Today Special Relativity dies

[quantumdude]

because, EVERYTHING cannot be relative.

Have you absorbed nothing of what we write?

The laws of physics and the speed of light are not relative. There you have it! There is your anchor of sanity to keep your ship from being tossed about in the sea of ambiguity.

something has to be real.

If you think that "relative" means the same as "unreal", then you are mistaken. Measured quantities that are subject to change under changes in inertial frames are real for the one who measures them.

it makes no sense to depict the universe as a place where two people can disagree on something and BOTH be correct.

No one is saying that it does make sense. What we are saying is that you have to be very specific about the statements you make. This can be easily illustrated, by the following example. Notice that I am taking an example that would be true even in a Galilean universe!.


If ship takes off along the +x-axis at 0.5c relative to the Earth, then an Earth bound observer would say, "The velocity of the ship is 0.5c in the positive x direction." However, an observer on a ship that is moving along the same axis with the same speed, but behind the ship, notices that he isn't gaining any ground on the first ship. He then rightly concludes that, "The velocity of the ship is zero."

Observer 1: "The velocity of the ship is 0.5c in the positive x direction."
Observer 2: "The velocity of the ship is zero."

Now, one might say: Oh, my, how can these two statements both possibly be correct? They directly contradict each other. Which velocity is "real"?

The problem here is that the statements are both ill-defined. We have to be more specific:

Observer 1: "The velocity of the ship relative to Observer 1[/color] is 0.5c in the positive x direction."
Observer 2: "The velocity of the ship relative to Observer 2[/color] is zero."

Specifying the parts in blue[/color] and red[/color] are necessary to make the statements well-defined. Notice that they also differentiate the statements, so that both can be correct simultaneously.

1=2 ? yes=no ?

No.

even with shrunken rulers (or whatever the heck zany contraptions you people measure with), the distance to be measured is also shrunken so "relatively" you should measure the same lengths if this were true

No, I never measure with a "shrunken ruler". It's always the other guy's rulers that are shrunken, as measured by me. Likewise, mine are shrunken as measured by him.

 

[ram1024]

Ah yes, the argument from personal incredulity. We see this all the time in debates with creationists. They also don't seem to understand that refusing to believe the evidence does nothing to discredit a theory with an overwhelming amount of evidential support. Maybe this thread belongs in the philosophy of science forum instead of theory development. That would be the proper place to debate the validity of accepting evidence that prima facie defies common sense.

which is why I'm using the evidence to contradict itself. completely relying on the observations and analysis of people who understand the theory and making them justify things that i believe to be paradoxial in the theory.

i wouldn't trust myself to supply my own experimental or mathematical evidence any more than you would. that is not my forte' :D

 

[quantumdude]

that's worded funny so I'm going to make an assumption that you're talking about the runner on train 2 keeping up with the midpoint of train one relative to him.

In that case, then both observers would report that they receive the light simultaneously.

 

[ram1024]

k good. now we move to conclusion... i think

 

[Janus]

because, EVERYTHING cannot be relative. something has to be real.

What makes you think that relative and real are mutually exclusive?

it makes no sense to depict the universe as a place where two people can disagree on something and BOTH be correct. 1=2 ? yes=no ?

The universe in under no obligation to behave by rules which you deem as making sense.

 

[Hurkyl]

it makes no sense to depict the universe as a place where two people can disagree on something and BOTH be correct.

Why not?

One common example is when two people face each other, they disagree on what is "left" and what is "right". Yet, they're both correct.

Another example is the pitch of the motor of a race car; people in front depict it as a high pitch, people behind depict it as a low pitch. Yet they're both correct.

The only reason you have problem with SR is that you refuse to accept that measurements of length and time are yet another thing that is relative.

 

[ram1024]

In that case, then both observers would report that they receive the light simultaneously

so here we have emitted simultaneously, and DETECTED simultaneously, despite difference in relative position to the emitters of the photons.

i thought SR was supposed to claim non-simultaneity for moving towards a light source vis-avis Case#3 post 1?

 

[ram1024]

The only reason you have problem with SR is that you refuse to accept that measurements of length and time are yet another thing that is relative.

i'm fine with people's perceptions being relative, I'm not going to divulge my master plan just yet, though

 

[Hurkyl]

'm fine with people's perceptions being relative

Ok, let me rephrase.

In one measurement system, the direction considered "left" can be exactly what another measurement system considers "right", yet both answers are correct.

If I put a sound detector in front of a race car, it will measure a sound higher pitched than an identical sound detector placed behind the race car, yet both are correct.


I specifically chose measurements that aren't psychological; they can be unambiguously performed by measuring devices.

 

[HallsofIvy]

Yet they do become unsychronized- the experiment you describe has been done (in a much more sophisticated form using cosmic rays) the experimental results have consistently supported relativity- events that were synchornized in one frame of reference are unsychronized in different frames of reference- that's the one sure thing in science: the experimental evidence.

 

[quantumdude]

so here we have emitted simultaneously, and DETECTED simultaneously, despite difference in relative position to the emitters of the photons.

