Forgive me for being a bit thick here but I'm just trying to understand some basics which were outside of my high school physics and we didn;t deal with in the limited Phys Chem I did at University.

Is there any conclusive evidence that GR/QT are more than mathematic models and are infact reality. Is it possible that Space and Time aren't actually components of the same thing for instance, but instead its just that the GR model works as if they are and can predict correct results with high degree of accurancy. I guess the second question is would it effect anything if this were the case? I ask becuase I can't help but wonder why the universe changes its nature at ~ the plank length

it seems contrary to reason to my admittedly uneducated brain on this subject that the laws of nature would not be mutally consistent at all scales.

Is it just gravity which is causing the problem or are the other forces also suffering at the plank length between two different models. If its just gravity then I want to know why (if anyone has a clue) gravity is so complex in comparison to the other forces.

PLease note, I'm not trying to propose an ATM here, just trying to understand GR and QT better.

How would one be able to tell the difference?

A model that 'predict correct results with high degree of accurancy' is as close to reality as you're ever gonna get in science.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

I agree that such may be an impossible thing to determine, save someone actually travelling at speeds where relativistic effects kick in and then coming back with data for analysis.

but in principle it does it not make a difference when considering alternatives. If a theory is complete at all observable (direct/indirect) scales then yes I think we can safely say that a model is a completely accurate representation(or at least is accurate enough that it doesn't matter one iota as you suggest), however if the model breaks down in such a fundamental fashion at a particular scale, can we be sure enough of it to reject out of hand any alternative because it doesn't fit into our current framework.

Obviously any such alternative must show that is equally as accurate over the domain of our theory and preferably have a larger domain and the responsibility lies upon the proposer to provide sufficeint evidence of such.

Basically I'm just trying to train myself to pick out the good and bad ideas, so I want to know what we have real evidence for in terms of factuality and what are our current best guesses.

I would say that GR and QT are our current best guesses, and they've been tested and tested. There are anomalies (e.g., dark matter) that have been explained in terms of the "current best guesses" that have also produced a cottage industry of alternative attempts. I like to think of it as the Win Megamillions physics lottery.

hh. Yep...and with regards to someone traveling at relativistic speeds...particles do that, and their relativistically changed half-lives near perfectly obey SR. The muons crashing through our heads every minute are a testimony to that effect...(and I'm beginning to think that the long term consequences of that are reflected more & more in our every day world...) pete

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A third rate theory forbids.
A second rate theory explains after the fact.
A first rate theory predicts.
A. Lomonosov

I think this statement is at the center of the problem you are having here. You are not alone, and it has nothing to do with any lack of formal training, but to me this statement exposes a widespread misconception about what physics actually does. The fault in the misconception is not with you, it is with how physics is sold in general, and not all knowledgeable physicists would necessarily agree with me here. You may view this as my own personal opinion, though it is a considered one and I feel fairly clear with these conclusions.

The statement suggests a perspective that nature really has certain laws that it follows, mathematical rules involving certain primitive elements (like mass and particles and forces and motion, etc.), and it is our job to discover them. When we do, the story goes, we will have no further conceptual problems, no inconsistencies-- the universe will open to us like an oyster. The issue is not so much whether or not we will ever fully succeed in this endeavor, it is whether or not this was ever the endeavor we embarked on in the first place. Is it plausible that nature "really does" consist of primitive elements interacting entirely in ways that our mathematics can describe, fully and at all scales and in all ways? Does nature really "solve equations" when it figures out how to behave? Or is this all a form of magical thinking on our part?

As you can tell, my claim is that a search for the true "laws" that nature itself actually follows has at no time ever actually been the endeavor of physics, it has never been a good description of what physics is-- especially as seen from hindsight. And if at no point in history has the above view been an accurate description of the state of affairs, why should we describe our situation in those terms now? Note, for example, that throughout the history of science, two things have been true:
1) physicists always thought they were much closer to understanding nature than they really were, from our "modern" perspective, and
2) they all called their own perspective the "modern" one.
At what point do we stop framing our progress in such unrealistic terms? The advance and progress of physics has been astonishing and powerful, but there's no need to describe it as something different from what it is.

