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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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    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 08:34 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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    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 05:52 AM.
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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 01:08 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 01:09 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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    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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    Forum Radioactive Isotope zinjanthropos's Avatar
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    Let's try this one: Is there evidence to suggest our universe may be a combination of universes?
    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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    https://www.spaceanswers.com/news/bi...-a-multiverse/

    What about that? If there is any "contact" there would have to be "combination" even if only minimally (I would have thought)

    I think it is probably speculation but it is nice to "watch that space"
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    Quote Originally Posted by geordief View Post
    https://www.spaceanswers.com/news/bi...-a-multiverse/

    What about that? If there is any "contact" there would have to be "combination" even if only minimally (I would have thought)
    I kind of hope it is evidence. Bubbles seem to be the most popular way to depict multiverse. When you watch kids play with soap bubbles there's always some that collide, combine, share a common membrane for a moment and then boom, one bubble. Always wondered when that happens if the shared membrane gives way and we're left with a larger bubble because the remaining bubble all of sudden contains the innards of the other and expands to make room? Any bubble dynamics experts out there? Can it be used as an analogy* for our universe?

    Let's say each universe is a different size and for example a small one smacks into an extraordinarily large one. Perhaps the large bubble is barely affected when the shared boundary breaks between the two but wouldn't a smaller universe all but disappear while a lot more space opens up for its contents? Doesn't this seem like sperm meets egg, sheesh?**

    * Not advocating that universes actually behave like soap bubbles or that our universe is a bubble
    ** or that the universe is alive
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    Quote Originally Posted by zinjanthropos View Post
    Let's try this one: Is there evidence to suggest our universe may be a combination of universes?
    Whenever I advocate a multiverse, it will always be the multiverse of the many-worlds interpretation of quantum mechanics. Is there any evidence for the existence of such a multiverse? I regard the notion of quantum superposition itself as evidence for the existence of a multiverse. But quantum superposition only manifests itself at microscopic scale, and the Born rule itself provides the reason that the quantum multiverse is unobservable at macroscopic scale: Distinct macroscopic states are orthogonal and orthogonal states do not exhibit interference. That is, orthogonal states (whether macroscopic or microscopic) behave as if none of the other states exist.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Fascinating stuff. I completely agree with KJW. Through the years I've pieced together a picture of the Universe as a quantum structure that is absolute. From the Big Bang all the way to the End of Time; all things that could happen, has happened, and we just simply observe our way through it. I believe that's what we consider the "present".
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by zinjanthropos View Post
    Let's try this one: Is there evidence to suggest our universe may be a combination of universes?
    Whenever I advocate a multiverse, it will always be the multiverse of the many-worlds interpretation of quantum mechanics. Is there any evidence for the existence of such a multiverse? I regard the notion of quantum superposition itself as evidence for the existence of a multiverse. But quantum superposition only manifests itself at microscopic scale, and the Born rule itself provides the reason that the quantum multiverse is unobservable at macroscopic scale: Distinct macroscopic states are orthogonal and orthogonal states do not exhibit interference. That is, orthogonal states (whether macroscopic or microscopic) behave as if none of the other states exist.
    Lets see if I understand. When the particle is in superposition, each position (not sure what word to use there) is in or part of a different universe?

    Edit: woke up this morning wondering that if one quantum particle can be everywhere at once then could all that's observable in what we call the universe be just one particle. Or could each particle be its own universe and what we think is our universe is just a special place where all these universes can exist or be observed?
    Last edited by zinjanthropos; July 28th, 2017 at 09:00 AM.
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    Quote Originally Posted by zinjanthropos View Post
    Lets see if I understand. When the particle is in superposition, each position (not sure what word to use there) is in or part of a different universe?
    I'm tempted to say "yes" but it is more complicated than that. Any given state is a superposition of other states. Thus, we can't attribute a single state to a single world. When we say that a photon passes through both slits, this is distinct from the photon passing through either one slit or the other slit, even if we don't know which slit the photon passed through. A superposition of states is distinct from a simple mixture of states. Perhaps the closest analogy is to consider an audio waveform as a superposition of different single-time pulses. It is also a superposition of different single-frequency sinusoidal waveforms. But note that even a single single-time pulse is a superposition of different single-frequency sinusoidal waveforms, and a single single-frequency sinusoidal waveform is a superposition of different single-time pulses. And there are other ways to decompose an audio waveform as a superposition of orthogonal functions. Thus, not only can an arbitrarily oriented plane-polarised photon be regarded as a superposition of vertically and horizontally oriented plane-polarised states, but it can also be regarded as a superposition of left and right circularly-polarised states.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    KJ... appreciate your input.

    in this last post are you intimating a particle is like an array of waves and with each wave there is a frequency, with which we need to tune into to observe?
    Last edited by zinjanthropos; July 28th, 2017 at 10:57 PM.
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    Here's my dumb question, but again it may not be so dumb. It could even be a GUT, in some analogous way.
    Take a deep breath.

    Is the universe made of chocolate!?

    Matter is chocolate. There are 2 types of chocolate, light (milk) and dark.
    Milk chocolate is light matter. Dark chocolate is dark matter. Light and dark energy are required for their production. Obviously, all energy on earth comes from the sun and some of it is locked into plants which humans use to commercially make chocolate.

    What is laughingly described as the universe is a chocolate sponge cake. The Milky Way galaxy is actually a milk chocolate whirl. The solar system is a milk chocolate wafer. The comets are granules of escaped sugar.
    Very occasionally the milk chocolate wafer moves into an area of dark chocolate (dark matter). The comets craving for the milk hurtle towards the sun and can hit the earth causing mass extinctions.

    Chocolate sauces.
    https://io9.gizmodo.com/the-universe...lat-1528303752

    https://en.wikipedia.org/wiki/Dark_M..._the_Dinosaurs
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    I'll expand it to what lies outside the universe.
    The Universe lies within a Chocolate Hazel Nutshell.

    The Universe in a Nutshell - Stephen Hawking
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    Yes off topic but please allow me this counter chocolate response .....

    I guess one could say no to chocolate universe and yes to one made of shit. Dark crap (mammals) and light (white) for birds. Does bring black holes into play. The universe is situated at the end of a digestive tract just beyond the BH event horizon. Matter at this point is solid, liquid or gas. New universes emerge from the BH every day only to disappear in a swirling vortex while gravity pulls others towards the boundary only to be swallowed up, recycled and reborn.
    Last edited by zinjanthropos; August 1st, 2017 at 12:07 PM.
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    Back to more on topic questions....

    Im a little confused as to whether a quantum particle exists in more than one place or if it is just the probability that does ?
    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 zinjanthropos View Post
    Does bring black holes into play. The universe is situated at the end of a digestive tract just beyond the BH event horizon. Matter at this point is solid, liquid or gas. New universes emerge from the BH every day only to disappear in a swirling vortex while gravity pulls others towards the boundary only to be swallowed up, recycled and reborn.
    According to this theory. baby universes are born within black holes as a by product of chocolate manufacture by the Great Chocolateer.
    A black hole should indeed look like this.

