Can we say that today is twice hotter than yesterday?

Supposing that yesterday’s temperature was 10ºC, if today it is 20ºC, it is not right to say that it is twice hotter than yesterday. First of all, the word “heat” is not well defined since I can say today is hot while other person says it is a bit cold. The notion of “heat” is not the same for everybody, such as the notion of being “tall” or “short”. It differs from person to person. The word “heat” becomes more confusing because the temperature scale accepts negative values. It does not happen when we measure the height of a Human Being, which is always positive. The previously mentioned sentence leads us to serious problems. If the double of heat means the double of temperature, it seems to be logical to say that yesterday it was 10ºC and today it is 20ºC, since temperature has risen twice, this is, yesterday’s temperature was multiplied by 2. But what should we do if yesterday it was -5ºC? If we multiplied this temperature by 2, we would not get twice the heat. On the contrary, it would be colder since -5ºC x 2 = -10ºC. Therefore the statement does not make sense when we are talking about negative temperatures.

So, I can’t use the phrases “twice hotter” or “twice colder”, can I?

You had better to avoid both of the phrases, because besides what have been said, we also have a problem that saying it is twice hotter or twice colder depends on the temperature scale we are using. Actually, 20ºC would be twice hotter than 10ºC. However, 10ºC (Celsius) correspond to 50ºF (Fahrenheit). So, 100ºF are twice 50ºF, which by its turn corresponds to approximately 37.8ºC. It raises serious problems since the notion of the double of the temperature is not the same for an American or for a Portuguese person!

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