As Disinfo Agent's words suggest, physics is about designing theories that predict outcomes in a unified and general enough way, and with few enough special caveats in each separate situation, that we feel we are actually gaining understanding and mastery over a wide set of phenomena. It was never about finding nature's "true laws", because we have zero evidence that any such thing actually exists, and physics never had any way to test that proposition anyway. So all physical theories have always had limitations and inconsistencies when pushed too far. Given this, why do we believe that physics was ever "supposed" to be any different from that? If you do one thing for millennia, and get better and better at it, but that thing always has a certain general attribute, at what point do we recognize that that general attribute was really just a core aspect of what we've been doing all along?

Ken G: Thanks for that, I'll think on what you have said and write back later on.

Although the substance of what Ken has said is the same as what I say, there is a difference of perspective between us. We arrive at the same conclusion, but, it seems, for different reasons.

Where Ken says, for instance:

...I would say instead that the issue is not so much what was the endeavour that physicists embarked on in the first place, but whether they can ever succeed in such an endeavour in such a way that no one can doubt that they have succeeded.

I hope Ken will forgive me, but I don't think it's fair to say that it was never the goal of physics to find the 'true laws' of nature, as it were. That absolutely is a legitimate goal of physics! The proof is that if you ask 100 physicists why it was that they decided to become physicists, a large proportion will tell you that it was because they wished to unravel the mysteries of the universe. Their obvious enthusiasm for their profession is not the attitude of cynics who never expect to succeed.

But -- I would add, and this is why we end up coming to essentially similar conclusions -- it's one thing what you aspire to achieve, and it's another thing altogether what you do manage to achieve when all has been said and done.

I'm trying my best to be clear, but I'm not sure I'm doing a good job, so allow me to rephrase what I mean: I think it it true and legitimate that physicists and scientists in general hope to learn the truth about the universe through science -- but this does not imply that they can ever claim to have succeeded!

There is nothing magical in being passionate about your craft. It's motivation; you'll find it in any profession, and the sciences are no exception. What nobody should do is assume that their passion proves anything whatsoever about how well physics maps into reality and vice-versa.

Trying to clarify what I mean again, it's O.K. to be enthusiastic about science, but you can never be completely sure that the picture of reality it provides is faithful in every detail.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

I will agree that your perspective here is quite common, even among practicing physicists, but I continue to maintain for the reasons I gave that this has never been a particularly accurate description of what physics is. It's actually quite a naive description, in point of fact. But that doesn't make it useless-- there are many naive views about all kinds of things that serve great and useful purposes, except in the occasional instances where they encounter their own limitations (stemming from being naive).

Ah, but that's a totally different matter. Of course the goal of physics is to unravel mysteries! It is the nature of mystery that is the issue in this thread. If you pick up a mystery novel, the goal is figure to out "whodunnit". It's quite cut and dried-- someone was the murderer, and the mystery is to figure out who, and then you check the back of the book and know if you were right or not.

But when applied to physics, that same kind of cut-and-dried thinking is naive. We say we have "solved a mystery" in physics simply when we have gained predictive power over some phenomenon using a quantitative description that unifies the various similar phenomena with a minimum of purely observed parameters. That's all that has ever been meant by "solving a mystery" in physics, so why we would ever think it will someday mean something else, or should mean something else, is itself a mystery to me.
I can only reiterate that there is not one single shred of cynicism in my views on what physics is. Indeed, I am a physicist. It is precisely my love for physics that motivates me to give it a fair description of what it actually is. Similarly, shall we love our romantic partners for who they really are, or for who we would like to imagine they are?
Again, nothing that I've said should be interpreted as saying that we never learn about our universe. Rather, what I've said is that the use of the word "truth" in the above statement cannot be the naive version that we so often see portrayed when people use the colloquial meaning of "the laws of nature". Of course we seek truth, and we find it, but it is a conditional truth-- conditional on our own process. It will never be "the laws of nature", nor should it ever be that. That was always just a false expectation from science, but we can get away with the more naive description often, much like we can get away with naive descriptions of almost everything else that humans do in their lifetimes. Naivete has its purposes, all I do is point it out, in the few instances (such as the OP) where it actually creates a problem.
I can agree with that wholeheartedly.
I'd take it a step farther: it's O.K. to be enthusiastic about science, but you should never imagine for an instant that the picture of reality it provides is faithful in every detail to anything but itself.

