Re: the two slits versus schrodinger's cat
From: Bjoern Feuerbacher (feuerbac_at_thphys.uni-heidelberg.de)
Date: 08/19/04
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Date: Thu, 19 Aug 2004 10:35:56 +0200
Greg Gerardin wrote:
> "Bjoern Feuerbacher" <feuerbac@thphys.uni-heidelberg.de> a écrit dans le
> message de news:cg034g$f9t$1@news.urz.uni-heidelberg.de...
>
> [snip]
>
>
>>>that's what I've just said. If you don't wonder what this all means,
>>> that's because you have either a technological or experimental goal,
>>>both generaly considered as part of the applied physics field...
>>
>>1) I did not say that I one should not wonder what this all means.
>>I even did not say that I do not wonder what this all means. I merely
>>pointed out that wondering "what this all means" is not physics.
>>2) Experimental physics has nothing to do with applied physics. It is
>>a part of physics on its own.
>>3) Wondering or not wondering "what this all means" has little to
>>nothing to do with if one works in theoretical, experimental, applied
>>physics or whereever. As a matter of fact, *I* work in theoretical
>>physics.
>
>
> 1) I never said that you said one should not wonder about what is the "real
> thing" behind the theory! Where did you see that?
You wrote above "If you don't wonder...". That implied to me that you
think I am not wondering that, and even said that one shouldn't do
that. Sorry for the misunderstanding.
> 2) Ok, sorry about my wrong definition of applied physics... I don't know
> where I've seen (i think i did, maybe not) that applied physics was a)
> physics related to engineering, and b) in a larger view, physics tested with
> labs applications (equipment, tools)... My error, sorry.
That's o.k.
I myself learned the difference only after one or two years of my
physics study... ;-)
> 3) You are cheating there.... "what this all means" is your own sentence,
> and in its first context, it *really* meant, "investigating the nature of
> reality" in opposition to "applying the theory without questionning".
Well, that's what I also meant here. But please notice that a phrase
like "the nature of reality" is quite vague.
> But now, you use this sentense as if it meant "doing philosophy with QT issues",
> which is completely different. You try to trick me!
No, I don't think that this is completely different. Questions like:
"What is reality?" belong to philosophy, not to physics.
> I know that you are a physicist, I know it from the beginning and I never
> doubted of your obviously higher level of understanding of the modern
> physics. I never meant to offend you pretending I knew more about it than
> you!!!!!! Sorry if I did, really. (in fact I feel like I don't belong to
> this newsgroup as most of you are professional scientists, or physics
> students).
No, I think most people in this newsgroup are crackpots, not
professional scientists. Y.Porat, kenseto, George Hammond, Jeff Relf,
FrankH, Mitchell, etc. The list is endless.
It's nice to see someone like you now and then, who honestly asks
questions and does not try to promote a cranky theory of his own. ;-)
> _But_ being a scientist (even a very good one), and knowing what is the goal
> of science from a social or societal point of view (that's the only point of
> view from which we can define the goals of science), those are two different
> things.
Err, I did not talk about the (social) *goals* of science. I talked
about the *point* of science, i.e. what's most important to do when
one is doing science.
> Just for the sake of it, here is the dictionary definition of
> science :
>
> "The observation, identification, description, experimental investigation,
> and theoretical explanation of phenomena"
I fully agree with that definition.
> As you can see, at least on a usual basis, science really is all about
> knowing the "phenomena behind the theory" (Identification, Investigation)
> and not only a description of it, even tho it's part of it.
One can argue that QM *is* an explanation of the phenomena. Just not an
explanation which we can understand in ordinary day language.
> And as you should concede, it's a rather frequent object of discussion, even
> among scientists, and finaly it might be just a question of personnality,
> interest or personnal ideology. No one win, no one lose, if you agree (only
> on that specidic question ;)
Well, I agree. ;-)
>>>For the last 80 years, physicists mostly improved existing theories
>>
>>Wrong. QFT is an entirely new development. So is string theory. So
>>are non-Abelian gauge theories. Etc.
>
>
> Maybe you should read the entire post before replying. You always ask
> things or give an opinion about thing I explain further in my posts (about
> the strings theory).
