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Thread: Dumb Questions Reborn

  1. #1 Dumb Questions Reborn 
    Forum Radioactive Isotope zinjanthropos's Avatar
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    I missed this part when the forum was down. To get another chance to ask dumb questions has lifted me up above my melancholy. I had some time to think of some incredibly dumb stuff (for me at least) so I'll start anew with this one.....It has to do with wave/particle duality and anti-particles.

    Part 1: Do posi and anti particles actually need to collide in order to annihilate one another? I'm thinking that since they can behave as waves then contact as a particle is not necessary.

    Part 2: if I try to observe an annihilation event as in above scenario, will it be impossible to do so? I say this because to observe it, would not the wave function collapse? Just want to know if there's annihilation going on when I'm not looking.

    Hope these qualify as being dumb enough


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    Moderator Moderator Markus Hanke's Avatar
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    These questions aren't dumb, in fact they are actually pretty non-trivial. Firstly it needs to be noted that creation and annihilation processes are something for which you need the full framework of quantum field theory to describe them, as they involve changes in the numbers of particles ( standard quantum mechanics describes only how a given ensemble of a fixed number of particles evolves ).

    1. An annihilation event would involve the interaction of two quantum fields ( e.g. an electron and positron ), so yes, interaction is necessary. Whether you describe the entities involved as particles or waves is irrelevant, since these are just two aspects of the same underlying physical reality - being an excitation of the quantum field.

    2. Is there a reality if there is no observer ? In quantum physics, there is a concept called "counterfactual definiteness" ( CFD ); this means the ability to meaningfully speak of quantum systems having definite properties, even if they have not been measured. While there are different interpretations in existence, the current consensus tends towards the recognition that CFD is lacking in our world - that means that quantum systems have no fixed properties other than those we determine through a measurement process. So essentially, reality is what you measure, everything else is simply potential and probability. This is not just a fancy idea; there is empirical data pointing towards that being the case ( look up "Bell Inequalities" if you are interested - it turns out that those are violated in our world, so we have to abandon either realism or locality ). Do take note though that applying these ideas to quantum field theory is quite non-trivial, and I can't say I fully understand all implications myself.


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    Quote Originally Posted by Markus Hanke View Post
    These questions aren't dumb, in fact they are actually pretty non-trivial. Firstly it needs to be noted that creation and annihilation processes are something for which you need the full framework of quantum field theory to describe them, as they involve changes in the numbers of particles ( standard quantum mechanics describes only how a given ensemble of a fixed number of particles evolves ).

    1. An annihilation event would involve the interaction of two quantum fields ( e.g. an electron and positron ), so yes, interaction is necessary. Whether you describe the entities involved as particles or waves is irrelevant, since these are just two aspects of the same underlying physical reality - being an excitation of the quantum field.

    2. Is there a reality if there is no observer ? In quantum physics, there is a concept called "counterfactual definiteness" ( CFD ); this means the ability to meaningfully speak of quantum systems having definite properties, even if they have not been measured. While there are different interpretations in existence, the current consensus tends towards the recognition that CFD is lacking in our world - that means that quantum systems have no fixed properties other than those we determine through a measurement process. So essentially, reality is what you measure, everything else is simply potential and probability. This is not just a fancy idea; there is empirical data pointing towards that being the case ( look up "Bell Inequalities" if you are interested - it turns out that those are violated in our world, so we have to abandon either realism or locality ). Do take note though that applying these ideas to quantum field theory is quite non-trivial, and I can't say I fully understand all implications myself.
    I note you are admitting your lack of understanding of the detail("implications") in this but I also notice that you have introduced the concept of "realism" ("realism or locality") ,

    On a general note can I ask you whether this idea of "realism" (as part of the theory ,I am assuming) bears any relation to the question that keeps arising from some people as to whether ,for example spacetime is a real thing or simply a model? (personally, I have accepted the model "interpretation" and am quite happy with that)

    Does this model interpretation help us out in these "particle collision " and "unobserved vs real" scenarios, too?

