Quantum Physics

And Im still not clear on how it relates to an observer in a time travelling box.

Pettytyrant101 wrote:And Im still not clear on how it relates to an observer in a time travelling box.

Seriously though, it does. Quantum entanglement led to the interpretive dilemma which Schrodinger was trying to clarify with his famous cat experiment (not for catlovers! )
Here's the Wiki link to refresh : http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat

Here's the different solutions to the dilemma from the article above. I was wanting to know which of these interpretations best fit Dr Who's internal rules, as they seemed not to be consistent.

Copenhagen interpretation
Main article: Copenhagen interpretation

The most commonly held interpretation of quantum mechanics is the Copenhagen interpretation.[5] In the Copenhagen interpretation, a system stops being a superposition of states and becomes either one or the other when an observation takes place. This experiment makes apparent the fact that the nature of measurement, or observation, is not well-defined in this interpretation. The experiment can be interpreted to mean that while the box is closed, the system simultaneously exists in a superposition of the states "decayed nucleus/dead cat" and "undecayed nucleus/living cat," and that only when the box is opened and an observation performed does the wave function collapse into one of the two states.

However, one of the main scientists associated with the Copenhagen interpretation, Niels Bohr, never had in mind the observer-induced collapse of the wave function, so that Schrödinger's cat did not pose any riddle to him. The cat would be either dead or alive long before the box is opened by a conscious observer.[6] Analysis of an actual experiment found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement.[7] The view that the "observation" is taken when a particle from the nucleus hits the detector can be developed into objective collapse theories. The thought experiment requires an "unconscious observation" by the detector in order for magnification to occur. In contrast, the many worlds approach denies that collapse ever occurs.
Many-worlds interpretation and consistent histories
The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point. The cat is both alive and dead—regardless of whether the box is opened—but the "alive" and "dead" cats are in different branches of the universe that are equally real but cannot interact with each other.
Main article: Many-worlds interpretation

In 1957, Hugh Everett formulated the many-worlds interpretation of quantum mechanics, which does not single out observation as a special process. In the many-worlds interpretation, both alive and dead states of the cat persist after the box is opened, but are decoherent from each other. In other words, when the box is opened, the observer and the possibly-dead cat split into an observer looking at a box with a dead cat, and an observer looking at a box with a live cat. But since the dead and alive states are decoherent, there is no effective communication or interaction between them.

When opening the box, the observer becomes entangled with the cat, so "observer states" corresponding to the cat's being alive and dead are formed; each observer state is entangled or linked with the cat so that the "observation of the cat's state" and the "cat's state" correspond with each other. Quantum decoherence ensures that the different outcomes have no interaction with each other. The same mechanism of quantum decoherence is also important for the interpretation in terms of consistent histories. Only the "dead cat" or "alive cat" can be a part of a consistent history in this interpretation.

Roger Penrose criticises this:

"I wish to make it clear that, as it stands, this is far from a resolution of the cat paradox. For there is nothing in the formalism of quantum mechanics that demands that a state of consciousness cannot involve the simultaneous perception of a live and a dead cat",[8]

however, the mainstream view (without necessarily endorsing many-worlds) is that decoherence is the mechanism that forbids such simultaneous perception.[9][10]

A variant of the Schrödinger's cat experiment, known as the quantum suicide machine, has been proposed by cosmologist Max Tegmark. It examines the Schrödinger's cat experiment from the point of view of the cat, and argues that by using this approach, one may be able to distinguish between the Copenhagen interpretation and many-worlds.
Ensemble interpretation

The ensemble interpretation states that superpositions are nothing but subensembles of a larger statistical ensemble. The state vector would not apply to individual cat experiments, but only to the statistics of many similarly prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial non-issue.

This interpretation serves to discard the idea that a single physical system in quantum mechanics has a mathematical description that corresponds to it in any way.
Relational interpretation

The relational interpretation makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction evolution, and all may be considered "observers." But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system.[11] The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of it being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to "collapse"; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to "collapse" into the same definite result, a cat that is either alive or dead.
Objective collapse theories

According to objective collapse theories, superpositions are destroyed spontaneously (irrespective of external observation) when some objective physical threshold (of time, mass, temperature, irreversibility, etc.) is reached. Thus, the cat would be expected to have settled into a definite state long before the box is opened. This could loosely be phrased as "the cat observes itself," or "the environment observes the cat."

