Question about relativity
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From: someone2 on 26 Jul 2010 06:23 On 23 July, 00:00, Glenn Spigel <glenn.spi...(a)googlemail.com> wrote: > On 16 July, 19:45, dlzc <dl...(a)cox.net> wrote: > > > Dear someone2: > > > On Jul 16, 8:37 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > On 16 July, 06:28,dlzc<dl...(a)cox.net> wrote: > > > > > trimming down... > > > > > On Jul 15, 4:37 pm, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > On 15 July, 15:29,dlzc<dl...(a)cox.net> wrote: > > > > > > On Jul 15, 3:02 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > Ah ok. So if they used the track as the clock, > > > > > > > and took into account the time they would have > > > > > > > expected the light to have reached them from > > > > > > > the track, > > > > > > > "the time they would have expected" > > > > > > ... is that rest time, or knowing the the tools > > > > > > of relativity time? > > > > > > I meant it in the sense that if an outpost sent > > > > > out a horse rider every hour along a path, and > > > > > the riders travelled at a set speed, that if one > > > > > was to be coming down the path towards the outpost > > > > > a certain speed, one could work out the expected > > > > > interval between meeting a rider, and still use > > > > > the meeting of a rider as a clock, though > > > > > wouldn't consider there to be an hour interval > > > > > between each when you'd expect to meet each rider. > > > > > Your expectation is correct, in that: > > > > 1) you are moving towards the outpost, and so you > > > > will encounter riders in less time than they > > > > depart the outpost, and > > > > 2) your time is dilated, so you'd not get riders > > > > every hour anyway. > > > > When you say time is dilated, I'm not sure whether > > > you mean that the propergation rate is faster than > > > at rest, or something other than that. > > > I mean what is defined by the physics community for "time dilation", > > as I understand it. If you insist on using your internal shorthand > > "propergation rate" we are going to get mired in translation errors. > > This is why I keep directing you to a simple, standard > > "textbook" (very light on math), that can help you learn the lingo, > > and the meanings. You have described "propergation rate" a few > > different ways so far, so you obviously have some preconceived notions > > that I don't intend to lance and remove for your personal health. I > > just am trying to answer your question, and I will try not to delve > > into your personal fantasies of what words "should" mean, or what > > words "should have been" chosen to convey meanings. > > > > > > In the same sense that if a picture of a horse > > > > > was beamed in light each hour, that heading > > > > > towards the light source beaming the pictures, > > > > > you could still calculate the interval you'd > > > > > expect between each picture, but you wouldn't > > > > > consider the interval to be an hour, since > > > > > you were moving towards the source. > > > > > *And* time is dilated for you. > > > > > > Likewise with the track, and the interval > > > > > between each lap. > > > > > > > > it wouldn't seem that light was travelling at c. > > > > > > > Only with a frame jump implied with using > > > > > > measurements from diffferent frames. > > > > > > > > It would simply be that the laws of physics > > > > > > > would propergate slower at high velocity (and > > > > > > > perhaps under high gravity, I don't know), > > > > > > > Know that gravity need have nothing to do with > > > > > > this. It creates orders of magnitude more math, > > > > > > for a correction of fractions of a percent. > > > > > > Ok, we can ignore gravity. > > > > > > > > such that the tick of a clock on board the > > > > > > > ship might synchronise with a lap of the > > > > > > > vehicle on the track while the ship is > > > > > > > stationary, but when approacing the track at > > > > > > > a higher speed it might synchronise with 5 > > > > > > > laps of the vehicle on the track for example. > > > > > > > Yes, given the correct closing speed and/or > > > > > > track length / speed. > > > > > > > > Since the propergation rate of the laws is > > > > > > > referred to as t (time), > > > > > > > Laws don't propagate. Laws aren't really laws. > > > > > > Theories describe sets of observations, > > > > > > including propagation. > > > > > > I wasn't suggesting that laws themselves > > > > > propergated, just that they contained a > > > > > propergation rate referred to as t (time). > > > > > Though perhaps I shouldn't have referred to t > > > > > as the propergation rate, and instead > > > > > of referred to it as an event synchronisation > > > > > indicator. > > > > > Time is a fundamental property of a system, and > > > > one way or another, we don't get time "contained > > > > in" anything. Time spans all theories... > > > > not all equations contain the event synchronisation > > > indicator variable though. > > > Then they are trivial, uninteresting, or have disguised / masked it in > > more complex quantities. Again you insist on dragging your personal > > fantasies into the conversation. No one knows what time is. Changing > > its name to four words, does not convey more meaning. In fact the > > choices you have made for its substitution are non-sequitur in most > > contexts. > > > > > > > > they talk about time going slower or faster > > > > > > > in particular frames of reference. Have I > > > > > > > understood this correctly? > > > > > > > Not quite. I think you have the concept, but > > > > > > the language is loose. Everything in a frame > > > > > > appears to be self-consistent, not "time going > > > > > > slower or faster". The differences in length > > > > > > and "time rate" occur when viewing *another* > > > > > > frame with enough difference in velocity, that > > > > > > relativity's effects are larger than the > > > > > > error-bars of measurement. > > > > > > I'm not sure that I have got the concept. > > > > > > I was thinking at the high velocity that the > > > > > observed rate of propergation on the ship will > > > > > have slowed relative to the track. Such > > > > > that radioactive decay on the ship would take > > > > > place slower than on the track. > > > > > Radioactive decay, chemical clocks, spring clocks, > > > > heartbeats, even hard boiling eggs, all will be > > > > slowed by the same amount. > > > > Yes, everything in the frame will propergate at a > > > slower rate relative to the track. > > > Whatever. > > > > > > To hopefully indicate what I mean, if > > > > > everything in an alternate universe things > > > > > propergated twice as