Number Density vs Energy Density of Radiation and Matter


by cp05
Tags: density, energy, matter, number, radiation
cp05
cp05 is offline
#1
May18-11, 03:24 PM
P: 11
I was going through my notes preparing for finals (this is my last one hooray!), and I saw that the Number Density of radiation and matter changes at the same rate (N=Na^-3) while the energy density is different (E=Ea^-3 for matter, E=Ea^-4 for radiation). I think I get why the energy densities for matter/radn are different (matter exists in 3 dimensions...while radiation exists in 4 because of time...is that remotely correct?), but I don't understand why the number densities are the same.

Thanks for the help!
Phys.Org News Partner Science news on Phys.org
Better thermal-imaging lens from waste sulfur
Hackathon team's GoogolPlex gives Siri extra powers
Bright points in Sun's atmosphere mark patterns deep in its interior

Register to reply

Related Discussions
Effect of ratio of energy density of matter and radiation on redshift Advanced Physics Homework 1
Mass density of stars from number density Astrophysics 0
At what redshift does energy density in matter equal energy density in radiation? Cosmology 5
Calculating Energy density in matter & radiation Cosmology 1
calculating the redshift at which radiation energy density equaled mass density Cosmology 4