What is space?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by kaneda, Sep 25, 2008.

  1. Saxion Banned Banned

    Messages:
    264
    The observable universe is seen to move away at speeds faster than light.

    It's a known fact.
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Vkothii Banned Banned

    Messages:
    3,674
    Um, that's a bit inaccurate. If something is moving away at speeds faster than light, we can't observe it, since no light ever gets to us.
    It's "known" because we can't assume there are no objects further away than the most distant we see.
    I think that's the postulate, at least.
     
    Last edited: Sep 29, 2008
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. superluminal . Registered Senior Member

    Messages:
    10,717
    Yes.

    Since we assume that we are not uniquely situated at the center of the universe, we also assume then that there is a distribution of matter that extends beyond our "hubble horizon". Our hubble horizon is defined by the distance at which objects are receeding from us faster than the speed of light. At this point, they still emit photons but the expansion of space FTL also redshifts this light ultimately to undetectability.
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. superluminal . Registered Senior Member

    Messages:
    10,717
    This can be safely ignored.

    kaneda, like many others here, thinks he is the first to have stumbled on the horrible, glaring, blatant, stupidly foolish mistakes of generations of conspiratorial, blind, dogmatic scientists and philosophers.
     
  8. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    19,125
    Then make it C. What's your point?
     
  9. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    19,125
    So what? It does nothing to detract from the definition of space.
     
  10. Saxion Banned Banned

    Messages:
    264

    Hold it for a second.

    You asked me what i was talking about, when i said..

    ''I know, but every square measurement of space has something. Even if it is not visible''

    So i replied, telling you about the Planck Space being square measurement, and it's at this level, spacetime is continuously bubbling with matter and energy.

    How does this not describe spacetime... and where did i ever say it would detract some definition?

    I was stating originally that there is no such this as empty space. That much i have proven to you all.

    Spacetime is a physical sheet, and there is no true ''empty space.''
     
  11. Roman Banned Banned

    Messages:
    11,560
    C wasn't in your definition.
     
  12. MarcAC Curious Registered Senior Member

    Messages:
    1,042
    I agree for the most part.

    The expansion of the universe is evidenced by (among other things) observing the redshift of the light which reaches us across billions of km-s of space-time. The redshift is due to the light from the galaxy being stretched as it has to travel across greater distances as the light sources move away from Earth. The further out we look in an expanding spherical shell from Earth, the greater the redshift (and recession velocity) with respect to radius. With extrapolation, at some radius, depending on what the Hubble constant is, the speed of the receding sources become faster than light.

    We should keep in mind that we look back in time when we look further. The furthest objects we see at some 13 billion light years distant, were at that distance, well... 13 billion years ago. The light we see just now, indicates that the object, 13Gya was moving away from us at speeds close to that of light. Now, that object is not 13 billion light years distant, it is at least (probably significantly more than) 26 billion light years distant. Naturally, then, if it didn't vanish beyond Hubble's horizon, or crash into God or something, it must be receding faster than light.
     
  13. MarcAC Curious Registered Senior Member

    Messages:
    1,042
    But would you really say the light is redshifted into undetectability, like radio or something? I think it's safer to say we just won't see it in any way or form because it's still travelling at c relative to Space.
     
  14. MarcAC Curious Registered Senior Member

    Messages:
    1,042
    I'd say that the motion of Space is evident as derived from Einstein's theories of Special and General Relativity. Mass curves the fabric of Space - the greater the mass density the greater the curvature. It was mathematically proven by Schwarzschild and has been shown to be the case through observations of eclipses and occultations. A (rotating) speeding mass will drag space(-time) with it in the direction of its (angular) momentum (frame dragging). This has been shown to be the case through experimental satellites (look up NASA GRACE or CHAMP if you're interested. If you're intrigued, see here.). So I'd say, at least relative to the masses anchored within it, and a flat topography, Space does move - i.e. topography changes.
     
  15. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    19,125
    Neither was A or B. Are you through?
     
  16. StrangerInAStrangeLand SubQuantum Mechanic Valued Senior Member

    Messages:
    12,855
    Space is not curved or square or any shape.
    Space is not fabric. There might be some "fabric???" in space.
    Space does not move. Space does not expand or contract.
     