Hold on: I thought both observers were located at the midpoint of the train. In other words, I thought that both of them were equidistant from the sources. If not, then they certainly will not both report having received the light pulses simultaneously. This has nothing to do with Einstein vs. Galileao, it's simple geometry.

i thought SR was supposed to claim non-simultaneity for moving towards a light source vis-avis Case#3 post 1?

It is nonsimultaneous for observers in a different inertial frame. But you set this up so that the clocks, the emitters, and the observers are all in the same frame, so SR effects don't even show up. They won't show up until a third party, who is moving relative to the frame of the original observers, enters the scene.

 

[ram1024]

or "flaws in the experiments"

might be more apt. we'll see as this discussion continues :D

 

[quantumdude]

or "flaws in the experiments"

No, that's not it. Professional physicists perform experiments to the most exacting standards possible. Each part of an experiment is worked out in great detail by a whole team of scientists. For some internet bozo to come along and suggest that they don't do their job correctly is just plain laughable. Really, what other profession is subject to this indignity? What would you say if someone who obviously has no clue about your profession (assuming you have one) were to come along and tell you that you don't really understand the thing that you go in and do all day, every day?

might be more apt. we'll see as this discussion continues :D

No, we won't see it in this discussion. It's not possible, even in principle, to determine if the experiments are at fault, because your thought experiments don't make any connection to the experiments.

 

[ram1024]

so do me a favor and go back to case #1 2, and 3 for me Tom and state your "true / false" predictions

i'm getting conflicting data from two people who i know to be good at this SR thing.

 

[quantumdude]

First I need you to answer my comments from Post #71. Are both observers at the midpoint of the train, or aren't they?

 

[ram1024]

Case #2:

[u]|(->                    (o)                    <-)|[/u]
   [u]|(->                    (o)                    <-)|[/u]
      [u]|(->                    (o)                    <-)|[/u]
         [u]|(->                    (o)                    <-)|[/u]

Platform is moving. SR concludes the photons (still emitted simultaneously) will be detected by the observer at the exact same time. (observer is standing exactly in the center of the platform, equidistant from both sources)

(True / False) ?

Case #3:

[u]|(->                    (o)                 <-)|[/u]
[u]|(->                       (o)              <-)|[/u]
[u]|(->                          (o)           <-)|[/u]
[u]|(->                             (o)        <-)|[/u]

Man is moving on platform towards an emitter. SR concludes that photons are NOT detected at the exact same time.(observer starts at the exact center of the platform, equidistant from the two sources and moves towards the right emitter)

(True / False) ?

 

[Hurkyl]

As case #2 is now stated, I revert to my original response (false). Since you don't specify the frame in which "simultaneously" is measured, the natural assumption is that you mean it is the frame in which the pictures are drawn.

Case #3 is similarly ambiguous; my true was, again, under the assumption that "simultaneously" is measured in the frame in which the pictures are drawn.

 

[wespe]

ram1024, I see that you still waste other's time. Please see that post#76 itself does not contain enough information to give answers.

If you didn't change the conditions, my understanding is:

The emitters are stationary wrt the platform in both cases. The emitters emit light simultaneously according to the clocks synchronized in the platform frame.

Case#2: Does the midpoint observer (co-moving with the emitters on the platform) detect the photons at the same time? (my answer is yes, so, True)

Case#3: Does the moving observer (moving towards one of the emitters) detect the photons at the same time, given that the observer was at the midpoint (according to clocks on the platform) when the photons were emitted ? (my answer is no, so, True)

ram1024, I must add that you don't deserve any attention if you insist on asking ambiguous questions.

 

[ram1024]

the emitters are welded TO the train and NEVER move relative to each other.

the conditions set forth are NOT ambiguous. you have answered as i expected SR to answer. Tom and Hurkyl are putting forth different answers though, but they're not really detailing their answers so it's hard for me to piece together where the difference in understanding is.

i'm pretty sure my outline of the experiment is not vague.

two synchronous clocks set a specified distance apart emitting a photon at what would be to THEM synchronous times (no inertial effects happen to one that do not also happen to the other). drop a moving observer in the center in one case, and in the other case a stationary observer but the whole train is moving.

i can continue to keep explaining it over and over using different words until you understand it exactly if you want, but in the interest of progress let's keep that to a minimum :D

 

[quantumdude]

the emitters are welded TO the train and NEVER move relative to each other.

That part is clear.

the conditions set forth are NOT ambiguous.

It's not the conditions, it's the questions. When you asked in the first 3 cases about simultaneity, you never specified which frame. As Hurkyl says, he was assuming that it was the frame of the train. But since you didn't say so, there's no way to tell.

Tom and Hurkyl are putting forth different answers though, but they're not really detailing their answers so it's hard for me to piece together where the difference in understanding is.

Where do we do that? I have yet to answer Cases 1-3, because the questions aren't well posed.

 

[wespe]

Yea, OK, I gave you your (true,true) answer. Now what is it you don't understand?

