BIG successes of Lisp (was ...)

[Michele Simionato]

<snip obversations about MWI>

I cannot let pass this thread without some personal observation.

1. First of all, let me point out that I have a background in Theoretical Physics
and I have done research for the last ten years in the fields of supergravity,
quantum field theory, cosmology and other more exoteric subjects. So, I do
think I qualify as a "theoretical enough" physicists.

2. Second, I do think I have an idea about what are the fields of interests in
Physics nowadays; I also know for sure that the idea I had when I was an outsider
to Physics was completely wrong, so others may be in the same situation as I was.

3. Do you know how many research conferences are devolved to the
Multi-World Interpretation of quantum mechanics with respect to the number
of conferences in other fields such as QCD, or neutrino Physics, or even
magnetic materials?
The answer is very few. Actually, if you skip the conferences organized by
philosophers, the interdisciplinary conferences, the parallel sessions on
bigger workshops and you concentrate only on research conferences, the
answer will be *very very* few.

4. If I ask to virtually every theoretical physicist I know (and I know a
lot of physicists) about the MWI, they say "Come on, let's do real Physics".

5. I never had a course on MWI; no university I know about teach it to students.
Students are always (and often only) taught the standard interpretation; and
in any case nobody would ever think to teach it "instead of" the standard
interpretation. It could be taught as an alternative view, but in my
experience (most or all) universities skip it completely.

6. If you ask why <exaggeration mode> nobody except dean professors near
retirement </exaggeration mode> is interested in MWI you will likely get
the following answers:

1. it is an old business;
2. it is only an interpretation, gives no new predictions, so why bother?
3. cannot be generalized to relativity, so it is not relevant;
4. there are much more interesting things to study.

I admit that I am a bit exaggerating here, but let me do it. If there are
physicists doing MWI reading this, please, you are free to flame me
Still all my experience in Physics tell me that MWI is dismissed by the
vast majority of Physicists, not on the basis of philosophical reasons,
but on the basis of pragmatical considerations such as "even if they are
right, I have something better to do".

7. The press has the ability of giving a completely false impressions about
what physicists are doing: you find lots of general public books about
MWI and philosophy of science, but very few about magnetic materials.
So, you have the impression that physicists prefer MWI over magnetic
materials, but actually the converse is much closer to the truth. Also,
I would bet that magnetic materials (which I do know a bit) are
mathematically much nicer than the MWI (which I don't really know, so
I may be wrong).

8. I do like philosophical questioning and I thing it is okay to ask
questions, but still people should be aware of the distinction
between speculations (something smart speculations, something
idiotic speculations) and scientifically relevant questions.
Now, smart speculations may turn out to become scientifically
relevant questions, but smart speculations are unfortunately so rare ...

A good rule of the thumb is "never believe anything you read and you don't
understand". Sometimes, you should not believe even what you think you
understand ...


Michele

P.S. I really liked the joke about solipsism

P.P.S. I don't blindly believe the standard interpretation. I think
it is a "wart" of Physics which will hopefully pass. I look
with interest to the new ideas on decoherence, dunno if there
are general public books on it yet, but I would read one if
I find it

 

[John J. Lee]

I cannot let pass this thread without some personal observation.

[...snip most of a huge list of arguments from authority...]

4. If I ask to virtually every theoretical physicist I know (and I know a
lot of physicists) about the MWI, they say "Come on, let's do real Physics".

Well, perhaps the sample consisting of "Physicists Michele Simionato
knows" has *some* merit <wink>, but the single serious survey of
"great and good" Physicists' opinions I have read about (sorry, can't
give reference... but I think it must have been either in one of those
flaky books by Frank Tipler, or in Deutsch's "The Fabric of Reality"
that I read about it) revealed that a large majority believed
(essentially -- obviously there are subtleties) in the MWI. Not sure
when that was carried out either, but it was back when Feynman was
still alive.

7. The press has the ability of giving a completely false impressions about
what physicists are doing: you find lots of general public books about

[...]

Perhaps, but that has no relevance to the question of the reality of
multiple universes, of course.

8. I do like philosophical questioning and I thing it is okay to ask
questions, but still people should be aware of the distinction
between speculations (something smart speculations, something
idiotic speculations) and scientifically relevant questions.

[...]

Precisely, and IMHO (as well as, if you want argument from authority,
rather cleverer folks, like Deutsch), it's *YOU* that's confused about
that distinction! This is a hugely important point, so I'm glad it's
that point that you picked out of the detail in this thread. Science
is about reality, not prediction, and the MWI is a theory, not an
interpretation.

Skipping back a bit:

4. there are much more interesting things to study.