    Black Hole Chocolate Cheesecake - Bake or Break
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    Quote Originally Posted by ox View Post
    Quote Originally Posted by zinjanthropos View Post
    Does bring black holes into play. The universe is situated at the end of a digestive tract just beyond the BH event horizon. Matter at this point is solid, liquid or gas. New universes emerge from the BH every day only to disappear in a swirling vortex while gravity pulls others towards the boundary only to be swallowed up, recycled and reborn.
    According to this theory. baby universes are born within black holes as a by product of chocolate manufacture by the Great Chocolateer.
    A black hole should indeed look like this.

    Black Hole Chocolate Cheesecake - Bake or Break
    I think you are making the dark art of chocolate making out to be simpler than it is.

    Clearly this is a recipe for failure as a chocolate cheesecake that falls in on itself cannot be called a true cheesecake.(although a chocolate soufflee may)
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    Quote Originally Posted by zinjanthropos View Post
    Back to more on topic questions....

    Im a little confused as to whether a quantum particle exists in more than one place or if it is just the probability that does ?
    "Congratulations to Drs. S. Haroche and D. Wineland for winning the Nobel Prize in Physics.

    They proved the correctness of the bizarre properties of quantum mechanics, i.e. that electrons can be two places at the same time."


    I haven’t met the post quota. I’m not sure what it is, but I can’t post links yet.

    I’ll send you a link of a layman’s summary at SciVillage.

    Damn, this site is slow. It takes forever to load.
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    What if Dark Matter that we infer around Visible Matter is nothing but the manifestation of a macro-sized probability function of the Visible Matter and the gravity leaks into our universe from close probabilities or realities overlapping our own universe? How's that for a dumb question? Epic, huh?
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    Quote Originally Posted by Metallicbeing View Post
    What if Dark Matter that we infer around Visible Matter is nothing but the manifestation of a macro-sized probability function of the Visible Matter and the gravity leaks into our universe from close probabilities or realities overlapping our own universe? How's that for a dumb question? Epic, huh?
    I have basically thought about this myself.

    But i see dark matter as regular matter before it has enough of itself to exist. Think about a car before it is put together. The smallest part may not be the smallest part. Most matter may be undetectable and not responding to anything. Would be interesting. We float around in a scrapheap, with bodies made from the best parts of the universe, dark matter being the scrapheap.

    Again... Just an idea.. and please correct me..
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    A topper to the Dark Matter question is what I also think about Dark Energy. What if our universe is a Black Hole from another universe (much more energetic than ours) and when that Black Hole feeds in that universe, it creates more space-time in this universe? Even more Epic-ness, huh?
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    We can always speculate about where the Dark Matter (85% of matter) came from. It's so dark it doesn't reflect light. This could be because the analogous dark syrupy chocolate absorbs all light.
    We could also live within a black hole, which in turn lies within another (Russian doll multiverse).

    Are We Living in a Black Hole?

    Understanding the geometrical shape of the universe could provide a clue. My money will go on a chocolate Easter egg.
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    If space is infinite then why or how can it expand? I'm thinking expansion of infinite space would be, if I'm allowed to say it, more likely to occur in a curved universe. I just can't visualize expansion for an endlessly flat universe so I figure this common layperson is missing something(s) as usual.
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    Just wondering if you've read Lawrence Krauss on this. A Universe From Nothing.
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    Quote Originally Posted by zinjanthropos View Post
    If space is infinite then why or how can it expand? I'm thinking expansion of infinite space would be, if I'm allowed to say it, more likely to occur in a curved universe. I just can't visualize expansion for an endlessly flat universe so I figure this common layperson is missing something(s) as usual.
    (don't quote me on this) .but are you sure you are using "curved" vs "flat" in the way it is normally used in this context?

    I don't think it is meant to refer to the shape of the universe as a whole but perhaps you do understand these terms better than I do.

    On the face of it I think most would disagree with your implication that an infinite universe cannot expand (but again perhaps I am misunderstanding you -and the subject as a whole)
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    Quote Originally Posted by geordief View Post
    Quote Originally Posted by zinjanthropos View Post
    If space is infinite then why or how can it expand? I'm thinking expansion of infinite space would be, if I'm allowed to say it, more likely to occur in a curved universe. I just can't visualize expansion for an endlessly flat universe so I figure this common layperson is missing something(s) as usual.
    (don't quote me on this) .but are you sure you are using "curved" vs "flat" in the way it is normally used in this context?

    I don't think it is meant to refer to the shape of the universe as a whole but perhaps you do understand these terms better than I do.

    On the face of it I think most would disagree with your implication that an infinite universe cannot expand (but again perhaps I am misunderstanding you -and the subject as a whole)
    Not implying anything and I don't know terms that well. However I think maybe I should have said closed instead of curved. Regardless I'll reword the question to read ' how do you add to something thats infinite in size? Not even sure if that sounds right.
    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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    Well "infinite" (to my mind ) is more a failure to measure than an indication of how big something actually is.

    So I can't see a problem in this size changing ,since we cannot quantify the difference anyway.

    I think ,though you might need an interlocutor who can see the wood for the trees rather than my pettifoggery and nit picking
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    If the universe is sufficiently larger than we thought, then the "Flat" measurement previously taken can be a small part of a much larger shallow arc; which of course, means the Universe is curved (Dr. Michio Kaku).
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    Quote Originally Posted by Metallicbeing View Post
    If the universe is sufficiently larger than we thought, then the "Flat" measurement previously taken can be a small part of a much larger shallow arc; which of course, means the Universe is curved (Dr. Michio Kaku).
    Is that in the same way that the Earth (or any ball) is flat in the immediate vicinity of the observer but is curved when larger measurements are taken ?

    Is MK just extrapolating from this (with no reason to know whether or not he might be right) ?

    Would the size of the universe have to be hugely greater than that of the observable universe for this to be possible?

    And no way to show if was true?
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    Quote Originally Posted by Zwolver View Post
    Quote Originally Posted by Metallicbeing View Post
    What if Dark Matter that we infer around Visible Matter is nothing but the manifestation of a macro-sized probability function of the Visible Matter and the gravity leaks into our universe from close probabilities or realities overlapping our own universe? How's that for a dumb question? Epic, huh?
    I have basically thought about this myself.

    But i see dark matter as regular matter before it has enough of itself to exist. Think about a car before it is put together. The smallest part may not be the smallest part. Most matter may be undetectable and not responding to anything. Would be interesting. We float around in a scrapheap, with bodies made from the best parts of the universe, dark matter being the scrapheap.

    Again... Just an idea.. and please correct me..
    I think this is like saying that at one time there was nothing but dark matter and regular matter arose out of it through some process. Whether that process still occurs or if it even exists might be worth a look. I wonder if dark matter holds a secret that if discovered will bring us closer to knowing what happened in the first few nanoseconds of the BB?
    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
    Quote Originally Posted by Metallicbeing View Post
    If the universe is sufficiently larger than we thought, then the "Flat" measurement previously taken can be a small part of a much larger shallow arc; which of course, means the Universe is curved (Dr. Michio Kaku).
    Is that in the same way that the Earth (or any ball) is flat in the immediate vicinity of the observer but is curved when larger measurements are taken ?

