Is this message right?
 

Hi! I had to send a message to a physics forum, but I'd like to know if it's syntactically and grammatically correct. Can you please check it out?

"Hi! I was taught that the dirac matrices are AT LEAST 4x4 matrices, so that means that I can find also matrices of higher dimensions. The question is: what do these higher-dimension-matrices represent? Are they just mathematical stuff or have they got a physical meaning? I ask that because in every textbook and in every course I used only the 4x4 matrices...
Thanks"

And just another thing: I used to start topics saying: "Hi there!": is this right or it sounds wrong/odd?

Thank you!

Your message seems fine to me, it appears to be grammatically correct at least. Also 'Hi there!' sounds fine, it's a perfectly acceptable expression to use in greeting in an informal setting.

Actually I think it should be "so that means that I can also find matrices of higher dimensions." I'm sure they'll understand you either way :)

And "Hi There!" is perfectly fine

seems cool! :cool:

It could read something like:

"Hi! I was taught that dirac matrices are AT LEAST 4x4 matrices, which means I can also find matrices of higher dimensions than that. The question is, what do these higher-dimension matrices represent? Are they purely mathematically abstract or do they have a physical meaning? I ask this because in every textbook I've used or course I've taken, I've only used 4x4 matrices.
Thanks"

I would not add the "than that".