You can look at the thread "Acceptance by pGRE Score -- Data dump! (winter 2015)" on this forum. If you look at the thread, you would find that the mean PGRE for admitted students as calculated on this forum was 820, whereas the median was 840. It seems to be always the case that the mean computed from the forum's sample is higher by approximately 30 points than the actual mean, in which case submitting your PGRE wouldn't hurt. I'm not sure what active matter is. Is it the physics department? If so, they would probably expect you to submit the PGRE if you have a physics background.