    Is MK just extrapolating from this (with no reason to know whether or not he might be right) ?

    Would the size of the universe have to be hugely greater than that of the observable universe for this to be possible?

    And no way to show if was true?
    I believe MK was talking about distant light from the far reaches of our universe that may not have reached us yet and if the universe was sufficiently larger than we expected then the universe may turn out to be curved; not flat. Speculation for sure, but not too far out of bounds. We continually invent better telescopes to see further into space. Maybe this story isn't finished.
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    Quote Originally Posted by zinjanthropos View Post
    Quote Originally Posted by Zwolver View Post
    Quote Originally Posted by Metallicbeing View Post
    What if Dark Matter that we infer around Visible Matter is nothing but the manifestation of a macro-sized probability function of the Visible Matter and the gravity leaks into our universe from close probabilities or realities overlapping our own universe? How's that for a dumb question? Epic, huh?
    I have basically thought about this myself.

    But i see dark matter as regular matter before it has enough of itself to exist. Think about a car before it is put together. The smallest part may not be the smallest part. Most matter may be undetectable and not responding to anything. Would be interesting. We float around in a scrapheap, with bodies made from the best parts of the universe, dark matter being the scrapheap.

    Again... Just an idea.. and please correct me..
    I think this is like saying that at one time there was nothing but dark matter and regular matter arose out of it through some process. Whether that process still occurs or if it even exists might be worth a look. I wonder if dark matter holds a secret that if discovered will bring us closer to knowing what happened in the first few nanoseconds of the BB?
    I'm sure I watched a YouTube video suggesting there may have been Dark Stars before there were visible ones and they may have been responsible for the formation of the first Black Holes. If I find it, ill post it.

    https://www.youtube.com/watch?v=1g64YJPYYWk
    Last edited by Metallicbeing; August 5th, 2017 at 07:36 PM. Reason: Add Link
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    Quote Originally Posted by Metallicbeing View Post
    Quote Originally Posted by zinjanthropos View Post
    Quote Originally Posted by Zwolver View Post
    Quote Originally Posted by Metallicbeing View Post
    What if Dark Matter that we infer around Visible Matter is nothing but the manifestation of a macro-sized probability function of the Visible Matter and the gravity leaks into our universe from close probabilities or realities overlapping our own universe? How's that for a dumb question? Epic, huh?
    I have basically thought about this myself.

    But i see dark matter as regular matter before it has enough of itself to exist. Think about a car before it is put together. The smallest part may not be the smallest part. Most matter may be undetectable and not responding to anything. Would be interesting. We float around in a scrapheap, with bodies made from the best parts of the universe, dark matter being the scrapheap.

    Again... Just an idea.. and please correct me..
    I think this is like saying that at one time there was nothing but dark matter and regular matter arose out of it through some process. Whether that process still occurs or if it even exists might be worth a look. I wonder if dark matter holds a secret that if discovered will bring us closer to knowing what happened in the first few nanoseconds of the BB?
    I'm sure I watched a YouTube video suggesting there may have been Dark Stars before there were visible ones and they may have been responsible for the formation of the first Black Holes. If I find it, ill post it.

    https://www.youtube.com/watch?v=1g64YJPYYWk
    Dark stars? Something totally different to dark matter.

    Dark stars being formed into black holes makes sense. What would be the difference between a dark star and a black hole anyway?

    Several comments about the video.. No like/dislike visible, no comments, only 450 views... Doesn't seem 100% credible though...
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    Can some one tell me the difference between each and if they attract or repel one another (pos vs pos, pos vs neg, neg vs neg):

    1. Positive and negatively charged particles
    2. Positive and negative matter
    3. Positive and negative energy
    4. Positive and negative gravity
    5. Positive and negative mass
    Last edited by zinjanthropos; September 12th, 2017 at 01:37 PM.
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    Quote Originally Posted by zinjanthropos View Post
    Can some one tell me the difference between each and if they attract or repel one another (pos vs pos, pos vs neg, neg vs neg):

    1. Positive and negatively charged particles
    2. Positive and negative matter
    3. Positive and negative energy
    4. Positive and negative gravity
    You left out pos vs neg mass (It is in the news) .
    Maybe you thought positive matter covered that.

    But apart from that I can't help.
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    Quote Originally Posted by geordief View Post
    Quote Originally Posted by zinjanthropos View Post
    Can some one tell me the difference between each and if they attract or repel one another (pos vs pos, pos vs neg, neg vs neg):

    1. Positive and negatively charged particles
    2. Positive and negative matter
    3. Positive and negative energy
    4. Positive and negative gravity
    5. Positive and negative mass

    You left out pos vs neg mass (It is in the news) .
    Maybe you thought positive matter covered that.

    But apart from that I can't help.
    I added it but I think 5 is enough. I was thinking positive and negative time and dimensions too. I wonder how many I missed?
    Last edited by zinjanthropos; September 12th, 2017 at 01:50 PM.
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    Quote Originally Posted by KJW View Post
    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.
    KJW said: “You can't see the version of yourself that is one second into the future from that given instant in time”.

    What differentiates the version that exists one second into the future from the version existing during “that given instant”? I suppose the answer has something to do with what you mean by “an instant in time”. Maybe whatever you think distinguishes one instant from another will help me understand what differentiates each “version”. [I don’t know if you remember, but you and I have had our differences when it comes to the notion that all events (past, present, and future) have equal footing; Markus advised me to persevere in trying to understand even if it seems to “not make any sense” to me. I decided to take his advice, but I never got the chance to further our previous discussions because the forum went down the gutter].
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    Probably been asked before.....What's the difference between a quantum particle and the vibrating string of string theory? I'm thinking a quantum particle would be made up of these strings if the theory is correct but I suspect it's way more complicated than that and I'm wrong.
    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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    Ok....time for a new 'questions from a dummy' segment: Is there any idea/evidence to suggest what classification of star it was that Supernova'd to produce our solar system? I mean we can spot remnants from other past exploding stars plus the fact that I am stardust as they say, leads me to think that even myself or my own composition is evidence of some type of star at least.
    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 Vexspits View Post
    Quote Originally Posted by KJW View Post
    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.
    KJW said: “You can't see the version of yourself that is one second into the future from that given instant in time”.

    What differentiates the version that exists one second into the future from the version existing during “that given instant”? I suppose the answer has something to do with what you mean by “an instant in time”. Maybe whatever you think distinguishes one instant from another will help me understand what differentiates each “version”.
    Oh, I see I neglected to answer this, and considering it's a topic I'm currently discussing in another thread, I should answer now.

