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Againwhat is a vaccum made of?

  1. Apr 11, 2012 #1
    Again..what is a "vaccum" made of?

    Dear All,
    I am new to this forum and hasten to add I'm not a Physicist. I'm a medic.
    I have read some of the previous threads regarding the above question (many thanks to all the contributors), but all threads seem to lead elsewhere, so I thought I would try again for more information. So here is the question again...
    If all particles and waves were removed from a chunk of space, what would the remaning space be made of? I am assuming that since the space would still exist, it must be made of something. Have I got this completely wrong? I would be most grateful for information and apologies if everyone is bored with this topic.
     
  2. jcsd
  3. Apr 11, 2012 #2
    Re: Again..what is a "vaccum" made of?

    I'm probably not qualified to answer this question. If I'm remembering everything correctly, there's nothing in this region of space to probe it, measure it. Therefore, it, um, as crazy as this may sound, doesn't exist, sort of because there's no way to verify if it exists because ... well ... I just explained why. Probably a rubbish answer, so ideally let's wait for someone more qualified to answer.

    EDIT: Oh, yea, vacuum energy! For some reason, I didn't think about that!
     
    Last edited: Apr 11, 2012
  4. Apr 11, 2012 #3
    Re: Again..what is a "vaccum" made of?

    Hi, you might want to look at this (vacuum energy)

    Cheers,

    Oli4
     
  5. Apr 11, 2012 #4
    Re: Again..what is a "vaccum" made of?

    Hi Desra, welcome to the forum.

    Firstly, the Heisenberg Uncertainty Principle states that no object can ever have definite properties. Since a vacuum would have a definite property, zero energy, this would cause the creation and annihilation of particle/anti-particle pairs, created out of nothing.

    On top of this, all of the universe is filled with a scalar field, known as the Higgs Field. This is what determines the mass of a particle, it is everywhere.

    But, I know why you're asking this question, you're interested in space itself. This is a far more difficult question, and I'll try to give you a good answer off of the best we know.

    First of all, we know from general relativity, space is certainly not nothing. Along with time, it composes a 4-dimensional spacetime. Spacetime sloshes space and time in between each other, in order to maintain the speed of light. (You can read more about this by researching special relativity.) In general relativity, Einstein realized that gravity is literally the curvature of spacetime, then altering the geodesic of objects traveling through it, making it appear as if there is a gravitational force. This is similar to how placing a bowling ball of a rubber sheet would curve it, drawing it any objects around the perimeter of the sheet.

    The question gets more difficult as we get smaller. The equations of general relativity break down in the face of extremely dense spaces, such as the quantum foam the uncertainty principle predicts should exist at the smallest points in spacetime. This foam would be a heavily distorted 'nugget' of spacetime, essentially becoming the building block of the larger universe.

    Theories of quantum gravity, that is, theories that try to reconcile general relativity with quantum mechanics, will have the final say on the issue of microscopic spacetime. Most theories of QG predict a quantized spacetime, meaning we could break space down to individual building blocks. Among these is Loop Quantum Gravity. If marcus finds this thread, he would provide a better explanation of what LQG says about the units of spacetime, I'm not an expert on LQG.
     
  6. Apr 11, 2012 #5

    Drakkith

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    Re: Again..what is a "vaccum" made of?

    Hold on all. I think we need to be very specific when we say what a "vacuum" is. Or what spacetime is. Otherwise I don't see this found anywhere. To my knowledge a vacuum is simply a region of space devoid of matter. To ask what a vacuum is made of is like asking what "nothing" is made out of. Also, attempting to say that spacetime is made up of something is similarly difficult.

    There very well may be a field of "vacuum energy", but should that be a different thing that a vacuum itself?
     
  7. Apr 11, 2012 #6
    Re: Again..what is a "vaccum" made of?

    Drakkith, the OP seemed pretty clear he wanted to get an idea what 'space' 'is', from this:
    I agree it is difficult to speak of the constituents of spacetime, that's why I left it as an open question to be answered by quantum gravity.

    If we say a vacuum is the absence of anything, we are left with the intrinsic properties of space. And by definition, a scalar field takes a value at every point in space, so whenever you have empty space, you have said field. For example, the Higgs Field.
     
  8. Apr 11, 2012 #7

    Nabeshin

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    Re: Again..what is a "vaccum" made of?

    Vector (and more generally, tensor) fields have the same property, not just scalar fields.
     
  9. Apr 11, 2012 #8
    Re: Again..what is a "vaccum" made of?

    There was a properties of space thread here where I think the conclusion was that totally empty space has no properties, it is just a location or a place and all the properties of the Universe are as a result of the properties and interactions of Bosons and Fermions.
     
    Last edited: Apr 11, 2012
  10. Apr 11, 2012 #9
    Re: Again..what is a "vaccum" made of?

    Tanelorn, are you speaking of the thread you started?

    There isn't really any evidence to say spacetime isn't real. Not that I'm saying there is, either. Gravitational waves carry energy, and they're just a traveling curvature in spacetime.
     
