Think about it this way.
Googles machine is as thick as 2 short planks.
They try to kid you its all about content, but how can it be?
Imagine you and me sit down with 100 books on a subject we know nothing about, and we're going to read them all and rank them in importance - suppose it's quantum physics, or how to smoke kippers, or anything else.
Unless we're experts in that field we can't do it - Google is a machine - it doesn't even understand the basic words, so how can it do it instead of a human?
By this I mean it might know that blue or green, or red, or orange, or pink fit into a table or database called "colours" but it doesn't understand what "colour" means, it has never experienced it, and it's impossible to express it in words.
Then think about the nuances of the English (or any other language) - a simple inflection, whether spoken or inferred in writing can give a totally different meaning to even a single word, or to a sentence depending on where the inflection is - "I really believe in santa claus" (said in excitement by a kid"), "I really believe in santa claus" (said sarcastically by a grinch), etc.
A human can read between the lines and infer the meaning, a machine can't.
So how then can it be an expert in every conceivable subject or search string that you might type into its search box, and tell you which is the best answer for that search?
It simply can't it has to defer its decision to someone else, someone who IS an expert in that field.
So in quantum physics then maybe Stephen Hawking is the genius, and any other well known and recognised expert in that niche, so if he has linked from his website to yours saying "wow, this guy is good on string theory" then Google can be pretty sure that you are the man for string theory, and can rank you accordingly.
If it was really trying to rank you by reading what you have to say, understanding the words, and understanding the topic, then we'd all have more to worry about than rankings in Google, because Arnold Schwarzeneger would be ramming his mechanical hand up your butt hole as we speak.
Google knows Jack Shit except what we tell it to think and know, and even then it's only by comparing what (it perceives to be) expert A saying something about that topic and website B that's talking about it, etc.
it's so hugely flawed - maybe Stephen Hawking is only talking about you being mr string theory because yours is the only book he's read - if he'd read the other 99 then he might think yours is pants.
Or maybe your his big mate and so he's trying to help you to shift books.
Google is as dumb as a rock, always has been, always will be, and until it can think and understand for itself then links will never die, they are the very core and backbone of the whole numb machine, and like I say, the day that changes is the day you need to stop worrying about rankings and start worrying about living.
Which is maybe what we should all be doing in the first place.