Light, Waves, Particles etc

Study matter and its motion through spacetime...

Moderators: Calilasseia, ADParker

Re: Light, Waves, Particles etc

#121  Postby twistor59 » Oct 09, 2011 8:30 am

Teuton wrote:
Teuton wrote:
0D objects and 1D objects exist only in the abstract realm of mathematics. Concrete physical objects are (at least) 3D objects.


This means that if there are atoms in the literal sense of the term, i.e. truly fundamental particles, then they must be simple, partless (componentless/constituentless) 3D atoms. Of course, many ask how it is possible for a 3D object to be spatially partless when any (nonzero) volume of space can be partitioned into smaller (nonzero) subvolumes. This is a good question and the only good answer might come from the theory called loop quantum gravity, according to which there are indivisible atoms of space that cannot be partitioned into any smaller subvolumes.

"According to loop quantum gravity, space is made of discrete atoms each of which carries a very tiny unit of volume. … One consequence of this is that there is a smallest possible volume. This minimum volume is miniscule – about 1099 of them would fit into a thimble. If you tried to halve a region of this volume, the result would not be two regions each with half that volume. Instead, the process would create two new regions which together would have more volume than you started with. We describe this by saying that the attempt to measure a unit of volume smaller than the minimal size alters the geometry of the space in a way that allows more volume to be created."

(Smolin, Lee. Three Roads to Quantum Gravity. New York: Basic Books, 2001. p. 106)

So, if a fundamental 3D particle occupies exactly one space-atom, then one can consistently and intelligibly say that it lacks spatial parts.
(It might be the case that the particle-atoms are ontologically reducible to the space-atoms so that the latter would be the fundamental physical objects.)

If there are no 3/4-dimensional particle-atoms or space/spacetime-atoms, then matter or space/spacetime is "gunky", i.e. then it is infinitely divisible and every part of it has proper parts ad infinitum. (This means that "gunky" stuff isn't ultimately composed of simple point-sized objects, which lack proper parts.)


Unfortunately, LQG is not yet in a state where we can talk about fundamental particles "occupying space-atoms". It is not yet known/agreed how to put matter into the LQG picture.
A soul in tension that's learning to fly
Condition grounded but determined to try
Can't keep my eyes from the circling skies
Tongue-tied and twisted just an earthbound misfit, I
User avatar
twistor59
RS Donator
THREAD STARTER
 
Posts: 4966
Male

United Kingdom (uk)
Print view this post

Ads by Google


Re: Light, Waves, Particles etc

#122  Postby hackenslash » Oct 09, 2011 10:44 am

mizvekov wrote:
hackenslash wrote:Still getting all your definitions from the dictionary of what colour is my lint.

What exactly is wrong with the definition of operator as pointed out in the link Teuton posted?


Nothing, except those objections already detailed. The problem I have is lending credence to the source. That particular source spends a lot of bandwidth on wibble.

Do you think these definitions support the notion that operators are not mathematical abstract objects?


The operators are as 'real' as the entities whose behaviour they're describing. In other words, if particles are 'real', then so are those quantities, because they are describing properties of those entities.
User avatar
hackenslash
 
Name: The Other Sweary One
Posts: 21366
Age: 49
Male

Country: Republic of Mancunia
Print view this post

Re: Light, Waves, Particles etc

#123  Postby mizvekov » Oct 09, 2011 10:56 am

hackenslash wrote:Nothing, except those objections already detailed. The problem I have is lending credence to the source. That particular source spends a lot of bandwidth on wibble.

Well, I haven't seen that, the articles there seem very fair and balanced, they do present multiple points of view. I can't see wibble, unless one would consider all of philosophy wibble, which in my opinion is a very prejudiced view.
And whenever they are talking about physics, it is usually an alright treatment of the subject, at least to an introductory level.
If you seen something wrong, maybe you should write about it to the stanford department of philosophy.

hackenslash wrote:The operators are as 'real' as the entities whose behaviour they're describing. In other words, if particles are 'real', then so are those quantities, because they are describing properties of those entities.

Well, that is a weird position, I think you are the only one in this thread holding to it.
By that account, do you also believe the number '5' is real because it describes the number of fingers I have in my left hand?
mizvekov
 
Posts: 314
Age: 35
Male

Brazil (br)
Print view this post

Re: Light, Waves, Particles etc

#124  Postby hackenslash » Oct 09, 2011 10:58 am

No, I'm not a Platonic realist. Nor do I need to be, because '5' isn't a property, while spin, angular momentum, etc, are.

I should also point out that I'm perfectly willing to be shown to be in error (indeed, I welcome it). I'm not a physicist, merely an interested layman.
User avatar
hackenslash
 
Name: The Other Sweary One
Posts: 21366
Age: 49
Male

Country: Republic of Mancunia
Print view this post

Re: Light, Waves, Particles etc

#125  Postby mizvekov » Oct 09, 2011 11:17 am

hackenslash wrote:No, I'm not a Platonic realist. Nor do I need to be, because '5' isn't a property, while spin, angular momentum, etc, are.

But '5' describes the property 'number of fingers' of my left hand.
And so does f(x) = 5, where x is distance to the moon, describes the same thing, but at least I would not say that function 'f' is real because it describes something which is very real and observable.
And similarly the operators, they are mathematical abstract objects which describe properties of the particles.
I mean, I am not saying it isn't possible to hold consistently the view that operators are 'real', and as far as controversy on ontology is concerned, this particular branch of physics is deep into it, but one thing that is very uncommon among physicists is to attribute reality into any mathematical objects. That particular thing raises red flags immediately.
mizvekov
 
Posts: 314
Age: 35
Male

Brazil (br)
Print view this post

Re: Light, Waves, Particles etc

#126  Postby hackenslash » Oct 09, 2011 11:44 am

Well, given the 'reality' of particles (ontological caveats aside for the moment, just for the sake of exploration), can we say that the property 'velocity' is real?

Of course, depending on which formulation of QM one is operating from, it's difficult to say whether or not a particle even has a definite velocity until such time as it is observed, but that aside, and given that some formulations insist that these properties are basic, then under those formulations, those operators are real things.

In the example you have given, the distance to the moon is, as you say, very real, but the number that describes it? This is the problem you run into when you speak of the number of fingers on your left hand. They have the real property of being fingers, but not the real property of 'fiveness', which would require support for Platonic realism.

I think the real problem here is that we're running into set-theoretic territory here, and while being a member of a set could be described as a property, it's problematic to insist that that membership has any 'reality'.

It's a thorny problem, to be sure.
User avatar
hackenslash
 
Name: The Other Sweary One
Posts: 21366
Age: 49
Male

Country: Republic of Mancunia
Print view this post

Re: Light, Waves, Particles etc

#127  Postby twistor59 » Oct 09, 2011 12:00 pm

Well a few posts back I proposed that the appropriate definition of "are" is "is modelled by", since modelling is all we ever do in theoretical physics. The only question then is whether you can be arsed to say, for example, "momentum is modelled by the eignenvalues of the Hermitian operator p." Or whether you say "momentum is a Hermitian operator"...
Either way people generally know what is meant.
A soul in tension that's learning to fly
Condition grounded but determined to try
Can't keep my eyes from the circling skies
Tongue-tied and twisted just an earthbound misfit, I
User avatar
twistor59
RS Donator
THREAD STARTER
 
Posts: 4966
Male

United Kingdom (uk)
Print view this post

Ads by Google


Re: Light, Waves, Particles etc

#128  Postby mizvekov » Oct 09, 2011 12:55 pm

twistor59 wrote:Well a few posts back I proposed that the appropriate definition of "are" is "is modelled by", since modelling is all we ever do in theoretical physics. The only question then is whether you can be arsed to say, for example, "momentum is modelled by the eignenvalues of the Hermitian operator p." Or whether you say "momentum is a Hermitian operator"...
Either way people generally know what is meant.

Well I agree in a sense that all you ever do in theoretical physics is model building, since that is the main goal, and here this language is appropriate. But theoretical physicists are not shy when talking about the nature of things, and here it can get a bit confusing. I am not concerned with the usage of language in this particular case, but whether the distinction is minded.
When for example one says "eignenvalues of the Hermitian operator are real", it's very explicit that what is meant here is their nature.
mizvekov
 
Posts: 314
Age: 35
Male

Brazil (br)
Print view this post

Re: Light, Waves, Particles etc

#129  Postby Teuton » Oct 09, 2011 2:22 pm

hackenslash wrote:
The operators are as 'real' as the entities whose behaviour they're describing. In other words, if particles are 'real', then so are those quantities, because they are describing properties of those entities.


The language of mathematics is doubtless real, but whether it truly represents an abstract mathematical reality wherein functions, numbers, and sets, etc. exist (as nonlinguistic entities) is another question.
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#130  Postby Teuton » Oct 09, 2011 2:29 pm

mizvekov wrote:
By that account, do you also believe the number '5' is real because it describes the number of fingers I have in my left hand?


There is a distinction between the numerical (number-word) "5" and the number 5, which is a nonlinguistic object; and there is a further distinction between the numerical <5> as an abstract word-type and its concrete word-tokens such as "5". (In the last sentence four concrete tokens of <5> are used.)
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#131  Postby Teuton » Oct 09, 2011 2:36 pm

mizvekov wrote:
But '5' describes the property 'number of fingers' of my left hand.


