JaKiri Posted January 30, 2004 Share Posted January 30, 2004 YT2095 said in post # :Phew, and I thought I was the only one there for a sec If you want the example of the torch beams, then a and b would both be c. (c+c)/(1+c*c/c^2) = 2c/(1+c^2/c^2) = 2c/2 = c. So the recession speed of two bits of light travelling at c in opposite directions is c. Link to comment Share on other sites More sharing options...
JaKiri Posted January 30, 2004 Share Posted January 30, 2004 YT2095 said in post # :then maybe you`de like to explain how a GPS works, are you saying they too are wrong when they give the current velocity of your vehicle? I find that relativistic effects are the least of your worries when it comes to the accuracy of GPSs. Link to comment Share on other sites More sharing options...
iglak Posted January 30, 2004 Share Posted January 30, 2004 MrL_JaKiri said in post # :No. why? i must be misunderstanding something if this is true. Link to comment Share on other sites More sharing options...
JaKiri Posted January 31, 2004 Share Posted January 31, 2004 iglak said in post # :why? i must be misunderstanding something if this is true. The speed of light looks like the speed of light to someone going the speed of light. Look at my posts on the 2nd page, and one on this one. Link to comment Share on other sites More sharing options...
YT2095 Posted January 31, 2004 Share Posted January 31, 2004 ok then, put in laymans terms, it seems like you`re trying to say that the faster you move, the more you slow down? or at least something like it, and that if you hit C then you stop? I expect that this is probaly quite wrong again or the best over simplified, but on behalf of myself and one or 2 others that have posted in this thread, is that anything like close to a working example? Link to comment Share on other sites More sharing options...
JaKiri Posted January 31, 2004 Share Posted January 31, 2004 YT2095 said in post # :ok then, put in laymans terms, it seems like you`re trying to say that the faster you move, the more you slow down? Nope. You still go the same speed. It's just that, as I've explained before, the recession speed isn't calculated a+b; that's incorrect, and it's something you're assuming. Link to comment Share on other sites More sharing options...
YT2095 Posted January 31, 2004 Share Posted January 31, 2004 CAN YOU then, explain it in Laymans terms as opposed to calcs and observations then? Link to comment Share on other sites More sharing options...
JaKiri Posted January 31, 2004 Share Posted January 31, 2004 YT2095 said in post # :CAN YOU then, explain it in Laymans terms as opposed to calcs and observations then? The maximum possible recession speed (or approach speed, of course) between two states of motion (as it were; 'rest frames' is more accurate) is a maximum of c, and the deviation between the actual and just adding them becomes greater as you move away from relative rest and towards lightspeed. Link to comment Share on other sites More sharing options...
YT2095 Posted January 31, 2004 Share Posted January 31, 2004 so working on the idea that a speedo in car works on RPMs of the wheel turning, you`re saying the faster you actualy travel, the more your speedo will be telling lies to you? Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 31, 2004 Share Posted January 31, 2004 That's what he's saying. Not that I get any of it. He still didn't answer my question about the flashlight, at least in a way I understand. The light from the flashlight would go 2x the speed of light, from the observer's point of view. Is that even POSSIBLE? Link to comment Share on other sites More sharing options...
JaKiri Posted January 31, 2004 Share Posted January 31, 2004 YT2095 said in post # :so working on the idea that a speedo in car works on RPMs of the wheel turning, you`re saying the faster you actualy travel, the more your speedo will be telling lies to you? THE RELATIVE SPEED OF AN OBJECT WITH SOMETHING AT REST IS UNCHANGED. IT'S ONLY WHEN YOU'RE ADDING VELOCITIES. Link to comment Share on other sites More sharing options...
JaKiri Posted January 31, 2004 Share Posted January 31, 2004 Cap'n Refsmmat said in post # :That's what he's saying. Not that I get any of it. He still didn't answer my question about the flashlight, at least in a way I understand. The light from the flashlight would go 2x the speed of light, from the observer's point of view. Is that even POSSIBLE? No matter your velocity relative to anything else, the speed of light relative to you (ie the speed it moves towards/away/whatever) will always be the speed of light. This is because all rest frames are equally valid, and you might as well say that everything else is going at the speed of light. Link to comment Share on other sites More sharing options...
YT2095 Posted January 31, 2004 Share Posted January 31, 2004 MrL_JaKiri said in post # : THE RELATIVE SPEED OF AN OBJECT WITH SOMETHING AT REST IS UNCHANGED. IT'S ONLY WHEN YOU'RE ADDING VELOCITIES. WELL YOU CAN SHOUT ALL YOU WANT TO, IT DOESN`T MAKE YOUR POINT ANY THE BETTER UNDERSTOOD! dUUUUGH! so how the hell does car A know what Car B is doing then? for cryin out loud man! Link to comment Share on other sites More sharing options...
