Exotic Matter

Janx said:

I've seen the Einstein quote about dice and god. Had he recanted his statement later in life?

Click to expand...

Nope. Though he got is Nobel Prize not for Relativity, but for his work on the Photoelectric Effect, a fundamentally quantum process, he had issues with the basic uncertainty of QM - he couldn't accept that the fundamental interactions between particles was not deterministic. He stood by his expectation that eventually, it would be shown that QM was incomplete, and that another theory would be developed that would show that the uncertainty was not real, but an artifact of insufficient information and understanding.

Back to QM, in the past, you've said QM helped us do modern electronics. Are you basically saying String Theory hasn't yielded anything (not just stuff, but tests that indicate the String ideas have merit)?

Click to expand...

Yeah. A fundamental principle of science is that a hypothesis must be, in some way, testable. For something like String Theory, this means it should make predictions that we can, at least in theory, test. We may not have equipment of sufficient sufficient precision to do it yet, but it should be possible in principle. General Relativity, for example, predicts that the orbit of Mercury should precess (and, it does). GR predicts that gravity waves exist, and it seems we've finally detected them. GR and QM both predict loads of physical effects we can look for, and observe.

String theories are a bit short in that department as yet. There are darned few (if any) experiments we can imagine doing, where we'd look at the results and say, "This result is due to the string-nature of reality." String theory has gotten to the point where it is consistent with many other theories for things we already observe, but that may just mean that String Theory is, mathematically, really just the same thing as, say, the Standard model. We'd say one model "is equivalent to" or "reduces to" the other.

Until we can demonstrate that string theory explains real physical effects not explained by other theories, it is really mostly a mathematical curiosity.

Well, I have been silent thus far and I cannot remain son. My opinion on this, as limited as it is, is tus:

1. I am one of the bigger skeptics on dark matter/energy.

2. I am not privy to knowledgeable on issues of what any of this thread is talking on.

3. My answer is going to seem very simplistic, maybe overly so.

4. I believe string theory has made some headway since the last year or two

** perhaps we just haven't seen the effects on computer detection equipment yet. It may be as unobtrusive as neutrinos, just not able to see them in visible light the same as proving the existence of inferred or ultraviolet without the proper equipment or materials.

We may not have had the computing power as yet to detect them.**

Scott DeWar said:

1. I am one of the bigger skeptics on dark matter/energy.

Click to expand...

Just to be clear, this has little to do with the string theory part of the discussion. To my knowledge, string theory does not remove the need for "dark matter" or "dark energy" to explain the behavior of the universe on the large scale.

4. I believe string theory has made some headway since the last year or two

** perhaps we just haven't seen the effects on computer detection equipment yet. It may be as unobtrusive as neutrinos, just not able to see them in visible light the same as proving the existence of inferred or ultraviolet without the proper equipment or materials.

We may not have had the computing power as yet to detect them.**

Click to expand...

Not that I'm aware. The problem isn't, "The theory makes predictions, but our machines aren't good enough yet." The problem is that the predictions string theories make are the same as those made by conventional models. So, there's nothing to say that string theory is the real thing we should be using. String theory is, at best, as good as the simpler models we already have, and doesn't give us anything fundamentally different.

I've seen one argument that string theories suggest that the force of gravity should be material-dependent. So, the pull of the Sun on a metallic asteroid should be different from the Sun's pull on an icy comet of the same mass. However, I've never seen any prediction of *by how much* the pull should be different. Just that they might be different. If you can't make a *particular* prediction, it doesn't count.

We can put on top of that the fact that (again, to my knowledge) nobody has observed such variance. It has to be pretty darned small to have eluded our notice, if it is there.

Umbran said:

Yes. We say that now, in hindsight. It turned out renormalization techniques, and quantum mechanics, were incredibly useful. But, there was a time before these tools were used, when Einstein was still saying that God doesn't play dice with the Universe. There was a time when QM was considered wacky, and many of the brightest felt it wouldn't go anywhere. My pofessors noted that there had been calls of the form, "Look at those infinities! It's clearly non-physical! Don't worry about it!" Aren't you glad they didn't listen to the naysayers?

So, I'm not a big fan of pre-judging. The results will speak for themselves, eventually.

Click to expand...

Oh, of course. I don't listen to naysayers either. But I will just say again that the development of quantum mechanics is a very different situation than what I mentioned above. And it's ok to have difficulties in the development of a theory. However, there is always a need for scientists to make educated guesses at what will be productive areas of research. My guess is that it is less productive to study theories that are just made up from whole cloth and then struggling to show that they are not nonsensical. Of course there's a spectrum, and it's worth trying things, but I am not the only physicist that questions, for example, why certain papers get press releases and others don't.

