Is Reading a Signal on a PMT "Direct" or "Indirect" Measurement?

Just to put a plug in for philosophy: What you describe is called the “Theory Ladenness of Measurement” by philosophers of science. It challenges, perhaps irrefutably, the idea that scientific quantities can be defined solely operationally.

The topic is part of the more general issue of scientific realism: That is, it it reasonable to believe that the unobservables entities or structures postulated by scientific theories are real? (After all, theories and what they postulate keep changing, or so it seems).

https://plato.stanford.edu/entries/measurement-science/#TheLadMea

https://plato.stanford.edu/entries/scientific-realism/

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So, then, it seems that even materialism is not truly concrete. We are directed toward the hard sciences to look for the facts, the truth. But, in the end, are things not as knowable as assumed? (Or have I gone too far with this conclusion?)

Weird.

I am not seeing any inconsistency between theory ladeness of measurement, and the idea that quantities can be defined operationally.

https://plato.stanford.edu/entries/operationalism/

I enjoy some philosophy, especially epistemology, but sometimes it can seem a bit far from what happens in practice. I don’t have much expertise in philosophy but I am an experimental physical chemist who teaches Quantitative and Instrumental Analysis classes. My comments below come from that experience.

I usually define a measurement as a signal that has some (mathematical) dependence on a change in some physical property of the sample. Practically, we don’t need to know why the dependence is there. We can (and students typically do) treat the translation from physical property to signal as a “black box”. We typically try to distinguish between three contributions to the signal:

  • the signal due to the analyte - this should have some functional form (linear is nice but not necessary)
  • signal due to random error - this generally follows some distribution (often Gaussian) and provides some uncertainty to the measurement
  • signal due to systematic error - this could be operator (mis-calibration), instrumental (background noise), or perhaps due to some other variable

So is the signal on a PMT direct or indirect measurement? I’m not sure the question makes a whole lot of sense really. I think it could be like asking is something is hot or cold. A PMT is a fairly direct measurement of photons in that it’s possible to “see” individual photon hits, but it’s also indirect in that the signal is still just a current flow caused by a cascade chain reaction of electron impacts that started with a single photon. I don’t need theory to record the current and look at its dependence on how much light hits the detector, but it’s often helpful when trying to interpret odd results.

Another example from my area is Beer’s Law (the undergrad’s favorite): A=\varepsilon b c . In this case we have a mathematical relationship between absorbance (A) measured and concentration (c) of analyte. Students don’t care why Beer’s Law works and are happy to use it as a “black box” tool. However, if you know the theory of how it’s derived you can be aware of problematic points (i.e. that it becomes nonlinear at high concentrations). I have no real way to determine how direct or indirect this measurement of concentration is.

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I agree @jordan.

Concepts like independent corroboration might be valuable here.

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Thanks for those very pertinent links. From what I can gather from this particular link, it would seem like there are measurements with elements of theory involved that have been crossed checked in some way with other types of measurements and confirmed, which seem to me would fall into the category of objective. Whereas when testing to confirm an entire theory there will be subjective aspects to the measurements until they are confirmed by cross checking with other types of measurements. Does that sound like more or less the gist of what’s being said?

I’m not sure the reason for the wording of the title? Maybe @T_aquaticus (sorry I think this was actually @dga471 who titled this) can clarify what he meant by that? It may be I said something to that effect somewhere? Or maybe a mixing up of distinctions? I’m more concerned with direct and indirect in terms of empirical access to a particular entity, e.g., object, event, etc. I’m still kind of unsure about how to approach that particular distinction. But that’s another discussion.

With measurement I’m more concerned with the objectivity of the measurements. I think we’re trying to sort out if theory-laden measurements would be considered objective vs subjective. I’m leaning more towards objective when confirmed by alternative principle of operation measurements, and subjective when not. How do you see it?

It seems like you do not have a working definition of objective and subjective. Things you subjectively think are convincing, you call objective. Things you subjectively determine are not convincing you call subjective. I’m not sure you or anyone else can tell us what lands thing on either side of that line.

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I think you have an important concept right: we build instruments based on a theory that is well confirmed, and then use those instruments to test less confirmed theories. (But as the article details, sometimes things are more complicated, with the link between theory and measurement being one iteratively improving the other).

I agree with other commenters that using terms like “objective” and “subjective” can be confusing, because there are many different ways to understand them. I personally stick with objective processes. Furthermore, whether a process is objective can depend on the domain of knowledge in which the process is being used.

For similar reasons, I avoid words like “fact” and “true” unless there is first some philosophical discussion and agreement on how the terms are being used.

Here is a link on scientific objectivity; the Introduction section defines what I mean by objective process (versus objective product). The rest of the article then addresses details which are mostly outside the scope of the this thread (although theory ladenness comes up again).

https://plato.stanford.edu/entries/scientific-objectivity/

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Sorry, fixed the title to make it more intelligible.

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What I’m not familiar with is how they go about actually confirming a theory using independent methods. But I would assume if the theory is confirmed in some independent manner that the iterations of improvement between measurements and theory would be reliable, and could in a sense be said to have an acceptable degree of objectivity. Am I on the right track?

Yes, I’ve come across this article before and found some of it useful for some of the conversations I’ve been having with others on this forum. However, I missed seeing the usefulness of distinguishing between product objectivity and process objectivity. Thanks for pointing that out.

Hmm, can you sight the examples of where I’ve done what you’re saying? If I’ve done that anywhere I’m certainly not aware of it. I think generally what I’ve been arguing for is this; If it’s independent of what someone thinks or feels it’s objective.

Hmm, how do we know if it’s independent? Is it that there are other observers? Is it that that it has to be something external to the person?

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It seems it would depend on the circumstances as to how to establish independence. If I’m understanding it correctly, here’s one example of using independent confirmation to establish objectivity from one of the articles @BruceS provided.

There would seem to be, at first glance, a vicious circularity if one were to use a mercury thermometer to measure the temperature of objects as part of an experiment to test whether or not objects expand as their temperature increases.

Nonetheless, Franklin et al. conclude that the circularity is not vicious. The mercury thermometer could be calibrated against another thermometer whose principle of operation does not presuppose the law of thermal expansion, such as a constant-volume gas thermometer, thereby establishing the reliability of the mercury thermometer on independent grounds.

If you want to pursue these questions, I think that studying philosophy of science is the way to go. The undergrad texts written by Godfrey-Smith, Ladyman, and Rosenberg are all good. There is also a Very Short Introduction to Objectivity that I found helpful . Also, search Wikipedia for the Merton Norms for related ideas.

All of these authors take the view that the role of philosophy of science is to understand what makes the practices of science successful.

How do we determine what the correct results are?

For the scientist, they don’t delve into these philosophical questions. They just assume that what they are measuring is real and move forward from there.

However, that doesn’t mean we should ignore the philosophical questions. These are still important questions to ask. The best we can do, IMO, is to settle on a metaphysical framework and refuse to change it even if it leads to answers we may not like.

That’s a very good description of how science works. The concept is rather straightforward. You start with a set of facts and theories that people accept as true, and then build towards a conclusion. It is the art of creating unavoidable conclusions.

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I commented on this in the thread linked to this discussion since it seems to be more on topic with that thread.