fast, then observations > > > > > within it should still fit with same 'laws of > > > > > physics'. > > > > > Why should that be the case? Adding additional > > > > Universes to this only muddies up matters. > > > > I'm not saying that it should should be the case > > > in all conceptual scenarios. Do you accept that > > > conceptually you could have a universe in which > > > things propergate at twice the rate of our > > > universe, and yet the observations within it still > > > fit with the same 'laws of physics'? > > > I can change c (and G, and h) to a value of 1, and still talk about > > this Universe. But in the appropriate system of units, distance and > > time don't compare to meters and seconds as easily. You are not > > establishing a different Universe, just rescaling this one. Check > > this out: > > >http://en.wikipedia.org/wiki/Buckingham_%CF%80_theoremhttp://en.wikip... > > > > The reason I mention it is to avoid confusion > > > over what we are referring to when we are > > > talking about time in physics. So I mention > > > it to make a distinction, to avoid a muddled > > > view. > > > The "mud" in this case is delivered to this thread by you. You > > apparently have some agenda against using standard nomenclature, or > > learning the knowledge set that answers your question on this topic > > will somehow endanger your presonal belief-set. I can point you at > > communication aids, but I cannot help your "mental illness". > > > > With the two universe view, you can see the > > > idea that the term 'time' can be used in the > > > sense that in one universe, things propergate > > > at twice the speed of the other universe. > > > See instead of time, you now describe something significantly > > different with "propergate". Mud. > > Well it might seem like 'mud' to you if you are unable to grasp what I > am meaning, and then consequently unable to say whether it is ok for > me to have understood what you are saying in these terms. > > I'll try to explain further what I am saying. Suppose you were to be > able to view a scene from each of two alternate universes through > magic viewing mirrors. When looking through them, the scene seems to > be of the same room in each, as though you were watching a video of > each if you will, except that in one it seems that the video is being > viewed on fast forward, such that everything in the speeded up > universe is happening twice as quickly as the other universe. If you > were to consider being an observer in each of the scenes, can you > understand that the same physics equations would hold in both. Such > that if you was a cup dropped in each scene, from the perspective of > an observer in each scene, the cup dropped the same amount of distance > in the 'time' measured by the clock on the wall. If 'time' t in the > physics equations is a variable measuring the synchronisation of > events, then you can see why it is unchanged in the two alternate > universes mentioned, since within each, the synchonisation of events > is the same. Though a different meaning of 'time' might be the rate > the events propergated at, and this is different between the two > universes, since in one the events propergate at twice the rate of the > other. > > I presume the issue of whether 't' in the physics equations refers to > event synchronisation was covered in the Bergson/Einstein debate. > Where the Einstein camp claimed Bergson didn't understand them, and > Bergson claimed they didn't understand him. I haven't read the debate > as I haven't seen a transcript of it, but hopefully you can visualise > the 'magic mirror' example above, and say whether when you use the > word 'time' are you meaning the synchronisation of events, and can you > understand what I am referring to when I say that the events in one > universe are propergating twice as fast as in the other, and would I > be correct in thinking that you might describe this as time being > faster in one universe relative to the other? > > > > Alternatively, using 'time' as in equations, > > > where it is an event synchronisation indicator, > > > the two universes > > > Same Universe, you've just applied a different scale. > > > > > > Since the propergation is measured in terms > > > > > of synchronisity. > > > > > No, it is not. > > > > How about I say the 'propergation is described > > > using terms of synchonisity'? > > > Use the language. Learn the language. I had to. > > > > > > The clock which measured a second would turn > > > > > twice as fast, while the ball dropped twice > > > > > as fast, so it would still drop at Xm/s in both > > > > > universes. The variable t would still indicate > > > > > the synchornisation of events. > > > > > Doesn't follow. Why don't you stick to *this* > > > > Universe, destroy whatever pre-copnceived notions > > > > you have about "synchornisation" and > > > > "propergation", and get "Spacetime Physics"? > > > > When you say it doesn't follow, are you saying that > > > it isn't necessary that the alternate universe > > > should be describle in the same terms of physics, > > > or that things propergating twice as fast in it > > > prevents it being describable in the same terms of > > > physics. > > > I'm saying changing c might have a change only in the > > meter_other_universe, and may have no effect on things that control > > the rate of radaioactive decay (for example). > > There though, you'd be imagining that some events propergated twice as > fast and not others. Use your imagination (as apparently Einstein did > quite often), and imagine a universe where all events propergated > twice as fast (as in the magic mirror scenario above). > > > > I have explained above why I am mentioning an > > > alternate universe. The reason I persist in > > > bringing up synchronisation and propergation, is > > > that unless I am clear about what 'spacetime > > > physics' is saying about the synchronisation of > > > events, I won't have 'got it'. > > > Spacetime Physics is a book, that I recommended in my first response. > > You clearly don't "got it". > > > > > > It seems to me that what you are referring to > > > > > as 'frames' are areas where the propergation > > > > > rate is deemed to be uniform. > > > > > They are defined as collections of objects / > > > > points that have a constant, uniform, > > > > non-accelerated motion. > > > > > > I might not be communicating this very well, > > > > > do you feel that you are able to understand > > > > > what I am saying? > > > > > See, I thought you were asking questions, not > > > > selling your preconceived, imagined meanings of > > > > words. If I have to learn your language before > > > > I can talk to you, this will take