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Big Bang Debate

I thought this conversation in my Comments section was worth putting up as a post. It's a bit long, but if you're interested:




Rex

Stevie, perhaps you can explain the current data that is used to support the Big Bang theory, and explain why it is philosophical in nature? For example, consider the cosmic background radiation. (There are many other things to consider.)




Me:

Here's the basic short answer to that: Science in the strict sense involves forming falsifiable hypotheses that are then confirmed by their positive instances. Clearly we can't form a 'When X conditions obtain, there's a Big Bang'. The Big Bang requires more of a comprehensive theory that involves the fitting together of lots of particular hypotheses; theoretical physicists look at experimental evidence and try to come up with a story (broad theory) that makes it all fit together. Broad theories of this type are what lead to backward speculation about the beginning of the universe. But broad theory building, while certainly part of the actual practice of what we call 'the scientific field' goes far beyond the principles of what is strictly science. You can of course broaden your definition of 'science', but then you lose out on what people think makes it plausible as a practice.

Bill, ou might also want to teach your children that the theory of gravity is just a theory--after all, in Matthew 12:29, Peter walks on water to Jesus (who is walking on water), which clearly contradicts the idea that two bodies attract each other with a force equal to -G*m*M/r^2. Maybe Newton's laws of motion are wrong also. Given all the wind and the lack of traction against the water, there doesn't seem to be equal and opposite forces involved. Clearly, a literal reading of the Bible produces a much better understanding of the workings of the physical world than does actually studying the physical world.

No one (except for 'the folk') actually understand gravity in that way anymore. From what I'm told, the dominant view now has something to do about how massive objects cause deformities in the space-time field, yadda yadda.

Even when gravity was understood that way, no one would be crazy enough to argue that it rules out the possibility of someone walking on water. It could only rule out a situation that was defined very narrowly in such a way that no other forces could have been acting. From what I remember the Bible just says "They saw Jesus walking on water" or something like that. That doesn't threaten the theory of gravity any more than my 'floating pen' on a magnetic base - you've seen those, right?

In any case, if the Bible suggests that Newton's laws/principles are wrong, then that's a point in favor of the Bible. Physicists dumped Newtonian physics ages ago - Newton was wrong - get with the program:P

Style Council, there's a difference between arrogance and confidence. The scientific process by construction lends confidence. It is the same process, formalized, that you use to determine with confidence that, for example, you cannot walk through walls (and develop ideas of solidity to explain this), and that heavy objects fall downwards (gravity), and so on. Do you think, maybe, if you pray hard enough, you will be able to walk through walls? Maybe not.

You're suggesting, I take it, that science is no more than a formalization of implicit inductive reasoning?

That might not be off base entirely, but science smuggles a lot more than that in. And in any case, it's doubtful that science accurately captures our implicit inductive processes. We don't even have a generally accepted system of formal rules for inductive logic - I don't even know if there are any contenders.




Rex

"When X conditions obtain, there is a Big Bang" does not a falsifiable prediction make. What does the trick is "When there is a Big Bang, then X conditions obtain." If we observe not-X, then we must conclude not-(Big Bang). Straightforward deductive logic, and that's exactly how the Big Bang is evaluated scientifically.

We may not know all the details--there's lots of cosmology that goes beyond what is meaningfully testable--but the basic idea that things are expanding and have been for a very, very long time is not really in question when one looks at the evidence.

My point about Peter walking on water is just that you don't throw out scientifically tested results because you happen to be particularly fond of a particular passage in the Bible. You might want to check the results again, and you might want to check your interpretation again, but it's pretty dangerous to assume that when there's an apparent conflict between an interpretation of the Bible and science, that it is always science that is wrong--even if you believe the Bible is the infallible word of God. Last I checked, humans weren't infallible at interpreting much of anything (which makes me wonder what the attraction is to infallible texts).