    Without wishing to cringe (well ,to be obsequious), I know that ,even with your confessed shortcomings you will have an incomparably better insight into this question than I will ever have (provided only that I have been able to pose a clear question)
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    Quote Originally Posted by geordief View Post
    I note you are admitting your lack of understanding of the detail("implications") in this but I also notice that you have introduced the concept of "realism" ("realism or locality") ,
    My lack of understanding refers to aspects of quantum field theory, which is something I am still self-studying.
    Realism means that, when you perform a measurement, the property you measure was already present prior to the measurement process; in other words, it refers to the notion that it is meaningful to speak of quantum systems having definite properties, even if no one measures them. Essentially, it means that measurement is a passive process, which simply reveals something that already preexisted.

    The consensus among most physicists these days is that (local) realism does not apply to our universe.

    This doesn't really have anything to do with whether or not spacetime is "real", whatever that is actually meant to mean. I think it is best to think of spacetime as a mathematical model, which has shown excellent agreement with experiment and observation in the real world. This is true for all other concepts in physics, too.
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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Markus, such great answers. You are special and the forum is fortunate to have you around.

    OK, Enough of that. One thing that has always bothered me was, and I think it's related to your recent answers, is simply the wave function and what happens when I gaze upon the visible universe. My head cannot get around how the entire universe could exist in multiple (probalistic?) states or be everywhere at once when there is only one and I'm actually a part of it. I'm thinking that when I look heavenward, at the same time I can't see myself. Did the act of observing something mean the observer changed roles with the observed? Hope I'm making myself clear, I have trouble trying to make sense of what I hear on this subject.
    Last edited by zinjanthropos; July 2nd, 2017 at 07:34 AM.
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    Quote Originally Posted by zinjanthropos View Post
    My head cannot get around how the entire universe could exist in multiple (probalistic?) states or be everywhere at once
    Can your head get around the idea that the future exists in a way that is every bit as real as the present? Consider yourself sitting in front of a computer monitor at a given instant in time. You can't see the version of yourself that is one second into the future from that given instant in time. Yet if you wait one second, you'll see that you are still sitting in front of a computer monitor, and every bit as real as you were a second ago. The essential thing to realise is that the version of you in the present is no more real than the versions of you in the future or in the past. Now, consider a physics experiment involving the trajectory of an object. To process the results of the experiment, one uses mathematics to describe the trajectory as a superposition of the different versions of the object at all the different times. But nowhere does the mathematics make one version at a particular time more real than the versions from other times. The different versions at all times are equally real. Indeed, from a mathematical perspective, the notion of things being more real than other things makes no sense at all. Thus, the intuitive notion that the present is more real than the past or future cannot be mathematically described. In other words, if we accept that mathematics describes our reality, then we must accept that the past, present, and future are all on equal footing. The same can be said about the set of all possible distinct spacetimes that make up a multiverse.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Quote Originally Posted by KJW View Post

    Can your head get around the idea that the future exists in a way that is every bit as real as the present.
    How a universe can be everywhere at once when there is only one place it can be is what puzzles me. Maybe I shouldn't consider the universe as an object that can be observed. I can't see all of it at any time, so does it mean that what I see is particle and the unobserved portion a wave?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    I find this present/past /future delineation difficult to understand.

    Especially, how do we define (or experience?) the present?

    I don't expect GR to be applicable here but on a subjective (which is a valid viewpoint as it is truly objective on its own terms**) level we cannot pinpoint a region of the perceptual system in our physical mind that is actually "straddling" this present experience.

    It is more like a fiction that we create for ourselves so as to navigate the multiple "presents" that are going on together.

    For example ,our different senses are following different "film scores" and yet we stitch them together so that they seem to us to represent the same moment (the onmarching "present")

    If my understanding of the situation is correct(or in the right ball park area) ,I also wonder whether any practical consequences could follow or whether this is purely a philosophical area where we tie ourselves up in knots in an attempt to unravel what is an underlying very simple situation(a little "knowledge" actually being an impediment to a truer understanding)

