On 1/21/2014 5:33 AM, Bruno Marchal wrote:
On 21 Jan 2014, at 06:47, Pierz wrote:
The question is whether a whole universe is created for each state in a superposition.
Deutsch seems unequivocal that it is.
Hmm, Deutsch might have change his mind. he was also sure that there is a base problem,
but he changes on it.
Liz is right. The differentiation of the universe is a local phenomenon. But the
universe is full of intracting things, and this made the differentiation spreading (at
sub-light speed though).
I'm just questioning a) whether that's what he really means and b) whether that is
necessary.
Deutsch prefers to abandon the idea of splitting universe. I follow him on that, but
this is almost a problem of vocabulary, and in english what happens is hard to simplify.
Imagine a particle in the state up + down, and imagine me, not looking at the
particle.
The quantum state "me X (up + down)" is the same state as (me X up + me X down). Is
there one me, or two me. Deustch would say "two me, but two fungible me". There is only
one 1p, but you have the choice of two 3p or one, according to the equality
me X (up + down) = (me X up + me X down).
The same happens for the rest of the universe. If I look at the particle, in the {up,
down} base, then I will differentiate (the two 3p me get two 1p me), or I will
bifurcate, that is there is one more 3p me.
In fact those wording are exactly equivalent by linearity.
And it is not only you, but any subset of the environment which big enough to effect
decoherence. Since there is lots of decoherence happening at a level below your conscious
recognition, these 'decohered, semi-classical worlds' are still the same world to you, or
put the other way 'you' are spread across these slightly different worlds. So there are
degrees or levels of "splitting".
I don't dig on that issue for two reasons.
- One general: I just do not find an infinity of universe extravagant. A finite numbers
of universe would seem more extravagant to me (and to most everythingers, by definition).
I don't know about infinite, but there must be many making up the level of observation;
otherwise it would be hard to realize probabilities like 1/pi.
Brent
- One with comp: there is zero such universe in that case, which nullifies that
"extravagance" problem. There is only {0, 1, 2, 3, ...}. Or {K, S, KK, KS, SK, SS, ...}.
It is equivalent.
Bruno
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