 

[ram1024]

i guess I'm failing to see how something detected simultaneously by one observer is not the same in every frame. therefore when i pose a question that says "does the observer detect the photons simultaneously" and you answer back "what frame" it makes no sense to me because no matter how i look at it if he does then he DOES if he doesn't then he DOESN'T. there's no frame that will turn one into the other.

so my response to "what frame" would probably be "pick one"

 

[wespe]

i guess I'm failing to see how something detected simultaneously by one observer is not the same in every frame. therefore when i pose a question that says "does the observer detect the photons simultaneously" and you answer back "what frame" it makes no sense to me because no matter how i look at it if he does then he DOES if he doesn't then he DOESN'T. there's no frame that will turn one into the other.
so my response to "what frame" would probably be "pick one"

Are you replying to me?

When you said "detected simultaneously", I did not ask "in which frame", because the detection occurs at one point if they are detected at the same time. When you said "emitted simultanously", I did ask "in which frame", because the emissions are separated by distance. OK?

So, since I gave you the answers you expected, assume that I'm interpreting your question as you intended. So again, what is it you don't understand?

 

[ram1024]

move to case #4 <stage 2>, wespe. it's not true or false it's more of an essay question :D

 

[O Great One]

Man, I can't believe everybody is giving you such a hard time ram1024. The man in all three cases does detect the photons simultaneously.

case 1: The man is exactly in the middle and the photons are emitted simultaneously in the frame of reference of the platform, therefore the man detects the photons simultaneously.

case 2: The man must receive the photons at the same time, otherwise there would be an absolute frame of reference, which is forbidden.

case 3: The man is equally distant from each emitter at the time of emission, therefore the man will detect each photon at the same time.

 

[quantumdude]

i guess I'm failing to see how something detected simultaneously by one observer is not the same in every frame. therefore when i pose a question that says "does the observer detect the photons simultaneously" and you answer back "what frame" it makes no sense to me because no matter how i look at it if he does then he DOES if he doesn't then he DOESN'T. there's no frame that will turn one into the other.

so my response to "what frame" would probably be "pick one"

I asked you "in which frame" with regards to the detection when I thought there were 4 trains, with different observers in different states of motion. The picture confused me a bit.

But now, as regards case 4, I am still confused because you originallly said that both observers are at the midpoint of the train. In response to that, I said that the detection is simultaneous for both. But then you said that the two have different positions relative to the emitters. So, I have to ask, which one is it? Are you considering displacement in another dimension, perpendicular to the axis of the train?

 

[ram1024]

actually if they're giving me a hard time it's probably because i deserve it :D

but I'm ridiculously patient and not really functioning under a deadline so meh, it doesn't matter :D

you have pointed out something interesting though with

case 3: The man is equally distant from each emitter at the time of emission, therefore the man will detect each photon at the same time.

that. say a man standing on a platform halfway to halfway (crap i better make a picture)

[u]|(->            (o)            (o)                        <-)|[/u]
                   observer1       observer2

at the time of emission, observer 2 is at the exact center. but at the exact moment the photons are emitted he starts running left and ends up at the position where observer one is. according to what you said he gets hit by photons from both sides simultaneously. but observer 1 just standing there doesn't. he gets hit by photon to the left first and then by photon to the right.

 

[wespe]

case 3: The man is equally distant from each emitter at the time of emission, therefore the man will detect each photon at the same time.

No, the photons meet at the midpoint of the stationary platform. The observer was at the midpoint, but moved to a further location, so he cannot detect them at the same time. I stand by my answer.

ram1024, I'm checking your case #4.

But there's a problem. Case#4bserver1 is not the same experiment as case#2. Because now there is acceleration involved. In case#2, we assumed the platform was inertial. I will think on this and post my reply.

 

[ram1024]

here's case #4 again
Case #4:

observer1
[u]|(->                    (o)                    <-)|[/u]
   [u]|(->                    (o)                    <-)|[/u]
      [u]|(->                    (o)                    <-)|[/u]
         [u]|(->                    (o)                    <-)|[/u]

observer2
[u]|(->                    (o)                    <-)|[/u]
[u]|(->                       (o)                 <-)|[/u]
[u]|(->                          (o)              <-)|[/u]
[u]|(->                             (o)           <-)|[/u]

Two trains side by side (4 clocks now, wheee!). both containing the exact same set up. in the first train, the whole train moves forward at 5ft/s. it starts moving the instant the photons are released. at the same moment on the other train, the platform is stationary and the OBSERVER runs ahead at 5ft/s.

who receives the photon from the right emitter first? who receives the photon from the left first? if they both receive photons at the SAME time, how can you justify previous responses that observer 2 on his own would receive photons NOT simultaneously but observer 1 WOULD.

some re-explaining (not changing the problem any), in train 1 the observer has his feet welded to the floor of the train. in train 2, the train has its wheels welded to the tracks. I'm dead serious :D.

okay that being said train 1 moves at 5ft/s to the right
and on TOP of train 2, observer 2 moves at 5ft/s to the right.

 

[ram1024]

Case#4bserver1 is not the same experiment as case#2. Because now there is acceleration involved. In case#2, we assumed the platform was inertial. I will think on this and post my reply.

we can ditch the acceleration and say train 1 was running along the track at 5ft/s the whole time and when it hit the point where both trains were aligned nose-to-nose, THEN the experiment begins

(it changes the outcome for my relativity but i don't think it does for yours (sr))