I will tell my wife known facts about the universe, and she will then tell me “well that could be fake how do we really know”. Even after explaining all the telescopes and other tools we have to find these facts. She still denies them.
Fantastic question, and one that really touches on fundamental points in science. This question will probably be closed because it's not a good fit for Space StackExchange,
but Skeptics StackExchange might accept it. philosophy.stackexchange might take it.
I'm sure other people have suggested more convincing lines of evidence, but here's one attempt, since you're here. Probably this won't be useful, but I'll try! People have been writing about this problem for many centuries, and far more eloquent versions exist.
In fact, we don't really know that things are known - our brains could just be making everything up! Or maybe the sky is an LCD panel, constructed to fool us into these beliefs (don't laugh! The firmament is an early version of this belief). At a certain point, we will have to trust that something is as it appears to be - science can't help you in the other case.
However, that point can be very close to heart - many profound truths about the universe can be discovered without trusting any other person - not least because many were first discovered by single persons alone!
if we can assume the trustworthiness of our own eyes, we can determine a lot of facts just from what we see around us.
There are countless examples of this.
For instance, the shape of the shadow that the earth casts on the moon, particularly during an eclipse, suggests that the earth is a sphere, or a disk, at least. Another point of evidence is that, on a clear day, ships can be seen to disappear into the distance from the bottom first.
You can measure the speed of light by putting a cracker in the microwave!
Of course, other explanations could be suggested for these facts - but, so far, these disagree with other points of evidence, like the orbits of the stars and sun; so, based on the available evidence, a spherical earth appears to be the most true explanation at hand so far.
From these simple facts, we can build a chain of trust to establish some really incredible things, like the cosmic distance ladder.
There is a second, unfortunate fact which has become very significant in society for the last half-century, which makes it difficult to trust what we hear.
Science fails if we believe things because they are said by someone important; science demands that we believe things because of how convincing the evidence is. However, in recent times, the evidence behind the amazing assertions we hear on the news is inaccessible to anyone who wants to interrogate it for themselves.
A newscaster says the earth is such and such billions of years old, but cannot mention the 50 million pages of data painstakingly collected from hundred of fields, all interlinking towards an in-assailable conclusion, that gave the scientist the confidence to suggest something so incredible.
The scientists are forced to write in a quick, jargon-filled shorthand, only understood by other experts, because they are now paid by the paper and pay by the page. We are forced to hear experiments filtered through press releases, because that is how grant-writers can rank the scientists.
One final point that may be of some interest.
I believe that the world because it is more fun this way. I believe the sun is a giant ball of hydrogen, and not a piece of charcoal held by falsework, first, because the sun can be heard with a radio telescope, and fire cannot, but second, because I hope that someday the same reactions may be produced on earth, to produce as fond a revolution as the water-wheel and windmill did for those of antiquity.
Ultimately, I personally believe in the veracity of the materials scientists when they say that the aluminum in the wings of the plane that delivers me safely to my loved ones can be bent 10,000 times by the air but must then be immediately replaced because of an invisible weakening of the atoms; the biologists when they say their corals have turned white; fundamentally, because the alternative is so much more boring.