Standard SRT problem need a standard SRT solution.

You asked what the observer sees. Naturally, the observer sees things from the perspective in which s/he is at rest, yes?
This isn't about assumptions, this is about answering the question "what does this observer see?" In essence, the only way to answer that question is to determine the time that passes in the observer's frame between events at the observer's position.

Note that I actually began from the observer's observation of an incoming tick rate of 3 per second, then worked back so the observer could discover the actual pulse rate and relative velocity of the other ship. The observer made no reference frame assumptions at all.


Now, as a point of interest, I determine the 3 per second rate by working in the observer's frame (using the relativistic doppler formula), but that doesn't matter because... In any reference frame, we can still predict using SRT that the incoming pulses will arrive three times faster than the outgoing pulses leave.

For example, let's use a symmetrical frame in which the two ships have equal and opposite velocity (this is not co-moving, by the way. Comoving means "at rest relative to each other").

I use SRT to predict that:
1) in this frame, ship A has v=0.5c and ship B has v=-0.5c (or the other way around, if you prefer - there are many symmetrical frames).
2) in this frame, both ship's pulses fire every 1.155 seconds.
3) in this frame, when either ship fires a pulse, the previous pulse is 0.577 light-seconds in front of the ship, therefore the pulses are spaced 0.577 light-seconds apart while in transit.
4) in this frame, each ship closes on the other ship's pulses at a rate of 1.5c, and therefore collects the other ships pulses once every 0.385 seconds.
5) 1.155 / 0.385 = 3. Each ship collects the other ships pulses three times faster than their own pulses leave.

 

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I don't think so.
Let's say I ask "how far to that tree?"
If you say "that tree is 10 metres from me", then I of course acknowledge that this is a valid, meaningful, and valuable measurement... but I also note that its validity is limited to a specific reference point.
"10 metres from me" is a valid answer. "10 metres" is not (unless the "from me" is implied or assumed).

Likewise, when the observer notes that their outgoing pulses leave once per second, I acknowledge the validity and value of that measurement, and note that its validity is limited to a specific reference frame - that in which the observer is at rest.
If I asked the observer "What is the tick rate?", then a response of "one second" is not a valid or meaningful unless "in my reference frame" is implied or assumed.

 

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You are right, of course. The analogy is limited, as all analogies are. In the tree analogy, position (distance) is the difference between references. In SRT, velocity is the difference.

The tree doesn't care what position you see it from... it just is.
But, the distance to the tree is affected by your position.

Similarly, the space-time separation between pulses is unaffected by reference frame, the time separation between pulses in that frame is.

When you say "actual tick rate as a physical pheno", I believe you are referring to the tick rate in the frame in which the source is at rest, yes?

 

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I think this is enough again...

I think your key question:

On what grounds is a calculation to be made with the assumption that the othership has all the velocity and dilation in a two ship universe?

Has been answered, but I'll repeat and elaborate:

When we're given the question "What does observer X observe?", how do we answer that question?

Well, the observer can only directly observe things that occur in the same place as themselves. They can only observe other things indirectly through the receipt of information in the form of light, sound, or physical contact.

So the question now becomes "What things occur at observer X's position?"
But this isn't enough, is it? The timing of the observed things is also important.
So, we'll try this... "What things occur at observer X's position, and what time elapses between those things?"
But hang on... since we're thinking about SR, we'd better be careful about relative expressions like "elapsed time". In what frame is the elapsed time measured? The answer is obvious - in the observer's frame. The frame in which the observer is stationary.

So, how about... "What things occur at observer X's position, and what time elapses between those things in the reference frame in which observer X is stationary?"


And now we can answer the question.

In short:
The question "What does an observer see?" can only be answered by considering the Universe from a perspective in which that observer is at rest.

 

Your response seem to try and imply an error in my statement. Such error is not present. Yes I have read what you posted but your problem is you mis-interprete the meaning of such relationships.

Show me where I have said any such thing. Don't think you can change either what I have said or the meaning of such statements. I have never implied much less said anythig like that.

Glad you finally agree watching me boil an egg is just a matter of watching and not participating in the physics. You watching makes no changes what-so-ever in the physics involved. (including the tick rate of the timmer).

Precisely, it is "Seen" however, it is NOT "boiled" but only in my frame and by my clock.

Dodging the issue and making innuendo really doesn't equate to having a superior view.

That is your perogative, however, I should point out here that you have failed to prevail in that thread with your view, so don't try to apply it here and be unwilling to face the physical realites and data available which disputes that view.

