Dax discussions of Beyond SM theories/including newcomer questions

[Lt_Dax]

Using your analogy though, imagine your person has one leg, what do you do stand, or sit? Or move onwards.

But this person (physics) still has two legs, but one is immobile. You try to get the stiff leg moving again, and stand still until you can move again, otherwise you fall over. The analogy works well because theory and experiment are never separated, by definition.

 

[JustinLevy]

There is also NO experimental evidence for anything BEYOND the Standard Model.

Gravity, hence this whole discussion.

Also:
Dark matter.
Dark energy.
Whatever the heck the results of LSND mean for neutrinos.
Possibly the g-2 result for muons.

My point remains: these pursuits for theory beyond the standard model ARE motivated by experimental results. If we had more data, our efforts may be more successful, but that is a separate issue.

@JustinLevy

So are you saying that decoupling from experiment is justified if we have no choice?

My main point was, and continues to be, these efforts are due to experimental evidence. Experiment is forcing us to add something new to our usual tools or postulates. All that remains is what is this? Experiment is forcing this choice. So how is it decoupling from experiment?

If we had a theory that explained all the experimental data fine, then a theory with many extra dimensions and strings and so on would of course be only useful for mathematical investigations. We don't have a simple theory of quantum gravity though.

I'm not convinced that you can learn anything about the universe without observing it.

I'm not suggesting we don't observe it. But ignoring the experimental evidence that shows our current theories are wrong, so we need to work to come up with a replacement theory, would be removing the "predictions" part of the scientific method.

Even if our ideas are correct they have to be tested

Yes. Hence the conference on experimental quantum gravity. Hence people trying very hard to get M-Theory to the point where they can calculate predictions like the mass of the electron, etc.

In some sense experiment is way way ahead of theory. We don't have a theory that can calculate predictions which can consistently match all of the experimental data yet. All simple approaches have shown to be wrong and ruled out. People are trying. People are working to do exactly what you are hoping for: holding experimental data king, and find a self consistent model to describe all this data. They have yet to succeed.

So complaining about that these theories predict beyond what can be measured yet seems moot. Let them continue working to even get a theory that matches all experiment first. We still have a long way to go.

This is why (@ Kevin Axion) I think the idea of ST "breakthroughs" is flawed - how do you tell if something is a breakthrough unless you test it to see if it is?

It is a breakthrough because after decades of trying, it is the first approach that seems like it could possibly work. It isn't even a full fledged "theory" yet, more of a framework. So much still needs to be done on the theory side before we can fully compare to experiment.

Who knows, maybe this idea won't match with the effective electron and muon masses or whatnot. But to complain that people aren't trying to find a "minimal" quantum gravity ... when that is exactly what people ARE trying to do ... well, it severely confuses me.

 

[JustinLevy]

By the way I won't participate in this thread any longer if it just becomes a means to sigh and groan and tell the student to wise up. The view of science I have may seem radical, but it was normal in the past.

I'm sorry to hear that.

I wish you wouldn't leave thinking that science isn't driven by the need to explain experimental results. Because it is. It is this drive that has lead to so many strange seeming suggestions for quantum gravity. No one can explain all the data quantitatively yet. People are trying very very hard.

 

[Kevin_Axion]

Precisely my point, if one is immobile you can't hinder the other. If theorists hadn't invented SST or LQG then experiments would proceed. But experiments have reached a plateau, until the LHC finally starts deciphering information then we may see new physics. But theorists are original thinkers, they imagine, much progress has been made in this fashion and experiments made the conclusions. We have different perspectives and I respect yours, and I do sound harsh, but that is only because people come on this general sub-forum and completely deter String Theory and only focus on one idea falsifiability. Although, you do raise very critical points and am willing to listen.

 

[Lt_Dax]

But to complain that people aren't trying to find a "minimal" quantum gravity ... when that is exactly what people ARE trying to do ... well, it severely confuses me.

These efforts would arguably be minimal if we had proof that a string is the only possible fundamental object.

 

[Kevin_Axion]

JustinLevy, I mean there is no experimental evidence for a theory Beyond the Standard Model, I do understand that there is remaining problems and physics beyond as I stated these ideas in my original post.

 

[Lt_Dax]

We have different perspectives and I respect yours, and I do sound harsh, but that is only because people come on this general sub-forum and completely deter String Theory and only focus on one idea falsifiability.

You may find it interesting that I view the falsifiability argument as a meaningless distraction - I care little about it, since an unfalsifiable theory may become falsifiable in the future; this is in my original post. My criticisms of ST are different, it's more to do with how we do science and how we discover real knowledge.

