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The Fabric Of Spacetime

  1. Dec 4, 2008 #1
    General Relativity has always fascinated me and I understand how the fudamentals of the so called fabric of Spacetime work, but never do I hear from anybody what the fabric of Spacetime is made out of. Is it some other type of natural force and if so is it related to the 4 fundamental forces.
  2. jcsd
  3. Dec 4, 2008 #2
    The "fabric" of spacetime is simply a clever analogy to help imagine the merging of the 3 spatial dimensions, and the single time dimension. When you see picures of spheres bending a sheet that looks like a checkerboard, the checkeroard represents spacetime.

    So, Spacetime is just what it implies; it's space and time.
  4. Dec 5, 2008 #3
    Spacetime can be envisoned as Penrose spin networks with integer edges representing areas and integer value nodes representing volumes..and these can be shown to evolve from string theory, although that's not how they were discovered. It can also be envisoned as membranesof vibrating energy; these are analalogous to strings moveing through space and sweeping out two or three or n dimensional spacetime...these are theoretical mathematical constructs, not proven experimentally.

    Right now nobody knows what spacetime is made of. Nobody knows what time is made of either, nor mass, nor energy....in fact you could claim it's rather embarassing or you could say:

    "We know much; we understand little"
  5. Dec 6, 2008 #4
    Right. So what does that mean exactly? What is space and what is time?
  6. Dec 6, 2008 #5
    I guess the real question is, are space and time real physical things? What do you think?
  7. Dec 8, 2008 #6
    after reading the response above, i am wondering what Naty1 is... anybody that can "envison (spacetime) as Penrose spin networks with integer edges representing areas and integer value nodes..." is a few points beyond me on the IQ scale.

    anyway, Yes, Virginia, there is an "aether" that is anaolgous to the fabric of spacetime (not that anyone has a clue what the aether is). but after dispensing with the original aether with SR, einstein, after the development of GR, finally decided that there was an aether after all which rather represented the "spacetime" which GR indicates is warped by the presence of mass. there has to be something that is being warped if GR is correct. and IMHO, GR is basically the correct approach, whereas i do not believe a "graviton" theory of gravity based on the exchange of particles is reasonable (which of course does not mean it wont be found correct at some point in the future, but it is very complex and confusing and far less elegant compared to envisioning a warped spacetime - not that warped space is not confusing, just less confusing...)

    here is a paper einstein delivered in 1920 discussing ether and relativity:
  8. Dec 9, 2008 #7
    I am a layman and not qualified.
    Space time is the dimention we percive in. Imagine a blind person reading brail where thier hands are the spacetime or as I see it the matter dimention. On its own it is infinite nothing, but introduce the brail lumps and bumps and you have perception. The brail is two other dimentions antimatter and light hence why we percive a 3D world. Gravity or the pressure of the matter dimention which we exsist in, is the process of smoothing the intrusional bumps. This universal force of gravity or you may think of it as decay is percived as time.
    So Spacetime is the matter dimension that we live in and percive in, but cannot see and can only view or percive objects or mass as indentations they make in our dimension.
    Gravity is time.
  9. Dec 9, 2008 #8
    I wish!! unfortunately not so. Just sharing a conceptual picture I read about ...

    I was referring to a diagram and explanation I saw in a recent book on physics....can't find it right now...May have been by Dr Kaku....anyway, the dynamic curving of spacetime was described as variations in a geodesic shaped framework of nodes and links....as mass/energy/pressure evolves and moves and modifys the shape of spacetime ,an edge may grow or shorten and nodes values vary in integers of Planck length....
  10. Dec 9, 2008 #9
    kaku=wizard :-)
  11. Dec 9, 2008 #10
    You can find discussions and some measure of working definitions via Wikipedia...

    They appear to be real and physical but nobody knows their fundamental consitutents. Space appears to be something; so does time; relativity implies both curve and expand and contract with velocity...maybe velocity is fundamental?? Maybe light, according to Penrose Twistor theory...nobody knows....

    It's like asking what is mass? Mass is made of atoms. Atoms are made of elementary particles...let's say quarks and electrons...They may be made of vibrating strings of energy. may be made of other undiscovered particles. Are particles wavelike or particle like? What are strings made of? fundamentally there is a lot we don't not know; we have mathematical based models that pretty well depict what we observe and explain most experimental results. But there is also a lot we don't understand.
  12. Dec 11, 2008 #11


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    Welcome to PF!

    Hi Sammyg! Hi chis! Welcome to PF! :smile:

    I quite like chis's answer (if I'm interpreting it right) …

    we can't "see" the fabric of space-time, we can only experience the imperfections, or bumps, in it …

    it's like the canvas that a painting is painted on or a tapestry is woven on … the canvas itself doesn't matter. :smile:
    No, I don't follow that … why is gravity time? :confused:
  13. Dec 13, 2008 #12
    Gravity is NOT time acording the relativity.