And, finally, I am saying that science is a formalization of the process of implicit inductive reasoning. It's not quite so implicit once it's formalized. It sidesteps the problem of what constitutes valid inductive reasoning by using hypothesis-falsification, which is basically deductive in nature. So the stance is effectively, "I'm not sure how far we can get with induction, or how valid it is, but we'll tentatively accept those propositions that we've tried to prove wrong and failed."

(At least, this is a formal-logic interpretation of what is going on. I don't think this is quite right, since reality seems based more upon principles of statistics and signal to noise than truth-values of propositions, but for a first pass this is pretty close.)




Me:

"When X conditions obtain, there is a Big Bang" does not a falsifiable prediction make. What does the trick is "When there is a Big Bang, then X conditions obtain." If we observe not-X, then we must conclude not-(Big Bang). Straightforward deductive logic, and that's exactly how the Big Bang is evaluated scientifically.

That works? Great! Then I'm going to prove intelligent design (by the Great Purple Chicken):

When the world is created by the Great Purple Chicken, then X conditions obtain.

(X conditions being an accurate description of the entire history of the actual world/universe).

That's falsifiable too.

So I guess the Great Purple Chicken is on equal standing with the Big Bang Theory?




Rex

The connection between the Big Bang and X is not simply a string of words. Rather, saying "the Big Bang" implies a bunch of premises, and one can follow the implications through until one reaches X.

For example, the Big Bang means that the universe started in a single explosion from a small area or point. When things explode, bits of that thing travel outwards. Therefore, if there was a Big Bang, then bits of the universe should travel outwards.

So the Great Purple Chicken theory would have to meet the same standards.

If, indeed, it actually implied X (as opposed to X or Y or Z or A or B or ...), then you'd find that "Great Purple Chicken" was in large part just a peculiarly-chosen synonym for "Big Bang".

Now, they might not be exactly the same implications--the Big Bang might predict X and W, while the Great Purple Chicken predicts X and V. Then you could test W and V and distinguish between the two. Or perhaps the Great Purple Chicken predicts X but is not informative regarding W or anything else. Then, if we observe X and we observe W, we tentatively pick the Big Bang hypothesis and discard the GPC hypothesis because the Big Bang is better tested and/or is more useful for predicting events. If the Big Bang can be easily described, and GPC is not easily described, then we pick the Big Bang because it's more convenient.

For example, the "walls are solid" hypothesis is simpler and provides stronger predictions than a "the east outer wall of my house is solid and the west outer wall of my house is solid and..." hypothesis.

The idea of falsification is a strong basis to start from, but one still has to use it properly in order to generate useful information.




Me:

The only significant difference between the Big Bang (BB) hypothesis and the Great Purple Chicken (GPC)is that I'm too lazy to specify particulars about what the (GPC) implies.

Here's why (GPC) wouldn't be just a synonym for (BB):

(BB) supposedly implies (with some degree of specificity) a particular world history that has our current time as being something like 12 billion years after the big bang. In between then and now, this and that and so on happened.

According to (GPC), none of that happened. The world was created, say, 150 years ago. The Great Purple Chicken created everything just the way it was 150 years ago, putting all matter in place and giving it the correct push to make it expand outward and behave in the ways it does now.

(GPC) is falsifiable, because if it had turned out that things weren't the way they are now, it would be falsified.

It isn't non-falsifiable because "if things were different, you could just say the Chicken created it in some different way" - no, the (GPC) hypothesis is fixed in the same way as (BB). If any of the details were changed it wouldn't be (GPC).

All of the implications of (GPC) for any time after 150 years ago are the same as they are for (BB), so there is no way to distinguish them as far as evidence goes (the same would be the case if GPC said the world was created ten seconds ago, of course).

ringing simplicity in as a criterion isn't going to get us anywhere.

If we were just in the business of coming up with convenient prediction-making models, then simplicity is just fine. In such a context we aren't concerned with accurate description at all, and have no pretensions of coming up with theories that actually describe the world. The Big Bang theory is useless in that context - it isn't happening again anytime soon, and it's not something we can control or manipulate. The origin of the universe is a pointless question from the standpoint of practically-oriented science/prediction-making.

