Interview with Steven Weinberg about Final theory
My name is Nasser Abbasi
interesting interview with steven Weinberg carried by the library of
science (by Walter Gelles), [typed without permission.]
Q. why do you say that a sense of beauty in physicists' theories is a
sign that we're making progress towards a final theory?
A. very often, the initial acceptance of a theory isn't really based on
experimental support, but rather, on the aesthetic response scientists
have towards the theory. This was true in good measure of Einstein's general
theory of relativity and the electroweak theory. Now, why should our sense
of beauty play a role comparable to experimental data? one reason may be that
behind all phenomena there really is a very beautiful, unified theory...what I
call a final theory. In fact, there almost has to be. If there was a theory
that was not beautiful, that had a lot of ugly, arbitrary elements, we would
never call it a final theory; we would go on looking for some more beautiful
thing underneath it. So the fact that by making theses aesthetic judgments, we
actually make progress, suggests that we may be catching hints of the beauty
in the final theory.
Q. How much predictive power world a final theory have?
A. The "standard model" of elementary particles and forces- the theory
we've been using for the last 15 years or so- has many arbitrary elements.
There are a number of constants (like masses and charges), and then there
are more fundamental things like the symmetries and the menus of particles
that furnishes the representations of the symmetry groups. all of these are
just taken from nature, we dont know why they are what they are. A final
theory had better be able to explain all these things.
This doesn't mean that a final theory will immediately enable us to calculate
everything we want. For instance, we already know the fundamental theory of
strong nuclear forces, but we still dont know how to use it to calculate
even a thing as basic as the mass of the proton. The calculation
is mathematically so complicated that for the present it is beyond our
reach. But though a final theory may not explain everything, it will have
enough predictive power--will explain enough about the standard model--so that
we'll be sure it's the right answer.
Q.How close are we to discovering a final theory?
A. There are many historical examples of people who thought we were very
close, and then it turned out we weren't so close...
I personally think that the discovery if string theories was a major step
towards a final theory; in fact they really represent the first time in the
history of physics that we've had a real place to look for a candidate for
a final theory. [with previous theories such as the standard model], there
done seem to be any theoretical framework in which gravitation made
mathematical sense on a quantum level. Now the string theories do that.
So I think there's at least 50-50 chance that some sort of string theory
will turn out to be pretty close to a final theory.
There is a definite sense of things converging towards a final answer, but that
doesn't necessarily mean we're going to reach the answer next year or in 10
years.
Q. Will scientists ever be able to devise experiments to test string theory?
A. Not directly, I suspect. I dont think we'll ever be able to detect
particles that correspond to excited states of a string. On the other hand,
if by using string theory we're able to calculate all the unknown quantities
in the standard model and if these figures turn out to agree
with experimental results, then that would be a verification of string theory.
Q. If a final theory is discovered, would theoretical physics come to an end?
would cosmology?
A. I imagine there wouldn't be much motivation to do particle physics except
perhaps in areas that overlap with astrophysics or nuclear physics. on the
other hand theoretical physics would continue. There are many fascinating
open problems in solid-state condensed matter, nonlinear phenomena,
turbulence, and chaos that would be left unsolved. The same is even more
true of astronomy and cosmology. No, the discovery of a final theory
would end just one kind of science: the search for those principles that
dont have any explanation in terms of deeper principles.
Q.Could a final theory tell us whether the universe is open, closed, or
oscillating?
A. It might. One reason we dont know what kind of universe we inhibit
is the problem of dealing with gravitation on the quantum level. if you
trace the universe back to ten or 20 billion years ago, you come to a time
when the universe was so condensed that you would have to apply rules of
quantum mechanics to the whole universe, not just to individual atoms and
nuclei. Nobody really knows how to do that. It's possible that when we learn
how, with the aid of a final theory, we'll discover that the universe has
to be open or closed or expanding or oscillating.
couple more questions one on importance of the superconducting super collider
for future progress of physics, and one on social consequences of final the
theory when discovered.
Barry Merriman
> interesting interview with steven Weinberg:
>
> Q. why do you say that a sense of beauty in physicists' theories is a
> sign that we're making progress towards a final theory?
