question: If atoms are almost completely air, how do we see anything?
comment: Atoms are not "almost completely air". Air is composed of molecules which are made up of atoms. Physical matter in an atom is dense, and we often define the boundaries of an atom by the spatial extent of the probability of its electron density field. When you see matter, you are seeing the interaction of aggregates of matter with visible electromagnetic radiation. These interactions don't necessarily occur just at the dense nuclei, but also at the fringes, promoting energetic transitions of electrons.
passages: Electrons form notional shells around the nucleus. These are naturally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically other electrons).
   The light and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove. – "On the nature of the Universe"
  
  Despite being similar to later particle theories, Lucretius's views were not generally accepted; light was still theorized as emanating from the eye.
  
  Ptolemy (c. 2nd century) wrote about the refraction of light and developed a theory of vision that objects are seen by rays of light emanating from the eyes.
   , showed that an image of a surface can be obtained by heating a sample and monitoring the atoms that evaporate from the surface. King and Bigas suggest it could be possible to form an image by scattering atoms from the surface, though it was some time before it was demonstrated
  
  The idea of imaging with atoms instead of light was subsequently widely discussed in the literature
   Given the equation for the de Broglie wavelength above, the same wavelength of a beam can be achieved at lower energies by using a higher mass beam. Therefore, if the objective were to study the surface of a material at a resolution below that which can be achieved with optical microscopy, it may be appropriate to use atoms as a probe instead. While neutrons can be used as a probe, they are weakly interacting with matter and can only study the bulk structure of a material
   While modelling atoms in isolation may not seem realistic, if one considers molecules in a gas or plasma then the time-scales for molecule-molecule interactions are huge in comparison to the atomic and molecular processes that we are concerned with. This means that the individual molecules can be treated as if each were in isolation for the vast majority of the time. By this consideration atomic and molecular physics provides the underlying theory in plasma physics and atmospheric physics even though both deal with huge numbers of molecules.
  
  Section::::Electronic configuration.
   In contrast, the Vaisheshika school gives an atomic theory of the physical world on the non-atomic ground of ether, space and time. (See "Indian atomism".) The basic atoms are those of earth ("prthivı"), water ("apas"), fire ("tejas"), and air ("vayu"), that should not be confused with the ordinary meaning of these terms. These atoms are taken to form binary molecules that combine further to form larger molecules. Motion is defined in terms of the movement of the physical atoms. Light rays are taken to be a stream of high velocity of "tejas" (fire) atoms. The particles of light can exhibit different characteristics depending on the speed and the arrangements of the "tejas" atoms. Around the first century BC, the "Vishnu Purana" refers to sunlight as "the seven rays of the sun".
   The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although some people can perceive light at slightly shorter wavelengths than this (see below). Insects, birds, and some mammals can see near-UV (i.e. slightly lower wavelengths than humans can see).
  
  Section::::Visibility.
   Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in the ice. Also they are also viewed in days when the sun hits the clouds in a perfect angle shining upon the area.
  
  There are three primary forms of crepuscular rays:
  
  BULLET::::- Rays of light penetrating holes in low clouds (also called "Jacob's Ladder").
  
  BULLET::::- Beams of light diverging from behind a cloud.
  
  BULLET::::- Pale, pinkish or reddish rays that radiate from below the horizon. These are often mistaken for light pillars.
   , showed that an image of a surface can be obtained by heating a sample and monitoring the atoms that evaporate from the surface. King and Bigas suggest it could be possible to form an image by scattering atoms from the surface, though it was some time before it was demonstrated.
   As with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of "atomic, molecular, and optical physics". Physics research groups are usually so classified.
  
  Section::::Optical physics.
   The first photographed atom was discovered in 2012 by physicists at Griffith University, Australia. They used an electric field to trap an "Ion" of the element, Ytterbium. The image was recorded on a CCD, an electronic photographic film.
  
  Section::::Social and cultural implications.
   Atom
  
  An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small; typical sizes are around 100 picometers (, a ten-millionth of a millimeter, or 1/254,000,000 of an inch). They are so small that accurately predicting their behavior using classical physics – as if they were billiard balls, for example – is not possible. This due to quantum effects. Current atomic models now use quantum principles to better explain and predict this behavior.
   As faster computing resources became available at lowered costs, the task of making measurements from microscope images of particles could now be performed automatically by machine without human intervention, making it possible to measure significantly larger numbers of particles in much less time.
  
  Section::::Image acquisition methods.
  
