indexed on google without www does that make a difference

I just noticed that my site has been indexed on google minus the "www." will this affect my ranking in anyway. I noticed this also happens for other sites too. Even this one.

Also what causes this?

google "swiftcolour" comes up as swiftcolour.com

 

It does make a difference. Remember, technically you can have your domain pointed with the www to one server and without to another, so as far as a Search Engine is concerned it's only natural that it will treat those URLs as autonomous sites.
The way to resolve this is to place an HTaccess redirect to the version you want to see indexed. You can also log in to your Google Webmaster Tools and configure which version of your site do you want the bot to index.

 

thanks for that info. ill get right on it.

 

But as long as it is just one showing, it should be fine. Unless both www. and another without is showing at same time, then that would be a problem.