Naked Science Forum

Non Life Sciences => Technology => Topic started by: EmmaHildyard on 09/08/2019 10:13:25

Title: Can we use physics to detect when people look at security devices?
Post by: EmmaHildyard on 09/08/2019 10:13:25
James has asked...

Can we use the double split experiment to detect if a person looks at a security device?

What do you think?
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Halc on 09/08/2019 12:02:08
Can we use the double split experiment to detect if a person looks at a security device?
The double slit experiment does not require observation, and most runs are done by machines without any necessity of being monitored.
That said, the sort of thing you ask is done today with cryptography
https://en.wikipedia.org/wiki/Quantum_cryptography

The idea is that the cryptographic keys (the numbers used to decrypt the coded message) can be distributed in a way that the data cannot be copied (looked at) without it being changed.  This guarantees that the recipient of the message is the only one who can read it.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: jimvideo on 09/08/2019 13:55:43
For simplicity I will call a device that uses the double split experiment to detect if someone has percieved the device a "quantum perception switch" or QPS.

If I put a QPS attached to the ceiling in the middle of a secure room would it send security a message any time somebody enters the secure room?

Would a cat activate the QPS?

Would a camera actiate the QPS?
Title: Re: Can we use physics to detect when people look at security devices?
Post by: alancalverd on 09/08/2019 16:28:28
The only way you would know that someone had perceived the device, would be to  decode their brain signals and recognise the bit that recognises the device. A PIR detector would be a lot simpler.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: evan_au on 09/08/2019 17:12:22
Quote from: jimvideo
If I put a QPS attached to the ceiling in the middle of a secure room would it send security a message any time somebody enters the secure room?
If you are using.a double-slit with visible light, then:
- when someone turns on the room lights, the dark bands will be less dark
- On the other hand, if the interference pattern is shielded from room lights, then it probably won't be affected by someone walking into the room.
- You may as well connect an alarm to the light switch or a door sensor

If you are using.a double-slit with electrons, then:
- when someone opens the door, all the air will rush in, and the bands will disappear
- but you may as well connect an alarm to the sealed door keeping the room in a good vacuum

Note that when we say "observe the photons in the double-lit experiment", we don't mean "look at the interference pattern behind the double slit".

We mean "put some device in one of the slits that is capable of detecting when a photon passes through that slit".
- So if you had clear instructions that everyone coming into the room was to cover up one of the slits with their finger, that would do the job!
- And if everyone had to walk between the slits and the wall, that would cast a detectable shadow,

But, as Alan said, an infra-red detector off some automatic lights would work a lot better.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: jimvideo on 09/08/2019 22:23:25
The amazing part of the double split experiment is simply observing the experiment causes the experiment to change. Responders are making assumptions that have noting to do with the post.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: jimvideo on 09/08/2019 23:11:34
Quote from: jimvideo
If I put a QPS attached to the ceiling in the middle of a secure room would it send security a message any time somebody enters the secure room?
If you are using.a double-slit with visible light, then:
- when someone turns on the room lights, the dark bands will be less dark
- On the other hand, if the interference pattern is shielded from room lights, then it probably won't be affected by someone walking into the room.
- You may as well connect an alarm to the light switch or a door sensor

If you are using.a double-slit with electrons, then:
- when someone opens the door, all the air will rush in, and the bands will disappear
- but you may as well connect an alarm to the sealed door keeping the room in a good vacuum

Note that when we say "observe the photons in the double-lit experiment", we don't mean "look at the interference pattern behind the double slit".

We mean "put some device in one of the slits that is capable of detecting when a photon passes through that slit".
- So if you had clear instructions that everyone coming into the room was to cover up one of the slits with their finger, that would do the job!
- And if everyone had to walk between the slits and the wall, that would cast a detectable shadow,

But, as Alan said, an infra-red detector off some automatic lights would work a lot better.

Putting aside if this is better or worse then any other device, can you answer if it would work?
Title: Re: Can we use physics to detect when people look at security devices?
Post by: alancalverd on 10/08/2019 00:16:32
The amazing part of the double split experiment is simply observing the experiment causes the experiment to change.
Rubbish. If you didn't observe it, how do you know what it did before you observed it?
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Halc on 10/08/2019 02:09:38
Responders are making assumptions that have noting to do with the post.
The responses mostly seem to be on topic, although there is a responder spouting nonsense.

