Against Realism: Examining the Meaning of Local Realism

[NateTG]

Yes, a quantum computer can resolve this kind of calculation very fast.

Quantum computers are not proven to solve NP hard problems in polynomial time, and, in fact, are strongly expected no to.

 

[AnssiH]

You obviously believe in some sort of "hidden variable" theory. Fair enough.

No, I don't particularly believe in hidden variables or copenhagen. I believe our ideas about what exist are currently wrong at a deeper level than where any of the mainstream interpretations reach. (Like what is "motion" and so on) I believe one day someone will figure out a really simple deterministic explanation and everybody will slap on their forehead and go "doh!"

Well okay maybe there's some arguments back and forth first :)

This isn't true in the case of quantum computers; the calculations are based upon quantum effects, such as quantum interference and entanglement, so you can't just say "it just acts as if the different calculations would interfere, but actually they don't; the calculation and the result just already exist in a static spacetime." Quantum computers actually prove that quantum interference and entanglement are real phenomenom; not just illusions of "static spacetime."

Obviously to interpret this in terms of static spacetime you also have to assume that what we see as a photon is in fact just a wave-like connection between two atoms over spacetime (i.e. something with "volume", which occupies all the possible "trajectories". and in such manner that the shape of the "beginning" of the travel is affected by the shape of the "end").
If you keep thinking about photons as little balls it won't help you at all to look at it from the point of view of its own inertial frame (where "delayed choice" experiments are not "delayed choice" at all), unless of course you imagine the situation as if this little ball bounces back and forth in time over every possible trajectory. But to think about it this way you are confusing a whole new concept of "time progression" within spacetime itself, so...

Of course no one can say which idea of photons is more correct metaphysically, but this is just what I'm saying about how our ideas about what exists and in what manner are just assumptions, and they are bound to remain as assumptions forever, although I believe we can still peel much deeper than where we currently are.

And that been said, you can't say that a photon moves as if it would interfere with itself; it actually does interfere with itself.

Of course it does, although again, if you talk about the phenomenon in different terms, it may become meaningless to say it metaphysically interferes with itself, because it is meaningless to assign any identity to the photon in the first place. If you consider the so-called "photon" to literally be the "beep" that the atom does (i.e. when we say "the atom received a photon"), and the beep to be caused by a wave-like energy finding its way over all the possible routes to that atom (note that this is different from a wave propagating to all directions), you could only say there is wave-like energy that interfered with itself and no photon with identity ever made any journey.

But the trick is of course that you'd have to consider this to happen not over space but over spacetime. And let it be said that my confidence in the existence of spacetime is not particularly high either, I think spacetime too is a concept that is very much incorrect from what really exists.

So, if I have to make a bet about an interpretation, just for fun, I bet they are all going to be considered ridiculous when some assumption about something very fundamental will fall in place and show us more accurate view of all the phenomena we observe. Something akin to the shift from relative motion to relative time in relativity. (here I go again, praising relativity... silly me :P )

You may be tempted to say "maybe MWI is just this idea", but to me MWI is like all the other interpretations, and they are basically arguing about whether everything is made out of "earth, air, water and fire" or from "solid, liquid and gas", or perhaps the fundamentals are "opaque" and "transparent" matterpieces, when they should be concentrating on much much deeper issues. Something like, how could inertia be fundamental? Think about that.

 

[Chaos' lil bro Order]

Here is a FAQ considering the MWI. You'll probably find answers for your future questions there. A single universe is irreversibly split into many universes when the quantum system involved in the splitting decoheres. But that doesn't mean the decoherence causes the splitting; the universes split all the time, be there interactions or not. Decoherence only distinguishes the universes from each other and therefore they can't interfere with each other anymore.



Yes, a quantum computer can resolve this kind of calculation very fast.

'A single universe is irreversibly split into many universes when the quantum system involved in the splitting decoheres.'

Fair enough. Now tell me the variables of the 'quantum system' and what constitutes 'decoherence'. I'm tired of all these big words being thrown around without any real meaning behind them. This is not true understanding IMO, its akin to cut and pasting a wikipedia entry or repeating popular phrases found in books like 'The elegant Universe'. Can this thread get down the to nitty-gritty already, its becoming muddied with pop-science and its really pissing me off now.

 

[Chaos' lil bro Order]

kvanti

Upon reading some of the text from your link I found this explanation on why universes split according to MWI:

'The precise moment/location of the split is not sharply defined due to the subjective nature of irreversibility, but can be considered complete when much more than kT of energy has been released in an uncontrolled fashion into the environment. At this stage the event has become irreversible.'

It appears that MWI defines the splitting of a universe as when an 'irreversible' event takes place in it. The example given was the irreversibility of thermodynamic processes. But the statement above says that the splitting event isn't even clearly defined due to the subjective nature of irreversibility. My word, this MWI theory is turning out to be a big joke the more I read about it. I mean heck, it can't even make sharp concrete predictions even within its own framework, so why should anyone take it seriously. It seems like just another theory that defers what we do not understand about our universe to some sort of mystical idea that's no more falsifiable than god. It hinges on a subjective process, lmao!

 

[AnssiH]

Perhaps I'll throw in couple of questions myself. I don't ask these in the intent to show MWI false, but to find out some details of the model.

From FAQ:
For two branches or worlds to interfere with each other all the atoms, subatomic particles, photons and other degrees of freedom in each world have to be in the same state, which usually means they all must be in the same place or significantly overlap in both worlds, simultaneously.

"All the other atoms etc..." refers to what? All the atoms in the universes? Or just all the atoms of some smaller system? I.e. is it enough if in two worlds there just happens to exist an identical geiger-counter in the same "place" for them to interfere, even if the rest of the atoms in these worlds are different?

How do we identify "place", or rather, what justifies us to even assume that space is like an invisible backdrop where each location has identity?

What do we mean with the parts being "simultaneously" at the same place. Does this mean they not only have to exist in the same "place" but also in the same inertial frame? (Since in relativity any object with volume will not occupy the same "place" simultaneously from two different inertial frames)

Worlds irrevocably "split" at the sites of measurement-like interactions associated with thermodynamically irreversible processes

What does "at the sites of measurements-like interactions" mean here. Is it just the "site" that splits or the whole universe? I.e. Only the parts in the geiger-counter it that moved irreversibly, or everything?

If it is latter, when do they split? If you are observing the geiger-counter from 10 lightseconds away, will you split 10 light-seconds after counter or simultaneously?

If latter, simultanously in which inertial frame and why?

If it's in your own simultaneity, what if you are approaching the geiger-counter at great speeds when the split occurs at the counter, and then brake into the same frame as the counter so that the split hasn't happened yet in this frame. Will the split reverse too?

Contact between a system and a heat sink is equivalent to increasing the dimensionality of the state space, because the description of the system has to be extended to include all parts of the environment in causal contact with it.

Are not all things causally connected to everything in the universe? Does MWI assume that "causal connection" is something that exists metaphysically, instead of just a loose semantical concept? If so, how does it exists?

And also, does MWI comment on what causes the photon to take one or another route in the beam splitter within one universe, or is it still just "non-caused", arbitrary thing?

(btw, I don't much appreciate how the FAQ states "There is no other quantum theory, besides many-worlds, that is scientific". This is just the kind of definition bending that you'd expect from religious people.

 

[kvantti]

AnssiH:

OK. Let's forget about photons. Electron is a particle that has an inertial frame and it can interfere with itself in the double slit. And yet, the electron is completely localized particle according to the Heisenberg picture. So classically thinking, for it to interfere with itself, it would have to go thru both slits at the same time and travel to all the possible directions after that. Then for some magical reason, the electron is observed only in one place.

I'll reply to your questions in another post, if no one else has before that.

Now tell me the variables of the 'quantum system' and what constitutes 'decoherence'.

Varying observables: spin, momentum, position, energy, time. These are all that I can recall.

Decoherence: the loss or absence of interference within a quantum system due to interaction (and therefore entanglement) with another quantum system. I can't explain it simpler. You should just study the concepts.

'The precise moment/location of the split is not sharply defined due to the subjective nature of irreversibility, but can be considered complete when much more than kT of energy has been released in an uncontrolled fashion into the environment. At this stage the event has become irreversible.'

You misinterpreted this. The splitting isn't sharply defined in one universe, because a single universe splits all the time in the multiverse, and you can't tell in which universe you are until the splitting has become irreversible due to decoherence within the quantum system that has been split. In other words, before you observe the state of the quantum system, you can be in every possible universe where the quantum state hasn't decohered yet. That is what the author means when he writes "the split is not sharply defined due to the subjective nature of irreversibility."