I reply before reading the entire post often, true. But when I find in
the remainder of the post something which counters my previous reply,
I go back and change my reply accordingly. Since I did not do this
here, I obviously did not find something which, IMO, counters my
point here. Looking again, I *still* see nothing below which would
change my point here.
>>>(so no "reel" progress at explaining the world, micro or macro)
>>
>>There was a *huge* progress in explaining the world in the last 80
>>years! E.g. we now know what protons and neutrons are composed of,
>>what holds them together, that the electromagnetic and weak forces
>>are only two different aspects of one and the same force etc. And in
>>the macro world, we have learned quite a lot about the universe - e.g.
>>that quasars exist and how they work, what the universe looks like
>>on the largest scales and how these structures formed etc.
>
>
> I didn't make myself clear about the macroscale, sorry. I meant that GR is
> still the macroworld reference theory.
Yes. So what? Newton's theory of gravity prevailed for over 200 years,
so 80 years is not that much!
> Of course we know a lot more know
> about our universe than in the past 80 years. The point was only about
> theory.
Agreed - on the macro scale, there were no new theories in the last 80
years, as far as I can see. The biggest change in an (already existing)
theory was when some years ago, it was discovered that the expansion of
the universe is accelerating, and we need the cosmological constant
after all.
But your point seems to have been that the attitude in QM ("shut up
and calculate") hinders the advance of science. What have theories
on the macro scale to do with that attitude in QM?
> Quasars, black holes, the expansion of the universe, all that was
> not known at that time, but this knowledge comes in large part from
> observation, not from a fundamental evolution in modern physics theories.
Agreed.
> For the quarks, you're right too. But did it make the fundamental theories
> evolve to a something new? (maybe, i don't know, it's a question)
I would say yes.
It was a huge advance in knowledge when it was found out that the strong
interactions can be described by a non-abelian gauge theory, that this
nicely explains confinement.
> About that electromagnetic/weak forces, there's nothing new here.
Yes, there is. For example, the idea of spontaneous symmetry breaking,
which is crucial for the electroweak theory, was an entirely new idea.
The Higgs as the cause for inertia was an entirely new idea.
> We know
> from the beginning that there is a potential for a theory that unifies
> the 4 forces. Unifying just two forces means that the theory behind this
> unification is incomplete or wrong.
No, not at all. Sorry, but you show here quite nicely that you know not
enough about this subject to make a judgement.
> I think that there is a strong feeling
> shared among scientists that the "good theory" will unify the 4 forces in
> one shot, not one after the other.
No, you are wrong about that. It's exactly the other way round. Particle
physicists agree that the unification occurs in steps, not all at once.
> We could talk about talk so much, I'd
> like to say more but I have to stop.
O.k.
>>>Of course there has been dramatic advances related precisely to QM and
>>>its (possible) applications (from laser to quantum computing, MNT,
>>>cold fusion, etc...) but nothing really happened on the matter of
>>>explaining what could possibly be a unified theory.
>>
>>Err, we have succeeded in unifying two of the four fundamental forces
>>and have good ideas about how to unify a third with these two already.
>
>
> I feel like it all just means that with powerful maths tools and by adding
> dimensions to dimensions to dimensions it *looks like* we're able to unify 2
> forces,
Unifying the electromagnetic with the weak force has nothing to do with
adding dimensions.
Unifying the electroweak with the strong force has also nothing (or
only *very* little) to do with adding dimensions ("very little" because
it looks like as if one needs supersymmetry for doing that consistently,
and supersymmetry needs something analogous to new dimensions).
And no, it does not merely "look like" as if we are able to unify
forces. With the electromagnetic and the weak force, we have indeed
succeeded in doing that.
> or we're able to unify GR and QT, or I don't know what.
Yes, for doing that, we will probably need additional dimensions.
> I'm quite
> sure there's something wrong with that complexification of the theory, don't
> you think?
I don't *like* the unification of the weak force (it looks somewhat
clumsy in some places), but I nevertheless think that it is right.
> (I KNOW, I'M REALLY NOT QUALIFIED TO TALK ABOUT THAT (it's just a
> feeling)) ;)
Yes, indeed. ;-)
>>And on the question how one could unify gravity with the other three
>>forces, *huge* progresses were made, although no consensus how it
>>really works has been reached so far.