So if we are going to discuss the origin of the universe, it is reasonable only to assume that we have some interest in the fact of the matter, which rules out our invocation of the simplicity criterion.




Rex

Simplicity gets us everywhere. (GPC) is incredibly, uselessly complicated--it is just a description of things now (or 150 years ago), plus an evidence-free postulate that things were created de novo 150 years ago such that it looked like the system had been in place for many billions of years.

The portion of the GPC that is not just a description is not testable, by construction. Therefore, there is nothing to distinguish GPC from any of the "models" that are just descriptions of everything that we know now. The 150 years thing is, therefore, not scientific.

GPC-style models must be a description of everything we know now, not "it turned out the way it is" as a generic statement, or it would *really* not be falsifiable, since by construction there is no observation that it could contradict. Furthermore, quite a few of our observations are probably in error in some way, which would falsify GPC, but there are deeper problems.

The class of models that describe everything we see now have no predictive power on their own. One can use them to make inferential models, using the scientific method, for example, but the whole point is that we're trying to make inferential models here, not just gather data. This is where the requirement for simplicity comes in--a simple model typically can be easily used to generate predictions about what one will observe in the future (or as one looks at more data regarding things that have happened in the past).

I'm not sure whether a maximum-power-for-the-size-of-the-theory criterion is better or worse than simply a minimum-size one; the latter is Occam's Razor, while the former seems potentially more useful. Either way, this is a way to pick out particularly helpful perspectives. When two perspectives end up being logically and experimentally equivalent, as was the case with the Schrodinger and Heisenberg formulations of quantum mechanics, people generally use whichever is more convenient at the time.

Of course, we have an interest in the fact of the matter, but the question is, what do we *mean* by the fact of the matter? There isn't any obvious linkage between truth-statements and matter. If we go back and look at things that we call facts, such as "fire is hot", we find exactly the kind of compact explanatory power based on evidence that one looks for with the scientific method.

That is, "fire is hot" is considered true because we have a general concept of hotness (and of fire), and all everyday evidence about the hotness of fire indicates that fire is hot and this is a very compact but powerfully predictive description of something we come across fairly often.




Me:

Simplicity gets us everywhere. (GPC) is incredibly, uselessly complicated--it is just a description of things now (or 150 years ago), plus an evidence-free postulate that things were created de novo 150 years ago such that it looked like the system had been in place for many billions of years.

The Big Bang Theory is just as much of an evidence-free postulate that things were created 150 years ago. There is no "looked like the universe had been in place for many billions of years" - that's a wild speculation that is entirely theory-based. The universe only "looks" that way if we accept a load of assumptions about its origins, how matter behaves, the consistency of such behavior, etc.

It's not unreasonable to say that man-made objects "look new" or "look old" because we have actual experience with the way these things change over time. We have absolutely no experience of what it is for planets and galaxies to change over millions and billions of years, so it would be preposterous to claim that the whole universe could just "look old".

Say this debate were between your version of the Big Bang theory and my alternative, BB+1. According to BB+1, the universe began in pretty much the same way as the Big Bang theory suggested, except that it started exactly one second later, and the initial conditions were exactly those that your theory says obtained one second after the Big Bang. So basically BB+1 says that the ball of mass (or whatever) was bigger to begin with.

You can't try to argue that the universe looks as if it is one second older than BB+1 says it is; given the laws and such posited by each of our theories along with the initial conditions each includes, we would expect the world to be just as it is now. And the same would be true if the theory was BB+20(seconds) - different initial conditions, but if we agree on how everything behaves afterward, same result.

So if instead of the Great Purple Chicken theory I'd put forth BB+12billionish-years, a theory allowing the same behavior of matter and such but including the assertion that the initial conditions simply were those that obtained 150 years ago (and these would be described to some level of specificity), you would have no grounds on which to say the universe "looks older". It "looks" as if it were created 150 years ago given particular starting conditions plus laws just as much as it "looks" as if it were created 12 billion years ago with different initial conditions and the same laws. If that argument isn't going to work for BB+12billionish-years, it's not going to work for the Great Purple Chicken hypothesis either.