That is do not expect to be able to make claims and restrict information which shows that view flawed and then claim you have prevailed. Since you have already deleted posts which undermined your position, it is obvious that your position has not been secured here.

 

Pete you raise a couple of very interesting and quite rational points. I will diogest and post some more however for the moment:
1]

This makes a lot of sense except that the pulses are not subject to prediction.

They, like the tree just are what they are.

We may like to use the "IF" factor but the light pulses are happening as they naturally do regardless of the "IF" factor.


I will post more tomorrow...BTW thanks

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Pete and others, I think we need to establish the very first concept.
The following simple diagram shows two objects.
They are the only two objects in this imaginary universe.
The only thing we know is that they have a closing velocity of 0.8c.

Simple question:

Which is moving?
A or B or Both or neither

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If we can reach an agreement on this simple question we may make some head way.

 

You so despreately want an either/or answer and you won't get one.

This is simple relativity from Galileo's time. If you are on A then B is moving. If you are on B then A is moving. (!?!?!?)

If you have the godlike perspective of looking at the picture as we do, then the motions of A and B can be measured as relative to us. But then the question is, what motion do we have? Let's call in a fourth observer... and a fifth...

But you said the only to objects in this universe are A and B. So the first statement of this post is all there is. How could it possibly be any other way? No offense meant here but this is so fundamental that it is given about 5 minutes in a high school physics class and you move on. This isn't even modern physics. Jeepers!

 

well it just shows how diverse we people are.

I am just as surprised at your answer as you are to my question. To me the answer is and can only ever be both objects are moving equally relative to each other. To me this is so obvious that I also cry out in frustration..."This isn't even modern physics Jeepers!".

The two objects are in a sea of nothingness and yet we can make an incredible assumption that one is at rest. How can this assumption be possibly made? What basis can an object be deemed as at rest in "nothingness" when the entire universes is those two objects.

To me, this issue is a very fundamental issue as to why SRT creates confusion.

To say that objet A is traveling to object B instead of simply saying that both objects are traveling towards each other is a fundametal philosophical question as well.

As there is no aether in our diagram, there is no way an object can be deemed to be at rest when compared to the other object unless we arbitarilly choose it to be so.

It comes down to which is the most natural solution. One that is not the subject of some arbitary decision.

I will run a thread in the philosophy forum....just to see what general response it gets.

 

The problem James is that there is essentially no way to make a choice. There is no basis to assume we can possibly know what object is doing what.

If I was on a third object and looked to left and saw A coming at me and looked to the right and saw B coming towards me then I have justification to state that I am somewhere in the middle between two objects. With some careful measurements I can even state my velocity position.

But in a two ship universe there is no such way of deciding the velocity I am travelling at, and can only assume that the objects are comming together and that is the limit of what I can determine.

 

QQ,

So you take the third position. What does a fourth observer say about you and objects A and B? Every time you draw a third observer, I can draw a fourth and declare an arbitrary velocity for myself wrt you and calculate all new velocities for the whole group.

This is why it's called relativity. The entire universe is relative. I predict a philosophical discussion of a two object universe and who is REALLY moving will get you zero satisfactory results. If you are on A, then you are stationary. If you are on B then you are stationary.

 

Of course there is. In your universe you are either on object A or B. There is no third place to be. If you are on A, you decide you are stationary and all is right with your world. No problem.

 

SL I am not thinking form a 3rd perspective.
The following animation "I think" shows my point.

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It really is a state of mind. Because you were raised on earth, you (and all humans) are so used to referencing things to a universal rest frame (the earth's surface) that it may not be intuitive to assume anything else. We all have to be shown the light at some point in our education. There's usually an "AHA!" moment associated with it, when we imagine ourselves in your two object universe.

 

QQ,

Your first animation (cool - how you do dat man?) is from a third perspective. Cogitate on that.

 

Am cogitating, am cogitating.zzzzzzzzzzz...ah ha.....why do you think I am using a 3rd perspective?
BTW that free software you pointed me to gave me the tools to do it...and whats even better I didn;t have to pay for it....so a big thanks to SL

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[now you are all gong to be plagued with Animations until I run out of ideas....ha]

 

SO SL what you are saying is that we take the second drawings perspective....and consider ourselves as A at rest?

 

It animates??? Wow How??

Anyway, in your universe there are only A and B. If you are on A you can ONLY assume B is moving toward you and vice-versa. Your first animation is from a third perspective moving such that A and B appear to have equal and opposite velocities.

 

Yes. Either that or B's perspective and you are at rest with B.