Ken, if that were so, then physics would be just a game, in the same sense as you once said mathematics was a game: internally consistent, but lacking a correspondence to anything besides itself.

If that were so, then physics would be useless! And I say 'useless' in the most pragmatic sense: why would engineers use physics to build better bridges, if there were no connection between the theory of physics and the actual behaviour of bridges?

I do realise that, and I did not mean to imply otherwise.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

How does that follow logically? I think you are misinterpreting my meaning when I say "true to itself"-- for physics, that means making successful predictions, and conveying a sense of understanding and mastery over the phenomena we observe (just like a baby dropping objects to make sure they will always fall until they are completely familiar with falling objects). Thus physics is not a "game" in analytic thinking, like mathematics is, because the ultimate arbiter is confrontation with experiment. Nothing I said above alters that in the least. There is no doubt the purpose of physics is to predict observations in as unified and simplified a way as is possible and desirable in any given context. That is precisely what physics is-- no less, and no more. How does admitting that truth make physics useless?

Thanks both,

Right so correct me if I'm wrong, but what I'm taking from this is that physics is more about predicting a set of 'patterns' within a domain of interest that are of use, hopefully for predicting and explaining within the terms of a possibly incorrect (in reality) framework than an actual picture of reality.

The universe may actually behave according to our laws or not, but in the scheme of science it doesn't matter, providing are models are making correct predictions, or the model can be readilly used to explain anomalies that occur.

This leads me to another important question though. If it doesn;t matter outside the expected domain of our model, and thus the fact that QT and GR don;t work outside of their respective scales can someone explain to me why there is such an importance on managing to get a model which can 'marry' the two frameworks?

From an aesphetic point of view I can understand the desire, but from my point of view, (given that we are searching for frameworks that are not actually describing the real per say, but instead trying to make useful predictions to try and explain something that matches our observations), I struggle to understand the validity of vast ammounts of research into frameworks such as String Theory which seem to spend there time describing a universe we cannot observe even indirectly, which doesn;t seem to be able to make meaningful predictions regarding observations we do make. WHilst the ideas they are describing are mind boggling and like good scifi strangly compelling, surely this (regardless of the interesting exercise in mathematics) is closer to pseudo science than real science at the moment. Am I missing something here?

Yes, I'd say your description here is demonstrably correct by inspection of the history of science, except that as far as the "actual picture" goes, I'd say it does indeed generate an actual picture, with stress on picture. That's just what physics has always been, from the start, and is not about to become anything different any time soon. (Indeed, many people seem unaware of the extensive role of pictures in physics, to the degree that you can ask ten different physicists at the frontiers of various subfields to say how they personally define or conceptualize a few common fundamental and primitive concepts, in terms of their picture of what these things "really are", and you should not be surprised to get ten different answers.)
Yes, that seems fair, and I'd further add that not only does it not matter to science, you'd be hard pressed to find a way to use science to even tell the difference between a successful picture and a "true" one. What is the scientific test for that? What scientific theory, in the history of the art, has passed that test?

Now, of course we all know that all past theories have had their flaws and limitations, but some would still contend that the fact that the theories are improving dramatically is evidence that they are "converging on the truth". But again, I pose the same question to those who hold that. The theories are getting better, much better even, we can show that easily enough. If that's all we can ever show, scientifically, then why would we ever need to assert anything beyond that?
It is because the whole purpose of scientific thinking is unification. I would say that what we call scientific knowledge is actually the marriage of familiarity with unification. We become familiar with various phenomena, and then we unify them with our quantitative theories, and then we say we understand those phenomena.

