# A short question

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I apologize if this doesn't belong here, first time posting on this board (or most any for that matter). I enjoy reading books and articles about physics and quantum physics, and I often read the ones that leave the math out and explain the concepts. However, for this question I have, I think might need to ask those who know the math:

What would happen to the commonly held laws of physics if we treated everything unobservable as nonexistant?

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Pretty much nothing I guess, assuming you keep the same math. To understand what I mean by that, you don't need to go to quantum mechanics. Take the concept of "force" in classical physics. Whether you treat it as something that physically exists or as a purely made-up concept created for performing calculations does not effect the outcome of a calculation or the actual process. Only the rather inconsequential interpretation ("see a force of work" vs. "see an effect that is commonly modelled via the concept of force").

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I apologize if this doesn't belong here, first time posting on this board (or most any for that matter). I enjoy reading books and articles about physics and quantum physics, and I often read the ones that leave the math out and explain the concepts. However, for this question I have, I think might need to ask those who know the math:

What would happen to the commonly held laws of physics if we treated everything unobservable as nonexistant?

Logically nothing.

Any departure from the laws brought about by a thing would be a means by which we could deduce the existence of that thing and hence observe it.

Take something that's difficult to observe, like the neutrino.

We know that, according to the laws of physics, momentum is conserved, but some forms of radioactive decay seem not to obey that law. From this we deduce that there must be something else involved. We thereby observe the existence of neutrinos.

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It depends on what you mean. Take action at a distance. If we remove the unobservable virtual particles, e.g. Coulomb's doesn't change, but now there is no explanation for it. Without virtual particles you lose (much of) QED and all that it tells us. And quarks? Quarks can't be directly observed — does that count? Remove them and a lot of the physics of nuclear structure falls apart.

There are a lot of things in physics that are constructs and not really observable. We see the the effects, but not the actual construct. Fields, for example. We can't observe fields themselves, we see the effects of them. Take them away and physics changes.

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The Laws of Physics condense us into nothing. I have no problem with treating nothing as non-existent. It could turn the Laws of Physics on its head and allow me to stop thinking that I am about to be sucked into a black hole.

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Wow, thank you so much guys, that actually helps clarify things quite a bit. Which would bring me about to another question, more along the lines of what I believe I was actually thinking.

So if the presence of an observer forces objects in quantum superposition down to a singular position or outcome, as has been theorized (but not proven I believe); when there is no observer present and there exists the setup of one object acting on another (say for example the moon pulling the tides), how could it be affecting the corresponding object in a linear way if it is, in fact in all possible positions at once?

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What would happen to the commonly held laws of physics if we treated everything unobservable as nonexistant?

That depends very much on what you mean by "unobservable", and also by what interpretation of quantum mechanics you ascribe to.

The kinds of observations physicists make are quite indirect. Take something as mundane as stepping on a bathroom scale to see how much you weigh. You aren't really observing your weight. You are observing the angular deflection of some pointing device. Yet you would never say "Wow! My diet is working! I only weight 37 degrees today!" For one thing, the scale isn't calibrated in degrees. For another, weight as angle doesn't make sense. That angular deflection is caused by a somewhat complex mechanism that converts the linear deflection of the scale's plate against a spring into that angular deflection. This linear deflection is no better than an angular deflection for representing weight. This linear deflection can be converted to force by assuming the spring in your scale obeys Hooke's law (which it doesn't). With this at hand, you could say "Wow! My diet is working! I only weigh 667 newtons today!" Physicists might think that is a good expression for weight, but colloquially and legally, weight means mass. One last thing needs to be done, which is to convert that 667 newton force value to a 68 kilogram mass value by assuming that this force results from a gravitational acceleration of 9.80665 m/s2 (which almost certainly isn't the acceleration due to gravity where you live).

And that's just for stepping on the scale on the morning. The path gets very indirect when it comes to observing things like photons, electrons, neutrinos, and quarks. I would say that those photons and other things of interest to physicists are "observable" even though the observations are quite indirect. With this concept of observability, the Copenhagen interpretation, taken to its logical positivism extreme, pretty much says that that which is utterly unobservable doesn't exist. A slightly less extreme view that still falls under the Copenhagen interpretation umbrella is that the existence of something that is utterly unobservable is irrelevant to physics (except when it's a useful fiction, such as wave function collapse).

