on in this thread.
8note 5y ago
If they're using baryon acoustic oscillations and the cosmic microwave background, theyre describing the amount of hadrons in the universe after these extra ones would have already become black holes, and be counted separately as "starting" as dark matter. A black hole enthusiast then needs to figure out why those black holes would form before big bang expansion
enkid 5y ago
Thanks for this. The galaxy formation seems to give the 30% matter, where does the 80% dark matter come from? I get that you measuring the density of stuff that has gravity to see how many galaxies form, but how do we know there's not more dust than we'd expect to make up for that missing 80%?
- xenophonf 5y ago
  The 80% number comes from the Dark Energy Survey (https://astronomynow.com/2017/08/05/survey-reveals-most-accurate-measurement-of-dark-matter-structure-in-the-universe/ https://astronomynow.com/2017/08/05/survey-reveals-most-accu...): DES scientists used two methods to measure dark matter. First, they created maps of galaxy positions as tracers, and second, they precisely measured the shapes of 26 million galaxies to directly map the patterns of dark matter over billions of light-years, using a technique called gravitational lensing. To make these ultraprecise measurements, the DES team developed new ways to detect the tiny lensing distortions of galaxy images, an effect not even visible to the eye, enabling revolutionary advances in understanding these cosmic signals. In the process, they created the largest guide to spotting dark matter in the cosmos ever drawn (see image). The new dark matter map is 10 times the size of the one DES released in 2015 and will eventually be three times larger than it is now. There's more info here: https://news.fnal.gov/2021/05/dark-energy-survey-releases-most-precise-look-at-the-universes-evolution/ https://news.fnal.gov/2021/05/dark-energy-survey-releases-mo... And here: https://www.darkenergysurvey.org/ https://www.darkenergysurvey.org/ Dust accounting for the missing 80% of matter and made out of normal matter would be visible in these surveys. It would block, reflect, or emit light. But it isn't visible despite bending light around it—and that's the dictionary definition of dark matter.
  - enkid 5y ago
    Awesome, thanks so much for the informative answers!
    - xenophonf 5y ago
      You're welcome.

ncmncm 5y ago

Yes, the number -- 4%, 6%, what have you -- has bounced all over in recent years. Probably 6% is more current than 4%. One of the problems with the standard model of the early universe is that whenever an observation -- e.g. mix of light-element isotopes, expansion rate, simulations -- produces a number different from its predictions, its prediction has been easily adjusted to match.

xenophonf 5y ago
One of the problems with the standard model of the early universe is that whenever an observation -- e.g. mix of light-element isotopes, expansion rate, simulations -- produces a number different from its predictions, its prediction has been easily adjusted to match. That's how the scientific method works. You come up with a hypothesis, you test it, you adjust it accordingly, and you re-test it. If you can't come up with tests for it, or if your measurements never match the hypothesis, you throw the hypothesis out. That's why string theory and MOND are getting crapped on in this thread.

8note 5y ago

If they're using baryon acoustic oscillations and the cosmic microwave background, theyre describing the amount of hadrons in the universe after these extra ones would have already become black holes, and be counted separately as "starting" as dark matter. A black hole enthusiast then needs to figure out why those black holes would form before big bang expansion

enkid 5y ago

Thanks for this. The galaxy formation seems to give the 30% matter, where does the 80% dark matter come from? I get that you measuring the density of stuff that has gravity to see how many galaxies form, but how do we know there's not more dust than we'd expect to make up for that missing 80%?

xenophonf 5y ago
The 80% number comes from the Dark Energy Survey (https://astronomynow.com/2017/08/05/survey-reveals-most-accurate-measurement-of-dark-matter-structure-in-the-universe/ https://astronomynow.com/2017/08/05/survey-reveals-most-accu...): DES scientists used two methods to measure dark matter. First, they created maps of galaxy positions as tracers, and second, they precisely measured the shapes of 26 million galaxies to directly map the patterns of dark matter over billions of light-years, using a technique called gravitational lensing. To make these ultraprecise measurements, the DES team developed new ways to detect the tiny lensing distortions of galaxy images, an effect not even visible to the eye, enabling revolutionary advances in understanding these cosmic signals. In the process, they created the largest guide to spotting dark matter in the cosmos ever drawn (see image). The new dark matter map is 10 times the size of the one DES released in 2015 and will eventually be three times larger than it is now. There's more info here: https://news.fnal.gov/2021/05/dark-energy-survey-releases-most-precise-look-at-the-universes-evolution/ https://news.fnal.gov/2021/05/dark-energy-survey-releases-mo... And here: https://www.darkenergysurvey.org/ https://www.darkenergysurvey.org/ Dust accounting for the missing 80% of matter and made out of normal matter would be visible in these surveys. It would block, reflect, or emit light. But it isn't visible despite bending light around it—and that's the dictionary definition of dark matter.
- enkid 5y ago
  Awesome, thanks so much for the informative answers!
  - xenophonf 5y ago
    You're welcome.