>
>
>
> Yes I've read about it... it deals with a fourth spatial dimension or
> something like that, right?
There is an approach with a fourth spatial dimension, but I don't know
much about it. The leading ideas are loop quantum gravity (which does
not need additional dimensions, AFAIK), and string theory (which needs
6 additional ones).
> Well a fifth dimension is better than 11 dimensions i guess ;)
If the experiments show that the description works better with 11
dimensions, we will have to accept that probably there *are* 11
dimensions, if we like it or not.
> To be honest, I'm absolutely enthusiastic about physics evolution from the
> recent years... I was more talking about those other 75 years.
Those other 75 years saw the development of Quantum Electrodynamics,
the best theory we ever had in physics, the development of Quantum
Chromodynamics, and the unification of the electromagnetic with
the weak force.
All done based essentially on QM. No interpretation of QM needed for
that - just the math.
>>>Sort of, but 80 years is quite too short to "purge" the Quantum Theory
>>>of all its technological possibilities.
>>
>>Perhaps.
>>
>>But what is your evidence for your claim above that science can't
>>"evolve" any longer?
>
>
>
> I never said that!
You said:
"But how can a "falsely right model" make science evolve? It can't!"
With "falsely right model" you meant, as far as I could understand,
a model for which the math works, the predictions agree with reality,
but the underlying idea is wrong. And you seemed to imply that this
is indeed the case in QM, with the "shut up and calculate" approach.
> On the contrary, I really feel like science will evolve
> a lot in the coming decade. If you remember correctly, my point was that if
> we only "shut up and calculate", science will not evolve, it will stagnate.
> Not that "science can't progress any longer"
As I said: the huge advances in QFT were essentially made with that
approach. No interpretation of QM was needed for these advances, only
the math.
>>>Anyway, I like
>>>that interpretation, I've been told it's largely based on the copenhague
>>>one.
>>
>>That would be news to me. As far as I understand it, it totally
>>contradicts the Copenhagen interpretation.
>
>
> I've read it just yesterday in a book "Schrodinger's cat and the Search for
> Reality", by John Gribbin.
O.k., probably John Gribbin knows more about that than I, so apparently
I was wrong.
> I thought it was sort of a "serious" book.
I agree.
> It
> talks about the history of QT/QM, from the beginning up to today, and
> there's a large part about the Many Worlds interpretation since it's the one
> the author beleives in. Gribbin says it's an evolution from the Copenhagen
> interpretation, i'll get back to you tomorrow with the proper quotes.
Thanks, I'll believe you even without the quotes.
Perhaps I should try to read this book sometimes, too... I already read
quite a bit about the history of QM, but not yet that book.
>>But I think before one tries to interprets QM, one first has to
>>understand it, i.e. the math behind it.
>
>
> well I'd love to understand the maths. In fact I'm seriously considering
> returning to school to study physics, but it's a minimum of what, 10-12
> years of arsh studies before you can label yourself a physicist...
For understanding the math of QM, 3 years are enough. If you concentrate
on that and neglect other things, even 2 years may be enough.
You could also try learning this on your own. You need a good knowledge
of Linear Algebra (vector spaces, matrices, operators, eigenvalues
and eigenstates), differential equations, and complex numbers.
Understanding integration and Fourier transformations is also helpful,
but not essential.
> i don't
> have to money to studies 10-12 years ;) I'll try to get the basis tho,
> from books.
Good luck!
A book which is probably good for people who don't want to start
with heavy math is this:
<http://www.amazon.de/exec/obidos/ASIN/0387542175/qid=1092904426/ref=sr_8_xs_ap_i1_xgl/028-2049499-0490160>
OTOH, if you want to have heavy math right from the beginning, try
this:
<http://www.amazon.de/exec/obidos/ASIN/0198520115/qid=1092904500/sr=1-1/ref=sr_1_11_1/028-2049499-0490160>
> Ok that's all for today. and really no offense meant. I'm just an awkward
> and pretentious dreamer :)
You're welcome.
If only all the people posting here would be as modest as you... (and I
include myself here! ;-) )
Bye,
Bjoern
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