    Four-dimensional spacetime can be regarded as a stack of three-dimensional spatial slices, each slice being an instance in time. In one slice is a person that is perceiving the nearby objects within that slice. One such nearby object might be a clock that is displaying the time corresponding to that slice. The person perceiving the clock will have a brain-state that corresponds to the perception of the displayed time. For the future slice, the future version of the person is perceiving the future version of the clock which is displaying the future time. The brain-state of the future version of the person corresponds to the perception of the displayed future time, as well as the memory of past displayed times. Our memory of past times provides us with the perception of the continuous passage of time (although we might also perceive the passage of time directly in a way similar to the perception of motion). Note that each slice has a version of the person perceiving the corresponding time of that slice, but no slice is distinguished from the other slices in a way that would make the present a special time in contrast to other times.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post
    Four-dimensional spacetime can be regarded as a stack of three-dimensional spatial slices, each slice being an instance in time. In one slice is a person that is perceiving the nearby objects within that slice. One such nearby object might be a clock that is displaying the time corresponding to that slice. The person perceiving the clock will have a brain-state that corresponds to the perception of the displayed time. For the future slice, the future version of the person is perceiving the future version of the clock which is displaying the future time. The brain-state of the future version of the person corresponds to the perception of the displayed future time, as well as the memory of past displayed times. Our memory of past times provides us with the perception of the continuous passage of time (although we might also perceive the passage of time directly in a way similar to the perception of motion). Note that each slice has a version of the person perceiving the corresponding time of that slice, but no slice is distinguished from the other slices in a way that would make the present a special time in contrast to other times.
    So all of the physical attributes (brain states, available sensory input etc) of any particular version are part of what makes each slice unique; effectively part of what defines a given time (slice). Would that be fair to say?
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    Quote Originally Posted by Vexspits View Post
    So all of the physical attributes (brain states, available sensory input etc) of any particular version are part of what makes each slice unique; effectively part of what defines a given time (slice). Would that be fair to say?
    Yes, but bear in mind that the physical world is also in a constant state of change. Also, as we get older, we become a little bit more decrepit.

    One thing worth noting is that if the entire universe at time 2 is identical to the entire universe at earlier time 1, then after time 2, there would be no memory of anything that occurred between times 1 and 2.
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Vexspits View Post
    So all of the physical attributes (brain states, available sensory input etc) of any particular version are part of what makes each slice unique; effectively part of what defines a given time (slice). Would that be fair to say?
    Yes, but bear in mind that the physical world is also in a constant state of change. Also, as we get older, we become a little bit more decrepit.

    One thing worth noting is that if the entire universe at time 2 is identical to the entire universe at earlier time 1, then after time 2, there would be no memory of anything that occurred between times 1 and 2.
    So far so good: nothing controversial about any of this. In fact, to me at least, it all seems self evident: I need not—to paraphrase you—“wrap my head around” any of what you’ve said in that last post. This brings us to what I can’t wrap it around: the co-existence of slices. It’s not that I don’t understand the metaphors (like the one Markus often uses: the pages of a book). What I don’t understand is why all the slices need co-exist.

    Everything you’ve said about the defining characteristics of a given slice would be true whether or not the slices co-existed. So it seems to be a difference that makes no difference. We both agreed, the defining characteristics of a slice are made up of a list of qualities such as brain states, available sensory inputs, and a whole host of other physical characteristics; and none of that is any less true even if that state of affairs (the one that defines a past slice) no longer exists.

    Why can’t we perceive future events? Isn’t the simplest explanation that the characteristics which will someday define them, simply don’t exist: Meaning: they simply aren’t there to produce any effects or to be themselves affected?

    On what empirical grounds do we justify the existence of future events? The philosopher Milič Čapek:

    "If we continue to postulate it, then we face the following dilemma: either to believe in their observability, which would contradict relativity; or to admit their intrinsic unobservability, but still insist on their existence; this would contradict the most elementary rules of scientific methodology. It is far simpler and sounder to place the unobservable future events into the same category as phlogiston, caloricum, mechanical ether, and other discredited…fictions".

    Let me be clear. I am not dismissing the possibility. When I first came to this forum, I would have written-off as patently absurd the idea that all events co-exist. But after conversations with Strange, Markus, and yourself, I’ve come to realize that the intuitive mental constructs drawn from our perceptions can't always be trusted. So the question, again, is about why future events “musts needs” exist (a quote of yours from a long lost thread on this forum). Aren’t the accurate predictions about “what clocks and rulers measure” satisfactory without all these claims about past, present, and future events co-existing?
    Last edited by Vexspits; March 18th, 2018 at 04:20 PM.
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    Quote Originally Posted by Vexspits View Post
    So far so good: nothing controversial about any of this. In fact, to me at least, it all seems self evident: I need not—to paraphrase you—“wrap my head around” any of what you’ve said in that last post.
    Let's be clear about what it is that one needs to wrap one's head around. Using the book analogy, there is no page representing the present that is distinguished from the other pages. In particular, there is no one reading the book. But in spite of that, we perceive reality as if there is a present that is distinguished from both the past and future times. Also, we perceive history in a definite order, with the past being remembered and the future being unknown. What one needs to get one's head around is how a physical reality that does not distinguish any particular time as the present appears to select a particular time to be distinguished as the present, with the passage of time presented in neat chronological order.


    Quote Originally Posted by Vexspits View Post
    What I don’t understand is why all the slices need co-exist.
    The existence of spacetime is demanded by the relativity of simultaneity. Two observers who are in motion relativity to each other differ in what they regard as the present. Using the book analogy, the book of one of the observers cannot be used by the other observer as each page of one book cuts across all the pages of the other book. So each of the observers need their own book. In other words, if only the present time of one of the observers physically exist, then both the past and future times of the other observer must physically exist. And since the principle of relativity demands that all observers are on equal footing irrespective of their motion, it must be concluded that the past and future times physically exist for all observers.


    Quote Originally Posted by Vexspits View Post
    Why can’t we perceive future events?
    I don't have a definite answer to this question. I strongly suspect that it is due to the second law of thermodynamics which imposes an arrow of time such that we remember the time when the entropy is lower but have no knowledge of the time when the entropy is higher. It would seem that there is only one past that leads to a given present and we remember that, and that a given present leads to many futures and we cannot know which.