Don't jump into conclusions.

 

[AnssiH]

AnssiH:

OK. Let's forget about photons. Electron is a particle that has an inertial frame and it can interfere with itself in the double slit. And yet, the electron is completely localized particle according to the Heisenberg picture. So classically thinking, for it to interfere with itself, it would have to go thru both slits at the same time and travel to all the possible directions after that. Then for some magical reason, the electron is observed only in one place.

Well I wouldn't consider any sub-atomic element in the atomic model to be a point-like particle at all, because our idea of a point-like things are based on stable pieces of matter. The stable elements that bring about this spatial stability as their emergent feature are probably not stable in the same manner at all. I don't have any answer as to the better description of what "electron" is, but let it be said that this question is indoubtedly going to be an important one (and incidentally it is one question that, AFAIK, troubled Einstein's mind greatly at his later years)

As an interesting philosophical excercise, consider Milo Wolff's spherical standing waves. Disregarding if his idea can be real or not, it is interesting to note how radically different fundamentals could bring about so similar measurable effects.

Also with experiments with electrons it becomes important to consider the reality of electromagnetic fields that are used to move the particles (and like I said, possibly the fundamental reality of motion)

More interesting but related problem, as I mentioned in the other thread myself, is that they have been able to make full atoms produce interference pattern. (I've been trying to find more details about these experiments)

Yet it doesn't seem to me at all that MWI "must be true", but instead my head is spinning with all the options that are still open and greatly unexplored (and cannot be explored without a decent army of scientists really spending time at taking the parts of this problem down and looking at it in completely new ways, like Einstein looked at the motion of light).

I'll reply to your questions in another post, if no one else has before that.

No hurry, I'll be away for about a week... Take care now!

 

[kvantti]

For two branches or worlds to interfere with each other all the atoms, subatomic particles, photons and other degrees of freedom in each world have to be in the same state, which usually means they all must be in the same place or significantly overlap in both worlds, simultaneously.

"All the other atoms etc..." refers to what? All the atoms in the universes? Or just all the atoms of some smaller system? I.e. is it enough if in two worlds there just happens to exist an identical geiger-counter in the same "place" for them to interfere, even if the rest of the atoms in these worlds are different?

The universes need to be almost identical for them to interfere. For example, when performing a double-slit experiment with single electrons, you get two significant sets of universes: in 50% of the universes the electron went thru the left slit and in another 50% it went thru the right slit. Since identical, these two sets of universes can interfere, giving the observed interference pattern after many electrons have been "shot" thru the slits.

If we observe which slit the electron goes thru, the universes decohere from each other and are not identical anymore. You get two sets of universes: in 50% of the universes the electron is observed to go thru the left slit and in another 50% of the universes thru the right slit. The universe is irreversibly split into two sets of universes that can't interfere with each other. So in this case we don't observe the interference pattern forming.

Does this mean they not only have to exist in the same "place" but also in the same inertial frame?

Yes, you just "look" the situation from the inertial frame of the quantum system in question. In the MWI, different inertial frames are just special cases of different universes. In other words, every inertial frame can be thought to be it's own universe (or rather, a different view of the same universe; likewise different universes are just different views of the multiverse). It is rather complicated, because the multiverse is a multidimensional "object". No one knows how many dimensions. String theory suggests 10 dimensions.

What does "at the sites of measurements-like interactions" mean here. Is it just the "site" that splits or the whole universe? I.e. Only the parts in the geiger-counter it that moved irreversibly, or everything?

Measurement-like interaction is any interaction that entangles the observed quantum system with the observers quantum state upon interaction. The whole universe is split, but the resulting universes don't have to differ radically; a single quantum event happening differently in two universes is enough for splitting. A double-slit experiment is a good example of this.

If it's in your own simultaneity, what if you are approaching the geiger-counter at great speeds when the split occurs at the counter, and then brake into the same frame as the counter so that the split hasn't happened yet in this frame. Will the split reverse too?

That is a question you need to ask from a quantum cosmologist; I have no clue... and I don't want to speculate.

Are not all things causally connected to everything in the universe? Does MWI assume that "causal connection" is something that exists metaphysically, instead of just a loose semantical concept? If so, how does it exists?

Every event that is causally connected with a certain quantum system is entangled with the quantum system. That is all there is to it.

And also, does MWI comment on what causes the photon to take one or another route in the beam splitter within one universe, or is it still just "non-caused", arbitrary thing?

The MWI is quite clear about it: in 50% of the universes the photon goes thru the beamsplitter and in another 50% it gets reflected from it. You end up in both universes, but because subjectivily you experience only one universe, it seems totally arbitrary. So you have 50% chance to experience one of the two sets of universes.

(btw, I don't much appreciate how the FAQ states "There is no other quantum theory, besides many-worlds, that is scientific". This is just the kind of definition bending that you'd expect from religious people.

This is true, but it is still the best FAQ about the MWI.

 

[RandallB]

Quantum computers . not proven to solve NP hard problems ... .

Couldn't find it used in other posts - What does "NP" stand for??

 

[NateTG]

Couldn't find it used in other posts - What does "NP" stand for??

NP is the set of problems whose answers can be checked in polynomial time.

 

[Chaos' lil bro Order]

Fine then, I think we disagree and nothing can be said by either to sway one's opinion on MWI.

One last question. What is the smallest event that can split a universe in two?

 

[kvantti]

Well I wouldn't consider any sub-atomic element in the atomic model to be a point-like particle at all, because our idea of a point-like things are based on stable pieces of matter. The stable elements that bring about this spatial stability as their emergent feature are probably not stable in the same manner at all. I don't have any answer as to the better description of what "electron" is, but let it be said that this question is indoubtedly going to be an important one (and incidentally it is one question that, AFAIK, troubled Einstein's mind greatly at his later years)

Particles are point-like in the way that they don't have any spatial size. In our most fundamental theory of reality (the quantum field theory) particles are quantas of energy of different quantum fields. How could energy have any "size"? The classical "size" of any particle is defined by its Compton wavelenght.

As an interesting philosophical excercise, consider Milo Wolff's spherical standing waves. Disregarding if his idea can be real or not, it is interesting to note how radically different fundamentals could bring about so similar measurable effects.

Same for the string theory. It is consistent with every observation because it doesn't make any new predictions at the energy scale we can handle nowadays with our most powerful particle accelerators. It isn't falsifiable.

Also with experiments with electrons it becomes important to consider the reality of electromagnetic fields that are used to move the particles (and like I said, possibly the fundamental reality of motion)

I see no problem seeing motion as an illusion... then again, I think the whole universe we perceive is an illusion of some sort.

More interesting but related problem, as I mentioned in the other thread myself, is that they have been able to make full atoms produce interference pattern. (I've been trying to find more details about these experiments)

Not just full atoms, but whole molecules too! In the '99 a research team was able to observe the self-interference of a http://wwwcsif.cs.ucdavis.edu/~cs175/Images/Buckyball.png is an article about the experiment.

So we have little balls of matter interfering with themselves. Nice.

Yet it doesn't seem to me at all that MWI "must be true", but instead my head is spinning with all the options that are still open and greatly unexplored (and cannot be explored without a decent army of scientists really spending time at taking the parts of this problem down and looking at it in completely new ways, like Einstein looked at the motion of light).

Yes, the MWI doesn't have to be true, but it is the simplest way to explain the physical behaviour of quantum phenomenom, like the self-interference of buckyballs. Thus, it is favoured by the Occam's razor and this is the main reason I prefer it over other interpretations.

 

[tehno]

Quantum computers are not proven to solve NP hard problems in polynomial time, and, in fact, are strongly expected no to.

I admit I'm dissapointed to hear that "secret" of a chess game will remain
undiscovered for a long time then.
I really thought that quantuum computer would resolve final status of the game in the near future...

 

[charlylebeaugosse]

Travis Norsen has written an article entitled "Against Realism". In it, he argues that the phrase "local realism" is not meaningful.

Against Realism (2006)

Abstract:
"We examine the prevalent use of the phrase “local realism” in the context of Bell’s Theorem and associated experiments, with a focus on the question: what exactly is the “realism” in “local realism” supposed to mean? Carefully surveying several possible meanings, we argue that all of them are flawed in one way or another as attempts to point out a second premise (in addition to locality) on which the Bell inequalities rest, and (hence) which might be rejected in the face of empirical data violating the inequalities. We thus suggest that this vague and abused phrase “local realism” should be banned from future discussions of these issues, and urge physicists to revisit the foundational questions behind Bell’s Theorem."