Certainly people like Deutsch do get quite pissed off that they have
to spend time defending what should be a done deal by now, taking time
away from more productive and interesting Physics work. In fact, he
loudly complains about it in his book, and not just wrt MWI: the same
problem occurs in evolutionary theory, for example (and there is
actually an interesting connection between MWI and natural selection).

[...]

P.S. I really liked the joke about solipsism

But that was *your* joke, Michele! It's merely your *interpretation*
of the data that I really exist -- in *reality*, I'm just a figment of
your imagination <wink>.

(But I guess it's okay to laugh at your own jokes if you're the
solipsist

P.P.S. I don't blindly believe the standard interpretation. I think
it is a "wart" of Physics which will hopefully pass. I look

[...]

Already has!


John

 

[Michele Simionato]

There *is* no fixed past.

George Orwell's "1984" makes always a great reading.

Michele

 

[Michele Simionato]

Even causality is frowned upon in some circles.

Then avoid those circles. When somebody questions the causality
principle
I always point out the Summa Theologica, Part I, Question XXV, art. 4,
"Whether God can make the past not to have been?".

---

Objection 1: It seems that God can make the past not to have been.
For what is impossible in itself is much more impossible than that
which is only impossible accidentally. But God can do what is
impossible in itself, as to give sight to the blind, or to raise the
dead. Therefore, and much more can He do what is only impossible
accidentally. Now for the past not to have been is impossible
accidentally: thus for Socrates not to be running is accidentally
impossible, from the fact that his running is a thing of the past.
Therefore God can make the past not to have been.


Objection 2: Further, what God could do, He can do now, since His
power is not lessened. But God could have effected, before Socrates
ran, that he should not run. Therefore, when he has run, God could
effect that he did not run.


Objection 3: Further, charity is a more excellent virtue than
virginity. But God can supply charity that is lost; therefore also
lost virginity. Therefore He can so effect that what was corrupt
should not have been corrupt.


On the contrary, Jerome says (Ep. 22 ad Eustoch.): "Although God can
do all things, He cannot make a thing that is corrupt not to have been
corrupted." Therefore, for the same reason, He cannot effect that
anything else which is past should not have been.


I answer that, As was said above (Question [7], Article [2]), there
does not fall under the scope of God's omnipotence anything that
implies a contradiction. Now that the past should not have been
implies a contradiction. For as it implies a contradiction to say that
Socrates is sitting, and is not sitting, so does it to say that he
sat, and did not sit. But to say that he did sit is to say that it
happened in the past. To say that he did not sit, is to say that it
did not happen. Whence, that the past should not have been, does not
come under the scope of divine power. This is what Augustine means
when he says (Contra Faust. xxix, 5): "Whosoever says, If God is
almighty, let Him make what is done as if it were not done, does not
see that this is to say: If God is almighty let Him effect that what
is true, by the very fact that it is true, be false": and the
Philosopher says (Ethic. vi, 2): "Of this one thing alone is God
deprived---namely, to make undone the things that have been done."


Reply to Objection 1: Although it is impossible accidentally for the
past not to have been, if one considers the past thing itself, as, for
instance, the running of Socrates; nevertheless, if the past thing is
considered as past, that it should not have been is impossible, not
only in itself, but absolutely since it implies a contradiction. Thus,
it is more impossible than the raising of the dead; in which there is
nothing contradictory, because this is reckoned impossible in
reference to some power, that is to say, some natural power; for such
impossible things do come beneath the scope of divine power.


Reply to Objection 2: As God, in accordance with the perfection of
the divine power, can do all things, and yet some things are not
subject to His power, because they fall short of being possible; so,
also, if we regard the immutability of the divine power, whatever God
could do, He can do now. Some things, however, at one time were in the
nature of possibility, whilst they were yet to be done, which now fall
short of the nature of possibility, when they have been done. So is
God said not to be able to do them, because they themselves cannot be
done.


Reply to Objection 3: God can remove all corruption of the mind and
body from a woman who has fallen; but the fact that she had been
corrupt cannot be removed from her; as also is it impossible that the
fact of having sinned or having lost charity thereby can be removed
from the sinner.

---

If God himself cannot go against the causality principle, how can we,
poor
physicists?

See http://www.ccel.org/a/aquinas/summa/home.html for more.


Michele Simionato

 

[Michele Simionato]

This is a bit too meta-physical, but then much of modern physics is like
that.

That's an incorrect view of much of modern physics. The fault is to
general public books which generates a false impression :-(

Michele

 

[Anton Vredegoor]

A good rule of the thumb is "never believe anything you read and you don't
understand". Sometimes, you should not believe even what you think you
understand ...

In Scientific American (I think it was the may 2003 issue) I read
something about parallel universes. One idea goes like this (adapted
to make it fit my brain).

