Ratio of matter to radiation density

In summary, the conversation discusses the ratio of matter to radiation density in the universe and whether it remains constant or varies over time due to the annihilation of matter to radiation and vice-versa. It is explained that as the universe expands, the density of both radiation and matter decreases, but at different rates. The volume that a given amount of matter occupies is proportional to the scale of the universe, while radiation is affected by the expansion of the universe and the wavelength of photons. The ratio of matter to radiation density is considered to be "fairly constant". The conversation also briefly mentions a paper on dark energy and a correlation between inertial mass density and the cosmological constant, but it is stated that such discussions are not allowed on the forum
  • #1
Ranku
410
18
Is the ratio of matter to radiation density constant in the universe? Or does it vary over time, as matter annihilates to radiation and vice-versa?
 
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  • #2
As the universe expands, both radiation and matter "thin out", but at different rates. Expansion of the universe decreases the density of radiation more rapidly than it decreases the density of matter.

If ##a \left(t\right)## is the linear scale of the universe (so ##a \left(t\right)## increases as time ##t## increases), then the volume that a given amount of matter occupies is proportional to ##a \left(t\right)^3##, and thus matter densities scales as ##1/a \left(t\right)^3##. Radiation is made of photons, and photon density also scales as ##1/a \left(t\right)^3##, but the expansion of the universe also scales the wavelength by another factor of ##a \left(t\right)##, so radiation energy density scales as ##1/a \left(t\right)^4##.
 
  • #3
Thank you for your reply. While I am aware of how matter and radiation vary with the scale factor, this is what I am trying to ascertain: is the total amount of matter and total amount of radiation in the universe constant, or does it vary because of annihilation of matter to radiation and vice-versa?
 
  • #4
Let ##\rho_r \left(t\right)## be the density of radiation and ##\rho_m \left(t\right)## be the density of matter. I think that you are asking "Is

$$\frac{\rho_m \left(t\right) a\left(t\right)^3}{\rho_r \left(t\right) a \left(t\right)^4}$$

constant?"

I think that this ratio is now fairly constant.
 
  • #5
Yes, that is what I am trying to ascertain. Could you please clarify what do you mean by "fairly constant"?

While I should not plug my own work, recently I published a paper online on dark energy where I argue for a correlation between inertial mass density and the cosmological constant. Thus, if total matter density were not to be constant, that would affect the rate of acceleration of the universe, and thereby provide a way to test the correlation. You may like to check out the paper at http://article.sapub.org/10.5923.j.astronomy.20140301.02.html
 
  • #6
Ranku said:
While I should not plug my own work, recently I published a paper online on dark energy where I argue for a correlation between inertial mass density and the cosmological constant. Thus, if total matter density were not to be constant, that would affect the rate of acceleration of the universe, and thereby provide a way to test the correlation. You may like to check out the paper at http://article.sapub.org/10.5923.j.astronomy.20140301.02.html
Ranku,

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  • #7
Unacceptable references have been removed and this thread is closed.
 

1. What is the ratio of matter to radiation density?

The ratio of matter to radiation density is a measure of the amount of matter and radiation present in the universe. It is typically expressed as a fraction or percentage of the total density of the universe.

2. How is the ratio of matter to radiation density determined?

The ratio of matter to radiation density is determined through various observational methods, such as measuring the cosmic microwave background radiation and studying the distribution of galaxies in the universe. These measurements provide insights into the relative amounts of matter and radiation in the universe.

3. How does the ratio of matter to radiation density affect the evolution of the universe?

The ratio of matter to radiation density plays a crucial role in the evolution of the universe. In the early stages of the universe, radiation dominated and drove rapid expansion. As the universe expanded and cooled, matter began to dominate, leading to the formation of structures like galaxies and clusters of galaxies.

4. Does the ratio of matter to radiation density change over time?

Yes, the ratio of matter to radiation density changes over time as the universe expands and evolves. In the early universe, radiation was much more dominant, but as the universe expanded and cooled, matter became the dominant component.

5. What is the current estimate for the ratio of matter to radiation density?

The current estimate for the ratio of matter to radiation density is approximately 5:1. This means that for every 5 units of matter, there is 1 unit of radiation. However, this ratio is expected to change as the universe continues to evolve and expand.

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