Philosophy of Science

Son Goku

I'm posting this here as the main Science board is a bit dead.

This subject comes up an awful lot in the philosophy, religion and humanities forums, but I thought it might be good to get the discussion going here.

I thought I'd begin by posting a physicists working philosophy that I wrote a while ago.

Make of it what you will.

There are five categories, basically, of observability or phenomena:

1. The directly observable:Footballs, trees, e.t.c.
That which is directly detectable by the human sensory apparatus.

2. The indirectly observable, phenomena class:
Things which leave traces or evidence of their existence on other, humanly observable, objects.
Examples: Gravity, electrons, black holes e.t.c.

3. The indirectly observable, constrained class:
Things which leave traces on the class above.
Example: Quarks. At high enough energies the readings from protons differ from lower energies.
A quark leaves a perturbation on the trace left by a proton rather than having a trace in its own regard.
We infer quarks from the subtle changes in the protons trace as you increase energy.

4. The indirectly observable, mathematical class:
Entities which leave no trace what so ever, at all and theoretically are incapable of leaving a trace. However excluding them from calculations gives incorrect results which don't match experiment.
Example: Loop and vacuum diagrams in quantum field theory.

5. The indirectly observable, ghost class:
Things which pop up in Quantum Field Theory, which don't seem to matter at all. They can't be observed nor does leaving them out of calculations give incorrect results.
Excluding them from a theory only decreases mathematical elegance.
Example: The Dilaton, instantons.

(Some argue that there should be a sixth class for these other things that I won't go into as it is a fringe issue.)

Depending on who you are, there will be different cut off-points for what you consider "real".

I myself would consider categories 1,2 and most of 3 real and I'm occasionally given to thinking that things in category 4 could be real.

Believing solely in category 1 as being real is very rare in a physicist.
Believing none are real is practically non-existent.

In different areas of physics believing different mixes of the categories is standard.
(example:
Particle Physics: 1,2 and 3.
Cosmology: 1 and 2.
String Theory: All of them.)

Panserborn

Nice organisation. Can't really comment as I'm a biologist (only look at category 1 and maybe an in-between 1.5 category since we can detect, observe and modify proteins but for the most part can't physically "see" them) but the classification is nice!

nesf

From 4 on the question of reality doesn't come into it imho. It's more that there is some plausability in them being real rather than them being real (ie observable). But, as we all know, what we can observe changes, so they may in the future become observable and thus "real". That doesn't mean they are real now though. Just that they are "predicted" in a sense.

Son Goku

nesf wrote:

From 4 on the question of reality doesn't come into it imho. It's more that there is some plausability in them being real rather than them being real (ie observable). But, as we all know, what we can observe changes, so they may in the future become observable and thus "real". That doesn't mean they are real now though. Just that they are "predicted" in a sense.

I should make it clear that I only occasionally think they may be real, given how much they are built into the theories they're found in. Although it is difficult to know what to think of them as the theory they are found in exclusively states that they will never be observed.

You only need them to make the observables come out right, but are they just a mathematical trick or something which actually exists?
The difficult thing is also that if you move to a different way of doing the theory the can disappear completely.

Class 4 probably causes the most philosophical problems. It's here that virtual particles and the interior of black holes live.

Civilian_Target

That's a strange way of thinking of things. I'd say 1 & 2 are real OK. 3 is not necessarily real, but it's convenient and sensible to presume these things are real anyway (there's a good chance Quark theory is wrong but at least we can use it if we assume it to be true). 4 is just a convenient description of things, a holding pan of things we can almost certainly assume are wrong but work for the moment. But I honestly don't see the philosophy behind any of it - science is just a detailed approximation of nature as we see it, it's going to be inaccurate in parts, hence the need to improve it all the time.

Son Goku

Civilian_Target wrote:

4 is just a convenient description of things, a holding pan of things we can almost certainly assume are wrong but work for the moment. But I honestly don't see the philosophy behind any of it - science is just a detailed approximation of nature as we see it, it's going to be inaccurate in parts, hence the need to improve it all the time.

The thing I find most difficult and the reason I use these classes, is because these are things that are accurate, I don't really care (in a philosophy of science manner) for the inaccurate theories.

For instance virtual particles, leave them out and we have an inaccurate theory. Leave them in and we have the most accurate theory in physics, QED, and yet QED itself says they can never be detected. What are we to make of such things?

I wouldn't regard them as mathematical tricks, simply because their physical interpretation falls out of the formalism too easily and yet I can't claim they're real in any way because they can't be detected.