Objective collapse theories require a modification of standard quantum mechanics to allow superpositions to be destroyed by the process of time evolution.

Why did it take so long for someone to consider the problem from the cats point of view? Thats the frst thing that occured to me about Schrodingers cat?

In relation to Amy I would say she is put in the position of ultimate observer, and that being transmitted throught the cracks exploding simutenously everywhere and everywhen causes the wave forms of Rory, her family and the Doctor to also be part of the rebooted universe.
In Who the travelers in theTARDIS act as observers- so they could go back to say 1980, alter some part of history- go to 2000 and have information about both the original time line without the change, and the new one with the change.
They stand at a thrid point observing the other two, even after one has ceased to have any physical reality.

Yes Amy's the observer and Rory's that poor Cat that's killed over and over

I'd been kind of leaning toward what they're calliing the relational interpretation

The relational interpretation makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction evolution, and all may be considered "observers." But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system. The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of it being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to "collapse"; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to "collapse" into the same definite result, a cat that is either alive or dead.

In this one, as the Who characters scatter and see seemingly contradictory things, they're all real within the frame of that observer, but they collapse into a single line when their experiences converge.

But what Amy was saying about remembering both having parents and not having parents at the same time, that sounds more like an observed superposition which would seem to be closer to the Many Worlds interpretation, but without the decoherence clause. That is, no collapse.

Again, I'm almost certainly overthinking this, but having walked through this minefield before I can't help but notice that Moffat and Co are marching squarely into the same field, but not necessarily following the paths. I need to watch more episodes, and then rewatch some episodes again before I'm entirely comfortable with this.

This has left out decoherence theory, which many now take as the resolution of the wave function collapse problem. A little hard to explain, but a wavefunction only remains 'pure' when nothing interacts with it. But as objects become larger thermal fluctuations are constantly interacting with a wave, leading to the classical behavior we are familiar with. Quantum weirdness comes from clean wave interactions, but the real world fuzzes out all these sharp probability jumps. I subscribe to this camp.

And I should add I don't think 'observers' should be part of physics in a fundamental way. In QM they just tell you when to stop treating the wave as a wave and start treating it as a probability distribution. This may seem like the observer is having an affect, but I feel the observer can 'decide' where to look at the whole chain of wavefunction evolution - it's like the prize is behind one of 3 doors. If you get to see that there's nothing behind one of the doors, it doesn't change the location of the prize, just the probability of it being behind one of the two remaining doors.

This brings up the famous question of whether you should change your guess, but that's a whole 'nother fun topic.

But doesnt the observer effect outcomes?

David with the Amy/Rory thing it is like the many worlds thing except Amy provides contiuity between them- so Rory that dies, get brought back as a Centurion, and who is at the wedding are all continous, despite a change of form and universe.
Amy acts like a reservoir of his pattern and provides his continuity. Which is why there is no collapse.

There's two ways the observer can affect outcomes. One is the physical effect of observation: if a photon has to bounce off an atom to show it's location, the atom is affected by this interaction. But the dratted photon could bounce off the atom whether or not an observer is there to see it.

This should not be confused with the collapse of the wavefunction, in which whoever is doing the calculation says 'okay, this damn thing has gone on long enough, let's convert the wave to probabilities and assume the atom takes one of those outcomes'. This is the true mystery of quantum mechanics, whether or not the person who stopped the wavefunction evolution calculation actually affected the physical wavefunction or not.

Since all the separate probabilities of things happening adds up to the wavefunction, in the many worlds interpretation they all continue to evolve, so the observer didn't affect the wavefunction, just the choice of which path to follow.

