Delayed Choice Quantum Eraser

[Sriram]

Hi everyone,

Here is a video of the Delayed Choice Quantum Eraser experiment 1999 which is a modified version of the Delayed Choice experiment of John wheeler 1984.

https://www.youtube.com/watch?v=0ui9ovrQuKE

Very interesting results. Future can affect the past.....

Cheers.

Sriram

[Stranger]

Future can affect the past.....

Or not.

These experiments are weird and they do raise questions but the situation is not as straightforward as some popular presentations suggest.

It's not emphasised much in the video but this is a quantum entanglement experiment. You can't actually decide whether or not to measure something after it's happened.

It's a bit like people saying that measurements on entangled pairs of particles demonstrate faster than light communication. Do they really? Well yes and no, sort of, it depends how you look at it. The fact is that if the two measurements are "space-like" separated (which means you'd need faster than light communication for one to affect the other) then the order in which the observations happened is observer dependant, so you cannot say that measurement A affected measurement B faster than light because another observer would put the measurement A happening after measurement B. What you have is a correlation that you can only find by transferring conventional information (slower than light) between points A and B.

In this situation, there is no actual interference at (locally, in time and space) detector 1 (in the simplified version on the video), you need the information from the other detectors in order to know which photons to look at. You can only find the pattern by superimposing the information from the other detectors onto the information from detector 1. So what we have again is a correlation that you can only confirm by passing conventional information (forward in time) from one measurement to the other.

So did what happened at detectors 2, 3, and 4 affect (backwards in time) what happened at detector 1, or did what happened at detector 1 affect (forward in time) what happened at 2, 3, and 4?

In fact, entangled particles behave as one system and if you know the result of one measurement you can infer the result of others, regardless of temporal or spacial separation, and the order doesn't really matter. In no case is it possible to actually communicate conventional information either faster than light or back in time.

The wiki article (Delayed-choice quantum eraser) has more.

[Sriram]

"In no case is it possible to actually communicate conventional information either faster than light or back in time."

This emphatic statement is what is wrong with some science people. It smacks of fanaticism and a very rigid notion of reality. A very old school attitude. Not very different from saying that 'Jesus is the only way'.

Reality can be stranger than we CAN imagine. We should be prepared for unexpected or even bizarre results. 

[Stranger]

"In no case is it possible to actually communicate conventional information either faster than light or back in time."

This emphatic statement is what is wrong with some science people. It smacks of fanaticism and a very rigid notion of reality. A very old school attitude. Not very different from saying that 'Jesus is the only way'.

It's actually a statement of what the mathematics of the appropriate theory says. What has been done in the experiment is predicted by the theory and the same theory leads to the conclusion I stated. In other words, the experiment confirmed the theory that tells us that we can't communicate conventional information either faster than light or back in time.

Reality can be stranger than we CAN imagine. We should be prepared for unexpected or even bizarre results.

Indeed we should - but you really can't point to an experiment that confirms a theory and then claim it's all about something that the theory specifically rules out. Not with any intellectual honesty, anyway.

[Sriram]

Wheeler's Participatory Anthropic Principle...

https://futurism.com/john-wheelers-participatory-universe

***********

Wheeler suggested that reality is created by observers and that: “no phenomenon is a real phenomenon until it is an observed phenomenon.” He coined the term “Participatory Anthropic Principle” (PAP) from the Greek “anthropos”, or human. He went further to suggest that “we are participants in bringing into being not only the near and here, but the far away and long ago.”

This claim was considered rather outlandish until his thought experiment, known as the “delayed-choice experiment,” was tested in a laboratory in 1984. This experiment was a variation on the famous “double-slit experiment” in which the dual nature of light was exposed (depending on how the experiment was measured and observed, the light behaved like a particle (a photon) or like a wave).

Unlike the original “double-slit experiment”, in Wheeler’s version, the method of detection was changed AFTER a photon had passed the double slit. The experiment showed that the path of the photon was not fixed until the physicists made their measurements. The results of this experiment, as well as another conducted in 2007, proved what Wheeler had always suspected – observers’ consciousness is required to bring the universe into existence. This means that a pre-life Earth would have existed in an undetermined state, and a pre-life universe could only exist retroactively.

