Simultaneity- a physics question

[Zeta-Flux]

davieddy,

But I think the paradox involves the door on the far side of
the barn opening when the rear of the rocket passes the
front door. The question to be resolved unambiguously by
all observers is "does the rocket crash into the back door
or not". (emphasis added)

And the event in italics depends on one's frame of reference (since none is specified), and so the question is not well-defined. Yes, I think I understand the paradox. For another version I found:

http://math.ucr.edu/home/baez/physic...barn_pole.html
----------------------------------------

ewmayer,

I understand that if one uses the Minkowski metric in defining distances in space-time, then the "order" of events depends on the observer. Oh, and I think that your statement "that's why it's called "relativity."" is not quite accurate. ;)

[davieddy]

Originally Posted by Zeta-Flux

davieddy,

And the event in italics depends on one's frame of reference (since none is specified), and so the question is not well-defined.

Since relativity is inherently "consistent", the ambiguity is always
to be found in the posing of the paradox.
But "the rear of the rocket passing the front door" is a clear cut
event identifiable by all observers. What is ambiguius is the frame
in which the back door opens simultaneously.

[Zeta-Flux]

davieddy,

What exactly is the clear cut observable? The event in question has to be measured and the measurement depends on one's frame. I suppose one could conflate the two events of measurement, but I don't think this is necessary.

So, in other words, what I meant by my statement is that the measurement of the event depends on the frame of reference. And since we only *know* what we can measure, talking about "when the rocket passes the barn door" is not well-defined, unless one posits a specified frame of reference from which to make the measurement.

Anyhow, that is how I understand it.

Best,
Zeta-Flux

[davieddy]

Originally Posted by Zeta-Flux

davieddy,

What exactly is the clear cut observable? The event in question has to be measured and the measurement depends on one's frame. I suppose one could conflate the two events of measurement, but I don't think this is necessary.

I think you are confusing relativity with quantum theory.
(Which is not the same thing as amalgamating them!)

If it makes for more of an "event", then say a protrusion
on the rear of the rocket flips a switch at the front of the barn.
One version of the "paradox" says that this switch opens the
back door of the barn.

In relativity, by "observer" we often mean a reference frame
completely populated by observers with synchronized clocks and GPS.
I think lack of this "omniscience" was what Einstein loathed in
quantum mechanics.

David

[xilman]

Originally Posted by davieddy

In relativity, by "observer" we often mean a reference frame completely populated by observers with synchronized clocks and GPS.

Thank you for posting this clarification.

As with "see", "light", "causal" and a number of other terms, relativity has its own jargon that has grown up over the last century. Newcomers are often misled by common words being used with specialized meanings.

Relativity is not special in this respect (ambiguity intended). Consider the many and varied meanings of the word "field" throughout mathematics and the sciences.

Paul

[davieddy]

Originally Posted by xilman

Consider the many and varied meanings of the word "field" throughout mathematics and the sciences.

Paul

I like to think I can distinguish the following:
1) A field of barley
2) A Galois field
3) A magnetic field

I'm sure this list is not complete.

David

[bsquared]

Originally Posted by davieddy

I like to think I can distinguish the following:
1) A field of barley
2) A Galois field
3) A magnetic field

I'm sure this list is not complete.

David

4) The field of physics (a field of study)

[davieddy]

Originally Posted by bsquared

4) The field of physics (a field of study)

That was quick

[xilman]

Originally Posted by bsquared

4) The field of physics (a field of study)

A set (another jargon term) together with two distinct operations (and another) on its elements (yet another), each forming a group (still another), and with further constraints on its structure (is that a jargon term?).

A Galois field is just a special case of this more general definition.

Paul

[xilman]

Originally Posted by bsquared

4) The field of physics (a field of study)

So far, only nouns have been considered. To get things started, here are a couple of verbal meanings.

To field (intransitive verb) --- an activity in which a cricketer may be engaged.

To field (transitive verb) a question -- an activity in which a politican may be engaged.

There are more.

Another noun: a quantum field. (I personally consider this to be quite different in nature from a magnetic field.)

Is a vector field something quite different (but related) to a magnetic field?


All this is getting us far away from the original question.

Paul

[davieddy]

Originally Posted by xilman

Another noun: a quantum field. (I personally consider this to be quite different in nature from a magnetic field.)

Is a vector field something quite different (but related) to a magnetic field?


All this is getting us far away from the original question.

Paul

Answers respectively:

In "quantum field theory" does the adjective(?) quantum refer to
the field or the theory?

I would say that a magnetic field was a special case of a vector field.

Yes but does it merit a new thread?