  The basic process by which imaging particle analysis is carried out is as follows:
  
  BULLET::::1. A digital camera captures an image of the field of view in the optical system.
   The SilEye-Alteino and Anomalous Long Term Effects in Astronauts' Central Nervous System (ALTEA) projects have investigated the phenomenon aboard the International Space Station, using helmets similar in nature to those in the ALFMED experiment. The SilEye project has also examined the phenomenon on Mir. The purpose of this study was to examine the particle tracks entering the eyes of the astronauts when the astronaut said they observed a LF. In examining the particles, the researchers hoped to gain a deeper understanding of what particles might be causing the LF. Astronauts wore the SilEye detector over numerous sessions while on Mir. During those sessions, when they detected a LF, they pressed a button on a joystick. After each session, they recorded down their comments about the experience. Particle tracks that hit the eye during the time when the astronauts indicated that they detected a LF would have had to pass through silicon layers, which were built to detect protons and nuclei and distinguish between them.
   Matter waves have a much shorter wavelength than visible light and therefore can be used to study features below about 1 µm. The advent of electron microscopy opened up a variety of new materials that could be studied due to the enormous improvement in the resolution when compared to optical microscopy.
  
  The de Broglie wavelength, formula_3, of a matter wave in terms of its kinetic energy, formula_7, and particle mass, formula_8, is given by 
   The sample is prepared on a microscope slide which is placed on the microscope stage. Once the sample has been focused on, then an image can be acquired and displayed on the monitor. If it is a digital camera or a frame grabber is present, the image can now be saved in digital format, and image processing algorithms can be used to isolate particles in the field of view and measure them.
   In atomic physics, the spectral optical depth of a cloud of atoms can be calculated from the quantum-mechanical properties of the atoms. It is given by
  
  where
  
  BULLET::::- "d" is the transition dipole moment;
  
  BULLET::::- "n" is the number of atoms;
  
  BULLET::::- "ν" is the frequency of the beam;
  
  BULLET::::- c is the speed of light;
  
  BULLET::::- ħ is Planck's constant;
  
  BULLET::::- ε is the vacuum permittivity;
  
  BULLET::::- "σ" the cross section of the beam;
  
  BULLET::::- "γ" the natural linewidth of the transition.
  
  Section::::Applications.:Atmospheric sciences.
   Section::::Photoionization microscopy.:Future directions and applications of photoionization microscopy.
  
  The same team of researchers that imaged the Hydrogen electron's wave function are now embarking on imaging the Helium (He) atom. They report that there are considerable differences since Helium has two electrons and that imaging of these electrons may actually enable them to 'see' entanglement.
   Atom optics
  
  Atom optics (or atomic optics) is the area of physics which deals with beams of cold, slowly moving neutral atoms, as a special case of a particle beam.
  
  Like an optical beam, the atomic beam may exhibit diffraction and interference, and can be focused with a Fresnel zone plate or a concave atomic mirror.
  
  Several scientific groups work in this field.
  
  Until 2006, the resolution of imaging systems based on atomic beams was not better than that of an optical microscope,
  
  mainly due to the poor performance of the focusing elements. Such elements use small numerical aperture;
   For most macroscopic objects, this wavelength is so short that it is not meaningful to assign a wavelength to them. A sodium atom traveling at about 30,000 m/s would have a De Broglie wavelength of about 50 pico meters.
  
  Because the wavelength for even the smallest of macroscopic objects is extremely small, diffraction of matter waves is only visible for small particles, like electrons, neutrons, atoms and small molecules. The short wavelength of these matter waves makes them ideally suited to study the atomic crystal structure of solids and large molecules like proteins.
   Human eye
  
  The human eye is an organ that reacts to light and allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can differentiate between about 10 million colors and is possibly capable of detecting a single photon. The eye is part of the sensory nervous system.
   Atomic dimensions are thousands of times smaller than the wavelengths of light (400–700 nm) so they cannot be viewed using an optical microscope. However, individual atoms can be observed using a scanning tunneling microscope. To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width. A single drop of water contains about 2 sextillion () atoms of oxygen, and twice the number of hydrogen atoms. A single carat diamond with a mass of contains about 10 sextillion (10) atoms of carbon. If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple.
   "Playboy" had rejected Asimov's story, so he submitted it to the "Magazine of Fantasy and Science Fiction", which published it in April 1965. The story has since been anthologized several times and was included in Asimov's collection "Nightfall and Other Stories" (1969).
  
  Section::::Plot summary.
  
  In the very distant future — about a trillion years in the future — humans have long since abandoned physical form. They exist as energy entities spanning space.
   Knowledge is explained by the principle that elements in the things outside us are perceived by the corresponding elements in ourselves. Like is known by like. The whole body is full of pores and hence respiration takes place over the whole frame. In the organs of sense these pores are specially adapted to receive the effluences which are continually rising from bodies around us; thus perception occurs. In vision, certain particles go forth from the eye to meet similar particles given forth from the object, and the resultant contact constitutes vision. Perception is not merely a passive reflection of external objects.
   Around the beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of supersaturated water vapor along its path. In 1911, Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles, such as fast-moving electrons.
  
  Section::::History.:Atomic theory.
  
presuppositions: Atoms are almost completely air. Atoms are almost completely air.
corrections: Atoms are not almost completely air. Air is composed of molecules which are made up of atoms.
raw_presuppositions: Atoms are almost completely air. Atoms are almost completely air.
raw_corrections: Atoms are not almost completely air. Air is composed of molecules which are made up of atoms.