I've cast shade on string theory, in the form of "been at it for decades, still not much in terms of testable predictions," form*. I have never said they shouldn't have bothered ever trying the theories out, though - I only gripe that after so long, perhaps we should have some of these brilliant people looking down other avenues. I believe I am officially without preference on Dark Matter models, other than noting that certain forms seem to have been largely ruled out by observations. Again, I don't believe I've ever said folks shouldn't have investigated the various models.

Click to expand...

No, I don't think so, and I don't think you'll find me saying here that people shouldn't have investigated various models, either, but rather that I personally feel certain directions are perhaps over-represented. It seems like you're saying the same thing about string theory just in this paragraph --- maybe it would be good to have smart people looking at other avenues. I've noticed that the EN World community (at least in this Misc Forum) is fairly curious about science, so I try to offer my professional opinion for those interested in what someone who reads a lot of papers and follows what's going on in this branch of physics on a daily basis thinks. I'm also not casting aspersions on Morris and Thorne. I suspect they didn't realize the kind of interest they would generate, either, since AFAICT their initial article was in a publication that is mostly for the professional development of physics teachers, not a normal research journal.

Scott DeWar said:

Well, I have been silent thus far and I cannot remain son. My opinion on this, as limited as it is, is tus:

1. I am one of the bigger skeptics on dark matter/energy.

Click to expand...

There's extremely strong evidence for dark matter. I made quite a long post about it last year in my AMA thread here. I'm happy to elaborate or answer questions, but that's a good place to start. There's also quite good evidence that the expansion of the universe is accelerating, which is due to what we call "dark energy."

Umbran said:

Not that I'm aware. The problem isn't, "The theory makes predictions, but our machines aren't good enough yet." The problem is that the predictions string theories make are the same as those made by conventional models. So, there's nothing to say that string theory is the real thing we should be using. String theory is, at best, as good as the simpler models we already have, and doesn't give us anything fundamentally different.

Click to expand...

I don't want to be too blunt, but that's just incorrect, actually. If you build a big enough particle collider, you will see a very distinctive spectrum of resonances ("new particles") corresponding to the vibrational states of strings. This will be on top of the other distinctive, but more model-dependent spectrum of resonances due to the presence of some kind of extra dimensions. Now, is it possible to make some other model without strings that looks exactly the same way? Yes, if you make up an infinite number of new particles with exactly the right properties. It is also possible to describe the solar system with the earth at the center if you ignore Newtonian gravity and set up a bunch of epicycles, but we don't think of that as being the correct thing to do.

It is of course not feasible to build a collider like this with current technology --- if you tried to scale up the LHC, you'd likely have to build something a significant fraction of the size of the solar system, given typical guesses about the scale of string theory. But the problem is exactly "The theory makes predictions, but our machines aren't good enough yet" for this most basic prediction.

Here's another prediction of string theory: the existence of gravity. That's a little flippant, but it's true --- no one expected gravity to turn up in string theory when it was first invented. No other theory can explain why there is gravity, either.

More on this later, at least if people are interested.

freyar said:

I don't want to be too blunt, but that's just incorrect, actually.

Click to expand...

I don't mind blunt - I've been wrong before, and I am sure I'll be wrong again. I hope I will not be like Einstein and not ever admit an error. But, be blunt, not everyone agrees with you. Or, in another way to put it, there are a few too many dodges to make me comfortable.

If you build a big enough particle collider, you will see a very distinctive spectrum of resonances ("new particles") corresponding to the vibrational states of strings. This will be on top of the other distinctive, but more model-dependent spectrum of resonances due to the presence of some kind of extra dimensions.

Click to expand...

I will grant you that if you do an experiment at high energy, but well below the Planck energy, and see such resonances, then yes, you'd have evidence for strings. Except... you might not see those things, and failing to see them doesn't invalidate the theory.

The models that predict these are based in perturbative string theory, no? That's explicitly an approximation, and to my understanding it is not at all clear that you expect that behavior in reality (which, as far as we can tell, is not perturbative). Last I read, M-Theory, in general, does not require such resonances. And there's a bazillion ways to collapse the multiple dimensions required by string theory down into 3d models that give particular predictions of what resonances you see - so, if you run an experiment, and it fails to show the resonances, you just say, "Well, I have the wrong perturbative series/compactification, but string theory hasn't been disproven!"

And, if you do somehow manage to run a test up a Planck energies, you still have an issue - more conventional theory also predicts that you will see some really strange things there (like black hole states), so you can't tell if what you are seeing is string theory, or something else.

Thus, the whole thing leans to the non-falsifiable. If you can always dodge and say that your theory is still correct, there's an issue.

Meanwhile, the most recent stuff I saw on quark-gluon plasmas coming our of the LHC *failed* to match the string models used to describe them. And no SUSY, though that should have been seen in Bs decay.