The portion of the GPC that is not just a description is not testable, by construction. Therefore, there is nothing to distinguish GPC from any of the "models" that are just descriptions of everything that we know now. The 150 years thing is, therefore, not scientific.

It's just as testable as the non-descriptive aspect of the BB.

BB says we had X starting conditions and Y set of laws describing the consistent behavior of matter/energy afterward. We can't test X of course, but Y is testable in two ways: We can, for one, come up with a model of X starting conditions and then "run" it through with Y set of laws to see what kind of outcome we would get. On BB, we would expect the model to look pretty much like the current, actual universe about 12 billion years after X starting conditions. If it didn't, BB would be falsified. The second way would be to perform experiments testing Y set of laws. Does matter/energy actual behave in accordance with those laws now, insofar as we can test it? If not, BB is falsified.

So what's the difference with GPC? You're right that in some aspects, GPC is another version of BB - it describes initial conditions and then gives a story about how the universe behaved afterward. But that's a similarity we would expect it to bear to any theory of the origin of the universe.

GPC says we had Z starting conditions, followed by behavior of matter/energy that can be described by Y set of laws/generalizations (which are the same as those posited by BB).

One differnce is that when we set up and run our models of BB and GPC, the BB model starts to look like the actual current universe after 12 billion years, while the GPC model looks like the actual current universe after 150.

The other is simply that BB and GPC provide different stories for the initial conditions and the laws. On BB, the initial conditions basically just happened to obtain - no explanation is given or asked for. On GPC, a Great Purple Chicken arranged it that way. On BB, the laws just happen to be what they do because, as a matter of fact, the universe exhibits certain patterns of behavior. Why? Who knows - that's not a question that even comes up on BB. On GPC, it is posited that the reason is that the Great Purple Chicken uses his magic to keep things working that way.

Granted, the chicken aspect of GPC doesn't add anything testable. It becomes a matter of faith, or of just making a guess. Perhaps it is best to remain agnostic and say that we don't know anything about why the initial conditions were what they were, or why energy/matter behaves in the way it does - we cannot support or rule out any kind of explanation for that. But if we are going to hazard a guess, it is every bit as reasonable to say the reason is the Great Purple Chicken as it is to say that it simply is that way, and there is not anything more to explain it.

Now, the important thing here is the relevant similarities between BB and GPC:

Just as we did with BB, we run a model of GPC based on Z initial conditions and Y set of laws. GPC is falsified if the model does not, at some point, look like the actual current universe. And again, GPC is falsified in the same way as BB if Y set of laws it posits do not describe the behavior of matter/energy that we actually observe in experimental settings.

GPC-style models must be a description of everything we know now, not "it turned out the way it is" as a generic statement, or it would *really* not be falsifiable, since by construction there is no observation that it could contradict. Furthermore, quite a few of our observations are probably in error in some way, which would falsify GPC, but there are deeper problems.

I don't know why you seem to think that GPC is the same as a model that simply says a chicken created the world just as it is in this very instant...

The GPC model has initial conditions just like BB. If you believe BB, then you're going to believe that X initial conditions are those that actually obtained 12 billion years ago. There's no significant difference between that and GPC, which has initial conditions that match the actual conditions of 150 years ago if GPC is true.

And as I've already noted, GPC includes laws/generalizations that are as testable as those of BB.

But, on to the main point, as I have other work to get to:

I've shown that BB and GPC are equivalent in all the important ways - they both include initial conditions, laws, and are testable. GPC is as valid a hypothesis as BB is. Both BB and GPC give us the same end result (the actual current universe). But they are clearly not the same, however you want to spin it; the initial conditions are different, and on GPC the universe is only 150 years old.

This is only a demonstration of what is widely accepted as being true - it is possible to have substantially different theoretical models that describe the same end result.

This principle is usually brought up in discussion of laws - we can formulate generalizations that accurately describe the behavior of matter/energy and that make predictions that are actually borne out. In the case of laws, the different generalizations are usually actually indistinguishable; there is no testable difference between them in principle. It is not entirely unreasonable to suggest that they simply may be differently worded but equivalent descriptions.

