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Concept of space as the vacuum

  1. Jun 14, 2003 #1


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    im sure it has been asked befor but i can find no referance on the web describing SPACE, it seems space has properties,
    it acts as a conduit for electromagnetic waves
    it can expand
    it seems to have for the want of a better word viscosity, "i reach this conclusion from the effects of frame dragging"
    it also seems to have electrical properties ie resistance.
    if the above is true then the concept of space as the vacuum is incorect.
    can someone give a better discription as to what space is?
    Last edited by a moderator: Feb 5, 2013
  2. jcsd
  3. Jun 14, 2003 #2
    I suggest you look into some General and special Relativity sites
  4. Jun 14, 2003 #3


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    SR deals with contractions and dilations that do not agree with common sence, even though observations have been made that agree with the predictions, its just the best theory we have so far.
    as i said in my first post i cannot find a discription of SPACE that has "properties", most refer to it as the vacuum.
    how do EM waves travel through space?
    how can you expand, bend a vacuum?
    how can a vacuum have electrical properties?
    what would be the best way to describe SPACE?
  5. Jun 14, 2003 #4


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    Re: space

    this is a totally fantastic question
    and I think 21st century math/phys will concentrate around it
    (I use historical hunches sometimes as a guide or crutch, watch trends and such)

    Hurkyl said something that bears on this just a day or two ago.

    He said "ditch the manifold and just use the network"!!!!!!!

    I will try to point you to Hurkyls post. It was in the SO(3)+LQG thread here at "theoretical" forum.

    Wheeler said "quantum foam"

    Notice that if you have a lot of suds in the dishpan you can make
    a network by putting a dot at the center of each bubble and connecting any two dots whose bubbles are in contact.

    So then you have the foam realized as a 3D network that you could model by gluing little matchstick legs together.

    Roger Penrose (all make obeisance!) had the idea like 30 years ago to throw out the smooth manifold and replace it with networks, so he invented a type of labeled network

    that (because of the crafty labeling) you can do some of the same things with as you can with a manifold (a curved space or spacetime)

    It could become a "now its particle now its wave" puzzle
    (the particle wave duality dates back to Einsteins 1905 paper on the Photoelectric effect)
    I mean-----space could be both a smooth manifold and a network of relationships----and the two explanations or modeled could end up sandwiched together inextricably like, say, plywood

    Maybe it is time----around 2005, around 100 years later---for another aggravating unfathomable paradox to be foisted upon us.
    Like "wave-particle" duality but this time about space itself.

    Anyway Wolram your questions very often are winners and this one I totally cannot answer----which I like very much.

    It is like standing on a cliff at Big Sur over the ocean with absolutely nothing in front of me but sky.

    I do think the question "what is space?" is a 21st century question. And I think Roger Penrose's thinking up "spin networks" in the 1970s has some possible bearing on how it
    may be eventually be answered. Otherwise I draw a complete blanck-------"blanck?" sounds like Max Blanck
    Last edited: Jun 14, 2003
  6. Jun 14, 2003 #5
    According to loop quantum gravity, space is quantized, is made of tiny loops. It has been always believed that light is a wave with the property of travel through the vacuum, but after all, is possible that light is a vibration of these loops
  7. Jun 14, 2003 #6


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    thanks for sensible reply MARCUS, its hard to believe that you dont have an ansewer, BUBBLES in space? i recall somthing about interwoven
    loops but my memmory fails as to where.
  8. Jun 14, 2003 #7


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    Hurkyl quote about ditching the manifold

    I found that post, it is halfway down the second page of the
    SO(3) plus Loop Quantum Gravity thread

    "Hypothesis: Can we completely ditch the manifold at this point and abstract the idea of a connection merely to something that acts on edges to give rotations?"

    I think this is a very contructive idea.
    I do not at all see how to do it (which makes it all the more interesting) and I think Penrose was trying to do it when he
    happened onto the idea of "spin networks"
    (he had gotten fed up with the frustrations attendent on modeling
    space with manifolds and wanted to break out of it)
    this is not to say that Penrose's or anybodys first attempts have been successful. I just dont know of any successful attempts

    Right now the motivation behind LQG is to achieve "background independence"

    Earlier approaches, like stringtheory, were background dependent and perturbative-----involving a fixed initial commitment to a manifold with predetermined metric.

    Background independence means "ditch the metric". Start with a manifold that has no built in arbitrarily chosen metric. So you start in some sense with no prejudices about the manifold. You start with a clean slate.

    So LQG represents some progress. But it still starts with a manifold-----the manifold just has no preconceived curvature, no prior commitment to a metric, no gravity-----and you start off with a whole Hilbert space of possibilities for what the metric and curvautre and gravity could be. So gravity is quantized in LQG from the very outset.