Suppose you're sitting in a chair in the middle of a virtual 2X2X2
cube. Next imagine a cube filled with protons (or some even smaller
particles) as tightly as possible. The difference between this cube
and the cube you are sitting in is that in your cube some of the
protons are absent. The cubes could possibly be represented by Python
long integers [1], where the full cube would be a long with all bits
set to one and different cubes would have some zero bits at
corresponding positions.

There can not be more different cubes than 2**(number of protons per
cube) so in an infinite universe (or even in a big enough universe) at
some distance from you a cube identical to the one you are occupying
would exist, or else one would need a very good reason why the cube
you are occupying is unique.

Anton

[1] How many protons would fit inside a 2x2x2 meter cube is left as an
exercise for the readers

 

[Michele Simionato]

OK - so why is it not possible to detect the superposition of that
cat? Why is the experiment still considered a thought experiment only?

As I understand it, you *could* perform the experiment, modulo problems
with the society for the protection of animals. Actually, those experiments
*have been* performed a number of times and are still performed. Of course,
they don't use cats, but they call "cats" the wave packets used in the
experiments.

Quantum mechanics (any interpretation of it) will predict that if you repeat
the experiment many times, you will kill the cat 50% of times. Now, if you
really do the experiment, you will really get this rate of success or
failure (depending if you like cats or not), since quantum mechanics
works.

The point and the crux of the discussion is: "what happens to
the cat *before* opening the box?" This is a matter of principle,
so the experiment is a thought experiment; thought experiment
does not mean it cannot be realized (it's the same for Einstein's
elevator experiment, the basis for the equivalence principle).

Now, according to Bohr's interpretation
the question simply does not make sense: I don't know anything about
the cat if I do not observe it. It does not make sense to ask if it is
alive or dead: the only thing that matters is that the cat will be dead
50% of times when I open the box, and dead the other 50%.
Common sense says that the cat is alive or dead independently from the
fact that I observe it or not. This is called realism. BTW, I am sure
you are already familiar with the concept, but let me be verbose.

The orthodox quantum mechanics interpretation is NOT realistic: it
does not assume anything about the state of the cat prior to observation.
In this line of thinking, few centuries ago the Bishop Berkeley asked
to himself something like this: what happens to a tree when I don't look
at it? Am I *really* sure that the tree is still there? What if a evil
devil makes the tree disappear when I don't look at it, and reappear
when I look at it? At the end Berkeley solved the paradox by saying
that the reality is real because of God: He is watching all the trees
all the time, so we may be sure that trees are still there even if
we are not watching them.

In the last couple of centuries we have
lost our faith in God (fortunately/unfortunately) so now there is
nobody watching the cat inside the box. For this reason we don't
know if it is alive or dead, and we say that it is in a superposition
state. What happens when we open the box (i.e. when we perform the
measurament) we don't know; for sure it is something bizarre which
we model with the wave function collapse argument, but there is
no doubt that the argument is weak and should be replaced by
something better. We use it for lack of better alternatives (the
MWI is not considered a good alternative by the majority of
physicists).

My point is that this is an INTERPRETATION: depending on your religious
belief you may find the realistic interpretation more or less appealing
(Einstein was against it).

This is not a point of Physics: both interpretation say that when we
measure we will get 50% of dead cats, and actually we get that. This
is Physics; the rest is speculation. You may adhere to the realist
interpretation, but in this case you must loose the property of
locality, and most people are so unhappy with this, that they
prefer to renonce to realism (there is a theorem that you cannot
get both realism and locality for free, and also experiments on
Bell's unequalities, so this is "for sure").

What it is really interesting it to understand how measurement works,
how to pass from microscopic to macroscopic, how to give a better
description of what happens behind the wave function collapse.
This is an *hard* job, but there is an active line of research on
*these* issues and I don't think we have lost hope. At the end, a theory
providing *new* verifiable predictions will emerge. A theory
providing the *same* predictions but a different interpretation
will not have any success, since results are more important than
interpretations (at least, to most physicists). We are more pragmatic and
less academic than other academic people, I think

I should have got the argument right, but please remember that
these topics are typically not taught in courses, since they are not
considered very relevant, and I have last studied Berkeley's argument
more than 15 years ago, so I may remember uncorrectly. Here I am giving
my opinion and I don't have an autoritative reference on the subject now.
So, my word should be taken "cum grano salis". On the other hand,
the word of everybody should be taken "cum grano salis"

HTH,

Michele Simionato

 

[Stephen Horne]

A good rule of the thumb is "never believe anything you read and you don't
understand". Sometimes, you should not believe even what you think you
understand ...

In Scientific American (I think it was the may 2003 issue) I read
something about parallel universes. One idea goes like this (adapted
to make it fit my brain).

