If im not measuring its not there?

[nnope]

Without getting too deep into the physics or philosophy of quantum mechanics, and I'm NOT talking about theory (no 'what the equations say') but if I'm not looking at my couch does that it mean at the moment it doesn't exist? Or if I'm not looking at my dad he isn't there but in the form of a wave?

 

[rootone]

No that is not quantum physics that is solipsism.
https://en.wikipedia.org/wiki/Solipsism

 

[nnope]

That is the idea I get when I read about some of the interpretations. I'm just a little confused that's why I asked the question.

 

[rootone]

Real quantum theories are ultimately about statistics and only are usefully applicable to things and events on subatomic scale.
The chances of the couch you are sitting on suddenly disappearing are so low that it's unlikely to happen within the lifespan of the Universe.

 

[bhobba]

but if I'm not looking at my couch does that it mean at the moment it doesn't exist?

No. Its being looked at all the time by the environment. A few stray photons from the CBMR, for example, is enough to decohere a dust particle and give it a definite position.

Thanks
Bill

 

[nnope]

I see basically everything is observing everything, so it is all there but in an isolated system things would work differently

 

[bhobba]

I see basically everything is observing everything, so it is all there but in an isolated system things would work differently

Exactly.

Isolating systems is very very hard, but not impossible.

When done some very strange effects appear:
http://physicsworld.com/cws/article/news/2010/mar/18/quantum-effect-spotted-in-a-visible-object

As technology progresses expect even stranger things to emerge.

Thanks
Bill

 

[nnope]

That is cool, so they basically cooled the thing down until there was no or close to zero vibrations left and it all went into superposition. when it is in superposition, what is the material like? do you think it still has mass? can it be moved?

Also when something is being measured for example Atom 1 measures Atom 2. is the measurement continuous or an on off sequence, so is atom 2 continuously jumping in and out of superposition at a very fast rate.

 

[bhobba]

That is cool, so they basically cooled the thing down until there was no or close to zero vibrations left and it all went into superposition. when it is in superposition, what is the material like? do you think it still has mass? can it be moved?.

I know no more detail that what the article says. But yes it would still have mass and can be moved.

Also when something is being measured for example Atom 1 measures Atom 2. is the measurement continuous or an on off sequence, so is atom 2 continuously jumping in and out of superposition at a very fast rate.

Its got to do with decoherene. At the lay level here is the book to get:
https://www.amazon.com/dp/B001S2QNLO/?tag=pfamazon01-20

Thanks
Bill

 

[nnope]

Its got to do with decoherene. At the lay level here is the book to get:
https://www.amazon.com/dp/B001S2QNLO/?tag=pfamazon01-20

I tried to give it a quick google search didn't understand anything... then
I found this
http://www.decoherence.de/
now that says time doesn't exist at a fundamental level.
I think ill stick to the book cause I didn't understand anything.
if someone can give me a quick rundown I will appreciate it

 

[bhobba]

Inow that says time doesn't exist at a fundamental levelt

Without reading what he says, I can assure you in QM time definitely exists.

Thanks
Bill

 

[StevieTNZ]

I tried to give it a quick google search didn't understand anything... then
I found this
http://www.decoherence.de/
now that says time doesn't exist at a fundamental level.
I think ill stick to the book cause I didn't understand anything.
if someone can give me a quick rundown I will appreciate it

Yes, that website is legit so you can take information from it. I've had email correspondence with Erich Joos some time ago.

 

[bhobba]

Yes, that website is legit so you can take information from it. I've had email correspondence with Erich Joos some time ago.

I suspect he is as well, but some things he says such as time doesn't exist are rather controversial to say the least. I am pretty sure what he means is not quite what the prosaic language he uses suggests.

Time most definitely exists in QM - eg the Schroedinger equation wouldn't make any sense without it.

He also says:
Decoherence can not explain quantum probabilities without (a) introducing a novel definition of observer systems in quantum mechanical terms (this is usually done tacitly in classical terms), and (b) postulating the required probability measure (according to the Hilbert space norm).

That's roughly true - but the devil is in the detail. It's also very interpretation dependant eg it isn't really true of BM which doesn't require a quantum definition of observation - it takes it on board but doesn't require it because objects have properties independent of observation.

Thanks
Bill

 

[nnope]

@bhobba
this is what it said
"explains also how the Schrödinger equation of general relativity (the Wheeler-DeWitt equation) may describe the appearance of time in spite of being time-less

There is no time at a fundamental level"
@StevieTNZ
thanks. I think I've still got a lot to learn before I can understand anything from that website without misinterpreting it.

