If glass is solid and made up of lots of atoms (like us) why is it possible to see through it?

Question

One of those silly questions... mind you, could you imagine the fun you'd have making yourself invisible? (As long as you don't trip and shatter into a million pieces!!)

Answer 1

1st -- tips of the hat to in-janier and lewis_brown for stopping by long enough to give the basic physics and most of all to Lewis for politely informing us that glass is not a liquid.

Glass is a liquid? Pull-eeze! How in the world do you come up with that one, people?

Glass "flows" -- ???

Glass flows in liquid state -- only.

Glass is solid until melted. Then and only then it's liquid.

Glass melts at 2600-2900 °F (1425-1600 °C) depending on its composition.

Where on Earth do you think glass is liquid or flows at bench temperature?

Anway, I originally stopped by just to ask the asker if he or she could see through black glass (or any other opaque glass)?

Answer 2

Glass is made from sand, which is primarily composed of quartz crystal. When heated hot enough the crystal turns to a liquid and the impurities(stuff that's not crystal) burn out and can be manipulated into glass items.
Quartz crystal is see through, transparent, or opaque in its natural state, so the process is really only manipulation and refinement (burning out the stuff you can see).
Glass does "flow" over time, since the properties that made the crystal solid were diminished when it got melted the first time. Some glass can be "Tempered"(sometimes looks green even from the top) which makes it much harder and more difficult to shatter. I believe this is done by heating a more pure sand to a higher temperature and then after it has been manipulated it is cooled very quickly

Answer 3

That whole glass liquid thing is an urban myth

"There have been many claims (especially by tour guides) that such glass is deformed because the glass has flowed slowly over the centuries. This has become a persistent myth, but close inspection shows that characteristic signs of flow, such as flowing around, and out of the frame, are not present. The deformations are more consistent with imperfections of the methods used to make panes of glass at the time. In some cases gaps appear between glass panes and their frames, but this is due to deformations in the lead framework rather than the glass. Other examples of rippling in windows of old homes can be accounted for because the glass was imperfectly flattened by rolling before the float glass process came into use."

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

Answer 4

This people are right glass is liquid. Never the less the glass doesn't absorb much in the visible region nor in th near infrared or near UV it obeys a window of transparence that has a name I don't remember, just like many crystals althoght glass is not a crystal. The general idea there is: there are some zones where electrons like to interact and others where that is not the case, visible is the last case for the electrons in a glass. For your invisibility see meta materials and negative index of refraction.

Answer 5

Light is broken up into photons that, together, travel in waves.

A photon can be thought of as a packet of 'light energy'. When the photon strikes an atom, it's absorbed. The atom absorbs the energy by raising at least one of the electrons orbiting the nucleus to a higher orbit (a higher orbital).

The atom generally won't stay at a higher energy level for very long. The electron will drop back to a lower orbit requiring less energy and will release the energy absorbed. The energy is released as a new photon.

There is no way to predict what direction the new photon will be released in. However, since most matter consists of many atoms, there are generally three possibilities: The new photon is released back out the same side the original photon came in (reflection), it is released out the opposite side (transparency, since the frequency is virtually identical to light entering the object), or the new photon can hit a different atom within the substance (absorption which results in heating of the material). Even in transparent and reflective objects, you can expect light to be absorbed and re-emitted by many atoms before it finally escapes out one side or the other (the many absorptions and re-emissions are why the speed of light through glass is slower than the speed of light through a vacuum).

The molecular structure of the material determines whether the light is more likely to eventually escape out the same side it came in on, escape out the other, or become trapped, endlessly travelling between atoms of the material. Regardless of the structure, you're talking about probability, so there is no material that is perfectly transparent, perfectly reflective, or perfectly absorbent, which is why you can still see your reflection in a window.

Equally important is the consistency in the amount of time between receiving a photon and emitting a new photon out one side or the other and the likelihood that the new photons are emitted in parallel directions - in other words, to be transparent, photons have to come out the opposite side in the same pattern that they entered. Even a rock is slightly transparent, at least in the sense that a miniscule number of photons will be emitted out the opposite side than they entered. However, unless the molecular structure of the material results in photons being emitted in the same pattern they entered, the light that does come out the other side will be meaningless.

In other words, you don't really see through glass. The photons emitted out the opposite side are not the same photons that entered. It's just that the photons emitted out the opposite side are emitted in the same pattern as the photons that entered.

