Let me first say that I have never been a science or math guy, but while I was looking for ebooks one night a couple of months ago, I found some lectures by Stephen Hawking and decided to read them. I thought a lot of the stuff was interesting, and since then I have read A Brief History of Time and The Universe in a Nutshell, and I think I mostly understood what I read. To the people here who know what they are talking about, what would be some good things to read for someone who is just discovering the world of physics?

Also, I have a dumb little question that has been hitting me in the head for a while. I know that light appears to travel at the same speed regardless of the speed of the observer. And I have heard that light has been slowed down and even stopped in experiments using super-cold sodium or whatever. My question is, does light still appear to travel at the same speed to different observers when it has been slowed down artificially? Is this important?

Say a mad scientist has some kind of laser shooting tank, and he is pissed off at you. So he's a mile down the road from you, and he's getting ready to shoot, but before he can pull the trigger, you turn on your light slowerdowner machine. How does it work? I don't know, but it slows the laser down to five miles per hour. So you see the laser coming at you at five miles per hour. But then the mad scientist starts chasing you running ten miles an hour, and you start running away from him (in the exact same direction the laser is shooting) at ten miles an hour. Does the laser appear to be travelling at the same speed as it was when you were standing still? Will the mad scientist ever pass the laser? Also, what if the mad scientist were to fire off the beam at five miles per hour, and then start driving the tank at ten miles per hour with the laser still shooting?

This sounds like something out of a cartoon, i know, but it has been puzzling me. Thank you for reading all of this, and I appreciate all of your thought power going towards helping solve my questions. Also, I'm sorry if this is something that everyone in the world except me knows, like I said, I am practically a complete n00b.

Also, I have a dumb little question that has been hitting me in the head for a while. I know that light appears to travel at the same speed regardless of the speed of the observer. And I have heard that light has been slowed down and even stopped in experiments using super-cold sodium or whatever. My question is, does light still appear to travel at the same speed to different observers when it has been slowed down artificially? Is this important?

This is a common snag that gives lots of beginners trouble. The crucial bit to understand is that what is referred to as "the speed of light" (or simply "c") in relativity theory refers to the speed of light moving through a vacuum. However, whenever light moves through any medium (air, water, crystal, whatever), it travels at a lower speed than c. It's this difference in specific light speeds of materials that causes light to bend when it transitions between media (this is how prisms work, and why underwater objects appear out of place when viewed from above the water). Another effect is Cerenkov Radiation, commonly observed in the cooling water surrounding nuclear reactors. It's caused by particles moving faster than the speed of light in water. This is possible because the speed of light in water is less than c, and so relativity has no problem with particles moving faster than that (but still less than c). Generally, the denser a material is, the slower light will move through it. It also turns out that when you cool atoms down to very, very cold, the speed of light though them can be made quite slow, which is what is going on in the example you mention. Lots of spooky stuff happens at very low temperatures, as the quantum behavior of atoms takes on a very different character in that regime. This is also where things like superconductivity occur.

As for your example of the angry scientist shooting a laser at you, he'd have to be shooting it through a medium of extremely cold atoms. But supposing that's the case, and the light is moving very slowly, you need not consider relativistic effects to figure out what speeds you and the scientist observe the laser to be moving at, since everything (including the laser) is moving at speeds much less than c. So you could literally jog along at the same speed as the laser pulse, if it were slowed down sufficiently, and it would appear stationary to you.

If the scientists starts moving faster than the speed of light in its current medium he will get something similar as what happens when an aircraft breaks the wave barrier, he will generate a canonic light shape.

My advice if you are interested in science is to keep reading the "soft" books, those who explain to you the weirds effects of scientific theories as oppose to ones who are teaching you the basics of the theories. Once you understand the basics, the whole of science's mysteries collapses and it loose much of its charm. For example, the great mental leap that Einstein did when he formula special relativity was to simple say; lets postulate that the speed of light is constant in all frame of reference. Further down the line, many radiation phenonmenon where shown occur at the speed of light. So information theorists said; lets postulate information cannot travel faster than light.

