Ratio of number density of photons to baryons

Help with conceptual understanding is requested due to the unavailability of the lecturer. In summary, the photon/baryon ratio is a constant value determined by the number density of CMB photons and baryons. It can be evaluated at different redshifts, such as z=0 and z=100, by considering the inverse proportionality of particle number densities to volume. Assistance with conceptual understanding can be sought in the absence of the lecturer.
  • #1
indie452
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Homework Statement



photon/baryon ratio = Np/Nb

Np, is the number density of the CMB photons
Nb, is the number density of baryons
Evaluate this ratio at the redshifts z=0 and z=100.

From my understanding, if interactions are negligable, particles cannot simply disappear. Therefore, particle number densities reduce inversely proportional to the volume.
This would mean that the ratio of CMB photons to baryons was constant. So how can I evaluate this at two different redshifts?
I ask here cause my lecturer is in germany this week and therefore not available.
Help with the conceptual understanding would therefore be appreciated.

Thanks
 
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!Homework Equations Np/Nb = constantThe Attempt at a Solution Assuming that the particle number densities reduce inversely proportional to the volume, then the ratio of CMB photons to baryons is constant. So Np/Nb = constant for both z=0 and z=100.
 

1. What is the ratio of number density of photons to baryons?

The ratio of number density of photons to baryons, also known as the photon to baryon ratio, is a measure of the abundance of photons and baryons in the universe. It is typically expressed as a fraction, with the number density of photons in the numerator and the number density of baryons in the denominator.

2. Why is the ratio of number density of photons to baryons important?

The ratio of number density of photons to baryons is important because it provides insight into the evolution and composition of the universe. It is a crucial parameter in models of cosmology and helps us understand the early stages of the universe and the formation of structures such as galaxies and clusters of galaxies.

3. How is the ratio of number density of photons to baryons calculated?

The ratio of number density of photons to baryons can be calculated by dividing the number density of photons by the number density of baryons. The number density of photons can be estimated from measurements of the cosmic microwave background radiation, while the number density of baryons can be estimated from observations of the abundance of light elements in the universe.

4. What is the current estimated value of the ratio of number density of photons to baryons?

The current estimated value of the ratio of number density of photons to baryons is approximately 5.4 photons per baryon. This value is based on observations of the cosmic microwave background radiation and the abundance of light elements, and is consistent with predictions from the standard model of cosmology.

5. How does the ratio of number density of photons to baryons change over time?

The ratio of number density of photons to baryons is believed to have remained constant throughout the history of the universe. However, as the universe expands and cools, the number density of photons decreases while the number density of baryons remains relatively constant. This results in the ratio of number density of photons to baryons increasing over time.

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