    That the future time already exists is evidenced by the delayed choice quantum eraser experiment in which outcomes appear to be the result of choices that are made in the future. Without invoking any communication from the future or any communication associated with the entanglement, the experimental result can be explained by considering the superposition of alternative spacetimes. Each of the alternative spacetimes contain both the particular experimental result and the future choice that produced that experimental result, with the temporal order of those events being unimportant, the correlation existing because they belong to the same spacetime.
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    Quote Originally Posted by KJW View Post
    The existence of spacetime is demanded by the relativity of simultaneity. Two observers who are in motion relativity to each other differ in what they regard as the present. Using the book analogy, the book of one of the observers cannot be used by the other observer as each page of one book cuts across all the pages of the other book. So each of the observers need their own book. In other words, if only the present time of one of the observers physically exist, then both the past and future times of the other observer must physically exist. And since the principle of relativity demands that all observers are on equal footing irrespective of their motion, it must be concluded that the past and future times physically exist for all observers.
    I think this is the key stumbling block for me. Clearly I don’t understand the relativity of simultaneity, since I still can’t see how it necessitates the co-existence of all events (past, present, and future). Perhaps if I lay out my description of it, you can explain to me where I’m going wrong. Alright, here we go: Two events can be deemed simultaneous by one observer while being deemed to occur successively by another for the following reasons: Because the two observers’ motion with respect to the two events might be different and because the sensory input related to those events is encoded on optical pulses that travel at a finite speed. This means the co-existing occurrence of two events in no way ensures that the encoded data pertaining to each event will strike the retina of a given observer at the same time, triggering a signature P3 wave of “conscious access” in his or her brain. Is this wrong? Or is there more to it than that? What am I missing?
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    Quote Originally Posted by Vexspits View Post
    Quote Originally Posted by KJW View Post
    The existence of spacetime is demanded by the relativity of simultaneity. Two observers who are in motion relativity to each other differ in what they regard as the present. Using the book analogy, the book of one of the observers cannot be used by the other observer as each page of one book cuts across all the pages of the other book. So each of the observers need their own book. In other words, if only the present time of one of the observers physically exist, then both the past and future times of the other observer must physically exist. And since the principle of relativity demands that all observers are on equal footing irrespective of their motion, it must be concluded that the past and future times physically exist for all observers.
    I think this is the key stumbling block for me. Clearly I don’t understand the relativity of simultaneity, since I still can’t see how it necessitates the co-existence of all events (past, present, and future). Perhaps if I lay out my description of it, you can explain to me where I’m going wrong. Alright, here we go: Two events can be deemed simultaneous by one observer while being deemed to occur successively by another for the following reasons: Because the two observers’ motion with respect to the two events might be different and because the sensory input related to those events is encoded on optical pulses that travel at a finite speed. This means the co-existing occurrence of two events in no way ensures that the encoded data pertaining to each event will strike the retina of a given observer at the same time, triggering a signature P3 wave of “conscious access” in his or her brain. Is this wrong? Or is there more to it than that? What am I missing?
    If you omit the notion of perception and consider only the physics of transmitting pulses of light and subsequently receiving reflections of those pulses of light from mirrors at given locations, then understanding the relativity of simultaneity will be much easier. In physics, an observer does not mean a person, but can be simply any detection device. And because the detection device is unspecified, it can be regarded as an ideal detection device. To define the "present" for a given observer at a given time t, the observer transmits a short pulse of light at time t–x/c towards a mirror at distance x from the observer, and receives the reflected pulse from the mirror at time t+x/c. The light pulse strikes the mirror and reflects from it at time t with respect to the observer. In other words, the light pulse reflects from the mirror at the same time as halfway between the times that the light pulse was transmitted and received. Suppose there is a second observer moving at velocity v relative to the first observer. This second observer meets the first observer at time t. This second observer performs the same experiment as the first observer (transmitting a short pulse of light at time t–x/c towards a mirror at distance x and receiving the reflected pulse from the mirror at time t+x/c). The question to be considered is how the time the first observer's light pulse reflects from his mirror compares to the time the second observer's light pulse reflects from his mirror, noting that the time t that is considered to be the "present" is the same for both observers (because this is the halfway time for both observers, and also the time the two observers met).
    Last edited by KJW; March 24th, 2018 at 03:55 PM.
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    Quote Originally Posted by KJW View Post

    If you omit the notion of perception and consider only the physics of transmitting pulses of light and subsequently receiving reflections of those pulses of light from mirrors at given locations, then understanding the relativity of simultaneity will be much easier. In physics, an observer does not mean a person, but can be simply any detection device. And because the detection device is unspecified, it can be regarded as an ideal detection device. To define the "present" for a given observer at a given time t, the observer transmits a short pulse of light at time t–x/c towards a mirror at distance x from the observer, and receives the reflected pulse from the mirror at time t+x/c. The light pulse strikes the mirror and reflects from it at time t with respect to the observer. In other words, the light pulse reflects from the mirror at the same time as halfway between the times that the light pulse was transmitted and received. Suppose there is a second observer moving at velocity v relative to the first observer. This second observer meets the first observer at time t. This second observer performs the same experiment as the first observer (transmitting a short pulse of light at time t–x/c towards a mirror at distance x and receiving the reflected pulse from the mirror at time t+x/c). The question to be considered is how the time the first observer's light pulse reflects from his mirror compares to the time the second observer's light pulse reflects from his mirror, noting that the time t that is considered to be the "present" is the same for both observers (because this is the halfway time for both observers, and also the time the two observers met).
    Hope I am not just muddying the water ,but which observer/detector decides what the spatial distance x is? It is not the same x for both detectors is it? (well it is when they meet,I think I see that.But only at that point)

    I formatted your post in one part...
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    Quote Originally Posted by geordief View Post
    Hope I am not just muddying the water ,but which observer/detector decides what the spatial distance x is? It is not the same x for both detectors is it? (well it is when they meet,I think I see that.But only at that point)
    During the writing of my post, I realised that what I was saying was ambiguous. However, I'm not expecting anyone to do any actual maths... I'm certainly not intending to do any. My aim was to describe the general approach as simple as I thought possible without diagrams. Anyway, the intention is that each observer performs the experiment identically in their own frame of reference. The distance x is numerically the same for both observers and is the distance in each observer's frame of reference. This implies that each observer has their own mirror. Perhaps I should have just referred to the Wikipedia article on the relativity of simultaneity.
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by geordief View Post
    Hope I am not just muddying the water ,but which observer/detector decides what the spatial distance x is? It is not the same x for both detectors is it? (well it is when they meet,I think I see that.But only at that point)
    During the writing of my post, I realised that what I was saying was ambiguous. However, I'm not expecting anyone to do any actual maths... I'm certainly not intending to do any. My aim was to describe the general approach as simple as I thought possible without diagrams. Anyway, the intention is that each observer performs the experiment identically in their own frame of reference. The distance x is numerically the same for both observers and is the distance in each observer's frame of reference. This implies that each observer has their own mirror.
    Yes I briefly did a double take here, but quickly concluded the second observer had his own mirror co-moving with him. The only remaining question about your particular example I have is: Were observers 1 & 2 co-terminus when they transmitted their respective light pulses? I suspect so, but your parenthetical statement in post # 61, "because this is the halfway time for both observers, and also the time the two observers met", led me to believe otherwise.

    In any case: Is the main thrust that a comparison between the intervals measured by each observer [which they use to assign a time, tx, to the event of their respective pulses being reflected] differ?
    Last edited by Vexspits; March 25th, 2018 at 08:26 PM.
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    Quote Originally Posted by Vexspits View Post
    Yes I briefly did a double take here, but quickly concluded the second observer had his own mirror co-moving with him. The only remaining question about your particular example I have is: Were observers 1 & 2 co-terminus when they transmitted their respective light pulses? I suspect so, but your parenthetical statement in post # 61, "because this is the halfway time for both observers, and also the time the two observers met", led me to believe otherwise.

