Observer effect (physics)
Encyclopedia
In physics
, the term observer effect refers to changes that the act of observation will make on the phenomenon
being observed. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner. A commonplace example is checking the pressure in an automobile tire; this is difficult to do without letting out some of the air, thus changing the pressure. This effect can be observed in many domains of physics.
to become detectable, a photon
must first interact with it, and this interaction will change the path of that electron. It is also possible for other, less direct means of measurement to affect the electron.
, ammeter
s and voltmeter
s need to be connected to the circuit, and so by their very presence affect the current or the voltage they are measuring by way of presenting an additional real or complex load to the circuit, thus changing the transfer function
and behaviour of the circuit itself.
, a standard mercury-in-glass thermometer
must absorb or give up some thermal energy
to record a temperature
, and therefore changes the temperature of the body which it is measuring.
The observer effect however, relates to the influence the observer has on a system. The superposition
principle (ψ = Σanψn) of quantum physics says that for a wave function ψ, a measurement will give a state of the quantum system of one of the m possible eigenvalues fn, n=1,2...m, of the operator
which is part of the eigenfunctions ψn, n=1,2,...n. Once we have measured the system, we know its current state and this stops it from being in one of its other states. This means that the type of measurement that we do on the system affects the end state of the system.
This is demonstrated in a common thought experiment using the double slit setup. Imagine a double slit experiment where quantum particles are fired towards the two slits. The quantum particles pass through the slits and hit a momentum sensor a distance of D behind the slits. The momentum sensor has the ability to be turned off and on via a pin which stops the movement of the sensor when it is hit by a quantum particle. When the pin is in place, no measurement of the momentum can take place. When the pin is removed, the sensor can recoil when struck by a quantum particle and by measuring the recoil determine from which slit the quantum particle came.
If the pin is removed and we can detect from which slit the particle came, then the wave-like passage through both slits cannot occur and no interference pattern will develop. However if we put the pin in place, and can no longer determine from which slit the particle passes through, then an interference pattern can develop. This can be taken a step further using the delayed choice experiment.
This thought experiment was proved correct experimentally. The people conducting the experiment found that when the sensor was turned off, an interference pattern developed, but when it was turned on, the interference pattern was destroyed. It was even found that the level of detection could affect the result.
The change of the wave function from ψ to ψn is called the collapse of the wave function and occurs when the measurement takes place. This collapse of the wave function is not explainable using the Copenhagen interpretation. Other explanations on why the wave function collapses have been developed such as that consciousness causes the collapse or hidden variable theory
.
The many-worlds interpretation
posits the existence of multiple universes in which an observed system displays all possible states to all possible observers. In this model, observation of a system does not change the behavior of the system—it simply answers the question of which universe the observer is located in. In some universes, the observer would observe one result from one state of the system, and in others the observer would observe a different result from a different state of the system.
. At a time when Native American cultures were rapidly disappearing, anthropologists were committed to preserving their unique cultures" . Disappearing cultures continue to be a problem, as people give up their old ways to become 'modern,' leading various organizations to try to reverse or at least slow down the loss of cultural knowledge.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, the term observer effect refers to changes that the act of observation will make on the phenomenon
Phenomenon
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...
being observed. This is often the result of instruments that, by necessity, alter the state of what they measure in some manner. A commonplace example is checking the pressure in an automobile tire; this is difficult to do without letting out some of the air, thus changing the pressure. This effect can be observed in many domains of physics.
Particle physics
For an electronElectron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
to become detectable, a photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
must first interact with it, and this interaction will change the path of that electron. It is also possible for other, less direct means of measurement to affect the electron.
Electronics
In electronicsElectronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, ammeter
Ammeter
An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes , hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters...
s and voltmeter
Voltmeter
A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to...
s need to be connected to the circuit, and so by their very presence affect the current or the voltage they are measuring by way of presenting an additional real or complex load to the circuit, thus changing the transfer function
Transfer function
A transfer function is a mathematical representation, in terms of spatial or temporal frequency, of the relation between the input and output of a linear time-invariant system. With optical imaging devices, for example, it is the Fourier transform of the point spread function i.e...
and behaviour of the circuit itself.
