John, Eric is right about the constancy of c being a *postulate* from which time-dilation and length contraction are derived. However, that doesn't discount your thought experiments as a way of probing the coherence of SR.
Imagine two friends with synchronized watches. One friend boards a train and zips away for a time at near c and then gets off and walks back to his friend so that they can compare the time on their watches. Which watch is ahead? Using the principles of SR I can come up with contradictory answers. harry Harry On Wed, Feb 19, 2014 at 3:45 PM, John Berry <[email protected]> wrote: > > > > On Thu, Feb 20, 2014 at 4:54 AM, Eric Walker <[email protected]>wrote: > >> On Wed, Feb 19, 2014 at 2:38 AM, John Berry <[email protected]>wrote: >> >> Are you arguing that this is impossible? >>> This is a thought experiment so it only has to be theoretically possible >>> to make such a measuring instrument. >>> >>> I would consider it obvious that such an instrument is possible. >>> >> >> I have no need to argue that it's impossible. Clarity of thought >> suggests that we start from something we already know about, rather than a >> hypothetical measurement I've never seen before. >> > > If it is reasonably and obviously possible, then it is valid. > If you wanted to do this experiment, there would be no great difficulty in > doing so. The separation and velocity of the of the moving platform may or > may not be beyond practical implementation. > >> >> About the possibility of the instrument -- I would assume any photon >> would be likely to be scattered during the first reading, and then, even if >> it was not, the act of being retransmitted to en route to the second >> detector would add in an unacceptable time delay that would invalidate our >> measurement. >> > > I have read that photon detectors can be put in double slit experiments > and while the wave function will be collapsed by knowing which slit the > photon went through, the photon wasn't absorbed. > Of course this is another ridiculous objection that makes it seem like you > would rather have a tooth pulled than accept an obvious truth. > > There could be many photons released in a single pulse, each detector only > absorbs a small number of photons. > > >> >> According to SR, no we wouldn't. >>> But if what was moving was anything else including a particle moving at >>> almost the speed of light. >>> If it was anything that can possibly be understood we would. >>> >>> Right now you are using circular reasoning that seems very much like >>> arguments for belief in God. >>> >> >> I think you misunderstand. You're claiming that SR is logically >> inconsistent. I'm hoping you can help me to understand this and come to >> the same conclusion. In order to do so, I have to be convinced that you're >> not setting up a straw man. Right now I'm persuaded of exactly the >> opposite. SR claims, as an assumption, that light in a vacuum, measured in >> an inertial frame, will be detected to be moving at *c*, no matter the >> reference frame. This is an axiomatic assumption based on empirical >> evidence. Einstein saw evidence that the speed of light would always be >> measured at the same velocity in an inertial frame, and then he asked the >> question of what would happen if this observation was turned into a fixed >> point, i.e., made into an axiom. He then derived a bunch of weird stuff >> about length contraction, time dilation, Lorentz invariance, etc. These >> were conclusions that were based on the earlier assumption (and other >> assumptions). >> > > Do you see the problem in your own statement? > > The speed of something being the same no matter how your position and > velocity may differ from other observers is by default an utter > impossibility. > > The 'bunch of weird stuff' is the only thing that could possibly help it > make sense, only there is no way it can as I have shown. > > SR only works if that weird stuff can make the speed of light look the > same to all observers, well it can't as I have shown. > The fact that you have taken on faith that this 'weird stuff' can make it > all make sense is the problem. > > Science isn't a religion, you aren't meant to take things that are > illogical on faith, not examine them and get dogmatic in your defence of > that thing. > > You are acting like we shouldn't bother our pretty little heads with how > this impossibility can occur. > > If you think that I am misrepresenting how SR argues the speed of light > may be measured to be the same, then please read how it makes these > arguments. > I have read such books long ago and recall the arguments. > > >> I'm not arguing that he was correct. I'm arguing that if we're to show >> that he was incorrect, we should stick to SR and not something that is >> different from SR. >> > > What? > > You are saying that if Einstein was incorrect we should still keep his > incorrect theory Special Relativity? > Keeping a theory known to be incorrect makes no sense at all. > Keeping it when it is incorrect and impossible when better theories fit > all the evidence, honestly I can't believe what I am reading. > > > > >> It's a question of logical reasoning, not faith. If we start talking >> about how time dilation and length contraction show how the speed of light >> will not be measured to be *c* in a vacuum traveling in an inertial >> frame, we've either come across a trivial logical inconsistency >> > > You consider it being illogical 'trivial'? > It means that it is not possible for it to be true. > > That is not trivial. > > >> (unlikely, but possible I suppose), or we've misunderstood one or two >> applications of the basic assumptions in SR. You cannot say that R is >> illogical, describe R,' pick apart R' (or attempt to pick it apart), and >> then transfer any conclusions back to R. I'm trying to help you to help me >> to better understand why SR is incorrect by helping you to avoid setting up >> a straw man argument. I'm pessimistic that this is going to go anywhere. >> > > Me too! > > If you refuse to have any understanding of how SR works, then anything I > argue will look very much like a straw man to you. > It is protection by ignorance. > > I do not understand much about quarks, if you were arguing a flaw in the > concept of colour or flavour, or that the top quark must be on the bottom... > > I would have no idea if your argument was right or wrong since my > understanding of quarks and their whimsical qualities is insufficient. > > But that would not mean that you were wrong, just that I would be wrong in > trying to argue it with you since I don't know enough about the subject. > > You need to read straight forward arguments made by SR on how these things > are possible (not abstract Math, Einstein said he didn't understand his own > theories once the mathematicians did their work up on it). > > But if you think that we should keep a theory shown to be incorrect, in > favour of theories that fit the evidence and are logical, then i am afraid > your thinking is too twisted and far from truth for there to be any > meaningful exchange. > > Hopefully on that point I am mistaken and have just constructed a straw > man. > > John > > > > >> Eric >> >> >
