Citeren meekerdb <>:

On 9/24/2012 8:02 PM, wrote:
Citeren meekerdb <>:

On 9/24/2012 9:28 AM, Stephen P. King wrote:
On 9/24/2012 12:02 PM, John Clark wrote:
Thus the moon does not exist when you are not looking at it.
Hi John,

I expected better from you! This quip is based on the premise that "you" are the only observer involved. Such nonsense! Considering that there are a HUGE number of observers of the moon, the effects of the observations of any one is negligible. If none of them measure the presence of the moon or its effects, then the existence of the moon becomes pure the object of speculation. Note that being affected by the moon in terms of tidal effects is a measurement!

So who or what counts as an observer. Young's slit experiments on fullerenes seem to indicate that a few IR photons or gas molecules qualify.


If I don't observe it, then it doesn't matter who/what else observes something, the rest of the universe is still a superposition. It doesn't matter whether or not an interference pattern can be detected.

?? I could matter. Suppose I bet you $100 there's no interference pattern when the buckyballs are hot? Then it would matter. But apparently it wouldn't matter whether anyone observed the IR photons or not.


Yes, but I would still think of me in the universe as a state of the form:

|me>|rest of the universe>

If you measure the z-component of a spin that is initially polarized in the x-direction, then I would describe the spin, you and the rest of the universe as a superposition, even if you tell me that you have measured without telling me the result of the measurement.

Even though my body will be entangled with the measurement result, I don't have any access to information about the result, so "|me>" (which I take to be everything that I am aware of) is exactly the same in both parts of the superposition and can thus be factored out of it. If this were not exactly true, you could not rule out me being able to guess the correct answer in more than 50% of the time.

Then the superposition of you having measured one result and you having measured another result can be interpreted as you being in the state before you performed the measurement. I can say that time doesn't really exist, the so-called time evolved state

|psi(t)> = exp(-i H t/hbar) |psi(0)>

can be re-interpreted as just the same initial state
|psi(0)> in a different basis. As long as the state has "evolved" in unitary way, you can still in priciple have access to the initial state. In practice, you can't because the observables you would have to apply are extremely non-local. Only when the "|me>" does not factor out of the entire state, does this become impossible, even in principle.


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