But BB and GPC are not indistinguishable in principle. It happens to be the case that we cannot actually go back in time and see if the universe was around 200 years ago, or if the furthest back we can go is 150 years. But anyone will recognize that it is not a trivial difference that one theory says the universe is 12 billion years old, while the other says it is 150 years old. It is just a matter of practical limitations that we cannot in fact come up with evidence to support one theory over the other.

The short of it all is this: We do not have, and cannot have (due to practical limitations) the kind of evidence that would support the Big Bang theory over other theories regarding the origin of the universe that are substantially different.

Sure, we can say that BB is simpler than GPC and other theories. But again, we're not just interested in how convenient each theory is for predictions; if that's all we wanted we wouldn't care about the origin of the universe. To say that BB's being simpler (if it were) makes it more likely to be true is something of a 'philosophical' assertion (though a pretty silly one).

Now you can ponder the relation of statements to facts of the matter all you like, but we're talking about 'The universe is 12 billion years old' versus 'The universe is 150 years old' here - so I should think that we agree that we have a pretty good idea about the relevant difference in the way things actually are that is associated with each statement. We understand that BB and GPC are substantially different, as we have a good idea as to the real world difference that one entails in relation to the other. We also understand that there is a fact of the matter about the issue; one really is a more apt description of the world (and its history), and not in a trivial way.




Rex

There is no "looked like the universe had been in place for many billions of years" - that's a wild speculation that is entirely theory-based.

You don't know what you're talking about. It's very hard to have a meaningful debate starting from a position of ignorance.

(Alternatively, maybe you're starting from a position of radical nihilism, in that you believe that everything is a wild speculation that is entirely theory-based, and knowledge of any sort is impossible.)

In any case, the speculation is not wild, and the theories upon which the apparent age of the universe is interpreted have themselves been well-tested.

Here's just one example. The universe, now, is pretty big. Light can only travel so fast, yet we can see things really far away. So, the universe looks like it's old enough for the light from the really far away things to have reached us.

If that doesn't seem non-wild and based on evidence, then I submit that you could be in a box just larger than your fingertips can touch, with illusions projected from the walls (stereoscopically), and with tactile objects appearing and disappearing within the box, and that any appeal to how things appear is just wild speculation that is entirely theory-based.

The universe only "looks" that way if we accept a load of assumptions about its origins, how matter behaves, the consistency of such behavior, etc.

It's not unreasonable to say that man-made objects "look new" or "look old" because we have actual experience with the way these things change over time.


This is absurd. Having actual experience about how matter behaves doesn't count, but having actual experience about how appearances change with time does count? What is the justification for this distinction?

You don't even watch the same objects the whole time, between when they are new and when they are old. You're making a load of assumptions about what it means to be an object, which old objects correspond with which new objects, and so on.

They just happen to be very good, and well-tested "assumptions". Likewise (with slightly less certainty) with assumptions that leads one to conclude that the universe is very old.

Initial conditions are not free. GPC has a vastly less compact description of initial conditions than BB. BB wins.

Predictive power does not only go forward in time, it also goes backward, or both backward and forward. BB wins there, too, because you can see things that appear to have happened far in the past and predict what you would expect to find evidence of farther in the past, or you can see processes that have unfolded in the past and expect to see the same unfolding with processes that start occurring now. For example, what does GPC say about the lifetime of our sun? BB wins again.

Also, if one has a class of theories that are pretty much equivalent and they differ in important but untestable ways--for example, suppose we have evidence that the universe was created 150 years ago, but we have no evidence regarding the color or species of bird that did it--then the appropriate scientific stance is to not commit to any particular class. It's not to say that no such bird exists just because you can't pin down which one--you just say you don't know which bird exists.

People who then promote Great Purple Chickens, as opposed to Subtle White Hummingbirds, are being non-scientific. But the point is that it doesn't really matter, materially, who is right or whether anyone is right. If the different claims cannot be distinguished via evidence, then they also cannot differentially impact the world (or at least, they can't until they leave some distinguishing trace).

