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metamorphiccat
57499.  Mon Mar 06, 2006 1:38 pm Reply with quote

Quote:
However, Ptolemy's model was beset with problems from the very start and never really explained planetary motion satisfactorially except in very vague terms.


Ptolemy’s model had absolutely no basis in physical reality. I never stated otherwise. Its initial form required significant modification, the epicycles on epicycles to which I referred in my original comment, and it became clumsy and overly complicated. However, with each successive modification, the model predicted planetary motion with increasing accuracy, and the level of accuracy of prediction in terms of the phenomena that could be observed at that time was remarkable in the context of that period in history. I agree that a literal comparison on the basis of the knowledge of the Universe we have now is unfair. I was not attempting a literal comparison. I was attempting to draw a parallel. I realise that my original comments must have been phrased in a way that did not make this absolutely clear, and for that I apologise. Allow me the opportunity to attempt a clarification.

The parallel I was trying to draw between these two points in history, Ptolemy’s time and ours, goes something like this. In Ptolemy’s time, the extent of our ability to observe the Universe was more limited than it is now. However, the observational data that could be obtained tallied with Ptolemy’s modified model (with epicycles and eccentricities) quite closely. Some observations were not predicted to a perfect degree of accuracy. A very few did not make sense. Measurement techniques were crude. But this was the extent of our knowledge at this time, and the theory was accepted because within the boundaries of what we knew it was reasonably accurate.

At the present, we have a theory of gravitation that appears, to the extent of our ability to make observations of the Universe, to be very accurate for many of our observations. Remarkable in the context of this period in history. There are a few observations that lead us to modify our cosmology to incorporate the existence of dark matter. I did not at any time state that there was no other evidence in support of the existence of dark matter. I am aware that there is some. The thought that I am trying to get across is that we have been here before many times. We have been absolutely sure that we were right. All our observations fitted the theory. But then we made more sophisticated observations, and our shiny theory began to look a little bit dimmer. We modified our theory, because we had believed in it for years and everyone knew it was correct. In some cases we were right, in some we were very wrong.

We do not currently have a means of observing everything that happens in the Universe. We do not necessarily need to do this in order to formulate valid theories about how the Universe works. But there is a limit to our current understanding, just as there has always been and always will be. We have developed techniques that enable us to see more than we ever have before, but we should still be aware that there are still limits to our knowledge. Our current theories may explain everything we see, but that does not make them the only explanation. It does not make them correct. But if there is no evidence to the contrary, we can accept them as valid until a better idea comes along. I don’t believe we should ever stop questioning them though.


Quote:
The theory of gravity covers just about everything in the universe. Yes there are definitely problems with some large scale observations, but in the vast majority of cases the current theory works extremely well.


These two sentences perfectly illustrate my next point. A model of a physical system that does not explain all observations made of that system to within a reasonable degree of accuracy does not provide a complete explanation of that system and cannot be said to be valid. It may require modification, or it may need to be abandoned in favour of another idea. Most data appearing to fit the model does not make it valid. Scientific theory does not get points for trying hard, or for nearly succeeding. It either fits the data or it doesn’t. If it only fits some data, it is not valid, however much of the data it does fit. It may provide sufficiently accurate predictions for a whole range of purposes. That does not make it true.

It is possible that there could be significant errors in the measurements, and that the contradictory data is not valid. But a scientist cannot simply decide to discard data because it doesn’t fit the theory he or she believes to be correct. That is not science.

 
dr.bob
57646.  Tue Mar 07, 2006 5:53 am Reply with quote

It sounds like we're violently agreeing here :)

I would go along with almost everything you've said here. I'll just make a couple of comments.

metamorphiccat wrote:
the observational data that could be obtained tallied with Ptolemy’s modified model quite closely......... At the present, we have a theory of gravitation that appears to be very accurate for many of our observations.


I've highlighted a couple of phrases there which make the point I was trying to point out. You originally said that our model of the universe fits the data as closely as Ptolemy's model fitted the data at that time. I'm trying to contend that our current model in fact fits the data much better. Though this is a personal belief and is impossible to prove since I don't have access to the published data from Ptolemy's time.

I guess it must've pushed a button somewhere since it sounded a bit like "today's theory is no better than Ptolemy's" which I wanted to make sure no-one thought even though I realise that's not what you were saying at all.

I did hear a theory of the philosophy of science which held that science proceeds by stretchng theories to fit the data until it breaks and is replaced by a new theory (yup, makes sense to me) that is no better than the previous theory (this bit, though, is utter bollox).

Hmm, sorry. Went off on a bit of a tangarine there. Back to the matter at hand.

metamorphiccat wrote:
It may provide sufficiently accurate predictions for a whole range of purposes. That does not make it true.


Scientific theories are definitely not true. Hence the name "theory". At it's most basic level, science says "we do not know anything. Here's a plausible sounding theory which seems to explain how things work. However, this is not some universal truth and we're currently working to figure out how we can improve it."