    Background independence seems clean and sound mathematically---how one would want it to be done----compared with the older fixed metric approaches. But it is still based on a smooth continuum or manifold. (just one with comparatively little structure)

    In reading about LQG I havent come across the idea that space is made of loops----tho the "labeled networks" may be closely related to loops. In LQG there is a 3D continuum, a manifold. It can have time incorporated into it making it 4D.

    All the mainstream approaches, my impression is, even if they involve networks, loops, strings---extended objects of some kind---have an underlying continuum in which these things live.

    that attractive lady, Fotini Markopoulos, was written up in Scientific American because of some ideas she seemed to be offering about a purely relational idea of space---but even her ideas, as I recall, had manifolds in them.

    We humans, who are after all just moderately-evolved fish, do seem for the most part to need continuums to think with

    I mean of course "continua":wink:
    Last edited: Jun 14, 2003
  9. Jun 14, 2003 #8
    I read about the quantized loops in a Discover article quite a bit ago. I guess it really didn't pan out for some reason.
  10. Jun 14, 2003 #9


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    Not to take bubbles seriously! John Archibald Wheeler who was Feynmann's research advisor at princeton and collaborated with him on some early attempt to quantize gravity....well he is famous for a lot of things and one of them is I think he made up the term "black hole" for Schwarzschild's solution of GR equations

    and one of Wheeler's pet notions is "quantum foam" as a picture of how space is down at the micromicroscopic level of Planck scale

    people always refer to planck scale as "10-33 centimeters"
    but it would be a great deal more accurate and just as meaningless to call it 10-38 of a mile-----that hits it within half a percent, whereas the centimeter figure is off by 60 percent.

    You mentioned "plebs" in some post. Compared with Wheeler everybody I can think of is plebs. He has extreme radical imagination and creativity and is a grand old man. If he says "quantum foam" then I accept it at least as a possibility of how things could be at very small scale. Cant say I understand what it means.
    Last edited: Jun 14, 2003
  11. Jun 14, 2003 #10


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    Everything is still on the table and the wheel is still spinning.

    Does anybody else think differently? Has the question been settled?

    Whatever you read about in Discover, don't sell it short (at least that is my advice)

    It is just that TO DATE whenever I have dug down into technical articles I always at some point bump into a manifold.

    It doesnt mean that people arent trying to find fundamentally different approaches.

    And I could be too limited in my info. someone could walk in here this minute and say there is a successful mainstream model of space with no continuum in it.

    Like abstract 3D chainmail made of little intertangled loops that do not live in any coordinate system whatever and tell each other where they are and whatever else they want to know without the aid of coordinates. This could happen this minute----there might be this mainstream theory I hadnt heard of---and someone could start talking about it right now and cite professional journal references out of arXiv---to give the thing some substance.

    I wish it would happen, but do not anticipate it.
  12. Jun 14, 2003 #11


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    Re: space

    Lee Smolin goes into detail on this topic in Three Roads to Quantum Gravity. While the main focus of the book is what space looks like on a quantum scale, he also briefly touches on the classic notion of spacetime as a field.

    An excerpt from the book:

    General relativity is a theory of fields. The field involved is called the gravitational field. It is more complicated than the electric field, and is visualized as a more complicated set of field lines. It requires three sets of lines. We may imagine them in different colors, say red, blue and green. Because there are three sets of field lines, the gravitational field defines a network of relationships having to do with how the three sets of lines link with one another......In fact, these relationships are all there is to the gravitational field. two sets of the field lines that link and knot in the same way define the same set of relationships, and exactly the same physical situation.
  13. Jun 14, 2003 #12


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    i am not an educated person, my list of properties for space is proberly wrong or incomplete may i sugest that someone with more knowledge compile a list, it wont ansewer my question but it may tell us if we are looking at a clock or field generator, figuritivly speaking of course...
  14. Jun 14, 2003 #13
    i thought that QM told us there was no such thing as empty space. (i.e. constant virtual particle/antiparticle generation and annihalation)
  15. Jun 14, 2003 #14
    Re: space

    Your notion that space or "The Vacuum" as people like to call it, is not an innocent bystander or blank background in world events is, in my opinion, right on. I think much work in the next era of Physics will be about what properties the vacuum has, and what roles does it play in events large and small. For 50 years people have been looking for non-baryonic dark matter, to no avail. It's about time we start asking if the vacuum might have properties beyond those known which might explain some things.
  16. Jun 16, 2003 #15
    Space is just a frame and nothing more. Space itself would nevertheless exist if there is not anyhing contained in it, tiny loops or whatever. That would be apsolute emptiness.

    Actually I do not believe that there is such a place in the whole universe, but it is other point.