>
> A... why should our sense
> of beauty play a role comparable to experimental data? one reason may be that
> behind all phenomena there really is a very beautiful, unified theory.
Wishful thinking. It could just as easily get extraordinarily complicated.
After all---if string theories are so simple, why are they so difficult
to work with?
--
Barry Merriman
UCLA Dept. of Math
UCLA Inst. for Fusion and Plasma Research
ba...@math.ucla.edu (Internet; NeXTMail is welcome)
Benjamin Weiner
>After all---if string theories are so simple, why are they so difficult
>to work with?
Actually, string theorists have already succeeded in coming up with the
Final Theory, answering all questions of physics, and so on. But they
realized that if they just came right out with it all, it would instantly
kill off their entire field - in fact, particle theory would become
obsolete and administrations might use this as an excuse for wholesale
eliminations of faculty lines, etc. So they burned the manuscripts, so to
speak. Kind of like Texaco suppressing Free Energy, or our favorite:
EVIL PHYSICISTS ARE HIDING THE TRUTH !!
John C. Baez
>In article <1993Jan16.2...@nntpd.lkg.dec.com>
abb...@star.enet.dec.com writes:
>> interesting interview with steven Weinberg:
>>
>> Q. why do you say that a sense of beauty in physicists' theories is a
>> sign that we're making progress towards a final theory?
>>
>> A... why should our sense
>> of beauty play a role comparable to experimental data? one reason may
>>be that behind all phenomena there really is a very beautiful, unified theory.
>Wishful thinking. It could just as easily get extraordinarily complicated.
>After all---if string theories are so simple, why are they so difficult
>to work with?
Of course it's wishful thinking, but the whole project of trying to
understand the universe is based on wishful thinking - there's no good
reason why it should be understandable to us (past the level of "yellow
fruit tastes good"). So I am in favor of
optimistically pursuing simple theories of fundamental processes - at
least before we start trying the complicated ones. My main grudge
against string theory as it stands is that it's NOT simple. E.g., the
fashionable heterotic string has fields moving leftwards and rightwards
along the string worldsheet; the left-moving sector is purely bosonic
and lives in 26 dimensions, while the right-moving sector is
supersymmetric and lives in 10 dimensions. The gauge group is E_8 x
E_8, E_8 being the largest exceptional Lie group. This is not *my* idea of
elegant simplicity. This is part of why it's difficult to work with.
Another reason is that the math involved is still being developed;
Newtonian mechanics seemed very difficult at the time because calculus
was new. Also, even simple theories may not be "exactly solvable," and
then it can take a lot of work to get precise quantitative predictions
from them. This is probably a generic phenomenon.
I am currently trying to find a bridge between string theory and the
loop representation of quantum gravity. My "wishful thinking" is that
this will make string theory a whole lot simpler than it is now. (I
have some evidence for this optimism, too.)
Robert Coe
> > A... why should our sense
> > of beauty play a role comparable to experimental data? one reason may be
> > that behind all phenomena there really is a very beautiful, unified
> > theory.
>
> Wishful thinking. It could just as easily get extraordinarily complicated.
> After all---if string theories are so simple, why are they so difficult
> to work with?
Maybe it's because they're wrong.
___ _ - Bob
/__) _ / / ) _ _
(_/__) (_)_(_) (___(_)_(/_______________________________________ b...@1776.COM
Robert K. Coe ** 14 Churchill St, Sudbury, Massachusetts 01776 ** 508-443-3265
Cosma Shalizi
>Actually, string theorists have already succeeded in coming up with the
>Final Theory, answering all questions of physics, and so on. But they
>realized that if they just came right out with it all, it would instantly
>kill off their entire field - in fact, particle theory would become
>obsolete and administrations might use this as an excuse for wholesale
>eliminations of faculty lines, etc. So they burned the manuscripts, so to
>speak. Kind of like Texaco suppressing Free Energy, or our favorite:
>EVIL PHYSICISTS ARE HIDING THE TRUTH !!
theory. Part of it involved Demokritos of Abdera's propounding the
Ultimate Theory in his _Greater World-System_ about -450 - a remarkable
accomplishment, since computers were not invented until the time of
Archimedes... and all of this, mind you, from the postulate that World War
III has already happened. We had a lot of time on our hands.