And today, gravity wave which is considered fascinating and cutting edge by so many people on these forums just comes from that last postulate. If gravity is instantanious, it violates the postulate that no information can travel faster than light so it must be going at c.

You may have heard that black holes stretches immensely any object that comes too close to their gravitationnal well. Thats because the difference on the gravity forces from the bottom of the object to the top of it are greater than the force that links the molecules together. These two constatations which were so challenging and mind bloggling at first, lost much of their charm once you understood the reasons; they make you say THATS IT!!

Once you learn science from the basic equations instead of from entertainment stories, the mysterious ideas of science stops wrestling in your mind and you loose the magic. It simply becomes a self constrained world by the postulations (since they are postulate become it is impossible to attribute them any logic other than they are there for hostoric reason and because the agree with experiment -or they wouldnt be postulate) of the theory. Once you understand the basic equations, the endless weird and fascinating possibilities collapses to obviousness given by the unproven postulates and since you know that the only reason these postulates are there is because they agree with experiment as opposed to logic, you loose faith on their ability to describe these weird interesting phenomenon until you actualy see them happening in experiements.

So what, physic is much more mind boggling when you do not understand the details.

Maybe I wasnt too clear with my previous post, let me rephrase.

The interesting stuff in science comes when your mind is been opened to possibilities it had never considered before. When reading "soft" books this happens every time you open one. When you understand the equations of physics, you realize that the next big mind reshaping thing won't come for the next 50 years, you need to look elsewhere to get that feeling ;)

Hope it makes sense.

While I would agree that there is something to be said for the childlike amazement that comes from a first encounter with physics, I would also argue that there is something to be said for the wonder that comes from a deep working understanding of the same. As a physicist, I don't think I've lost my sense of wonder. Quite the opposite in fact, I think my sense of wonder is one of the most important reasons why I do physics. The wonder I feel when I learn something new about the world is in some ways more profound than the wonder any newcomer can feel. It is precisely the inability to escape that sense of wonder, the intense desire to learn and understand new things, that drives people to science. And science doesn't disappoint in my opinon. I am biased however. :)

RoscoHowOriginal,

Are you looking for more good "popular" books or are you wanting to dive in to introductory technical works?

Thanks for the explanations everyone. I think I get it now.

Physics Monkey,

I want to "dive into introductory technical works," as you put it, my only worry is that while I don't want something too "dumbed-down," I don't think I'm ready for something written for, say, a college student taking physics classes. Could you (or anybody) reccomend some reading material for someone who knows somewhat more than the layperson, but not as much a student?

Thanks

actualy yes, http://www.learner.org/resources/series42.html

You do need to register but its well worth it. Made by PBS.

....Could you (or anybody) reccomend some reading material for someone who knows somewhat more than the layperson, but not as much a student? Thanks This will sound very selfserving, but I rarely mention my book DarkVisitor here.

I wrote book to attract students to physics who would never intentionally open a physics book. Thus, the first four chapters are a "hook" with little science, but if you visit the books site, www.DarkVisitor.com, a subpage will list all the physics that is hidden in the scary story of the world's greatest disaster. Life in the norther hemisphere is extinguished. - (I live in Brazil, so I was careful ;) with the trajectory / timing of the unseen visitor now approaching from space.) The "dark visitor" is probably a small Black Hole, but a whole chapter discusses this and other possiblities.

Principle character is astronomer Jack who has fit slight residual perturbation of Pluto's orbit to roughly predict the DV's trajectory. He is currently too busy looking for gravitational lens efffects to learn more accurately the trajectory, and asked his historian friend (Billy T.) to write a book warning the general public. Jack fears CIA etc. will confiscate his photographic records, quitely migrate "high ups" /their friends etc. in government to southern hemisphere, after first discrediting him, (or simply "disapearing him") etc.

One of the first aspects of the disaster is the ice of new rapid-onset ice age (caused by DV's gravitational impulse to Earth. New orbit is a 378 day year with eccentricity e = 0.0836 and apogee in northern hemisphere's summers - too cool to melt all prior winter greatly increased snow falls. Not a big change. The new e is less than Mar's is, but now Earth is "just on the edge" of a permanent ice age and could, even in the present orbit, get locked into one when greater albedo effects are considered.) The ice accumulating on land makes all global ports useless in about one decade and stops oil imports, trade, factories close, etc.