Bearing that in mind, I'd like to take issue with one thing you said:

metamorphiccat wrote:
Scientific theory does not get points for trying hard, or for nearly succeeding. It either fits the data or it doesn’t.


All scientific theories are doomed to failure. Eventually some more data will be produced which doesn't fit the theory and a new theory will be needed. This new theory will then extend our knowledge of the universe. It's happened before and I've no doubt it'll continue to happen.

However, those previous theories that have been proved wrong are not worthless. I think they do score points for explaining as much of the data as they could and leading us towards further understanding. It would've been almost impossible to leap into relativity from a standing start. It was thanks to the pioneering work of people like Newton and Maxwell that laid the foundations that Einstein was able to build on. Thus, those earlier theories definitely had some merit.

Even Ptolemy's ideas should be considered a stepping stone to knowledge since it eventually made people realise just how extremely unlikely it was that the Sun and planets went 'round the earth.

 
Gray
57647.  Tue Mar 07, 2006 5:58 am Reply with quote

Quote:
Scientific theory does not get points for trying hard, or for nearly succeeding. It either fits the data or it doesn’t. If it only fits some data, it is not valid, however much of the data it does fit. It may provide sufficiently accurate predictions for a whole range of purposes. That does not make it true.

If you have an instrumentalist approach to science (i.e. if you are a technologist) then you aren't remotely interested in whether something is 'true' or not (or even whether the concept of 'truth' exists at all). You only care whether you can accurately predict the behaviour of the world (and your machine) using a model - even an incomplete one.

Newton's theory, though now shown to be incomplete, is perfectly adequate for making any kind of observation concerning most objects on Earth that aren't moving at a significant proportion of light speed. Whether it's 'true' or not is irrelevant. I can see an amusing cartoon of two construction engineers studying a blueprint of a new bridge and one scratching his chin and saying:
Quote:
Yeah, I agree that we can put a cantilever truss over here to spread that load, but is this rule of thumb we'll use to calculate the stress actually true, Bill?


Karl Popper put forward a briliant argument that instrumentalism had no place in science, but also that idealising one's models as 'truth' was a fallacy in the first place. Science, he said, does not attempt to establish truth because it can never know what it does not yet know, and has not uncovered. All science can do is amass theories that work 'so far'.

I'm immediately suspect of any scientist who tries to sell their theory as 'truth' (Dawkins included) because by that point they're just evangelits, attracting only belief (which also has no place in science).

The problem is that people can't be satisfied with the honest answer of science "we don't know, but this theory looks promising". They want all or nothing, and the media only strengthens this misconception, giving scientists - and their results - an impossible image to live up to.

 
metamorphiccat
57903.  Tue Mar 07, 2006 6:42 pm Reply with quote

dr.bob and Gray, I agree with both of you. Non-violently in both cases. I hope that science is about asking questions, and the ideas are there to give us something to question. I really hope we never stop asking questions or testing our ideas, and I think we're far too ready to sit back and accept things as gospel truth because they seem to fit ok.

You're both spot on that we'll never get to the truth. I did try very hard to avoid using the word. That was where I was trying to go with my original comment. That we should keep questioning our ideas even when they appear to fit. Keeping the search going until we find something that fits perfectly, but in the context that we never will find something and this will be the thing that always keeps us questioning. I shudder to think what we'd do with the truth if we had it.

But just to pick on one thing dr.bob, your comment on the use of the word 'theory'. I made almost exactly the same statement as you a couple of years ago and was humiliated in front of the people I'd least like to look stupid in front of. Perhaps there's an argument I could have thrown back, but I haven't found it yet. In a scientific context, the word 'theory' can be used to represent a body of knowledge associated with a topic or subtopic. So it isn't always used in the 'it's only a theory' (as in, it's just an idea we have little or no evidence to support) context. The choice of word does carry a sort of implied acknowledgement that it isn't the right answer, I suppose. Which I find reassuring.

Oh, and I'm a graduate engineer. If I ever caught myself saying
that rules of thumb weren't perfectly adequate in an appropriate context, I'd worry about my normal brain functions. If it looked like I was suggesting otherwise, I wasn't, and I'm sorry to have been so unclear in expressing my meaning.

 
Gray
57953.  Wed Mar 08, 2006 4:39 am Reply with quote

No no, that's quite alright. I'm a graduate engineer too (although have since 'moved on') and our practicals were pretty much ruled by thumbs.

I think there's still a problem with scientific theories (and paradigms) when you find one that fits the experimental results exactly - it's still completely possible that it's not the 'correct' theory - i.e. the one that explains mechanistically what is going on.

I think this is the case with quantum mechanics (and probably dark matter, however close they get) - statistical analysis fits QM data pretty much perfectly everywhere it's applied, but it seems insane to most scientists that statistics is the mechanism behind QM. But hey, if it works, and allows us to have this conversation over the internet (silicon chips are the direct technological products of QM after all) then fine - we'll stick with it.

