Help me understand Reference Frame

Factual Questions
1

This isn’t so much a question as an appeal.

I’ll include a link to a wikipedia article if only to give an idea of where I’m coming from.

I have heard three coincidental arguments recently, each of which referred to “Einstein’s Reference Frame.” (Scare quotes to convey oversimplification on my part.)

In the most extreme case, the argument seemed to be that Einstein’s theory of Special Relativity made specific claims about the possibility of objective observation; going so far as to say that it is superfluous

Reading the wiki article linked above, I cannot make sense of any of those arguments without moving outside of the realm of physics.

Since I am appealing for help in understanding the idea, I’ll try to give some indication of my current understanding, or lack thereof.

Physics: Observers are subject to their circumstances in measuring physical characteristics.

Linguistics: Language often uses different means of specifying concepts such as location relative to the possibly variable subjects of different sentences.
This is my interpretation. So, to give an idea of what I understand, I could say: You are reading my post–or: This is the post I have written–or: You are reading the post I have written.

You are the subject in one case, I am the subject in another, and the last case attempts to relate three subjects (You, me, and the post).

As always, it is challenging to ask about a subject without understanding it. The wiki article makes use of a simple situation wherein two cars are maintaining constant speeds, with one overtaking the other. Hopefully, similar situations will be sufficient in this thread.

I am almost purely interested in this topic with a view toward objective observation and analysis.

2

That’s a common misapprehension, but it’s almost exactly the other way around. In pre-Einsteinian days, there was “Galilean Relativity” which posited that the laws of the universe did not change when observed in a moving vehicle - a useful principle that explained why we don’t feel the Earth moving as it spins and orbits. The discovery of Maxwell’s equations for EM fields seemed to suggest that electromagnetism (and thus light) would work differently in a moving vehicle - allowing you to tell whether a vehicle was moving relative to the “universal frame of reference”. Einstein figured out how to preserve the idea that the laws of the universe don’t depend on the motion of the observer - it ought to be called Einstein’s theory of invariance.

3

But I didn’t explain what “frame of reference” means - it’s the set of relationships between two observers that allows either one to predict/interpret what the other one will see when a common set of events is observed.

4

Sorry to be naive, but doesn’t the concept of a set of relationships simply describe the situation where separate observers see separate sets of results?

5

I don’t think you’re being naive; this is just a tricky concept to get across.

Let me borrow an example from a nearby discussion thread. Suppose you are doing experiments with static electricity at your kitchen table. You see the laws of electromagnetism being followed. Meanwhile, someone flying by your kitchen at a high rate of speed watches those same experiments - everything that he sees happen will also be consistent with the laws of physics, but he will interpret what happens as a demonstration of electric and magnetic forces. Special Relativity provides a way for him to predict what you will see from your point of view and vice versa - and the fancy term for point of view (combined with the rules for converting from one to another) is a “frame of reference”

6

Prior to Einstein it was assumed that measuring devices would always operate the same way everywhere in the universe: A clock in a moving train will tick at the same rate as in in the station, a ruler in an orbiting spacecraft will be the same length as a ruler back on earth, and so on.

What Einstein discovered was that if two measuring devices are *moving *relative to each other, they will make different measurements. So if you make a measurement it’s not enough to just stay how many inches long something is, or how many seconds went by. You have to specify which reference frame you’re measuring from, i.e. which set of clocks and rulers you’re using.

7

So…

It is fair to say that [Capital ‘O’] Objectivity is NOT impinged upon by the concept of reference frame in the least?

Which is to say: Measuring the same physical subject from one reference frame–and possibly finding a different set of data–does not affect the set of data observed from another reference frame?

…inertial or otherwise?

8

Yes to both - all observers will view the same physical laws, and even though they may observe (for example) different durations or distances between events, their differing observations do not alter the underlying event. Objectivity is not eradicated.

9

I don’t know what you mean here by “affect”. Can you give a more specific example?

10

I don’t know that you could say that it’s not impinged in the least.

Once, it might have been considered an objective fact that event A happened before/after event B according to all observers. With special relativity, that is no longer true–there is only a subjective truth for a given observer.

The concept of objectivity is not changed, but the class of things it’s possible to be objective about is.

11

That is a good point. It’s worth noting that all observers in the same frame of reference will agree as to which event was first, and that the two events A and B will not have a causal relationship (A didn’t cause B and B didn’t cause A). In special relativity, events that are causally related will be seen as being in the same order by all observers.

12

Does the quality of the item measured change because perspective of the measurer has changed?

13

Oh wait…
Now the thread has changed…

14

Only in the same way that the concept of objectivity is compromised by me saying some event happened to the right of me, while some other observer (near me facing in the opposite direction) says it happened to the left of her. Everyone knows and accepts that observations containing phrases such as “to the right” and “to the left” are observer-dependent, and are not bothered by that.

All special relativity did was modify the set of phrases to include some things that we previously thought were observer-independent, such as “at the same time as”.

15

No. Looking at a box from one side you’d say it was 6 feet wide and three feet deep. Moving around to the other side, you’d say it was three feet wide and six feet deep, but the box remains the same. Relativity is the same kind of thing (with some slightly more elaborate math and some less-than-obvious consequences, of course).

ETA: I like leahcim’s way of putting it slightly better than mine.

16

I stand by post #12 however:
You’re asking for an example. That’s tough.

I want to state that, regardless of reference frame, there are objective qualities that are not superfluous.

Is there any way that “Einstein’s” reference frame can be applied to the idea that the subjective experience–a bystander’s experience of observing a ball thrown from a fast-moving train moving faster than the thrower’s experience of having thrown the ball from the same train–does not change the actual event of the ball itself having been thrown?

I guess I’m begging the question there.

Does a reference frame change the concept of objectivity? Doesn’t the idea of reference frame necessitate that objectivity be consistent between frames? …that the same physical events are only viewed differently from different perspectives?

17

Again, I apologize for being thick, but… isn’t that–by definition–[Capital ‘S’] subjective?

18

Yes. That’s the point. It is a subjective statement and someone else could observe the same event and make the opposite observation. E.g. a person standing at the same point as me, but facing the opposite direction would say the event happened on his left. This type of subjectivity is well-known an uncontroversial.

But no one looks at this fact and concludes from it, “because we are capable of making subjective statements about reality, therefore objectivity is bunk”. Neither should we draw that conclusion from the less well known “subjective observations” of relativity.

19

Is that the nature of “Reference Frame”?

I’m not being argumentative. And I’m not trying to contradict you, nor anyone else who has or might respond.

But, isn’t the concept of ‘reference frame’ substantively distinct from simple ‘perspective’ as it applies to an idea like: “where-you-happen-to-be-standing-at-the-moment?”

20

No, a reference frame is basically “where-you-happen-to-be-standing-at-the-moment” with an additional “how-fast-are-you-moving-at-the-moment” and “how-much-you-are-accelerating-at-the-monent”.