 

[nnope]

oh I posted my comment before reading yours Bhobba ignore it lol.

I believe most of my understanding of quantum mechanics is probably wrong because most of the time I don't understand what people actually mean when they try and explain something. I'm always misunderstanding

 

[bhobba]

this is what it said"explains also how the Schrödinger equation of general relativity (the Wheeler-DeWitt equation) may describe the appearance of time in spite of being time-less

I suspect its this Block-world stuff. Its off-topic here, and rightly so IMHO. I think its basically BS - but Google is your friend, and you can make up your own mind.

Thanks
Bill

 

[nnope]

I'd like to believe time does exist, otherwise how would we experience any changes in the universe.

 

[Abbott287287]

If everything is being looked at (measured) all the time by its environment, why does the wave pattern show in the double slit before a measuring device is used? Why is the environment not causing the wave to collapse? Thanks in advance!

Isnt the OPs opening question the same as Einsteins comment about the moon?

 

[nnope]

If everything is being looked at (measured) all the time by its environment, why does the wave pattern show in the double slit before a measuring device is used? Why is the environment not causing the wave to collapse? Thanks in advance!

Isnt the OPs opening question the same as Einsteins comment about the moon?

I remember being told that the double slit experiment Is conducted in way where there is no interference from the environment with the electrons until they are measured but some of the other guys know more than me maybe they can give more detail

 

[Abbott287287]

I remember being told that the double slit experiment Is conducted in way where there is no interference from the environment with the electrons until they are measured but some of the other guys know more than me maybe they can give more detail

Not sure how that could be done, but you would think Einstein would not make the moon statement if that were the case. He would know it was just a lack of interaction that caused the results of the DS. And isn't that still being debated, and the reason for multiple interpretations? No one is still certain what the cause of waveform collapse is?

 

[bhobba]

I remember being told that the double slit experiment Is conducted in way where there is no interference from the environment with the electrons until they are measured but some of the other guys know more than me maybe they can give more detail

It works because photons interact weakly with the environment.

Thanks
Bill

 

[bhobba]

Not sure how that could be done, but you would think Einstein would not make the moon statement if that were the case.?

It is true that Einstein knew QM very well carrying Dirac's classic text with him at all times - it was basically his bible on it. Also it is incorrect to say Einstein didn't think QM correct. There was a famous exchange between Einstein and Bohr where Einstein bought his last and most devastating attack on QM. Long into the night Bohr laboured to defeat it - which he finally did. He presented his refutation and Einstein tipped his hat, literally, to Bohr. From that point on he never questioned it was correct - but to his dying day believed it incomplete.

But knowledge of decoherence was not well developed in those days. In fact both Einstein and Bohr were wrong:
http://scitation.aip.org/content/aip/magazine/physicstoday/article/58/11/10.1063/1.2155755

No one is still certain what the cause of waveform collapse is?

Collapse is not part of QM - only some interpretations. And in those that have it its a mystery for some (eg some versions of Copenhagen) and trivial for others (eg GRW).

What decoherence has done is for many interpretations morphed collapse to the problem of outcomes ie why we get any outcomes at all. Its a mystery for some (eg Copenhagen or Ignorance Ensemble) and trivial in others (eg BM an MW).

Thanks
Bill

 

[nnope]

Sorry to be such a pain but would you mind giving me a run down of what decoherence is, just in brief

 

[bhobba]

Sorry to be such a pain but would you mind giving me a run down of what decoherence is, just in brief

It converts a superposition to a mixed state. In a mixed state we have definite outcomes but but do know know which outcome will occur. Basically you can say collapse has occurred - but we don't know the actual outcome - just there is one.

I really can't explain it any better at the lay level, so if you want further detail I will have to leave it to others.

I have tried in the past and it just leads to long threads with the lay person never quite getting it.

Please read the book I suggested.

Thanks
Bill

 

[Abbott287287]

It works because photons interact weakly with the environment.

Thanks
Bill

Why would they react to a measuring device then?

 

[bhobba]

Why would they react to a measuring device then?