too long. Get > > > > "Spacetime Physics", and see what the language > > > > of relativity is. > > > > > ... > > > > I am asking questions, and not trying to sell a > > > "preconceived, imagined meanings of words". I > > > clarify my current thoughts, to give a context to > > > the question, in order that you may fashion the > > > most informative response. > > > I am not a trained pony. You have tried to mold what I said into the > > structure that you have already decided fits this Universe, and your > > understanding of it. And you keep feeling like telling me about your > > internal *broken* system will somehow get me to agree to using it, or > > to continue trying to decipher it. I tell you now directly, I tire of > > this game. > > Sounds like you need to relax a bit, and maybe just read what I am > actually saying, rather than what you think I might be saying, in > light of the motives that you are imagining me to have. > > > Such that if you can understand what I mean by > > > 'propergation rate' for example, and you know > > > yourself to mean something other than that by > > > 'time dialation' then you can say so. > > > SO. > > > > The way I have understood it so far, is that > > > at high velocity, > > > At *different* velocity, high or not. If the difference is high, > > measurement differences are easier to detect. > > > > things propergate slower, such that > > > "radioactive decay, chemical clocks, spring > > > clocks, heartbeats, even hard boiling eggs, all > > > will be slowed by the same amount", and so if > > > 'time' of events on board was measured by a > > > onboard (slowly propergating) clock, 'time' > > > could be said to have 'dialated'. > > > Dilation (note the spelling) describes the scaling of "the passage of > > time" from one frame into the other. > > > > I appreciate the help you have given so far > > > though, but if you feel that the issue will > > > take too long to clarify, and wish to stop, then > > > that's fine, you've already been a help. > > > I'd recommend, again, "Spacetime Physics" by Taylor and Wheeler. > > > > > > > > > You said the vehicle traveled 100mph, presumably > > > > > > > > in its own frame, and it travels really close to > > > > > > > > exactly one year, so: > > > > > > > > 100 * 24 * 365.25 (just averaging the year) = > > > > > > > > 876,600 miles, in just under 2 hours. > > > > > Note to self. The speed of light is 186,000 miles per second, not per > > > > hour. No observation of apparent FTL is expected. > > > > > ...> > By the way, you think your ship is "really fast"? Check > > > > > > this out... > > > > >http://www.fourmilab.ch/documents/OhMyGodParticle/ > > > > > > I took a quick look at the link, and it seemed that > > > > > the particle only appeared to be going near to light > > > > > speed according to an observer in another frame. An > > > > > observer on the particle would have considered it to > > > > > be travelling 14705200000c if I have understood it > > > > > correctly. > > > > > No, this requires a frame jump. Duration in the > > > > particle's frame, and distance in the rest frame. > > > > Ah ok, now I have seen the definition of a 'frame' > > > that you provided I can see that if an observer changes > > > velocity they change frame. > > > What separates frames (in special relativity) is relative velocity. > > > > > > The people in the ship measure the distance they > > > > > are about to travel (to the track) while at rest, > > > > > one frame (similar to the track and car's frame) > > > > > > then measure with an on board clock how > > > > > long they took to travel it. > > > > > Second frame, one that is separated from the other > > > > by *massive* acceleration. > > > > > > Where was the frame jump? > > > > > Distance in the rest frame, and duration in > > > > the moving frame. If they measure distance > > > > while moving, they get the same speed of > > > > 99.99999%c, just as you specified, for the > > > > trip. They can use parallax, subtended size > > > > of the track, intensity of source, and all will > > > > yield the distance as just a tad over 3.9 light > > > > hours away (as they cross the "rest frame 1 > > > > light year away" mark. > > > > Thanks > > > You can thank me by reading the links, and perhaps picking up the book > > (or even downloading the Motion Mountain physics chapter) I have > > directed you towards. > > > Things will be clearer when you encounter descriptions of relativity > > and relativisitc effects on the internet, and you won't have these > > basic questions. Mostly based on an incorrect internal model of the > > Universe. I can't fix your model, only you can. Dear Dlcz, The post I am replying to was my own btw, I had just forgot to switch the email account I logged onto Google with. I'd just like to summarise my understanding of what you've said regarding the track so far. That as the ship approaches the track, time will dilate for the ship, such that the journey only appears to take a short time, whereas for the person on the track, it will seem as though the approaching ship was travellinng close to the speed of light, and had taken slightly less time than light would have been expected to, to have travelled the distance. As you said: --------------------- SHIP... 3.9 hours "really" passes onboard the ship. Only they travel 3.9 light hours to pass the mirror. And they measure c as c. TRACK... 1 year passes on the track. They (might) see the distant ship leave the "1 light year point" about 3.9 hours before the ship blows by them. The light is 1 year in transit, and the ship just that little bit longer. And c is measured as c in the track's frame. --------------------- Now if there was a clock on the approaching ship and it flashed a light signal every hour, and one at the mirror which flashed a light signal every hour, I am assuming that by the time the ship reached the mirror, the observer at the mirror and the observer on the ship will have observed 3 flashes of light from the ship's clock. Those on the ship will have observed 24*365 flashes from the mirror's flashing clock, as would the observer at the mirror. If that is correct, could you please explain to me in terms of flashes what would have been expected if the ship was stationary, and the track had been moving towards it at near light speed instead. Would 1 year really have passed on the ship, and 3.9 hours really passed on the speeding track?