Suppose you're sitting in a chair in the middle of a virtual 2X2X2
cube. Next imagine a cube filled with protons (or some even smaller
particles) as tightly as possible. The difference between this cube
and the cube you are sitting in is that in your cube some of the
protons are absent. The cubes could possibly be represented by Python
long integers [1], where the full cube would be a long with all bits
set to one and different cubes would have some zero bits at
corresponding positions.

There can not be more different cubes than 2**(number of protons per
cube) so in an infinite universe (or even in a big enough universe) at
some distance from you a cube identical to the one you are occupying
would exist, or else one would need a very good reason why the cube
you are occupying is unique.

That has little to do with the many worlds interpretation of waveform
collapse. These 'universes' do not interact with each other in the way
that superpositions of particles do.

Actually, if you imagine that cube full of protons again, according to
quantum theory many of those protons may be in superposed states. That
is, a single proton may be in several states, including being in
several positions.

How many states may a single proton have within that cube? Well, it
isn't just the number of combinations of possible superpositions of
states of protons. For example, the state where two superpositions
happen to be identical (indistinguishable state - think of polynomials
with repeating roots) but other superpositions have measurably
different states would have measurably different consequences to that
where there is only one occurence of each uniquely recognisable
superposed state for that proton. In fact, you can have an infinitite
number of states for that cube of space with only one proton in that
space by simply counting all possible sets of superposed states for
the proton.

Which means that the number of possible states of matter is not finite
even if we ignore the states where some superposed states of a
particular proton are inside the cube while others are outside it.

I hope you also realise that your cube, defined in space only, is not
sufficient to define a parallel universe. Each proton has momentum as
well as position, and a proton may well have an infinite number of
possible kinetic energy levels. The cube thus becomes a hypercube with
time as one dimension, and each proton is represented by a curve - not
just a single point position. How many curves can exist in that
hypercube, even for a single proton?

Even ignoring momentum, what about quantum uncertainty - just because
the current state of that cube is identical (and ignoring any
influence from surrounding cubes of space) the future states of
different instances of the supposedly parallel universe may play out
differently. We may well discover in future a more general model which
recovers perfect determinism, but given current evidence we cannot
assume that.

Finally, how can you assume that there is only a finite number of
possible positions of a proton within that space? A quick look at
relativity tells us that space is not like graph paper. Spacetime
itself may have different shapes, dependent on matter outside as well
as inside that cube.


There are, of course, important theories which measure the amount of
information in any region of spacetime - and the amount of information
turns out surprisingly small - but I am not convinced that the measure
is of all information in that region as opposed to, for instance, all
information that is accessible to an outside observer. Certainly there
is something rather odd going on which cannot be explained by proton
counting.

 

[Stephen Horne]

The point and the crux of the discussion is: "what happens to
the cat *before* opening the box?" This is a matter of principle,
so the experiment is a thought experiment; thought experiment
does not mean it cannot be realized (it's the same for Einstein's
elevator experiment, the basis for the equivalence principle).

Not exactly. When we look at superpositions of subatomic particles,
there are observable artifacts of the interactions between
superpositions - the interference patterns. Without those
interactions, the theory of superpositions would be pointless as there
would be no effects of superposition to observe - the theory would
have no predictive or explanatory power.

My point is that the cat is superposed in the same way as the
subatomic particle, and yet we are unable to observe any artifact of
that superposition. *All* we can see is a single state resulting from
the waveform collapse when we observe the cat, but this is
emphatically not the case with subatomic particles where we can
observe artifacts of the superposition itself.

This has been answered, however, by the simple fact that interference
patterns are the only observable artifact of superpositions - it would
be rather hard to fire a cat through two narrow slits simultaneously,
it would also be rather hard to observe the resulting interference
pattern, and certainly the animal protection charities would be pretty
upset with you if you tried it ;-)

 

[Michele Simionato]

But it's certainly true that some theories (the Copehagen
interpretation itself, for example, or the Inquisition's explanation
of the motions of the Solar System) that people continue to believe in
are indefensible because they arbitrarily reject the very existence of
some part of reality that another theory successfully explains. To
quote David Deutsch: "A prediction, or any assertion, that cannot be
defended might still be true, but an explanation that cannot be
defended is not an explanation".

How does MWI generalize to quantum field theory? If it does not generalize,
as I will bet it is the case (I would know otherwise) it explain much *less*
than the standard interpretation. Between two theories, one explaining
more and one explaining less, we prefer the one that explains more.
It is as simple as that and it explain why MWI is not popular at all
outside philosophical circles. I will gladly admit that the orthodox
theory is not perfect, but it is the best we have, at least according
to most physicists. There are always exceptions (Deusch): please do
mistake the exceptions for the norm.


Michele Simionato

 

[John J. Lee]

In the last couple of centuries we have
lost our faith in God (fortunately/unfortunately) so now there is

[...]

