On 30/11/2017 5:31 am, John Clark wrote:
On Tue, Nov 28, 2017 at 10:59 PM, Bruce Kellett
<[email protected] <mailto:[email protected]>> wrote:
>
I see no reason all the Everett worlds have the same physics,
>
Everettian worlds follow from assuming that the Schrödinger
equation applies everywhere without exception, so that all
physical evolution is unitary. A change in the underlying physics
-- such as a change in the value of fundamental constants,
Planck's constant or Newton's constant for example -- would not be
unitary, so cannot occur in MWI.
Why can't it be unitary?? Show me why if
Newton's constant had any value other than
6.754* 10^-11 m3 kg^−1 s^−2
the sum of all quantum probabilities would no longer add up to exactly
1. If you can really do that then you've just derived Newton's
constant directly from first principles and you should but a ticket to
Stockholm right now because you're absolutely certain to win the next
nobel Prize.
Although unitarity does mean that probabilities always sum to unity,
that is a consequence of unitary evolution, not a definition of it. A
unitary transformation is one that can be reversed: so the unitary
operator U can be written as exp(-iH), for example, and the complex
conjugate (or the adjoint for hermitian operators) is the inverse
transformation.
So for changes in constants to be unitary, there needs to be a hermitian
operator that brings about these changes. But changes in constants only
make sense for dimensionless constants such as the fine structure
constant, and there is currently no theory as to how this would change
in a unitary manner.
>>
lets assume you're right, then the string theory multiverse
must be larger than the many worlds multiverse incorporating
everything in Everett's version and MORE; after all if it
contains universes with radically different laws of physics it
must also contain more modest things like a world where my
coin came up heads instead of tails.
>
I would suggest that there is no such world. Whether a coin comes
up head or tails on a simple toss is not a quantum event;
Do you actually think reality can be neatly divided
between quantum and non-quantum events? A unstable atom has a 50%
chance of decaying and producing a easily detectable high speed
electron, if the electron is detected a computer controlled robot arm
turns my coin to heads, if it detects no electron it turns my coin to
tails.
Of course, if you set up a situation in which a quantum event is
amplified to give a difference in macroscopic outcomes, such as in
Schrödinger's cat, then you can say that the macroscopic uncertainty has
a quantum origin. But the majority of quantum events are not amplified
in this way -- they simply occur randomly in large numbers so that the
expectation value is unaffected by individual uncertainties.
>
Also, in the Level I multiverse it is quite unlikely that the
initial conditions could differ to an extent such that everything
was identical in the two worlds up to your coin toss.
Quite
unlikely
events are going to happen if the number of universes is large
enough, and if there are a infinity of worlds then anything with a
non-zero probability is certain to happen in some universe.
Except events of measure zero.
>
Worlds are not random objects, they follow the laws of physics, so
given some initial conditions, the future is determined in a
deterministic Everettian MW scenario. It is not the case that
everything logically possible happens -- only those things that
follow from the initial conditions
But there is not just one initial condition, there are as many
initial condition
s as there are universes.
But there may well be outcomes that are impossible, whatever the initial
conditions -- the laws of physics rule out many things that appear to be
logically possible.
>
the laws of physics cannot be broken.
Yes but what are the true laws of physics? Kepler thought that the
fact there were 7 and only 7 planets was a law of physics that could
be derived from pure mathematics.
He was wrong. We may be as wrong as Kepler about some of our laws.
The laws of physics governing the universe do not care whether we know
them or not -- they still cannot be broken.
Bruce
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