-----

My questions for your consideration:

1. What does realism mean to you?

2. Einstein said: "I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it." Is this realism?

3. In your opinion, is "realism" an assumption of Bell's Theorem? If so, where does it arise?

==========
For such matters, see
Einstein, Tolman, and Podolsky, Physical Review 37, (1931) 780-781
to wash out many errors that tend to make Einstein much more naive than he really was.

 

[setAI]

Quantum computers are not proven to solve NP hard problems in polynomial time, and, in fact, are strongly expected no to.

ehem:

using quantum computation to solve NP complete problems:

http://www.arxiv.org/abs/quant-ph/9912100
http://www.arxiv.org/abs/quant-ph/9801041
http://www.arxiv.org/abs/quant-ph/0508177

 

[RandallB]

Found it! --- NP stands for Nondeterministic Polynomial Time ...
NP-completeness difficult stuff.
But for this line of reasoning to confirm that QM and the MW interpretation of it (That MWI is an interpretation of QM may just be my opinion) is correct don’t we have to assume that the Classical view must be deterministic.
Has it been shown that Classical cannot be Nondeterministic, or is that something that is just assumed?

 

[AnssiH]

Yes, you just "look" the situation from the inertial frame of the quantum system in question. In the MWI, different inertial frames are just special cases of different universes. In other words, every inertial frame can be thought to be it's own universe (or rather, a different view of the same universe; likewise different universes are just different views of the multiverse). It is rather complicated, because the multiverse is a multidimensional "object". No one knows how many dimensions. String theory suggests 10 dimensions.

A bit off-topic but I have to make sure, don't the extra dimensions in string theory just refer to the fact that the strings would have to move/vibrate in more than 3 dimensions? (Which to me sounds like the dimensions could be just as well thought of as some completely different property than spatial dimensions, like an ordinary string could vibrate spatially and by "colour", etc...)

Particles are point-like in the way that they don't have any spatial size. In our most fundamental theory of reality (the quantum field theory) particles are quantas of energy of different quantum fields. How could energy have any "size"? The classical "size" of any particle is defined by its Compton wavelenght.

Yeah, definitely concepts like "size" need to be viewed critically here, but not only that, also we must view critically any sort of concept of particles. And the whole concept of "identity". Not only when we imagine identity to such thing as "photon", but even if we think about the universe as if it's one big continuous "fluid" where particles exists as stable standing waves (or whatever), we have still tacked identity to this "fluid". It may seem very obvious that something must have an identity in objective reality, but it must be noted that this intuitive view has bitten ourselves in the ass so many times on so many issues, that I'm becoming convinced that "identity" is a non-sensical concept as far as metaphysics is concerned. For example, it is completely arbitrary and without any empirical evidence, to assume that locations of space or spacetime have any identity to them. It is odd that physicists ever expected it to be so.

And having said that, even though we "kind of" understand the above, we still naturally imagine QM-situations in terms of things that have identity to themselves (instead of being stable patterns onto which one can arbitrarily tack identity, like onto a "standing wave" or a "shadow"). The fact that we consistently find such behaviour as we could expect a quantum mechanical electron to cause, does not mean there must "really" be a metaphysical electron. It just means there is some process causing this behaviour. Just like the fact that we consistently find our shadow to follow us, doesn't mean there actually is such an object with identity as a "shadow".

As a more concrete point in case, we can talk about how a photon, if energetic enough, can turn into an electron, or more vaguely, how energy can turn into matter (or vice versa), but is it not much more proper to understand that all these "fundamental particles" are not in fact fundamental at all. It is not like the energy as one fundamental thing just magically turns into some other fundamental thing (that has "fundamental inertia"). It's more proper to understand these particles as emergent features of whatever causes them, and their behaviour is also, after all is said and done, governed by their underlying causes (and I think one important question is going to be "what is charge metaphysically?").

I see no problem seeing motion as an illusion... then again, I think the whole universe we perceive is an illusion of some sort.

Well, the problem with calling something an "illusion" is that it means one basically just refuses to give any cause to some phenomenon. Sure we should expect motion to be something different from what it readily seems, but even more so we should expect "time" to be something different than what it seems, because it is a concept that is derived from "motion". I get a rash from the interpretation that the flow of time is just "an illusion in a static spacetime", because that is the same as saying "reality is static and conscious experience is magic". I understand the need for the word in some cases but it really is very very dangerous word that ought to be avoided :)

That being said, what is very important to understand is that as long as one talks about the concept of spacetime, he must also remember that nothing moves in spacetime. We are so used to the idea of "motion" that otherwise astute people often confuse the concepts of "spacetime" and "motion" together in incoherent ways. For example when they talk about how a photon "moves back and forth" in spacetime.

It must be understood that if spacetime is what is used to describe motion, you cannot then assert that something is in fact moving inside spacetime, for you would need a new time dimension to describe that motion. The matter of the fact is that metaphysical spacetime and metaphysical motion are mutually exclusive concepts. We can only have one or another. And to assert that only our "consciousness" moves in spacetime is also an assertion about motion "within" spacetime, regardless of if you call it an "illusion" or not.

This is not just a minor mathematical problem that can be dismissed, but it in fact highlights very concretely the problems of such assumptions as the metaphysical existence of spacetime (strictly speaking, the observable predictions of relativity don't require spacetime to exist because relativity of simultaneity cannot be directly observed). I don't think anyone has been able to actually make any explanation about how the "illusion of flow of time" could be achieved if nothing is in motion in reality, but everybody are very willing to dismiss the whole problem as meaningless because you really don't bump into it until you get to the philosophy of the mind, which may seem unrelated to physics, but it is not.

(Let it be said that I understand our subjective experience is very different from its immediate "causes" in objective reality, which is why I say it is an emergent feature of its parts)

Not just full atoms, but whole molecules too! In the '99 a research team was able to observe the self-interference of a http://wwwcsif.cs.ucdavis.edu/~cs175/Images/Buckyball.png is an article about the experiment.

So we have little balls of matter interfering with themselves. Nice.

This is very interesting. Thanks.

-Anssi

 

[AnssiH]

Not just full atoms, but whole molecules too! In the '99 a research team was able to observe the self-interference of a http://wwwcsif.cs.ucdavis.edu/~cs175/Images/Buckyball.png is an article about the experiment.

Does anyone have more information about this?

-Anssi

 

[selfAdjoint]

Try http://www.physics.usu.edu/peak/phys_2710_fall06/Complementarity.pdf#search=%22double%20slit%20buckyball%22" . A good general description of various double slit experiments including the buckyball one, and does elementary calculations using DeBroglie wave length.

 

[kvantti]

A bit off-topic but I have to make sure, don't the extra dimensions in string theory just refer to the fact that the strings would have to move/vibrate in more than 3 dimensions? (Which to me sounds like the dimensions could be just as well thought of as some completely different property than spatial dimensions, like an ordinary string could vibrate spatially and by "colour", etc...)

Yes, the extra dimensions first came up because they were needed to represent the one-dimensional strings. But the six extra dimensions can also thought to be the "landscape" in which the different universes of the multiverse exist:

String theory proposes that the many different types of subatomic particles are really just different vibrations of tiny strings that are like minuscule rubber bands. The catch is that it only works if the strings have several extra dimensions in which to vibrate beyond the dimensions we see.

Why don’t we see the extra dimensions? A proposal dating to 1998 claims we’re trapped in a three-dimensional zone within a space of higher dimensions. Other three-dimensional zones, called “branes,” could also exist, less than an atoms’ width away yet untouchable. The branes are sometimes called different universes, though some theorists say they should be considered part of our own because they can weakly interact with our brane in some ways.

http://www.world-science.net/exclusives/060330_multiversefrm.htm

Yeah, definitely concepts like "size" need to be viewed critically here, but not only that, also we must view critically any sort of concept of particles. And the whole concept of "identity". Not only when we imagine identity to such thing as "photon", but even if we think about the universe as if it's one big continuous "fluid" where particles exists as stable standing waves (or whatever), we have still tacked identity to this "fluid". It may seem very obvious that something must have an identity in objective reality, but it must be noted that this intuitive view has bitten ourselves in the ass so many times on so many issues, that I'm becoming convinced that "identity" is a non-sensical concept as far as metaphysics is concerned. For example, it is completely arbitrary and without any empirical evidence, to assume that locations of space or spacetime have any identity to them. It is odd that physicists ever expected it to be so.

Yeah its funny, we can only observe the properties particles exhibit (mass, spin, charge etc.) and make models of the interactions and relations of those properties. So we don't acutally observe the particles, just their behaviour.
As I quoted Lee Smolin on the other forum, "a point in spacetime is not defined by its location -- its defined only by what physically happens at it." This is just fancy way of saying that we can't assing any specific "location" to spacetime itself; only to events in spacetime.

