If the whole world believed in a lie, would that make it the truth?

It would make it their truth and all they need is a herd that believes the same to set their beliefs in stone.

There must be some truth to be discovered.

To be honest, yes. As no one would be able to tell you what the truth was.

We believe plenty of lies everyday.

We accept a whole lot of things as true - until they are not. Some are misunderstandings, some are distortions of statements and some may be lack of knowledge. Remember when eggs were bad for us? May not have been a lie or not, or just a miss-statement that became accepted.

it will be even been truth but people started believing it , believe and truth are different thing to each other , you can believe anything and will be change time but truth will never change

No

The whole world could believe the sun revolved around the Earth, but that wouldn't make it true. It all depends on what kind of truth you're referring to.

That would make it some people's truth. But not the truth itself.

Aww heck no! I can stand alone.

An Orwellian truth.

Nope

No

Realism is the belief that reality exists outside of our minds