If it’s 0 degrees today, and it’s twice as cold tomorrow, what’s the temperature tomorrow?
There is no answer to that, at least none that we can agree on. There is no universal standard temperature from which point positive is “warm” and negative is “cold.”
Assuming you mean 0°C, that’s 273.15K. Twice as cold would be 136.58K, or -136.58°C.
Most temperature readings are not always exctly 1 or 2 or 25 degrees exactly thery are always read as whole numbers because that is what thermometers have painted on them…so in all likelyhood the exact temperature would not be 0 degrees…it was probably 0.1 degrees for example …so if it is twice as cold then it would be 0.2 degrees if we chose the above example:
Nope, freezing point is only an arbitrary point. Minus 136 degrees or so would be “half the temperature” in thermodynamic terms. But I doubt if it’ll get that cold 
(despite last night’s frost… I thought this was meant to be mid May?)
Well, the only time that “twice as cold” “twice as hot” etc would have any real meaning would be when you’re dealing with a temp scale that has it’s zero at absolute zero. 40F isn’t twice as hot as 20F, but 40K is twice as hot as 20K.
You didn’t mention a temp scale, but I’d say the answer would be halfway between absolute zero and the zero of whatever scale you’re using. Assuming that you’re using celsius, it’d be about -136 degrees.
Of course, I could be wrong…
How do you guys justify using 0 C as a standard? 5 degrees C is pretty cold - if it gets twice as cold, it’ll be 10 degrees C???
If I were to invent a scale, I’d use 20 degrees C as a standard. Twice as cold as 10 degrees C would be 0 degrees C, and twice as hot as 30 would be 40. But there is no ready-made scale you can use.
This is one of those thingimajig thingies where the statement is a non-something or other and it should in pedanto-world be ‘half as hot’
cold is not a thing, it’s a non thing. hot is the thing, ‘cold’ is the lack of hot.
And therefore “twice as cold” is equivalent to “half as hot”, and what Mikahw and I said is right. Or are we missing something, too?
No. ‘half as hot’ is right. It’s kind of what I said.
I thought the reformulation in of Kelvin and then deviding by two was correct, too. Celsius or Fahrenheit are not ratio scales, whereas Kelvin is. But I can see src4’s(and lobsang’s point: “half as cold” may not be the same as “halve the temperature”.
So whaddaya mean, brainfizz? Was your question about physical scales (that question is answered) or about how to quantify the experience of cold?
I saw it as someone’s sig and was a little baffled!
I also thought that it would mean -136 degrees, but when I thought about it, it would feel more than twice as cold. So, since our bodies feel cold relative to our body temperature, the answer may well be -36.5 degrees.
Temperature measurements can be just about as precise as you wish them to be, if you get a sophisticated enough measuring device. They are certainly NOT “always read as whole numbers.” Even commonly available mercury or alcohol thermometer are available with 0.1 deg C gradations.
As for the rest of your post: what? 
I’ve wondered this problem for ages, and this seems like the right place to ask:
Suppose on one particular day, 40% of the people like the President, and 60% do not like him. Then, more people start liking him. Which poll results would lead you to say that “He is twice as popular as before.”
Would it be:
A) 80% for, 20% against, because twice as many people like him; or
B) 70% for, 30% against, because half as many people dislike him; or
C) Perhaps there is a different way to calculate it. It bothers me that A and B are such very different situations: In A, it is a 4 to 1 ratio, but in B it is merely 2.33 to 1.
You are asking a quantitative question about a concept (“cold”) that cannot be quantified. (“Temperature,” on the other hand, can be quantified.)
For that matter, how do you quantify how cold you feel? You mention that “our bodies feel cold relative to our body temperature,” but body temperature is not equal to ambient temperature unless you are dead. The rate of heat loss from your body depends not only on ambient temperature, but also on the clothing you are wearing, wind speed, if you are immersed in water, etc. Indeed, a person nearing death from hypothermia may not feel cold at all!
The “neutral temparature” for humans is between 40 and 36 degrees celsius.
When the skin gets colder than 18 degrees, pain, not cold, is experienced. “Cold” applies thus to the range 36-18 degrees.
People can discriminate around a 2% change is temperature (0.36 degrees). If we take this as our unit, then there are 36-18/0.36 = 50 "cold"steps. Now, it depends on how warm your skin is at 0 degrees, but with these numbers you can define “half as cold”, couldn’t you?
Say you skins temperature is 34 at zero degrees (-2 steps on the cold scale) in order to get to -4 steps, your skin needs to be 0.72 degrees cooler. How you want to achieve that, is entirely up to you (turn down the heating, undress, use a fan)
Someone help me out here, but I seem to remember something from high school chemistry that the time for a chemical reaction increases by ‘x’ percent for every 10 degrees centigrade increase in temperature.
Am I making up scientific principles in my head again?
Going with Goodbeem’s 40-36C ambient temperature, I arbitrarily assign the standard at 38C. A given time period’s average temperature at a given location will be algebraically compared with the standard of 38C to determine whether the time period is cold or warm. To properly use the term “twice as cold,” the speaker will need to reference a time period that can be assigned the label “cold,” using that standard, then determine that the time period under discussion deviates twice as far from the standard as does the reference. Example:
The daylight hours on the plaza in front of City Hall in Santa Ana California recorded an average temperature of 25C.
38C - 25C = 13C
13C X 2 = 26C
38C - 26C = 12C
The time during the night that the temperature drops to 12C is the time that we can meaningfully say that the plaza in front of City Hall in Santa Ana, California is “twice as cold” as during the daytime.
Alternatively, the location that records an average daylight temperature of 12C during the same time as Santa Ana records 25C will be meaningfully described as “twice as cold.”
I hope this method proves useful to some of you. For me, it is useful as a tool for confirming me in my attitude that the phrase “twice as cold” is an unhelpful usage that should be avoided as much as possible.
Ravenman, you’re not hallucinating (well, at least on the chemical reactions increasing with temperature, anyway. )
It’s a decent rule of thumb kind of thing, but chemical reaction rates more or less double for every 10 degree celcius rise in temperature. So that’s 100% increase for a 10 degree rise or 50% decrease for a 10 degree drop. That 's cumulative, of course, so a 30 degree drop in temp means the reaction is (1/21/21/2) one eighth as fast.