Let me give you an example of why I ask this.
Let's say I lay a pen I have measured to be 5 1/2" on the table. It measures 5 1/2" long from that reference.
I walk away 10 feet, and look at it from that reference. It measures 1" long from that reference.
I walk farther, until I reach a reference where the pen doesn't even look like it is there anymore. It doesn't even exist from that reference.
So are all those reference frames accurate? Or does only one really represent the truth?
I believe only one actually represents the truth. The pen is actually in existence, and it is 5 1/2" long.
OK< so your problem is that you don't understand what a reference frame is. Those are NOT different reference frames you described! It is *one* reference frame. When you were 10 feet away, you did NOT measure the pen to be 1". You might have measured the angular width to be some angle. But then you could use trigonometry to figure out the size to be 5 1/2". When you walked far enough away that you didn't see it, you could have used a telescope or binoculars to do a similar thing and still find it to be 5 1/2"/ It *does* still exist in that perspective! You just need better instruments to detect it.
Remember that a reference frame gives positions and times to *all* events in spacetime, at least potentially. So, yes, in the *common* frame of all your perspectives above, the pen is the same length 5 1.2".
The reason your different perspectives are NOT different frames is that you were at rest to each other in all of them. The pen was not moving with respect to you in any of the measurements you took. To be in a different frame (at least in special relativity), you have to be moving with respect to each other.
So, next important concept. If you were out in space in a sealed spacecraft, there is no way to tell *from inside the spacecraft* whether you are moving or not. This is called the principle of relativity. So, for example, if you watch the motion of a bunch of objects, they will appear *to you* the same whether the spacecraft is going at 50% of c or is at rest with respect to the Earth. One consequence of this is that everything it *at rest* in its own reference frame. Another is that when talking about speeds, it only makes sense to talk about relative motion (I am moving past you at 50% of c) and not absolute motion (I am moving at 75% of c).
So, different reference frames are moving with respect to each other at spme speed and in some direction.
So, to continue your description of the pen, in all your perspectives above, the pen was 5 1/2" inches. That is its length in that one reference frame.
But, suppose that I am in a spacecraft going past you at 86% of the speed of light and just as I pass that same pen, I do a quick measurement of it by taking a photograph or whatever (the method of measurement isn't relevant here). I will determine that pen to be 2 3/4" long. Somebody else in my rather large spacecraft, looking from 10 meters away might have to use trigonometry to measure the length, but they will also measure the pen to be 2 3/4".
These are different reference frames. This is NOT simply a matter of perspective. In each frame, you get to make whatever measurements you want from whatever position you want and make calculations based on geometry or trigonometry. For the frame moving past at 86% of c, there is NO place where you can be where that pen measures to be 5 1/2". In that frame, the pen measures 2 3/4" no matter how you find the length. It is the real length of that pen in that frame.
By symmetry, suppose that spacecraft has a pen and that those on the spacecraft measure it to be 5 1/2". This is the value from all perspectives moving with the spacecraft (at rest with respect to the spacecraft). Now, *you*, who are going at 86% of the speed of light past the spacecraft measure *their* pen. What you will find is that in all *your* perspectives (but same frame!) that pen on the spacecraft is 2 3/4" long.
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