How do you get past the invisible thing on 6th gym no Pokemon ruby?

You're likely talking about the Invisible Wall in the 6th gym of Pokemon Ruby. This isn't actually an "invisible thing", but a trick that requires a specific move to overcome.

Here's how to get past the Invisible Wall:

1. Get a Pokemon with the move "Cut". You can obtain Cut from the Move Tutor in Slateport City, located in the house to the left of the Pokemon Center.

2. Use "Cut" on the Invisible Wall. Once you have a Pokemon with Cut, simply use the move on the wall. This will clear the way and allow you to continue through the gym.

Note: If you are having trouble finding the Move Tutor, make sure you have spoken to the Gym Leader, Wattson, before attempting to get Cut. This will trigger the event that allows you to learn Cut.

Let me know if you have any other questions!