  11. Apr 13, 2012 #10
    Re: Again..what is a "vaccum" made of?

    You have to define what you mean by 'vacuum'. The vacuum of space is filled with 'stuff' we don't fully understand. You cannot remove all 'particles' and waves...nor time.....maybe someday in the future...Space requires time to exist.

    A quick answer: there is negative pressure, a Higgs field, and virtual particles [and fields] which seem to be constituents of space, as well as particle horizons in the 'vacuum of space'....we don't know how to 'remove' them and if we did I suspect 'space' would be something very different....analogous to removing the charge of an electron, or its mass...it becomes something else.

    I recently posted this description: Nothingness of the vacuum

    https://www.physicsforums.com/showthread.php?t=593405&highlight=nothingness+vacuum

    At the moment 423 people have looked, no comments.....


    also, lots of insights here: 'What is a particle.' [how they come from the 'vacuum'.

    https://www.physicsforums.com/showthread.php?t=386051

    Note that what you observe depends on your frame of reference..accelerating or not.

    Relativists typically say spacetime is NOT made of something. But it curves and exhibits time dilation and length contraction, so I think that is too simple. You sure seem to need space and time for a vacuum....

    The Hawking Hartle no boundary proposal of about 25 years ago [for the beginning of the universe before Planck era, before the big bang] suggests space existed then time emerged.....

    I just posted about that to see what experts think of the theory nowadays:

    Status of Hawking Hartle no boundary proposal

    https://www.physicsforums.com/showthread.php?p=3861934#post3861934

    This is a quantum theory which hopefully gives a different perspective than general relativity.


    Separately, A grand unified theory [of everything] is not yet available...maybe unifying quantum and relativity will someday provide that. But meantime, it is believed that everything we observe is part a a single symmetric whole: so space, time, mass, energy, etc, all somehow emerged from a 'bang' and changed form during the big bang phase transition and loss of symmetry in our universe; Each now APPEARS as a different entity. So far, as an example, the weak force and electromagnetic force have been mathematically 'unified'...called electroweak unification .....we have some insights how they are really the 'same'...but gravity has not been unified 9included] , nor have we found the fundamental relationship of all these to space and time....nor the vacuum.
    stay tuned.
     
  12. Apr 15, 2012 #11
    Re: Again..what is a "vaccum" made of?

    Mark M, yes, there is the thread I started, but there are also several others which are similar.
     
  13. May 3, 2012 #12
    Re: Again..what is a "vaccum" made of?

    Many many thanks for all your remarkable insights. I am learning exponentially though grappling with the complexity of it all.
     
  14. May 3, 2012 #13
    Re: Again..what is a "vaccum" made of?

    I have never heard of this way of explaining things.
    general relativity predicts that mass is compacted energy and that space and time form a 4 dimmensional space-time, it also says that you cant "see" the differece between any of the coordinate in spacetime , without a point of referense. but i cant really se how spacetime and mass and energy can be the "same thing" but it has just aquired different properties? could you please explain this further ?
     
  15. May 3, 2012 #14
    Re: Again..what is a "vaccum" made of?

    Spacetime, mass and energy are not same thing. Naty1 said they all emerged from Big Bang which is correct.

    Initially there was nothing and then it exploded :).
     
  16. May 3, 2012 #15
    Re: Again..what is a "vaccum" made of?

    maybe i just understand this wrong , but she said that " they now APPEAR to be different entities " and that they just changed through the process .
     
  17. May 3, 2012 #16
    Re: Again..what is a "vaccum" made of?

    I've always thought of mass (not matter, mass) and energy being effectively the same thing. Add some energy to an object in any way, and you necessarily get an increase in mass, as described by E=mc2 (or the more general form that takes velocity into account). For instance, a stretched spring will have slightly more mass than an unstretched one made of the same amount of the same material.
     
  18. May 3, 2012 #17
    Re: Again..what is a "vaccum" made of?

    - Suck all the air and dust out of a given volume and you have a classic "vacuum", but you still have solar neutrinos shooting through (among other things).
    - Shield the solar neutrinos (good luck), and you still have cosmic rays (among other things).
    - Shield the cosmic rays, and you still have radio waves (among other things).
    - Shield all particles, waves and fields from the earth, sun, stars, supernovae, etc., and you still have cosmic background radiation (among other things).
    - Suck out and shield all regular particles, waves, and fields from external sources, and you still have dark matter and dark energy (among other things).
    - Suck out and shield all external energy/matter including dark kinds and you still have particles appearing in your volume due to quantum foam.
    - Find some way to suppress the quantum foam, and you still have the Higgs field.
    - Find some way to remove/suppress the Higgs field, and you still have spacetime itself.
    - Get rid of all this stuff and spacetime itself, and what are you left with? I think at this point the question has no meaning because you have removed everything that would give it meaning.
     
  19. May 6, 2012 #18
    Re: Again..what is a "vaccum" made of?

    I should simply add that not only do we not know exactly what a 'vacuum' is made of', we also don't know what any other constitutent is 'made of either'....not energy, not an electron, not time, etc,etc... Mostly mathematical physics describes what is observed and as you can probably tell, deciding what underlies our observations is really really difficult.
     
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