So, it may be that a Great Purple Chicken created the universe 150 years ago, to look as though it had been around for billions of years; it may even have created everything 10 minutes ago, with our memories and this discussion fully formed (why not?--if it can put every photon in place as if it had traveled from distant stars, surely constructing memories isn't so hard). But in these cases, it is still appropriate to behave as if the universe had been created billions of years ago, since it was designed to behave as if this were the case.

This is exactly the same thing we do everyday. It might be that all walls are insubstantial, but invisible pixies push on us really hard when we touch a wall, so we can't go through. We can't rule this out with everyday experience. We just say, hey, walls are solid. (If we really want to worry about it, then perhaps pixies are implementing that which we call the solidity of walls--either way, we can't walk through them.)




Me:

You don't know what you're talking about. It's very hard to have a meaningful debate starting from a position of ignorance.

Rex, you've clearly given up on the discussion and demonstrated your own lack of understanding - particularly by your insistence on ignoring almost all of the arguments.

But nevermind that. Answer this question. You said:

Here's just one example. The universe, now, is pretty big. Light can only travel so fast, yet we can see things really far away. So, the universe looks like it's old enough for the light from the really far away things to have reached us.

Now please at least try to refute this counter-argument (if you're interested in participating in the discussion):

We don't know that the universe is really big. We detect light and other forms of radiation coming in at us.

We infer that this light/radiation is coming from stars and other matter that's really far out there. We have the light, but that doesn't require the existence of such objects. The Chicken could have set up the appropriate light and radiation conditions 150 years ago and it would look just the same.

So we have two options for describing how the universe looks:

1. It looks like it is 12 billion years old and had X starting conditions.

2. It looks like it is 150 years old and had Y starting conditions.

Both would entail it looking the same way to us as it does now.

So tell me why you pick 1 over 2?

If you're going to keep yapping about 'simplicity', then define simplicity and refute my arguments as to why simplicity is irrelevant in a context when our purpose is not making predictions.




Rex

I am ignoring things that appear not to be coherent arguments. I also already answered the question regarding why one prefers X over Y. But I will do so again, since you asked specifically.

In particular, perhaps the problem is that you have not yet managed to come up with a scenario where predictions are not a relevant part of the picture.

Simplicity is somewhat subjective, because it is difficult to precisely define human cognitive abilities, and it is really measured with respect to that. However, it is closely related to the minimum description length in a hypothetical content-neutral language. Those things that can be described compactly are "simple", and those that cannot are less "simple".

Both conditions 1 and 2 entail it looking the same way as it does now (as does the condition where the world and our memories were created ten minutes ago).

However, suppose one considers the radiation observed that appears to have been emitted by a distant star. In describing this information, you can either say

(1) The radiation was emitted 50,000 years ago from a star and has spread out spherically since then, or

(2a) The radiation was created 150 years ago as if it had been emitted 50,000 years ago from a star and had then spread out spherically since then, or

(2b) The radiation was created 150 years ago at (huge list of locations) traveling in the direction (huge list of angles).

Now, (1) is simpler than (2a), which makes it easier to deal with. In any case, (2a) is for all practical purposes indistinguishable from (1) since one could say that "the past" instead of GPC had created what was there 150 years ago. And (2b), which is a non-equivalent description, is much more complicated.

If you can come up with a scenario where there aren't predictions to be made, or descriptions to be written, then I'll address those arguments.

I am not particularly concerned with those cases where one doesn't care about predictions--if one doesn't care about the scientific method, it can't make them care--but only those where predictions cannot be made or descriptions are of equal utility and convenience in making predictions.




Me:

In particular, perhaps the problem is that you have not yet managed to come up with a scenario where predictions are not a relevant part of the picture.

You might as well have skipped the rest of your comment - the argument that one is simpler than another is an interesting conversation on its own, but not the one we're having here. The real question we're looking at now is why simplicity, so I'll stick to that for our purposes here.