From: Glenn Spigel on 28 Jul 2010 08:42 On 17 July, 03:27, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > On Jul 16, 10:49 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > On 16 July, 08:40, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > > > On Jul 15, 7:37 pm, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > On 15 July, 15:29, dlzc <dl...(a)cox.net> wrote: > > > > > > Dear someone2: > > > > > > On Jul 15, 3:02 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > On 15 July, 05:08,dlzc<dl...(a)cox.net> wrote: > > > > > > > On Jul 14, 5:13 pm, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > > On 14 July, 20:56,dlzc<dl...(a)cox.net> wrote: > > > > > > > > > On Jul 14, 11:43 am, someone2 <glenn.spig...(a)btinternet..com> wrote:> On 14 July, 19:10,dlzc<dl...(a)cox.net> wrote: > > > > > > > > > > > On Jul 14, 9:40 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > > > > wrote: > > > > > > > > > ... > > > > > > > > > > > > > I was thinking that since although the light > > > > > > > > > > > > would be travelling away from the observer at > > > > > > > > > > > > the speed of light, and thus be 0.75 light years > > > > > > > > > > > > in front of the observer after 0.75 of a year > > > > > > > > > > > > ... just not the observer's year. > > > > > > > > > > > > > (and thus have reached the mirror by the time > > > > > > > > > > > > the observer is about 0.75 light years from the > > > > > > > > > > > > mirror), > > > > > > > > > > > > No. > > > > > > > > > > > > > it would only have travelled 0.25 light years > > > > > > > > > > > > back towards the observer, after the 1 year. > > > > > > > > > > > > At the speed you have indicated, the moving > > > > > > > > > > > observer is just some short distance from the > > > > > > > > > > > mirror (a few million miles, say) when the > > > > > > > > > > > light hits. > > > > > > > > > > > Ah this might seem to be a misunderstanding of > > > > > > > > > > mine then. I thought that unlike a car on a > > > > > > > > > > motorway where if car A was travelling at speed > > > > > > > > > > x-y, and car B was travelling at speed x, car B > > > > > > > > > > would only seem to pull away from car A at y mph, > > > > > > > > > > with light I thought, the idea was that even if > > > > > > > > > > the space ship is going at near the speed of > > > > > > > > > > light, the fired beam would still appear to travel > > > > > > > > > > away from it at the speed of light. > > > > > > > > > > It does. But *in the ship's frame*, the > > > > > > > > > rest distance of 1 light year can be > > > > > > > > > measured (by the ships' instruments) by many > > > > > > > > > different methods to be about 3.9 light hours. > > > > > > > > > > > Likewise if the observer was travelling towards > > > > > > > > > > an incoming light beam at the near the speed of > > > > > > > > > > light, the light would only appear to travel > > > > > > > > > > towards the observer at the speed of light. > > > > > > > > > > Correct. > > > > > > > > > > > Are you saying that this is not the case, and > > > > > > > > > > that if a beam of light is fired from an object > > > > > > > > > > moving at velocity x in the same direction as > > > > > > > > > > the light beam, that the light beam will only > > > > > > > > > > appear to move away from that object at c-x? > > > > > > > > > > No. What I am saying is that "time dilation" and > > > > > > > > > "length contraction" are two faces of the same > > > > > > > > > coin. Please look at the link I provided, > > > > > > > > > at minimum. Or here, if you have the stomach for > > > > > > > > > it. > > > > > > > > <snip link now broken by Google.Groups> > > > > > > > > > > Everyone sets themselves up for "frame jumps", > > > > > > > > > since "common sense" says that measurements by > > > > > > > > > different observers "must be" the same for > > > > > > > > > all frames. It is sometimes close enough where > > > > > > > > > our "common sense" is trained, but it is a > > > > > > > > > serious mistake at speeds close to c. > > > > > > > > > > It is even detectable at the speed of aircraft > > > > > > > > > (special relativity), and/or altitudes of a few > > > > > > > > > hundred feet (general relativity), if you can > > > > > > > > > integrate the effects over time. > > > > > > > > > The question is about the frame of reference of > > > > > > > > the observer that is approaching the tracke. I'm > > > > > > > > not sure where this frame is ever left, so I'm > > > > > > > > not clear on where you are suggesting frame > > > > > > > > jumping is taking place. I thought you were > > > > > > > > saying that the observer approaching the track > > > > > > > > would find themselves only a small distance away > > > > > > > > from the track as the beam of light they fired > > > > > > > > reached the mirror, since you said: > > > > > > > > > "At the speed you have indicated, the moving > > > > > > > > observer is just some short distance from the > > > > > > > > mirror (a few million miles, say) when the > > > > > > > > light hits." > > > > > > > > ... the "few million miles" in the frame of the > > > > > > > track and car, of course. > > > > > > > > > Though if they were, then I'm not clear how > > > > > > > > the light appeared to them to be leaving them > > > > > > > > at the spead of light, since it is only a little > > > > > > > > bit ahead of them. > > > > > > > > ... because their clock is running slow, and > > > > > > > their lengths contracted, they can measure c > > > > > > > to be the same friendly constant... > > > > > > > > > I am assuming that they will be using the vehicle > > > > > > > > going around the track as their clock, > > > > > > > > Why would they do that? Even at constant speed, > > > > > > > the rate of vehicle motion will be extraordinarily > > > > > > > fast when approaching the track, and > > > > > > > extraordinarily slow when departing from the other > > > > > > > side. Much easier just to carry your own clock with > > > > > > > you. Like "heartbeats" if nothing else. > > > > > > > > > taking into account how long it takes the light > > > > > > > > to reach them at their given position. Or is it > > > > > > > > that if they did this, that the light would not > > > > > > > > seem to be leaving them at the speed of light, > > > > > > > > but only if they used a clock on board their > > > > > > > > ship, such that measured by that onboard clock > > > > > > > > the journey appears to have taken less time, > > > > > > > > Bingo. > > > > > > > Ah ok. So if they used the track as the clock, > > > > > > and took into account the time they would have > > > > > > expected the light to have reached them from > > > > > > the track, > > > > > > "the time they would have expected" > > > > > ... is that rest time, or knowing the the tools of relativity time? > > > > > I meant it in the sense that if an outpost sent out a horse rider > > > > every hour along a path, and the riders travelled at a set