See definition 24.1 on page 2 of this 12 page pdf for the definition of an unobservable state in control systems theory:

https://ocw.mit.edu/courses/6-241j-dynamic-systems-and-control-spring-2011/2f03f88e1a714f3ccdb0b7b3f05a2c55_MIT6_241JS11_chap24.pdf

a state q of a system is unobservable if its initial condition is indistinguishable from the zero initial condition.

In economics there is a concept called the natural rate of interest and it is held to be unobservable (which is why some experts argue it is irrelevant due to non-existence):

https://www.frbsf.org/research-and-insights/publications/economic-letter/2003/10/the-natural-rate-of-interest/

In the long run, economists assume that nominal interest rates will tend toward some equilibrium, or “natural,” real rate of interest plus an adjustment for expected long-run inflation.

Unfortunately, the “natural” real rate of interest is not observable, so it must be estimated.

These concerns about unobservable states relate to our conceptual math models for physical or economic systems and not to the philosophy of classifying human perceptions using the naked eye versus instruments that extend our perceptions.

The bacteria seen under a microscope are thought to be images which are magnified by the properties of light and lenses. When there is sufficient light, and proper instrument design, we assume the images are accurate representations of what is seen with the instrument due to our coherent theories of light and lenses. We make semiconductors by sending light through photomasks and lenses to reduce the size of physical features in the semiconductor structure, and we do so very effectively, incorporating the principles of chemistry, optics, and materials science. But if we speculate about what we see or otherwise detect using a microscope, telescope, or scientific instrument it raises the question of what is observable versus unobservable.

See definition 24.1 on page 2 of this 12 page pdf for the definition of an unobservable state in control systems theory:

https://ocw.mit.edu/courses/6-241j-dynamic-systems-and-control-spring-2011/2f03f88e1a714f3ccdb0b7b3f05a2c55_MIT6_241JS11_chap24.pdf

a state q of a system is unobservable if its initial condition is indistinguishable from the zero initial condition.

In economics there is a concept called the natural rate of interest and it is held to be unobservable (which is why some experts argue it is irrelevant due to non-existence):

https://www.frbsf.org/research-and-insights/publications/economic-letter/2003/10/the-natural-rate-of-interest/

In the long run, economists assume that nominal interest rates will tend toward some equilibrium, or “natural,” real rate of interest plus an adjustment for expected long-run inflation.

Unfortunately, the “natural” real rate of interest is not observable, so it must be estimated.

The Natural Rate of Unemployment (NAIRU) is another controversial variable which is thought to be greater than zero, but otherwise cannot be measured directly, and which could be considered unobservable:

https://www.cbo.gov/sites/default/files/110th-congress-2007-2008/workingpaper/2007-06_0.pdf

In the context of macroeconomics, the two political problems are keeping the currency stable against episodes of inflation or deflation and fostering maximum employment using fiscal and/or monetary policy. NAIRU is rejected by some Post-Keynesian economists who argue that fiscal policy should be used to employ everyone who wants a job that fits their skills. The point I am making is that arguments over observable and unobservable variables infect politics and economics.

These concerns about unobservable states relate to our conceptual math models for physical or economic systems and not to the philosophy of classifying human perceptions using the naked eye versus instruments that extend our perceptions.

The bacteria seen under a microscope are thought to be images which are magnified by the properties of light and lenses. When there is sufficient light, and proper instrument design, we assume the images are accurate scaled representations of what is seen with the instrument due to our coherent theories of light and lenses. We make semiconductors by sending light through photomasks and lenses to reduce the size of physical features in the semiconductor structure, and we do so very effectively, incorporating the principles of chemistry, optics, and materials science. But if we speculate about what we see or otherwise detect using a microscope, telescope, or scientific instrument it raises the question of what is observable versus unobservable.

See definition 24.1 on page 2 of this 12 page pdf for the definition of an unobservable state in control systems theory:

https://ocw.mit.edu/courses/6-241j-dynamic-systems-and-control-spring-2011/2f03f88e1a714f3ccdb0b7b3f05a2c55_MIT6_241JS11_chap24.pdf

a state q of a system is unobservable if its initial condition is indistinguishable from the zero initial condition.

In economics there is a concept called the natural rate of interest and it is held to be unobservable (which is why some experts argue it is irrelevant due to non-existence):

https://www.frbsf.org/research-and-insights/publications/economic-letter/2003/10/the-natural-rate-of-interest/

In the long run, economists assume that nominal interest rates will tend toward some equilibrium, or “natural,” real rate of interest plus an adjustment for expected long-run inflation.

Unfortunately, the “natural” real rate of interest is not observable, so it must be estimated.

These concerns about unobservable states relate to our conceptual math models for physical or economic systems and not to the philosophy of classifying human perceptions using the naked eye versus instruments that extend our perceptions.

The bacteria seen under a microscope are thought to be images which are magnified by the properties of light and lenses. When there is sufficient light, and proper instrument design, we assume the images are accurate representations of what is seen with the instrument due to our coherent theories of light and lenses. We make semiconductors by sending light through photomasks and lenses to reduce the size of physical features in the semiconductor structure, and we do so very effectively, incorporating the principles of optics. But if we speculate about what we see or otherwise detect using a microscope, telescope, or scientific instrument it raises the question of what is observable versus unobservable.

See definition 24.1 on page 2 of this 12 page pdf for the definition of an unobservable state in control systems theory:

https://ocw.mit.edu/courses/6-241j-dynamic-systems-and-control-spring-2011/2f03f88e1a714f3ccdb0b7b3f05a2c55_MIT6_241JS11_chap24.pdf

a state q of a system is unobservable if its initial condition is indistinguishable from the zero initial condition.

In economics there is a concept called the natural rate of interest and it is held to be unobservable (which is why some experts argue it is irrelevant due to non-existence):

https://www.frbsf.org/research-and-insights/publications/economic-letter/2003/10/the-natural-rate-of-interest/

In the long run, economists assume that nominal interest rates will tend toward some equilibrium, or “natural,” real rate of interest plus an adjustment for expected long-run inflation.

Unfortunately, the “natural” real rate of interest is not observable, so it must be estimated.

These concerns about unobservable states relate to our conceptual math models for physical or economic systems and not to the philosophy of classifying human perceptions using the naked eye versus instruments that extend our perceptions.

The bacteria seen under a microscope are thought to be images which are magnified by the properties of light and lenses. When there is sufficient light, and proper instrument design, we assume the images are accurate representations of what is seen with the instrument due to our coherent theories of light and lenses. We make semiconductors by sending light through photomasks and lenses to reduce the size of physical features in the semiconductor structure, and we do so very effectively, incorporating the principles of chemistry, optics, and materials science. But if we speculate about what we see or otherwise detect using a microscope, telescope, or scientific instrument it raises the question of what is observable versus unobservable.