On the Nature of Light

19th Century beliefs about the nature of light continue to hamper a study of light.

Early 19th Century physics was characterized by  support for various theories that were subsequently disproved such as the theory that atoms were the smallest particles of matter and  an atom of  one element could not be converted to  another element.  J.J. Thomson  disproved the first theory with his discovery of the electron  in 1897.  Physicists also  discovered that the processes of nuclear fission and nuclear fusion could change an atom of one element to an atom of another element.

Unfortunately the 19th Century debate suggesting that light must BE a particle or BE a wave survives.  The confusion comes in part from the fact that in some situations light acts like a particle  and in other situations acts like a wave.

The standing joke when I studied light in the 60's was about the university that taught  that light was a wave on Monday, Wednesday and Friday; and taught that light was a particle on Tuesday, Thursday and Saturday.  My professor took a different approach.  He taught light as a wave for half a semester and light as a particle the other half. 

This  false  dichotomy continues to hamper an understanding of light (i.e., electromagnetic radiation).    Some physicists have tried to get around the dichotomy  by suggesting that light consists of particles that may actually  be something called wavicles. 

This idea implies a misunderstanding of what a wave is.  A wave involves  particles  forming temporary sets which momentarily function in unison.    Air molecules normally move around like ping pong balls in a bingo machine.  However, when a sound wave passes through  air the separate molecules temporarily  function as if they were entangled with each other as they pass along the sound energy to adjacent air molecules.  Once the wave has passed the air molecules return  to  moving  independently.

Physicists ignore the fact that if light  is a form of energy it cannot be a particle or be a wave although particles or waves might transfer it from one location to another like particles and waves transfer kinetic energy from one location to another.  Particles are ultimately matter, not energy.  Waves involve the movement of matter.  Particles and waves  transfer energy, but they are not energy.

If I throw a baseball the kinetic energy  produced by the movement of my arm is transferred to the baseball which then transfers that kinetic energy to whatever it hits, such as a bat, a glove or perhaps a window.  An underwater earthquake may transfer its kinetic energy to a tsunami wave which may then transfer that energy to objects on  a shore a thousand miles away.

Waves transfer kinetic energy much more effectively than particles.  The energy used to move a guitar string wouldn't propel a particle very far.  However, that movement produces a wave which can  travel a hundred feet or more and reach anyone in an auditorium.  Such kinetic energy waves are commonly called "sound waves" because they produce a physical sensation in the human ear which the brain interprets as  sound.

Waves can transfer complex sounds from many instruments to the human ear in a manner that allows all the sounds to be heard even though they come from different locations.  Light waves would  be more likely to be able to transfer  light in a variety of colors and intensities  in a way that allows the eye to recognize different colors than would individual particles emitted from various  locations.

In a classic experiment in quantum physics an individual photon carrying light energy approaching two different gates will go through one gate on some occasions and the second gate on other occasions.  If light from Mars were leave the surface as individual photons they would quickly become jumbled together so no details could be seen from Earth.    .

Although there are situations in which the transfer of light can be explained as involving particles (photons),  many situations such as mirror reflections can only be explained as involving waves.  If particles produced a mirror image, objects  that aren't directly in front of the mirror would be reflected as being on the opposite side of the room because the particles would hit the opposite side of the mirror.  Some reflective surfaces can produce the effect of light going around a corner.

One of the problems about light as a wave is the need for something to be "waving" as  Professor Michael Fowler  points out in some of his lectures. 

Some type of aether has long been suggested as what might be waving.  However, an aether would only be necessary to transfer light waves through space.  Physicists have long ignored the possibility  that electrons in atoms could transfer light waves just as easily as  they transfer electricity. 

The transfer of light waves by electrons would explain why the passage of light through some substances causes heating but not other substances.    The process would be similar to the process by which the passage of electricity causes heating.

Resistance to the passage of electricity causes heating.  Resistance to the passage of electromagnetic radiation could function in the same way.

A possible explanation for the fact that radiation passes through the atmosphere with minimal heating would be that electrons in gas molecules could pass along a wave without resistance because the molecules move independently.  Electrons in solids might have less ability to pass along radiation without resistance because the atoms they are part of are held in place in a matrix.

Air molecules can transfer sound waves even though they normally move in a highly disorganized fashion because they can temporarily act as if they were all connected together and acting in unison to transfer complex sounds.  Why couldn't electrons, which can transfer energy through a wire in a highly organized manner, temporarily organize to transfer electromagnetic waves.

Water waves may cause small boats to begin moving back and forth because all of the boat must move at the same time rather than having adjacent molecules  move independently as water molecules do.    Moving electromagnetic  waves through a solid  might require  entire groups of atoms to move in order for the electrons  to transfer  the energy as a wave just like an entire boat must move for the kinetic energy in water waves to be transfered to the other side of the boat.  The motion of atoms is what physicists define as heat.

The issue of how a light  wave  could move through space remains.  Some type of "aether" would be  the most likely explanation.

Physicists claim there must be some type of matter they cannot detect because the matter they can detect seems insufficient to be all the matter of the universe.  They usually describe this matter as being "dark", but transparent matter would be even harder to detect than matter that was dark.   

Dark objects don't  emit or reflect light, but they  can block light if they pass between the source of the light and the observer.  Light can pass through  transparent matter without  being easily detected.

Transparent matter can be very difficult to detect.  In some cases it may be detectable because some frequencies of light don't pass through, or because the light that passes through isn't as bright.

Astronomers have noticed that light coming from distant galaxies seems to have been shifted toward the red end of the light spectrum.  The greater the distance from earth the greater the red shift.  Some have suggested that this red shift indicates the relative velocities of earth and the distant galaxies.  However, the shift could also be due to passage through transparent matter such as what has traditionally been called an aether.

A problem with the theory that the shift indicates movement away from earth is that everything seems to be moving away from earth, but the Hubble telescope images indicate that some distant galaxies are moving toward each other, including the movement of our galaxy toward the Andromeda galaxy.  Thus it would be more likely that some distant galaxies would show movement toward earth with a shift toward the blue end of the spectrum instead of a uniform red shift.  Also the relative motion would vary among galaxies rather than being uniform based on the distance from earth.

The false dichotomy that light must BE a wave or BE a particle continues to hamper  an understanding of light in the 21st Century.  If light is a form of energy it cannot be a particle or a wave because both involve matter.  However, both particles and waves could transfer light energy from location to another just like particles and waves transfer kinetic energy from one location to another.