  17. Saxion Banned Banned

    Messages:
    264

    I never said spacetime was square. I said the Planck Space was a square measurement.

    Space is curved, in the presence of matter.

    Space is expanding, due to the cosmological constant.
     
  18. kaneda Actual Cynic Registered Senior Member

    Messages:
    1,334

    Another empty statement from an empty head. Any fool can say something is wrong when they don't give a reason why.
     
  19. kaneda Actual Cynic Registered Senior Member

    Messages:
    1,334
    A long way of saying that the combined speed of two objects moving away from each other can exceed light speed.

    Perhaps you would like to explain what space is before you can say it expands, and that it breaks the light barrier? If light could be redshifted sufficiently, it would go to the microwave part of the spectrum.
     
  20. kaneda Actual Cynic Registered Senior Member

    Messages:
    1,334


    Is this space being dragged or is it just the effect of gravity from a spinning source?
     
  21. losfomoT Unregistered User Registered Senior Member

    Messages:
    125
    In the context you are using, you should be calling it space-time, not space. I think the problem (and a very wide-spread problem it is) is that you and others assume space-time (or 'space') to be a physical thing like fabric. It is not. The terms 'space-time' and 'frame dragging' refer to mathematical models that we (people) have created to describe the forces that we see.

    There is no physical 'fabric' called space that curves and expands... space is simply the distance between objects.

    You can say that 'space is expanding' the same way you can say 'the distance between objects in the universe is increasing'
     
  22. MarcAC Curious Registered Senior Member

    Messages:
    1,042
    True, but the effect still shows up in space.
    I prefer to see it as a kind of fabric or 3d matrix.

    The Planck length is dictated by the smallest Black Hole Schwarzchild radius physical theory can deal with - otherwise singularities end up outside the event horizon, and all hell breaks loose. The quantum foam/action/activity... /whatever below the Planck length is largely thought to be evidenced by the Cassimir effect - place two objects close enough together and you may observe a deflection, attractive or repulsive based soley on the geometry of the bodies and their proximity (dictates the sum of the wavelengths of attractive vs repulsive potentials/'standing waves' that can form in the small space between). Van der Waal's forces between neutral molecules can also be thought of as manifestations of quantum foam interactions, I've heard. Intrigued? See here.

    What that says to me is that space is by no means just a unit of measurement (distance) because activity appears to occur below the Planck minimum (like the singularity beyond the event horizon of a black hole). It is something (a constitution things). Saxion might agree.

    There's a difference between an object moving inSpace and an object moving with Space.

    Consider a balloon with the earth as a green dot with a blue dot distance "a" away, followed by a white dot distance 2a away, and a red dot distance 4a away - all in one straight line. In one second blow the balloon up by a factor of 2 (a becomes 2a, 2a becomes 4a, 4a becomes 8a). The blue dot moved away at "a" units/s, the white dot moved away at 2a units/s and red at 4a units/s. How would it look from the white dot? Earth would have moved away at 2a units/s, blue at a units/s and red at 2a units/s. So, for proportional increase in recession velocity with increasing distance in all directions, you're left with the natural conclusion that - the expansion is isotropic (the same everywhere we look). That is what Hubble first observed, and what we observe today - the Hubble flow.

    You have to realise why we assume it must be Space expanding. If it is really just the objects moving through Space, then if there is anything beyond Hubble's horizon, they will be moving faster than Einstein's speed limit ("in/through/relative to" Space). That would mean we need new Physics to explain those speeds, or we can say God slowed them down (we'd have to assume there's nothing beyond Hubble's horizon).

    Please Register or Log in to view the hidden image!

    Also, if we assume objects are moving out, and space is 'static' then how do we deal with the conservation of energy?
     
    Last edited: Oct 4, 2008
  23. MarcAC Curious Registered Senior Member

    Messages:
    1,042
    It is a gravitational effect of a spinning mass on space-time. It isn't equivalent to a tidal effect or a perturbation due to mass inhomogeneities. This is in Einstein's world, of course, where mass curves space. Drop the spinning heavy ball with quick-glue on the rubber sheet and the sheet, sinks, and starts to twist.
     

Share This Page