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RECENT POSTS IN THIS TOPIC

Georgina Woodward: on 4/25/15 at 4:15am UTC, wrote Reiterating: It is switching from a theoretical superposition of isolated...

Georgina Woodward: on 4/24/15 at 23:45pm UTC, wrote I wrote "So it seems the physical equivalent of wave function collapse is...

Georgina Woodward: on 4/16/15 at 7:28am UTC, wrote That 'picture of what is occurring also explains why outcomes are...

Georgina Woodward: on 4/15/15 at 3:48am UTC, wrote Interesting podcast, nice hearing GianCarlo Ghirardi decribing that he...

Steve Agnew: on 4/4/15 at 14:40pm UTC, wrote Collapse in this context, of course, means collapse of the wavefunction,...

Zeeya Merali: on 3/27/15 at 10:28am UTC, wrote Yesterday afternoon at the quantum foundations meeting in Erice (supported...


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TOPIC: Collapsing Physics, Celebrating Ghirardi [refresh]
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FQXi Administrator Zeeya Merali wrote on Mar. 27, 2015 @ 10:28 GMT
Happy birthday Ghirardi!
Yesterday afternoon at the quantum foundations meeting in Erice (supported by COST) we celebrated the 80th birthday (somewhat in advance) of GianCarlo Ghirardi who famously worked on collapse models, in an attempt to deal with the quantum measurement problem. He’s the “G” in GRW collapse theory. (Ghirardi is pictured here — a bit fuzzily —being presented with a gift by Catalina Oana Curceanu and Detleft Duerr.)

Free Podcast

Physicists Angelo Bassi and GianCarlo Ghirardi discuss collapse models. From the COST quantum foundations meeting in Erice, Italy.



LISTEN:







Go to full podcast



I’ve just posted a special podcast with interviews with physicist and meeting organiser Angelo Bassi and Ghirardi himself. Bassi talks a bit about the motivation behind collapse models and what they are, but they basically try to help explain why the classical world we see around us involves people and things in definite places, while one small scales, particles exist in a fuzzy uncertain realm.

The idea is that the wavefunction of particles can undergo spontaneous collapse, but in the case of individual particles, the odds of this happening are slim, so on the microscopic level you should see the same sort of things that standard quantum mechanics predicts. But when you bring lots of particles together in a macroscopic object, the probability of collapse shoots up — and hence they behave classically.

But how do you test this idea? There’s nothing in principle in standard quantum mechanics that prevents ever larger particles (even cats) being in quantum superposition, if you can prepare your experiment carefully enough (which is tough to do). By contrast, GRW predicts that above some certain mass limit, collapse is inevitable, no matter how pristine your experiment. So that gives you something different to search for.

In a previous post, I mentioned matter-wave interferometry experiments. Yesterday, FQXi’s Hendrik Ulbricht, of the University of Southampton, talked about efforts to see quantum effects in ever larger objects — cold atoms, molecules, metal clusters or nano particles, and even cantilevers — but at the moment they are not well-developed enough to be able to test collapse models. Another problem is that if you carry out such a test and you do see a loss of quantum effects, it might have been caused by problems with the experiment, and decoherence due to interactions with the environment, rather than revealing something fundamental.

You can hear more on the podcast.

Physics Dog!
The blurry image shows a dog who apparently loves physics — he gatecrashed the meeting for two days running (in search of Schrodinger’s cat?). The first time, he ran onto the stage with the lecturer, who was speaking about quantum biology. The second time, he stopped in front of the stage and barked loudly at the speaker, who was talking about string theory. Make of that what you will!

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Steve Agnew wrote on Apr. 4, 2015 @ 14:40 GMT
Collapse in this context, of course, means collapse of the wavefunction, not collapse of the universe. I have a hard time with all of the obsession with wavefunction collapse since it is an artifact of our continuum gravity. Once we get a quantum gravity, this issue will collapse.

Superposition states are possible with gravity states, but would be very difficult to measure here on earth. Perhaps at the Lagrange L1 with an atom interferometer we could see a gravity superposition state.

We do experience superposition states all of the time with our neural wave packets, but for some reason, this is not obvious to anyone else except me. The neural state that we experience before we actually choose between action and inaction represents a superposition of two aware matter packets that represent these two possible futures.

Is the chair here or is it there? Our views of superposition are confused by space and motion, which are emergent and not intrinsic concepts. Unlike space, there is no illogic for a superposition in time since simultaneity keeps objects separate from each other. Instead of momentum, its matter equivalent drives action in time.

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Georgina Woodward wrote on Apr. 15, 2015 @ 03:48 GMT
Interesting podcast, nice hearing GianCarlo Ghirardi decribing that he liked about collapse models and how theory changes mustn't alter what we already know about the universe.

There was a phrase he used which was "definite perception". It is the thought that 'our' perception is definite, singular, and that is how therefore macroscopic reality is that is in part the problem...

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Georgina Woodward replied on Apr. 16, 2015 @ 07:28 GMT
That 'picture of what is occurring also explains why outcomes are probabilistic rather than fixed and certain.Consider the unobserved free falling spinning coin again. Not only is it a superposition of states because there is no reference frame-making all frames equally valid it is also in flux altering what would be observed from each reference frame as time passes. Incidentally, more varied than just two faces as it is the measurement protocol that 'condenses' outcomes into just one of two bits.

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Georgina Woodward wrote on Apr. 24, 2015 @ 23:45 GMT
I wrote "So it seems the physical equivalent of wave function collapse is switching consideration from what is occurring unseen, the behavior or flux of the absolute unmeasured entity to the 'definite perception' singular fixed view of an observable produced by a measurement protocol or fixed reference frame sample."That's not quite right

It is switching from a theoretical superposition of...

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Georgina Woodward replied on Apr. 25, 2015 @ 04:15 GMT
Reiterating: It is switching from a theoretical superposition of isolated observables (outcomes), not yet formed, as a Definite Fixed State observable is produced upon observation. What exists in Object reality, prior to measurement, are proto- observables conjoined with the carrier.

The (Definite Fixed State) observables do not exist in space-time prior to the observation. Space-time is...

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