too-open-minded Posted August 17, 2012 Posted August 17, 2012 So in a vacuum, it is or its not constant? I see that this topic is debatable and were not really sure yet if light moves at a constant rate in a vacuum or not. Can anyone give me any information, books, links, etc on the subject?
mathematic Posted August 17, 2012 Posted August 17, 2012 The topic is not debatable. The speed of light in a vacuum is constant. http://en.wikipedia.org/wiki/Special_relativity
too-open-minded Posted August 18, 2012 Author Posted August 18, 2012 I really need to just start buying books and stop reading crap off the internet.... 1
Klaynos Posted August 18, 2012 Posted August 18, 2012 I really need to just start buying books and stop reading crap off the internet.... Yep, that's a good plan. If you say what you're interested in we can point you in the right direction. And not all sources on the web are bad.
too-open-minded Posted August 18, 2012 Author Posted August 18, 2012 Theoretical physics! any good links?
ajb Posted August 18, 2012 Posted August 18, 2012 I see that this topic is debatable and were not really sure yet if light moves at a constant rate in a vacuum or not. The constant speed of light in vacuum is well tested directly and indirectly, so much so that it is a defined constant in SI units. The value is 299,792,458 metres per second exactly as the length of the metre is defined from this and the SI definition of one second. Because of this, no experiment can improve on the accuracy of this speed in SI units but rather effect the precise definition of a meter.
too-open-minded Posted August 19, 2012 Author Posted August 19, 2012 Go ahead and delete this thread, i'm not trying to challenge the meticulous work of thousands of scientists who made sure light moves at a constant rate. I'm just interested in things that defy our modern principles of knowledge because thats what makes the biggest leaps and bounds. Plus i'm kind of gullible so that doesn't help my interest. You can take this thread down, sorry for the silly question.
ajb Posted August 19, 2012 Posted August 19, 2012 You can take this thread down, sorry for the silly question. It is far from a silly question, but it is one with a well-known answer. 1
StringJunky Posted August 19, 2012 Posted August 19, 2012 (edited) Theoretical physics! any good links? See what you can get out of this: http://www.phys.unsw.edu.au/einsteinlight/jw/module3_weird_logic.htm Edited August 19, 2012 by StringJunky
too-open-minded Posted August 19, 2012 Author Posted August 19, 2012 I don't really understand time dilation or a good bit of the information on that page. Basically their saying the speed of light is a constant. If you are traveling the speed of light and turn your headlights on, you wont see the light. They didn't say that but thats what I got out of it with the whole C+V part at the beginning. I guess time dilation is somewhat like hearing a fire truck coming down the road? Its the same intensity of sound but it sounds different with your relative position to it. So is time dilation like relative positioning? I looked at the page on time dilation and the whole concept of something with a higher speed having a slower moving clock is hard for my to grasp especially with my inadequate knowledge in physics. I'm bad at math and only know the most basic physics equations. I'm going to reteach myself math with SI units in hopes that can make it easier, sparking my interest but I still get bored with just simple algebra and geometry.
Ronald Hyde Posted August 20, 2012 Posted August 20, 2012 While this is a very simple question to ask, and the answer is a resounding 'yes', people should not think that it is a trivial question, or that the answer is unimportant. Because it is true for all of space, throughout all of time, and independent of the method of measuring C, it is a general law of Nature. It provides many ways for deducing important consequences in the World. The fact that C can always be set equal to 1 means that space and time can be expressed in the same units, and retain those units forever.
zapatos Posted August 20, 2012 Posted August 20, 2012 Basically their saying the speed of light is a constant. If you are traveling the speed of light and turn your headlights on, you wont see the light. They didn't say that but thats what I got out of it with the whole C+V part at the beginning. If you are travelling near the speed of light and turn your headlights on, you will see the light from the headlights moving away from you at c.
too-open-minded Posted August 21, 2012 Author Posted August 21, 2012 But theoretically what if you are traveling the speed of light? You probably wouldnt be able to see the light, right? I know its physically impossible for something with mass to travel the speed of light, just asking theoretically.