That's just exactly what science is, so it makes perfect sense to always seek greater unification. There's nothing wrong with trying to unify GR and QM, and we may well succeed someday, for all I know. But when we do, you may be certain that the new theory will have its new issues, limitations, and inconsistencies-- albeit at more and more difficult scales to access (so the new theory will certainly be a great improvement if and when it comes). I would say it is the height of naivete to expect otherwise, common though it may be to do so. And again, there's nothing really wrong with naivete, it is basically a tool of our minds-- but we should expect to stumble over questions like your OP.
Yes, you are missing two things: 1) the aesthetics of science are actually pretty important, and by themselves justify the actually rather puny resources that are dedicated to the process, and 2) the practical applications of science are even more important, and often hard to predict going in. Note that neither the aesthetics nor the applications are predicated on the requirement that science be an asymptotically converging discovery of the "real laws of nature", or that it ultimately should result in a complete description of all reality with no limitations and no domains of applicability.

Nevertheless, the belief that nature is described by beautiful, unified and relatively simple laws has been a major factor in the pursuit and development of basic theoretical physics. Certainly it was a major motivating factor for both Einstein and Dirac. Wigner's essay The Unreasonable Success of Mathematics in the Natural Sciences provides a nice overview. Whether such laws actually exist or not, the pursuit of that goal is what has driven much of the development of physical law. I prefer to believe that it is an achievable goal (but I make no predictions on when that goal will be achieved.)

The eternal mystery of the world is its comprehensibility…. The fact that it is comprehensible is a miracle. – Albert Einstein

All true-- people may be motivated by all kinds of strange beliefs! Newton was motivated by alchemy, as we all know. There's a difference between what physics is, and why choose to do it. Same for art, or religion.

Nothing is lost in framing that pursuit in the way I have. It's all the same pursuit, merely described in a way that is more accurate to what really happens. The argument reminds me of people who say that if you know why rainbows happen, they are not beautiful any more-- how does seeing something for what it is destroy its aesthetic appeal? And I agree wholeheartedly with your Einstein quote, and see it as fully supporting the description I've given-- comprehensibility is indeed a mystery, and one that physics itself was never intended to explain, and consequently never will.

And not so strange ones, too.

I thoroughly agree with DrRocket's post. More comments later.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

I don't think we really have a disagreement.

Physics does not attempt to explain why nature is explainable. Physicists simply accept that it seems to be explainable and exploit that aspect of nature. .

If an explanation as to WHY nature is comprehensible is desired, one should consult a theologian or a philosopher, be extremely patient if one expects an answer, and not expect the answer to that question itself to be comprehensible. .

That is indeed a clear statement of our central agreement here.
And I think I can actually offer a partial answer to that why, though not a very satisfying one: nature is comprehensible because what we define by the word nature is precisely those aspects of it which we can comprehend. We are looking in the mirror, and seeing our own intelligence staring back-- and saying "my don't we look smart?". But even that doesn't explain why we can calculate an isolated hydrogen atom to so many decimal places of accuracy-- it is more an explanation of why the only thing we can calculate to that accuracy is an isolated hydrogen atom, and why we cannot test more decimal places than that.

`

Perhaps nature is comprehensible in terms of mathematical models just because it is the part of nature that is explainable in those therm that we are able to understand.

Or perhaps nature really does follow rules formulated in terms of mathematics and we have been able to uncover and understand a significant fraction of those rules.

I do not know any means of distinguishing between these two cases. But I prefer to believe the second version, and it seems to have been a principle that has been accepted by and useful to many others in discovering and formulating the laws of nature as we currently understand them.

But then I am an unapologetic reductionist. For a slightly different perspective you might want to read Robert Laughlin's A Different Universe, Reinventing Physics from the Bottom Down. It is interesting reading and not really so different as one might think from the conventinal viewpoint, whatever that is.

Right, there is no way to demonstrate it is one or the other, I merely point out that the first is a completely face-value description of what science is, and the second adds an unnecessary layer of philosophy/belief. It is not really a scientific question to ask why does science work, because science begins after the assumption that it works, and from then on it concentrates on precisely what does work. Put differently, when some theory does not work, we never bother ourselves with why that theory didn't work, we just move on.

As an article of faith, there is no problem with any such belief. I was being a bit facetious above when I asserted that "people believe all kinds of strange things"-- some beliefs may seem more acceptable than others, but at some level, all beliefs that cannot be demonstrated as true are somewhat "strange". That does not make them invalid, a point I often make when scientists start bashing religion (for example). To anyone who believes that nature really does follow certain identifiable "natural laws," not just that we can compare nature to certain laws generated by our own intellect and get good agreement (over an amazingly wide class of situations), I would say that they have (probably inadvertantly) elevated science to the level of a religion, because only the latter version is actually substantiated within science itself.