And having said that, even though we "kind of" understand the above, we still naturally imagine QM-situations in terms of things that have identity to themselves (instead of being stable patterns onto which one can arbitrarily tack identity, like onto a "standing wave" or a "shadow"). The fact that we consistently find such behaviour as we could expect a quantum mechanical electron to cause, does not mean there must "really" be a metaphysical electron. It just means there is some process causing this behaviour. Just like the fact that we consistently find our shadow to follow us, doesn't mean there actually is such an object with identity as a "shadow".

Are you referring to some hidden variable theory?

As a more concrete point in case, we can talk about how a photon, if energetic enough, can turn into an electron, or more vaguely, how energy can turn into matter (or vice versa), but is it not much more proper to understand that all these "fundamental particles" are not in fact fundamental at all. It is not like the energy as one fundamental thing just magically turns into some other fundamental thing (that has "fundamental inertia"). It's more proper to understand these particles as emergent features of whatever causes them, and their behaviour is also, after all is said and done, governed by their underlying causes (and I think one important question is going to be "what is charge metaphysically?").

Particles are quantas of energy according to quantum field theory. Why this explenation isn't satisfactory to you? When a particle decays to other particles, its just different field interactions changing the energy (of the quantum field) into another form. In the case of a photon, the electromagnetic interaction "splits" the quanta of the neutral spin 1 field into two quantas of the charged spin ½ field if the conditions are appropriate for this kind of interaction to happen. According to QED atleast. Charge is the probability for the charged spin ½ field (or the electron field) to interact with the neutral spin 1 field (the em-field).

Well, the problem with calling something an "illusion" is that it means one basically just refuses to give any cause to some phenomenon. Sure we should expect motion to be something different from what it readily seems, but even more so we should expect "time" to be something different than what it seems, because it is a concept that is derived from "motion". I get a rash from the interpretation that the flow of time is just "an illusion in a static spacetime", because that is the same as saying "reality is static and conscious experience is magic". I understand the need for the word in some cases but it really is very very dangerous word that ought to be avoided :)

Conscious experience isn't magic; the quantum state of a persons consciousness just differs at every area of spacetime, giving illusion of the "flow of time". The entropy of the brain increases when "moving forward" in time, or in other words: the quantum state of the consciousness is more disordered in the "future" areas of spacetime. And consciousnes doesn't "move" within spacetime (as you suggested before), but instead consciousness exists at every area of spacetime where the persons brain exist; just that in different areas of spacetime, the quantum states of the consciousness differ from each other.

That being said, what is very important to understand is that as long as one talks about the concept of spacetime, he must also remember that nothing moves in spacetime. We are so used to the idea of "motion" that otherwise astute people often confuse the concepts of "spacetime" and "motion" together in incoherent ways. For example when they talk about how a photon "moves back and forth" in spacetime.

Yes. Nothing moves in spacetime. Motion can be viewed completely as an illusion: when you observe some object moving, you really just remember the "past" position of the object differing from the "present" position of the object. When this happens continuously, you see the object "moving".

It must be understood that if spacetime is what is used to describe motion, you cannot then assert that something is in fact moving inside spacetime, for you would need a new time dimension to describe that motion. The matter of the fact is that metaphysical spacetime and metaphysical motion are mutually exclusive concepts. We can only have one or another. And to assert that only our "consciousness" moves in spacetime is also an assertion about motion "within" spacetime, regardless of if you call it an "illusion" or not.

Yup, nothing moves inside a static spacetime continuum, not even consciousness.

I don't think anyone has been able to actually make any explanation about how the "illusion of flow of time" could be achieved if nothing is in motion in reality, but everybody are very willing to dismiss the whole problem as meaningless because you really don't bump into it until you get to the philosophy of the mind, which may seem unrelated to physics, but it is not.

It has been explained. I just never realized your point until now... and now I feel stupid.

 

[AnssiH]

Yeah its funny, we can only observe the properties particles exhibit (mass, spin, charge etc.) and make models of the interactions and relations of those properties. So we don't acutally observe the particles, just their behaviour.
As I quoted Lee Smolin on the other forum, "a point in spacetime is not defined by its location -- its defined only by what physically happens at it." This is just fancy way of saying that we can't assing any specific "location" to spacetime itself; only to events in spacetime.

Yeah, exactly

The fact that we consistently find such behaviour as we could expect a quantum mechanical electron to cause, does not mean there must "really" be a metaphysical electron. It just means there is some process causing this behaviour. Just like the fact that we consistently find our shadow to follow us, doesn't mean there actually is such an object with identity as a "shadow".

Are you referring to some hidden variable theory?

Nah, I'm not very fond of hidden variable theories, at least not when they still assume particles are at all times entities with spatial stability (i.e. "like tiny balls").

I'm just saying that we shouldn't look at any observed stable pattern as more than just that; a stable pattern. Any stable pattern, like a shadow of a building or a standing wave inside a room, could be understood as a stationary entity because there is a sense of stability to their existence, but physically we can't say they are entities that are just "sitting there", but instead there are stable patterns whose stability is a result of an active process.

And such appears to be the case for matter as well. Matter is not something that is just "sitting there". There is an active process that keeps what we call an atom (or a buckyball molecule) spatially stable.

It is possible that the relative motion between such spatially stable patterns is mechanically explainable by some model that also explains just why is there such spatial stability, and such models are likely to make very different assumptions about what exists fundamentally (as compared to the standard model), and may give QM phenomena a completely deterministic footing. E.g. the locations where we observe electrons (or phenomena associated to electrons) are not necessarily required to be such places where an entity called "electron" would have had to move in any Newtonian sense at all, and this assertion is, I believe, completely valid option for a realist.

So you could say my belief is that we just haven't figured out the proper model yet, but that we are capable of doing so by letting go certain particularly sticky assumptions about reality.

Conscious experience isn't magic; the quantum state of a persons consciousness just differs at every area of spacetime, giving illusion of the "flow of time". The entropy of the brain increases when "moving forward" in time, or in other words: the quantum state of the consciousness is more disordered in the "future" areas of spacetime. And consciousnes doesn't "move" within spacetime (as you suggested before), but instead consciousness exists at every area of spacetime where the persons brain exist; just that in different areas of spacetime, the quantum states of the consciousness differ from each other.

Yes. Nothing moves in spacetime. Motion can be viewed completely as an illusion: when you observe some object moving, you really just remember the "past" position of the object differing from the "present" position of the object. When this happens continuously, you see the object "moving".

When you say "when this happens continuously", are you not invoking an idea of motion? (For there is no sense of something happening continously without pointing out continuous "moments" from spacetime)

Obviously it is very understandable idea that the "state of the brain is different at every area of spacetime" and it is only expressing the past at any particular "moment" we choose to point at in the spacetime, but even then, we cannot really say what is it - metaphysically - that is doing this choosing and pointing. Why do we ever feel like there is a "now" moment?

I believe the most popular way to understand spacetime is to just consider the future and the past to exist at all times (so to give a simple ontology for the relativity of simultaneity), and in such case all the states of the brain exist "all the time", and metaphysically there is no such thing as "now moment" at all except for our subjective experience. This is why Einstein said "time is just an illusion" etc...

But this view fails completely to account for what is it physically, that causes the "now moment" to exist in subjective experience. It must be something in the physical world causing this, yes?

For these reasons, I must consider the possibility that it really is "motion" instead of "time" that exists metaphysically. It is often stated that "for there to be motion there needs to exist time", but this is immediately invalid argument, because the semantical concept of "time" is what is derived from the fact that we observe motion. If things really are in motion and there really exists only present (not the past and the future), it would readily explain why the sense of "flow of time" exists in our subjective experiences.

Note that even if you consider it to be "time pointer" that "flows" in spacetime to give us the experience of "present moment", it is not meaningful at all to give any "speed" to this pointer. Regardless of its speed (or direction) through the static spacetime, the subjective experience "at the pointer" would be the same (for our sense of time depends on how reality is expressed physically in the brain). It is probably this fact that gives people confidence to the idea that time does not flow at all, but we should not forget that we would still need that "pointer" to exist, otherwise we have not given any explanation about why there is any subjective experience at all, and to me this just shows how the idea of time as a dimension is a non-sensical one and doesn't fit very well to ontological reality, even if it's a handy tool.

Consider the difference between "describing the motion of a physical system in an instantaneous manner, such as the brain in spacetime, and really experiencing the motion of a physical system; such as having a subjective experience. Consider this thought experiment:

If you take a snapshot copy of a physical brain and freeze all its motion (by some magic), does it still have a conscious experience of everything being still? No, for this would require thoughts (about stillness) to exist above physical motion.

