Do HTTP paths have to start with a slash?

I have a question regarding the HTTP format. The first line of a HTTP request looks something like this:

GET /path/to/resource.txt HTTP/1.1

or in other words:

METHOD URI HTTP-VERSION

Is it required that the URI starts with the / character so that /path/to/resource.txt would be the same as path/to/resource.txt and both are valid?

And if a leading / is not required, are GET / HTTP/1.1 and GET HTTP/1.1 the same too? (two spaces between GET and HTTP/1.1)