Young Universe Creationism disproved in one easy step (image: UGC 8335)

Explanation: This pair of interacting galaxies is about 200,000 light years across.¹ You can see how stars have been ejected out of each galaxy by the collision, and the galaxies themselves are severely distorted. This collision has clearly been going on for millions of years, not thousands. There are many other beautiful examples of such collisions, such as NGC 4676 and ESO 77-14.

1: I got this figure as follows: the galaxies are 400 million light years away (source) and have an apparent size of 1.7 arcminutes (source). An arcminute is one sixtieth of one degree. With these numbers, it's simple to use Pythagoras to arrive at the size of the object.