Cosma Rohilla Shalizi
In Real Life: li...@soda.berkeley.edu
larval physicist
--
"I'd love to hold you/ I'd love to kiss you/ I ain't got time for that now."
-Talking Heads, "Life During Wartime"
"Death needs Time for what it kills to grow in."
-William S. Burroughs, "Ah Pook is Here"
Barry Merriman
> ba...@arnold.math.ucla.edu (Barry Merriman) writes:
> > > A... why should our sense
> > > of beauty play a role comparable to experimental data? one reason may be
> > > that behind all phenomena there really is a very beautiful, unified
> > > theory.
> >
> > Wishful thinking. It could just as easily get extraordinarily complicated.
> > After all---if string theories are so simple, why are they so difficult
> > to work with?
>
> Maybe it's because they're wrong.
Sure they're wrong, but thats besides the point.
Obviosuly, we can only work with theories that are simple enough for us to
understand, and that guarantees a certain level of simplicity, either
in the theory or in its applications.
But these are all statements about _us_, not the universe. So I still
see no reason to think the universe is simple. Rather, we'll only
ever understand those parts of it that are.
Robert Coe
> Obviously, we can only work with theories that are simple enough for us
> to understand, and that guarantees a certain level of simplicity, either
> in the theory or in its applications.
I accept that, but....
> But these are all statements about _us_, not the universe. So I still
> see no reason to think the universe is simple. Rather, we'll only
> ever understand those parts of it that are.
For at least the last 300 years, the really major advances in our under-
standing of the universe have come not from the discovery of increased com-
plexity (important as such discoveries have been), but from the eventual
realization that the complexity could be best understood in the context of
a more global, but ultimately simpler, synthesis. That this keeps happening
may not be a reason to think that the universe is simple. But it is a reason
to suspect that the complexity is not fundamental, but arises from the cumu-
lative effect of the application of simple - and discoverable - principles.
Matt McIrvin
>For at least the last 300 years, the really major advances in our under-
>standing of the universe have come not from the discovery of increased com-
>plexity (important as such discoveries have been), but from the eventual
>realization that the complexity could be best understood in the context of
>a more global, but ultimately simpler, synthesis.
Maybe. And I hope this continues. But it is a little disquieting to
me to observe the state of affairs with the electroweak theory.
This is a theory with great predictive and explanatory power,
that simplifies things in the sense that it identifies weak interactions
as a gauge phenomenon. However, it has some seemingly kludgey aspects, and
calling it a "unification" theory is a bit of a stretch since it has
a non-simple gauge group with two coupling constants, not to mention
the Higgs, and a weird structure with regard to the quarks and leptons.
Compare this with QCD. QCD is simplicity itself by comparison. The
gauge group remains unbroken down to low energies and the couplings
are all vector couplings. There's no fundamental scalar necessary, or
groupings by chirality into gauge singlets and doublets. The downside is
that nobody can do really good calculations since the coupling is so strong.
Now, I fervently hope that this picture, which seems to be groping
toward extreme elegance, turns out to emerge from something simpler and
more beautiful. But I worry that the reason the electroweak part
of the standard model seems so much more complicated than the QCD part
might be that it's better verified! Might QCD turn out to require nasty
tweaking once we get better ways to check theory against experiment?
Of course, the picture is remarkably unified compared to what existed
some decades ago; we're fairly certain that quantum field theory is at
the root of it all, at least down to very small scales, and gauge
interactions seem to be responsible for everything except (possibly)
the Higgs.
--
Matt McIrvin
Matt Austern
> Of course, the picture is remarkably unified compared to what existed
> some decades ago; we're fairly certain that quantum field theory is at
> the root of it all, at least down to very small scales, and gauge
> interactions seem to be responsible for everything except (possibly)
> the Higgs.
I would take out that "possibly". That is: I don't know whether or
not a Higgs really exists (I'm skeptical), but whatever it is that
breaks SU(2)xU(1), I don't think it can be done by pure gauge
interactions. Even if you believe in Technicolor, chiral symmetry
breaking isn't enough: you need something to give mass to the
technifermions, so you've only deferred to problem to a higher energy
scale.
