Relativity of Count – Spin Counter

I have a question that I feel needs an answer concerning James S Saint and PhysBang. Do either of you feel you have sufficiently responded to each other’s assertions concerning this topic. If you believe you have responded exhaustively, then either agree or agree to disagree and leave it at that.

I’m happy to leave it at that. As long as people are able to realize that it might be the case that JSS is simply not talking about anything to do with the topic he claims to be discussing.

To my knowledge, he hasn’t actually addressed the OP. His remarks are merely concerning me, how wrong I am, how I should go read, I should show him more of how to resolve the puzzle, his opinion of me, and what others should do because of it (the very definition of “ad hominid”).

Ignoring him doesn’t shut him up nor inspire him to actually address the topic at hand rather than his opinion of me or anyone else. So yeah, I’d say that I have answered his topic relevant replies sufficiently.

Ok, then there shouldn’t be further need to address one another. If it continues, I will lock this thread and remove any remarks to each after this post.

James, I’m a little confused as to how your light-based transverse spin counter measures distance. Its spin doesn’t seem to be associated with motion along the track, because 1) it is light, so its motion is not caused by contact with the track, and 2) it is transverse, so track is never a tangent to the path of the light around the circumfrence of its spin (which seems essential to a spin counter. In that case, it seems that the “spin counter” is just a light clock, as Physbang has suggested.

I apologize if my questions are basic, but as I said to MMP in the other thread, the best place to start is to figure out what everyone is saying, so that we can get identify and resolve the core issues.

(Aside: Farsight, what’s the difference between a start being “really” flattened, and only being observed to be flattened? I don’t mean that sarcastically or rhetorically. For all intents and purposes, the star is flattened for the observer in motion. Would it be possible to devise an experiment that would distinguish between “real” and “observed” flattening? You’ve mentioned an orthoganal observer, but that just seems to either put another observer in the stationary reference frame, or to introduce yet another frame of reference into the question, without truly answering the question. I tend to favor saying that it’s “really” flattened, just because, for all possible applications of the idea (as far as I know), it can be treated that way.)

The issue is one of counting. The train measures the length of his journey to take only perhaps 9 seconds whereas the station measures it to be perhaps 10. There are no dilation effects for motion in the transverse directions. They both see the transverse spin counter taking the same amount of time per spin because it is spinning in a transverse direction which is the same for both observers. This results in them counting a different number of spins for the same journey.

Or do I need to prove that transverse motion to the station-train motion is not affected in either time or length? Lorentz didn’t argue against that notion. I don’t know anyone who does except those who don’t really understand the equations. Space-time is given the coordinates of {x,y,z,t}, the changing distance between the train and the station is the x.

So you don’t have to take my word for it; Modern Physics

Btw, it doesn’t really even appear flattened. One cannot measure length in the line of motion. That is why you have 2 eyes - parallax.

But simply rotating a light clock to be orthogonal to the direction of motion couldn’t be enough to undo time dilation. Wikipedia provides this illustration of why this won’t work:
EDIT: this image didn’t work in the image tags. See it here.
This isn’t a light wheel, but the principle is the same. The distance D is greater than L when the two observers are in motion, even though the motion is orthoganl to the axis on which L sits (e.g. if motion is along the x axis, L is in the direction of y).

ASIDE_____

I’m not really talking about “appearances”, but about observed length. There are many ways to measure legth, and any could be used to meaure a distance in a moving frame (for instance, travel time of a photon)

EDIT: I added a divider to keep the aside aside.

I don’t really see the connection you are trying to make with the Wiki page.

This is what I am talking about;

Transverse Spin Non-Dilation.jpg

But it’s clear from the diagram that the distance traveled around the spiral path is greater than that traveled around the circular path, right? Similarly, in the wikipedia article, the distance traveled along D is greater than the distance traveled along L. Even though the motion of the light is orthogonal to the motion of the clock, the path is still longer for the moving observer, so the clock measures time to be passing more slowly.

How is this a spin counter? It seems to just be a light clock.

A) the train doesn’t see the spinner moving forward, so it sees only the transverse spin.
B) the component of the forward motion of the spinner is transparent and irrelevant to the station.

The spinner doesn’t change spin speed just because it was pushed along its axis.

A) Yes, and the station does see the spinner as moving. If the movement changes the calculation of the distance traveled, one will see the change and one will not.

B) What do you mean by “transparent”? Do you agree that the moving observer measures a different distance traveled by the light in the example given in the Wiki article? How does the motion of the spinner differ? Isn’t the path along a spiral of radius r greater than the path along a circle of radius r?

It doesn’t “change spin speed”, but it’s not really spinning, is it? A photon is traveling in a circle.

The station sees his own spinner and the trains spinner in the same “light”, traveling in parallel. In the simpler case of a light spinner, neither can see anything but the light traveling at the speed of light along its fixed path.