Answer 6

When a photon strikes a material, it will be absorbed by an electron, thereby raising the electron to a higher energy state. The amount by which the electron's energy is increased depends on the wavelength of the light. If the electron is raised to a stable state, the photon is permanently captured, and the light is absorbed. In a transparent material, photon capture raises the electron to an unstable state, causing the photon to be re-emitted. Thus in glass, crystal quartz, etc. a photon is passed like a hot potato from one electron to another until it comes out the other side.

Answer 7

Yes, true glass is an extremely viscous liquid and transparent to visible light. There are many solid crystal structures, however, that are transparent to visible light. ie diamond, water crystal(ice), crystal SiO2 (Quartz) the same chemical as liquid glass.

Many of the chemicals that make up people are transparent yet we are very opaque. There are many reasons for this.

- One reason is simply that some of the chemicals absorb light at various frequency until all frequencies are fairly attenuated.

_ A second reason is, believe it or not, light travels at different speeds through different materials depending on the density of the material, so if two transparent materials of different densities that are close together causes the light wave to bend in the direction of the material that transmits the light slower. All of this bending causes the light to become very diffused or opaque.


A note about the visible light verses other electromagnetic waves: yes for visible light transparency the most important quantum energy level to consider is electron orbital level, but for IR light it starts to become more important to consider vibrational states. The vibrational states of SiO2 make it fairly opaque to most ranges of IR light. It is also opaque to many other ranges of the electromagnetic spectrum for various other reasons.

Sorry, if this is more of an answer than you were looking for.

Answer 8

OK, first of all, glass is not a fluid. The viscosity of glass (how easily it flows) at room temperature is about a billion times more than that of lead. So if the glass in old windows was thicker at the bottom because it had flowed down over time, think what would have happened to the lead holding it in place! The reason old glass is thicker at the bottom is because it was made by spinning molten glass into a large disc and then cutting the disc into small sheets. The disc was thicker near the outside edge because of centrifugal force (physicists don't like that term, but I won't go into that now...).

Now, why glass is transparent. Of course, everything is made up of atoms, but there are different sorts of atoms - about 100 different sorts occur naturally, and each sort corresponds to one of the chemical elements. As well as occurring in their pure forms, atoms can join together to form molecules. Atoms are made up of a nucleus surrounded by electrons. Molecules are formed when two or more atoms share some electrons and become more "stable" as a result.

Light is (this is a simplified view) made up of particles called photons. When a photon hits an atom or molecule, the details of what happens depend on what sort of atom or molecule it is, and what other atoms and molecules are nearby. This is because it is the electrons that determine the behaviour. Usually one of three things will happen: reflection, absorption or transmission.

"Reflection" is what tends to happen at the surface of metals: the light bounces off. "Absorption" is where some or all of the energy of the light is turned into heat. This happens to different extents with different substances. Molecules with double and triple chemical bonds (formed by their electrons) tend to absorb light of specific colors and are often found in dyes.

If neither reflection nor absorption happens to an appreciable extent, "transmission" occurs. This is where light passes through a substance. When this happens, the light changes course each time it goes from one substance to another. This is called "refraction". The angle by which it changes course is determined by the "refractive indices" of the two substances.

In passing through a completely flat pane of glass, a beam of light is refracted twice: once on entering the glass, and once on leaving it. Because the sides of the pane are parallel, it ends up coming out in the same direction in which it went in, so the glass looks totally transparent.

In fact, if you look carefully at a thick piece of glass, you can see all three effects at once. You can see through the glass, so transmission is happening. There is a certain amount of reflection from the surface, particularly if you look along the glass surface. If the glass is curved or flat but very thick (and you move it around), you can see refraction - the view through it is distorted. Finally, look at the glass end-on and you'll see it looks greenish (for most glass). This is because the glass is absorbing red and blue light more than green.

As a final note, glass is transparent to visible light, but opaque to most ultraviolet light. So in a sense it's only transparent because that's the way we see it.

Answer 9

Actually, technically glass is a fluid, not a solid
It just flows extremely slowly. But, if you look at the glass in very old windows, it is obviously thicker at the bottom than the top.

Answer 10

Glass is not solid it is a liquid, if you look at a piecee of glass that has been in a window for many years you will find that the bottom is slightly thicker than the top