Question 1

Why does the United States still use the Fahrenheit scale instead of Celsius?

Accepted Answer

The United States retains the Fahrenheit scale primarily due to historical inertia, industrial legacy, and the massive cost of infrastructure conversion. When the metric system was heavily promoted in the 1970s via the Metric Conversion Act of 1975, the adoption was strictly voluntary, and public resistance was high. Because Fahrenheit provides a highly granular 0-to-100 scale that perfectly brackets the extremes of the North American climate, the general public found no compelling daily benefit to switching to Celsius. Furthermore, replacing millions of HVAC thermostats, industrial gauges, oven dials, and weather reporting systems would cost billions of dollars without providing a commensurate economic return for domestic operations.

Question 2

What exactly is absolute zero, and has it ever been reached?

Accepted Answer

Absolute zero is the theoretical temperature at which all macroscopic thermal motion ceases, defined as 0 Kelvin, -273.15 °C, or -459.67 °F. At this point, particles retain only their quantum zero-point energy, meaning they vibrate at the lowest possible physical state allowed by quantum mechanics. Absolute zero has never been reached, and according to the laws of thermodynamics, it is impossible to reach because doing so would require a system to be perfectly isolated from the rest of the universe. However, scientists have used magnetic cooling and lasers to chill specific atomic systems to fractions of a billionth of a degree above absolute zero (picoKelvins), creating exotic states of matter like Bose-Einstein condensates.

Question 3

Is there a maximum possible temperature, just as there is a minimum?

Accepted Answer

Yes, theoretical physics posits a maximum possible temperature known as the Planck temperature, which is approximately $1.416 	imes 10^{32}$ Kelvin (142 nonillion degrees). At this unfathomable temperature, which is believed to have existed only a fraction of a second after the Big Bang, the wavelength of the thermal radiation emitted by a body becomes equal to the Planck length. The Planck length is the smallest measurable distance in physics; therefore, any temperature higher than the Planck temperature would result in particles possessing so much energy that their gravitational forces would be as strong as their quantum forces, causing the known laws of physics and the fabric of spacetime to entirely break down.

Question 4

What is the difference between "Celsius" and "Centigrade"?

Accepted Answer

There is no mathematical difference between Celsius and Centigrade; they refer to the exact same temperature scale. The term "centigrade" simply means "100 steps" in Latin, which described the 100 degrees between the freezing and boiling points of water on Anders Celsius's scale. For centuries, "centigrade" was the common term. However, in 1948, the 9th General Conference on Weights and Measures (CGPM) officially dropped the term "centigrade" in favor of "Celsius" to honor the inventor and to eliminate confusion with the "centigrade" angular measurement used in some European countries (where a right angle is divided into 100 centigrades). Today, "Celsius" is the only scientifically correct term.

Question 5

Why do Celsius and Fahrenheit intersect at exactly -40 degrees?

Accepted Answer

The intersection at -40 degrees is a mathematical inevitability caused by the difference in the zero points and the rate of change (slope) between the two scales. Because Fahrenheit degrees are smaller than Celsius degrees (by a ratio of 5/9), the Fahrenheit scale "moves faster" numerically as you move away from their respective zero points. If you set the conversion formula $F = (C 	imes 1.8) + 32$ such that $F = C$, you get the algebraic equation $X = 1.8X + 32$. Subtracting $1.8X$ from both sides gives $-0.8X = 32$. Dividing 32 by -0.8 yields exactly -40. Therefore, -40 °C and -40 °F represent the exact same level of thermal energy.

Question 6

How do I convert a temperature difference or interval, rather than an absolute temperature?

Accepted Answer

Converting a temperature interval (a change in temperature) is fundamentally different from converting a specific temperature point, and this is a common source of errors. When converting an interval, you ignore the zero-point offsets (+32 or +273.15) and only use the degree magnitude ratios. If a room's temperature increases by 10 °C, you convert this interval to Fahrenheit by multiplying strictly by 1.8. Therefore, a 10 °C increase is an 18 °F increase. If you mistakenly applied the full formula and added 32, you would erroneously calculate a 50 °F increase. For Kelvin and Celsius, a 10 °C interval is exactly equal to a 10 K interval.

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