Back in the 1980s, Feynman stated concerns that there was rather too much hype and groupthink surrounding string theory, and I don't see a lot of evidence that's gone away. How many times does a model we've been trying to develop for 40 years have to fail to meet expectations before we collectively stop apologizing for it? So, as you say above - yes, I think it fair to say that at this point string theory is over-represented, and we should start putting more legitimacy on other avenues of thought. While there may be some people here or there working on other things, it seems to me that the community as a whole really has all the eggs in one basket.

Umbran said:

I will grant you that if you do an experiment at high energy, but well below the Planck energy, and see such resonances, then yes, you'd have evidence for strings. Except... you might not see those things, and failing to see them doesn't invalidate the theory.

Click to expand...

The models that predict these are based in perturbative string theory, no? That's explicitly an approximation, and to my understanding it is not at all clear that you expect that behavior in reality (which, as far as we can tell, is not perturbative). Last I read, M-Theory, in general, does not require such resonances. And there's a bazillion ways to collapse the multiple dimensions required by string theory down into 3d models that give particular predictions of what resonances you see - so, if you run an experiment, and it fails to show the resonances, you just say, "Well, I have the wrong perturbative series/compactification, but string theory hasn't been disproven!"

Click to expand...

While I will grant that we don't know the final high-energy description of M-theory yet and can't give a quantitative prediction, the expectation would be to have membrane resonances there. As for the perturbative/nonperturbative issue, one of the neat/amazing things about the framework of string theory is that almost every point in parameter space, even if it looks naively nonperturbative, can be mapped to another description where perturbation theory works pretty well. (Remember that the coupling constant doesn't actually have to be that small for perturbation theory to be ok.) So you would generically (in the technical sense) see stringy/membrany resonances with some width. They'd only mush out and become indistinguishable (and get pushed right up to the Planck scale) in an unusual area of parameter space. So, say you don't see the resonances. Then, just as in every other theory/model, you can put limits on parameters. This is worth emphasizing. If I have any proposed theory, there is some kind of free parameter(s) to fit to experiment, and your prediction depends on those parameters. So the totally normal case of "falsifiability" means being able to put limits on free parameters. It's only when you have some way to measure parameters and then make an additional measurement that you can make a quantitative and possibly unique prediction. String theory is no different than any other theory in that way. Now, by the time we can build a Planck-scale (or even a bit below) accelerator, it's quite possible we could measure various parameters of string theory with cosmological measurements (or, more precisely, say what the parameters would be if string theory correctly describes cosmology), which would allow quantitative predictions for the collider results. Again, falsifiable like anything else.

And, if you do somehow manage to run a test up a Planck energies, you still have an issue - more conventional theory also predicts that you will see some really strange things there (like black hole states), so you can't tell if what you are seeing is string theory, or something else.

Click to expand...

Again, generically, the string resonances should be lower-energy than black holes. And, of course, to understand quantum black holes in a particle collider, you need some kind of quantum gravity theory, none of which are conventional field theories. In more general situations, yes, it is generally possible to cook up a quantum field theory that does basically anything that string theory or any other CPT-preserving unitary theory can do. But that may require a lot of epicycles. At what point do you allow Occam's razor?

Thus, the whole thing leans to the non-falsifiable. If you can always dodge and say that your theory is still correct, there's an issue.

Click to expand...

Let me ask a rhetorical question. Do you think quantum field theory is falsifiable? I can certainly falsify specific quantum field theories, but within the framework of QFT, it's possible to get many many different results and/or avoid all kinds of limits. It's a similar situation with string theory --- there are many possibilities overall, but a given set-up can be ruled out or limited as normal.

Meanwhile, the most recent stuff I saw on quark-gluon plasmas coming our of the LHC *failed* to match the string models used to describe them. And no SUSY, though that should have been seen in Bs decay.

Click to expand...

We need to be careful here. We've so far been talking about string theory as a "theory of everything" (or ultimate description of the universe). With the quark-gluon plasma issue, you're now talking about string theory as a dual description of nuclear physics, meaning it's a way to calculate in a theory (quantum chromodynamics) where calculations by usual means are prohibitively difficult. In that case, it would have been a big surprise to see quantitative agreement between the string models and the experiment, because the precise string models used are not supposed to describe real-world QCD closely but rather similar theories which are a bit easier to work with. The lesson here is that QCD is hard, and we have a way to go with both traditional methods and dual string theories. It's worth noting that the first qualitative understanding of quark-gluon plasma results from RHIC was due to a dual string theory model.

As for supersymmetry, you're again talking about limits on parameter space. Yes, there are now strong limits on the minimal version of SUSY, though it's not nearly closed off yet (I'd warn against articles in the popular press about that, though, since the "SUSY is ruled out" soundbite sounds so good despite being inaccurate according to community consensus). On the other hand, the Standard Model is a far-from-minimal extension of the subatomic physics we knew 100 years ago, so it's maybe not so surprising if low-energy supersymmetry turns out to be non-minimal.

