Go straight to the patent: US20110106895

This approach is very different from the earlier search
model of using authority as a measure of trust. In a
document-based world (such as the early days of
the Internet when only web pages existed), trust was
measured by how credible a document was. The
credibility was measured by how many citations (links)
a web page received. This is why link building is such
an important aspect of SEO. Web pages need links to
improve their credibility or “trust” in the eyes of the search
engines. This, in turn, improves their rankings.

But, as the patent states, in a social environment, you
don’t measure trust by authority; instead, you measure it
by intimacy. For example, if a family member recommends
a good restaurant, you’re more likely to believe them than
an anonymous reviewer online. That’s because you know
your family member, and because of that relationship/
closeness, you have trust.

Social search represents considerable opportunity for
search engines because they want to deliver more
personalized search results. But in order to do so, they
need to understand who you know and how well you
know them. Tapping into your online social signals allows
them to do just that.

Here’s a reminder of what Google said about social search in 2011: