Consciousness as an active part in modern physics

[vanesch]

Hi,after some PM discussion that went into this direction and a short check, I want to persent here a summary of some of the ideas involved concerning a link between the consciously experienced subjective world and physics. First of all, it is probably interesting to find out the controversy between "materialism" (which states that the physical world includes whatever is "consciousness") and "dualism" which is supported by some arguments that the physical world can never entirely explain all aspects of consciousness. A summary of the concepts involved can be found here:

http://www.iep.utm.edu/c/consciou.htmWhat I will write here subscribes in a way to the dualist notion, where consciousness is something extra-physical. However, it finds its roots in the physical world.My point was the following: modern theories of physics (GR and QM) need a non-trivial relationship between the physical ontology (corresponding to a mathematical object in the theory) and the subjective experience by consciousness. This is in contrast to the Newtonian frame where a much more evident 1-1 relation can be seen. In order for this to make sense of course, some form of a dualistic vision on consciousness is necessary because a purely materialistic view cannot do.

But first, what about the Newtonian frame ? In the Newtonian frame, one can (almost) keep a purely materialist vision, if one associates consciousness to a physical structure (say a brain), because it is possible, because of the *physically ontologically meaningful concept of universal time* to recognise an ontologically existing 3-dim space with a brain state, which will then evolve according to that other, ontologically existing universal quantity, time, which "ticks away".
Of course, in a deterministic Newtonian frame, it is always possible to construct a 4-dimensional "static" manifold, and as such to attach an ontology to a 'spacetime'. This remark is sometimes made, that there is no fundamental difference between the 4-dim static manifold in Newtonian physics, and in relativity. However, the point is that this 4-dim manifold in Newtonian physics is entirely facultative. We don't NEED the concept of a 4-dim manifold as an ontological reality in Newtonian physics.What happens in GR ? There, the postulated ontology is a static 4-dimensional manifold. We now NEED this structure, it is not facultative anymore. GR has no real meaning without the concept of a 4-dim manifold. So "yesterday" and "tomorrow" are different regions of that manifold (and even only make sense with respect to a specific world line). Yesterday exists no less than tomorrow or today. Nevertheless, we are consciously ONLY aware of "today". So I argued that you need AN EXTRA POSTULATE which maps, in a non-trivial way, the entire "state of the brain" which is a 4-dimensional structure (the worldline of the brain) onto ONLY ONE SLICE corresponding to "now" and that slice is what is subjectively experienced by the consciousness that is conjugated to that brain.
Although that brain's birth still exists somewhere on the manifold, and its death too, the consciousness of the brain only experiences ONE slice of it, namely the "today" slice. And as there is NO ontologically existing universal time parameter anymore, "ticking away", there is no PHYSICAL way to select this timeslice. This has hence to be done by a non-trivial mapping from the physical ontology (4-dim structure) to the subjective experience of a conscious being. However, this is often not explicitly stated, because locally the equations LOOK like those of a Newtonian observer, with his space and time coordinates. Nevertheless, the time coordinate is now just that: a coordinate. It is not a physically existing quantity anymore that has a specific value (and hence determines a specific slice). In Newtonian physics, one could claim that only ONE value of the time parameter "had ontological existence" (and that yesterday and tomorrow did not exist). This is not possible anymore in relativity.Next comes in quantum theory. A popular (although not (yet?) standard) view on quantum theory is the relative state (or many worlds) interpretation, which claims essentially that ONLY ONE TERM in the cosmic wavefunction is consciously experienced by a conscious being - which explains the apparent probabilistic nature of QM. Usually, this meets a lot of critique because "introducing consciousness in a physical theory is somehow a bad idea". But I wanted to argue that *this was already the case when we took up general relativity with its spacetime manifold*.

 

[vanesch]

The QM case is discussed here:

http://cornea.berkeley.edu/pubs/Duality_of_psycho-physics.pdf

It is also interesting to check out other papers here

http://consc.net/biblio/6.html#6.3a

However, I'm not aware of similar papers on GR.

 

[hypnagogue]

Hi vanesch, thanks for the interesting argument. A couple of questions and comments:

So I argued that you need AN EXTRA POSTULATE which maps, in a non-trivial way, the entire "state of the brain" which is a 4-dimensional structure (the worldline of the brain) onto ONLY ONE SLICE corresponding to "now" and that slice is what is subjectively experienced by the consciousness that is conjugated to that brain.
Although that brain's birth still exists somewhere on the manifold, and its death too, the consciousness of the brain only experiences ONE slice of it, namely the "today" slice. And as there is NO ontologically existing universal time parameter anymore, "ticking away", there is no PHYSICAL way to select this timeslice.

1) How, if at all, does entropy figure into the story here? If we take it that the arrow of time is fixed by the manner in which entropy in a system tends to increase (which is a purely physical phenomenon), how does that factor into your argument?

2) What exactly is meant by a timeslice? I assume you mean something that captures spatial extent but not temporal duration. However, on the objective side, it's not clear that any given conscious event can be meaningfully mapped onto a spatial 'snapshot' of the brain; that is, the minimally sufficient physical conditions in the brain that are associated with conscious experience may all involve physical events evolving through time. On the subjective side, it seems that even the most temporally compact components of consciousness actually occur over a duration of time (the so-called "specious present"; see here for an elaboration). So the physical mapping problem might not be one of picking out individual timeslices, if a timeslice is understood to have no temporal duration.

3) It might also be fruitful to give some consideration to cognitive functions. Might one be able to say that the manner in which our brains store short term and long term memories, and the manner in which these memories inform our current conscious experience in the here-and-now, is something that may create an illusory sense of the flow of "now" out from the past? If not, why not? If so, might this be a way of solving the problem of consciousness of the 'now' without needing an explicit mapping of the kind you mention?

 

[vanesch]

First of all, I'd like to point out that what I wrote is of course speculative. I only wanted to indicate that we could take "a step back" when considering the relationship between consciousness and physical reality, by associating a conscious experience not *directly* with that physical reality, but through some "window" ; that window itself being of course not a physical degree of freedom (otherwise we'd be back to case 1). I'm brought here mainly because of the relative-state interpretation of quantum theory (in my opinion the only one that sticks to the currently existing formalism - which doesn't mean it cannot change in the future). But it occurred to me, as I said, that one already has to postulate such a relation in the frame of classical relativity - though on a much less involved way.

1) How, if at all, does entropy figure into the story here? If we take it that the arrow of time is fixed by the manner in which entropy in a system tends to increase (which is a purely physical phenomenon), how does that factor into your argument?

If we accept that a conscious experience "just is", then we could argue that the "illusion" of an arrow of time is given by the memory of the body, which has clear correlations with macroscopic quantities in what's experienced as "the past" and doesn't have any "souvenirs" of these macroscopic quantities in what's experienced as "the future".
A bit like on a picture (= the conscious experience) of somebody running, you have a clear indication of the motion of the person, although it is a static image. In other words, we define past as "what we remember" and we define future as "what we expect".

2) What exactly is meant by a timeslice? I assume you mean something that captures spatial extent but not temporal duration. However, on the objective side, it's not clear that any given conscious event can be meaningfully mapped onto a spatial 'snapshot' of the brain; that is, the minimally sufficient physical conditions in the brain that are associated with conscious experience may all involve physical events evolving through time. On the subjective side, it seems that even the most temporally compact components of consciousness actually occur over a duration of time (the so-called "specious present"; see here for an elaboration). So the physical mapping problem might not be one of picking out individual timeslices, if a timeslice is understood to have no temporal duration.

Yes, and (in relativity) the brain is not a single point of space either. So we are actually talking about associating a conscious experience with a rather localized lump of spacetime, which, in the eigenframe of the brain, would extend spatially over the width of the brain, and in time, over the typical "time it takes". So the "window" would not be a singular function, but some smooth weighting and averaging function over a small region of spacetime.

 

[vanesch]

3) It might also be fruitful to give some consideration to cognitive functions. Might one be able to say that the manner in which our brains store short term and long term memories, and the manner in which these memories inform our current conscious experience in the here-and-now, is something that may create an illusory sense of the flow of "now" out from the past? If not, why not? If so, might this be a way of solving the problem of consciousness of the 'now' without needing an explicit mapping of the kind you mention?

This is an argument that was already made, but the point I'm trying to make is not so much "the arrow" as "the position". Why am I experiencing "today" and not "my birth", or my 20th birthday, or my 80th birthday (if that one exists) ? All these moments are on an equal level, ontologically, in relativity (at least, that's how I understand it), because the 4-dimensional manifold has ontological existence. It is *this* which is different in Newtonian physics, because "universal time" could have a specific value, which is "now", and my 20th birthday has no ontogical existence, nor my 80th birthday. I mean, the "pointer" on the Newtonian time axis could be something "real out there" (and then of course I only experience what corresponds to that pointer: it is part of the physical ontology). But in the static 4-dim manifold, there is all right an eigentime, which is a COORDINATE along the worldline of the brain center of gravity, but ALL of the points along this line have "equal physical ontology". There's nothing that singles out "today" from other points. So it seems that something "ticks" along that line, as was the universal time in the Newtonian frame. But that "something that ticks" has no physical ontology. It is "integrated in the window function that puts up the relationship between my brain and the subjective experiences that go with it" (at least, that's what I'm proposing here).
You could even put "many trains of consciousness" on the same brain (4-dim structure). Maybe another consciousness is experiencing my birth. And another one is experiencing my 80th birthday. But the one "I" have, is now typing on PF.

 

[Careful]

This is an argument that was already made, but the point I'm trying to make is not so much "the arrow" as "the position". Why am I experiencing "today" and not "my birth", or my 20th birthday, or my 80th birthday (if that one exists) ?

As I said in our PM, your just like too much science fiction and Newtonian physics. First of all, I do not see why the Newtonian situation is different from the one in GR (in this respect), since in your reasoning, you would need a universal awareness of the *value* of the time parameter. Both in Newton and GR, you are dealing with time reversal invariant *deterministic* systems, implying that you can compute how it was for t < t_0 and t > t_0. In that sense, the past and future exist, but that does not imply of course that we observe them now (in Newton at t=t_0, in GR at the specific gauge fixed starting point of your worldline where you decided to evolve the Einstein equations). So, I give you again the GR intepretational scheme which does not need any sort of consciousness:
(a) the Einstein equations are objectively true
(b) our fluid matter models (where the fluidum is constrained to satisfy the weak energy condition) are adequate, and the ideal PLATONIC matter model satisfies the same constraint
(c) local time for a matter density = eigentime of the corresponding worldline
(d) observation : at a particular small interval of your worldline you receive signals coming from the thickened past lightcone, you process them like a computer and have a limited visibilty such that signals with a too weak intensity go unnoticed.
(e) fixing the initial conditions : repeat (d) long enough such that you can make a reasonable extrapolation in order to guess what happens at that part of the universe where you cannot be

(d) implies you observe a smeared out *localized* now, since you can process signals such as the ticking of your watch at a rate according to (c) - relative motion is enough to get a (non universal) now! It is obviously incorrect to state that all points along a worldline have the same ontological status, the are clearly distinct (for example because they have a different past) (c) can even be dropped to some extend by going over to Weyl gravitation. (e) is a necessary requirement in every physical theory, even Newton.

It seems to me you are wondering *where* you are on your worldline. In GR the situation is vastly BETTER in that respect than in Newtonian physics since we have a universal PHYSICAL starting point (that is our extremely tidy big bang), in Newton, we can make any time translation we want. So you can express your moment of birth in the physical time it took for local matter densities to group together into an embryo you are starting from the big bang (you can even know objectively which of these clumpings you are in the 4-D manifold by studying your past).

You seem to have the strange idea that although you experience now monday 21 of November 2005, there might *now* be a copy of you on a worldline very close to yours at a date you labelled 13 december 1975.
That is of course entirely excluded and even meaningless in GR : *now* has a local meaning (as prescribed before) and the earthly *now* is a matter of AGREEMENT; we earthinhabitants have once met at one place and set our watches equal and departed again. For earth, such procedure works well since the gravitational field is very weak. In the good old times, *now* was relative to the position of the sun at the sky or the position of the wave front at the beach in one of its tides (the Greeks were more relativists than Newton in that respect). So, *now* for you cannot be linked to *now* in 1975 by CONVENTION and as mentioned before, they are clearly distinguishable by their past relative to the BB (not: big boobies ).

 

[vanesch]

As I said in our PM, your just like too much science fiction and Newtonian physics. First of all, I do not see why the Newtonian situation is different from the one in GR (in this respect), since in your reasoning, you would need a universal awareness of the *value* of the time parameter. Both in Newton and GR, you are dealing with time reversal invariant *deterministic* systems, implying that you can compute how it was for t < t_0 and t > t_0. In that sense, the past and future exist, but that does not imply of course that we observe them now (in Newton at t=t_0, in GR at the specific gauge fixed starting point of your worldline where you decided to evolve the Einstein equations).

No, this is exactly what I tried to point out. In Newtonian mechanics, you CAN CONSTRUCT, if you want to, a 4-dimensional "spacetime" (that is what you do when you say that you can calculate solutions for all values (past and future) of t. But, I can consider that as a mathematical nicety that DOESN'T HAVE TO CORRESPOND TO AN ONTOLOGICAL REALITY. A bit like I could do complex continuation of, I don't know, any real function. It is not necessary to associate this complex continuation to a really existing thing out there.

You CAN get around, in Newtonian physics, with assigning only an ontology to a certain time slice. There could be some universal godfather or whatever (I don't want to get into religious debate here of course, it is just a pictorial representation) that PUTS THE TIME DIAL TO november 2005. As such, time is not a "parameter" but a value of an ontological quantity. It also corresponds to a parameter in our theory, and if we put the value of the parameter in the theory equal to the value the deity put on the dial, then we will find the "world right now". Then there is only ONE reality, namely the one corresponding to the time dial set by that deity. And we can of course use the laws of nature as to how this reality looks like when he puts the dial to another value.

It seems to me you are wondering *where* you are on your worldline. In GR the situation is vastly BETTER in that respect than in Newtonian physics since we have a universal PHYSICAL starting point (that is our extremely tidy big bang), in Newton, we can make any time translation we want. So you can express your moment of birth in the physical time it took for local matter densities to group together into an embryo you are starting from the big bang (you can even know objectively which of these clumpings you are in the 4-D manifold by studying your past).

Yes, but the ontology of GR makes that the embryo I was, is still there, and my dead body too. It has no less existence than my body I experience right now. Nevertheless, I don't feel like I'm dying or being an embryo. In Newtonian physics, you can simply say that there is NO ontological existence to me being an embryo or me being dead, because this only happens when the deity puts the dial onto the right value, which he didn't: he put it to november 2005. So there's only an ontological reality to november 2005. So it is normal that I'm aware of my body in november 2005. But you do NOT have your universal dial anymore in GR. Some part of the manifold is still my birth, some part is me dying, some part is my 20th birthday, and some part corresponds to november 2005 for me. I only experience november 2005. Why ?

You seem to have the strange idea that although you experience now monday 21 of November 2005, there might *now* be a copy of you on a worldline very close to yours at a date you labelled 13 december 1975.
That is of course entirely excluded and even meaningless in GR : *now* has a local meaning (as prescribed before) and the earthly *now* is a matter of AGREEMENT; we earthinhabitants have once met at one place and set our watches equal and departed again.

I can assure you that it is not a convention that I'm not having my twentieth birthday party right now, or that I'm being born right now. BTW, I was not talking about a copy on a worldline CLOSE to me, I was talking about a copy on MY worldline, but on another value of my eigentime. Maybe a copy of me IS having a party as my 20th birthday. Why is that copy experiencing that, and not me ?

 

[Careful]

** No, this is exactly what I tried to point out. In Newtonian mechanics, you CAN CONSTRUCT, if you want to, a 4-dimensional "spacetime" (that is what you do when you say that you can calculate solutions for all values (past and future) of t. But, I can consider that as a mathematical nicety that DOESN'T HAVE TO CORRESPOND TO AN ONTOLOGICAL REALITY. You CAN get around, in Newtonian physics, with assigning only an ontology to a certain time slice. There could be some universal godfather or whatever (I don't want to get into religious debate here of course, it is just a pictorial representation) that PUTS THE TIME DIAL TO november 2005. **

You DO need the Universal godfather to obtain what it is you want but again, it is wrong. There is NOTHING in Newton which gives you t=0 PHYSICALLY and in our calendar t=0 is the birth of Jezus Christ. If we would take the birth of the profet Mohammed and stick to the counting of time which is inspired by the physics of our solar system then we wouldn't be in 2005 now. In GR, the big bang does this for us in the most natural way.

** As such, time is not a "parameter" but a value of an ontological quantity. **

Time is of course a parameter in Newtonian physics (this is universally accepted by earthlike physicists).

** Then there is only ONE reality, namely the one corresponding to the time dial set by that deity. And we can of course use the laws of nature as to how this reality looks like when he puts the dial to another value.
Yes, but the ontology of GR makes that the embryo I was, is still there, and my dead body too. It has no less existence than my body I experience right now. Nevertheless, I don't feel like I'm dying or being an embryo. In Newtonian physics, you can simply say that there is NO ontological existence to me being an embryo or me being dead, because this only happens when the deity puts the dial onto the right value, which he didn't: he put it to november 2005. **

The SAME thing is achieved by my postulate (c). Why are you refusing to comment on this ? You basically ask me what in GR would tell me that my unborn children do not´exist yet. And I tell you that GR dynamically provides you with a t = 0 (the big bang), which in conjunction with (c) gives us a (local) arrow and measure of time. Moreover, GR is a ONE WORLD theory, so the FACT that I live and experience a localized now (and that I have such and such distance to the big bang) implies that my unborn children do not yet exist. Perhaps, you want to engage yourself in a discussion why I know that I exist and why I think the clock which is ticking next to me is not imaginary. This is IRRELEVANT: the fact that I percieve a ticking clock in conjuction with (a) the one world in GR (b) my hypothesis (c) and (c) the big bang is sufficient to lead to the latter conclusion. I do NOT have to bother about the possible existence of other worlds: that is the beauty of GR. This implies that my dead body has not the same ontological status as I have for me and all other people I meet. GR tells me only to bother about the WORLD within my perception, that is the signals I (the machine) recieve, that is what RELATIVE means. Now, you can start arguing that we are not all equally calibrated: that is why in physics we use more simple and predictable machines which are easy to calibrate. So, the philosphy is that as long as there are no mechanisms which can bring ourselves back into our past (future), the past (future) does not *exist* (by definition) anymore (yet).

** So there's only an ontological reality to november 2005. So it is normal that I'm aware of my body in november 2005. But you do NOT have your universal dial anymore in GR. **


The point of GR is that 2005 is NOT UNIVERSAL at all, it is a mere agreement which works well because clocks tick almost like in Minkowski on our planet !

** Some part of the manifold is still my birth, some part is me dying, some part is my 20th birthday, and some part corresponds to november 2005 for me. I only experience november 2005. Why ? **

See the previous... (by definition)

** I can assure you that it is not a convention that I'm not having my twentieth birthday party right now, or that I'm being born right now. **

Yes, it IS! See the previous...


** BTW, I was not talking about a copy on a worldline CLOSE to me, I was talking about a copy on MY worldline, but on another value of my eigentime. Maybe a copy of me IS having a party as my 20th birthday. Why is that copy experiencing that, and not me ? **

Worldlines in GR are only assigned to ONE matter density, my postulate (c) avoids this complication.

 

[vanesch]

You DO need the Universal godfather to obtain what it is you want but again, it is wrong. There is NOTHING in Newton which gives you t=0 PHYSICALLY and in our calendar t=0 is the birth of Jezus Christ.

I'm of course not talking about the 0 of the time scale, which is only a coordinate on the 1-dimensional time manifold in Newtonian physics. But in Newtonian physics, you can give an ontological meaning to that parameter, because ONE point on that axis is special, it is "now". (Newton said "time flows uniformly", so he meant that this point is somewhere on the time axis, I presume). The coordinate of that special point is what we call "t", in Newtonian physics, and of course the value of that point t depends upon how we have choosen to label the non-special points on the axis.

But in GR, there is no such special point. There may be a special point which is the big bang (then why am I not experiencing the big bang - apart of course from the fact that I didn't exist). But what's special about today ? I can calculate the eigendistance from "today" to other events, true, and I will find that that agrees. I'm not saying that I'm supposed to find disagreements. I'm just saying that there is something special about "today" because I experience "today" and that there is NO way, in GR, to make "today" special over "yesterday" and over "tomorrow". In Newtonian physics there was such a means, because of the universal time (not the universal measure of time with respect to some "origin", no, the fact that time was an ontologically existing thing in nature, which could, hence, have a specific point which was "today" and which denied ontology to the past and the future. That would then mean that there is no sense to be given to "me experiencing consciously last month", because nothing ontologically exists corresponding to "me last month". But "me last month" exists very well in GR, so I don't see why this is not consciously experienced - but I know that that's not "me" (maybe another "me" does experience this).

So something has to single out "today" as special on my world line. Not that I cannot calculate back on my world line what my age is - it will fit with the other parts of my conscious experience (namely what I saw on the calendar and so on). But "me yesterday" exists. "me tomorrow" exists. Nevertheless, I don't experience it. I only experience "me today". What distinguishes "today" from "tomorrow" or from "yesterday" on my world line?

Time is of course a parameter in Newtonian physics (this is universally accepted by earthlike physicists).

Well, time is a coordinate system on a one-dimensional manifold. But "today" is not a parameter of course, it is a special point on that one-dimensional manifold.

And I tell you that GR dynamically provides you with a t = 0 (the big bang), which in conjunction with (c) gives us a (local) arrow and measure of time. Moreover, GR is a ONE WORLD theory, so the FACT that I live and experience a localized now (and that I have such and such distance to the big bang) implies that my unborn children do not yet exist.

No, because the same body of yours also has a slice with a slightly bigger distance to the big bang where you DO have your children. We all agree that the slice of time which you experience right now is a bit closer to the big bang, and that this is fully compatible with you not having your unborn kids yet. But we all agree also that there is another slice, still a bit closer to the big bang, when you were a kid yourself. So why are you NOT experiencing THAT slice, or that FUTURE slice, but only "today's" slice ?

Perhaps, you want to engage yourself in a discussion why I know that I exist and why I think the clock which is ticking next to me is not imaginary.

No, that's not what I want to discuss.

There's a slice of "you" who looks at the clock and sees 9 PM
There's another slice of "you" who looks at the clock and sees 8 PM
There's still another slice of "you" who looks at the clock and sees 11 PM
...
You only are consciously aware of ONE slice. Why ?
In Newtonian physics, there could be a "kink" on the timeline that says "now", making that point special. But not in GR.

I do NOT have to bother about the possible existence of other worlds: that is the beauty of GR. This implies that my dead body has not the same ontological status as I have for me and all other people I meet. GR tells me only to bother about the WORLD within my perception, that is the signals I (the machine) recieve, that is what RELATIVE means.

Hehe, I almost got you into MWI here ... But let us keep to GR for the moment.

So, the philosphy is that as long as there are no mechanisms which can bring ourselves back into our past (future), the past (future) does not *exist* (by definition) anymore (yet).

Now that's hard to do in GR, isn't it ? Can chunks of the 4-manifold be declared "not existing anymore ontologically", so that only your time slice "now" exists ? And the future timeslices "come into existence" ? THAT is exactly what I could do in Newtonian physics because I didn't NEED the ontology of the 4-manifold. But in GR, I'm screwed if I try to deny existence to certain events, no ? Because it would introduce a foliation of the manifold ?

** So there's only an ontological reality to november 2005. So it is normal that I'm aware of my body in november 2005. But you do NOT have your universal dial anymore in GR. **
The point of GR is that 2005 is NOT UNIVERSAL at all, it is a mere agreement which works well because clocks tick almost like in Minkowski on our planet !

You're starting to get parts of my argument, great

If november 2005 were universal, then that could have been a special point with "now" status. But in GR you cannot do that. So NOTHING physical can be postulated to single out november 2005. Nevertheless, that's what I'm consciously experiencing. So this is the NON-TRIVIAL RELATION BETWEEN PHYSICAL ONTOLOGY (the 4-manifold and the part of it that corresponds to my brain) and my subjective experience of "it is november 2005 and I'm typing on PF".

** I can assure you that it is not a convention that I'm not having my twentieth birthday party right now, or that I'm being born right now. **
Yes, it IS! See the previous...

I don't know about you, but I do NOT have the subjective experience of being born right now... :tongue:

** BTW, I was not talking about a copy on a worldline CLOSE to me, I was talking about a copy on MY worldline, but on another value of my eigentime. Maybe a copy of me IS having a party as my 20th birthday. Why is that copy experiencing that, and not me ? **
Worldlines in GR are only assigned to ONE matter density, my postulate (c) avoids this complication.

Because yesterday there was no matter ? It is only there today ?

 

[Careful]

**
But in GR, there is no such special point. There may be a special point which is the big bang (then why am I not experiencing the big bang - apart of course from the fact that I didn't exist). ***

Hem, hem, denial of the BB is enough to get kicked off this forum as far as I understand I would miss you though :tongue2:

** I'm just saying that there is something special about "today" because I experience "today" and that there is NO way, in GR, to make "today" special over "yesterday" and over "tomorrow". **

Again, this is my postulate (c). I gave you a logical explanation for this, the rest you say about why Newtonian physics *can* make sense of this applies also to my scheme (this is just logic since (c) is nothing but a LOCALIZED NEWTON HYPOTHESIS).


** So something has to single out "today" as special on my world line. Not that I cannot calculate back on my world line what my age is - it will fit with the other parts of my conscious experience (namely what I saw on the calendar and so on). **

(c) does that in my scheme


** But "me yesterday" exists. "me tomorrow" exists. **

No, no, perhaps in another world, but not in mine and all fellow compadres I meet. I gave you the logical reasoning already. If you would be so kind to give a specific comment on that...


** Nevertheless, I don't experience it. I only experience "me today". What distinguishes "today" from "tomorrow" or from "yesterday" on my world line? **

(c) + the fact that I exist (and you were not going to doubt that).

** No, because the same body of yours also has a slice with a slightly bigger distance to the big bang where you DO have your children. We all agree that the slice of time which you experience right now is a bit closer to the big bang, and that this is fully compatible with you not having your unborn kids yet. But we all agree also that there is another slice, still a bit closer to the big bang, when you were a kid yourself. So why are you NOT experiencing THAT slice, or that FUTURE slice, but only "today's" slice **

Because I exist and by comparison see that I am an (physical :tongue:) adult.

** No, that's not what I want to discuss.
There's a slice of "you" who looks at the clock and sees 9 PM
There's another slice of "you" who looks at the clock and sees 8 PM
There's still another slice of "you" who looks at the clock and sees 11 PM
...
You only are consciously aware of ONE slice. Why ? **

(c) + I exist.

** Hehe, I almost got you into MWI here ... But let us keep to GR for the moment. **

Don't sell the skin of the bear yet :tongue:

** Now that's hard to do in GR, isn't it ? Can chunks of the 4-manifold be declared "not existing anymore ontologically", so that only your time slice "now" exists ? **

There is no time slice involved (how many times do I have to repeat that). There is only my world line, me = I exist, and the past lightcone of me = NOW (the rest is just extrapolation and guesswork based upon data over a large period of time we recieve); therefore my universe and that of my compadres which I meet.

** And the future timeslices "come into existence" ? THAT is exactly what I could do in Newtonian physics because I didn't NEED the ontology of the 4-manifold. But in GR, I'm screwed if I try to deny existence to certain events, no ? **

No, the only relevant future is my future lightcone (I do not need to bother about the rest). Look: call myself A and you B, I send a signal to you, 3 minutes later I receive a signal from you in which you communicate what you have done in the time between receiving my signal and sending back yours according to your local clock. Based upon MY personal knowledge (and whatever I can look up in the library) I can make a reasonable space time MODEL and guess the moment at my worldline when you received my signal (by using my local notion of space and the exponential map in my pet space time). Nature seems to tell us that there exists a *universal* arrow of time such that all these local PET spaces coincide.

** Because it would introduce a foliation of the manifold ? **

NO, NO, NO...

**You're starting to get parts of my argument, great
If november 2005 were universal, then that could have been a special point with "now" status. But in GR you cannot do that. So NOTHING physical can be postulated to single out november 2005. **

YES it can, my ancestors, 34 bloodlines ago met in the past at planet Earth to decide upon one clock measure and starting point. Since then clocks are ticking and everything is registered. This meeting CAN be dynamically singled out in GR (local matter densities clumping together and specific sound waves being created).

**
I don't know about you, but I do NOT have the subjective experience of being born right now... :tongue: **

I am registering typing at my computer now.


**Because yesterday there was no matter ? It is only there today ? [/QUOTE] **

Yesterday there was matter, and tomorrow there will be. I know that yesterday has past because my distance to the BB has been increased. You seem wanting to pull me into a many world declaration for physics, comment first specifically on my single world theory.

 

[vanesch]

Your postulate (c) was:

(c) local time for a matter density = eigentime of the corresponding worldline

Does that mean now that what is consciously experienced "now" by any matter density is a special value of eigentime since the big bang ? Is that what you mean ? The value of eigentime since the big bang that *for me* corresponds to the number of seconds along the worldline of an electron in my brain that corresponds to "november 2005" and that all conscious creatures are experiencing THAT number of seconds ?
But, not all particles making up my brain will have the same "eigentime since the big bang", and I can imagine that certain brains will made up of particles that had a slightly longer or shorter worldline since the big bang. As such, what is "november 2005" for my neighbour (as measured since the big bang along the eigentime of the worldline of my neighbour's brain) might very well cross MY eigentime of the worldline when my eigentime reaches october 2024. Does that mean that my neighbour is experiencing something in what for me is his past (because we all are experiencing a certain eigentime which corresponds to "november 2005" since the big bang, right ?) ? That while I see him, he's in fact not conscious of the state that I see him in, but that he's still experiencing when I had my birthday party (where I invited him) some 19 years ago, while I see him in "his future" right now ?

No, this is not tenable. There is no specific value of eigentime since the big bang which indicates that THAT eigentime is now to be experienced consciously, by all conscious creatures (and not the day before or the day after). In Newtonian physics, that WAS possible: you could postulate that there WAS a special time, called "now" (and which, according to a certain coordinate system, got the coordinate "november 2005") which IS to be experienced by all conscious creatures, simply because OTHER times could be postulated not to exist ontologically.

But you cannot postulate my past "not to exist" on the 4-dim GR manifold. You can only postulate my past "not to exist for ME, when I am on a specific point on my worldline" but clearly that is only related to my conscious experience of "now".

This is what I am trying to make clear. That there is a non-trivial relationship between a special point on my worldline, and my subjective experience, such that that special point corresponds to my subjective "now" experience.

 

[vanesch]

I would like to add the following to my previous post, in order to make sure that there is no elementary misunderstanding.

I understand your postulate (c), and I know that the eigentime, as a coordinate along the worldline plays perfectly well the role of the t-parameter in dynamical equations, and if things are slow enough and flat enough, that this coordinate coincides with a local Newtonian model. I'm absolutely NOT putting that in question. I know that this parameter gives rise to about the same equations of any time evolution that one can think of, like, say, the diffusion of some ink in a glass of hot water, or the propagation of a signal through some wires or whatever usual dynamical phenomenon one can think of. And indeed, this establishment often leads people to conclude that this parameter (eigentime) is then the local equivalent of what used to be the global time parameter in Newtonian physics. I think this is what you try to explain me since a few PMs and posts. But I'm NOT disputing this at all. I know that, no problem - maybe in the mean time, you think I have a totally weird view on GR (not to say that I totally misunderstood the theory).

What I'm saying is only the following. This eigentime t is a coordinate, which you can turn into a parameter which parametrises successive time slices, "just as in Newtonian physics, only locally". Up to there, no problem. The problem resides in THE ONTOLOGY. If you only consider t as a parameter occurring in an equation in Newtonian physics, you would have the same problem as the one I am trying to outline. But in Newtonian physics, you can AVOID simply calling t a "parameter", you can give it the meaning of the coordinate of a really existing timeline out there on which there is a special bubble, called "now". This option exists in Newtonian physics. It is rarely if ever explicitly said, but it can be done ; if that's done, you can give special status to "now" ; you can even go as far as to say that only that spacetime slice in the Newtonian spacetime has ontological existence, "is" out there. As such, the fact that I experience subjectively "now" is no mystery: it is the only thing which exists out there.

But it is THIS possibility which is not possible anymore to the local t parameter in GR on a world line. There, it is reduced to just being a coordinate, which indeed parametrises the space slices along the world line, and which occurs in dynamical equations, but which has NO special status for "now"... unless you explicitly INTRODUCE such a "now" point ON EACH INDIVIDUAL worldline of a conscious being, and associate that "now" point with the subjective conscious experience of that being. But it is not a *physically indentifiable point*.
And you are getting closer to it when you say:

(c) + the fact that I exist (and you were not going to doubt that).

or:

There is no time slice involved (how many times do I have to repeat that). There is only my world line, me = I exist, and the past lightcone of me = NOW (the rest is just extrapolation and guesswork based upon data over a large period of time we recieve); therefore my universe and that of my compadres which I meet.

where there's an embryo of the idea that *something* else is needed to PICK the "now" point along your body's world line ; you call it "I exist", "my universe" etc...

The "I" that "exists" indeed: your subjective experience which experiences "now" and which corresponds to a particular point on that worldline.

The other points on your worldline can correspond to "souvenirs of yourself of some time ago" but infact they are not: those souvenirs are encoded in the structure of your brain NOW (otherwise you would not remember them), and to what you project yourself into in the future (and of which your brain has no souvenirs). Nevertheless, if we take GR seriously, those future points EXIST on the same level as the "now" point, or as the past points on your worldline. But you only experience ONE point of it, and that's what I'm trying simply to indicate: you only experience a part of what "is" out there ; one point on your entire worldline.

You feel of course where I want to go to in MWI: if the quantum state of your body consists of several terms, you can then only experience ONE of these terms, in the same way as you only experience ONE point along your worldline in GR. I admit that it is weirder, more involved, less clean and all that. But the basic idea is that the picking out of ONE particular aspect of the state of your body (one point along the worldline ; one term in its wavefunction) and have this aspect of its physical state determine your subjective experience, is not an inconceivable proposition.

 

[Careful]

** Your postulate (c) was:
Does that mean now that what is consciously experienced "now" by any matter density is a special value of eigentime since the big bang ? **

I simply say that I exist and (c) indicates the rate at which MY time is running, therefore I experience a ``now´´. The big bang just indicates the beginning of time and I can express my position on my world line relative to it. Now, as a robot, I receive mainly signals from other organized matter forms in my past (recent) lightcone (recent can be well defined by using the exponential map and the priviliged notion of space defined by my worldline) since signals coming from far away are too weak to be noticed (unless they correspond to focused bundles such as can be achieved with a laser). In these signals I can recognize shapes and structures (by making use of my database) and I can imagine how the world is beyond me extrapolating the knowledge I have from the past.

** Is that what you mean ? The value of eigentime since the big bang that *for me* corresponds to the number of seconds along the worldline of an electron in my brain that corresponds to "november 2005" and that all conscious creatures are experiencing THAT number of seconds ? **

No ! My brain exists only due to a particular matter clumping in the ovary of my mother (the time of construction of the ``computer´´ by the parents). Since then, I am learning through observation using the decoding device which is stored in my genes and historical records of any kind; moreover I am capable of improving my learning capacities. I am existing through my own observation, and the observation of others. November 2005 is just a time agreement between certain nations on the globe (and actually 5 november 2005 in China, could well be 4 November 2005 in the US).

** But, not all particles making up my brain will have the same "eigentime since the big bang", and I can imagine that certain brains will made up of particles that had a slightly longer or shorter worldline since the big bang. **
Sure, but that is not relevant (this is just a variant of the twin paradox). Neuron (A) at an instant I_A can communicate with a neuron on a neighbouring worldline INDEPENDENT of the history the material which made up this other neuron (B) has since the big bang (actually it has for sure not been a neuron for most of the time).
What I call neuron A could have been already in 500 people (and be born and desintegrated 500 times), it could even be made up of dust of several other neurons) while neuron B only in 499 cases. This is easy to imagine since a neuron is simply a very specific low entropy entity which has only a structural stability for a finite amount of time. Thus it is only relevant how old the last structurally stable neuron is (and its moment of birth has been roughly registered by my mother).

** As such, what is "november 2005" for my neighbour (as measured since the big bang along the eigentime of the worldline of my neighbour's brain) might very well cross MY eigentime of the worldline when my eigentime reaches october 2024. **

True (in principle but not in practise on the scale of the earth), but this is not the issue. November 2005 is an agreement for a particular piece of the globe.

** Does that mean that my neighbour is experiencing something in what for me is his past (because we all are experiencing a certain eigentime which corresponds to "november 2005" since the big bang, right ?) ?

As said: eigentime is *not* the clocktime we use on the continents: even if you fly over the ocean there is a small twin effect. It is just that these two notions of time coincide very well in practice (due to the weak gravitational field and the relatively low velocities when compared to c). Perhaps it is good to give a definition which says when two material objects A and B (I am A and you B) are in the same world and ``aware´´ of each other. Take A on a particular instant I_A of its worldline (between its birth and death) which he calls now (this is an allowed statement because of (c) and A says ``I exist´´), suppose A receives signals (at that instant) which show another robot B (which he assumes not to be transmitted by a third party), then A has knowledge of B (for example creatures at the other end of the universe which receive a message from the second world war). Now suppose A receives a message from B (which was sent at t_B on his clock) and sends immediatly a copy of this message back + another question which is received by B at r_B, then A is in the communication range of B and all events of B in the interval [t_B, r_B] cannot be distinguished by A at I_A. Morover, in this interval B experiences A to be ``present´´. Now, signals turn 8 times around the Earth in one second and human perception time is around 1/10 th of a second. Therefore, for all practical purposes on the dimensions of the Earth t_B = r_B. This is the *illusion* of simultaneity concerning all inhabitants on the Earth and it is actually the interval [t,t+1/10] which WE call now. Obviously this *now* will not be the same for someone else at the other end of the universe. This is how we make observations in reality, we are not aware of a *spacelike* slice in the universe. I see now you have posted something else, but I will respond to that later on.

 

[vanesch]

Concerning the quote below, thank you, but I know all that. I'm simply not able to make you see the point I'm trying to raise, sigh.

You are explaining me below why it is that, ONCE I AM IN A CERTAIN POINT ON MY WORLD LINE, I experience things the way they are ; what I experience when I'm doing experiments with clocks in airplanes and all that. But I'm not disputing that at all.

I'm just saying that you're only experiencing A CERTAIN POINT ON YOUR WORLD LINE, which is a special point, called NOW.

This is "strange" because the other points on your worldline ALSO exist, not simply as a mathematical construct, but they are postulated to exist "out there". But you don't experience them. So something singles out that NOW point over all the others. ONCE you have accepted that you experience that point, all the rest follows of course, and you will find consistent results.

This is different in Newtonian physics: you can postulate that "yesterday" and "tomorrow" simply don't exist. As such, there is no surprise that you "only" are consciously aware of "today": the other timeslices don't exist. The only ontological reality is 3-dimensional. A 4-dim spacetime construction in Newtonian physics is just a mathematical extension with no corresponding ontology, and hence the "t-parameter" parametrising the different t-slices doesn't represent anything physical (just a parameter that parametrises illusionary extensions of the 3-dimensional ontology in 4 dimensions). And of course, a specific value of that t-parameter corresponds to the existing timeslice, and that is what we call the time "now".

But this is - as far as I understand - not possible in GR: the 4-dim manifold has to have ontological existence. And then it is strange that of all my 4-dimensional existence, I only experience one 3-dim slice.

One remark: I don't, of course, experience a "past light cone". I only experience a small 3-dim volume corresponding to about the size of my brain, and it is in this 3-dim volume that the sensory information is coded from events that happened in my past light cone, which make me conclude that other things happened. I'm only aware of the state of my brain, not of a signal I am receiving. When I talk about a time slice, I'm only talking about a time slice some 20 cm across. I can only be indirectly aware of things in my past lightcone, because these things changed the record of my brain. But my direct subjective experience is only aware of the state of matters in the volume of my brain (or maybe even a smaller part of it).

 

[Careful]

**
I'm just saying that you're only experiencing A CERTAIN POINT ON YOUR WORLD LINE, which is a special point, called NOW. **


This is postulate (c) + I exist in my framework for *one* person. Your objection was immediatly : but what about the nows for all other persons? Why shoud these *nows* form a differentiable spacelike hypersurface, so that when A sees B, B is spacelike related to A and not in the future of it? Which dynamical agreement in GR can make sure that this is the case ? At that moment you inferred that eigentime from the BB might not do it because of the existence of gigantic focal points. Since you know that there is no GENERIC way to dynamically assign a *now* which has the above mentioned features, you conclude that one has to add a parallel mental world.

The scheme I elaborated upon is all you can do generically (there is one robot which observes). Now, our universe is a very SPECIAL one, it is almost static and spatially flat (very close to Friedmann) and all deviations galaxies bring along are by no means sufficient to deform these constant t surfaces such that they are not achronal anymore. On the large scale, our universe is expanding which prevents it from consisting in the forseeable future of gigantic (supermassive) focal points which are exactly capable of folding space such that is not achronal anymore. Gigantic black holes are of no importance here since the metric gets only troublesome behind the event horizon and we cannot observe this part of the universe anyway. Similarly, the world is probably full of tiny black holes, or spinning ``singularities´´ but these are so small that they do not change the latter conclusion FAPP. So, our initial conditions are so special that eigentime starting from the BB *is* providing the *now* WE experience (and not just I). I already hinted the analogy somewhere with the second law of thermodynamics which needs the same special initial conditions to hold.


**This is different in Newtonian physics: you can postulate that "yesterday" and "tomorrow" simply don't exist. As such, there is no surprise that you "only" are consciously aware of "today": the other timeslices don't exist. **

As mentioned the same can be done for *one* person generically, and for the WHOLE universe simultaneously in very special circumstances such as small deviations from Friedmann.


** I only experience one 3-dim slice. **

That remains incorrect.


** One remark: I don't, of course, experience a "past light cone". I only experience a small 3-dim volume corresponding to about the size of my brain, and it is in this 3-dim volume that the sensory information is coded from events that happened in my past light cone, which make me conclude that other things happened. **

What we call *now* is a tiny sufficiently tickend *lamphat* such that it is closed at the top (I only know my past, not anything spacelike to me).


** I'm only aware of the state of my brain, not of a signal I am receiving. **

That is your preferred consciousness lecture (unnecessary in my view for our universe). If our universe were not so good and almost flat (at least in our galaxy), we would not be here because gravitation would destroy us (some kind of anthropic argument).


** When I talk about a time slice, I'm only talking about a time slice some 20 cm across. **

You do not need your whole brain to store some data, no ?

** But my direct subjective experience is only aware of the state of matters in the volume of my brain (or maybe even a smaller part of it **

Your brain is not ``aware´´ instantaneously.

 

[vanesch]

This is postulate (c) + I exist in my framework for *one* person. Your objection was immediatly : but what about the nows for all other persons? Why shoud these *nows* form a differentiable spacelike hypersurface, so that when A sees B, B is spacelike related to A and not in the future of it?

I think we're running in circles. I will ask you: does the event "me celebrating my birthday 3 years ago" have an ontological meaning or not in GR ? I mean, is there something that exists, out there, that corresponds to "me celebrating my birthday 3 years ago" or doesn't it exist ?

Does "you have your 4th kid" (assuming one day you'll have 4 kids) exist in the GR ontology or not ?

 

[Careful]

I think we're running in circles. I will ask you: does the event "me celebrating my birthday 3 years ago" have an ontological meaning or not in GR ? I mean, is there something that exists, out there, that corresponds to "me celebrating my birthday 3 years ago" or doesn't it exist ?
Does "you have your 4th kid" (assuming one day you'll have 4 kids) exist in the GR ontology or not ?

No, we are not running in circles. You just want to assume that GR is nothing BUT the Einstein equations and then all your objections are of course justified. I say that if you want a meaningful interpretation of GR, you just have to add a localized Newton hypothesis for every small tube around a worldline. This, is what I call (c) and it clearly determines a NOW for me. Now, an extra problem is that the whole universe seems to observe the same *now* (that is why you love Newton so much). In my previous message, I said this can be solved by using the very specific initial conditions of the universe. Dynamically, you can do this as follows: just take Einstein Hilbert and put in by means of Lagrangian multipliers the harmonic condition for four scalar fields (that is the Gaussian gauge). Now, when suitable initial conditions are used, this gauge does not break down due to focal points. This is precisely what happens for the Friedmann universes and the slight perturbations of it in which we live. It goes without saying that the gaussian gauge condition DOES break down in quantum gravity; Karel Kuchar has done quite some work on that (1991). Once we have this *global* dynamical gauge you can have the same interpretational scheme as Newton has (and you do not need consciousness for that, you simply state that all material objects are in one and the same slice).

In quantum gravity this is all much harder: as I said before, quantization in the gaussian gauge suffers from considerable difficulties (just due to these wild initial conditions which cause its breakdown). In causal dynamical triangulations for example, a kind of harmonic gauge condition is build in kinematically (as is a beginning of time through the Hartle Hawking boundary conditions). In causal sets, one goes over to a universal counting time (arrow is given by partial order) and in LQG, one just starts from an arbitrary foliation. In classical relativity, you have many globally defined dynamical time functions (the harmonic just being one - albeit the most natural); one could also take the volume of the past lightcone as the dynamical measure of time (again t=0 being fixed by the big bang). The latter is particularly robust concerning focal points.

So, yes, you *can* get a global dynamically determined *now* in GR. You simply have to add your favourite time function to the action by means of a Lagrangian multiplier. This is ALSO what we do in Minkowski for example: Minkowski is dynamically singled out by (i) Ricci = 0, (ii) constraint : Weyl = 0 (iii) Harmonic constraint wrt. a flat spacelike hypersurface.

 

[vanesch]

Please reply also to my previous post.

Here, I would simply like to make a few extra comments.

**
I'm just saying that you're only experiencing A CERTAIN POINT ON YOUR WORLD LINE, which is a special point, called NOW. **
This is postulate (c) + I exist in my framework for *one* person. Your objection was immediatly : but what about the nows for all other persons? Why shoud these *nows* form a differentiable spacelike hypersurface, so that when A sees B, B is spacelike related to A and not in the future of it? Which dynamical agreement in GR can make sure that this is the case ? At that moment you inferred that eigentime from the BB might not do it because of the existence of gigantic focal points. Since you know that there is no GENERIC way to dynamically assign a *now* which has the above mentioned features, you conclude that one has to add a parallel mental world.

Yes, right. Well, at least, that there has to be a specific relation between the physical ontology and the subjective observation, which makes you experience "now".

The scheme I elaborated upon is all you can do generically (there is one robot which observes). Now, our universe is a very SPECIAL one, it is almost static and spatially flat (very close to Friedmann) and all deviations galaxies bring along are by no means sufficient to deform these constant t surfaces such that they are not achronal anymore. On the large scale, our universe is expanding which prevents it from consisting in the forseeable future of gigantic (supermassive) focal points which are exactly capable of folding space such that is not achronal anymore. Gigantic black holes are of no importance here since the metric gets only troublesome behind the event horizon and we cannot observe this part of the universe anyway. Similarly, the world is probably full of tiny black holes, or spinning ``singularities´´ but these are so small that they do not change the latter conclusion FAPP. So, our initial conditions are so special that eigentime starting from the BB *is* providing the *now* WE experience (and not just I). I already hinted the analogy somewhere with the second law of thermodynamics which needs the same special initial conditions to hold.

You seem to be postulating here something I wasn't aware off. If I understand you well, you seem to say that there are 2 things: the 4-dim manifold, and then still a kind of UNIVERSAL parameter, which indicates WHICH eigentime since the big bang is "special" so that it exists "now". (this was the role of time in the Newtonian frame). So if "eigentime since the big bang equals the "special time" it ontologically exists, and if it corresponds to a brain, then that is what is experienced by the consciousness associated with that brain, is that it ?

But it is difficult to establish an eigentime since the big bang for something like a brain, that is made up of different particles with different histories. Don't you think that, over 15 billion years, differences in eigentime of a few 10s of years can be accumulated ? Now, this brings me to the example I gave: this means that if my neighbour's brain is made up of particles that "got 10 years late" since the big bang, I'm actually just dealing with him as a zombie, because he's consciously experiencing 10 years ago, when I'm experiencing "now" and the body I see "now" of him is not conscious.
(and when it will become conscious, namely when the parameter which indicates which point should be experienced consciously has shifted 10 years, I won't be experiencing consciously my body at the party anymore, but 10 years later ; while at that point, my neighbour experiences the party).

And in any case, we are having some difficulties, because for this external parameter (which indicates which is the value of eigentime that is "now") to coincide with an ontological reality, you'd have to assign "reality status" to only certain events - which indeed, might not even make up a smooth surface and the entire 4-dim manifold looses its "reality status" in GR.

**This is different in Newtonian physics: you can postulate that "yesterday" and "tomorrow" simply don't exist. As such, there is no surprise that you "only" are consciously aware of "today": the other timeslices don't exist. **
As mentioned the same can be done for *one* person generically, and for the WHOLE universe simultaneously in very special circumstances such as small deviations from Friedmann.

I wasn't aware one could deny ontology to the 4-dim manifold in GR, to only keep those points which were on eigentimes of a certain value since the big bang. And as I tried to argue, I'm sure that even small deviations introduce differences of a few years after 15 billion years, which would mean that most of the matter around me wouldn't even have an ontological existence "now", because their ontological existence (as determined by the external clock, as in Newton) would be slightly late or early.

** I only experience one 3-dim slice. **
That remains incorrect.
** One remark: I don't, of course, experience a "past light cone". I only experience a small 3-dim volume corresponding to about the size of my brain, and it is in this 3-dim volume that the sensory information is coded from events that happened in my past light cone, which make me conclude that other things happened. **
What we call *now* is a tiny sufficiently tickend *lamphat* such that it is closed at the top (I only know my past, not anything spacelike to me).

There's a specific POINT in your brain that you are aware of ?

** I'm only aware of the state of my brain, not of a signal I am receiving. **
That is your preferred consciousness lecture (unnecessary in my view for our universe). If our universe were not so good and almost flat (at least in our galaxy), we would not be here because gravitation would destroy us (some kind of anthropic argument).

This has nothing to do with relativity, it is even recognized in the materialist view. Cut all the nerves leading to your brain and you'll know that what you're only aware of, is your brain status. Seeing, hearing and so on are illusions of receiving signals. It is only because they change the brain status that you experience them.

** When I talk about a time slice, I'm only talking about a time slice some 20 cm across. **
You do not need your whole brain to store some data, no ?
** But my direct subjective experience is only aware of the state of matters in the volume of my brain (or maybe even a smaller part of it **
Your brain is not ``aware´´ instantaneously.

Well, it is aware "instantaneously" of its status, no ? You mean, it is not instantaneously aware of external stimuli before they are processed. But I don't care about that, I'm talking about whatever it is that determines my conscious subjective experience. Some part of the brain is responsible for it, and the status of that part - which DETERMINES my conscious experience - well, determines my conscious experience, no ? So if that is in a certain state, then that IS my conscious experience (instantaneously) no ? But I didn't want to go into detailled neurological considerations. I just take the "thing which determines my subjective experience" as "my brain" ; it might be only part of it.

 

[vanesch]

No, we are not running in circles. You just want to assume that GR is nothing BUT the Einstein equations and then all your objections are of course justified. I say that if you want a meaningful interpretation of GR, you just have to add a localized Newton hypothesis for every small tube around a worldline. This, is what I call (c) and it clearly determines a NOW for me. Now, an extra problem is that the whole universe seems to observe the same *now* (that is why you love Newton so much). In my previous message, I said this can be solved by using the very specific initial conditions of the universe. Dynamically, you can do this as follows: just take Einstein Hilbert and put in by means of Lagrangian multipliers the harmonic condition for four scalar fields (that is the Gaussian gauge). Now, when suitable initial conditions are used, this gauge does not break down due to focal points. This is precisely what happens for the Friedmann universes and the slight perturbations of it in which we live. It goes without saying that the gaussian gauge condition DOES break down in quantum gravity; Karel Kuchar has done quite some work on that (1991). Once we have this *global* dynamical gauge you can have the same interpretational scheme as Newton has (and you do not need consciousness for that, you simply state that all material objects are in one and the same slice).

Ah, I was not aware of this possibility and you are honestly technically hitting me with stuff I don't know about.
So the 4-dim manifold has no ontological status in GR ? This is really new to me.
But, eh, doesn't that mean that general covariance goes down the drain ?
Can you kindly explain me a bit more the technical stuff you're adressing here, I'd like to know more about it.

 

[Careful]

** Please reply also to my previous post. **

I think I did already.

** Here, I would simply like to make a few extra comments.
Yes, right. Well, at least, that there has to be a specific relation between the physical ontology and the subjective observation, which makes you experience "now". **

drop the word subjective (it has a dirty consciousness smell ) and I agree.

** You seem to be postulating here something I wasn't aware off. If I understand you well, you seem to say that there are 2 things: the 4-dim manifold, and then still a kind of UNIVERSAL parameter, which indicates WHICH eigentime since the big bang is "special" so that it exists "now". (this was the role of time in the Newtonian frame). So if "eigentime since the big bang equals the "special time" it ontologically exists, and if it corresponds to a brain, then that is what is experienced by the consciousness associated with that brain, is that it ? **

Correct, except the last two lines. Eigentime corresponds to a brain ?
It is simply as follows: we observe we exist (again: you were not going to doubt that). There is an objective roadmap given by GR (the spacetime) and a universal (dynamical) time function which labels a present. By observation, we can know where we are on the roadmap just like you can get out of the desert by observing your relative position to the stars.

** But it is difficult to establish an eigentime since the big bang for something like a brain, that is made up of different particles with different histories. **

Again, our brain does not ``intrinsically´´ establish this eigentime (our brain exists and registers only some time after I was conceived). My brain just observes, therefore it is by definition existing, therefore it corresponds to some time after the big bang in a notion of space where all observing creatures live (by hypothesis). The exact time label is only of academic interest. You seem to be looking for the hand of God ...

** Don't you think that, over 15 billion years, differences in eigentime of a few 10s of years can be accumulated ? **

That is not what we observe and in the Friedmann universe, this is actually exact. Our universe is very, very special ... (generically whe should be killed by gigantic black holes and/or naked singularities)

** Now, this brings me to the example I gave: this means that if my neighbour's brain is made up of particles that "got 10 years late" since the big bang, I'm actually just dealing with him as a zombie, because he's consciously experiencing 10 years ago, when I'm experiencing "now" and the body I see "now" of him is not conscious.**

Ok, I understand that, but our universe does not work that way and GR allows for spacetimes with only contact between the living (even in Gaussian gauge).

** I wasn't aware one could deny ontology to the 4-dim manifold in GR, to only keep those points which were on eigentimes of a certain value since the big bang. And as I tried to argue, I'm sure that even small deviations introduce differences of a few years after 15 billion years, which would mean that most of the matter around me wouldn't even have an ontological existence "now", because their ontological existence (as determined by the external clock, as in Newton) would be slightly late or early. **

But the whole business of cosmology turns around the choice of a universal time parameter and perturbation theory around static spacetimes.

**There's a specific POINT in your brain that you are aware of ?**

Not a point of course (but something much, much smaller than 20 cm). Awareness is just a click in some control centre when some data is stored there and there in your brain. It seems to me that you are willing to go into this clicking business ad infinitum - which click is ``consciousness´´ and what clicks are perception ? I just define a materialistic control unit and every click there is BY definitìon ``conscious´´. It could be that there are sub-control units and so on... You postulate that this is not realistic and need a ghost state. So what?? I have just given you a full scheme which can do it without and still does what you want it to do.

 

[Careful]

Ah, I was not aware of this possibility and you are honestly technically hitting me with stuff I don't know about.
So the 4-dim manifold has no ontological status in GR ? This is really new to me.
But, eh, doesn't that mean that general covariance goes down the drain ?
Can you kindly explain me a bit more the technical stuff you're adressing here, I'd like to know more about it.

You can find some Kuchar references on gr-qc (if you cannot find them, I shall look it up for you). No, general covariance does not go down the drain; the full action principle with the Gaussian gauge condition is still fully covariant (because these coordinates have a special *dynamical* status with respect to some intial hypersurface). You could do the same trick for picking out the Killing time in the Kerr solutions as the preferred dynamical notion of time. Actually some people are just trying to do that for quantum gravity (in the ordinary sense): just restrict yourself to the sector with two (commuting) killing fields. It is useful in the sense that we seem to observe this at sufficiently large averaging scales, but I do not expect FUNDAMENTAL progress to come from such direction.

 

[vanesch]

I've still some troubles with what you wrote.
Is it correct that you say that there is, according what you state, ONLY an ontological status to all the events on the worldline of a particle that are on a particular value of their eigentime measured since the big bang ?

When you write:

** Don't you think that, over 15 billion years, differences in eigentime of a few 10s of years can be accumulated ? **

That is not what we observe and in the Friedmann universe, this is actually exact. Our universe is very, very special ... (generically whe should be killed by gigantic black holes and/or naked singularities)

This would mean that we can never have a situation such as in the "twin paradox". It is sufficient that I build my spaceship and do a trip which will shift my eigentime with the one on Earth by 10 years (or 10 minutes, if you want), and I HAVE suddenly that impossible difference.

Now, that was my problem, if the Earth only EXISTS when her eigentime is a certain value since the big bang (and so is mine), then when I cross, after my trip, the worldline of the earth, IT WOULD SIMPLY NOT BE THERE because, for that given value of universal ontological eigentime, the Earth is not at THAT event, because it is ontologically on another spot on its worldline when I get there and when the universal eigentime IS at the value of the crossing for me (so that I'm ontologically there).

And electrons that did a trip in an accelerator wouldn't be there anymore either. So I don't think it is tenable that there is only ontological existence for something when its eigentime since the big bang is at the "now" value, as I understand what you are saying.

In Newtonian physics that problem doesn't occur, and it wouldn't occur either in perfectly symmetrical solutions of GR where there is indeed a global time coordinate. But then you cannot allow relatively locally for particles to make special trips, because that de-synchronizes their eigentimes. If it are the eigentimes which determine ontological existence, then the desynchronized particles would simply disappear from existence as observed by others. My twin brother would not be here today, his now would be yesterday, and my now is today, so we wouldn't meet. His "pointer" would not be on his worldline at the crossing point when 'my pointer' crosses it again.

 

[Careful]

** I've still some troubles with what you wrote.
Is it correct that you say that there is, according what you state, ONLY an ontological status to all the events on the worldline of a particle that are on a particular value of their eigentime measured since the big bang ? **

No, I did not say that. I said that there is an ontological status to every event on a worldline corresponding to a particular value of a dynamically determined time function f (so an ontology relative to f). Which time function to choose is a very difficult and subtle issue.

**
This would mean that we can never have a situation such as in the "twin paradox". It is sufficient that I build my spaceship and do a trip which will shift my eigentime with the one on Earth by 10 years (or 10 minutes, if you want), and I HAVE suddenly that impossible difference.**

Nah, a few seconds is already difficult enough to achieve . So, clearly eigentime along the worldline is not suitable in this case (although it is sufficient for our purposes in cosmology). My favorite time function T is the length of the longest past oriented timelike curve to the big bang (this coincides with the cosmic time in the Friedmann universes): every eigentime
*tau* along a worldline can be expressed with respect to this one (by definition tau < T). The surfaces of constant T are by definition spacelike and only not differentiable on a set of measure zero where focal points occur with respect to the BB surface (but who cares about that?). So, you could argue that it is T that really ticks (although it is a non local definition) and that the aging of objects depends on the relative tau versus T ratio at a certain point (the larger this ratio at a certain spacetime event, the older the object). But indeed, we have to go over to a universal time function which is *independent* of the worldlines of the observers although the latter is sufficient FAPP. :uhh: FAPP ?? hmmm... I must be suffering from a widespread desease here. :tongue2:

 

[Ratzinger]

I don't want to interupt, but allow me to ask one minor question. What do you mean exactly by physical ontology here?

thanks

 

[hypnagogue]

Hi vanesch, I've been thinking about your argument and although I initially found it somewhat compelling, I think I may have struck on a good counterargument. Hopefully I have not misunderstood what you're trying to get across and can usefully advance the discussion.

So, your main conceptual material to work with here is that

1) according to GR, from a God's eye view, the universe looks like a static 4-dimensional manifold where no region in 4D space has privileged ontological status over the others.

From this you raise an ontological problem of how/why it is that I (you) experience this moment in time rather than another one, since my ontological status right now (in a very basic sense) is no different from my ontological status at any time in my past or future.

To help things along, I would like add an additional postulate:

2) Consciousness is inextricably tied to physical brain function. So, for practical purposes, we can regard the basic ontological status of consciousness in the same way we regard the basic ontological status of associated brain events. So, essentially, we can say that consciousness has real ontological existence if and only if we can say that associated physical brain processes have real ontological status. Hopefully that is not a point of contention.

The reason I introduce (2) is that I believe there may be some muddling assumptions or concepts at work here with regards to understanding consciousness. But because we are interested in ontological status here, if we reasonably assume that the ontological status of consciousness must always be anchored to, or at least isomorphic with, the ontological status of associated physical events, then we can advance the discussion without having to talk about consciousness per se. We can substitute physical events for conscious events into the argument without losing the underlying thrust of the discussion, and this will hopefully eliminate any potential confusions arising from understanding consciousness in particular.

Now, I will simplify things further by considering a very simple toy universe U. Suppose U consists of only one spatial dimension (call it the x axis) and that U contains only three pointlike objects A, B, and R lying on the x axis, such that A is located one unit away from R, and B is located two units away from R.

U is essentially a stand-in for the 4D spacetime manifold of our universe. It is a static, unchanging place; all things in U have equal ontological status (there are no ontologically privileged locations); and we can discern between the two objects A and B in U by reference to a reference point R. Just as well, A and B can be considered physical kinds of things, but for our purposes in the context of this discussion, they stand in for distinct conscious moments, e.g. my consciousness now as I type this as opposed to what I was experiencing exactly 24 hours ago.

So, vanesch has expressed perplexity in why it is that we consciously experience "now" as opposed to e.g. some moment in time yesterday or tomorrow. Translating this into our toy model as explained above, this is equivalent to perplexity as to why A is A and not B. After all, there is no privileged ontological status to any regions of U; so why is it that A is A (why am I experiencing right now) and not B (why am I not experiencing tomorrow)?

This seems not so much an issue of consciousness per se, but one of haecceity (this-ness) or what is talked about in philosophy as indexicality. Without having read much about the latter, I will say that intuitively it is sometimes difficult to wrap one's head around questions like this because they do not seem to yield much to further scrutiny; they seem to have a basic, axiomatic flavor to them. Perhaps we could say something like A is identical to B if an only if all properties and relations pertaining to A also pertain to B. In the case of U, all properties and relations pertaining to A do of course pertain to A, but this is not the case with A and B (because of different relations to R), so they are distinct. In any case, I do think we could say that we need not express perplexity at the fact that we experience one moment in time rather than another to any greater or lesser extent to the fact that in U, A is A and not B.

Ascending from the toy model and applying this to the original scenario, if (1) is true then we could say that indeed, our experience of today ontologically exists to just the same extent as our experience tomorrow or yesterday ontologically exists. The reason we experience "now" and not some other time is perhaps just something very basic, the same sort of thing that allows it to be the case that e.g. my computer desk is located over *here* and not over *there.*

In more detail, my brain exists over some extent of spacetime from birth to death, and what I experience at any given subjective instant is directly related to what goes on in my brain over some very brief, objective time span. If (1) is true, then in some sense there is a series of subjective instants existing side by side in static 4D spacetime corresponding to "me," with none of them being ontologically privileged over the others.

So how is the conscious now "selected"? If the above reasoning is right, then it seems most correct to say that the conscious now is not really "selected" at all, in any special sense. This apparent selection is perhaps just an illusion created by the causal dynamics underlying the existence of my consciousness. Start from the God's eye view of my worldline and arbitrarily pick out any small slice S upon it. Because of the way the physical structure of my brain is at S, and because of the causal relations linking physical brain activity to consciousness, I experience consciousness at that time as a subjective instant. I do not experience tomorrow or yesterday because, with respect to that particular physical situation in S, my physical brain constitution is distinct from what it was yesterday and will be tomorrow. Essentially, I experience now and not tomorrow because slice S from my worldline is slice S and not slice S' from tomorrow. S need not be ontologically privileged or selected; it just needs to be distinct from S' (and more generally, from all other slices on my worldline).

Here is another angle that perhaps will also shed light on the problem. Suppose we meet and sit at a table together to talk. Why do you experience *you yourself,* your brain, in that situation instead of experiencing what is going on in *my* brain? If you think about it, it's quite a similar question to the one of why you experience now instead of another time (suppose e.g. some time in your distant past when your brain was quite different physically from how it is now). The primary difference is that we are emphasizing spatial separations here as opposed to temporal ones. I submit that the problem of why you experience now and not tomorrow is not fundamentally different from the problem of why you experience "you" and not "me."

 

[vanesch]

A quick response, I'll come back to it later:

Here is another angle that perhaps will also shed light on the problem. Suppose we meet and sit at a table together to talk. Why do you experience *you yourself,* your brain, in that situation instead of experiencing what is going on in *my* brain?

Exactly, I find that one of the more compelling reasons for dualism, honestly. And you can even get into more wild situations when you start making copies of bodies... and THAT is exactly what seems to happen in quantum theory ; so I considered the "why now" question only as "warmup" for the real fireworks of quantum theory.
If we stick to quantum theory as we know it today, then to each individual physical process corresponds a UNITARY operator that operates on the STATE of "the system", but you can end up by taking the system as the universe, or at least a big chunk of space where we are.
Now, that's pretty annoying, because it means that body states will end up in highly non-classical states. Indeed, if we consider the following: Joe is going to do an experiment on a particle that is in a state |a>:
|ignorantJoe> |a> --> unitary evolution --> |JoeSawA> |a>
If the particle were in the state |b>, we'd have:
|ignorantJoe> |b> --> unitary evolution --> |JoeSawB> |b>
But if the particle was in the state u|a> + v|b> then we end up with:
|ignorantJoe> (u|a>+v|b>) --> unitary evolution --> (u|JoeSawA> |a> + v|JoeSawB>|b>)
So this is a funny situation: Joe's body appears in two totally distinct states in "the state of the world": one where he saw the red light, and another where he saw the green light.
And the funny thing is: Joe has PROBABILITY u^2 to experience the A state, and PROBABILITY v^2 to experience B.
Now, people take a shortcut and say that "the state of the world has collapsed" but 1) it would be strange that Joe can collapse the state of the world and not the particle itself and 2) there's no known PHYSICAL process that can do such a thing, because - in current QM - all physical processes are described by a unitary operator.
That's why Everett proposed that *no such collapse occurs* and that hence Joe's body REALLY IS in this superposed state - it is indeed what the strict application of quantum theory requires if you stick to it. All these interpretational schemes are called "relative state" or "many world" interpretations (MWI).
But you now clearly have a boosted version of the "why do I experience now" question, namely "why do I experience JoesawA and not JoesawB ? And moreover, HOW DO WE GET THOSE PROBABILITIES OUT ?
You can even do more wild things, where people get into different branches and then meet again (this is the MWI explanation of the "non-local effects" in EPR situations).
So I wanted to propose, following Wigner, something like a "worldline" of a subjective experience, that branches according to the probability rules. But I thought that it then becomes necessary to "have a worldline for your conscious experience" that traces through your different alternative bodystates. And I thought that GR was a 'warm up' exercise for that.

 

[Careful]

**
Exactly, I find that one of the more compelling reasons for dualism, honestly. And you can even get into more wild situations when you start making copies of bodies... and THAT is exactly what seems to happen in quantum theory ; so I considered the "why now" question only as "warmup" for the real fireworks of quantum theory.**

When I sit before my computer, typing in this message, I do not experience *my* brain (and certainly not that of anyone else) - in the sense that I do not register all neurotransmitters doing their job. I simply am aware of the commands my brain is sending to my fingers, that is the text which is being typed, I do not care about the specific mechanism doing it. Vanesch, I thought moreover that hypnagogue was specifically telling not to go to this parallel ghost world (if it would exist) for the particular reason that it is simply isomorphic to the physical constitution of the brain (and in math we all know that isomorphic copies are abundant). I know of course that in your quantum world there is something *more* to it


**
That's why Everett proposed that *no such collapse occurs* and that hence Joe's body REALLY IS in this superposed state - it is indeed what the strict application of quantum theory requires if you stick to it. All these interpretational schemes are called "relative state" or "many world" interpretations (MWI).
But you now clearly have a boosted version of the "why do I experience now" question, namely "why do I experience JoesawA and not JoesawB ? And moreover, HOW DO WE GET THOSE PROBABILITIES OUT ?
You can even do more wild things, where people get into different branches and then meet again (this is the MWI explanation of the "non-local effects" in EPR situations).
So I wanted to propose, following Wigner, something like a "worldline" of a subjective experience, that branches according to the probability rules. But I thought that it then becomes necessary to "have a worldline for your conscious experience" that traces through your different alternative bodystates. And I thought that GR was a 'warm up' exercise for that**

Aha, but how to *define* this worldline ?? It must clearly be something continuous and even satisfying a deterministic mechanism (I went to the toilet and knew quite well what would happen in the next 4 minutes, no quantum fluctuations there... ) ! On the other hand you must reproduce the *exact* (within an acceptable margin of error) quantum statistics when repeating an experiment sufficiently many times. As I said 85 posts ago, you are just shifting the cat to another perverse level. Face it: at the macroscopic level, we live in ONE world, and the cat problem is exactly to explain HOW QM descends from its many world crap to the solid one word experience.

Clearly the GR warm up has been in the wrong category, let's hope the QM race is better. :tongue2: Seriously, I think your GR point of view comes from Minkowski ; I always try to warn people for the interpretational pitfalls of it (which are not present in GR where objective ``embarquation´´ events exist).

 

[vanesch]

I don't want to interupt, but allow me to ask one minor question. What do you mean exactly by physical ontology here?

Well, a physical theory consists of a mathematical formalism, and then something that makes it into a physical theory. That "something" can be seen in two different ways. One is purely epistemological: the mathematical formalism is only a kind of algorithmic prescription to calculate outcomes of experiment. I think that approach is a poor one, for several reasons, but that's not the debate here.
Most obviously, a physical theory has the ambition to *describe* a real world "out there". It is a working hypothesis that there IS a real world out there. This means that at least SOME mathematical objects in the theory are to be identified with the real world out there. Not all of them, but the *essential* mathematical structures should be identified. This is then the "ontological part" of the theory. The thing you imagine that "exists really out there" and that corresponds to a mathematical construction in your theory. You have of course a certain liberty in doing so, which gives you different visions (interpretations if you like).
But if you require "certain general physical principles" to apply to certain elements in your theory, then I would say that it is almost for sure that the things you want your principles to applied to, are part of the ontological description of your theory.
For instance, in Newtonian physics, the 3-dim Euclidean space is almost for sure part of the ontology (no matter what flavor of Newtonian physics you use).
And I was somehow convinced that the 4-dim spacetime manifold was part of the ontology of relativity.
In quantum theory, the state vector in hilbert space is often taken as part of the ontological description of the world.

 

[vanesch]

2) Consciousness is inextricably tied to physical brain function. So, for practical purposes, we can regard the basic ontological status of consciousness in the same way we regard the basic ontological status of associated brain events. So, essentially, we can say that consciousness has real ontological existence if and only if we can say that associated physical brain processes have real ontological status. Hopefully that is not a point of contention.

Hmm. I would only read it in one way - think about the philosophers' zombie. It is not because a certain brain function is present that it must necessarily give rise to some consciousness. But in order for a consciousness to be present, I agree that it must be related to a brain function. Isn't this the entire materialist - dualist debate ? Solipsism is a possibility - in fact an almost necessity - to resolve the issue you raised and I oversaw (probably because I'm already too much with my nose in a solipsist viewpoint!).

So, vanesch has expressed perplexity in why it is that we consciously experience "now" as opposed to e.g. some moment in time yesterday or tomorrow. Translating this into our toy model as explained above, this is equivalent to perplexity as to why A is A and not B. After all, there is no privileged ontological status to any regions of U; so why is it that A is A (why am I experiencing right now) and not B (why am I not experiencing tomorrow)?

This is indeed a very good point, and I didn't realize that the problem was *already* present in the Newtonian frame in a certain sense, and that came because I considered there to be a natural association of MY BRAIN with "subjective experience". The theory that only my brain has subjective experience is totally in agreement with all I know, but it is entirely true that this IS already a non-trivial assignment of conscious experience with the physical ontology. Now, whether there are subjective experiences associated to other physical constructions, such as your brain, my desk computer or whatever, is a totally unanswerable question (this is the "hard problem", no ?). If I take as working hypothesis that the answer is "no", then we have solipsism ; if not, well, then there are several non-trivial assignments from the physical ontology to different subjective "worlds". If (to come as close as possible to your point 2)) to *every* possible part of the physical ontology that CAN support a subjective experience, there IS such an experience, then we just have SEVERAL of these mappings.
And in fact, these mappings are what I wanted to talk about in the first place.
So or this is accepted as a triviality - but in that case, I don't see why people object to the quantum version of the story - or this is ALREADY a problem in the Newtonian frame.
Because, as I said, the ontology in quantum theory assigns several "classical" states at the same time to the same physical structure, as in:
u |JoeSawA> |a> + v|JoeSawB> |b>
If we are now allowed to *pick out one* and say that, well, you simply *happen to be* JoeSawA, then there is NO interpretational problem to quantum theory. This is then on the same footing as (in GR):
"well, you HAPPEN to experience your brain state today"
or (as you point out)
"Well, you HAPPEN to experience point A"
or, in Newtonian physics:
"well, you happen to experience patrick's brain state"
It is this "picking out one which you happen to experience" that I called the non-trivial relationship between the entire physical ontology and the subjectively experienced world.

This seems not so much an issue of consciousness per se, but one of haecceity (this-ness) or what is talked about in philosophy as indexicality.

Ok, great, that philosophers had already a name for it when physicists were calling each-other names over it

In any case, I do think we could say that we need not express perplexity at the fact that we experience one moment in time rather than another to any greater or lesser extent to the fact that in U, A is A and not B.

No, the point is that people (like our friend Careful) consider a "many worlds interpretation" of quantum theory a totally crazy idea, while it is - at least as I understand it - not in any way more crazy than to say that "well, I happen to experience state |JoeSawA> even if |JoeSawB> is also part of the same ontology, at the same time, of the same body.
I tried to link it to the fact that in GR, *the same body* has an ontology which is also not "completely experienced" (namely all of the body's world line, containing its future and past configurations).
And I think you're right that it is even not in any way more special than saying that "I" (= the subjective experiences of my conscious world) happen to experience patrick's brain, and not your brain.

Ascending from the toy model and applying this to the original scenario, if (1) is true then we could say that indeed, our experience of today ontologically exists to just the same extent as our experience tomorrow or yesterday ontologically exists. The reason we experience "now" and not some other time is perhaps just something very basic, the same sort of thing that allows it to be the case that e.g. my computer desk is located over *here* and not over *there.*
In more detail, my brain exists over some extent of spacetime from birth to death, and what I experience at any given subjective instant is directly related to what goes on in my brain over some very brief, objective time span. If (1) is true, then in some sense there is a series of subjective instants existing side by side in static 4D spacetime corresponding to "me," with none of them being ontologically privileged over the others.

Great ! We're on the same wavelength here...

So how is the conscious now "selected"? If the above reasoning is right, then it seems most correct to say that the conscious now is not really "selected" at all, in any special sense. This apparent selection is perhaps just an illusion created by the causal dynamics underlying the existence of my consciousness. Start from the God's eye view of my worldline and arbitrarily pick out any small slice S upon it. Because of the way the physical structure of my brain is at S, and because of the causal relations linking physical brain activity to consciousness, I experience consciousness at that time as a subjective instant. I do not experience tomorrow or yesterday because, with respect to that particular physical situation in S, my physical brain constitution is distinct from what it was yesterday and will be tomorrow. Essentially, I experience now and not tomorrow because slice S from my worldline is slice S and not slice S' from tomorrow. S need not be ontologically privileged or selected; it just needs to be distinct from S' (and more generally, from all other slices on my worldline).

You are reading my thoughts ! (which, by itself, would falsify your reasoning here... )

Here is another angle that perhaps will also shed light on the problem. Suppose we meet and sit at a table together to talk. Why do you experience *you yourself,* your brain, in that situation instead of experiencing what is going on in *my* brain? If you think about it, it's quite a similar question to the one of why you experience now instead of another time (suppose e.g. some time in your distant past when your brain was quite different physically from how it is now). The primary difference is that we are emphasizing spatial separations here as opposed to temporal ones. I submit that the problem of why you experience now and not tomorrow is not fundamentally different from the problem of why you experience "you" and not "me."

Great. Now that we have all that, it is not in any way MORE surprising that, given a quantum state where my body occurs in 2 different states, I just happen to experience ONE of both, right ? But that's exactly the Many worlds view on QM!

 

[vanesch]

Aha, but how to *define* this worldline ?? It must clearly be something continuous and even satisfying a deterministic mechanism.

No, it is quite simple: you "happen to be" (= you happen to experience subjectively) the state of |careful1> in already a very complicated state of the universe.
Now, |careful1> will undergo (as part of a unitary evolution) an entanglement with something else:
|careful1> |stuff> ==> a |careful1a> |stuffa> + b|careful1b> |stuffb>
Your "quantum world line" now has to bifurcate: with probability |a|^2, you'll next "happen to be" careful1a, and with probability |b|^2, you'll "happen to be" careful1b, as a fundamentally stochastic process.

This gives you indeed a succession of states which are *almost* continuous (like the projection of a movie, which gives you also the impression of continuity), but it is not deterministic ; it is probabilitic on a fundamental level.

 

[Careful]

No, it is quite simple: you "happen to be" (= you happen to experience subjectively) the state of |careful1> in already a very complicated state of the universe.
Now, |careful1> will undergo (as part of a unitary evolution) an entanglement with something else:
|careful1> |stuff> ==> a |careful1a> |stuffa> + b|careful1b> |stuffb>
Your "quantum world line" now has to bifurcate: with probability |a|^2, you'll next "happen to be" careful1a, and with probability |b|^2, you'll "happen to be" careful1b, as a fundamentally stochastic process.
This gives you indeed a succession of states which are *almost* continuous (like the projection of a movie, which gives you also the impression of continuity), but it is not deterministic ; it is probabilitic on a fundamental level.

Nonsense! My state |Careful1> is *not* part of a unitary evolution (you have stated that very clearly before), it is just something we paste to |stuff> which evolves according to unitary evolution. It is clear that you are sucked into a preferred basis problem. So, unless you give me a physical theory of preferred orthogonal macroscopic perception states, we cannot even proceed here (since the process would be as discontinuous as we like then). But let me show some goodwill and ignore this issue for now (!). Now, you have to explain me WHY it is that our perception behaves very, very deterministically since you CANNOT obtain such behaviour from a fundamental probabilistic theory.

 

[Careful]

Great. Now that we have all that, it is not in any way MORE surprising that, given a quantum state where my body occurs in 2 different states, I just happen to experience ONE of both, right ? But that's exactly the Many worlds view on QM!

I am glad you found someone to accompany you on the quest of turning Einstein around in his grave. You simply seem to ignore the objective way out I have given to you (perhaps this is too easy for you). Concerning the further ``problem´´ you see why A is A and not B in Newtonian space; you seem to have forgotten the word DEFINITION. In the same way you could ask why your name is Patrick and not Hasnvec: you seem to ignore the simple reality that this is just the name given to you by your parents and accepted by the adminstrative officer at the time. I assure you that when I call you Hasnvec now (and remember that you were previously Patrick) that this is not going to change anything about the ontological status you have in my database. For example I still know that you are the MWI science fiction robot with for all other purposes (FAOPP) rather intelligent views.

 

[vanesch]

Nonsense! My state |Careful1> is *not* part of a unitary evolution (you have stated that very clearly before), it is just something we paste to |stuff> which evolves according to unitary evolution.

No, |careful1> is a state of your body. |careful2> (which I didn't mention) is another state of your body which can occur somewhere else in the state of the universe, no matter. You happen to experience the |careful1> state (and if you like, another "you" is experiencing the careful2 state, or not). It is not the "state of a consciousness", it is that the subjective experiences your consciousness is subjected to, is simply associated to the state |careful1>.
|state_of_universe> = (|careful1*> |stuff> + |careful2> |otherstuff>) |stillotherstuff>
after evolution:
|state_of_universe2> = (a |careful1a*> |stuffa> + b|careful1b> |stuffb> + |careful2> |otherstuff>) |stillotherstuff>
The * shows "what you happen to be" ; in this case, with probability |a|^2.
I wanted to make the analogy with GR: your body is in different states, namely the state that corresponds to "today", the state that corresponds to "yesterday" etc... but you happen to experience only the "today" state.
As hypnagogue pointed out, there are several brains around, but you happen to experience one of them.
Well, in the same way, you happen to experience the "careful1" state of your body.
Or this is an issue (namely why do you only experience the "careful1" state ), but then this is also an issue (that was my point) for the "why do you only experience your body in the "now" state, or "why do you only experience careful's body" and not "joe's body" ; or this is not an issue, and one can say: hey, you don't experience joe's body because you "happen to be" careful's body ; hey, you don't experience yesterday, because you "happen to experience" today ; but then I say: then it is not an issue either that you happen to experience the careful1 state.

It is clear that you are sucked into a preferred basis problem.

Nothing stops me from postulating a preferred basis ; it is all part of the mapping between the ontology (the state of the universe) and what you happen to experience subjectively (the "you happen to be" mapping). Now, the more *natural* these postulates are, the better the theory of course, but even if I have to make a blunt list of what are the preferred basis states, that's always possible. The postulated preferred basis of bodystates is then simply the different states that correspond to different possible subjective experiences.

Now, you have to explain me WHY it is that our perception behaves very, very deterministically since you CANNOT obtain such behaviour from a fundamental probabilistic theory.

I don't see that point at all. Clearly for about all "classical" phenomena, there's an overwhelmingly high Born probability to just follow closely the classical path, and any deviation of it is highly improbable ; moreover these classical states correspond (apparently - or almost as a DEFINITION of classical state - to the preferred basis states of different subjective experiences). So by an overwhelming probability, you will always go for the state that corresponds to what you'd expect of a deterministic evolution. The bifurcation only comes in when we look at phenomena that have comparable quantum probabilities, and then, indeed, we do not have the impression that things happen deterministically ! When you listen to a geiger counter, the "hearing of the click" is not perceived as something deterministic, no ? So your subjective experience "jumping to the state 'I heard a click' " is not surprising in that case, no ?

 

[vanesch]

Concerning the further ``problem´´ you see why A is A and not B in Newtonian space; you seem to have forgotten the word DEFINITION. In the same way you could ask why your name is Patrick and not Hasnvec

Ok, if that is not a problem to you, fine. But then I don't see why it IS a problem to you that you happen to be |careful1a> and not |careful1b>. It just happens to be so, I could then also say. What is then so unsurmountable with *this* notion, and NOT with the "you happen to be Joe" argument ?

 

[Careful]

Ok, so no mental states here, just physical brain states.


**I wanted to make the analogy with GR: your body is in different states, namely the state that corresponds to "today", the state that corresponds to "yesterday" etc... but you happen to experience only the "today" state.
As hypnagogue pointed out, there are several brains around, but you happen to experience one of them.
Well, in the same way, you happen to experience the "careful1" state of your body. **

How, how, first of all your GR scheme has shown not to be necessary at all. Second, even if I would just about consider your scheme, then the jump you make in the quantum case is much more exotic ! In your GR system, the perception states correspond to the different states (on a worldline) in a deterministic system (and as such evolve through well prescribed rules) while in QM your PHYSICAL BRAIN (ah yes, you just told me that |careful1> was my physical brain state) simply makes crazy jumps.


** Or this is an issue (namely why do you only experience the "careful1" state ), but then this is also an issue (that was my point) for the "why do you only experience your body in the "now" state, or "why do you only experience careful's body" and not "joe's body" ; or this is not an issue, and one can say: hey, you don't experience joe's body because you "happen to be" careful's body ; hey, you don't experience yesterday, because you "happen to experience" today ; but then I say: then it is not an issue either that you happen to experience the careful1 state. **

No, no, no not at all ! In all these non quantum situations, my brain state exists and evolves. In the quantum case your brain state just exists, but it obeys the laws of randomness (by the way do not forget that this is all not necessary in GR - I just do this for sake of academic exercise).

** Nothing stops me from postulating a preferred basis ; it is all part of the mapping between the ontology (the state of the universe) and what you happen to experience subjectively (the "you happen to be" mapping). Now, the more *natural* these postulates are, the better the theory of course, but even if I have to make a blunt list of what are the preferred basis states, that's always possible. **

Sure, why not? Just put in by hand what outcome you expect from a theory and then call it predictive :rofl: When I started to learn physics, I always had the silly idea that if I would work out dynamical equations of motion corresponding to some strange initial conditions, I might discover new macroscopic phenomena I never imagined. That is: the theory should tell us what to expect, not us to the theory.

** The postulated preferred basis of bodystates is then simply the different states that correspond to different possible subjective experiences. **

I am sure you are aware of them all !

** Clearly for about all "classical" phenomena, there's an overwhelmingly high Born probability to just follow closely the classical path, and any deviation of it is highly improbable **

But your brainstate is not classical (albeit there is quite some grey mass usually). Moreover, what you say is not correct at all for classical chaotic phenomena (such as the weather). If you let U run for some while, your brain would switch from rain, to sun, to storm every 0.1 seconds ! (quite an exciting world you have there).

** moreover these classical states correspond (apparently - or almost as a DEFINITION of classical state - to the preferred basis states of different subjective experiences). **

Well, you are aware of all your possible subjective experiences I see... Moreover, another problem with your picture is that these different macroscopic brain states CANNOT be orthogonal; otherwise the process your brain runs through is totally discontinuous (see what happens then in the book of Penrose).

** So by an overwhelming probability, you will always go for the state that corresponds to what you'd expect of a deterministic evolution. **

Naah, think about the weather ...

**The bifurcation only comes in when we look at phenomena that have comparable quantum probabilities, and then, indeed, we do not have the impression that things happen deterministically ! **

See weather (you will need reduction of the state here and your physical brain WILL have to take into account its own history before it undergoes the next ``spontaneous´´ click).