No, "5" stands for an object, while "number of fingers (of your left hand)" stands for a concept.
"The number of fingers of my left hand is 5" is an identity statement:
"The number of fingers of my left hand = 5."
("Number of fingers of my left hand" stands for a concept, but the definite description "the number of fingers of my left hand" stands for an object just like the numerical "5".)
The numerical "5" is part of the predicate "has 5/five fingers", which represents the property of having 5/five fingers; but this doesn't mean that "5" alone represents a property rather than an object.
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#132  Postby mizvekov » Oct 09, 2011 3:06 pm

Teuton wrote:
mizvekov wrote:
By that account, do you also believe the number '5' is real because it describes the number of fingers I have in my left hand?


There is a distinction between the numerical (number-word) "5" and the number 5, which is a nonlinguistic object; and there is a further distinction between the numerical <5> as an abstract word-type and its concrete word-tokens such as "5". (In the last sentence four concrete tokens of <5> are used.)

Ofcourse I meant here the non-linguistic object number 5, didn't think a distinction was warranted.
Teuton wrote:No, "5" stands for an object, while "number of fingers (of your left hand)" stands for a concept.
"The number of fingers of my left hand is 5" is an identity statement:
"The number of fingers of my left hand = 5."
("Number of fingers of my left hand" stands for a concept, but the definite description "the number of fingers of my left hand" stands for an object just like the numerical "5".)
The numerical "5" is part of the predicate "has 5/five fingers", which represents the property of having 5/five fingers; but this doesn't mean that "5" alone represents a property rather than an object.

Yeah, I used the words in a very informal way, what i meant was what you just said, "having five fingers" is/represents a property of my left hand, not that the number 5 itself was a property.
mizvekov
 
Posts: 314
Age: 35
Male

Brazil (br)
Print view this post

Re: Light, Waves, Particles etc

#133  Postby Teuton » Oct 09, 2011 3:19 pm

twistor59 wrote:That sounds like philosophy speak. Even the Susskind quote. Statements like "a point is too simple", "It sounds unreasonable".. point to speculation, not science.


As you probably know, natural science was formerly called natural philosophy.

twistor59 wrote:
We started with "concrete physical objects are (at least) 3D objects". The problem is with the word "are". I don't know how philosophers interpret it, but "are" for me in this context could be replaced by "is modelled by".


I'm sure it is mathematically very practical to model particles and strings as 0D or 1D objects, but the question is whether or not these are only mathematically idealized models, i.e. whether or not particles and strings are really 0-dimensional or 1-dimensional (if they exist).
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#134  Postby Teuton » Oct 09, 2011 4:34 pm

Teuton wrote:
I'm sure it is mathematically very practical to model particles and strings as 0D or 1D objects…


But doing so is nonetheless physically problematic, at least with regard to point-particles:

"Questions about the electron's dimensions exerted a formative influence on the development of physics. Classical electrodynamics precluded the electron from being a point particle. A point particle would have an infinite self-energy (a clearly absurd consequence). Thus, it followed that the electron was an extended particle."

(Arabatzis, Theodore. Representing Electrons: A Biographical Approach to Theoretical Entities. Chicago: University of Chicago Press, 2006. p. 41)

"If the electron is taken to be a point charge, its self-energy is infinite and difficulties arise for the Dirac equation."

(Daintith, John, ed. Oxford Dictionary of Physics. 6th ed. Oxford: Oxford University Press, 2009. p. 153)
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#135  Postby Teuton » Oct 09, 2011 4:56 pm

As for strings, how could a concrete physical object possibly have a (nonzero) length but no (nonzero) width?
(There are infinitely many possible nonzero widths below, say, 10-100mm.)

Brian Green writes (in The Fabric of Reality) that strings are "one-dimensional vibrating filaments of energy."
Green apparently says that strings consist of energy, which would mean that energy is some stuff of which physical things can consist—but it is not! What Greene can coherently say is that strings are ontologically reducible to tiny vibrationally energized zones of spacetime that are string- or loop-shaped. For then those (3- or 4-dimensional) zones (or regions) are the true bearers or havers of the string energy without consisting of that energy. (Things have, possess, instantiate, or exemplify their properties, but they don't consist of, aren't composed of or constituted by them.)
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Ads by Google


Re: Light, Waves, Particles etc

#136  Postby Teuton » Oct 09, 2011 5:29 pm

I think we cannot help but regard spacetime itself as a plenum rather than a vacuum (in the literal sense), i.e. as a kind of (postmechanistic) ether, i.e. as an ur-stuff or ur-matter that is the fundamental substantial medium and matrix of physical reality.

"About the time relativity was becoming accepted, studies of radioactivity began showing that the empty vacuum of space had spectroscopic structure similar to that of ordinary quantum solids and fluids. Subsequent studies with large particle accelerators have now led us to understand that space is more like a piece of window glass than ideal Newtonian emptiness. It is filled with 'stuff' that is normally transparent but can be made visible by hitting it sufficiently hard to knock out a part. The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo."