These conclusions lead many scientists to speculate that the universe is fine-tuned for life. This is how Wheeler’s Princeton colleague, Robert Dicke, explained the existence of our universe:

“If you want an observer around, and if you want life, you need heavy elements. To make heavy elements out of hydrogen, you need thermonuclear combustion. To have thermonuclear combustion, you need a time of cooking in a star of several billion years. In order to stretch out several billion years in its time dimension, the universe, according to general relativity, must be several years across in its space dimensions. So why is the universe as big as it is? Because we are here!”

[Reference: Cosmic Search Vol. 1 No. 4

Physicist Andrei Linde of Stanford University adds: “The universe and the observer exist as a pair. I cannot imagine a consistent theory of the universe that ignores consciousness.”

***********

[Stranger]

So off we go on another quantum-woo hunting tangent...

Wheeler's Participatory Anthropic Principle...

https://futurism.com/john-wheelers-participatory-universe

Which is just somebody else trying to push a particular, minority interpretation of quantum mechanics. It is simply not the case that the "results of this experiment ... proved ... [that] observers’ consciousness is required to bring the universe into existence" - that is an interpretation - and one that has very little support amongst scientists.

[Outrider]

Wheeler's Participatory Anthropic Principle...

https://futurism.com/john-wheelers-participatory-universe

***********

Wheeler suggested that reality is created by observers and that: “no phenomenon is a real phenomenon until it is an observed phenomenon.” He coined the term “Participatory Anthropic Principle” (PAP) from the Greek “anthropos”, or human. He went further to suggest that “we are participants in bringing into being not only the near and here, but the far away and long ago.”

This claim was considered rather outlandish until his thought experiment, known as the “delayed-choice experiment,” was tested in a laboratory in 1984. This experiment was a variation on the famous “double-slit experiment” in which the dual nature of light was exposed (depending on how the experiment was measured and observed, the light behaved like a particle (a photon) or like a wave).

Unlike the original “double-slit experiment”, in Wheeler’s version, the method of detection was changed AFTER a photon had passed the double slit. The experiment showed that the path of the photon was not fixed until the physicists made their measurements. The results of this experiment, as well as another conducted in 2007, proved what Wheeler had always suspected – observers’ consciousness is required to bring the universe into existence. This means that a pre-life Earth would have existed in an undetermined state, and a pre-life universe could only exist retroactively.

These conclusions lead many scientists to speculate that the universe is fine-tuned for life. This is how Wheeler’s Princeton colleague, Robert Dicke, explained the existence of our universe:

“If you want an observer around, and if you want life, you need heavy elements. To make heavy elements out of hydrogen, you need thermonuclear combustion. To have thermonuclear combustion, you need a time of cooking in a star of several billion years. In order to stretch out several billion years in its time dimension, the universe, according to general relativity, must be several years across in its space dimensions. So why is the universe as big as it is? Because we are here!”

[Reference: Cosmic Search Vol. 1 No. 4

Physicist Andrei Linde of Stanford University adds: “The universe and the observer exist as a pair. I cannot imagine a consistent theory of the universe that ignores consciousness.”

***********

Where Wheeler's hypothesis falls down is his assumption that the only action that can collapse a quantum waveform is a conscious observation; any subsequent reaction which relies on the result of the collapse occurring 'causes' the waveform to collapse.  Observation is indeed one of those reactions, but ongoing physical activity that relies on the result will equally cause the collapse.

O.

[Stranger]

At the opposite extreme of possible interpretations, we have Gerard 't Hooft (joint winner of the 1999 Nobel Prize in Physics) suggesting that we might be able to return to an entirely classical underlying theory:

Quantum Mechanics from Classical Logic

"Any classical, discrete, time reversible system can be naturally described using a quantum Hubert space, operators, and a Schrödinger equation. The quantum states generated this way resemble the ones in the real world so much that one wonders why this could not be used to interpret all of quantum mechanics this way. Indeed, such an interpretation leads to the most natural explanation as to why a wave function appears to "collapse" when a measurement is made, and why probabilities obey the Born rule."

Also: The Cellular Automaton Interpretation of Quantum Mechanics.

I'm not suggesting that he's 100% right or that we can 100% rule out a role for consciousness but it should illustrate just how many, very different, interpretations are possible.