speed, that > > > > if one was to be coming down the path towards the outpost a certain > > > > speed, one could work out the expected interval between meeting a > > > > rider, and still use the meeting of a rider as a clock, though > > > > wouldn't consider there to be an hour interval between each when you'd > > > > expect to meet each rider. > > > > > In the same sense that if a picture of a horse was beamed in light > > > > each hour, that heading towards the light source beaming the pictures, > > > > you could still calculate the interval you'd expect between each > > > > picture, but you wouldn't consider the interval to be an hour, since > > > > you were moving towards the source. > > > > > Likewise with the track, and the interval between each lap. > > > > > > > it wouldn't seem that light was travelling at c. > > > > > > Only with a frame jump implied with using measurements from diffferent > > > > > frames. > > > > > > > It would simply be that the laws of physics > > > > > > would propergate slower at high velocity (and > > > > > > perhaps under high gravity, I don't know), > > > > > > Know that gravity need have nothing to do with this. It creates > > > > > orders of magnitude more math, for a correction of fractions of a > > > > > percent. > > > > > Ok, we can ignore gravity. > > > > > > > such that the tick of a clock on board the > > > > > > ship might synchronise with a lap of the > > > > > > vehicle on the track while the ship is > > > > > > stationary, but when approacing the track at > > > > > > a higher speed it might synchronise with 5 > > > > > > laps of the vehicle on the track for example. > > > > > > Yes, given the correct closing speed and/or track length / speed. > > > > > > > Since the propergation rate of the laws is > > > > > > referred to as t (time), > > > > > > Laws don't propagate. Laws aren't really laws. Theories describe > > > > > sets of observations, including propagation. > > > > > I wasn't suggesting that laws themselves propergated, just that they > > > > contained a propergation rate referred to as t (time). Though perhaps > > > > I shouldn't have referred to t as the propergation rate, and instead > > > > of referred to it as an event synchronisation indicator. > > > > > > > they talk about time going slower or faster > > > > > > in particular frames of reference. Have I > > > > > > understood this correctly? > > > > > > Not quite. I think you have the concept, but the language is loose. > > > > > Everything in a frame appears to be self-consistent, not "time going > > > > > slower or faster". The differences in length and "time rate" occur > > > > > when viewing *another* frame with enough difference in velocity, that > > > > > relativity's effects are larger than the error-bars of measurement. > > > > > I'm not sure that I have got the concept. > > > > The slowing of a moving clock is caused by how you measure its rate > > > and the effects of relative simultanity. Same deal with the length of > > > a rod. All the clocks are identical and tic at the same rate, as > > > measured in their rest frame. Move the clock to a different rest > > > frame and it will tick at the same rate as the clocks already in that > > > frame. Same deal with a meter rod. It is the same length as all > > > other meter rods in the frame, and when moved to another frame will be > > > the same length as the meter rods in that frame. > > > > To set up your coordinate system put a clock at each end of a rod. To > > > sync the clocks flash beams of light back and forth between the > > > clocks. Since light travels the same speed in either direction, when > > > the clocks are adjusted so the light takes the same time to travel the > > > length of the rod in either direction the clocks are in sync. > > > > Now switch to a second frame that is moving relative to the first. > > > You set up a series of rods and clocks and sych them. Now watch as > > > the first rod passes by and a light flashes along its length. The > > > light is moving at c as measured by your stationary clocks. Because > > > the first rod is moving relative to you, you calculate that the light > > > is traveling at c+v relative to it. Note that it is a calculation, > > > not a direct measurement. We call this a closing speed. Flash the > > > light in the opposit direction and you get c-v. > > > > If we measure how long it takes the light to travel the lenght of the > > > rod in opposit directions we get different times. But we know that an > > > observer moving with the rod measures the light to take the same time > > > in either direction. The reason he is able to do that is because, > > > from our perspective, his clocks are out of sync. Remember, they were > > > set based on light traveling at c relative to the moving rod. So both > > > frames measure the speed of light to be c in their own frame while > > > calculating it to be c+/-v in the other frame. > > > Though if the clocks had a light on them, and when they were in synch > > both lit up together, when they don't appear to light up together as > > the as the rod passes, isn't this just due to the difference in > > distance from each clock (as it flashes its light) to the observer?> All the clocks in the moving frame are out of sync relative to ours. > > No. We have determined the time of the flashes based on the time > showing on the synchronized clock adjacent to them. That eliminates > the travel time of the travel time for the light to reach the > observer. The two frames dissagree because they both measure the > speed of light to be c in their own frame but calculate it to be > something else in the other frame. > > [snip] I had misunderstood, I was thinking you were suggesting that there were two clocks at either end of a rod, moving past the observer in a different rest frame, and to that observer they weren't in synch with each other, but to an observer in the same rest frame as the clocks they were. [In case I hadn't misunderstood: What I mean by being in synch, is that the first clock flashes its green light simultaneously with the second clock flashing its blue light, and this being observed assuming you take into account the time (as measured by a clock in the observer's rest frame) required for the light from each to reach the observer. Maybe a misunderstanding lies there. I'm not clear on how that eliminates the travel time for the light to reach the observer. I thought all we had done was synch the clocks in a given rest frame with each other, by setting them such they both receive a broadcasted flash of light from the other clock at 1 second after their own broadcast, and receive the reflection of their own broadcast back after 2 seconds