If you wait for 10 minutes and take a snapshot of the state of the original brain, and modify the copy-brain manually into the same state, you have essentially inserted all the memories from that past 10 minutes into the brain, and if you now set the copy into motion, it surely would claim to have had a subjective experience of the past 10 minutes as if time was flowing smoothly.

But can conscious experience exist if time moves ahead in discreet steps? What if you do NOT set the brain into motion, but instead just project a new state onto it every 10 minutes? Would it still have a conscious experience of a smooth flow of time? What if you project a new state onto it once every year? Could you imagine the possibility, that while reading this, your experience right now of "this moment" is not real but is instead one that is "going to be updated into your brain a year from now"?

I think the more you think about these issues, the more inclined you become to consider the possibility that it is in fact motion that really exists, instead of a static spacetime block.

-Anssi

 

[kvantti]

So you could say my belief is that we just haven't figured out the proper model yet, but that we are capable of doing so by letting go certain particularly sticky assumptions about reality.

That is possible.

When you say "when this happens continuously", are you not invoking an idea of motion? (For there is no sense of something happening continously without pointing out continuous "moments" from spacetime)

Well, spacetime is a continuum, so even if there is no motion, there is continuity. We observe this continuity as motion.

Why do we ever feel like there is a "now" moment?

Because we experience the increase of entropy in the brain as "flow of time" and "now" is just an illusion of this process. Try to remember what you did 0,1 seconds ago. Confusing?

For these reasons, I must consider the possibility that it really is "motion" instead of "time" that exists metaphysically. It is often stated that "for there to be motion there needs to exist time", but this is immediately invalid argument, because the semantical concept of "time" is what is derived from the fact that we observe motion. If things really are in motion and there really exists only present (not the past and the future), it would readily explain why the sense of "flow of time" exists in our subjective experiences.

You don't need to derive "time" from the concept of motion. You can just say that "time is a thing that enables the state of a system to change". But then again, a state of a system cannot change without motion.

Note that even if you consider it to be "time pointer" that "flows" in spacetime to give us the experience of "present moment", it is not meaningful at all to give any "speed" to this pointer. Regardless of its speed (or direction) through the static spacetime, the subjective experience "at the pointer" would be the same (for our sense of time depends on how reality is expressed physically in the brain). It is probably this fact that gives people confidence to the idea that time does not flow at all, but we should not forget that we would still need that "pointer" to exist, otherwise we have not given any explanation about why there is any subjective experience at all, and to me this just shows how the idea of time as a dimension is a non-sensical one and doesn't fit very well to ontological reality, even if it's a handy tool.

Consider the difference between "describing the motion of a physical system in an instantaneous manner, such as the brain in spacetime, and really experiencing the motion of a physical system; such as having a subjective experience. Consider this thought experiment:

If you take a snapshot copy of a physical brain and freeze all its motion (by some magic), does it still have a conscious experience of everything being still? No, for this would require thoughts (about stillness) to exist above physical motion.

If you wait for 10 minutes and take a snapshot of the state of the original brain, and modify the copy-brain manually into the same state, you have essentially inserted all the memories from that past 10 minutes into the brain, and if you now set the copy into motion, it surely would claim to have had a subjective experience of the past 10 minutes as if time was flowing smoothly.

But can conscious experience exist if time moves ahead in discreet steps? What if you do NOT set the brain into motion, but instead just project a new state onto it every 10 minutes? Would it still have a conscious experience of a smooth flow of time? What if you project a new state onto it once every year? Could you imagine the possibility, that while reading this, your experience right now of "this moment" is not real but is instead one that is "going to be updated into your brain a year from now"?

I think the more you think about these issues, the more inclined you become to consider the possibility that it is in fact motion that really exists, instead of a static spacetime block.

I have thought the same from the perspective of the multiverse. In the multiverse, the quantum states of the universes actually are "snapshots" from the point of view of the observer. Every possible snapshot exists and these snapshots are connected with each other with the laws of nature. That is, when you have quantum states A and D, you can't get from A -> D without going thru B and C first. Same with the quantum states of the brains. The quantum states are separated by Planck times (the multiverse is a discrete system). This accounts for "continous" conscious experience aswel.

So, again, I see no problem from the perspective I see things.

 

[AnssiH]

Well, spacetime is a continuum, so even if there is no motion, there is continuity. We observe this continuity as motion.

Because we experience the increase of entropy in the brain as "flow of time" and "now" is just an illusion of this process. Try to remember what you did 0,1 seconds ago. Confusing?

The question is how is it that we experience an increase of entropy as flow of time? Perhaps this has more to do with relativity and philosophy than with QM, but nevertheless, the important point to pick up is that it is not really a satisfying explanation to say reality is a static spacetime block where nothing moves (where the whole concept of "now" is non-sensical), and that it is the continuity that we observe as motion. Of course I understand how this continuity describes motion, but that is not the same as really producing an experience of motion.

For reality to produce an conscious experience of motion, something in physical reality must be different "now" from "a moment ago" (even if these are misleading concepts).

Consider your own subjective experience. You have an experience that "now" is different from "yesterday", and surely your subjective experience is caused by something that exists in reality? Something "real" is causing your experience, right? Surely then something in reality is in different state "now" than it was "yesterday". Even if you consider yesterday still exists in spacetime, you need that pointer to experience the "now". It is not possible that in reality absolutely NOTHING is in motion or changes, because that would require your subjective experience to be something that is not part of reality.

So what I'm saying is that if you believe there is a spacetime, you have to commit to this idea absolutely before it is a valid ontological interpretation, and in that case you lose all sense of motion from reality, UNLESS you posit there is also pointer that moves in spacetime (so to make difference between today and yesterday for a given subjective experience), which then again is in conflict with the idea that there is no motion, but only a spacetime.

And to postulate that spacetime is static but pointer is in motion is not very elegant; why would there exist both, metaphysical motion and spacetime?

You don't need to derive "time" from the concept of motion. You can just say that "time is a thing that enables the state of a system to change". But then again, a state of a system cannot change without motion.

Yeah, that's the problem. Sure, it is not readily given that time is derived from motion, but what is given is that we can only expect to have either real time-dimension or real motion, but not both.

If we choose it is time dimension that exist, then the problem is, like you said, the state of the system cannot really change without motion. Of course the only system we really know to exist "in motion" is "subjective experience". Can it be different from one moment to the next if there is no motion?

But if we choose it is motion that exists, it becomes little bit clearer. We stroll around the Earth and observe motion. We may notice that each time a pendulum swings, our heart beats exactly 4 times, or a rotating wheel does exactly 5 revolutions. So we assume the "time" it takes for the pendulum to swing is constant (at least as compared to all the other physical systems around us).

So just now, by comparing the motion of different systems we have built a concept of time, and we might say "I'll run around the building in 50 pendulum swings". This doesn't mean there had to be "time dimension" underneath it all to make this running possible, for we could expect "motion" to be something that "just exists" in a fundamental sense. (Albeit it is still non-sensical to talk about the "speed" of this fundamental motion)

I have thought the same from the perspective of the multiverse. In the multiverse, the quantum states of the universes actually are "snapshots" from the point of view of the observer. Every possible snapshot exists and these snapshots are connected with each other with the laws of nature. That is, when you have quantum states A and D, you can't get from A -> D without going thru B and C first. Same with the quantum states of the brains. The quantum states are separated by Planck times (the multiverse is a discrete system). This accounts for "continous" conscious experience aswel.

Does there exist a metaphysical "now" moment in MWI, or is reality still a set of static spacetime blocks?
If its latter, you still need something to change when subjective experience does.

 

[kvantti]

The question is how is it that we experience an increase of entropy as flow of time?

I can't help but repeating myself: it's an illusion. The way we experience "the flow of time" is the only way we can experience it. For example, when your reading this text the entropy of your brain increases when it records the information you're reading. Because of the information your brain has recorded you have more memories of events, like reading this text. This gaining of new memories increases the entropy of your brains and gives an illusion of "flow of time". The fact that we experience "a present moment" is due to the fact that we can't remember the future; your brains haven't yet recorded future events. When the future events are recorded, you experience them as being in the "present" and after that, when your brains have recorded more events, in the "past".

For reality to produce an conscious experience of motion, something in physical reality must be different "now" from "a moment ago" (even if these are misleading concepts).

Something is different between "a moment ago" and "now" (from the perspective of subjective experience): the amount of information stored in your brains.

