[ExI] Probability is "subjectively objective".

Lee Corbin lcorbin at rawbw.com
Tue Jul 15 22:48:05 UTC 2008


John Clark writes

>> He's [Feynman] holding up too highly some weird notion of
>>"understands".  There are plenty of people who've been
>> doing QM calculations all their lives and understand what
>> they're doing.
> 
> Feynman was not alone, Niels Bohr wasn't exactly a lightweight and he said:
> 
> "Anyone who is not shocked by quantum theory has not understood it."

When he said that, "everybody" had been raised on
classical physics. To anyone raised on classical physics,
it is shocking (or probably they don't understand it).
But notice that even Bohr (contrary to Feynman) is
acknowledging that some shocked people understand it.

I don't know how people feel today who were completely
innocent of all this, and very naive, when they simply took
Physics IA, IB, and then Quantum Theory, worked all the
problems in all three courses and built up their confidence.
This has happened a *lot* during the last thirty years. Do
they feel shocked?  My guess is that a lot of them find
Quantum Theory to be just Physics 1C, and take it in stride.

>> Was ist das "instantaneously"?
> 
> It means that I got into my spaceship and traveled at 99% the
> speed of light to visit my friend in the Virgo Cluster a billion light
> years away.

How do you know that it's you moving and not the Milky
Way and the Virgo Cluster that're moving? 

> After a billion years I got there and find that a billion
> years ago

Hah. So you too never really understood SR. It is
tricky.

> what I was doing to my particle was changing what
> was happening to his particle a billion light years away a 
> billion years ago.
> 
> I can accept that the above must be true because I can get numbers
> out of the concept and test it, but I still find it weird. I make no claim
> to understand how the world could possibly be that bizarre, I know it
> is but I have no mental picture, I just crank the numbers. If you do
> understand it you have my (skeptical) admiration.
> 
>> That kind of idea is reference-frame dependent.
> 
> Yes, the concept of "Instantaneously" is reference-frame
> dependent, but the distance between 2 events in space-time is not,
> it's always the same,

You're trying to think of "spacetime interval", but without
much success.  Work these problems to get clear:

You and your friend ten million light years apart
synchronize your clocks via light signals. Then at
an agreed upon time, you both explode a flash
bulb. Problem 1:  A guy flying right past your 
shoulder towards your friend calculates which
event to have happened first in his frame of 
reference, your flash bulb going off, or his?
Problem 2: Someone exactly half way between
you is moving at nearly light speed at the same
instant (according to you and your friend's frame
of reference) that your flash bulbs explode. Which
even occurs first in his frame of reference? Perhaps
you have to draw spacetime diagrams with two
sets of axes to make sure you get the right answer---
I do.

> and in my example that distance is very large
> indeed, far too large for even light to cause an
> effect. And yet something did.

The measurement you made here "caused" nothing
to occur there. You split your universe locally, and
your friend splits his (also just locally). The splits
move at the speed of light. Eventually they join up.
Each instance of you finds himself with the right instance
of your friend, so that your measurements jibe. That's
all.

>> All that's happening is that the outcome of a measurement *here*
>> is correlated with the outcome of a measurement *there*.
> 
> All? ALL! Here is a billion light years from there!

Not to someone moving past you at .999999999999c.  To him,
youse are just a few yards apart.

Lee




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