 

[Kevin_Axion]

Yes, real knowledge precisely what we are lacking. I suppose you are right in that sense. We need real knowledge through experiments, but Theoretical knowledge is just as convincing. I suggest the idea of Bekenstein-Hawking Radiation, an unobserved phenomena but widely accepted. It is because it just seems right, as does SST, that doesn't mean it is though.

 

[JustinLevy]

These efforts would arguably be minimal if we had proof that a string is the only possible fundamental object.

Come on, are you seriously suggesting people are not searching of a minimal description of quantum gravity?

People would LOVE to find a consistent 4-d field theory version of quantum gravity.

You ask why is string theory considered an advance, it is because this appears to be a possible explanation. This is a huge step forward.

Would you feel more comfortable if we worded it as:
For decades no consistent approach to quantum gravity could be found. People tried to add many different degrees of freedom, or use other mathematical tools, to cancel out divergences. Nothing seemed to work. String theory represents our first data point for finding an upper bound on the minimal amount that needs to be added to find a consistent theory of quantum gravity.

Theorists worked hard to get this data point. The information provided by this data-point should not be dismissed.

It's an awkward way to word it, but as already stated, there is no mathematical nor experimental claim that string theory IS the minimal explanation. I did not claim it was the minimum. I explicitly stated the opposite.

 

[JustinLevy]

JustinLevy, I mean there is no experimental evidence for a theory Beyond the Standard Model, I do understand that there is remaining problems and physics beyond as I stated these ideas in my original post.

You seem to be making the same claim that Dax is making, which is confusing me.

How is experimental evidence of gravity, NOT experimental evidence beyond the standard model? Same with dark matter, which is not in the standard model either.

If you claim there isn't evidence beyond the standard model, then all efforts to get theories beyond the standard model DO appear to have no experimental motivation. Which falls right into Dax's complaint.

EDIT:
To make it more clear, I am trying to separate two things:
1) Experimental Evidence showing our current theories are wrong (or at least need adjusting/ something added)
2) Experimental data on gravity at a scale where the quantum corrections become clear over the classical effects

We already have #1. We have yet to get a theory to resolve this. In this sense, experiment has been ahead of theory for close to a century.

We do not have #2. This does not mean we don't have evidence for something "beyond the standard model", or need for figuring out how to get GR as a classical limit of a quantum theory.

 

[Kevin_Axion]

I am saying that dark matter and dark energy aren't concepts that give us a framework but yes they do suggest something beyond the Standard Model.

 

[bcrowell]

It seems to me that some of the responses to Lt_Dax have involved a lot more hand-wringing and ruffled feathers than was necessary. I think Lt_Dax's original post was spot on. If it hurts people's feelings, then the right response is to calm down, put those feelings aside, and try to write a response that answers intellectual points with intellectual points.

There is a reason it's called theoretical physics.

What is this supposed to mean? Does it mean that theoretical physics is not supposed to make contact with experiment?

The answer is easy I don't understand why we always have to revisit the issue.

1.we have experimental data: we use it

2.we don't have experimental data:
a. we do what we can
b. we do nothing

Choose between a and b.

Well, my opinion is that the answer should be 2b, in the sense that pursuits like LQG and string theory should get zero institutional support. (And this is not the same as saying that nobody will ever do any work on them. Once someone has tenure at a university, you can't stop him/her from working on something s/he finds compelling.)

 

[Kevin_Axion]

Yes it is supposed to make contact with experiment but you don't need experiments to research theoretical physics, it's a purely logical subject based on reason and deduction. Others would differ as the OP has and I absolutely accept that viewpoint I was just expressing my own.

 

[negru]

Well, my opinion is that the answer should be 2b, in the sense that pursuits like LQG and string theory should get zero institutional support. (And this is not the same as saying that nobody will ever do any work on them. Once someone has tenure at a university, you can't stop him/her from working on something s/he finds compelling.)

Well you see this is the issue. If the problem with "dubious" research is the funding, I'd have to agree with you. However, I also find "research" in literature, or humanities in general to be pretty worthless. Does that mean we should cut funding?

And why should tenured people be allowed to work on whatever they want? What's so special about them? Pretty much all universities receive federal funding whether they're private or not, so it's still tax money funding tenured profs.

 

[MTd2]

Well you see this is the issue. If the problem with "dubious" research is the funding, I'd have to agree with you. However, I also find "research" in literature, or humanities in general to be pretty worthless. Does that mean we should cut funding?

