The smallest objects that the naked eye can see are about 0.1 mm long. That means that under the right conditions, you might be able to see an amoeba, a human egg, and a paramecium without using magnification.
As the image sent to the eye by way of the lens increases, you see an object more easily, even though its physical size has not changed. Experts believe that the naked eye — a normal eye with regular vision and unaided by any other tools — can see objects as small as about 0.1 millimeters.
At absolute best, humans can resolve two lines about 0.01 degrees apart: a 0.026mm gap, 15cm from your face. In practice, objects 0.04mm wide (the width of a fine human hair) are just distinguishable by good eyes, objects 0.02mm wide are not. Read more: What is the smallest known star in the Universe?
Answer 1: The smallest object that we can see using a microscope (in a general sense) is atom, whose size is around 0.1 nano meter. This technique is called Scanning tunneling microscope (STM).
Generally speaking, the human eye can see debris and dust that are approximately 25 microns in size. To understand just how small this is, consider that a single hair from your head averages about 70 microns in diameter or 30 times larger than the largest fine particle.
Human eyes can only see objects. larger than 40 microns and the average size of. bacterias is around 2 microns.
A human hair is approximately 70 microns, give or take 20 microns depending on the thickness of a given individual's hair.
Scientists' current understanding is that quarks and gluons are indivisible—they cannot be broken down into smaller components. They are the only fundamental particles to have something called color-charge. Quarks can have a positive or negative electric charge (like protons and neutrons).
No one has ever really seen an atom. Humans like to see something before they believe in it. I am sure there are some people who object to that since there have been claims that electron microscopes have imaged atoms.
Atoms are so small that it's almost impossible to see them without microscopes. But now, an award-winning picture of an atom shows a single particle in an electric field—and you can see it with the naked eye if you really look hard.
We see our world in a huge variety of colour. However, there are other “colours” that our eyes can't see, beyond red and violet, they are: infrared and ultraviolet.
Hint: The unaided human eye can see down to slightly less than 100μm. Everyone can see the diameter of a human hair, which is approximately 100μm (0.1mm). It depends on the convex lens present in the eye and its resolving powers.
HOW MANY COLORS CAN HUMANS SEE? Researchers estimate that most humans can see around one million different colors. This is because a healthy human eye has three types of cone cells, each of which can register about 100 different color shades, amounting to around a million combinations.
The human eye can only see visible light, but light comes in many other "colors"—radio, infrared, ultraviolet, X-ray, and gamma-ray—that are invisible to the naked eye. On one end of the spectrum there is infrared light, which, while too red for humans to see, is all around us and even emitted from our bodies.
But studies have shown that adults who lose the sight in one eye have declines in their abilities to accurately track moving objects, to judge distances, and to perceive depth.
Again, atoms never touch in the everyday sense of the word for the simple reason that they don't have hard boundaries. But in every other sense of the word "touch" that has meaning at the atomic level, atoms certainly touch.
Since atoms don't have a solid surface, in one sense there's nothing to “touch,” because there's never a situation where one boundary meets another boundary.
Note: According to the law of conservation of energy, the matter cannot be created nor be destroyed. Hence, an atom cannot be destroyed and it cannot be broken into smaller particles. The atoms mainly consist of three primary particles and that is electron, proton, and neutron.
The idea is that a quark star is an intermediate stage in between neutron stars and black holes. It has too much mass at its core for the neutrons to hold their atomness. But not enough to fully collapse into a black hole.
The term dark matter was coined in 1933 by Fritz Zwicky of the California Institute of Technology to describe the unseen matter that must dominate one feature of the universe—the Coma Galaxy Cluster.
WHAT ARE QUARKS MADE OF? Quarks, as we know them, are elementary particles, meaning they don't have any constituents. Matter is made up of quarks: protons, neutrons, and quarks are the basic components of all matter. There are six quarks overall, which are separated into three pairs (or families).
Most human hair is One-thousandth of inch, or 0.001 inch. The most common size in the thickness rating for plastic sheeting is 6 mil. This is 6-thousandths of an inch, or 0.006 inch.
To put it simply, the fullness of your ponytail tells how thick your hair is. The average thickness of human hair is 0.003-0.005 inches [2].
Depending on hair color, the average person has between 90,000 and 150,000 hairs on their head. It is safe to say that no one has more than a million hairs.