Can you ever go back to previous worlds?

When you travel through the portal to the next world are you ever able to go back to the world you left behind and continue its levels?

It's not possible to get back to previous worlds. Instead, when you travel through the portal, all of your coins are lost, your levels are reset, and you are awarded boom stones which you can use to purchases permanent upgrades. Your best times are recorded on each map that you cleared and you are able to update those times by clearing the maps faster this time.

This is a sort of prestige type system which allows you to play through the game over and over and collect boom stones. I recommend if you have the coin to buy permanent upgrades to your skills before you reset that you spend them as such.