    We know that EM waves are propagated through vacuum. If vacuum would be absolute emptiness that would not be possible.
  17. Jun 16, 2003 #16


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    You know, there's something bothering me. Since virtual particles can pop in and out of the vacuum, wouldn't this be able to be used as a yardstick which can differentiate between a static observer and a constant velocity moving observer?
  18. Jun 16, 2003 #17


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    That is an interesting idea. I don't see how the moving observer would see the vacuum as any different---can you describe some possible effect.

    This is all in the context of special relativity----we arent worrying about gravity I assume.
    And here is something kind of exciting about that. In 1976 or so a Canadian physicist Bill Unruh (BC) discovered that an ACCELERATING observer would see a different vacuum from
    someone at rest or in uninform motion. The vacuum would be hot, or just slightly warm, depending on how much acceleration. The radiation produced in the vacuum is called Unruh radiation.
    It is sort of analogous to the Hawking radiation produced at the event horizon of a BH.

    In fact you use the same formula-----g/2pi----to calculate the Hawking temp of a BH and you do the Unruh temp of acceleration.
    I remember seeing Unruh's article in Physical Reviews Series D a long time ago and being stunned. None of these things completely make sense which is why they are so nice:wink:

    Well I think your idea of being able to tell motion will probably not work---can't visualize it---but it would be very good to TRY to see how it might be done, because would clarify ideas. And you are already close to something very interesting, with your thought, namely Unruh temperature of acceleration.
  19. Jun 17, 2003 #18


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    I know not much about high level physics... My thought in this is something of a blend between GR and QM. As maximus had put it:

    If particle-antiparticle pair can pop in and out of the vacuum, and we know that the pair can only exist in a short period of time let's call it T, before it vanishes into the vacuum again and this is an assumption that I make (I don't know whether this is true or not or have known or anything but this is the crucial part... that the particle-antiparticle pair pop out and after T, vanish back again at the very same place or at a deviation allowable by uncertainty principle), then if we were to have two observer and if one observer sees that during T, the particle-antiparticle pair has a velocity relative to that observer, then by the assumption I've made, this should tell us that the observer is moving absolutely. Likewise if the other observer sees that the pair is stationary relative to him => observer is stationary.

    As I said the whole argument is based on this assumption. I made this assumption because if the pair were to pop out and vanishes somewhere, the question is why must it vanishes somewhere else and not the initial place it actually pops out, and if it really vanishes somewhere very far away from the initial point,then even the uncertainty principle can't explain this deviation.

    I just read on this Unruh's law from Smolin's Three Roads to QG. It defines random motion as heat and it says that the accelerated observer has a horizon in which beyond it he will not know what is happening and by quantum fluctuations two photons will be created as pair but one will reside beyond her horizon, thus from his observation, the photon which he can see is random => heat.

    I'm in doubt here. How fast must he accelerate in order for him to detect a temperature rise? What if this situation is applied to the microscopic world like particles in accelerators or any circular motion or electron in nucleus. Yes, we know that the electron doesn't really orbit the nucleus like what Bohr said but still can the electron experiences Unruh?
  20. Jun 17, 2003 #19
    i don't know if this critical assumtion is correct. first of all, are you suggesting that the velocity of the virtual particles can be used as a refrecnce frame (and a constant) to measure relative velocities of observers? why can't you just use EMwaves like everybody else! and anyways, i don't know if the virtual particles in guestion are a constant. will they still mainfest in a situation of altered velocities? (like in a space ship) maybe they hold true in such a situation like most other laws of physics do, except light and hold the same properties regardless of velocites. (therefore not a constant like EMwaves) do you follow me?
  21. Jun 17, 2003 #20


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    By coincidence I was just doing this calculation in the "Astronomy" Q/A gamethread in PF's Astronomy forum.

    The formula for the temperature T associated with some acceleration g

    is T = g/2pi

    with the temperature and acceleration in planck units (which Unruh used in his original 1976 paper)

    This means that the temperature rise is extremely small for even an incredibly rapid acceleration.
    The amazing thing to me is that there should be any temperature at all associated with acceleration----even this extremely tiny temperature.

    In metric terms the planck unit of acceleration is 5.56x1051 meters per sec per sec

    and the planck unit of temperature is 1.417x1032 kelvin.

    So for an example think of temperature of 1.4 femtokelvin
    as 10-47 of the planck temperature (a kind of extreme big bang temperature higher than anything we have nowadays)

    Unruh's formula T = g/2pi then says that the acceleration g to produce that temp must be
    2pi x10-47 in planck units of acceleration.
    I already mentioned what a unit of acceleration is in metric terms.
    This 2pi x10-47 planck units comes to 350 kilometers per second per second.

    this is a huge acceleration just to produce a tiny 1.4 femtokelvin temperature, which i cannot imagine how anyone could detect. It is a weird effect and perhaps we should be grateful that it is so slight.:wink:
    Last edited: Jun 17, 2003
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