At this point, the debate boils down to this:

You're demanding that simplicity is relevant to considerations regarding the origin of the universe; I'm saying it's not.

I think we agree that simplicity is a fine criterion when all we care about is making predictions; if that's what we want, we might as well select the model that is easier to use if we have two that give us identical predictions about the future.

But you go on to say:

If you can come up with a scenario where there aren't predictions to be made, or descriptions to be written, then I'll address those arguments.

But you have not established that our making predictions automatically buys you justification for the simplicity criterion. As I explained, it makes sense if all you care about are predictions. But if you care about predictions/descriptions, and more, you aren't necessarily justified in invoking simplicity.

And that's the situation we're in when it comes to speculation about the origin of the universe. We are concerned about accurate descriptions in this case. We want the right theory.



Can you give any reason for us to think that a simpler alternative will be the right one in this way?


Rex

Scientifically, I don't think you can have more. You get descriptions, and you get predictive power. To the extent that one calls a theory "right" when it gives compact desciptions and powerful predictive capabilities, then this will give you theories that are "right". The compactness is partly a matter of convenience, and partly based on the experience of compact theories usually holding up well (which suggests something about the structure of the universe).

We have a great deal of evidence that these conclusions are unusually solid compared to other sources of human knowledge, save for direct experience which we appear to analyze using the same method (i.e. is it simple, predictive, descriptive--if so, then that is what we believe). For example, Newtonian mechanics is still considered the "right" description of what happens at moderate speeds and masses.

If we want all this and more, then the scientific method is not built to help us out. If one wants to supplement a scientific description of the world with additional beliefs that are not (currently, anyway) scientifically testable, such as the immorality of polygamy and polyandry, that's fine.

But when one starts throwing out science in favor of of untested/untestable beliefs, then there is a problem, just like when one starts throwing out direct sensory experience in favor of untested/untestable beliefs.

So if you ask me if there's a reason to prefer simplicity in untested/untestable beliefs, then the answer is no, not particularly, as long as the belief is sufficiently simple for someone to comprehend (something that is too complex to comprehend probably cannot be held as a belief anyway). As a personal matter, one might wish to tend towards simpler beliefs just out of convenience.

The (2a) interpretation of GPC is a belief of this type.

If you ask me if there's a reason to prefer simple tested beliefs over more complex untestable beliefs, then the answer is yes, absolutely, at least to the degree that one values sanely operating in the physical world.

The (2b) interpretation of GPC is probably of this type.




Me:

Scientifically, I don't think you can have more. You get descriptions, and you get predictive power. To the extent that one calls a theory "right" when it gives compact desciptions and powerful predictive capabilities, then this will give you theories that are "right".

Wouldn't this suggest, then, that the question of the origin of the universe is not really a scientific matter?

You say:

But when one starts throwing out science in favor of of untested/untestable beliefs, then there is a problem,

But I fail to see how adopting the Big Bang theory is any less a throwing out of science in favor of untestable beliefs than is adopting GPC - if we're in 'scientific mode' then we shouldn't be demanding that our theories are "right", only useful, but people who adopt the Big Bang theory do tend to believe that is is right.

The Big Bang is testable in some sense - some of its predictions (those involving the condition of the world now) can be falsified, but theories like GPC are testable in the same way.

Preferring to believe simpler theories when the simplicity criterion does not really apply (when we are interested in truth), just as a matter of personal preference for convenience, is fine of course. But if we admit that this is our reason for adopting one belief over another, that gives us reason to be quite moderate in our committment.

The compactness is partly a matter of convenience, and partly based on the experience of compact theories usually holding up well

We have experience that compact theories usually hold up well? I'm not entirely sure what you mean by that...

If you mean historically, of our major theories in the practice of science, you have a selection bias problem; if scientists prefer simpler explanations as a matter of policy, you wouldn't expect to find less compact theories that were found to 'hold up' (as well as the more compact theories) just because they aren't usually being considered.