That's debatable. From my viewpoint, it is the first scenario which adds a layer of complexity to the world, by assuming that there's a part of it we'll never have access to. This assumption is as much belief that cannot be empirically established as the opposite view.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

Not so-- it is a trivial matter to demonstrate that our current physics is not capable of describing all the phenomena that occur at all scales. Even the concept of "scale" is part of that very physics, and most likely has its own limitations when applied to reality. What's more, one needs only look at the defining characteristics of science to notice that something is being left out there, as it is perfectly natural to expect when choices are made about what constitutes a successful way to acquire knowledge, that the knowledge so acquired must be subordinate to those choices. The burden of proof falls on those who claim "nothing is left out by my scheme for understanding nature", not on those who say "prove it".

But perhaps more to the point is the issue of adding no unnecessary baggage to what science actually is. When one cites a law of nature, at what point does one need to assert "since this is an actual and true law of nature, I am justified in asserting it"? At no point, science, as it is practiced to this day, simply does not have any phase of the process that looks like that. Indeed, what it really looks like is "I will choose this description of nature to base my calculation on, as it has proven successful in similar types of calculations, and I am choosing to assume that my situation will be similar. We won't know how well I did until we actually compare to observations". That is science.

Wait a minute... our current physics?

I was not talking about current physics -- obviously, current physics can't explain everything. I meant physics in abstract, both current and future.

It's natural to expect that as physics progresses it will become better and better at explaining/describing the world. The question is will physics ever be able to reach all that exists? I say that this question is undecidable. Science cannot answer it. (Nor can any other method of inquiry.)

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

Yes. Astonishingly, I am basing my comments about what physics is on what physics is.
Again, my point is not that physics can't explain everything, that is obvious to all-- my point is that at no time has it ever been the point of physics to explain everything. For example, it has never been the point of physics to explain why physics works, nor has it ever had any capacity to do that-- and isn't about to start (it would be untrue to its own defining characteristics).
Yes, and I said so myself many times on this thread. At issue is, what is an explanation in physics, and at what point should we say we have "described the world"? The question here is not, will our theories become more accurate and more complete, but rather, should they be thought of as converging on some true set of laws that nature itself actually uses to function, laws which encompass nature and are the same thing as nature. The issue is, on what basis should we adopt, purely on faith, that such laws even exist, and moreover, why should it be viewed as necessary or advisable for scientists to think that way, when it is not a necessary step anywhere along in the scientific process? (And, I might add, has been such a categorically foolish perspective throughout the entire history of the human scientific endeavor.)

Physics is not just what it is today. It's also what it was in the past, and what it will become in the future.

The question of whether physics will one day be able to explain the whole of reality (the language says it all) only makes sense in a framework that includes future possibilities.

The proposition that physics does not explain everything in physical reality today is trivial and unworthy of discussion. I'm sure that even the most diehard adepts of scientism would admit that the physics of our time (and, by extension, the science of our time) can't explain everything. So what? Keep digging and you'll find more.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

The same statement may be made about whether fortune-telling will ever be able to explain the whole of reality. The statement is irrelevant, at issue is what fortune-telling as we know it today is, and the same for physics.
Nor is it an important part of my argument, I'm talking about what physics is, what its whole purpose is and how we gauge its progress, not where it is in that progress (which is, clearly, "somewhere in the middle").
On that we can certainly agree.

A recent BA blog post reminded me of this discussion:

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

No doubt all human endeavors leave some kind of indelible footprint on the scientific mode of inquiry. The error is when scientists mistake a footprint for a dinosaur.

How can we ever possibly know what "reality" at the subatomic level ever is? To investigate the Planck length, we would need accelerators the length of the Milky Way, and then it would still only be an indirect observation in a bubble chamber.

And the Planck length is a product of today's QM. Find a "better" theory, and this limit might be redefined as even smaller.

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“He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever”
Chinese proverb
"All you need in this life is ignorance and confidence - and then success is sure." - Mark Twain.