--
Matthew Austern Just keep yelling until you attract a
(510) 644-2618 crowd, then a constituency, a movement, a
aus...@lbl.bitnet faction, an army! If you don't have any
ma...@physics.berkeley.edu solutions, become a part of the problem!
SCOTT I CHASE
>
>Compare this with QCD. QCD is simplicity itself by comparison. The
>gauge group remains unbroken down to low energies and the couplings
>are all vector couplings. There's no fundamental scalar necessary, or
>groupings by chirality into gauge singlets and doublets. The downside is
>that nobody can do really good calculations since the coupling is so strong.
>
>Now, I fervently hope that this picture, which seems to be groping
>toward extreme elegance, turns out to emerge from something simpler and
>more beautiful. But I worry that the reason the electroweak part
>of the standard model seems so much more complicated than the QCD part
>might be that it's better verified! Might QCD turn out to require nasty
>tweaking once we get better ways to check theory against experiment?
Indeed. QCD is much less well tested than the Electoweak sector of
the Standard Model. And QCD has defects, such as the Strong CP problem,
which are not near being resolved anytime soon. I suspect, and this,
of course, is pure speculation, that the apparent simplicity of QCD
is the result more of our Strong Ingorance than due to any intrinsic
"fundamentalness."
Ultimately, we probably will begin to see better hints of whatever
simple underlying theory may exist when we have a better idea of
the proper ingredients of such a theory. If there comes a day when
we have some confidence that we have a list of all the particles that
exist, or, on the contrary, some proof that they constitute an infinite
set, then perhaps the simplicity of the whole thing will become more apparent.
In the meantime, I view the Standard Model as a necessary and appropriate
but probably flawed synthesis. Thirty years of collecting data and
fleshing out the theory have allowed us to construct one coherent explanation
that accounts for many of the facts at hand. But it is probably only
the first of several such steps which we will take on the way to
a complete theory.
This is getting too philophophical. Time to stop.
-Scott
--------------------
Scott I. Chase "It is not a simple life to be a single cell,
SIC...@CSA2.LBL.GOV although I have no right to say so, having
been a single cell so long ago myself that I
have no memory at all of that stage of my
life." - Lewis Thomas
Matt McIrvin
>I would take out that "possibly". That is: I don't know whether or
>not a Higgs really exists (I'm skeptical), but whatever it is that
>breaks SU(2)xU(1), I don't think it can be done by pure gauge
>interactions. Even if you believe in Technicolor, chiral symmetry
>breaking isn't enough: you need something to give mass to the
>technifermions, so you've only deferred to problem to a higher energy
>scale.
You mean "give mass to the ordinary fermions," don't you?
People are still messing around over here with somehow doing that
with extended technicolor bosons, with a "sideways" vertex that
changes a fermion to a technifermion. To me, it seems that
the most realistic models are incredibly baroque, and it's
disquieting to think that the whole motivation is to solve the
gauge hierarchy problem so that the buck can be passed to some
truly humongous GUT gauge group up at 10^15 GeV.
--
Matt McIrvin
Matt Austern
> >Even if you believe in Technicolor, chiral symmetry
> >breaking isn't enough: you need something to give mass to the
> >technifermions, so you've only deferred to problem to a higher energy
> >scale.
>
> You mean "give mass to the ordinary fermions," don't you?
No, I really did mean what I said: I agree that giving mass to the
ordinary fermions in technicolor models is a problem (and that the
proposed solutions to it are extraordinarily ugly, as well as being on
very shaky ground phenomenologically), but it isn't the problem that I
was referring to.
The point is that if the technifermions are massless, then the
technipions will be massless too, since they're just the Goldstone
bosons associated with chiral symmetry breaking. Now that would be OK
if there were only three technipions (they would just become the W and
Z longitudinal modes), but in any technicolor model that's even
semi-realistic, you end up with more than three technipions: the only
way you'd end up with just three of them is if you only had two
technifermions, i.e., if the technicolor global symmetry were
SU(2)xSU(2).
So, somehow, you have to start out with massive techifermions, so
that, as in the case of QCD, the technipions are only approximately
Goldstone bosons. So you're back to the same mess: since
technifermion masses aren't gauge invariant, where do those masses
come from?
--
Matthew Austern Maybe we can eventually make language a
ma...@physics.berkeley.edu complete impediment to understanding.