(Laughlin, Robert B. A Different Universe: Reinventing Physics From the Bottom Down. New York: Basic Books, 2005. p. 121)
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#137  Postby twistor59 » Oct 09, 2011 5:42 pm

Teuton wrote:
twistor59 wrote:That sounds like philosophy speak. Even the Susskind quote. Statements like "a point is too simple", "It sounds unreasonable".. point to speculation, not science.


As you probably know, natural science was formerly called natural philosophy.

twistor59 wrote:
We started with "concrete physical objects are (at least) 3D objects". The problem is with the word "are". I don't know how philosophers interpret it, but "are" for me in this context could be replaced by "is modelled by".


I'm sure it is mathematically very practical to model particles and strings as 0D or 1D objects, but the question is whether or not these are only mathematically idealized models, i.e. whether or not particles and strings are really 0-dimensional or 1-dimensional (if they exist).


Emphasis mine. You need to say exactly what you mean by "are". How would you determine if the statement was true or false ?
A soul in tension that's learning to fly
Condition grounded but determined to try
Can't keep my eyes from the circling skies
Tongue-tied and twisted just an earthbound misfit, I
User avatar
twistor59
RS Donator
THREAD STARTER
 
Posts: 4966
Male

United Kingdom (uk)
Print view this post

Re: Light, Waves, Particles etc

#138  Postby Teuton » Oct 09, 2011 5:57 pm

twistor59 wrote:
Teuton wrote:
I'm sure it is mathematically very practical to model particles and strings as 0D or 1D objects, but the question is whether or not these are only mathematically idealized models, i.e. whether or not particles and strings are really 0-dimensional or 1-dimensional (if they exist).

Emphasis mine. You need to say exactly what you mean by "are".


It's the is/are of predication. "Particles are 0-dimensional" means "particles have the property of being 0-dimensional".

twistor59 wrote:
How would you determine if the statement was true or false ?


I don't know how the question could be decided experimentally, but there are conceptual a priori reasons against the view that 0D, 1D, and 2D things can adequately be called physical objects or substances rather than (geometrically ideal, abstracted) boundaries of those. And there are metaphysical/ontological a priori reasons for doubting or even denying that particles and strings can have less than 3 spatial dimensions.
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#139  Postby Teuton » Oct 09, 2011 6:06 pm

As for the concept of a field quantum: Is a field quantum anything else but a quantized amount of energy had by a field zone (or space/spacetime zone)?
If no, then if particles are ontologically reduced to field quanta, they are no longer objects or substances (in the strict ontological sense) but energetic attributes or modes of fields or space/spacetime. That is, then the fundamental physical objects/substances are either fields or space/spacetime. (I think that fields are themselves ontologically reducible to collection of attributes or modes of spacetime; and so the one irreducible, truly fundamental substance or substrate of physical reality is spacetime itself, which could be called the world-body.)
"Perception does not exhaust our contact with reality; we can think too." – Timothy Williamson
User avatar
Teuton
 
Posts: 5461

Germany (de)
Print view this post

Re: Light, Waves, Particles etc

#140  Postby twistor59 » Oct 09, 2011 6:41 pm

Teuton wrote:
twistor59 wrote:
Teuton wrote:
I'm sure it is mathematically very practical to model particles and strings as 0D or 1D objects, but the question is whether or not these are only mathematically idealized models, i.e. whether or not particles and strings are really 0-dimensional or 1-dimensional (if they exist).

Emphasis mine. You need to say exactly what you mean by "are".


It's the is/are of predication. "Particles are 0-dimensional" means "particles have the property of being 0-dimensional".

twistor59 wrote:
How would you determine if the statement was true or false ?


I don't know how the question could be decided experimentally, but there are conceptual a priori reasons against the view that 0D, 1D, and 2D things can adequately be called physical objects or substances rather than (geometrically ideal, abstracted) boundaries of those. And there are metaphysical/ontological a priori reasons for doubting or even denying that particles and strings can have less than 3 spatial dimensions.


But those conceptual reasons can't carry much weight because according to some formulations of the holographic principle, space may be essentially two dimensional and the 3rd dimension may not be fundamental. If space is two dimensional then objects which occupy it may be at most two dimensional.
A soul in tension that's learning to fly
Condition grounded but determined to try
Can't keep my eyes from the circling skies
Tongue-tied and twisted just an earthbound misfit, I
User avatar
twistor59
RS Donator
THREAD STARTER
 
Posts: 4966
Male

United Kingdom (uk)
Print view this post

PreviousNext

Return to Physics

Who is online

Users viewing this topic: No registered users and 1 guest