Even if you consider yesterday still exists in spacetime, you need that pointer to experience the "now". It is not possible that in reality absolutely NOTHING is in motion or changes, because that would require your subjective experience to be something that is not part of reality. So what I'm saying is that if you believe there is a spacetime, you have to commit to this idea absolutely before it is a valid ontological interpretation, and in that case you lose all sense of motion from reality, UNLESS you posit there is also pointer that moves in spacetime (so to make difference between today and yesterday for a given subjective experience), which then again is in conflict with the idea that there is no motion, but only a spacetime.

You don't need a pointer. The "now" is at every point of spacetime. The "nows" of your brains (and thus your consciousness) just differ from each other.

Of course the only system we really know to exist "in motion" is "subjective experience". Can it be different from one moment to the next if there is no motion?

Yes, it can. You just have to keep in mind that "subjective experience" is determined by the amount of information you have acces to and while the amount of information in your brains increases, you experience time "flowing".

But if we choose it is motion that exists, it becomes little bit clearer. We stroll around the Earth and observe motion. We may notice that each time a pendulum swings, our heart beats exactly 4 times, or a rotating wheel does exactly 5 revolutions. So we assume the "time" it takes for the pendulum to swing is constant (at least as compared to all the other physical systems around us).

So just now, by comparing the motion of different systems we have built a concept of time, and we might say "I'll run around the building in 50 pendulum swings". This doesn't mean there had to be "time dimension" underneath it all to make this running possible, for we could expect "motion" to be something that "just exists" in a fundamental sense. (Albeit it is still non-sensical to talk about the "speed" of this fundamental motion)

The problem with only three dimensions is that the state of a three dimensional space can't change unless there is time; you would have only static 3D space. So, if you wan't to describe events in three dimensional space you need to use time, and the time component can be described as an extra dimension, giving total of four spacetime dimensions.

Does there exist a metaphysical "now" moment in MWI, or is reality still a set of static spacetime blocks?
If its latter, you still need something to change when subjective experience does.

Nope, there is no "now" in the MWI. You could say that "reality is a static multispacetime block". This "multispacetime block" is the multiverse. This is a simplified way to see it and it doesn't describe all the properties of the multiverse.

 

[AnssiH]

It takes time to understand motion. But motion can exist without time.

Hmmm, we aren't making much progress... Let it be said, that I used to think of flow of time as an illusion much like you describe. I understand why people think this way. But some philosophy reveals that this view is not unproblematic at all. You must dig way deeper to really see the problems, and in particular form strong understanding about how we comprehend anything with semantical concepts and how we build those concepts in a mechanical sense.

So, let's see if we can clarify this a little bit from another angle. I'll try to proceed with careful steps. It doesn't matter if we disagree or not after this.

This is certain; We cannot claim "time must exist fundamentally, because otherwise there would not be motion".

We cannot claim this, because just like we can assert that "time" is what exists fundamentally (without cause), we can assert that "motion" is what exists fundamentally. The choice between is - to an extent - arbitrary. Just because our comprehension is based on concepts and classifications of reality, and because we need to use the semantical concept of "time" to express motion, does not mean reality works with semantical concepts also. We are forced to invoke the semantical idea of "time" to talk about "motion", but motion can still "really exist" without any fundamental entity like "time" dictating this change.

Otherwise we could also say that "numbers" or "vectors" must exist fundamentally, claiming that without numbers and vectors there could not exist "clusters of bananas" or "velocity addition", etc... Just that we need some concept to express something in reality doesn't make it of fundamental existence. (Note that any conscious experience is also a case of expression of reality, caused by the brain)

So we can establish that the choice between "time" and "motion" is somewhat arbitrary. Still agree?


Another thing that is almost certain is that "fundamental time" and "fundamental motion" are mutually exclusive; both cannot be fundamental.

I say "almost certain" because it is conceivable to imagine that time exists as a static dimension and it is read by a pointer/worldline that moves. It's conceivable but not very elegant, for various reasons.

If anything is allowed with motion, we could just as well expect it is the physical things, on which our subjective experience is based, that are in motion. If nothing is allowed with motion, this would include our subjective experience which certainly is "something". And more importantly, once we have described the structure of spacetime, our semantical concept of "motion" (of worldline) becomes meaningless as an explanation to the change in the subjective experience. The subjective experience could not detect which way this "motion of worldline" happens, because the worldline is not a homunculus entity (it is not "fundamental consciousness"). This well-known argument about the static existence of spacetime actually puts fair amount of mud on the idea that "time" is a prerequisite of motion.

So, to get any further with the issue, we must assume that "time" and "motion" cannot BOTH exist as fundamentals. Still agree?

At this point, people who have chosen the path of "fundamental time", are forced to resort to the claim that the flow of time in subjective experience is "an illusion". This they justify with the comfortable fact that reality is just an expression of the past in the brain at any given moment. But this claim does not so much explain anything as it ignores the problem. None of the states of the brain would be more "real" than any other state, yet in subjective experience one is, at a time, more real than others. Clearly this needs more words.

And here we get to the hard parts. It is difficult to explain it all briefly, but I'll try.

The issue is not so much about "how the expression of reality exists at any given moment", but to explain how is it that within subjective experience there is motion, if "nothing is allowed with motion". It is one thing to imagine the whole spacetime history of a brain, and another to understand a process of conscious experience occurring to that construction. When you have assumed that it is time that exists fundamentally, ontological descriptions of reality tend to get very muddy very quickly.

Considering the philosophy of the mind, it quickly becomes clear that it's better to understand consciousness in the sense that we are NOT conscious of "successive moments", but rather we are merely conscious of the "change" that happens. This becomes concrete in many cases. Any sensory stimulation must have a spatial AND temporal aspect to it before you can be conscious of it (the patterns in the neurons must actually change). The semantical concepts our brain builds are always juxtapositions of each others (They make sense without "fundamental meaning" only because there are "differences" to them; something is what something else is not). In many many ways, our subjective experience is about change, and for this reason it is absolutely impossible to really comprehend anything without invoking an idea of motion or change. You simply will not be able to describe subjective experience without invoking some idea of motion or change at some point. We are so used to change, that sometimes it takes considerable effort to just notice this conflict.

To say "...the entropy of your brain increases..." is invoking an idea of motion. To say "...the fact that we experience 'a present moment' is due to the fact that we can't remember the future" is invoking an idea of motion; it suggests one to imagine a metaphysical "moment" that is "real" at one particular "instant" but not at another instant.

At the face of it this all may seem like an indication that "time" could really be what exists fundamentally, just beyond our comprehension, but as you get closer and closer to understanding "static time" in an absolute sense (as in there is no motion anywhere at all), it merely clarifies the fundamental aspect of the problem of change within our subjective experience.

Subjective experience is caused by reality. Agree? If nothing changes in reality, nothing is causing change in subjective experience. This looks like a dead end.

Although, like I said, the correct choice between "fundamental time" and "fundamental motion" is not given. It could still be either one. But what is given is that if you build your model of reality around fundamental motion, things get very much clearer (Albeit any ideas about the "absolute speed" of that motion are still non-sensical).

And with current empirical knowledge, you can choose to do that. Like I said, it actually is NOT at odds with relativity, because relativity does not allow for direct observation of relativity of simultaneity. You can understand all the observable time effects as different relative speeds of the physical motion/processes (in different environments), although the more "descriptive" way to express this mathematically is probably much less elegant than Lorentz-transformation (Mathematical elegance is different from ontological elegance).

We still need to use the concept of time to "comprehend" motion semantically (to express it), but we must understand that it really is just a semantical concept, and reality does not work on semantical concepts. It just works under some fundamentals, of which we try to make sense by building semantical models of reality, that are always incorrect to some extent, because they are merely an expression of the real thing. Map is not the territory.

I hope that was not too confusing. It really is difficult to be brief with such a massive subject as this.

 

[kvantti]

Hmmm, we aren't making much progress...

Yeah and I think I know why: you see things from a Newtonian point of view while I see things from the point of view of relativity. This conversation would go on and on without progress, because we just see things too differently. You see problems where I don't and vice versa.

I'm too tired to answer your whole post at the moment, I had three hours of sleep last night, and now I'm off to take a nap. Be back later etc.

 

[AnssiH]

Well I guess then we are just going to have to disagree.

Although, if you find the reality of static spacetime likely, why do you consider MWI to be simpler than this:

https://www.physicsforums.com/showthread.php?t=130623

Isn't it simpler to just assume that light (and everything) exists in spacetime in static sense just the way we find it to exist, instead of imagining a model of many worlds that would produce the same behaviour? After all, you have to think about the trajectory of light as "single object" in spacetime, then why couldn't it exist fundamentally just the way we find it?