And btw, a light spinner can actually be arranged pretty easily with a standing wave laser setup. You merely measure the wave length of the standing wave to “count the spins” with the assumption that light is traveling at c. If the standing wave changes when you speed up along with the spinner by your side, you would have to conclude that light doesn’t always travel at c.

No one sees that path. We all agree that the train’s time gets dilated. That is all the Wiki article is about.

We are talking about what each observe sees. The train cannot see the spinner slow down just because the train sped up because the spinner is not spinning in the direction of the travel. This is obvious in the case of the light spinner. Also the station doesn’t see any change in his own spinner. The problem is that the train thinks it only took 9 secs to make the journey and the station thinks it took 10. So they end up counting a different number of spins.

Looking at the other guy’s spinner, they each see the same count as their own, but still different from each other’s reported count.

All that is happening is that they are measuring the train velocity as being different than what the other is measuring due to the time dilation.

Emm… is there a relevant difference?

Yes. The thought experiment began as a wheel on a track, where the circumfrence of the wheel times the number of spins of the wheel equals the length of the track. But a light “spinner” is not connected to the length of the track in the same way. In what way does this “spin counter” differ from a simple clock, about which the hands “spin” around the face? The spinning of the hands would similarly produce a different “count”, but that would similarly have nothing to do with the length of the track.

On the contrary, it is precisely because the speed of c is equal in all frames that the standing wave should be expected to change. The Wikipedia demonstrates time dilation by showing that a light being reflected between two plates moves a greater distance when the plates are in motion relative to a stationary observer. Because of this difference, the time it takes the light to complete the trip changes. In the same way, because the distance between the two plates is different in the moving and stationary frame, the standing wave would need to have two different wavelengths.

You’ve got it Carleas.

James, this is the crucial point. The electron is such a spinner, where the perimeter is moving at c. Whether it’s tracing out a circular path or a helical path, it’s moving at c. One helical rotation has a longer path length than one circular rotation, so the spin rate is reduced, hence time dilation. It’s a circular form of the simple inference of time dilation on the wiki time dilation page. You’re effectively a collection of spinners, so you don’t notice that a comoving spinner is going round at a reduced rate.

Oh give it a break. You both KNOW that the observer on the train must himself see light traveling at the same speed. Someone else seeing that skewed view must also see light traveling at the same speed, thus the skewed viewer would see the train itself moving slower.

You are forgetting that the train does NOT see the path you are. The train only sees a spinning wheel, not a helical travel path.

And Carl, I gave up on the inline spinner. I mentioned that and rewrote the OP using only a transverse spinner.

If you’re motionless with respect to a star and you’re 300 million kilometres from it, it looks spherical. But when you start moving rapidly towards it in your gedanken spaceship, it immediately looks flattened. You know that instantaneous action-at-a-distance isn’t possible, and that it would take a thousand seconds for any change in the star to become apparent to you, so you know it hasn’t “really” changed. You can say it’s real enough for me, and that to all extents and purposes the star has changed from this shape O to this shape |. However I’m a similar observer, and I too have accelerated towards the star from an orthognal direction. We communicate over the gedanken subspace radio and plot our respective observations on a common star-chart. You draw the star likethis | and I draw it like this ― , and we’re smart enough to know we can’t both be right. Hence we work out that we each have a different perspective on the star, and that what we describe as “in our frame” is in truth “in our state of motion”. The situation is analagous to us looking at a DVD on a table-top from different angles. We know it isn’t really oval:

As I just mentioned on the other thread, how you measure time changes the dilation of it (thus all other associated dilations).

Excellent point.

The observer on the train sees light travelling at the same speed because he and his clocks are in essence made of it. He calibrates his clock using the local motion of light, then he uses his clock to measure the speed of light. See below. It’s actually going slower “within his frame”, but he can’t see that it is.

This is all right except that it’s all wrong. The changes of SR are not ones of perspective, they are ones of the fundamental location of where events occur. SR tells us where things will be if we use the best possible ideal measurement. If I send a rocket to hit the surface of a star and I only assume that it looks flattened, I will miss it. If one learns how to apply SR correctly, we can predict exactly what ever reference frame will identify as the dimensions of an object as long as we have the knowledge of the dimensions in one frame. We know, before we accelerate, what dimensions a star will have in any given frame of reference in which we might make ourself at rest in. We know, before we accelerate, that we are currently flattened relative to that frame of reference. We know that if we use that frame of reference to identify the physics of our current scenario and we only assume that we merely look flattened that we will make predictions that are incorrect.

With a disc-shaped object seen from the side, we can make adjustments to our estimation of the size and shape of the object that will make our predictions more correct. We cannot do this with the transformations of SR–they are already assuming that we have ideal measurement.