I would like to believe the wavefunction is some kind of calculational fiction and the universe itself continues to collapse the wave function as atoms bounce off other atoms, etc, but nobody has managed to make it work in a way that everyone is satisfied. For the most part physicists just shut up and calculate.

halfwise wrote:This has left out decoherence theory, which many now take as the resolution of the wave function collapse problem. A little hard to explain, but a wavefunction only remains 'pure' when nothing interacts with it. But as objects become larger thermal fluctuations are constantly interacting with a wave, leading to the classical behavior we are familiar with. Quantum weirdness comes from clean wave interactions, but the real world fuzzes out all these sharp probability jumps. I subscribe to this camp.

I think I'm with you, but just to make sure could you put this in terms of cats and blue boxes?

Pettytyrant101 wrote:But doesnt the observer effect outcomes?

David with the Amy/Rory thing it is like the many worlds thing except Amy provides contiuity between them- so Rory that dies, get brought back as a Centurion, and who is at the wedding are all continous, despite a change of form and universe.
Amy acts like a reservoir of his pattern and provides his continuity. Which is why there is no collapse.

One of the basic assumptions of all these lines of reasoning is that any two observers in the same situation would observe the same thing. Otherwise we're probably talking about perception rather than objective reality. Then we're getting into dreams where logical arguments can't follow.

If the argument is that we are following Amy's point of view, so we are seeing the story as an observer sharing her frame of reference, that's OK, but we have to allow for other frames of reference. For example, when Amy apparently summons the Doctor out of nothingness to her wedding by "remembering", that's OK from her perspective as long as we understand that there is another point of view where the Doctor existence is continuous and Amy's wedding pops out of nothingness. Then we've got two paths that are equally valid and "collapse" at this point.

But I don't think that's what your saying, is it?

no- there is nothing in the abslute sense outside the cracks- no existence.
So there can be no continuation from their persepctive between entering the cracks and when Amy pulls them back out.
Rory dies- and when he reappears he has no memory of inbetween dying and being Roman- and al the Roman stuff is programming that all the fake romans have, not anything from Amy.
Amy is the only contious point there. And its her who recontinues Rory and the Doctor from a point where they had otherwise stopped.

That's what I thought you were saying.

So I would say that Amy my perceive Rory and the Doctor as the same people as before, but since there is no continuity of physical bodies or of minds ( or even soul for that matter), objectively these should be considered completely different people.

After all, the only thing that links them as in any sense "the same" is that Amy perceives them as "the same", and Amy is far from an objective observer.

Does that sound like a valid possible interpretation, or can you find a flaw?

I wouldnt consider them different people.
Amy has their 'pattern' as it went into the cracks pouring through her head- and thats what she restores.
I would say it was more like a ST transporter- whats recovered at the other side is a patten of the original- so there is continuity betwen the two.

If you're thinking that Star Trek transporters actually kill the person on the platform before reconstructing a duplicate at the destination, then I'd agree that they're similar. But I'm definitely taking the shuttlecraft!

You and Doctor Mccoy David!

But essentially yes- thats how I see the Rory situation regards Amy- with in this case Amy's mind acting something like a transporter pattern buffer.
The original is pulled apart but the pattern of the whole is retained and reconstructed.

So then you're saying that Amy's mind in some way contains all the memories, knowledge and wisdom of a Time Lord in complete enough form that it can be reconstructed exactly, and complete with a functional Tardis? That seems like a lot of data for a human mind to absorb through relatively limited contact. Or do you allow for major errors and omissions?

The process of being recreated from nothingness (complete with formal attire) also seems to have been much less of a shock to The Doctor's body and mind than regeneration is. To me when I saw it, that strongly suggested that he had some continuity in between blowing up and the wedding, and enough time to change clothes at least.

As for transporters, I'd say you discount Dr McCoy's medical opinions at your own peril!

Transporters in general keep continuity through time, so I like to think of them as retaining continuity within the spacial dimensions by sort of turning our existence in the 3 default spacial dimensions sideways, (kind of like a venetian blind opening,) and literally transporting this existence along other spacial dimensions, to be unfolded on the other side, all the while preserving complete continuity (Sort of like taking a short cut on the face of the earth by flying through the air or burrowing underground.) If they're actually constructing new copies of Captain Kirk and Spock to rematerialize on the planet, why don't they just retain the original copies to command the Enterprise in their absence, instead of turning command over to Sulu?

