Temperature Scale

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The scale in the above diagram is logarithmic, so each tick mark represents a temperature 1,000 times higher than the tick below it. On this scale, the difference between the Sun's surface temperature and room temperature is a small fraction of the range of temperatures opened by the invention of laser cooling. The temperature of the first BECs was determined by watching the cloud of trapped atoms expand when the trap was turned off. At the coldest temperatures represented here, temperature is defined in terms of the energy contained in each degree of freedom of the atoms, including internal degrees of freedom. The so-called spin temperatures—based on the spin degree of freedom—of ultracold atoms have been measured down to 50 picokelvin. If we compare this diagram to Figure 21 of Unit 4, we see that the Planck scale of interest in high-energy physics is off the chart at 1032 K. (Unit: 5)