whats the diffrence?

An alias is just another name for yourself. An alter ego makes you act like a different person.

EXAMPLE: My alias is George.My alter ego Made me slap the teller at the bank.

Alias-a false name used to conceal one's identity; an assumed name: The police files indicate that “Smith” is an alias for Simpson.

Alter Ego- a second self; a perfect substitute or deputy: His adviser acts as his alter ego during his absence. (So when you hear of people with split personalities, that second personality would be considered their alter ego)

They are very similar.

Alias refers to the alternative name, like a nickname. It could have / encapsulate a special meaning associated with the person.

Alter ego refers to the personification, the idealistic self by choice of that person. It is a description of what quality / characteristic a person identifies himself or herself with.

Difference is beautiful that make chose