sci.physics.relativity

"kenseto" wrote in message
news:47cff412$0$6512$4c368faf@...
>
> "harry" <@> wrote in message
> news:1204737336_649@sicinfo3....
>>
>> "kenseto" wrote in message
>> news:47ceba97$0$4936$4c368faf@...
>> > The SRians in this NG claim that a longer pole can be trapped inside a
>> > shorter barn from the barn frame point of view.
>>
>> Not exactly "trapped"...
>
> For a brief period it is trapped.

OK if you mean that for a farmer who quickly closes the doors, it appears as
if the door is trapped inside for a split fraction of a second (until it
makes a hole in the door).

>> > This can only happen if
>> > there is real physical contraction of the pole from the barn frame
>> > point
>> > of view.
>>
>> That's roughly the way Einstein formulated it. But different people mean
>> different things with "physical" and "real". IOW, you're diving into
>> philosophy here.
>
> You can look up the dictionary what physical and real mean.

More precisely, with , physical (selected):

2. of or pertaining to that which is material: the physical universe;
the physical sciences.

3. noting or pertaining to the properties of matter and energy other
than those peculiar to living matter.

4. pertaining to the physical sciences, esp. physics.


People who adhere to 2) or 4) will surely agree, but perhaps not all people
who adhere to 3). And then there are nuanced opinions such as mine according
to which there is a physical change eventhough the contraction is apparent.

>> > OTOH SR deny physical length contraction.
>>
>> Wrong, SR does not address such questions - as a result, every year new
>> publications about it see the light.
>
> Sure it does. It says that a moving pole can fit into a shorter barn for a
> brief period of time.

There is no disagreement about that question - it's independent of the
question if the cause is "physical" or not.

>> > It says that length
>> > contraction is a geometric projection effect.
>>
>> Not SR but geometers say so. Are you a geometer?

>> > Much like that you see me to
>> > be shorter from a distance and you see me to be shorter from a
>> > distance.
>> > It
>> > seems that the SRians want to have it both way.
>>
>> Not all "SRians" are geometers! For example, to my knowledge AE never
>> made
>> the claim that length contraction is a geometric projection effect. He
>> did
>> discuss the "physical meaning" of length contraction and time dilation
>> and
>> he concluded that clocks that move in a circle "go more slowly" than
>> stationary ones.
>
> So clocks in relative motion are really running at different rates. That
> is
> not geometric projection.

It's not clear what he exactly believed. As for me, I do think that clocks
in relative motion are really (or "physically") running at different rates.
Of course, these rates can be depicted by geometric projections that tell us
how those truly different rates appear to observers.

[...]

Harald