    **I mean ,it is possible to consider our own individual mental apparatuses as mini/micro scientific experiments ,although we have to somehow abstract ourselves from the internal processes to do so.We have to "look at ourselves looking at the outside world"
    Last edited by geordief; July 7th, 2017 at 04:52 AM.
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    KJW
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    Quote Originally Posted by zinjanthropos View Post
    Quote Originally Posted by KJW View Post
    Can your head get around the idea that the future exists in a way that is every bit as real as the present.
    How a universe can be everywhere at once when there is only one place it can be is what puzzles me. Maybe I shouldn't consider the universe as an object that can be observed. I can't see all of it at any time, so does it mean that what I see is particle and the unobserved portion a wave?
    I'm not sure if I've interpreted your question in the same way as you intended, but my interpretation is about the multiverse where all the possible outcomes of an experiment are in superposition, and although only one outcome is observed, all of the possible outcomes are equally real. That is, all of the possible outcomes are occurring ostensibly at the same location in space and time, though they are at different locations in the multiverse itself. This is similar to the notion that the two different versions of yourself one second apart are ostensibly at the same location in space, though they are at different locations in spacetime.

    An alternative albeit similar interpretation is about the notion that a particle in the double-slit experiment travels through both slits. And the notion of a single-particle wavefunction is that the particle is simultaneously at all locations within the domain of the wavefunction. But in this case, one shouldn't regard the particle as being at multiple individual locations, as the wavefunction itself is the true nature of the particle, and that the notion of particles being at individual locations only occurs if individual locations are being measured for the presence of the particle.

    One point that needs to be made is that the position of an object has no meaning except in relation to other objects. Thus, it makes no true sense to speak of different points in the multiverse as being the same point in spacetime, or even to speak of different points in spacetime as being the same point in space. That is, where I speak of being ostensibly at the same location, there is an implicit regard to the context of the physical surroundings. Sometimes I say to people that you can't hammer a nail into space.
    Last edited by KJW; July 9th, 2017 at 12:08 PM.
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    Quote Originally Posted by geordief View Post
    I find this present/past /future delineation difficult to understand.

    Especially, how do we define (or experience?) the present?

    I don't expect GR to be applicable here but on a subjective (which is a valid viewpoint as it is truly objective on its own terms**) level we cannot pinpoint a region of the perceptual system in our physical mind that is actually "straddling" this present experience.

    It is more like a fiction that we create for ourselves so as to navigate the multiple "presents" that are going on together.

    For example ,our different senses are following different "film scores" and yet we stitch them together so that they seem to us to represent the same moment (the onmarching "present")

    If my understanding of the situation is correct(or in the right ball park area) ,I also wonder whether any practical consequences could follow or whether this is purely a philosophical area where we tie ourselves up in knots in an attempt to unravel what is an underlying very simple situation(a little "knowledge" actually being an impediment to a truer understanding)

    **I mean ,it is possible to consider our own individual mental apparatuses as mini/micro scientific experiments ,although we have to somehow abstract ourselves from the internal processes to do so.We have to "look at ourselves looking at the outside world"
    The question of why we perceive time differently to space is an interesting one. However, in classical relativity, objects are world-lines in spacetime (point-particle trajectories are one-dimensional curves). But why we experience a particular present at any given instant can be understood in terms of a version of the anthropic principle: We experience a given time because that is the time our brains are perceiving at that time. The same is true at all times even though we only experience a single time at any instant. Thus, although we experience single instants in time and even a continuous temporal ordering of events, there is no such thing as an objective present.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Forum Masters Degree Implicate Order's Avatar
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    Quote Originally Posted by zinjanthropos View Post
    How a universe can be everywhere at once when there is only one place it can be is what puzzles me. Maybe I shouldn't consider the universe as an object that can be observed. I can't see all of it at any time, so does it mean that what I see is particle and the unobserved portion a wave?
    Great to be back guys. Where else can you chew the fat about the Big Ideas :-)

