Is /æ/ pronunced like the shortened version of /ɑː/?

• /æ/ is a near-open front unrounded vowel
• /ɑ/ is an open back unrounded vowel

They are different vowels with different tongue positions. The tongue position for /æ/ is near-open and front, meaning the tongue is nearly as low as it can go, and pushed towards the front of the mouth. The tongue position for /ɑ/ is open and back, meaning the tongue is as low as it can go and pushed towards the back of the mouth. The tongue height is almost the same but the frontness is very different.