Humanities can arguably be in touch with reality. But some areas of it, like paranormal research, still get funding from governments. I think QG and paranormal are in the same zone of priority according to bcrowell.

 

[Lt_Dax]

@Justin Levy

To make it more clear, I am trying to separate two things:
1) Experimental Evidence showing our current theories are wrong (or at least need adjusting/ something added)
2) Experimental data on gravity at a scale where the quantum corrections become clear over the classical effects

We already have #1. We have yet to get a theory to resolve this. In this sense, experiment has been ahead of theory for close to a century.

We do not have #2. This does not mean we don't have evidence for something "beyond the standard model", or need for figuring out how to get GR as a classical limit of a quantum theory.

This is the key. I think some have mistakenly thought that I don't believe there is evidence that our current theories need revising. On the contrary, one thing I have emphasized repeatedly is that not only do we have such evidence, but we probably have a lot more than we think (the "long list of unsolved problems" concept).

The main cause of confusion is that some people are saying that such evidence justifies developing entire 'frameworks' aside from experiment. This is bizarre because the actual point shows that we are not devoid of data or experimental oddities (I think this is a pernicious myth). The trend towards massive model building such as string theory is a separate issue, and seems motivated more by grandiose desires to build a theory of everything, not a lack of unsolved observational problems to work on.

My view, which could be overly simplistic, is that we should do theoretical physics by examining experimental problems. The g-2 may be a good example, and there are other examples (which people have mentioned) of where we need to extend or revise the standard model. The development of ST seems to be a separate exercise. I'm sorry to say, I find the concept of doing 'theoretical research' alone somewhat strange. The g-2 people, for example, do their research in concert with experimentalists. The other two main divisions of theoretical physics (Lattice Gauge Theory, Particle Phenomenology) fit the "old", proper definition of what theory is. The meaning of the word "theory" really does matter. If it didn't matter, then we can basically just do anything we want, no matter how wild. If "theoretical" physics is no longer a part of physics (an experimental science by definition), then that would probably result in a huge mountain of 'theory' papers which say a lot but explain very little.

So I don't question that there is physics beyond the standard model, I think there is evidence for that already, I want to make that clear. My main question is about why string theorists use such incredible language to describe what they are doing. Is it really justified to say we have had a "revolution" (or two, no less) even though it hasn't been confirmed experimentally? The two real revolutions of the early 20th century were tightly linked to experiment, front and back.* The Standard Model in the 60s and 70s is a brilliant example of a highly predictive theory which was developed and verified at famous particle accelerators in the USA and CERN in cooperation with theorists, but even with this level of success, they never ever made unwarranted claims about the importance of the theory. They knew that they could only be sure it was right up to a certain energy scale. Wilsonian renormalization taught us that beautifully.

Again regarding language, why do we describe the development of string theory as discovery? This is not a question regarding its usefulness in pure mathematics, or how interesting it is, it is a question about whether we can discover a real fact about the universe by writing down a new equation. In the Standard Model, didn't we write down equations to explain new observations (e.g. the QCD lagrangian wasn't written down before we had experimental knowledge of the features of the strong force). String theory doesn't just claim to explain what we already know, it is so unconstrained that it results in a unified theory (which may or may not be the case) and even branes and multiverses (which may or may not exist). Is this discovery? I'm still certain we've never done anything like this in the past, and surely it is false that we don't have any new data to work with?

* Not only that, but the judgment of whether something is a revolution is not made by the practitioners of the subject at that precise moment. It is typically made in the future, and it is typically made by others. So what makes Green, Witten et. al. so comfortable using these words?

 

[Lt_Dax]

By the way I'm still not purely making assertions - my questions are not all rhetorical. If any cool heads can explain why pure model building can be real discovery even without experiment, then I welcome it.

One thing I may anticipate is the "argument from beauty" - i.e. Dirac did it, so that's what we're doing. Well, I think there are essential differences (Dirac didn't develop the theory with exotic objects and dimensions, only new matrices), but apart from anything else, to use an old quark physics pun, truth comes before beauty. (This may be why Dirac was nervous about calculating g from his equation and left it til the next day, assuming he was nervous).

 

[suprised]

What is routinely neglected in these discussions, is that there are, as a matter of fact, extremely non-trivial computational results! For example, state counting in black holes. This is a theoretical arena where the two pillars of modern physics, GR and QM, seem to clash and strings provide a way to reconcile these. It is very non-trivial that this, and many other things, do work at all! This is what has been "discovered" and the reason for excitement.

