Sam asked:
What definitions of the term ‘scientifically impossible’ have been suggested?

Answer by Craig Skinner
There are 5 different types of impossibility. Here they are, each with an example:
1. Logical impossibility (fixed by logic) eg a ball can’t be red all over and not red all over at the same time.

2. Analytic impossibility (fixed by meanings of words) eg a bachelor can’t be a married man.

3. Physical impossibility (fixed by physical features in our world) eg a man can’t jump 3 miles into the air using only the power of his own body.

4. Nomological impossibility (fixed by laws of nature) e.g. a ray of light can’t reflect off a mirror at any angle other than the incidence angle.

5. Metaphysical impossibility (fixed by the nature of things) eg water can’t be anything but H2O.
There is no separate type of ‘scientific’ impossibility. The term usually refers to nomological impossibility (contrary to laws of nature eg it’s scientifically impossible to travel faster than light); sometimes to physical impossibility e.g. it’s physically impossible to build a cube of pure gold with sides 1000 miles long, there’s not enough gold in the whole known universe. I think the term is best reserved for nomological impossibility. Of course scientific laws are only the current best explanation for our observations, are held provisionally, and may change as knowledge advances, so that we shouldn’t be too dogmatic when pronouncing something scientifically (nomologically) impossible.