But if you mean something like that of all the theories we might come up with, assuming we had no bias for the simpler, we would find that the more compact ones hold up better, I don't see how you could be right. It is generally accepted that for any finite set of data, there are an infinite number of models that could be used to describe it. So for every simple theory that you would count as 'holding up', there are many (probably infinitely many) alternative theories that would also hold up just as well, as they would be compatible with all observed data.

And actually, since I take it that only one theory out of such a large, maybe infinitely large, set of theories compatible with the data set can be the simplest theory, it would seem that most of the theories that 'hold up' are not simple. We choose to use the simplest ones that are compatible with the data, but out of all of our potential choices, most that hold up are not simple.

(which suggests something about the structure of the universe).

Even if it were true that compact theories hold up well in comparison to less compact theories, what would that suggest about the structure of the universe?

I don't see how the way we can describe our experience of the universe necessarily affords us any insight into its very structure.

For example, Newtonian mechanics is still considered the "right" description of what happens at moderate speeds and masses.

By whom? I don't think I know anyone who would make such a claim. People might admit that Newtonian mechanics makes predictions that are generally right, but the claim about people considering it a right description seems very dubious.




Rex

Wouldn't this suggest, then, that the question of the origin of the universe is not really a scientific matter?

At some point, yes, but it's not entirely clear what that point is. It's certainly early enough for the "Big Bang" to be considered factual; details of what exactly it was that caused it, how big the starting system was, and such, are currently difficult to test (people are trying). But the basic idea that the universe was a lot smaller and is expanding outwards does not appear to be in serious doubt.

The Big Bang is testable in some sense - some of its predictions (those involving the condition of the world now) can be falsified, but theories like GPC are testable in the same way.

Yes, but you only get those predictions with the (2a) interpretation of GPC, which basically says, "Everything is just as you'd expect if there were a Big Bang, except a Great Purple Chicken made everything 150 years ago to look that way." If you stay away from the interpretations of the nature of time and history, it's basically the Big Bang, so it's reasonable to say that the Big Bang part is "right", and the decorations with chickens or lack thereof are not science.

Preferring to believe simpler theories when the simplicity criterion does not really apply (when we are interested in truth), just as a matter of personal preference for convenience, is fine of course. But if we admit that this is our reason for adopting one belief over another, that gives us reason to be quite moderate in our committment.

Yeah, that's part of science too. Committments are supposed to be tentative.

Also, there is a really good reason for favoring simple models over incomprehensibly complex models, as the latter cannot be used, tested, or even meaningfully be true-for-us.

It is generally accepted that for any finite set of data, there are an infinite number of models that could be used to describe it.

Right, but we don't have access to all of those models. We only have access to moderately-sized models, but we have access to vast data sets. This rather limits how many models we're likely to come up with that explain the data and are not equivalent to each other. Generally, we'd expect to come up with zero models, or one if we're lucky.

Even if it were true that compact theories hold up well in comparison to less compact theories, what would that suggest about the structure of the universe?

It suggests that the fundamental behaviors of the universe are, at least in part, not terribly complicated (i.e. basic interactions involve a low information content). It didn't have to be that way, but the success of, for instance, particle physics depends upon the existence of simple rules.

I can easily imagine a universe where such things were uncomprehensibly complex, or were directed by whimsical intelligences, or whatever. Fortunately, this does not appear to be the case.

People might admit that Newtonian mechanics makes predictions that are generally right, but the claim about people considering it a right description seems very dubious.

It's a matter of terminology, I suppose. Newtonian mechanics works very well over a range of situations. Quantum mechanics works well over a larger range, simplifying to Newtonian mechanics in one limit. Relativisistic mechanics works well over a different larger range, also simplifying to Newtonian mechanics. We have data that none of these can explain, and know of areas for which we cannot sensibly make predictions (e.g. quantum gravity). So they're all in the same boat. You either call none of them right, or all of them right. I prefer to call them all right, with the understanding that "right" only applies to their accuracy in a certain regime, since if I fail to call the "right", it is not clear that I can call anything "right". That seems like a loss of a perfectly useful concept.

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