 

[kvantti]

Isn't it simpler to just assume that light (and everything) exists in spacetime in static sense just the way we find it to exist, instead of imagining a model of many worlds that would produce the same behaviour? After all, you have to think about the trajectory of light as "single object" in spacetime, then why couldn't it exist fundamentally just the way we find it?

That is basically same as saying "we don't know how things work, they just are the way they are". The static spacetime approach doesn't explain why we observe the world as indeterministic even though it should be deterministic from the point of view of a static spacetime.
The MWI is the simplest physical interpretation for explaining quantum mechanics. This is a fact. People don't see this because the change in paradigm is so huge, so incomprehensible, that they reject it straight handed. But the fact is that the MWI is a consequence of a very simple postulate: the mathematical formulation of QM describe the behaviour of a quantum mechanical system; not just probabilities of different behaviours (as in Copenhagean). From this postulate emerges the whole idea of the multiverse.

I like to think that the mathematical formulation of classical mechanics describe the way macroscopic systems behave. Same with quantum mechanics.

 

[AnssiH]

That is basically same as saying "we don't know how things work, they just are the way they are". The static spacetime approach doesn't explain why we observe the world as indeterministic even though it should be deterministic from the point of view of a static spacetime.

Well it's true that spacetime interpretation doesn't say anything about the indeterminism by itself (although it probably would be quite trivial to make all kinds of assertions about it that would be basically impossible to confirm), but as of the "we don't know how things work, they just are the way they are", that is the case with all models. Especially when we talk about ontological interpretations, they are literally just cases of selecting different "things" to exist fundamentally (like multiverse). This is what I critizised earlier in this thread and I certainly don't see reason to commit to any particular selection of "fundamentals".

The MWI is the simplest physical interpretation for explaining quantum mechanics. This is a fact. People don't see this because the change in paradigm is so huge, so incomprehensible, that they reject it straight handed.

Well I personally don't have any problems in making paradigm shifts, since I am convinced that any worldview that we are capable of is essentially a circle of beliefs; not fundamentally attached to any sorts of truths. And for the same reason I think it is just wrong to encourage anyone to commit to any interpretation, and whatever interpretation is the "simplest" really depends on what sorts of problems you are tackling (and to an extent how familiar you are with some interpretation).

For example, earlier you mentioned that Deutsch challenges doubters by asking "where else do the calculations happen if not in other worlds since there are too many degrees of freedoms for one universe" (or something like that). This particular idea about how many degrees of freedom there are is assuming that a photon experiences one particular moment in a Newtonian way (in which moment there are this or that many degrees of freedom). But it is not very difficult to understand the same system as if the photons bouncing "back and forth" in spacetime are affected by the "future" measurement of each others. The degrees of freedom all exist in single universe now, but it doesn't really make sense to say that the calculations happen in many worlds anymore. At any rate, the observable behaviour of the system is the same in either cases. This is true for any model; you can always build arbitrary number of mechanisms to explain any behaviour.

But the fact is that the MWI is a consequence of a very simple postulate: the mathematical formulation of QM describe the behaviour of a quantum mechanical system; not just probabilities of different behaviours (as in Copenhagean). From this postulate emerges the whole idea of the multiverse.

I believe this postulate would hold true for spacetime interpretation too...(?) The critical difference seems to be different terminology and different concepts to refer to time, and that with spacetime interpretation the idea about information transfer is different from "just particles"; it is rather a connection over all space in one universe instead of series of lines in many universes. Very similar, but so very different... :I

 

[kvantti]

-- but as of the "we don't know how things work, they just are the way they are", that is the case with all models.

No, it isn't the case with all models. Some interpretations explain the physical behaviour behind quantum mechanical phenomenon, others don't.

Especially when we talk about ontological interpretations, they are literally just cases of selecting different "things" to exist fundamentally (like multiverse). This is what I critizised earlier in this thread and I certainly don't see reason to commit to any particular selection of "fundamentals".

The multiverse is a direct consequence of the postulate, not some tought up concept.

And for the same reason I think it is just wrong to encourage anyone to commit to any interpretation, and whatever interpretation is the "simplest" really depends on what sorts of problems you are tackling (and to an extent how familiar you are with some interpretation).

I'm not encouraging anyone, I'm stating a fact. The Occams razor decides which interpretation is the simplest.

For example, earlier you mentioned that Deutsch challenges doubters by asking "where else do the calculations happen if not in other worlds since there are too many degrees of freedoms for one universe" (or something like that). This particular idea about how many degrees of freedom there are is assuming that a photon experiences one particular moment in a Newtonian way (in which moment there are this or that many degrees of freedom). But it is not very difficult to understand the same system as if the photons bouncing "back and forth" in spacetime are affected by the "future" measurement of each others. The degrees of freedom all exist in single universe now, but it doesn't really make sense to say that the calculations happen in many worlds anymore. At any rate, the observable behaviour of the system is the same in either cases. This is true for any model; you can always build arbitrary number of mechanisms to explain any behaviour.

It doesn't matter which quantum effects the quantum computer uses to calculate, photons or molecules, but it matters that a qubit can be in a superposition of state, ie. in the states |+1> and |-1> simultaenously. Either you interpret that qubits are in these states simultaenously in one universe or that they exit in only one state in one universe and in the other state in another universe, and that these universes superpose if the qubits are in decoherent state.

I believe this postulate would hold true for spacetime interpretation too...(?) The critical difference seems to be different terminology and different concepts to refer to time, and that with spacetime interpretation the idea about information transfer is different from "just particles"; it is rather a connection over all space in one universe instead of series of lines in many universes. Very similar, but so very different... :I

Nope, the postulate is specific to MWI only:

Although several versions of MWI have been proposed since Hugh Everett's original work[1], they contain one key idea: the equations of physics that model the time evolution of systems without embedded observers are sufficient for modelling systems which do contain observers; in particular there is no observation-triggered wavefunction collapse which the Copenhagen interpretation proposes. The exact form of the quantum dynamics modeled, be it the non-relativistic Schrödinger equation, relativistic quantum field theory or some form of quantum gravity or string theory, does not alter the content of MWI since MWI is a metatheory applicable to all quantum theories and hence to all credible fundamental theories of physics. MWI's main conclusion is that the universe (or multiverse in this context) is composed of a quantum superposition of very many, possibly infinitely many, increasingly divergent, non-communicating parallel universes or quantum worlds.

http://en.wikipedia.org/wiki/Many-worlds_interpretation#Outline

 

[AnssiH]

-- but as of the "we don't know how things work, they just are the way they are", that is the case with all models.

No, it isn't the case with all models. Some interpretations explain the physical behaviour behind quantum mechanical phenomenon, others don't.

It is the case with all human models about anything at all, not just QM interpretations. This is just elementary philosophy. A model is a set of "fundamentals"; something that is not caused but "just is" (and from which all the observable phenomena spring).

In the case of MWI, it doesn't explain how multiverse exists, it doesn't explain how photons exist, it doesn't explain why the universes affect each others the way they do. It says "they just do", which is what any other model says about their fundamentals.

Any explanation of any physical behaviour is at the bottom of it all an assumed set of fundamentals that are "not caused".

You can argue that some models explain more with simpler elements (note the history of the models of an atom, or the evolution from geocentric model of universe to heliocentrism to current ideas). Can we say that MWI explains more with less? How do we even measure that its fundamentals are simpler than those of other models? The meaning of "simplicity" is not unambiguous here.

And also, how can we make sure that MWI doesn't break reality into too small pieces? After all, it posits all this happens by things that we cannot directly observe, and these things also have functions that could also be broken into smaller and smaller elements. How do we judge where should the peeling end?

Also, any human idea is directly based on other ideas and vice versa, in a self-supporting fashion. This is why human understanding is "semantical" and capable of novel predictions. And this is also why any idea makes sense only if you have assumed a certain set of "truths". How can we measure that the particular set of assumptions - that make MWI possible - are true?

These are all important questions when we talk about ontology, and MWI is ontology more than "just physics".

And these above issues need to be understood at much deeper level than most people do. Most people do not appreciate what it means to claim something is "true". Even "true" and "false" are metaphysically non-sensical concepts, and I don't mean this in a naive way of "we cannot really know if this or that is true", but I mean the very method of classification of reality into "fundamental elements" is the only method with which an animal can make any predictions about its environment, but it is also always an arbitrary form of expressing reality. In many concrete ways that are not readily appreciated, just looking at an apple is a case of believing there is an apple there. Because you can only be conscious of your worldview, not the reality directly.

So, I just see it happening all the time that people assert something they believe in as "undeniable truth", without understanding it is undeniable only in so far that some other assumptions in their particular worldview are true. If the existence of god has been an undeniable truth your whole life, your proof of this is that world exists (for it could not without "the creator"). And it is fairly easy to see the circular fashion of the logic behind intelligent design, but all models are fundamentally like that. This is a restriction of semantical understanding.