Thermodynamics
In thermodynamicsThermodynamics
Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
, a standard mercury-in-glass thermometer
Mercury-in-glass thermometer
A mercury-in-glass thermometer, also known as a mercury thermometer, was invented by German physicist Daniel Gabriel Fahrenheit in 1724 and is a thermometer consisting of mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the...
must absorb or give up some thermal energy
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....
to record a temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, and therefore changes the temperature of the body which it is measuring.
Quantum mechanics
The Heisenberg uncertainty principle is also frequently confused with the "observer effect". The uncertainty principle actually describes how precisely we may measure the position and momentum of a particle at the same time — if we increase the accuracy in measuring one quantity, we are forced to lose accuracy in measuring the other.The observer effect however, relates to the influence the observer has on a system. The superposition
Quantum superposition
Quantum superposition is a fundamental principle of quantum mechanics. It holds that a physical system exists in all its particular, theoretically possible states simultaneously; but, when measured, it gives a result corresponding to only one of the possible configurations.Mathematically, it...
principle (ψ = Σanψn) of quantum physics says that for a wave function ψ, a measurement will give a state of the quantum system of one of the m possible eigenvalues fn, n=1,2...m, of the operator
which is part of the eigenfunctions ψn, n=1,2,...n. Once we have measured the system, we know its current state and this stops it from being in one of its other states. This means that the type of measurement that we do on the system affects the end state of the system.This is demonstrated in a common thought experiment using the double slit setup. Imagine a double slit experiment where quantum particles are fired towards the two slits. The quantum particles pass through the slits and hit a momentum sensor a distance of D behind the slits. The momentum sensor has the ability to be turned off and on via a pin which stops the movement of the sensor when it is hit by a quantum particle. When the pin is in place, no measurement of the momentum can take place. When the pin is removed, the sensor can recoil when struck by a quantum particle and by measuring the recoil determine from which slit the quantum particle came.
If the pin is removed and we can detect from which slit the particle came, then the wave-like passage through both slits cannot occur and no interference pattern will develop. However if we put the pin in place, and can no longer determine from which slit the particle passes through, then an interference pattern can develop. This can be taken a step further using the delayed choice experiment.
This thought experiment was proved correct experimentally. The people conducting the experiment found that when the sensor was turned off, an interference pattern developed, but when it was turned on, the interference pattern was destroyed. It was even found that the level of detection could affect the result.
The change of the wave function from ψ to ψn is called the collapse of the wave function and occurs when the measurement takes place. This collapse of the wave function is not explainable using the Copenhagen interpretation. Other explanations on why the wave function collapses have been developed such as that consciousness causes the collapse or hidden variable theory
Hidden variable theory
Historically, in physics, hidden variable theories were espoused by some physicists who argued that quantum mechanics is incomplete. These theories argue against the orthodox interpretation of quantum mechanics, which is the Copenhagen Interpretation...
.
The many-worlds interpretation
Many-worlds interpretation
The many-worlds interpretation is an interpretation of quantum mechanics that asserts the objective reality of the universal wavefunction, but denies the actuality of wavefunction collapse. Many-worlds implies that all possible alternative histories and futures are real, each representing an...
posits the existence of multiple universes in which an observed system displays all possible states to all possible observers. In this model, observation of a system does not change the behavior of the system—it simply answers the question of which universe the observer is located in. In some universes, the observer would observe one result from one state of the system, and in others the observer would observe a different result from a different state of the system.
Social sciences
In anthropology, sociology, and archaeology, this refers to the obvious bias to record what a civilization is like before the observer was there to observe it. Introducing Western ideas into pre-contact peoples was one of archaeology's main concerns during the late 1900s, and "can be understood in part as the product of the American salvage anthropologySalvage anthropology
Salvage anthropology is related to salvage ethnography, but involves the collection or salvage of cultural artifacts and even human remains as its method. In the late 19th century native populations were on the decline and early anthropologists feared that native societies would go extinct...
. At a time when Native American cultures were rapidly disappearing, anthropologists were committed to preserving their unique cultures" . Disappearing cultures continue to be a problem, as people give up their old ways to become 'modern,' leading various organizations to try to reverse or at least slow down the loss of cultural knowledge.
See also
- Double-slit experiment
- Interpretations of quantum mechanics
- Uncertainty principleUncertainty principleIn quantum mechanics, the Heisenberg uncertainty principle states a fundamental limit on the accuracy with which certain pairs of physical properties of a particle, such as position and momentum, can be simultaneously known...