Again, I think the statistics are against you, Michele! Most people
on the planet believe in a God. Most Americans believe in a God.
Dunno for sure about Europeans, but I'd be surprised if it were
otherwise.

My point is that this is an INTERPRETATION: depending on your religious
belief you may find the realistic interpretation more or less appealing
(Einstein was against it).

This is not a point of Physics: both interpretation say that when we
measure we will get 50% of dead cats, and actually we get that. This
is Physics; the rest is speculation. You may adhere to the realist

That way of thinking (instrumentalism) is seductive, but wrong. I
refer you to Deutsch's book again (getting repetetive, I know).

interpretation, but in this case you must loose the property of
locality, and most people are so unhappy with this, that they

[...]

Not in the MWI (I'm extremely hazy on this point now, though :-( if I
ever did really understand it).

What it is really interesting it to understand how measurement works,
how to pass from microscopic to macroscopic, how to give a better
description of what happens behind the wave function collapse.
This is an *hard* job, but there is an active line of research on

[...]

It's rather easier if you accept the MWI, of course.


John

 

[John J. Lee]

(e-mail address removed) (John J. Lee) wrote in message news:<[email protected]>... [...]
How does MWI generalize to quantum field theory? If it does not generalize,
as I will bet it is the case (I would know otherwise) it explain much *less*

See Q14 of:

http://www.hedweb.com/manworld.htm

(MWI FAQ, which also gives details of that popularity contest I
mentioned. I think their wording on this point ("metatheory") is
perhaps a bit misleading, mind.)

than the standard interpretation. Between two theories, one explaining
more and one explaining less, we prefer the one that explains more.
It is as simple as that and it explain why MWI is not popular at all
outside philosophical circles. I will gladly admit that the orthodox
theory is not perfect, but it is the best we have, at least according
to most physicists. There are always exceptions (Deusch): please do
mistake the exceptions for the norm.

<sigh> I've already answered those points.


John

 

[robert]

A good rule of the thumb is "never believe anything you read and you don't
understand". Sometimes, you should not believe even what you think you
understand ...

In Scientific American (I think it was the may 2003 issue) I read
something about parallel universes. One idea goes like this (adapted
to make it fit my brain).

Suppose you're sitting in a chair in the middle of a virtual 2X2X2
cube. Next imagine a cube filled with protons (or some even smaller
particles) as tightly as possible. The difference between this cube
and the cube you are sitting in is that in your cube some of the
protons are absent. The cubes could possibly be represented by Python
long integers [1], where the full cube would be a long with all bits
set to one and different cubes would have some zero bits at
corresponding positions.

There can not be more different cubes than 2**(number of protons per
cube) so in an infinite universe (or even in a big enough universe) at
some distance from you a cube identical to the one you are occupying
would exist, or else one would need a very good reason why the cube
you are occupying is unique.

Anton

[1] How many protons would fit inside a 2x2x2 meter cube is left as an
exercise for the readers

<G>
are we allowed to assume that the protons will compress into true cubes,
or that they remain true spheres?
</G>

(no, i'm not about to do the arithmetic)
robert

 

[Michele Simionato]

[...snip most of a huge list of arguments from authority...]

No, no, please don't get me wrong!
The whole point of my post was an encouragement to DO NOT believe
authority (including mine, of course). If I wrote something like
"I have a background in Theoretical Physics with ten years of
research experience ... etc. etc." this has not to be interpreted
as "Ah, I am so much better than you".

Of course not. You should not believe me because of authority,
nor you should not take my word for granted. Also, you are perfectly
free to adhere to Deutsch views, I am not trying to convince you.
But when I see a statement such as

"It's a bit of an embarrassment to Physics that some physicists
apparently still believe in the Copenhagen interpretation"

I simply cannot let it pass.

I do think this statement is strongly misleading and I cannot let
people in this newsgroup to get a false impression abot Physics. False in
my own view, of course. But here is the reason why I pointed out my
background in Physics: my background is very relevant in this context
(how popular is MWI between physicist). For sociological questions like
this, first hand experience does matter: I do know from the inside what
physicists really do; and there is a big difference between reading
books and being a physicist. So, I think I was perfectly right in
stressing my background before presenting my observations. You may
believe me or not, but at least you know that I talk for direct
experience.

Well, perhaps the sample consisting of "Physicists Michele Simionato
knows" has *some* merit <wink>

How may physicists do you know, personally? Not offence intented, but
first hand experience does matter, as I said. Not only I know lot of
physicists (I was at conferences with big names such as Mandelbrot,
Higgs, Seiberg ... etc.) but, more importantly, I do know the
opinion of the other physicist about those "great names".
You will be surprised how much irrespectful it is.

but the single serious survey of
"great and good" Physicists' opinions I have read about (sorry, can't
give reference... but I think it must have been either in one of those
flaky books by Frank Tipler, or in Deutsch's "The Fabric of Reality"
that I read about it) revealed that a large majority believed
(essentially -- obviously there are subtleties) in the MWI. Not sure
when that was carried out either, but it was back when Feynman was
still alive.

