What is knowledge except concepts about reality? For example I have a concept about what an atom is. My concept maybe more or less accurate to the reality of what an atom is. However I can never directly perceive an atom.
You actually never directly perceive anything. When you see, your eyes detect light and processes it before sending the information to the brain. When you hear, your ears detect and process sound before sending that information to the brain. So, you do not directly hear a dog that is barking. Your ears detect a sound and your senses and brain interpret that sound as a dog barking. You don't directly see objects in front of you. Your eyes detect light and your eyes and brain process that information to give an image of what you 'see'.
Every sensory mode has 'illusions' associated with it. None are even close to being perfect. We see a very small part of the electro-magnetic spectrum, so we don't even detect infra-red or ultraviolet, let alone radio waves or gamma rays. Our eyes have only three types of color detectors, so we often 'see' two physically different colors as the same. Our retinas automatically detect borders, relative brightness, and movement, leading to a host of optical illusions playing on that automatic processing. Our attention can affect whether the information gets to our consciousness, and expectations can affect how it is processed. We seem to be programmed to see faces, even where no face exists.
The overall process is quite far from perfect. And this is the case in different degrees for ALL of our senses.
So, no, your senses will not be able to detect an atom without help. But if we put an electron microscope into the information pathway between you and the atom, you will. Your eyes cannot detect infra-red, but if you put night vision goggles on, you will be able to. Yes, there is another mechanism between the object and you, but there was already quite a bit of mechanism between already.
What then makes it objective?
I will delay this for a bit.
I used to live where it was cold. I could when I was younger cause myself to feel warm.
So object reality... When I was 13, I was playing baseball in a open field barefoot. I played the entire game. at at the end of the game someone pointed out to me that my foot was covered in blood. Turns out I had a piece of glass from a broken bottle maybe a inch wide and half as long stuck in the bottom of my foot. I didn't feel any pain from that and don't know how long I had been running on it. It fascinated me that I could ignore or alter perceptions caused by object reality. So object reality need not affect my subjective experience. I don't know the extend that this is possible. There are yogis that can control their perception of object reality.
As I noted before, your attention and our expectations can affect how we interpret what our senses present to us. Sometimes, our senses do processing even before presenting the information. And they can be wrong in how they do this.
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From my experiences, the mind creates a perception of reality that can't be trusted really. We can to some degree alter that perception of reality. What I question is the perception provide by the mind we have no conscious control over. If I can consciously change my perception of reality to a limited degree, how much more is the sub-conscious mind capable of altering my/our perception of reality?
In some situations, a great deal. Many drugs will play with perceptions, for example.
I think we have to trust that perception, but I don't so much. If I can't trust my perception of reality, what basis is left to me really, to define objective truth?
Damn good question. I'm not going to answer it in full.
Let's do an easy case where we *know* our perception is wrong. Take an optical illusion. How do we know our senses are wrong? If, for example, we have an illusion where two lines of the same length *look* to be different lengths, we can use a different sensory mode (touch) or an assumption of constancy and the same mode (by covering up the parts producing the illusion) to show the inconsistency. The *objective* reality of the sameness of the lengths is determined by some other sensory experience that we 'trust more'. We can see and rely on a measuring stick to show the lengths to be the same even if our eyes trick us.
So, we use our senses as a first approximation. We test our perceptions through as many different modes as we can. And we can get information that is reliable *up to a certain approximation*. That will then let us create other ways to detect or measure things (measuring sticks, clocks, etc) that will occasionally show where our perceptions get things wrong. This allows us to get a *better approximation*. This creates a cycle of better and better approximations and better and better detectors that extend and correct our senses. At each stage, we test all previous stages. And we realize there are other people with perceptions similar to our own and their perceptions and measurements agree with our own. This produces a 'consensus reality' that has been perceived and measured repeatedly and is considered to be 'trustworthy'.
Objective truth is, hopefully, what we approach via these successive approximations.