Discussion Overview
The discussion revolves around the energy received by Earth from the cosmic microwave background (CMB), focusing on its intensity and how to calculate the total energy hitting the Earth annually. Participants explore various methods and assumptions related to this calculation.
Discussion Character
- Exploratory
- Mathematical reasoning
- Technical explanation
Main Points Raised
- Chris initiates the discussion by asking how much energy from the CMB hits the Earth each year, expressing uncertainty about the measurability of this energy.
- One participant cites a CMB intensity value of 4.005 x 10^{-14} J/m^3 from Wikipedia, suggesting that Chris should calculate the total energy using the Earth's surface area.
- Another participant points out that the cited value is a volumetric density and suggests using a different value of approximately 10^{-14} W/m^2 instead.
- There is a discussion about the need to multiply the energy density by the speed of light to convert to a power measurement, but one participant notes that the random direction of the CMB radiation introduces additional complexity.
- Chris shares his calculations, including the energy density, Earth's radius, surface area, and speed of light, ultimately estimating about 1.53 x 10^6 Joules per second from the CMB.
- Another participant proposes using the Stefan-Boltzmann law to calculate the power received, suggesting that the Earth acts as a black body and provides a detailed calculation leading to a power output of about 1.6 Gigawatts.
- This participant also addresses a hypothetical concern about the energy received from the CMB compared to the energy emitted by the Earth, emphasizing that the Earth radiates significantly more energy back into space.
Areas of Agreement / Disagreement
Participants express differing views on the appropriate values and methods for calculating the energy from the CMB, with no consensus reached on the final approach or results. Multiple competing models and calculations are presented.
Contextual Notes
Participants note limitations in their calculations, including assumptions about the directionality of CMB radiation and the choice of intensity values. The discussion reflects varying interpretations of the CMB's energy density and its implications for energy calculations.