JaKiri Posted January 31, 2004 Share Posted January 31, 2004 YT2095 said in post # : WELL YOU CAN SHOUT ALL YOU WANT TO, IT DOESN`T MAKE YOUR POINT ANY THE BETTER UNDERSTOOD! dUUUUGH! so how the hell does car A know what Car B is doing then? for cryin out loud man! I can now use the quote in its native form. I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question. 'Car A' 'knowing' what 'Car B' is doing is utterly, utterly irrelevent, (ignore this bit if you don't know what I'm talking about already, it'll probably confuse matters: although always possible by the nature of information exchange) and you may as well say 'How does car a know what car b is doing??? when you're adding together the speeds under newtonian mechanics (ie a+b). It's not a property of the car, it's not a property of the speed it's going at, it's a property of the universe, and exists with respect to rest frames. Link to comment Share on other sites More sharing options...
iglak Posted January 31, 2004 Share Posted January 31, 2004 MrL_JaKiri said in post # : The speed of light looks like the speed of light to someone going the speed of light. Look at my posts on the 2nd page, and one on this one. you mean the candle light flashlight stuff? ahh... i see... then all i don't get is special relativity (darn, and i thought i understood it!), i need to look it up. Link to comment Share on other sites More sharing options...
NSX Posted January 31, 2004 Share Posted January 31, 2004 MrL_JaKiri said in post # : No. a+b is a fine working approximate until you reach higher velocities. Like MrL says. Speeds on our Earth are pretty far from relativistic motions. For simple Earth speeds like you say, YT, cars, classical mechanics is good enough. iglak said in post # :you mean the candle light flashlight stuff? ahh... i see... then all i don't get is special relativity (darn, and i thought i understood it!), i need to look it up. It's a long lookup Link to comment Share on other sites More sharing options...
-Demosthenes- Posted January 31, 2004 Author Share Posted January 31, 2004 I've been reading the posts, but I honestly don't completely understand it. Can we put it all in a nutshell, just for me? I think I know "what" but I don't think I know "why". Signed--Confused Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted January 31, 2004 Share Posted January 31, 2004 I'm confused too. Link to comment Share on other sites More sharing options...
JaKiri Posted February 1, 2004 Share Posted February 1, 2004 Why is because the speed of light is constant for all observers. Everything else is due to it, and the mathematics derives from it. If you want something better, then I'm afraid the only other explanation is 'that's the way it is' Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted February 1, 2004 Share Posted February 1, 2004 Ok, let me restate my question. I'm not satisfied with the way you answered. You are going the speed of light. You turn on a flashlight and point it forward. The light would accelerate ahead of you at the speed of light. To another observer, that light is going twice the speed of light. Not possible, right? So what would the light do? Link to comment Share on other sites More sharing options...
JaKiri Posted February 1, 2004 Share Posted February 1, 2004 Cap'n Refsmmat said in post # :Ok, let me restate my question. I'm not satisfied with the way you answered. You are going the speed of light. You turn on a flashlight and point it forward. The light would accelerate ahead of you at the speed of light. To another observer, that light is going twice the speed of light. Not possible, right? So what would the light do? For a start, it wouldn't accelerate. Light isn't subject to forces in the same way as ordinary matter. Furthermore, the observer would see the light going at the speed of light too. Not twice, but once. The speed of light is a bad speed to do things at in this kind of discussion, though, as time technically does not exist and therefore you can't have done anything. Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted February 1, 2004 Share Posted February 1, 2004 "Furthermore, the observer would see the light going at the speed of light too." So that means the light would appear to stay in the flashlight (relative to the observer), because it is going the speed of light and so are you. Link to comment Share on other sites More sharing options...
JaKiri Posted February 1, 2004 Share Posted February 1, 2004 Cap'n Refsmmat said in post # :"Furthermore, the observer would see the light going at the speed of light too." So that means the light would appear to stay in the flashlight (relative to the observer), because it is going the speed of light and so are you. The speed of light is a bad, bad example, you see, and not only because it's impossible. It's much better to view things going just under the speed of light, it'll help you understand better. Link to comment Share on other sites More sharing options...
Cap'n Refsmmat Posted February 1, 2004 Share Posted February 1, 2004 So what happens if you are going 99.999999999% of the speed of light, and you do that. Then it is going ALMOST twice, which isn't possible. Link to comment Share on other sites More sharing options...
JaKiri Posted February 1, 2004 Share Posted February 1, 2004 Cap'n Refsmmat said in post # :So what happens if you are going 99.999999999% of the speed of light, and you do that. Then it is going ALMOST twice, which isn't possible. What will happen is that the light will be moving at c in the rest frame of the observer, and you will be going 99.9999999% of the speed of light, so the light moves away from you veeerrry sloooowly. In your rest frame, however, the light moves away from you at c. This is consistent, because time slows down the faster you go (relative to the rest frame). Hold on, I'll do a worked example. Lets say you're going 99.999999 whatever% of the speed of light. According to the person that is watching, it'll take quite some time for the light to move one light second away from you, because you're only just going slower than it. (1 light second being 299792458m) According to you, of course, the light will only take ONE second to go one light second away from you. However, your time is slowed because you're going so close to the speed of light, and the factor by which it's slowed is exactly the same multiple as between your one second and his few hours. There's also a factor of length contraction, but that makes it a bit more complicated to word (the light second you see isn't the same as the light second the person at rest sees, distance wise) You see? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now