Temperatures, Energies, and Lengths

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Theoretical physicists tend to use units of length, energy, and temperature interchangeably. Energy is related to temperature through the expression E = kT, where k is Boltzmann's constant, so high energies correspond to high temperatures. Energy is proportional to 1/length, as we saw in section 2 and as we will see in a different context in Units 5 and 6. So, high energies and temperatures correspond to short distances. The scale in the diagram above is logarithmic, so each tick mark is separated by a factor of 100,000. It is amazing to realize that physics at the Planck scale is closely related to physics on cosmological scales nearly 60 orders of magnitude larger. (Unit: 4)