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Physics 18 Online
OpenStudy (kainui):

Operators question

OpenStudy (kainui):

If I know that two operators commute (if necessary we can assume they are Hermitian): \[[A,B]=0\] Is this enough to imply that: \[[\sqrt{A},B] = 0\]

OpenStudy (astrophysics):

They don't commute, that's why they're called commutators which is basically how badly they don't commute.

OpenStudy (astrophysics):

Nerd

OpenStudy (kainui):

!! The commutator tells you how much they commute, if their commutator is 0 they 100% commute, just look: \[[A,B]=0\] \[AB-BA=0\] \[AB=BA\] \[\uparrow\]commutes!

OpenStudy (astrophysics):

You can't do that

OpenStudy (kainui):

boom just did

OpenStudy (kainui):

fite me

OpenStudy (astrophysics):

\[AB \neq BA\]

OpenStudy (astrophysics):

Omg

OpenStudy (astrophysics):

Please don't say it's just a prank bro next

OpenStudy (astrophysics):

Wait "bra" get it

OpenStudy (kainui):

it's real life, son

OpenStudy (astrophysics):

\[[x,p]=0\] \[xp-px=0\] \[xp \neq px\]

OpenStudy (astrophysics):

put a function there and check

OpenStudy (kainui):

Hahaha stop trolling me

OpenStudy (astrophysics):

I'm serious lol

OpenStudy (astrophysics):

They don't commute :S

OpenStudy (kainui):

\[[x,p]=0\] \[xp-px=0\] add \(px\) to both sides \[xp-px+px=px\] use parenthesis to see the obvious: \[xp+(-px+px)=px\] if you agree that \[-px+px= 0\] then you disagree with: \[xp \neq px\]

OpenStudy (astrophysics):

YOU CAN'T JUST DO THAT

OpenStudy (astrophysics):

You need to be careful with operators

OpenStudy (kainui):

Hahaha, no you are misguided somehow, probably been playing with x and p operators too much.

OpenStudy (astrophysics):

I think you're messing with me

OpenStudy (kainui):

Haha, I wish I was now, unfortunately you're wrong :P

OpenStudy (kainui):

if A and B commute, their commutator is 0, it's exactly why it's defined this way, give me an example of two operators that commute which don't have commutator 0.

OpenStudy (astrophysics):

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