Because science is largely funded by technologists (who want a financial return), that's the scientific attitude all over - if it works, stick with it. When it stops working, have another look. In a way, the fantastic accuracy of the QM model is its own downfall - while it works so well, people won't be that tempted to look too hard elsewhere for an explanation.

I think the whole discussion about truth, theories, paradigms and sufficiency - and the whole incremental evolution of knowledge - is a fascinating area. Have you read any Popper? I'd really recommend The Logic of Scientific Discovery - it's a bit long-winded, but, like Feynman, he's the only one you can trust when it comes to complete honesty and integrity about science.

Dawkins uses the word 'fact' all over the place, and is asking for trouble because most non-scientific people (and even lots of scientists) think that 'fact' means 'truth', whereas all it means is 'really, amazingly robust theory'. But theory it is - you were right, but they misunderstood you.

 
Tas
57960.  Wed Mar 08, 2006 4:56 am Reply with quote

Quote:
I'd really recommend The Logic of Scientific Discovery - it's a bit long-winded, but, like Feynman, he's the only one you can trust when it comes to complete honesty and integrity about science.


Sorry to butt in, and be pedantic (hehehehe) but how can he be like Fenyman, AND be the only one?

This is a seriously QI thread, btw, chaps and chapesses.

:-)

Tas

 
Gray
57987.  Wed Mar 08, 2006 6:30 am Reply with quote

D'you know, I thought exactly the same thing the moment I clicked 'Submit'. :-D

 
dr.bob
58005.  Wed Mar 08, 2006 7:26 am Reply with quote

metamorphiccat wrote:
But just to pick on one thing dr.bob, your comment on the use of the word 'theory'. I made almost exactly the same statement as you a couple of years ago and was humiliated in front of the people I'd least like to look stupid in front of.


I'm sorry to hear that. Especially as I think you were in the right there.

metamorphiccat wrote:
In a scientific context, the word 'theory' can be used to represent a body of knowledge associated with a topic or subtopic. So it isn't always used in the 'it's only a theory' (as in, it's just an idea we have little or no evidence to support) context.


True, however you could still argue the value of the body of knowledge that's been built up over the years. Measurements and data are only as good as the equipment used to make them. As science progresses, equipment becomes more accurate and measurements become more precise. Sometimes this extra precision shows up problems with the data which simply weren't possible to detect before.

I guess the phrase "it's only a theory" does imply a lack of worth. Certainly a theory that explains how a lot of things work is worth a lot more than something just thought up on the spot, and it is useful for certain calculations. However, as I think we've already established here, that's a very different thing from knowing the truth. It is simply the best explanation we currently have. It's better than other theories (there's the value of the theory, I guess) but it's not perfect.

There's also the problem that any theory can be disproved by some suitably radical data, and it's impossible to predict when this data will be measured. For example, it's possible that one day gravity will act in the opposite direction for a while. Granted, this is extremely unlikely given the gazillions of measurements of gravity that have been done over the last few thousand years, but nobody can say it's completely impossible and, if it ever did happen, we'd have to invent a completely different theory of gravity.

That's obviously an extreme example. However, there are other theories (or, I guess more accurately, other parts of theories) which are supported by considerably fewer practical measurements and are, therefore, a little more likely to be shown up by some rogue data.

 
grizzly
58055.  Wed Mar 08, 2006 10:18 am Reply with quote

Quote:
This is a seriously QI thread, btw, chaps and chapesses.


I'm glad I started it. Although I must say that my brain could cope a lot better with the dark energy/matter discussion than this Philosophy of Science argument at the moment.

 
samivel
58056.  Wed Mar 08, 2006 10:21 am Reply with quote

Tas wrote:
This is a seriously QI thread, btw, chaps and chapesses.



I'd just like to second this view


;)

 
Tas
58074.  Wed Mar 08, 2006 11:03 am Reply with quote

Quote:
I'm glad I started it. Although I must say that my brain could cope a lot better with the dark energy/matter discussion than this Philosophy of Science argument at the moment.


What with that, this thread and the Communism thread, I think my brane may overload and spew goo-ey stuff everywhere!

:-)

Tas

 
grizzly
58090.  Wed Mar 08, 2006 11:56 am Reply with quote

<Opens umbrella in front of the computer screen>

 
metamorphiccat
58097.  Wed Mar 08, 2006 12:16 pm Reply with quote

I'll add to the comments on this being decidedly QI. I probably don't need to say that considering how often I've commented, but still, it's certainly got me thinking.

 
dr.bob
58271.  Thu Mar 09, 2006 6:07 am Reply with quote

That is, after all, what this site is all about.

At least, when it's not cracking awful jokes about prawn again christians :)

 
grizzly
58274.  Thu Mar 09, 2006 6:11 am Reply with quote

Anyone else noticed that there hasn't been a post that is on topic since yesterday lunchtime?

:-)

 

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