Who is making argument from authority now?

Precisely, and IMHO (as well as, if you want argument from authority,
rather cleverer folks, like Deutsch)

Arguments from authority have the problem that you can always choose
your preferred authority, so you are always right. I would not qualify
Deutsch or Tipler as "great" physicists, but this is beside the point.
I would qualify Albert Einstein as a "great" physicist. He didn't believe
the Copenhagen interpretation either; he believed in the hidden variables theory.
Such a theory has been proved to be wrong by real world experiments,
so he was wrong. Everybody (unless he is Dutch) can be wrong, so please
let's stop the arguments from authority. The argument from personal
experience is different in the sense that at least I am not invoking
somebody else to support my views.

Finally: notice that I didn't make any specific claim against MWI
in this posts, I limited myself to few sociological observations
and a few facts. An objective fact is the number of conferences
about MWI theory. Please, look at
http://www.physics.umd.edu/robot/confer/confmenu.html
and compute yourself the percentage of conferences about MWI
(including or not including the ones mixed with philosophy
conferences).

Also, please believe that physicist are no stupid, so there must
be some reason why there is relatively little active research about MWI.
BTW, you may interpret this statistical observation as a disguised
argument from authority and you may be right, but it is so difficult
to get rid of arguments from authority!

I write all this for the benefit of c.l.py regulars, anybody has
the right to follow Deutsch's views, but they should not be presented
as dominating in the physics community ("some physicists
apparently still believe in the Copenhagen interpretation").

Michele Simionato

 

[Michele Simionato]

In Scientific American (I think it was the may 2003 issue) I read
something about parallel universes. One idea goes like this (adapted
to make it fit my brain).

Suppose you're sitting in a chair in the middle of a virtual 2X2X2
cube. Next imagine a cube filled with protons (or some even smaller
particles) as tightly as possible. The difference between this cube
and the cube you are sitting in is that in your cube some of the
protons are absent. The cubes could possibly be represented by Python
long integers [1], where the full cube would be a long with all bits
set to one and different cubes would have some zero bits at
corresponding positions.

There can not be more different cubes than 2**(number of protons per
cube) so in an infinite universe (or even in a big enough universe) at
some distance from you a cube identical to the one you are occupying
would exist, or else one would need a very good reason why the cube
you are occupying is unique.

Anton

I fail to see the argument, sorry. OTOH, I have few observations
that may be of interest (even if way off topics, as all of this
most interesting thread

According to the inflationary paradigm (which is a serious
paradigm with observational support) we live in a small
portion of the entire Universe. That means the following:

1. the observable Universe, i.e. the causally connected part of the
Universe, is next to nothing with respect to the full Universe;

2. there could be infinitely many other words in the outer part of the
Universe;

3. the cosmological horizon is expanding with time, so those others
worlds will become available to us if we wait a few billions years;

4. we still live in an inflationary epoch, so the rate of expansion
of the universe will increase with time.

I would consider all these points (including the last one, only discovered
2-3 years ago) serious science. This means, they may be wrong, but they are
serious, based on some experimental/observational evidence.

So, I would say that serious science (at least serious according to me
can accept many worlds in the inflationary context: actually it predicts
them. The real point is that there is only ONE universe that matters, i.e.
the casually connected part of the Universe where we live: the rest of
the Universe cannot influence us in any way. Nevertheless, it influenced
us in the far far away past (when we were in causal contact with a much
bigger part of the Universe) and it will influence us in the far far
away future, as the cosmological horizon increases.

Nowadays, the causal radius of the Universe is something like 45 billions
of light years (notice that the Universe is 15 billions of years old,
but the causal radius is not 15 billions of light years, since the concept
of "distance" is rather tricky in general relativity), so it contains
only 10^52 cubes of 2x2x2 meters. I strongly disbelieve that in some of
the other cubes there is a copy of myself replying to a copy of Anton
Vredegoor in a copy of c.l.py.

10^52 is a very little number as compared to infinity!

Moreover: reasoning about infinity is tricky. An infinite Universe does not
necessarely means that all possible combinations are available. The
set of even numbers is infinite, but does not contain any copy of the
number "2", nor it contains any odd number, by definition.
It is quite risky to make any statement about infinity, unless you are
talking about a very specific kind of infinite that we have under mathematical
control, such as Cantor theory of transfinite sets. So, be careful:
the infinity of mathematicians and physicists is quite different
from the infinity of the philosopher.


