Keep your cool

We must convert to Kelvin first. $\large 0℃=273.15K$ Halving the temperature, we get $\large\frac{273.15}{2}K=136.575K=0-136.575℃=-136.575℃$ Rounding to the nearest integer , the answer is $\large\color{#20A900}{\boxed{-137℃}}$

That would depend on what temperature scale you are using. The scale which places zero degrees at the absolutely coldest point is called the Kelvin scale. It has the same degree divisions as Celsius does. "Absolute zero," or zero kelvins, is the coldest temperature possible. So, if you are measuring in kelvins, twice as cold is not possible.(0/2=0) However, if you are using the Celsius scale, zero degrees is actually 273.15 degrees above absolute zero. So, twice as cold would be -136.575 degrees Celsius. Similarly, absolute zero in Fahrenheit is -459.67. Thus, from zero degrees F, twice as cold would be -229.835 degrees F.

There is no twice as cold but half as hot in absolute temperature to be strict. However, answer wanted is understood.

Twice as cold as 0°C: -136.575°C or -213.835°F

Twice as cold as 0°F: -(145+ 167/360)°C or -229.835°F {Half of -459.67°F}