I just read Steven Hawking's "A Brief History of Time" for the first time ever. I had wanted to read it for a long time and it finally came to my library's digital collection, so I could borrow it without driving 20 miles to the library--I love digital libraries!
The book is an attempt to make some very extreme and difficult concepts in physics accessible to the layman, a noteworthy and praiseworthy effort! While it falls quite short in most areas, failing to clarify or simplify to the level where a Ph.D. engineer can understand most of the concepts, it does at least present the background information concerning early developments and basic knowledge reasonably well.
Is everything expanding? (The Red-Shift)
With the development of large telescopes that can see very distant stars, Hawking says a man named Hubbell in the early 1900's found what is known as a "Red-Shift" in the light that reaches us. In an overly simplified summation, stars have an atmosphere that absorbs some of the light they give off, and the elements that absorb the light do so for only certain colors. For example, (fake example for clarity) Iodine in a stars' atmosphere absorbs orange light, so the light we see in the telescope is missing orange, but if this missing-orange light is red-shifted, then the missing light is actually just a little redder than orange.
What causes a "Red-shift"? Hubbell found that as the distance to stars increased, the amount of the red-shift also increased, on average. So what caused this red-shift? The physicists of the time settled quickly on the Doppler Effect as the explanation. The Doppler Effect, simplified, is seen when something shooting a wave at you is moving away--it in effect stretches out the wave making it longer and causing a red shift in light. You can hear the Doppler Effect in sound (which travels in waves) as a train passes you. As it approaches the sound waves are crunched together, making the sound higher, and when it passes the waves are stretched out, and sound lower in pitch. Physicists, then and now, believe that the further stars are, away from us, the faster they are moving away from us, hence what is known as an expanding universe, which must have been all close together a long time ago, and leading to a belief in a "big-bang" at the "beginning of time". Not only that, but more distant objects appear to be moving away faster.
My own notes on the above the above facts and theory: If objects are moving away faster, the further they are from us, they must be accelerating. On Earth, whenever there is an acceleration, there must be a force that causes it, according to the basic physical law F=ma (Force =mass times acceleration). So, in essence, cosmologists(physicists that think about large scale stuff) maintain there is some basic, unknown, force acting on every bit of mass in existence, making it accelerate away from all other mass. Hawking never actually says what that force is supposed to be, or even mentions it in any way, probably because it does not exist, as far as anyone can tell.
Alternate hypothesis: (NONE of the material in this section is even mentioned in the book) Fortunately, there are other ways that light can be red-shifted. In fact, when Hubbell found the red-shift, an alternate theory was advanced which came to be know as the "Tired Light Hypothesis", in which light waves lose energy over time. This loss of energy produces just exactly the same red-shift as the Doppler effect would produce for an accelerated expanding universe. Light waves, as real physical things, it was thought by certain scientists, should not be perpetual motion machines, but should behave as all other phenomena ever seen on Earth, and lose energy over time. In fact, light waves have now been shown by experiment to do just that, by a process called "particle creation" or "pair creation", where small amounts of the energy in light waves are converted to matter. Not only that, but as everything on earth appears to lose energy in proportion to how much it has, and the red-shift of light appears to be higher at higher energies, this energy loss precisely fits the pattern observed for all energy storages on earth.
When any theory is given a name, as unexciting as "Tired Light Hypothesis", it is likely doomed to be dismissed by people looking for pizazz and interest, and predictably this theory lacked much adherence or enthusiasm, and was ultimately mostly forgotten. Which is a real shame because it is so much more realistic and in line with all the observations of real systems on earth and nearby. All energy carriers lose energy over time in proportion to the energy difference between themselves and the background level. That is the second law of thermodynamics: in any real process there is an energy loss. But physicists, it seems, have chosen to believe the most bizarre and unlikely explanation. A real boon, no doubt, to science fiction writers, but a real bane to reality grounded engineers and earth-scientists.
Olbers' Paradox(Why is the night sky dark?)
According to Hawking, "The only way of avoiding the conclusion that the whole night sky should be as bright as the surface of the sun would be to assume that the stars had not been shining forever but had turned on at some finite time in the past." This was based on the assumption that the universe was infinite so there should be stars in any particular direction from us.
However, Hawking doesn't mention the very plausible explanation of light wave decay over time. Again, the Tired Light Hypothesis! Should a light wave be a perpetual motion machine? Should it behave differently than everything on Earth, which loses energy over time? If the Earth is the key to the universe, and things happen here the same general way they do everywhere else, if our laws of physics are the same as other places, there should be a loss of energy over time.
The Background Radiation
Hawking spends a great deal of time talking about the 3 degrees Kelvin background radiation. This radiation is extremely low energy heat waves. Just as you can feel heat radiation from a hot pan, these waves exist everywhere in space coming and going in all directions.
Hawking's explanation of where this background radiation comes from is, I have to say, pretty hard to grasp, but it seems to have something to do with some early conditions envisioned as part of the "Big Bang". He seems to imply that the existence of background radiation is some sort of proof that there really was a big bang. What this proof is, is never quite explained though, and simple laymen, engineers, and earth scientists, are left saying "Huh?"
Fortunately, we have again that tired old hypothesis, the Tired Light
Hypothesis, to come to the rescue with a simple, consistent, and
expected mechanism--degraded light waves from long ago. If there are lots of stars in all directions and their light waves are losing energy over time, then this background radiation would be expected. Our 3deg K radiation simply becomes the temperature of empty space, where almost all the light waves have lost as much of their energy as they
can.
If the energy in light waves behaves as all energy on earth does, then it
must be measured against a background level. The best example of this is
thermal energy, which contains energy according to the temperature
difference between a hot thing and the background temperature. Just as
waste heat close to the background temperature can do no useful work,
so, when a light wave loses enough energy, it becomes part of the
background "soup" of spent light waves, and has no potential to do any
more work. Therefore it has no more tendency to lose more energy.
Gravity and Entropy
Hawking talks at length about the elemental forces that we know exist in the real world
((To be continued...))