For simplicity I will call a device that uses the double split experiment to detect if someone has percieved the device a "quantum perception switch" or QPS.
What exactly do you suppose this QPS does?  If it watches the door of the room, then it detects the person directly, and the double slit setup seems to not even be required.  So it is watching only the double-slit setup.  Exactly what would distinguish the experiment running with or without an observer?  You can win a Nobel prize if you can answer that.

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If I put a QPS attached to the ceiling in the middle of a secure room would it send security a message any time somebody enters the secure room?
Only a Schrodinger's box is secure.  I'm willing to posit one, even though the best one ever built barely managed to contain an object just large enough to see without instruments.

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Would a cat activate the QPS?

Would a camera actiate the QPS?
Depends on what it is set up to detect.  You haven't told anyone this.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: jimvideo on 11/08/2019 23:13:13
For simplicity I will call a device that uses the double split experiment to detect if someone has percieved the device a "quantum perception switch" or QPS.
What exactly do you suppose this QPS does?  If it watches the door of the room, then it detects the person directly, and the double slit setup seems to not even be required.  So it is watching only the double-slit setup.  Exactly what would distinguish the experiment running with or without an observer?  You can win a Nobel prize if you can answer that.

The way I understand the double slit experiment is the observation can be made with the naked eye, so a casual observer would activate it just by looking at it. This should be more efficient then the more processor intensive ways of detecting people. If a device is required to make the observation then the QPS would not work the way I imagine it would.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Halc on 12/08/2019 01:01:38
The way I understand the double slit experiment is the observation can be made with the naked eye, so a casual observer would activate it just by looking at it
This is an incorrect understanding. Quantum mechanics simply says that in any system (like the double slit experiment), the results are probabilistic and can be computed from the wave function.  There is no mention of human interaction in QM.
You are perhaps getting your information from a site (typically the religious ones) that promote something like the Wigner interpretation (which is not science) that says human consciousness is what causes wave function collapse, but even Wigner himself backed down from his own interpretation because it leads to solipsism (the view that only you exist, and everybody else is a product of your observation of them).
That interpretation is the only interpretation that seriously posits that humans (or one human) are special, an anthropocentric view.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: evan_au on 12/08/2019 14:33:38
Quote from: JimVideo
The way I understand the double slit experiment is the observation can be made with the naked eye
Yes, you can observe a double-slit interference pattern with the naked eye (and a microscope). But observing the interference pattern does not cause the wavefunction (or interference pattern) to collapse.

You can even observe one or both slits with visible light, and this will not cause the wavefunction to collapse.
- This is because photons rarely interact with each other - the photons going to your eye do not interact with the photons going through one slit or another
- So you cannot tell which slit a particular photon went through, using visible light.
- You would need to put your eye up to one slit - that will cause the wavefunction to collapse.

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the QPS would not work the way I imagine it would.
Probably the most accurate statement you've made on this subject.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Bored chemist on 12/08/2019 19:25:03
By (bad) analogy with Schrodinger's cat: Until you open the box, the cat is dead and alive.
The cat has observed the outcome and has, from the cat's perspective, survived or not.

You don't get to know which until you open the box and inspect the cat.

In a similar way, the person did, or didn't look at the sensor.
From their point of view, they know if they did or not.
But you don't find out unless you"open the box" and ask them.

It's not going to work.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Halc on 12/08/2019 20:16:33
By (bad) analogy with Schrodinger's cat: Until you open the box, the cat is dead and alive.
More or less correct, yes.
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You don't get to know which until you open the box and inspect the cat.
This statement makes it sound like the cat (before opening) is dead OR alive, not in superposition of being both dead and alive.  The 'or' view lives on only in a few interpretations that are arguably losing support.  But the view is admittedly not falsified.  Such a view would disagree with your top statement.

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From their point of view, they know if they did or not.
It's not about knowing or not, it's about if it really is 'both dead and alive' or not.  Double-slit experiment does not work if the photon goes through one slit or the other in most interpretations.  If it goes through one of the two slits, it would make the same pattern as you get with only one slit.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Bored chemist on 12/08/2019 20:20:38
This statement makes it sound like the cat (before opening) is dead OR alive, not in superposition of being both dead and alive.
How does the cat feel about this?
To avoid arguments about animal intelligence, it's easy to consider that you are the cat.
Somewhere in a distant star an atom fissioned and sent out a gamma ray.
That ray crossed interstellar space and plowed into the embryonic  you where it caused a lethal mutation- so you were never born.
Or, since you are here, it didn't

It's conceivable that we are in some more complex version of the cat experiment and that, thus far the experimenter has not yet opened the box.
He thinks you are in a superposition of states.
You know better.