Back in the 1980s, Feynman stated concerns that there was rather too much hype and groupthink surrounding string theory, and I don't see a lot of evidence that's gone away. How many times does a model we've been trying to develop for 40 years have to fail to meet expectations before we collectively stop apologizing for it? So, as you say above - yes, I think it fair to say that at this point string theory is over-represented, and we should start putting more legitimacy on other avenues of thought. While there may be some people here or there working on other things, it seems to me that the community as a whole really has all the eggs in one basket.

Click to expand...

Interestingly, I used to work at CalTech, where of course Feynman spent a large part of career, and so has John Schwarz, known as "the father of string theory" (and, at least until his recent retirement, the resident of Feynman's old office). From what Schwarz and others who were there with Feynman have told me, Feynman was not so negative about string theory in general as his famous quote would lead you to believe and was in fact supportive of Schwarz's work, at least.

Anyway, I'm starting to feel like we're just getting into a back-and-forth (and rather away from the OP's topic) between just the two of us, so I'll leave with a last couple of thoughts unless other posters ask for more information:
1) It's certainly fair to have an opinion that string theory is over-represented. It's an opinion. I'd note that there are actually quite a few people working in different areas of quantum gravity. Though they are not as unified in what they're working on, I wouldn't classify it as "all the eggs in one basket." Anyway, it's also fair to note that there is sometimes overlap between different approaches (including string theory) and that all approaches to quantum gravity face the same fundamental obstacle in making predictions --- they have to extrapolate over about 16 orders of magnitude in energy. If you think quantum gravity is worth understanding, it's going to take time, no matter what approach you favor.
2) If it seems like string theorists have been "apologizing" a lot, it's because a relatively small handful of physicists decided to attack it in the popular press. There isn't a need to apologize --- string theory has actually been remarkably productive whether or not it is an ultimate theory of everything. I don't have time to type it all out, but it has led to numerous important discoveries in mathematics (related to more than one Fields medal), new ways to evaluate scattering amplitudes of relevance to the LHC, dual formulations of many field theories, phenomenological models of extra dimensions and cosmology, and recently improved understanding of complex systems in condensed matter physics also through dualities.

So from what I gather, when we talk about exotic matter, we're more in the realm of fiction than science. It's strictly a placeholder value to make a formula work? Is that a fair assessment?

If we're in the realm of fiction, let's make the assumption that matter with such properties exists.
To overcome the problem of a particle that repels instead of attracts (at the same strength, but negative, of normal attraction), could it be possible that said particle has magnetic properties? That during a planet'ss formation it could have attached itself to a ferrimagnetic material? Thus allowing deposits to form on the planet. And I don't possible in the sense of, it's fiction so anything is possible. I mean, is there any rule that says an material with a repelling force can't also be magnetic?

I wonder if anyone, as an intellectual exercise, has tried to figure out what such matter would look like. I mean, if you know all the properties of a certain particle, shouldn't it be possible to know what color it has, and how it feels?

Joker said:

It's strictly a placeholder value to make a formula work? Is that a fair assessment?

Click to expand...

It is not *strictly* a placeholder. There are examples of things that we are pretty sure exist, but just aren't like the normal matter that makes up your dinner table. And it isn't usually so much that you put a placeholder value in to make an equation work - that's just making crap up.

In some instances, the exotic matter has never directly observed the material, but *everything* we know and observe says it should exist (neutronium, degenerate matter). In others, it is the most reasonable physical interpretation that best describes what we see in the universe (Dark Matter and Dark Energy, f'rex). And in yet other instances, it is a result of asking, "Assume this effect occurs. What does that imply?" If the effect doesn't actually happen, then the material probably doesn't exist. This is the wormhole-exotic matter case. This last is the more speculative.

And I don't possible in the sense of, it's fiction so anything is possible. I mean, is there any rule that says an material with a repelling force can't also be magnetic?

Click to expand...

Well, in most cases, you are positing the existence of a material to fit a very particular problem. In such cases, you are fairly restricted in terms of what properties the stuff can have and still be consistent with what we do know. Dark Matter, for example - if it interacts by means other than gravity and perhaps the weak nuclear force, it won't fit what we observe in the universe.

If you want ot create complete fiction, and posit a material with arbitrary properties, that's fine, but this solves no problems.

I wonder if anyone, as an intellectual exercise, has tried to figure out what such matter would look like. I mean, if you know all the properties of a certain particle, shouldn't it be possible to know what color it has, and how it feels?

Click to expand...

Well, individual particles do not have "color" in the visual sense, nor texture. These are properties of matter in bulk, often dependent on how the material comes to be - carbon can be opaque grey graphite powder, or clear solid diamond, for example.