for example. Though as these synchonised clocks were mounted on the back of a very long train for example, and there was an observer at a station which the train passed. As the first clock passed the observer it would be moving away at v, while the second clock would be approaching at v. The light (let's say green) from the first clock, would seem to travel at c - v towards the observer, whereas the light (let's say blue) from the second clock would seem to travel at c + v towards the observer. Thus even if the clocks flashed when they were equidistant (there might be an issue about how distance is measured here, here I am assuming the mid point between the two clocks in the clock's rest frame) from the observer, it would take slightly longer for the green light to reach the observer than the blue light, and thus the green light and the blue light might not appear to flash in synch.] dlzc was certainly talking about an issue of synchonisation, such that the if you had synchonised a clock on the space ship and one on the track by the mirror, that as the space ship approached the track at near light speed, the flashes on the clock on the ship would no longer be simultaneous with the flashes on of the clock on by the mirror. As shown by when the ship comes to an abrupt stop at the mirror, both the observer on the ship and the observer on the mirror can confirm the number of times the clock on the ship flashed and compare it to the number of times the clock on the track flashed. dlzc said: --------------------- SHIP... 3.9 hours "really" passes onboard the ship. Only they travel 3.9 light hours to pass the mirror. And they measure c as c. TRACK... 1 year passes on the track. They (might) see the distant ship leave the "1 light year point" about 3.9 hours before the ship blows by them. The light is 1 year in transit, and the ship just that little bit longer. And c is measured as c in the track's frame. --------------------- Are you in agreement with dlzc there, and is this the synchonization issue you are talking about? If so, then there was a clock on the approaching ship and it flashed a light signal every hour, and one at the mirror which flashed a light signal every hour, I am assuming that by the time the ship reached the mirror, the observer at the mirror and the observer on the ship will have observed 3 flashes of light from the ship's lock. Those on the ship will have observed 24*365 flashes from the mirror's flashing clock, as would the observer at the mirror. If that is correct, could you please explain to me in terms of flashes what would have been expected if the ship was stationary, and the track had been moving towards it at near light speed instead. Would the clock on the year really have passed on the ship, and 3.9 hours really passed on the speeding track?
From: Glenn Spigel on 28 Jul 2010 08:56
On 28 July, 13:42, Glenn Spigel <glenn.spi...(a)googlemail.com> wrote: > On 17 July, 03:27, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > > On Jul 16, 10:49 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > On 16 July, 08:40, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > > > > On Jul 15, 7:37 pm, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > On 15 July, 15:29, dlzc <dl...(a)cox.net> wrote: > > > > > > > Dear someone2: > > > > > > > On Jul 15, 3:02 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > > On 15 July, 05:08,dlzc<dl...(a)cox.net> wrote: > > > > > > > > On Jul 14, 5:13 pm, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > > > On 14 July, 20:56,dlzc<dl...(a)cox.net> wrote: > > > > > > > > > > On Jul 14, 11:43 am, someone2 <glenn.spig...(a)btinternet.com> wrote:> On 14 July, 19:10,dlzc<dl...(a)cox.net> wrote: > > > > > > > > > > > > On Jul 14, 9:40 am, someone2 <glenn.spig...(a)btinternet.com> wrote: > > > > > > > > > > > wrote: > > > > > > > > > > ... > > > > > > > > > > > > > > I was thinking that since although the light > > > > > > > > > > > > > would be travelling away from the observer at > > > > > > > > > > > > > the speed of light, and thus be 0.75 light years > > > > > > > > > > > > > in front of the observer after 0.75 of a year > > > > > > > > > > > > > ... just not the observer's year. > > > > > > > > > > > > > > (and thus have reached the mirror by the time > > > > > > > > > > > > > the observer is about 0.75 light years from the > > > > > > > > > > > > > mirror), > > > > > > > > > > > > > No. > > > > > > > > > > > > > > it would only have travelled 0.25 light years > > > > > > > > > > > > > back towards the observer, after the 1 year. > > > > > > > > > > > > > At the speed you have indicated, the moving > > > > > > > > > > > > observer is just some short distance from the > > > > > > > > > > > > mirror (a few million miles, say) when the > > > > > > > > > > > > light hits. > > > > > > > > > > > > Ah this might seem to be a misunderstanding of > > > > > > > > > > > mine then. I thought that unlike a car on a > > > > > > > > > > > motorway where if car A was travelling at speed > > > > > > > > > > > x-y, and car B was travelling at speed x, car B > > > > > > > > > > > would only seem to pull away from car A at y mph, > > > > > > > > > > > with light I thought, the idea was that even if > > > > > > > > > > > the space ship is going at near the speed of > > > > > > > > > > > light, the fired beam would still appear to travel > > > > > > > > > > > away from it at the speed of light. > > > > > > > > > > > It does. But *in the ship's frame*, the > > > > > > > > > > rest distance of 1 light year can be > > > > > > > > > > measured (by the ships' instruments) by many > > > > > > > > > > different methods to be about 3.9 light hours. > > > > > > > > > > > > Likewise if the observer was travelling towards > > > > > > > > > > > an incoming light beam at the near the speed of > > > > > > > > > > > light, the light would only appear to travel > > > > > > > > > > > towards the observer at the speed of light. > > > > > > > > > > > Correct. > > > > > > > > > > > > Are you saying that this is not the case, and > > > > > > > > > > > that if a beam of light is fired from an object > > > > > > > > > > > moving at velocity x in the same direction as > > > > > > > > > > > the light beam, that the light beam will only > > > > > > > > > > > appear to move away from that object at c-x? > > > > > > > > > > > No. What I am saying is that "time dilation" and > > > > > > > > > > "length contraction" are two faces of the same > > > > > > > > > > coin. Please look at the link I provided, > > > > > > > > > > at minimum. Or here, if you have the stomach for > > > > > > > > > > it. > > > > > > > > > <snip link now broken by Google.Groups> > > > > > > > > > > > Everyone