Ronald Hyde Posted August 21, 2012 Posted August 21, 2012 But theoretically what if you are traveling the speed of light? You probably wouldnt be able to see the light, right? I know its physically impossible for something with mass to travel the speed of light, just asking theoretically. It's not only impossible practically, it's impossible theoretically too. If it were possible theoretically, it would be possible practically too. Otherwise the validity of a physical theory would be meaningless.
too-open-minded Posted August 21, 2012 Author Posted August 21, 2012 I didn't mean theoretically in the literal sense. I should have said hypothetically, i'm sorry.
imatfaal Posted August 21, 2012 Posted August 21, 2012 I didn't mean theoretically in the literal sense. I should have said hypothetically, i'm sorry. Problem is as follows - if you are travelling at the speed of light, even in a thought experiment, then you cannot use special relativity or most of modern physics for your calculations. So as soon as you hypothesise a massive body travelling at the speed of light then all bets are off and you can almost say anything you want. This applies to much of science - if you ignore an axiom or postulate of a theory, then whatever answer you get out has no validity. it might be right or it might be wrong but whatever it is is pure chance and you know it is invalid as soon as you break an axiom 1
Ronald Hyde Posted August 21, 2012 Posted August 21, 2012 I didn't mean theoretically in the literal sense. I should have said hypothetically, i'm sorry. If you meant hypothetical it's still not possible. You can't set up a hypothetical situation where you have a massive body and accelerate it to the speed of light. Not and be consistent with Special Relativity. If you suspend SR the speed of light is either undefined or infinite, which makes the hypothetical situation meaningless. So you see how the question really has no answer.
too-open-minded Posted August 22, 2012 Author Posted August 22, 2012 I do, and I agree with you and imatfaal. The ships mass would theoretically grow to the size of the universe if it reached the speed of light. Which physically couldn't happen. So it just throws the whole question out the window. I was just trying to get an understanding of the speed of light with that hypothetical happening. Well what is the fastest an object with rest mass can travel before really odd things start to happen? I guess that question is out of whack to because technically their is no propulsion technique powerfull enough to reach the speed of light. I understand what you guys are saying, thankyou for being patient with me. I'm just a very very curious person.
too-open-minded Posted August 26, 2012 Author Posted August 26, 2012 (edited) Meh regardless of whether or not the speed of light is constant. We do know it moves at about the same speed wherever we have tested it. two questions What difference does light travel when its not in a vacuum? like when its in glass and things? I understand this has something to do with electron absorption. If we had 2 pounds of lead. one pound in a solid block and one pound in different sized chunks. the block in one particle accelerator and chunks spread apart in another. Would light travel the same distance or would the block absorb more light? I'm sure it would take more than 2 pounds but lets say an equal amount of lead in each accelerator with one having enough lead to fully cover the circumference of the inside of the accelerator. Edited August 26, 2012 by too-open-minded
StringJunky Posted August 26, 2012 Posted August 26, 2012 (edited) What difference does light travel when its not in a vacuum? like when its in glass and things? I understand this has something to do with electron absorption. AFAIK a photon only travels in a vacuum (a vacuum lies between atoms), otherwise it is absorbed by an electron. In a material, like glass, an incoming photon meets an electron giving it energy to try to move up to the next higher energy level/orbital but it is insufficient (in materials with transparent properties) so the electron promptly drops back down to the rest state and releases the photon, whereupon it travels to the next one and the process is repeated. Edited August 26, 2012 by StringJunky
too-open-minded Posted August 26, 2012 Author Posted August 26, 2012 Okay so basically if its not transparent then it is reflected off the surface and no photons permeate through? 1
too-open-minded Posted August 26, 2012 Author Posted August 26, 2012 Nobody ever understand my questions the problem is my education is so shitty. I'm trying to encompass something big but I have a small vocabulary.
StringJunky Posted August 27, 2012 Posted August 27, 2012 (edited) Nobody ever understand my questions the problem is my education is so shitty. I'm trying to encompass something big but I have a small vocabulary. There's nothing wrong with your question: Emfield is distracting it with his own pet ideas and objections which is not allowed here in the classical physics section. Your question (post 32) is answered by quantum electrodynamics which is concerned with electron-photon interactions and it is these interactions which determine the reflection/absorption/transmission properties of materials. Perhaps someone more knowledgeable than I can link you to some good sites that explain the basic idea around the reflection/transmission properties of materials in QED terms for layman. QED: The strange theory of light and matter by Richard Feynman is a well-known book written for the general reader that is well-regarded. Edited August 27, 2012 by StringJunky
too-open-minded Posted August 27, 2012 Author Posted August 27, 2012 I'll look into that book. I really would like to ask some questions to anybody with some experience with a particle accelerator. Theirs so many weird seemingly random experiments I have in my head, a good amount of them to do with particle behavior.
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