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Comment by boothby | Hacker News Reader

Hot* take: -233 is too cold for Celsius. I'm okay with folks reporting critical temperatures in C once they get near room temperature, but this is only 40K (which is blazingly hot in my world, but regardless).

But, it's cool to see the boundaries pushed on the McMillan limit, and that figure with a lazy Susan of sputtering targets looks fun.

* pun acknowledged

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I'm curious by what measure you suggest it's "too cold". Kelvin is an offset celsuis, so it's not like we're talking about an innapropriate order (like 10 000 000 grams vs. 10 tonnes).

I would understand if it detracted from one's understanding, but I think this format is more accessible than assuming everyone knows what kelvin are, and it's explained in the first sentence. This is journalism, accessibility to science should be lauded while maintaining brevity for , IMO.

Frame of reference. Kelvin immediately tells you the distance from absolute zero, which is at least somewhat relevant in this context. Celsius tells you the distance from liquid water which isn't very helpful in understanding the figure.

I think fewer people know the offset between K and C than the fact that 0K represents absolute zero.

-196℃ is another point of reference that might be familiar to people interested in, ehm, cold.

Nitrogen melting point. Essentially the highest low temperature at which you can cheaply do supercold stuff.

(I meant nitrogen boiling point.)

For the layman, 0 degrees celsius is also a good proxy for the distance to "room temperature" superconductor.

> I'm curious by what measure you suggest it's "too cold".

I'm accustomed to thinking about superconductors in an environment on the order of around ~0.01K. And, it's worth spending a little time understanding absolute temperature. Take, say, Zirconium -- its critical temperature is around 0.55K. This new material's Tc is around 40/.55 = 73 times hotter. This perspective is useful if you're thinking about how much work it'll be to get something down to a given temperature. So you've kinda hit my complaint on the head -- it's precisely because temperatures of that magnitude don't make sense to me. And I'd expect folks reading phys.org to be unsurprised by temperatures reported in K.

There’s another more fundamental reason to use Kelvin here, linearity.

100K is twice as hot as 50K, while the idea of twice as hot is meaningless in C or F.

Isn’t it the exact opposite? It you talk to people about something being “twice as warm” or “half as warm” people will assume you are talking about a scale in celcius or something closely related? Because it doesn’t make sense to say “the bedroom is freezing it’s 3/100th colder than the living room!” And no one saying “the bedroom is half as warm as the living room” will be interpreted to be saying that it’s -127 degrees celcius.

No I mean this in a physics sense, not ‘feelings’ sense.

If there is a physical phenomenon that depends on temperature, you can’t use C or F in that calculation unless the temperature parameters somehow cancel out.

So, if y = Tx, twice the temperature means y is twice if x is constant. But only if it’s in Kelvin.

In a “physics sense” there is no such thing as warm or cold those are language constructs not physical properties of materials. In physics there is temperature. You don’t say “the metal bar is 20 warm” you say “temperature is 20 degrees celcius” something having “twice the temperature” isn’t the same as being twice as warm or twice as cold.

I'm not sure if you got the point but I'll repeat. I am not talking about language.

40C is not twice the temperature as 20C, but 40K is twice the temperature as 20K.

You are using language and you seem to make an equivalence of temperature to warm/cold which doesn’t work. Now your saying that it only makes sense to use kelvin because it’s the only scale that doubles when you double it (which is actually also false they all do that). When in fact the concept of “twice as warm” is a fuzzy language construct which matches better to celcius. Which isn’t surprising as both the language and celcius scale are designed around our subjective experience.

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