sets themselves up for "frame jumps", > > > > > > > > > > since "common sense" says that measurements by > > > > > > > > > > different observers "must be" the same for > > > > > > > > > > all frames. It is sometimes close enough where > > > > > > > > > > our "common sense" is trained, but it is a > > > > > > > > > > serious mistake at speeds close to c. > > > > > > > > > > > It is even detectable at the speed of aircraft > > > > > > > > > > (special relativity), and/or altitudes of a few > > > > > > > > > > hundred feet (general relativity), if you can > > > > > > > > > > integrate the effects over time. > > > > > > > > > > The question is about the frame of reference of > > > > > > > > > the observer that is approaching the tracke. I'm > > > > > > > > > not sure where this frame is ever left, so I'm > > > > > > > > > not clear on where you are suggesting frame > > > > > > > > > jumping is taking place. I thought you were > > > > > > > > > saying that the observer approaching the track > > > > > > > > > would find themselves only a small distance away > > > > > > > > > from the track as the beam of light they fired > > > > > > > > > reached the mirror, since you said: > > > > > > > > > > "At the speed you have indicated, the moving > > > > > > > > > observer is just some short distance from the > > > > > > > > > mirror (a few million miles, say) when the > > > > > > > > > light hits." > > > > > > > > > ... the "few million miles" in the frame of the > > > > > > > > track and car, of course. > > > > > > > > > > Though if they were, then I'm not clear how > > > > > > > > > the light appeared to them to be leaving them > > > > > > > > > at the spead of light, since it is only a little > > > > > > > > > bit ahead of them. > > > > > > > > > ... because their clock is running slow, and > > > > > > > > their lengths contracted, they can measure c > > > > > > > > to be the same friendly constant... > > > > > > > > > > I am assuming that they will be using the vehicle > > > > > > > > > going around the track as their clock, > > > > > > > > > Why would they do that? Even at constant speed, > > > > > > > > the rate of vehicle motion will be extraordinarily > > > > > > > > fast when approaching the track, and > > > > > > > > extraordinarily slow when departing from the other > > > > > > > > side. Much easier just to carry your own clock with > > > > > > > > you. Like "heartbeats" if nothing else. > > > > > > > > > > taking into account how long it takes the light > > > > > > > > > to reach them at their given position. Or is it > > > > > > > > > that if they did this, that the light would not > > > > > > > > > seem to be leaving them at the speed of light, > > > > > > > > > but only if they used a clock on board their > > > > > > > > > ship, such that measured by that onboard clock > > > > > > > > > the journey appears to have taken less time, > > > > > > > > > Bingo. > > > > > > > > Ah ok. So if they used the track as the clock, > > > > > > > and took into account the time they would have > > > > > > > expected the light to have reached them from > > > > > > > the track, > > > > > > > "the time they would have expected" > > > > > > ... is that rest time, or knowing the the tools of relativity time? > > > > > > I meant it in the sense that if an outpost sent out a horse rider > > > > > every hour along a path, and the riders travelled at a set speed, that > > > > > if one was to be coming down the path towards the outpost a certain > > > > > speed, one could work out the expected interval between meeting a > > > > > rider, and still use the meeting of a rider as a clock, though > > > > > wouldn't consider there to be an hour interval between each when you'd > > > > > expect to meet each rider. > > > > > > In the same sense that if a picture of a horse was beamed in light > > > > > each hour, that heading towards the light source beaming the pictures, > > > > > you could still calculate the interval you'd expect between each > > > > > picture, but you wouldn't consider the interval to be an hour, since > > > > > you were moving towards the source. > > > > > > Likewise with the track, and the interval between each lap. > > > > > > > > it wouldn't seem that light was travelling at c. > > > > > > > Only with a frame jump implied with using measurements from diffferent > > > > > > frames. > > > > > > > > It would simply be that the laws of physics > > > > > > > would propergate slower at high velocity (and > > > > > > > perhaps under high gravity, I don't know), > > > > > > > Know that gravity need have nothing to do with this. It creates > > > > > > orders of magnitude more math, for a correction of fractions of a > > > > > > percent. > > > > > > Ok, we can ignore gravity. > > > > > > > > such that the tick of a clock on board the > > > > > > > ship might synchronise with a lap of the > > > > > > > vehicle on the track while the ship is > > > > > > > stationary, but when approacing the track at > > > > > > > a higher speed it might synchronise with 5 > > > > > > > laps of the vehicle on the track for example. > > > > > > > Yes, given the correct closing speed and/or track length / speed. > > > > > > > > Since the propergation rate of the laws is > > > > > > > referred to as t (time), > > > > > > > Laws don't propagate. Laws aren't really laws. Theories describe > > > > > > sets of observations, including propagation. > > > > > > I wasn't suggesting that laws themselves propergated, just that they > > > > > contained a propergation rate referred to as t (time). Though perhaps > > > > > I shouldn't have referred to t as the propergation rate, and instead > > > > > of referred to it as an event synchronisation indicator. > > > > > > > > they talk about time going slower or faster > > > > > > > in particular frames of reference. Have I > > > > > > > understood this correctly? > > > > > > > Not quite. I think you have the concept, but the language is loose. > > > > > > Everything in a frame appears to be self-consistent, not "time going > > > > > > slower or faster". The differences in length and "time rate" occur > > > > > > when viewing *another* frame with enough difference in velocity, that > > > > > > relativity's effects are larger than the error-bars of measurement. > > > > > > I'm not sure that I have got the concept. > > > > > The slowing of a moving clock is caused by how you measure its rate > > > > and the effects of relative simultanity. Same deal with the length of > > > > a rod. All the clocks are identical and tic at the same rate, as > > > > measured in their rest frame. Move the clock to a different rest > > > > frame and it will tick at the same rate as the clocks already in that > > > > frame. Same deal with a meter rod. It is the same length as all > > > > other meter rods in the frame, and when moved to another frame will be > > > > the same length as the meter rods in that frame. > > > > > To set up your coordinate system put a clock at each end of a rod. To > > > > sync the clocks flash beams of light back and forth between the > > > > clocks. Since light travels the same speed in either direction, when > > > > the clocks are adjusted so the light takes the same time to travel the > > > > length of the rod in either direction the clocks are in sync. > > > > > Now switch to a second frame that is moving relative to the first. > > > > You set up a series of rods and clocks and sych them. Now watch as > > > > the first rod passes by and a light flashes along its length. The > > > > light is moving at c as measured by your stationary clocks. Because > > > > the first rod is moving relative to you, you calculate that the light > > > > is traveling at c+v relative to it. Note that it is a calculation, > > > > not a direct measurement. We call this a closing speed. Flash the > > > > light in the opposit direction and you get c-v. > > > > > If we measure how long it takes the light to travel the lenght of the > > > > rod in opposit directions we get different times. But we know that an > > > > observer moving with the rod measures the light to take the same time > > > > in either direction. The reason he is able to do that is because, > > > > from our perspective, his clocks are out of sync. Remember, they were > > > > set based on light traveling at c relative to the moving rod. So both > > > > frames measure the speed of light to be c in their own frame while > > > > calculating it to be c+/-v in the other frame. > > > > Though if the clocks had a light on them, and when they were in synch > > > both lit up together, when they don't appear to light up together as > > > the as the rod passes, isn't this just due to the difference in > > > distance from each clock (as it flashes its light) to the observer?> All the clocks in the moving frame are out of sync relative to ours. > > > No. We have determined the time of the flashes based on the time > > showing on the synchronized clock adjacent to them. That eliminates > > the travel time of the travel time for the light to reach the > > observer. The two frames dissagree because they both measure the > > speed of light to be c in their own frame but calculate it to be > > something else in the other frame. > > > [snip] > > I had misunderstood, I was thinking you were suggesting that there > were two clocks at either end of a rod, moving past the observer in a > different rest frame, and to that observer they weren't in synch with > each other, but to an observer in the same rest frame as the clocks > they were. > > [In case I hadn't misunderstood: > > What I mean by being in synch, is that the first clock flashes its > green light simultaneously with the second clock flashing its blue > light, and this being observed assuming you take into account the time > (as measured by a clock in the observer's rest frame) required for the > light from each to reach the observer. Maybe a misunderstanding lies > there. > > I'm not clear on how that eliminates the travel time for the light to > reach the observer. I thought all we had done was synch the clocks in > a given rest frame with each other, by setting them such they both > receive a broadcasted flash of light from the other clock at 1 second > after their own broadcast, and receive the reflection of their own > broadcast back after 2 seconds for example. > > Though as these synchonised clocks were mounted on the back of a very > long train for example, and there was an observer at a station which > the train passed. As the first clock passed the observer it would be > moving away at v, while the second clock would be approaching at v. > The light (let's say green) from the first clock, would seem to travel > at c - v towards the observer, whereas the light (let's say blue) from > the second clock would seem to travel at c + v towards the observer. > Thus even if the clocks flashed when they were equidistant (there > might be an issue about how distance is measured here, here I am > assuming the mid point between the two clocks in the clock's rest > frame) from the observer, it would take slightly longer for the green > light to reach the observer than the blue light, and thus the green > light and the blue light might not appear to flash in synch. Actually I think this is wrong. If the clocks flashed when they were equidistant, the light I would expect to take the same amount of time to reach the observer. > ] > > dlzc was certainly talking about an issue of synchonisation, such that > the if you had synchonised a clock on the space ship and one on the > track by the mirror, that as the space ship approached the track at > near light speed, the flashes on the clock on the ship would no longer > be simultaneous with the flashes on of the clock on by the mirror. As > shown by when the ship comes to an abrupt stop at the mirror, both the > observer on the ship and the observer on the mirror can confirm the > number of times the clock on the ship flashed and compare it to the > number of times the clock on the track flashed. > > dlzc said: > --------------------- > SHIP... > 3.9 hours "really" passes onboard the ship. Only they travel 3.9 > light hours to pass the mirror. And they measure c as c. > > TRACK... > 1 year passes on the track. They (might) see the distant ship leave > the "1 light year point" about 3.9 hours before the ship blows by > them. The light is 1 year in transit, and the ship just that little > bit longer. And c is measured as c in the track's frame. > --------------------- > > Are you in agreement with dlzc there, and is this the synchonization > issue you are talking about? > > If so, then there was a clock on the approaching ship and it flashed a > light signal every hour, and one at the mirror which flashed a light > signal every hour, I am assuming that by the time the ship reached the > mirror, the observer at the mirror and the observer on the ship will > have observed 3 flashes of light from the ship's lock. Those on the > ship will have observed 24*365 flashes from the mirror's flashing > clock, as would the observer at the mirror. > > If that is correct, could you please explain to me in terms of flashes > what would have been expected if the ship was stationary, and the > track had been moving towards it at near light speed instead. Would > the clock on the year really have passed on the ship, and 3.9 hours > really passed on the speeding track? |