what is real?

In day to day life we tend to take us and the world around us as generally definable and defined phenomena, which we are perceiving objectively with our senses. Consequently we assume that the distinction between real and unreal or true and false can be made objectively. However, modern science and mystics through the ages alike observe that on closer examination, there is no objective reality.

the mystical and the scientific understanding

Sciences claim, what we experience as real, depends very much on our means of perceiving. Mystics claim, that it all depends very much on the perceiver. And indeed, if we take the mystical approach and look, who is perceiving, we cannot come to a clear definition. It's impossible to say unambiguously, who we are. What we can do, however, is to exclude, what we are not, for example
"You are never, what you think you are, and reality is never, what you think it is."
Why? Because any thought that appears on your inner screen is a representation of an object or a group of objects of your sensual impressions and not the object or the group of objects itself. The mind never deals with the world out there directly, it is identifying and naming phenomena and thus creating internal symbols, words and sentences from the impressions it receives through the senses. With this realisation the hypothetical objectivity of our world is fading and is replaced by interrelating symbols within ourselves, which are transformed into chains of thought in our brains. These processes are happening so fast, that we usually don't realize their complexity and also fail to notice that each perceiver has his own version of an object.
The ancient yogis and rishis of the East understood the illusionary character of the world of phenomena through self observation and created the terms maya or samsara for the fleeting world of material and virtual objects.
Perhaps you will argue, that natural sciences with their clear definitions are contradicting these observations. That was true in the 18th and 19th century, but since Einstein, Heisenberg, Bohr and the development of quantum physics the view of the mystics has been confirmed to be much more appropriate than the views of the old objective science. Here are a few examples from the world of science, which point in a similar direction:
1. P.D. Ouspensky, a Russian scientist, who worked with George Gurdjieff, is giving a nice example from mathematics:
Anybody will agree that 1+1=2, right? If you, however, allow infinite as a value, you can make an equation ∞+1=∞, because infinite is always infinite, whether you add something or take something away. Then you take ∞ on both sides away and you're left with 1=0! That's why the mathematicians have to exclude infinite and zero for certain operations, because math will not work otherwise. Which means, however, that mathematics is only true within a certain defined range and not absolutely, universally and indefinitely. When we look into realms beyond the mind the defined range is not valid any longer. Even Stephen Hawking, one of our best scientists, admits in one of his books, that all of our scientific statements are only valid, because they give us a reasonable explanation and allow certain predictions about a phenomenon. There is no guarantee that a formula, which works today, will also work tomorrow.
2. For a long time people believed in the flatness of the earth. Most of us laugh about it today, but for a 15th century carpenter it was an experiential truth, that our planet is level like a pool table. Spheres were not rolling down to the left or right, when he built an even table and generally in his and his family's life the concept of a flat earth worked perfectly well. So in fact the idea of the world as a sphere would have sounded rather weird to him. After Columbus, Kopernikus, Galilei and Newton the opinion of the majority changed and people, who still believed in a flat earth were seen as ignorant, which also isn't quite appropriate, as from the view of our carpenter it was close enough then and still is now. Even in our present day to day lives we are still partially thinking in terms of a geocentric plain, i.e. when we are talking about sunrise or sunset. Meanwhile Newton's gravitational laws have been proven inaccurate to some extent by Einstein and his formulas will probably be improved by somebody else one day...All in all we can say that instead of looking at "true or untrue" we are dealing with concepts that allow us better predictions and others are allowing not so good predictions.
3. The coastline paradox: The measured length of the coastline [of an island] depends on the method used to measure it. Since a landmass has features at all scales, from hundreds of kilometres in size to tiny fractions of a millimetre and below, there is no obvious size of the smallest feature that should be measured around, and hence no single well-defined perimeter to the landmass. Various approximations exist when specific assumptions are made about minimum feature size. (from Wikipedia, full article see here: the coastline paradox). Obviously this observation is not only valid in regard to the coastline of an island but to many objects and processes in our world.

macrocosm and microcosm

Let's start with looking at our planet, where we walk around every day. Picture 1 is Makena beach on Maui with wonderful golden sand. Picture 2 is a little bit of this sand in a close up. There are about 2500 grains of sand in picture 2:

beach sand One m² of the beach contains about 400 of our close up pictures, which is about one million grains of sand. The whole beach is about 80 000 m², so we have about 80 billion grains of sand on Makena Beach. Now extend your vision and imagine somebody collecting all the sand from all the beaches of the world on one big pile. What a huge collection of grains that would be! According to http://www.cosmotography.com/ researchers at the University of Hawaii have calculated this number by dividing the volume of an average sand grain by the volume of sand covering the Earth's shorelines. The volume of sand was obtained by multiplying the length of the world's beaches by their average width and depth. The number they calculated was seven quintillion five quadrillion (that's 7 500 000 000 000 000 000 or 7.5 billion billion) sand grains!

With the image of this huge pile of sand in mind, let's take a look into the sky. The picture shows just a small portion of the night sky with the constellation Orion, a part of Taurus and a lot more celestial bodies from our galaxy:

stars There are a lot of little white dots, the stars, visible with the naked eye. But many, many more, when looking through a telescope. 100 to 400 billion stars in our galaxy are the present estimate. Scientists have calculated that the number of stars in the known universe, which consists of approximately 2 trillion galaxies, is even bigger than the number of grains in our huge pile of sand. Even though the total amount of stars can be only a rough estimate, certainly a few more zeros must be added to our above number of sand grains.
Our earth is very, very tiny in comparison with the vastness of the universe and humans are even tinier.

But before you are overcome by depression and emotions of complete smallness, take a look at our pile of sand again and single out one grain only. Imagine taking a tiny chisel and hammer and splitting it up into it's atoms, you will be getting an even larger number of atoms within one tiny grain than the number of stars in the universe. (Picture retrieved from enigmatics)

. atoms Our bodies are more than a million times bigger than a grain of sand. So we are incredibly big in relation to atoms and particles.
The picture shows a model of silicon dioxide molecules (SiO2), which are the main components of a grain of sand. We have no means of taking pictures of these structures, they are way beyond the range of electronic microscopes. But from experiments we know, that the infinitesimal structure should look somehow like this. The light green balls represent the silicon atoms, each one being connected with two of the smaller dark green oxygen atoms.
You may see now, how easy it is to feel superior or inferior just by comparing the size of your body-mind-system to atoms or to stars.
But in our day to day life we don't see galaxies or atoms, instead we only have to deal with a range of medium sized phenomena ranging in most cases from a grain of sand to our sun, which affect our practical lives. If it wouldn't be so, life would be impossible. We can't be simultaneously aware of whole the macrocosm, where a black hole might be gobbling up a whole galaxy millions of light years away, and of the microcosm, where countless physical processes are going on almost unnoticed in our body, while we sleep or work. our world. The limitation of perception is necessary for the functioning of our body-mind-system. We are living in a small corridor between the very small and the very big and only in this range sentient beings are ocurring. The limits, which are defining for our range of perception, are changing constantly and are different for each being. There is no objective reality. Every phenomenon is relative.