There are other, more modern interpretations of quantum mechanics than the Copenhagen interpretation. Each has its weirdnesses. They pretty much have to; quantum mechanics is a bit (more than a bit) weird.

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That depends very much on what you mean by "unobservable", and also by what interpretation of quantum mechanics you ascribe to.

The kinds of observations physicists make are quite indirect. Take something as mundane as stepping on a bathroom scale to see how much you weigh. You aren't really observing your weight. You are observing the angular deflection of some pointing device. Yet you would never say "Wow! My diet is working! I only weight 37 degrees today!" For one thing, the scale isn't calibrated in degrees. For another, weight as angle doesn't make sense. That angular deflection is caused by a somewhat complex mechanism that converts the linear deflection of the scale's plate against a spring into that angular deflection. This linear deflection is no better than an angular deflection for representing weight. This linear deflection can be converted to force by assuming the spring in your scale obeys Hooke's law (which it doesn't). With this at hand, you could say "Wow! My diet is working! I only weigh 667 newtons today!" Physicists might think that is a good expression for weight, but colloquially and legally, weight means mass. One last thing needs to be done, which is to convert that 667 newton force value to a 68 kilogram mass value by assuming that this force results from a gravitational acceleration of 9.80665 m/s2 (which almost certainly isn't the acceleration due to gravity where you live).

And that's just for stepping on the scale on the morning. The path gets very indirect when it comes to observing things like photons, electrons, neutrinos, and quarks. I would say that those photons and other things of interest to physicists are "observable" even though the observations are quite indirect. With this concept of observability, the Copenhagen interpretation, taken to its logical positivism extreme, pretty much says that that which is utterly unobservable doesn't exist. A slightly less extreme view that still falls under the Copenhagen interpretation umbrella is that the existence of something that is utterly unobservable is irrelevant to physics (except when it's a useful fiction, such as wave function collapse).

There are other, more modern interpretations of quantum mechanics than the Copenhagen interpretation. Each has its weirdnesses. They pretty much have to; quantum mechanics is a bit (more than a bit) weird.

I think what I was trying to get at originally (though the question has kinda mutated thanks to all the replies from you fine folks) was what would happen if you discounted all the things that were not directly observable. i.e. external forces "outside" the range of a fixed experiment, and things that we could perceive the effects of, but not the effector itself.

I was kind of trying to figure out the question that popped into my head one day: What would happen to our view of the world if everything the we couldn't observe (as in: us as observers in the classical sense) didn't actually exist until we observed it? I understand that there's the theory of quantum superposition, wherein everything exists in all possible staes until observed, but I also recently watched Leonard Susskind's lecture on he possibility of the observable world being a hologram, so I was trying to reconfigure the two ideas in my own head with the help of people much more knowledgeable than myself.

My apologies for the vagueness, I should have come right out and said all of this in the beginning, but at that point I barely had the idea of the question in mind, much less it's rationale.

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...convert that 667 newton force value to a 68 kilogram mass value...

Try telling someone you mass 4.66 slugs and see how many odd looks you get.

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Try telling someone you mass 4.66 slugs and see how many odd looks you get.

That's off-topic, but when used without a qualifier, the word pound denotes either a unit of money or a unit of mass. Never force. The units of force in the customary system are the pound-force and poundal (which nobody uses).

I think what I was trying to get at originally (though the question has kinda mutated thanks to all the replies from you fine folks) was what would happen if you discounted all the things that were not directly observable.

One issue here is that "directly" qualifier. That's why I used the bathroom scale as an example in my previous post. Hardly anything is "directly" observable. I think what you want is "somehow" observable.

I was kind of trying to figure out the question that popped into my head one day: What would happen to our view of the world if everything the we couldn't observe (as in: us as observers in the classical sense) didn't actually exist until we observed it?

That's a good question. David Mermin asked that question in Is the moon there when nobody looks? Reality and the quantum theory, Physics Today, April 1985, http://www.iafe.uba.ar/e2e/phys230/history/moon.pdf.

The thing that really throws a monkey wrench in the works is Bell's Theorem. It demands that you have to throw out something very dear. You either have to toss locality (what happens in Vegas stays in Vegas, at least for a little bit of time) or counterfactual definiteness ("realism") (the Moon is there even when we don't look at it). Pick your poison ...

Edited by D H

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