    Viewed as a system the only real universal context that we can experience without projecting our assumptions is that which is made available within our light-cone (the hubble volume surrounding a single point in spacetime) .....or that which is causally connected. As participants, we need to consider our universe from 'inside out' as opposed to a universe from 'outside in'. Fortunately observers situated on this planet share a vast portion of their hubble volume with others and thus a shared reality. I share your concern with a viewpoint that treats the universe objectively as 'one place'. I err on the side of a viewpoint that allows for a multiverse, but as opposed to separate distinct realms with different physical laws, a multiverse arising from an array of different possible interpretations arising from perspectives taken from different points in space-time. To compare different perspectives we need to transform the complete system from one perspective to another (apply a phase shift from one 'universal state' to another). A superposition of states arises from the different perspectives taken from different vantages in spacetime, each equally valid, as they simply arise from system processes applicable within each hubble volume.
    Last edited by Implicate Order; July 11th, 2017 at 12:09 AM.
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    Quote Originally Posted by Implicate Order View Post
    Quote Originally Posted by zinjanthropos View Post
    How a universe can be everywhere at once when there is only one place it can be is what puzzles me. Maybe I shouldn't consider the universe as an object that can be observed. I can't see all of it at any time, so does it mean that what I see is particle and the unobserved portion a wave?
    Great to be back guys. Where else can you chew the fat about the Big Ideas :-)
    .
    I thought the 40 days in the outback was up long ago.As the great man said ,we were just killing time till you came back
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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Sat down the other night and listen to a TED talk given by Brian Greene. In it he went on about multiverses and extra dimensions. Personally I can't believe I actually got through reading The Elegant Universe one time awhile back. Seemed pretty heavy then, still does but I think I'm actually getting some of this stuff and that's a scary thought.

    Anyways he mentioned that our universe may be one of several billions and billions of universes and that occasionally ours is going to make contact with another. Now it would seem to me that if the numbers are true then perhaps occasionally's status should be elevated to likely always being in contact. If so then what would we see as evidence of it or exactly what should we look for?

    I also picture in my mind each universe surrounded by some sort of protective membrane but I'm in doubt whether this would be the case. So what would constitute a boundary between universes.........extra dimensions and shapes, fields of some sort, or what is the best current scientific hypothesis?
    All that belongs to human understanding, in this deep ignorance and obscurity, is to be skeptical, or at least cautious; and not to admit of any hypothesis, whatsoever; much less, of any which is supported by no appearance of probability...Hume
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    Quote Originally Posted by geordief View Post
    Especially, how do we define (or experience?) the present?
    You cannot experience anything but the present. Awareness always happens in the "now" - you can be aware of memories, or of future plans, but those are just mental objects that exist here and now. We do not have direct access to either the past or the future, so it is the faculty of awareness itself that defines the present.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by geordief View Post
    Especially, how do we define (or experience?) the present?
    You cannot experience anything but the present. Awareness always happens in the "now" - you can be aware of memories, or of future plans, but those are just mental objects that exist here and now. We do not have direct access to either the past or the future, so it is the faculty of awareness itself that defines the present.
    So ,is there a general consensus that ,as an objective physical reality the concept** of "presentness" has no validity?

    Can we go further (is it "further" ?) and say the concept of (absolute?) "objectiveness" also has no firm validity ?

    (was Lewis Carroll implying this when he made his famous comment through Alice about words and meanings -after all he was quite a noted mathematician/logician I seem to remember,and also a reactionary one wrt the evolution of physics at that time again if I remember well)
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    Philosophy ( of science ) isn't really my area of expertise, so I can't authoritatively answer this. In mathematical terms, "the present" is just a hypersurface of constant time, as measured by a given clock, and can be precisely defined. Actual measurements are a different story, since clocks have a finite resolution, and there is also the uncertainty relation to be considered.

    I am not really sure what you mean by "absolute objectiveness" - can you explain ?
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    Quote Originally Posted by Markus Hanke View Post

    I am not really sure what you mean by "absolute objectiveness" - can you explain ?
    Probably something of a strawman insofar as it is something that feels like it should exist but when examined more closely may not be able to be pinned down.

    But I think the general idea is (in philosophy which is not my area of expertise) that "reality" can be considered as either entirely (or fundamentally) based on our perceptive experience of it or that it exists independently of it.

    I only claim to be familiar with the question (as I have come across it) and not to be able to flesh out the arguments (since I have not seriously studied it and ,if I had would not be a good student either )

    Sorry not to be more help
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