It is simply not so that string theory is an unmotivated "belief" and people just say: well let's postulate that we have those little strings and see what comes out. If it doesn't work, we "believe" instead in membranes, or yellow octopi, for that matter.

On the contrary, strings are a framework, or machine, that seems to "work" and make sense as a physical model, whenever one checks something, so many people view this as very meaningful and not as a random idea. This is a very important point and sets it apart from countless other attempts that have been tried in the past. Whether it directly or indirectly applies to nature is a different question. It is in principle testable, so qualifies as a scientific theory despite certain people want to deny this.

 

[Lt_Dax]

@suprised, you make some interesting points, but I'm not convinced that what makes a scientific theory is falsifiability - as I've said before, I think this is given greater importance than it deserves. An unfalsifiable idea may become falsifiable as technology advances, so it's irrelevant. All ideas are falsifiable in principle. Something only achieves theory status when it has been experimentally confirmed (and repeatedly!). We say this to creationists all the time when they claim that evolution is only a theory. Is it one rule for creationists, another for us?

It is very clear that string theory is not just a random idea. From what I know of it, it is a remarkable construction, but I think you can see that the implications of string theory go way beyond just state counting in black holes. It opens up a whole new can of worms, a vast array of new predictions. The demands upon String Model to make it String Theory are very big. (I might not be expressing this viewpoint very clearly so i apologize if that's the case.)

The real test of a 'theory of everything' is that it can explain everything, old experimental results and new experimental results. Isn't that a tall order?

 

[suprised]

Well what one calls theory is semantics, there is eg in mathematics also the theory of modular forms and countless other "theories", so the string phyisicists just don't care how their field of research is called and go on. It is the self-declared critics who are obsessed with this kind of questions, in particular with falsifiability.

The string physicists are more interested in positive questions, like what can be learned from the results and how to make further progress. This is right now mainly conceptual, ie about understanding how things works. An example is holography in quantum gravity, which is a spin-off of string theory and seems to be a central point of quantum gravity. Many see this as one of the most important insight in theoretical physics in the last decades; if the naysayers would have had their will, this kind of research would have been stopped since long, and an enormous damage would have resulted. Fortunately, and for good reasons, the naysayers don't matter! Most of them are not even scientists.

Of course ultimatively the goal is to make contact with experiment, but this goal is far away (if it ever can be reached), so people content themselves with more modest goals for the time being. They are difficult enough.

 

[Kevin_Axion]

That's exactly the points I was trying to address, surprised, you're a string theorist, correct?

 

[Lt_Dax]

Well what one calls theory is semantics, there is eg in mathematics also the theory of modular forms and countless other "theories", so the string phyisicists just don't care how their field of research is called and go on. It is the self-declared critics who are obsessed with this kind of questions, in particular with falsifiability.

Semantics (meaning) really does matter! It's unfair of you to call me a self-declared and obsessed critic because of that. The meaning of things really does matter, because if words can mean anything, then the discussion becomes meaningless. (And as I've said, I don't care about falsifiability because all ideas are "in principle" falsifiable).

Your comment about parts of mathematics which are called "theories" illustrates the point. I'm not talking about those parts of mathematics which can be called "formal theories" - where the word formal is used because we adhere to mathematical standards of proof. I am talking about "empirical theories" - which is what we mean when we call something a scientific theory. "Proof" in what scientists call a theory means something different.

Maybe the problem is that many string theorists trained as mathematicians, so they think that the only thing that matters is proof in mathematical sense?

The string physicists are more interested in positive questions, like what can be learned from the results and how to make further progress.

Again, your semantics are unclear to me. What do you mean by "results"? Part of the whole problem seems to be that people involved with speculative models feel comfortable with building upon results which haven't been rubber stamped by experiment yet. In the past, you could only build such a house of cards if you know that the foundations are correct.

In real science, contact with experiment is not a "goal", it is part of the enterprise. Right up until the 1980s it was always very close by.

Here's the problem: even for very high energy physics which might require something like a string theory, the cry of being devoid of experiments is false. Cosmological or even some condensed matter physics results may be capable of showing things which we can't do in a super accelerator (again some of these reports have been prominent lately). The point is that you develop a theory from these results, not in anticipation of them. This is what the creationism cartoon was mocking.

(And I believe there is a lot to be learned about how science works from the evolution/creation debate).

By the way, I'm beginning to wonder if string theorists often find no further recourse than a personal attack of some form. I realize that some of what I say is uncomfortable, but I'd prefer a crystal clear answer to some of my questions than accusations about personal character.

 

[negru]

@suprised, you make some interesting points, but I'm not convinced that what makes a scientific theory is falsifiability - as I've said before, I think this is given greater importance than it deserves.