Michele Simionato

 

[Michele Simionato]

In the last couple of centuries we have
lost our faith in God (fortunately/unfortunately) so now there is

[...]

Again, I think the statistics are against you, Michele! Most people
on the planet believe in a God. Most Americans believe in a God.
Dunno for sure about Europeans, but I'd be surprised if it were
otherwise.

My fault, I was too concise and I didn't express clearly what I meant.
Here is what I had in mind when I wrote "In the last couple of centuries
we have lost our faith in God ...":

1. the "we" has to be qualified as "we scientists and educated people";
2. the "lost our faith in God" has to be interpreted as "lost our faith
in God as a way of scientific explanation of reality".

Look at the context: I was talking about Berkeley, who had the possibility to
recur to God as a way of ensuring realism; this possibility is (fortunately/
unfortunately) precluded to modern science, just in the same sense that we
cannot invoke angels as an explanation for the motion of planets.

I was by no means implying that most of people (or most of modern scientists)
are unbelievers. This would simply be not true. I meant that there is a
consensus in the modern scientific community that we cannot use God as a
way of scientific explanation. Things were different at the time of Berkeley.

Also I had in the back of my mind the idea that in the Germany of the
twenties, after the World War I, there was quite a luck of faith in
the traditional concept of God (see books such as "Demian" by Herman
Hesse, for instance) and it is not strange, in that historical/philosophical
context that somebody came out with concepts like the indetermination principle
or the refusal of realism. I would not expect those concepts coming out
in the context of victorian U.K., for instance. Not that I am advocating
the view that Physics is determinated by the sociological context, but
certainly it is influenced by it. Vice versa, the sociological context can
be influenced by Physics (expecially after we made the bomb).


Michele Simionato

 

[John J. Lee]

[...snip most of a huge list of arguments from authority...]

[...]
But when I see a statement such as

"It's a bit of an embarrassment to Physics that some physicists
apparently still believe in the Copenhagen interpretation"

I simply cannot let it pass.

I do think this statement is strongly misleading and I cannot let
people in this newsgroup to get a false impression abot Physics. False in
my own view, of course. But here is the reason why I pointed out my
background in Physics: my background is very relevant in this context
(how popular is MWI between physicist). For sociological questions like
this, first hand experience does matter: I do know from the inside what

Well, we simply disagree about the epistemology of this, and the
statement of mine that you quote just reflects that disagreement. A
discussion of popularity can't clear that up.

[...]

Who is making argument from authority now?

<cough, splutter> I was responding to you! Am I to be reprimanded for
responding to your anecdotes with an actual survey?

Arguments from authority have the problem that you can always choose
your preferred authority, so you are always right. I would not qualify

[...]

<gasp> How *dare* you aim this at me, when *YOU* posted an enormous
list of arguments from authority, and *I* told you off for doing so?
Even in the section you quote, I explictly labelled my parenthesised
comment as argument from authority (hence invalid). The cheek of it
*ASTOUNDS* me!

I hereby give up on this thread in disgust, this'll be my last post
(the rest of the NG will be very pleased to hear ;-).

Finally: notice that I didn't make any specific claim against MWI
in this posts, I limited myself to few sociological observations

Yes, I was QUITE well aware of that! ;-)

and a few facts. An objective fact is the number of conferences
about MWI theory. Please, look at
http://www.physics.umd.edu/robot/confer/confmenu.html
and compute yourself the percentage of conferences about MWI
(including or not including the ones mixed with philosophy
conferences).

If you read my posts, you would know that I *agree* with you that the
fact that this is still an issue is unfortunate and takes time away
from more important issues of new Physics.

Also, please believe that physicist are no stupid, so there must
be some reason why there is relatively little active research about MWI.

Yep, because there's probably not much to be done on MWI in itself. I
agree with you there.

I write all this for the benefit of c.l.py regulars, anybody has
the right to follow Deutsch's views, but they should not be presented
as dominating in the physics community ("some physicists
apparently still believe in the Copenhagen interpretation").

OK, I give you that, I shouldn't have implied that that the overall
number (or fraction) of CI-believers or non-MWI-believers was small
(though I certainly don't know whether it's a majority or not -- and
I'm afraid your anecdotes don't persuade me that you do, either).
Amongst jobbing Physicists (rather than the "great and good" of that
survey), I would *guess* the fraction of CI-believers or people who've
never really thought about it is much higher (partly because some
parts of the 'front-line' of Physics, cosmology and quantum
computation in particular, tend to rub the inadequacy of CI in your
face).


John

 

[Michele Simionato]

Not exactly. When we look at superpositions of subatomic particles,
there are observable artifacts of the interactions between
superpositions - the interference patterns. Without those
interactions, the theory of superpositions would be pointless as there
would be no effects of superposition to observe - the theory would
have no predictive or explanatory power.