Its an experimental fact photons are transparent to and interact weakly with things like air, which is the usual environment of the double slit, and are absorbed by other things like the barriers. Why is actually a bit advanced:
https://www.physicsforums.com/insights/do-photons-move-slower-in-a-solid-medium/
'A solid has a network of ions and electrons fixed in a “lattice”. Think of this as a network of balls connected to each other by springs. Because of this, they have what is known as “collective vibrational modes”, often called phonons. These are quanta of lattice vibrations, similar to photons being the quanta of EM radiation. It is these vibrational modes that can absorb a photon. So when a photon encounters a solid, and it can interact with an available phonon mode (i.e. something similar to a resonance condition), this photon can be absorbed by the solid and then converted to heat (it is the energy of these vibrations or phonons that we commonly refer to as heat). The solid is then opaque to this particular photon (i.e. at that frequency). Now, unlike the atomic orbitals, the phonon spectrum can be broad and continuous over a large frequency range. That is why all materials have a “bandwidth” of transmission or absorption. The width here depends on how wide the phonon spectrum is.'

Thanks
Bill

 

[Abbott287287]

Its an experimental fact photons are transparent to and interact weakly with things like air, which is the usual environment of the double slit, and are absorbed by other things like the barriers. Why is actually a bit advanced:
https://www.physicsforums.com/insights/do-photons-move-slower-in-a-solid-medium/
'A solid has a network of ions and electrons fixed in a “lattice”. Think of this as a network of balls connected to each other by springs. Because of this, they have what is known as “collective vibrational modes”, often called phonons. These are quanta of lattice vibrations, similar to photons being the quanta of EM radiation. It is these vibrational modes that can absorb a photon. So when a photon encounters a solid, and it can interact with an available phonon mode (i.e. something similar to a resonance condition), this photon can be absorbed by the solid and then converted to heat (it is the energy of these vibrations or phonons that we commonly refer to as heat). The solid is then opaque to this particular photon (i.e. at that frequency). Now, unlike the atomic orbitals, the phonon spectrum can be broad and continuous over a large frequency range. That is why all materials have a “bandwidth” of transmission or absorption. The width here depends on how wide the phonon spectrum is.'

Thanks
Bill

Thanks Bill. That is one of the clearest and easy to understand answers I have read. What happens when the recorder is left off and the wave pattern shows again however? I can't figure out what is changing. Again, thanks in advance!

 

[Nugatory]

Sorry to be such a pain but would you mind giving me a run down of what decoherence is, just in brief

Bhobba has already recommended the Lindley book ("Where does the weirdness go?") and I strongly second that recommendation - it's the best layman-friendly explanation I'm aware of.

For a quick rundown (and be aware that I am waving my hands, cutting some corners, and grossly oversimplifying here):
It's easy (at least in principle - in practice, not so much) to prepare a single particle in a superposition of "it's here" and "it's there", and to isolate it from the environment (prevent it from interacting with anything else) so that it stays in that state. However, a macroscopic system consists of an enormous number of individual particles, and its overall macroscopic behavior will come from the collective interactions of all of these particles. It turns out that these interactions combine to cancel out any macroscopic superpositions; if we could prepare the macroscopic system in a 50/50 superposition of "it's here" and "it's there", half the time it will very quickly evolve into "it's here" and the other half of the time it will as quickly evolve into "it's there". Thus, the laws of quantum mechanics accurately describe the weird behavior of individual quantum particles, but they also accurately predict that a large number of particles evolving according to those laws will collectively behave in classical non-weird ways. "Decoherence" is the name we give the latter phenomenon.

(There is an analogy with statistical mechanics and the classical behavior of gases. A single gas molecule in a box will bounce around at random - at any moment it may be pushing on the top of the box, or the bottom, or one of the sides, or not pushing on the box at all if it's floating around in the middle. However, if I put enough gas molecules in the box all of this randomness will average out; at any given moment there will be an approximately equal number of molecules pushing in all directions and the system as a whole will obey the ideal gas law $PV=nRT$. That is, gas pressure is a phenomenon that emerges from the collective interactions of a very large number of particles none of which individually are doing anything that looks anything like exerting an equal pressure in all directions. Likewise, the classical behavior of a macroscopic object emerges from the quantum behavior of the individual particles of which it is composed; that's decoherence).

 

[bhobba]

What happens when the recorder is left off and the wave pattern shows again however? I can't figure out what is changing.

I don't understand what you mean by wave-pattern showing. In the double slit exactly the same thing happens if the photons are absorbed and recorded or not recorded - it makes no difference. I am scratching my head why anyone would think it would.

Thanks
Bill

 

[nnope]

Thanks @bhobba and @Nugatory, its all starting to make sense to me now. I'm just curious about the time discussion we had earlier but ill leave that for another thread at a later date