So who exactly gives it greater importance than it deserves? The people who work on it? It's their business what they're interested in. The people who fund it? See my post above.

 

[Lt_Dax]

So who exactly gives it greater importance than it deserves? The people who work on it?

No, the usual low-quality critics of string theory who haven't really thought about it. The problem is that string theorists then spend too much time trying to claim that string theory is in principle falsifiable, even though it is irrelevant either way.

And I have to say, if someone's career is publicly funded, then the public has a say in what they work on. It's our job to explain to people how we're advancing physics. If they're self funded, then that's different.

 

[negru]

By the way, I'm beginning to wonder if string theorists often find no further recourse than a personal attack of some form. I realize that some of what I say is uncomfortable, but I'd prefer a crystal clear answer to some of my questions than accusations about personal character.

What you're saying is neither uncomfortable nor new, just usually uninformed, if you don't know what kind of results surprised is referring to. There have been a great deal of results coming out of string theory which apply to day-to-day physics, like scattering amplitudes in qcd. Today the easiest way to compute scattering amplitudes is via string theory.
Not to mention things like the klt relations. This has all been discussed hundreds of times on this forum. Just these applications to scattering amplitudes means that string theory will never go away, because it is directly intertwined with gauge theory and gravity. If there's any other qg theory out there, it will either be eaten by string theory, or eat it itself.


But of course, if string theory only says new things about old stuff, it wasn't actually needed in the first place, and if it says something completely new it's out of touch with reality.

 

[negru]

No, the usual low-quality critics of string theory who haven't really thought about it. The problem is that string theorists then spend too much time trying to claim that string theory is in principle falsifiable, even though it is irrelevant either way.

And I have to say, if someone's career is publicly funded, then the public has a say in what they work on. It's our job to explain to people how we're advancing physics. If they're self funded, then that's different.

You have good intentions, but seriously, the public doesn't know the difference between quantum physics and teleportation. Most people who come to this forum don't know this, despite having a greater than average interest in physics.

This isn't to say that whoever gives the money shouldn't have the last say, but the say will always be uniformed. The public will want to continue research in QM because they want teleportation, and they will want research in string theory because they want wormholes.

 

[Lt_Dax]

There have been a great deal of results coming out of string theory which apply to day-to-day physics, like scattering amplitudes in qcd. Today the easiest way to compute scattering amplitudes is via string theory.

Why reinvent the wheel? I'm not uninformed about these "results", so please don't make uncalled for accusations, I just don't view them as necessary. If they are just a calculational device, then are you saying that you don't really believe strings exist? Is this just like using complex plane integration to simplify tricky integrals in the real plane?

Just these applications to scattering amplitudes means that string theory will never go away, because it is directly intertwined with gauge theory and gravity.

Has this "calculational device" approach ever explained things which the standard model could never explain? Has it made new predictions beyond the standard model which we can search for soon? If the answer to both is no, then was it a waste of time?

 

[friend]

Maybe it would help to think in more general terms what a theory of everything would accomplish and what issues it would raise.

It might be with experiment we can discover smaller and smaller particles, and with time we can discover more interesting mathematical structures that describe them. But just because we can measure the properties of these smaller particles doesn't mean that we have an explanation for them. And just because we can predict their rate of occurance doesn't mean we understand why they exist.

We will always be asking why things are as they are until we can derive physics from the principles of reason alone. I think that's the ideal for a theory of everything, to be derived from logic alone. Such a theory would explain where the principles of QM and GR come from to begin with and why the SM has the constants it has. And I'm not so sure we're far off from that goal.

Then what becomes of the questions of falsifiability? Can you falsify a mathematical equation? Can you falsify a logical deduction? If the logic is impecible that give the physical prediction, then what are we to think if measurements are contrary? What are we to question, our sight or our reason? Perhaps that delemma is one reason many may be uncomfortable with supporting such efforts. Yet, isn't it the ultimate goal of science to "explain" everything - to prove that the universe is perfectly logical - to derive physics from logic?

 

[Lt_Dax]

This isn't to say that whoever gives the money shouldn't have the last say, but the say will always be uniformed. The public will want to continue research in QM because they want teleportation, and they will want research in string theory because they want wormholes.

Are you saying that we can just work on what we want, with a loose definition of how to build a scientific theory, because the unwashed plebians won't be able to tell the difference either way? I'm not comfortable with that view of the public.

 

[negru]

Has multiplication explained anything that addition could never explain?

Has QFT ever explained anything SR and QM could never explain?