    In any case: Is the main thrust that a comparison between the intervals measured by each observer [which they use to assign a time, tx, to the event of their respective pulses being reflected] differ?
    The two observers meet at the halfway time for both observers. For each observer, the light pulse reflects from a mirror at the same time as halfway between the transmission and reception of the light pulse. The halfway time for each observer is at the same time as the halfway time for the other observer. Therefore, one might expect that the light pulse reflects from the mirror for each observer at the same time also, but this is not the case. The notion of the "present", like other things in relativity, is dependent on the observer.
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    Again hope I am not sidetracking but somewhere recently (perhaps in this thread?) it was said that there is no mathematical way to model the present.

    Yet we seem to be accepting that 2 observers ,moving relative to one another have different judgements of what is the present.

    So there does seem to be a mathematical definition for each observer's "present". and it seems to be based on the setup with shining a light at a distant object and "harvesting" the reflection.

    I still (obtusely?stupidly) don't see how this defines the particular "present".

    Is it just a way of co-ordinating the timeline of any particular observer with that of the distant object in a predictable way?

    Is that the gist of KJW's link
    https://en.wikipedia.org/wiki/Relati...f_simultaneity

    Forget "the present" and hang everything around the simplest definition of simultaneity between two separated objects?
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    Quote Originally Posted by geordief View Post
    Again hope I am not sidetracking but somewhere recently (perhaps in this thread?) it was said that there is no mathematical way to model the present.

    Yet we seem to be accepting that 2 observers ,moving relative to one another have different judgements of what is the present.

    So there does seem to be a mathematical definition for each observer's "present". and it seems to be based on the setup with shining a light at a distant object and "harvesting" the reflection.

    I still (obtusely?stupidly) don't see how this defines the particular "present".

    Is it just a way of co-ordinating the timeline of any particular observer with that of the distant object in a predictable way?

    Is that the gist of KJW's link
    https://en.wikipedia.org/wiki/Relati...f_simultaneity

    Forget "the present" and hang everything around the simplest definition of simultaneity between two separated objects?
    I have to admit, over the years I’ve sifted through numerous depictions and never have I come across this precise example, or anything worded in this particular way. I seem to be getting bogged down by it. So I’ll try another tactic. From the wikki page KJW linked us to:“If one reference frame is assigned precisely the same time to two events that are at different points in space, a reference frame that is moving relative to the first will generally assign different times to the two events….” So from this we might say: In one reference frame the two events that are at different points in space are part of a particular present, and yet those same two events in another reference frame are not—one is in the past relative to the other. So I think (fingers crossed) this is the basic point he is trying to make about how the labels “past”, “present”, and “future” are arbitrarily assigned to the events by the respective observers.
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    Quote Originally Posted by Vexspits View Post

    I have to admit, over the years I’ve sifted through numerous depictions and never have I come across this precise example, or anything worded in this particular way. I seem to be getting bogged down by it. So I’ll try another tactic. From the wikki page KJW linked us to:“If one reference frame is assigned precisely the same time to two events that are at different points in space, a reference frame that is moving relative to the first will generally assign different times to the two events….” So from this we might say: In one reference frame the two events that are at different points in space are part of a particular present, and yet those same two events in another reference frame are not—one is in the past relative to the other. So I think (fingers crossed) this is the basic point he is trying to make about how the labels “past”, “present”, and “future” are arbitrarily assigned to the events by the respective observers.
    I think you got it. That is my understanding too. It is a very,very basic point .

    As an example, If we look out to the stars and happen to see two events in the sky that occur within ,say I day of each other (maybe 2 unrelated supernovae) we can bet our bottom dollar that someone on a far distant planet**(or just a recording machine on a far distant planet) will ,if it sees the same 2 supernovae see them in the reverse order to ourselves.

    And another observer on a different far distant planet will quite likely see the 2 supernovae in the same order we did with probably a different time separation.

    ** well ,unless that planet is improbably more or less stationary wrt ourselves perhaps.Then they would (I think) see the events in the same order.
    Last edited by geordief; March 26th, 2018 at 12:20 PM.
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    Quote Originally Posted by geordief View Post
    Quote Originally Posted by Vexspits View Post

    I have to admit, over the years I’ve sifted through numerous depictions and never have I come across this precise example, or anything worded in this particular way. I seem to be getting bogged down by it. So I’ll try another tactic. From the wikki page KJW linked us to:“If one reference frame is assigned precisely the same time to two events that are at different points in space, a reference frame that is moving relative to the first will generally assign different times to the two events….” So from this we might say: In one reference frame the two events that are at different points in space are part of a particular present, and yet those same two events in another reference frame are not—one is in the past relative to the other. So I think (fingers crossed) this is the basic point he is trying to make about how the labels “past”, “present”, and “future” are arbitrarily assigned to the events by the respective observers.
    I think you got it.
    Perhaps. However, I still don’t understand how any of it would lead one to conclude that Julius Caesar exists while I type these letters. Although I can understand how “past”, “present”, and “future” assignments are arbitrary [because the magnitude of the intervals between the events themselves and the events of their observation are merely circumstantial—having to do with things like relative motion with respect to an event], I can’t understand how that, in itself, inexorably leads one to the conclusion that an event persists while various observers register clock readings in their respective frames. It might be the case, but it need not be.

    In post #57, KJW pointed out that “…the physical world is in a constant state of change”, but this does not in any way prevent “fixed data” about some state of the physical world “encoded on optical pulses” from being bandied about it and stored in a variety of mathematical sequences in various memory devices. Sure, because of this, various observers (ideal or otherwise) might come to different conclusions about whether or not two events were simultaneous, but not to any definitive conclusion about whether or not they co-existed. I think everyone participating in this thread would agree that these two are not synonymous. So when it comes to bolstering the notion that all events co-exist, why appeal to the relativity of simultaneity at all?

    Of course, I’m probably wrong about the point KJW was trying to make. There is something in his example and his description of it that seemed more compelling to me than the examples typically published in popularizations. I think a better understanding of his example might help me better reckon with this idea that all the "time slices" of spacetime exist.
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    Quote Originally Posted by Vexspits View Post
    Quote Originally Posted by geordief View Post
    Quote Originally Posted by Vexspits View Post

    I have to admit, over the years I’ve sifted through numerous depictions and never have I come across this precise example, or anything worded in this particular way. I seem to be getting bogged down by it. So I’ll try another tactic. From the wikki page KJW linked us to:“If one reference frame is assigned precisely the same time to two events that are at different points in space, a reference frame that is moving relative to the first will generally assign different times to the two events….” So from this we might say: In one reference frame the two events that are at different points in space are part of a particular present, and yet those same two events in another reference frame are not—one is in the past relative to the other. So I think (fingers crossed) this is the basic point he is trying to make about how the labels “past”, “present”, and “future” are arbitrarily assigned to the events by the respective observers.
    I think you got it.
    Perhaps. However, I still don’t understand how any of it would lead one to conclude that Julius Caesar exists while I type these letters. Although I can understand how “past”, “present”, and “future” assignments are arbitrary [because the magnitude of the intervals between the events themselves and the events of their observation are merely circumstantial—having to do with things like relative motion with respect to an event], I can’t understand how that, in itself, inexorably leads one to the conclusion that an event persists while various observers register clock readings in their respective frames. It might be the case, but it need not be.