Title: Re: Can we use physics to detect when people look at security devices?
Post by: Halc on 12/08/2019 22:13:05
How does the cat feel about this?
The various interpretations describe it differently.  QM proper does not attempt to describe it.  If you assume the cat is in a particular state, you are assuming the principle of counterfactual definiteness:
Quote from: wiki
the ability to speak "meaningfully" of the definiteness of the results of measurements that have not been performed (i.e., the ability to assume the existence of objects, and properties of objects, even when they have not been measured).
This principle is intuitive, but Bell proved that it cannot be true unless information can travel faster than light, violating principle of locality.  So first step in choosing a QM interpretation is to choose one or the other principle (or discard both as some do).

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To avoid arguments about animal intelligence, it's easy to consider that you are the cat.
That would probably be Wigner's friend experiment, same thing but with a human in the box.   This is the same as the cat, except in an interpretation (like Wigner's) that posits that humans (or one human) are special preferred observers of the universe.

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Somewhere in a distant star an atom fissioned and sent out a gamma ray.
That ray crossed interstellar space and plowed into the embryonic  you where it caused a lethal mutation- so you were never born.
Or, since you are here, it didn't
Obviously it didn't.  But to somebody (far more distant) who never measured the fission event or measured me, I perhaps (depending on his view) am in a state of superposition of existing or not.  Maybe you're an MWI person who says there's a different world without me in it.  That's a valid interpretation.  Few people understand MWI.  I get enough of the gist of it to choose another interpretation, but I don't go around on science forums asserting that my interpretation must be correct.  I do that, but only on philosophy forums where the arguments involved are relevant.

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It's conceivable that we are in some more complex version of the cat experiment and that, thus far the experimenter has not yet opened the box.
Of course.  If you don't think that way, it is like the people that think that Earth is stationary and everything else is moving.  The universe revolves around me.  That's been one of my primary axioms, that we're not special in any way.  Part of being not special is not assuming we're outside the box.

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He thinks you are in a superposition of states.
You know better.
You can't tell any more than the cat can.
Title: Re: Can we use physics to detect when people look at security devices?
Post by: Bored chemist on 13/08/2019 19:44:05
That would probably be Wigner's friend experiment, same thing but with a human in the box.
That's essentially the point I was making. (Together with the idea that you might be in the box without knowing it- especially if the box is big enough).

So, you might be the "cat".
Are you in a superposition of being alive and dead?
Certainly, the intuitive answer to that is "no".


My view on the OP is that, in the same way that you, or Wigner's friend, knows the answer before you open the box, the "Bad Guy" in the OP already knows if he looked at the camera or not.
That wavefunction is, apparently already collapsed.
So there's no way that it can be interrogated to find out anything about what the Bad Guy did (or didn't do).


Title: Re: Can we use physics to detect when people look at security devices?
Post by: Halc on 13/08/2019 20:32:44
That would probably be Wigner's friend experiment, same thing but with a human in the box.
That's essentially the point I was making. (Together with the idea that you might be in the box without knowing it- especially if the box is big enough).

So, you might be the "cat".
Are you in a superposition of being alive and dead?
Different interpretations give different answers to such questions, so sans picking one, anybody who says one way or the other has no way to back his claim.

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Certainly, the intuitive answer to that is "no".
Intuition will not serve you well in this subject matter.  Quantum physics is anything but intuitive.

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My view on the OP is that, in the same way that you, or Wigner's friend, knows the answer before you open the box, the "Bad Guy" in the OP already knows if he looked at the camera or not.
I didn't give that answer.  I said the answer is interpretation dependent.  If you pick one, perhaps I can answer the question.
Copenhagen interpretation is meant to be a epistemological interpretation, not a metaphyscial one, despite the fact that some people take the wording as metaphysical statements.  So its about what one knows, and not necessarily about what is.  Most of the other interpretations are metaphysical, that is, about what is.

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That wavefunction is, apparently already collapsed.
Again, interpretation dependent.  Some deny wave function collapse.