Title text:
Unstoppable force-carrying particles can't interact with immovable matter by definition.
Transcript:
[An arrow pointing to the right and a trapezoid are labeled as 'Unstoppable Force' and 'Immovable Object' respectively.]
[The arrow is shown as entering the trapezoid from the left and the part of it in said trapezoid is coloured gray.]
[The arrow is shown as leaving the trapezoid to the right and is coloured black.]
[Caption below the panel:] I don't see why people find this scenario to be tricky.
Source: https://xkcd.com/3084/
The expression as I heard included "an irresistible force."
Yeah, irresistible force is the version I know. Now I'm wondering if there are even more versions. Are they regional deviations?
While not what you're asking for, but fun fact, in Asia, this sort of paradox is represented by the story of the all-piercing spear and the unpierceable shield in Chinese philosophy. So in Chinese and Japanese, the word for 'paradox' or 'contradiction' literally means 'spear-shield' (矛盾).