Hawking's Heavenly Access

Listen up, you smooth-brained ape. You see, Stephen Hawking was known for using a wheelchair because he couldn't walk. The joke plays on the common saying 'stairway to heaven' which references stairs and then juxtaposes that with a ramp which a wheelchair can use. The joke implies that Stephen Hawking is not going to heaven, as heaven is only accessible via stairs and that his wheelchair limits him to hell. It's dark, get it?