The multiverse is a direct consequence of the postulate, not some tought up concept.

Even when the postulate is that the formulation describes directly a QM system, you still have to interpret what are the fundamental elements whose behaviour the formulation describes. This is nothing more than an interpretation. In spacetime interpretation we could also say that the formulation "describes directly what really happens". Now, I hear you when you say "it is not the probabilities that the formulation describes", and I tend to agree; copenhagen says too much and is probably incorrect. But MWI doesn't make anything fundamentally differently; it just posits "these are the things that exist" and draws a relationship between those things and the mathematical formulation about the observable effects.

So I don't know how you can claim MWI is not a thought up concept. It includes many many many assumptions that it holds true, before it can get to the final conclusion about many worlds. I know this automatically because human thinking is like that. This should not be too difficult to see.

(And this is why it is immediately erroneous to claim that a working quantum computer proves MWI. Just because you understand its behaviour by the assumptions made by MWI doesn't mean it cannot work in any different fashion)

I'm not encouraging anyone, I'm stating a fact. The Occams razor decides which interpretation is the simplest.

This is what I'm talking about. Little bit more philosophy into the picture please. Just what do you think are facts? And do you understand that Occam's razor can also be used by anyone just the way they please? I could say that by the Occam's Razor, I wish to cut out the many worlds and just have the one we can actually remember. And when you ask me to explain QM behaviour in single world, I can just claim that the nature of light, and everything, "just fundamentally exists" in advanced & retarded sense, until there exists a thermodynamically irreversible event. All I've done is selected another arbitrary set of fundamentals and no natural observer can demonstrate the difference.

It doesn't matter which quantum effects the quantum computer uses to calculate, photons or molecules, but it matters that a qubit can be in a superposition of state, ie. in the states |+1> and |-1> simultaenously. Either you interpret that qubits are in these states simultaenously in one universe or that they exit in only one state in one universe and in the other state in another universe, and that these universes superpose if the qubits are in decoherent state.

...or you look at the nature of light and matter completely differently; i.e. understand their existence with different underlying concepts. (Note; this is not a hidden variable idea. This says more about reality than some hidden variable theory. It mostly says a photon is a particle as much as a rainbow is an object)

In the end I just want to stress that I am not refuting MWI as invalid, but I am very very worried about people getting emotionally attached to different sorts of models too much, and not really understanding why any model is necessarily just an arbitrary set of fundamentals, and cannot directly be shown true by the very nature that these models exist. For as long as you do not appreciate this fact, you do not abide to scientific philosophy, but to religious philosophy. You can never truly "unlearn" whatever set of assumptions holds your worldview together until you understand just how does your worldview exist. And if you can't do that, your thinking becomes rigid (and breeds reptiles of the mind, as Blake puts it ;)

 

[kvantti]

There is a fine line between a model that describes phenomenon mathematically and a model that explains phenomenon physically.

If I would have to teach quantum mechanics, I would probably do it without intepretations. But then I'm basically just teaching the maths behind it.

Occams razor:
a model that is based on fewer assumptions, and gives the same experimental predictions as some other model that is based on more assumptions, is the simpler model out of the two and should be used to explain the phenomenon. In other words: the simpler the model, the better.

How can you interpret that in many ways? It may be that the MWI isn't the right approach to reality, but at the moment it is the simplest way to explain the quantum mechanical phenomenon. So if you don't want to set [model = reality], you can just say that "particles behave as they would behave if they would travel along every possible path from A to B."

 

[AnssiH]

There is a fine line between a model that describes phenomenon mathematically and a model that explains phenomenon physically.

If I would have to teach quantum mechanics, I would probably do it without intepretations. But then I'm basically just teaching the maths behind it.

I'm pleased to hear that. Although, I guess it is also important to say something about different interpretations, just not in too "factual" fashion. It should be stressed that it is pushing the conversation towards philosophy, and then you have to take into account the knowledge about knowledge.

Occams razor:
a model that is based on fewer assumptions, and gives the same experimental predictions as some other model that is based on more assumptions, is the simpler model out of the two and should be used to explain the phenomenon. In other words: the simpler the model, the better.

How can you interpret that in many ways? It may be that the MWI isn't the right approach to reality, but at the moment it is the simplest way to explain the quantum mechanical phenomenon. So if you don't want to set [model = reality], you can just say that "particles behave as they would behave if they would travel along every possible path from A to B."

Yeah, that's what I oftentimes say, and even then I stress that it may be there are no particles in existent during the travel since we only see the reaction of the atoms. There are all kinds of paradigm shifts conceivable that could change the picture considerably, but still keep the same observable effects.

And about occams razor, I do think it has got some merit, but at some point it becomes unambiguous just what is considered the simplest model; it depends on how you judge "simplicity" or "elegance".

For example, when people believed that Earth is the center of the universe and all the planets and stars go around it, this was not just because of religious reasons or natural arrogance of man to place himself in the center of the world. This was because if you look up into the sky, the planets really do go around us!

So, the geocentric model was the one to choose. I'm not saying it was a stupid model at that point in time; it was the right one to choose from the experimental data, but it was a grave disservice to science to shut out alternative models.

There were experts who spent their whole lives studing geocentric model and attaching other models on top of it so that it was the basis of considerable amount if scientific models. When it turned out that every once in a while some planets move backwards for a while, their minds were so rigidly set into the geocentric model (which explained so much) that they thought the simplest way to explain this retrograde motion was to assume that some planets move in a figure of eight instead of in circles; that they perform a little backward orbit every year which to us looks like they go backwards. (You could for example posit that there are invisible planets rotating to opposite directions whose immense gravity causes the figure of eight)

And if you look at it, and you happen to assume geocentric model is true, you could validly argue that it is the simplest way to explain this. "We cannot just throw a wonderfully elegant geocentric model away due to one little observation; the model explains so much. The retrograde motion proves there are dark planets causing the figure of eight orbits"

And the way that progress happens is that the society unlearns; the old experts just die and young guns who have not invested into the old models perform a paradigm shift and decide heliocentric model is the way to go, albeit it means much of the investements of the previous generation need to be thrown away. This cycle is very natural to human thinking, and there likely are many kludges in modern models similar to "figure of eight orbits".

It has been observed that in very large galaxes the outer stars do not abide to Newtonian law of gravity: "every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them."

Namely, the outer stars move faster in their orbits than they should if they were to remain on stable orbits. This is now "proof" that there is invisible matter outside the galaxy pulling the stars (decided my Occam's razor), just like the retrograde motion was a proof of figure of eight orbits. The reason this is a proof is that Newton's law is "obviously true".

But it is not particularly hard to form a simple modification to the Newtonian law that would claim that at large distances the gravitational pull does not fall down "proportional to the product of their masses", and considering the possibility of quantum nature of gravity, it is kind of reasonable to expect there could be this sorts of effects.

The important question is; how do you really judge which one is more elegant way to go? To decide that the law of gravity is correct and thus there is invisible matter between galaxies, or to perform a deeper paradigm shift and look at gravity in a completely new way?

So, again, I'm not saying that the idea of dark matter is "definitely wrong". I'm just asking why do we consider it to be by far the most likely model?

Btw, I'm pretty pleased that the concept of "dark energy" is so vague about the nature of it; it implies that some sort of paradigm shift to gravity may well be in order, and the same paradigm shift could well place the idea about the birth of the universe (in big bang theory) into completely new light also.

All in all, the history of science is pretty fascinating thing, and looking at the way that scientific progress has happened in the past implies a lot about the modern theories and hopefully shows people better ways to recognize validity and invalidity between different ideas.

One fascinating pattern is how we have step by step placed ourselves further and further away from some priviledged position within the universe. Even now, although we do not consider ourselves to be at any sort of center point spatially, we kind of privilege ourselves temporally; we think we exist very near to the birth of the universe, when other galaxies are still visible and so on... Investigating a paradigm shift where our miniscule view of the universe only seems to imply a nearby birth event (by its local behaviour) might just be fruitful. (After all, it is hard to substantiate the idea that in the beginning of spacetime there exist an event which marks the creation of the whole spacetime, the end and all. This, if anything, is placing semantical concepts into conflicting positions)

If only the current experts had not invested their whole lifes into the big bang theory... :I

 

[Chaos' lil bro Order]

QM is flawed, is that a simple enough of a model for you?

 

[rewebster]

QM is flawed, is that a simple enough of a model for you?

Aren't all theories flawed, then, as none are perfect (or totally accepted as the true theory)?