How do we measure energy density of radiation?

In summary, the energy density of matter is approximately 0.3 and is measured through galaxy motion and gravitational lensing. The energy density due to vacuum is 0.7 and is measured through the expansion rate, with dark energy as the main suspect. The radiation density is approximately 10^-4 and is measured directly through the Cosmic Microwave Background (CMB). Other sources, such as radiation from exploding stars, do not significantly contribute to the overall radiation density.
  • #1
binbagsss
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I have that the energy density of matter approx 0.3 , so this is measured by galaxy motion / gravitational lensing etc, that's fine.

I have that the energy density due to the vacuum is 0.7, so this is measured by the expansion rate- the common suspect being dark energy.

I have radiation contribution approx 10^{-4}. How is this measured? Or is this theoretical?

Thanks
 
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  • #2
The radiation density is the energy density of the CMB, and has been measured directly.
 
  • #3
Chalnoth said:
The radiation density is the energy density of the CMB, and has been measured directly.

nothing else contributes? like when a star explodes, the EM radiation given off then e.g?
 
  • #4
binbagsss said:
nothing else contributes? like when a star explodes, the EM radiation given off then e.g?
Not to any significant degree. The CMB comprises nearly all of the radiation ever emitted, by energy density.
 
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1. How is energy density of radiation measured?

The energy density of radiation is typically measured by calculating the amount of energy present per unit volume. This can be done using a variety of instruments, such as a calorimeter or a spectrometer, which are specifically designed to measure the energy of radiation.

2. What units are used to measure energy density of radiation?

The most commonly used unit for measuring energy density of radiation is joules per cubic meter (J/m3). However, other units such as watt-hours per cubic meter (Wh/m3) or electron volts per cubic meter (eV/m3) may also be used depending on the specific application.

3. What factors affect the energy density of radiation?

The energy density of radiation can be affected by several factors, including the type of radiation (e.g. electromagnetic, particle), the intensity or strength of the radiation, and the distance from the source of radiation. Other factors such as the medium through which the radiation travels and any barriers or shielding can also impact the energy density.

4. How does energy density of radiation relate to radiation exposure?

Energy density of radiation is directly related to the amount of radiation exposure an individual receives. In general, the higher the energy density of the radiation, the greater the potential for harm to living organisms. This is why it is important to monitor and limit exposure to sources of high energy density radiation, such as X-rays or nuclear radiation.

5. Can energy density of radiation be converted into other units?

Yes, energy density of radiation can be converted into other units depending on the specific application or calculation. For example, it can be converted into units of power (energy per unit time) by multiplying by the speed of light. It can also be converted into units of dose (energy per unit mass) by factoring in the type of radiation and the material it is passing through.

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