🙂

I have never argued against that and it is a result that could be predicted using Newtonian physics although of course there is no such thing as an immovable nor non-deformable object 😉

However we were talking about relativity which can again be illustrated using Newtonian physics.

Two identical cars each travelling at 50 mph crash head on - the "damage" will be exactly the same as if one was travelling at 70mph and the other 30mph or one was travelling at 10mph and the other 90mph or if one was stationary and the other travelling at 100mph or indeed if one was reversing at 10mph and the other going forward at 110mph.  What is important is the relative closing speed.