    In post #57, KJW pointed out that “…the physical world is in a constant state of change”, but this does not in any way prevent “fixed data” about some state of the physical world “encoded on optical pulses” from being bandied about it and stored in a variety of mathematical sequences in various memory devices. Sure, because of this, various observers (ideal or otherwise) might come to different conclusions about whether or not two events were simultaneous, but not to any definitive conclusion about whether or not they co-existed. I think everyone participating in this thread would agree that these two are not synonymous. So when it comes to bolstering the notion that all events co-exist, why appeal to the relativity of simultaneity at all?

    Of course, I’m probably wrong about the point KJW was trying to make. There is something in his example and his description of it that seemed more compelling to me than the examples typically published in popularizations. I think a better understanding of his example might help me better reckon with this idea that all the "time slices" of spacetime exist.
    I think I agree.This "co-exist" idea only applies ,in my mind when two events share the same place in space and time.
    I don't co-exist with you because we are separated by a small distance.

    I think I was told that the idea that spacetime was a single object where the "past", "present" and "future" were all unified like some kind of a Damien Hirst shark was a misunderstanding and that it was only the model that looks like that.

    Some people may want to ask whether , if the Sun disappeared would it disappear for us instantly or only upon "arrival after 8 minutes.

    I think life is too short for that kind of a question.
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    Quote Originally Posted by Vexspits View Post
    Quote Originally Posted by geordief View Post
    Quote Originally Posted by Vexspits View Post

    I have to admit, over the years I’ve sifted through numerous depictions and never have I come across this precise example, or anything worded in this particular way. I seem to be getting bogged down by it. So I’ll try another tactic. From the wikki page KJW linked us to:“If one reference frame is assigned precisely the same time to two events that are at different points in space, a reference frame that is moving relative to the first will generally assign different times to the two events….” So from this we might say: In one reference frame the two events that are at different points in space are part of a particular present, and yet those same two events in another reference frame are not—one is in the past relative to the other. So I think (fingers crossed) this is the basic point he is trying to make about how the labels “past”, “present”, and “future” are arbitrarily assigned to the events by the respective observers.
    I think you got it.
    Perhaps. However, I still don’t understand how any of it would lead one to conclude that Julius Caesar exists while I type these letters. Although I can understand how “past”, “present”, and “future” assignments are arbitrary [because the magnitude of the intervals between the events themselves and the events of their observation are merely circumstantial—having to do with things like relative motion with respect to an event], I can’t understand how that, in itself, inexorably leads one to the conclusion that an event persists while various observers register clock readings in their respective frames. It might be the case, but it need not be.

    In post #57, KJW pointed out that “…the physical world is in a constant state of change”, but this does not in any way prevent “fixed data” about some state of the physical world “encoded on optical pulses” from being bandied about it and stored in a variety of mathematical sequences in various memory devices. Sure, because of this, various observers (ideal or otherwise) might come to different conclusions about whether or not two events were simultaneous, but not to any definitive conclusion about whether or not they co-existed. I think everyone participating in this thread would agree that these two are not synonymous. So when it comes to bolstering the notion that all events co-exist, why appeal to the relativity of simultaneity at all?

    Of course, I’m probably wrong about the point KJW was trying to make. There is something in his example and his description of it that seemed more compelling to me than the examples typically published in popularizations. I think a better understanding of his example might help me better reckon with this idea that all the "time slices" of spacetime exist.
    I think I agree.This "co-exist" idea only applies ,in my mind when two events share the same place in space and time.
    I don't co-exist with you because we are separated by a small distance.

    I think I was told that the idea that spacetime was a single object where the "past", "present" and "future" were all unified like some kind of a Damien Hirst shark was a misunderstanding and that it was only the model that looks like that.

    Some people may want to ask whether , if the Sun disappeared would it disappear for us instantly or only upon "arrival after 8 minutes.

    I think life is too short for that kind of a question.
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    Quote Originally Posted by Vexspits View Post
    I still don’t understand how any of it would lead one to conclude that Julius Caesar exists while I type these letters.
    Suppose that only the present exists. Then we would conclude that because Julius Caesar is in the past that he doesn't exist. But there is the possibility of an observer who is very far away, moving very fast away from us, and is in our present such that Julius Caesar is in his present and therefore exists. Thus, we have a contradiction that establishes that the present isn't the only time that exists.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post
    But there is the possibility of an observer who is very far away, moving very fast away from us, and is in our present such that Julius Caesar is in his present and therefore exists. Thus, we have a contradiction that establishes that the present isn't the only time that exists.
    This could only happen of the distant observer utterly ignores the fact that his distance means that his observation of Caesar is thousands of years out-of-date.
    Why would he make such an egregious error?
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    Quote Originally Posted by DaveC426913 View Post
    Quote Originally Posted by KJW View Post
    But there is the possibility of an observer who is very far away, moving very fast away from us, and is in our present such that Julius Caesar is in his present and therefore exists. Thus, we have a contradiction that establishes that the present isn't the only time that exists.
    This could only happen of the distant observer utterly ignores the fact that his distance means that his observation of Caesar is thousands of years out-of-date.
    Why would he make such an egregious error?
    I don't think he is referring to what this observer "sees" happening on the Earth, but what would be happening by taking Relativity of Simultaneity into account. Imagine a spaceship flying past the Earth at .866 c at exactly 12:00:00 AM Jan 1, 2019 Zulu and he sets his clock to match. 100 days later, on Mar 11, 2019 by his clock, he is seeing light from Earth that left sometime on Jan 26th Earth time, so he will be "seeing" the events of Jan 26th. However, by time dilation, According to the Earth clocks, the ship clock was running 1/2 as fast, so when the ship clock reads 100 days later, the Earth clocks reads 200 days later and it is Jul 20, 2019.
    But according to the ship, it was the Earth clocks that were running slow, thus he "knows" that only 50 days has past on Earth in the 100 days his clock measured and it is "now" 50 days past Jan 1. 2019 or Feb 20. 2019 on Earth (even though he is seeing events from From Jan 26 on Earth. Thus for Earth, the "now" represented by the ship clock reading Mar 11 is the same "Now" as Jul 20 on Earth, while for the ship, it is the same "now" as March 11 on Earth.