According to the ST tech manual the transporters take a copy of the position of every part (using the Hesenberg compensators to achieve it!) and then the pattern is uploaded to the buffers- the original is then destroyed and the pattern reconstitueted at the destination.
In the ST books Mccoys objecions are based on his belief that the person at the other end is not the original.

With Amy the information is not contained in her human mind, its contained in the cracks themselves, she just has the ability to access and reconstitute that information.
She doesnt recreate them, she restrres the patterns stored in the cracks.

Most of what you guys are talking about loses me. But I can say that in quantum 'teleportation' there's a whole nother set of stuff that's just put into the same state as the original, it copies, doesn't transport. very much like the star trek transporters. I can see the need to destroy the original, that's a lot of energy!

I like my understanding of transporters better. Yours is more of a cloner/slaughterer. There are so many things that would be possible if the transporter could store people and reproduce them at will. No real risk if Kirk is killed by the aliens on the planet surface. They just push the button and make a copy of the one they sent. For that matter, having taken a copy, why not send 100 Kirks to the surface? Or enlarge the ship's buffers and hold the whole crew in memory until they're needed. So many things fall apart with this model. I prefer to think that McCoy is just unable or unwilling to grasp travel though alternate spacial dimensions.

For the same reasons I prefer to think of the Doctor and Tardis as having come to the wedding from an alternate spacial/temporal pathway. The tuxedo seems to point clearly to this. I know it seems to contradict some of the timey-wimey stuff about the end of everything, but it leads to fewer paradoxes than allowing that these infinite patterns exist outside of all timelines but can be summoned at will by a simple thought.

In ST TNG when Scotty appears in it that is basically what happens Dave- his pattern has been stored in the buffer for decades in a permenent loop to stop it degrading (the buffers can normally only hold the pattern for so long befre natural degradtion starts to occur)- in theory there is no reason beyond ethics why you couldnt use a transorter to clone someone- indeed this more or less is what happens to Riker resulting in two of him.

In the case of Amy its not a thought that brings them back- she is using her memory to retireve information stored in the cracks. The info is not in her head, but she is the only one in the universe who can access the info in the cracks as she is in a sense a part of them.

Pettytyrant101 wrote:- in theory there is no reason beyond ethics why you couldnt use a transorter to clone someone-

So ethics has kept everybody from creating life with transporters, but not destroying life every time they use this infernal device?
This is definitely not the utopia Gene R. had in mind!

The info is not in her head, but she is the only one in the universe who can access the info in the cracks as she is in a sense a part of them.

Do we know this? It's a big universe, and there were cracks opening all over it. But not one other sentient being was near one?? Jut curious.

I mean, you were commenting recently on the USA-centric nature of movies where Earth is attacked. Doesn't it strike you as a bit odd that the Only Being in the Whole Universe with this super power happens to be Scottish?

Do we know this? It's a big universe, and there were cracks opening all
over it. But not one other sentient being was near one?? Jut curious.- David

Amy is th eepicentre- the TARDIS was at her house in her time (whe River went there) when it exploded- thats why Amy is the centre of it all.

you were commenting recently on the USA-centric nature of movies where Earth is attacked.- David

On e of my main gripes with RTD era was its londoncentric view of the universe.
Who is a British show so its not suprising the cast is British.
But no I dont like it so much when it gets stuck earth centric let alone UK centric. (One of the reasons I am not a fan of the 3rd Doctor era is the settting- permenently stuck in England)

''On e of my main gripes with RTD era was its londoncentric view of the universe.
Who is a British show so its not suprising the cast is British.
But no I dont like it so much when it gets stuck earth centric let alone UK centric. (One of the reasons I am not a fan of the 3rd Doctor era is the settting- permenently stuck in England)'' Petty

thats funny because thats the reason I love RTD, its the Londoncentric storylines, I really love it when they meet Dickens and Shakespeare, anything in Victorian London is really interesting too. I havent yet seen an alien world thats more fascinating.

btw is it true that the Earth has 5 mini-moons?

This is just, weird.