He is denying the torment of the grave on the grounds that if he were to open a grave he would not see any change

No File Exists
Check below answers in case you are looking for other related questions:
Do the blessing and torment in the grave happen to both the body and the soul or to one of them only?
Settling of scores among the animals on the Day of Resurrection

No File Exists
Related Answers:
The reason why the torment of the grave is hidden from man
The gathering of mankind and the animals
Do the dead visit or feel or see one another in their graves?
Do the blessing and torment in the grave happen to both the body and the soul or to one of them only?
Settling of scores among the animals on the Day of Resurrection

Recommended answers for you:
Performing Another ‘Umrah While in Makkah
What can a woman who is menstruating do on Laylat al-Qadr?
Using the birth control pill and the coil
He wants to marry a girl with whom he had a relationship
The seven sins that doom a person to Hell