    With enough relative speed difference, You could have a ship, for the same reasons, it is still somewhere during the Time of Julius Caesar on the Earth. Now this does not mean that an occupant of this ship would actually be aware of Julius Caesar, because they would be seeing events on Earth that occurred generations upon generations before Caesar was born. They would only know that events occurring "Now" on Earth according to them are happening a very long time after the events they are presently seeing.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    Dumb questions may stimulate conversation better than anything so here goes. What I'm trying to do and probably incorrectly is question how the wave function collapse relates to things that aren't really there. So with that in mind, are rainbows and mirages really objects? I mean our eyes are picking up photons reflected from an object, no? Is a rainbow really another way of viewing water droplets/ice crystals? Is the water mirage on a hot highway really asphalt? Is it all because of our equipment, like do all animals with vision see the same mirage or rainbow?
    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 zinjanthropos View Post
    Dumb questions may stimulate conversation better than anything so here goes. What I'm trying to do and probably incorrectly is question how the wave function collapse relates to things that aren't really there. So with that in mind, are rainbows and mirages really objects? I mean our eyes are picking up photons reflected from an object, no? Is a rainbow really another way of viewing water droplets/ice crystals? Is the water mirage on a hot highway really asphalt? Is it all because of our equipment, like do all animals with vision see the same mirage or rainbow?
    What about those drawings tat are like Maryline Monroe when looked at one way and a skull and crossbones the other

    We can make up our own reality (or is it that our reality is forced upon us by the weight of our previous choices?)

    Anyway "reality" is a charged word and of course we have to define it (or just "wisely" avoid working with it).

    You are surely aware of how scientists treat the "reality" concept (with a very ,very ,very long shovel **)

    In answer to your mirage question could the same be asked of a hole? What is the "object" there ,the border of the hole or the hole "itself" ?

    **should that be "spoon"?
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    Quote Originally Posted by zinjanthropos View Post
    ... are rainbows and mirages really objects? I mean our eyes are picking up photons reflected from an object, no? Is a rainbow really another way of viewing water droplets/ice crystals? Is the water mirage on a hot highway really asphalt? Is it all because of our equipment, like do all animals with vision see the same mirage or rainbow?
    More like reflection and refraction depending on the observer's position.

    So, here's my extra special dumb question. Are we living in parallel universes, where there are multiple copies of us? Proof could lie in how we remember, like this guy explains.
    https://www.youtube.com/watch?v=VQ19fIDzOlg
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    Quote Originally Posted by Janus View Post
    With enough relative speed difference, You could have a ship, for the same reasons, it is still somewhere during the Time of Julius Caesar on the Earth. Now this does not mean that an occupant of this ship would actually be aware of Julius Caesar, because they would be seeing events on Earth that occurred generations upon generations before Caesar was born. They would only know that events occurring "Now" on Earth according to them are happening a very long time after the events they are presently seeing.
    If you had to explain what you meant by “still somewhere during the Time of Julius Caesar on the Earth” (without taking anything for granted), how would you phrase it? What is the sense of the statement? And why did you find it necessary to caution us about thinking the occupants of this particular ship might be aware of Julius Caesar?
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Vexspits View Post
    I still don’t understand how any of it would lead one to conclude that Julius Caesar exists while I type these letters.
    Suppose that only the present exists. Then we would conclude that because Julius Caesar is in the past that he doesn't exist. But there is the possibility of an observer who is very far away, moving very fast away from us, and is in our present such that Julius Caesar is in his present and therefore exists. Thus, we have a contradiction that establishes that the present isn't the only time that exists.
    Correct me if I’m wrong, but it seems to me that in this section, “…is in our present such that Julius Caesar is in his present….” you are using the word “present” in two different ways; and perhaps the contradiction you speak of is a result of this indiscriminate usage? In the first part “is in our present” you seem to be saying that the ship dweller coincides with us in some way or other that makes it possible for him to be observing Julius Caesar—hence the “such that” in your clause. In the second part, you seem to be saying that Caesar is in the ship dweller's present because he’s observing him. I guess what I’m trying to determine is this: Did you mean that the far-off, swiftly-moving ship dweller is in our present in exactly the same way as you meant that Julius Caesar is in his? Or is there a difference in meaning?
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    Quote Originally Posted by Vexspits View Post
    Did you mean that the far-off, swiftly-moving ship dweller is in our present in exactly the same way as you meant that Julius Caesar is in his?
    Yes, in exactly the same way.

    Let's make one thing clear: Being in the present of an observer is not the same as being observed by the observer. We do not see the distant observer, and the distant observer does not see Julius Caesar. Being in the present means being at the same time, whereas what we see is in our past.

    The events that are in the present of a given observer can be defined as: Suppose an observer emits a brief pulse of light at time = T1 in his frame of reference, the pulse of light reflects off a mirror at a given location, and the reflected pulse of light returns to the observer at time = T2 in his frame of reference. Then the event at which the pulse reflects off the mirror is in the present of the observer at the time halfway between T1 and T2 (time = ½(T1+T2)). The relation "is in the present of" is not symmetric. Thus, "Y is in the present of X" does not imply that "X is in the present of Y". The events which are in the present of X depend on the velocity of X but not on the velocity of Y, whereas the events which are in the present of Y depend on the velocity of Y but not on the velocity of X. This reflects the notion that time and the notion of simultaneity are relative to the observer.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Vexspits View Post
    Did you mean that the far-off, swiftly-moving ship dweller is in our present in exactly the same way as you meant that Julius Caesar is in his?
    Yes, in exactly the same way.

    Let's make one thing clear: Being in the present of an observer is not the same as being observed by the observer. We do not see the distant observer, and the distant observer does not see Julius Caesar. Being in the present means being at the same time, whereas what we see is in our past.

    The events that are in the present of a given observer can be defined as: Suppose an observer emits a brief pulse of light at time = T1 in his frame of reference, the pulse of light reflects off a mirror at a given location, and the reflected pulse of light returns to the observer at time = T2 in his frame of reference. Then the event at which the pulse reflects off the mirror is in the present of the observer at the time halfway between T1 and T2 (time = ½(T1+T2)). The relation "is in the present of" is not symmetric. Thus, "Y is in the present of X" does not imply that "X is in the present of Y". The events which are in the present of X depend on the velocity of X but not on the velocity of Y, whereas the events which are in the present of Y depend on the velocity of Y but not on the velocity of X. This reflects the notion that time and the notion of simultaneity are relative to the observer.
    Ok. I think I’ve got part of it. An event on the distant earth being “in the ship dweller’s present” is not defined by something as trivial as his observing the event, but rather by what he’ll reckon to be the date on the earth while he logs some particular interval (by his lights) from the time at which he “coincided” with the earth; and that reckoning is achieved by considering what interval would have transpired on earth clocks “by taking Relativity of Simultaneity into account”. Of course he has no knowledge of what is happening on this date (which I gather is what Janus meant when he said: “Now this does not mean that an occupant of this ship would actually be aware of Julius Caesar”), but the date could, quite conceivably, be one on which (according to earth history) the reign of Julius Caesar was still in progress. Which means his “present time slice” includes Julius Caesar. Is that roughly the idea?
    Last edited by Vexspits; June 16th, 2018 at 12:51 AM.
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    Was looking at how one would calculate the volume of the observable universe. The sites I peeked at say the universe is a sphere and thus the calculation was done with that in mind. Of course I get confused by this. When I listen to physicists like Krauss, space is flat. On top of that I have in the back of my mind that space is nothing. If space is flat and nothing can a volume be calculated? When a scientist says space is flat are they really saying it's 2D or 3D as in having a thickness? Where have I gone wrong?
    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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