Well, I think real is everything people can realize and observe/discover by using their sense organs.
Do you trust your eyes? Try this experiment....
Close your left eye and stare at a small object about 10 feet away with your right eye. Keep your focus on that object. Now extend your right arm straight out in front of you and hold the tip of your 1st finger up so that it covers the object you're looking at. Now very slowly rotate your arm to the right at the shoulder while keeping the arm straight and the finger at the same level as before. Keep your focus on the distant object all the while. As your fingertip sweeps through about 20-25^ off-line with the distant object, you'll notice in your peripheral vision that the tip of your finger briefly disappears. When that happens, move your arm around until you can hold it at the precise angle where the fingertip remains invisible. Remember, this is with your peripheral vision--you're still focused on the distant object. Flick your gaze to your fingertip and it reappears. Flick back to the distant object and it's gone again.
Your fingertip disappears at that angle because it's then in line with the dead spot on your retina where the optic nerve attaches. There are no rods or cones there. That area, very close to being directly in front of you, is a blind spot. You've got another one just like it on the left side. But you don't perceive these blindspots in everyday life because you're brain "Photoshops" the image. It pastes a piece of the nearby background over the blindspots so you don't notice them unless you're looking for them with an experiment like this.
So, there's proof that every waking moment, what you perceive is at least partially a product of your own imagination. And your imagination is so good that you don't even realize you're not perceiving reality. So how can you trust any of your senses at any time?
And there is just one reality where 6.6 billions humans live in which is more than rather obvious. I don't know different realities, dimensions and parallel universes and I also can't find any single sign beside a lot of different fantasies out of human brains.
You sound like the guys who gave Gallileo such a hard time. It makes me wonder why you don't burn Orbiter as an heretical text
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Do you perceive any of Earth's motion through space? No, and neither does anybody else. Just relying on your senses, it's "rather obvious" that we live in a Ptolemaic universe, because the only motion we can perceive is that of the everything out there circling around Earth.
As everybody on this forum knows, that ain't how it works. However, there are still cultures on this planet that truly believe in the geocentric arrangement, and even that the Earth is flat. Such people have a different perception of reality than we do. So it's not "rather obvious" that we all have the same perception of the same reality.
In addition, Ptolemaists and Flat Earthers have a MUCH easier time supporting their position than we do. Everybody can agree that the senses back up their assertions. We have to prove our position via complex mathematics and observations made by fancy tools, which require further complex mathematics to interpret.
Physicists and cosmologists, if believed to be serious or not, can 'believe' anything they want. People don't even need to be scientists to do so
It's not a question of belief. I can believe in the Church of the Subgenius if I want to, but that doesn't make it real.
You really should read up on quantum physics and cosmology. If you accept that Kepler and Newton were improved upon by Einstein, then you should accept that more recent workers have improved upon Einstein. They're the 1st to admit they don't know all the answers yet. Why do you think they just built that Large Hadron Collider over in your part of the world?
The balance of things at present is that there is far more to the universe than meets the eye. There's all that dark matter (or maybe MoND) and dark energy, for 2 things. But beyond that, the universe seem to require either parallel universes or extra dimensions, or both, for things to work out as they have. Nobody yet knows, but we will someday. You can choose to believe in this or not, but you're pretty much the same as a Ptolemaist these days if you don't.