My point is that the cat is superposed in the same way as the
subatomic particle, and yet we are unable to observe any artifact of
that superposition. *All* we can see is a single state resulting from
the waveform collapse when we observe the cat, but this is
emphatically not the case with subatomic particles where we can
observe artifacts of the superposition itself.

There is no such a big difference between the Scroedinger's cat experiment
and the narrow slits experiment:


| |
| |
A | S
P | |
-> | |
B |
| |
| |

The particle P passes through one of the slits A,B and ends its life on the
screen S, producing a spot. Getting the spor corresponds to opening the box in
the cat experiment. If you repeat the experiment many times
with many particles, the distribution of the spots is an interference
pattern. But if you perform the experiment with a single particle, then
you have 50% of probability of getting the spot in the upper side of the
screen, and 50% in the lower side (assuming a symmetrical experimental
disposition). This corresponds to have the cat 50% of times alive
and 50% of times dead when we open the box. Having only seen the spot in S,
it does not make sense to ask whether the particle passed through A or through
B, exactly in the same sense that it does not make sense to ask if the cat
is dead or alive before opening the box (this according to the
orthodox interpretation). If you watch to see if the particle really passes
for A you necessarely perturb the system. For instance, you can close the
slit B, and make sure that the particle passes trought A, but then the
interference disappear.
When the particle reach S and you get the spot, then the collapse
of the wave function happens. It is less spectacular than opening
the box, but in principle it is the same operation. I will not
claim that the collapse is understood, not that it is an easy
task to understand it :-(

Michele Simionato

 

[Stephen Horne]

There is no such a big difference between the Scroedinger's cat experiment
and the narrow slits experiment:


| |
| |
A | S
P | |
-> | |
B |
| |
| |

The particle P passes through one of the slits A,B and ends its life on the
screen S, producing a spot. Getting the spor corresponds to opening the box in
the cat experiment. If you repeat the experiment many times
with many particles, the distribution of the spots is an interference
pattern. But if you perform the experiment with a single particle, then
you have 50% of probability of getting the spot in the upper side of the
screen, and 50% in the lower side (assuming a symmetrical experimental
disposition). This corresponds to have the cat 50% of times alive
and 50% of times dead when we open the box. Having only seen the spot in S,
it does not make sense to ask whether the particle passed through A or through
B, exactly in the same sense that it does not make sense to ask if the cat
is dead or alive before opening the box (this according to the
orthodox interpretation). If you watch to see if the particle really passes
for A you necessarely perturb the system. For instance, you can close the
slit B, and make sure that the particle passes trought A, but then the
interference disappear.
When the particle reach S and you get the spot, then the collapse
of the wave function happens. It is less spectacular than opening
the box, but in principle it is the same operation. I will not
claim that the collapse is understood, not that it is an easy
task to understand it :-(

OK, but there is still an artifact. In order for a sufficiently large
number of repetitions to build an interference pattern, the points on
S cannot be simple projections of P through A or B.

With the cat, the there are two possible final states - either the cat
is alive or dead - essentially the 'projections' of the initial
radioactive decay through the cause-and-effect chain with the detector
and poison.

There is still a clear artifact at the microscopic scale (the point
detected on S is NOT a simple projection through either A or B)
whereas no such artifact can be detected at the macroscopic scale (the
cat ends up either alive or dead, just as it would without any quantum
considerations).

I don't claim to understand quantum theory by any means, but I do know
that in principle if there were no artifacts of quantum effects no
sane human would have invented them.

So why don't we find cats that are half-dead and half-alive (between
the projections of A and B), or cats which are more dead than dead
(further to the A side than the projection of A)?

Perhaps cats simply don't have a particle/wave duality issue to worry
about.

 

[Michele Simionato]

(e-mail address removed) (Michele Simionato) writes:
OK, I give you that, I shouldn't have implied that that the overall
number (or fraction) of CI-believers or non-MWI-believers was small
(though I certainly don't know whether it's a majority or not -- and
I'm afraid your anecdotes don't persuade me that you do, either).
Amongst jobbing Physicists (rather than the "great and good" of that
survey), I would *guess* the fraction of CI-believers or people who've
never really thought about it is much higher (partly because some
parts of the 'front-line' of Physics, cosmology and quantum
computation in particular, tend to rub the inadequacy of CI in your
face).

Please, take a look at my publication list (it is enough to search for
my name at http://www.slac.stanford.edu/spires/hep/) and you will see that
I have published research papers in the domain of early Universe cosmology.
In my experience, the beliefs of people in the field are different
from what you say.
I prefer not to comment on the "jobbing physicist" part.

Michele Simionato