    But an argument could be made that gravity is the fabric of spacetime...that gravity is the geometry of spacetime...
  14. Dec 14, 2008 #13
    Gravity bends Space-Time?

    hi everyone...
    i had a doubt regarding how light bends owing to a gravitational field as gravity is a property of mass and light (photon) is a massless entity..
    experts here suggested that light follows a geodesic path and its the Space-time continuum that bends not d light itself..
    Now the question that perturbs me is how cud the space bend at the first place??
    even if it does.. what happens in the case of a black hole where d light emitted by it is engulfed by itself.. is the space curving all around it self?
    if it is so.. than there must form a cavity in the continuum......! this whole thing struggles to ascend to my faculties...
    please help.

    P.S. : I am a graduating student and m not savvy to all the cosmological termnologies, its a humble request that u keep the reasoning down to simplest of levels.. thankyou:wink:
  15. Dec 14, 2008 #14
    Re: Gravity bends Space-Time?

    Here's what I think:

    Gravity is caused by the 'pressure' space-time exerts on a body, such as the Sun or Earth. The simplest way to describe it is the trampoline model. Imagine a trampoline flat on the ground, and you place a 20lb bowling ball in the center, the "space-time" or fabric of the trampoline is going to warp around the ball, causing everything that gets just a little to close to be pulled in. Now you have to imagine that the fabric of space-time is not just horizontal, but vertical, and every degree in between, so it folds "space-time" all around it. The same thing happens in space, we feel not a pulling force from the earth, but pressure from space-time actually pushing against us from above.

    A black hole is just a super dense object in space, with so much gravity that it's pulling everything into a singularity.

    So, that leaves the question, what is space-time? Space-time = Dark Matter. We simply don't have the the tools to detect it or prove it's existence, but we will, hopefully sooner than later. The properties of dark matter, once discovered, will prove the theory I'm explaining above, which is essentially GR. It also explains why as you approach the speed of light, the pressure from DM is what slows you back down and would require you to have infinite power. It's like trying to go too fast in an airplane, the friction from the air is what's holding you back from going faster.

    This is simply my perception on GR and DM, and how I would like to believe everything works. Hopefully one day I find out this is true, because at these levels anyway, it works.
  16. Dec 14, 2008 #15
    Re: Gravity bends Space-Time?

    Now in your theory you would have to define what this 'pressure' is, you cannot just say what it does...
    For example, space-time pressure is a tendency of space-time to...

    And btw, air friction doesn't put any limit your speed - you could still travel at a relativistic speed in air, but you would just burn out pretty fast...
  17. Dec 14, 2008 #16
    I thought I did describe what the pressure was, but I will clarify. The pressure is the pushing of the fabric of space-time against a body within it.

    Space-time pressure is the tendency of space-time to fold around objects within it.

    How can you say air friction does not put a limit on speed? I understand that air can be moving independently of the objects within it, but as soon as you travel faster than the air is moving, if at all, it causes friction. This isn't my theory, this is my take on the principles of GR.
  18. Dec 14, 2008 #17
    Are you sure that you are talking about the same space-time as Einstein did? He said space-time was majorly curved by stars and planets, and since objects tend to take the shortest paths in space-time, they accelerate towards that star/planet. Now, what you are saying, that space-time tends to fold around objects in it, could explain gravity, but I don't see how it puts a constant c-limit on speeds

    It does cause friction, but you can still move against it... at any speed you want slower than c
  19. Dec 14, 2008 #18
    Re: Gravity bends Space-Time?

    thanx iRish WaKe..
    ur explanation cleared my doubts pretty well..
    but one thing still remains tangled is.. this 'pressure' pushes 'bodies' within the space-time.. but LIGHT is certainly NOT a body.. y does and how does a black hole eats up (its own) light??
  20. Dec 14, 2008 #19
    Re: Gravity bends Space-Time?

    Space-time curvature around a black hole (inside the event horizon) is so great that the shortest path in space-time that light traveling away from it could take is back into it.

    And I do believe (unless it's all messed up in my head) that Hawking proved that black holes radiate because otherwise it would've contradicted the Second Law of Thermodynamics.
  21. Dec 14, 2008 #20
    I was essentially talking about 2 different things, guess I shouldn't have? I didn't say that the folding of space time put a limit on speed. If that is what you or anyone else is thinking that's what I said, then sorry for the confusion, because I wasn't.

    I was simply saying that space-time is something, it's not just empty space. It is dark matter. Empty space, space-time, the vacuum of space, dark matter, whatever you want to call it, they are all one in the same. This is what I got out of Einsteins theories. That 'something' is what causes you to need infinite power to accelerate to c.
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