The North's winter's are milder at perigee (closer to sun than currently) but the southern oceans, then in their summer, are more rapidly evaporating to cover most of Earth with clouds - the deep snow falls that sometimes come in early spring's under similiar mild / cloudy conditions, occur almost everyday for months. For example, Washington DC gets more than 100 feet of snow first winter after DV has passed, and as the ice sheet moves south in US and Europe, the albedo increases and it goes down hill from there rapidly until Florida in under thick ice etc.

We southerns lose most of our cities to torential rains / summer floods - heavy rains every summer night, but we can still grow rice in the higher land and have no snow accumulating, except high in the Andees Mountains.

You can read book for free - See web page for details. - You will be surprized how much physics you will learn without any study - Dark Visitor is a physics text disguised as a scary story. For example, Kepler's three laws are all there, explained and used in calculations, but never even named - that would be like "teaching" and my intended reader would realize that is in fact what I am doing. (Jack must explain a lot of things to physics ignorant Billy T.)

You will also learn a lot about mechanism of climate. - For example: why winds generally come from the West in US, why Oslo is warmer in winter than Boston, despite Oslo being 2000Km closer to the North Pole, all about ocean cirulation flows, Taylor instabilities, as "salt fingers" from Med out flow fall into the colder Atlantic flow, etc.

RoscoHowOriginal,

Yeah, you are in a tough spot. On the popular side, I've found Feynman's book "QED: The Strange Theory of Light and Matter" to be quite good. Feynman's lectures, while technical, are very readable, but they won't really teach you how to do physics. John Gribbin's book, "In Search of Schrodinger's Cat" is a good popular intro to quantum mechanics. "Chaos" by James Gleick is an excellent introduction. There also lot's of good relativity books floating around including a non-technical/low level book by Einstein.

As far as jumping in is concerned, I think the very best place to start is "An Introduction to Mechanics" by Kleppner and Kolenkow. I'm afraid this book may be too advanced though, based on your description of your level. If you can handle it though, this is the best place to start learning physics. Otherwise you might turn to any of the standard college books. This may still be too high a level, but I'm afraid I just don't know anything more low level that still claims to be technical. If you are really interested and want to get somewhere in physics, you're going to have pick up basic calculus and mechanics (if you don't know them already). In the meantime, you could read the non-technical books. I'm afraid this isn't what you wanted but I just don't know anything more inbetween. Feel free to comment.

Hmm. Well I have always sort of had math phobia, and this has discouraged me from learning more than I had to about science (ever since middle school, when we learned about the periodic table and math became required). The last math I took was the basic college algebra class required for a journalism major, and I got through that with few problems, but I'm afraid that anything more advanced than that might as well be in Chinese. Would it be possible to hack my way through the books you mentioned stopping to learn the math as I need to, or do I just need to face my fears and become comfortable with a higher level math than I am used to?

And that PBS thing looks pretty cool, I am looking forward to checking that out when I get home from work. Thanks. And thanks to everyone who has given me advice and information. I was intimidated at first to post on a physics board not knowing very much about physics, but everyone has been very helpful. This does not seem to happen very often on the internet, and I appreciate it. :cool:

Yeah, unfortunately I'm of the opinion that you will need at least some advanced math to get much of anywhere. The good news is that you can get quite far with just a basic knowledge of calculus especially if you're willing to take some mathematical results on faith. So the answer to your question is yes, you could hack your way through those books especially since a lot of them develop the basic tools as they go.

Don't despair however, (most) mathematicians are bad at physics! This just means that there is a lot more to physics than just math. You need some basic skills to be conversant in the language of physics, but it's much more important to start developing a physical intuition.

I'll try to think of some other good books.

P.S. To all you mathematicians out there, I was just kidding. Or was I ... :p

RoscoHowOriginal: Try Shrodinger's Kittens and the Search for Reality by John Gribbin. It describes Quantum Theory nd is readable by a non mathematician.

Feynman - Six Easy Pieces