This conversation is closed.

How do the cosmologists account for the time gap of the distant galaxies' images?

First of all I am no phisycist of any kind, I am just a physics enthusiast.
The question that is bugging me in the notion of ever accelerating expantion of the universe is how do we know that the universe is accelerating right now. The images of the furthest galaxies are bilions years old and they are images of the younger universe, a universe that perhaps was 'still exploding', the force that caused the Big Bang was still effecting the matter in the universe. Hence it's only natural that those distant objects appear to be moving away from each other faster than the ones that are closer to us.
We don't and won't know what happens there 'now' and this might be the problem. Not "we're too late to see what happened" but "we're too soon to see what the outcome is/will be".
Please, let me know what is unclear and/or wrong in my reasoning, I'll try my best to lay out my idea.

  • thumb
    May 2 2012: No it IS the case that we are too late to see what is happening there now. Now is Now everywhere in the universe what is happening in those distant galaxies is happening now... we are just able to to see those nows becuse what we use to see them in the first place is light. Light which takes time to get here so, the light that left the early universe, because it's takes so long to travel the vast distances is only just reaching us.
    When we look out at the distant parts of the universe we are basiclly looking back in time!
    • May 3 2012: Exactly. Hence the farther out we observe, the older the red shift. And since red shift increases with distance, one should conclude that over time expansion has been slowing down. But that's not the conventional wisdom, so where is the flaw in my thinking?
      • thumb
        May 13 2012: Not too sure what you are thinking by your term "... the older the red shift"
        'Red shift' refers to how the light we observe is 'shifted' towards the Red end of the spectrum. Like the sound of a train as it goes pass, the waves get spread out lowering the pitch. Light also comes to us as waves. As the source speeds away from us we see these waves slowing down and therefor at a lower frequency (More reddy). The Red shift doesn't get older, what changes is the amount of Red Shift we measure.

        The Shift towards Red is greater at further distances because the further we look out we see those objects moving away from us faster than ones closer to us. The fact that the Red Shift has been mearsured as increasing is evidence that the expansion is speeding up, not slowing down... If it were slowing down the observed Red Shift would decrease.
        • May 18 2012: The question is how do we account for the time gap between distant objects measured.
          As you say "The Shift towards Red is greater at further distances because the further we look out we see those objects moving away from us faster than ones closer to us." but those objects are also more distant in time. Their red-shifted light was emitted earlier than the light of those closer objects.
  • Apr 30 2012: Another question, if I may piggy back it on this thread: How do we know that the red shift we observe is not an illusion of non-linear space and time? We know that time does not progress into the future at the same rate everywhere. We know that space expands near a mass and that time's progression is different "where" space expands. We are told that near a black hole, time is incredibly slow, that a resident there would age much more slowly than a resident here on earth.

    Then the logical observer in a linear world (call him a linear observer) makes the following deductions:

    If objects at the fringe of our universe are moving apart faster, we might conclude that the distance between objects near the edge of the universe (call it the mass horizon) is greater than that near the center of the universe where expansion occurs more slowly. The linear observer then deduces that the "mass denisity" of the universe decreases toward the mass horizon. Further, as the mass density decreases, the linear observer concludes that space shrinks and the passage of time accelerates near the mass horizon. The linear observer pauses here to recognize that, although space shrinks, distances should not change because measuring sticks also shrink. However, if the passage of time accelerates, then more time should elapse as light travels those distances and, measured in light-years, those distances should be greater. Unless ... the acceleration in the passage of time allows light to travel faster, rendering the measured distance no different.

    The linear observer notes here that beyond the mass horizon, time accelerates until eternity elapses in what seems an instant here on earth, rendering the universe's "edge" infinitly distant.

    So, as seen from the center of the universe by a linear observer, is the expansion of the universe just a relativistic illusion? Perhaps the terms "here," "there," "now," and "then" are meaningless in a universe where time and space are not absolute.
  • Apr 30 2012: The Andromeda and Milky Way galaxies are indeed closing the gap between them. Andromeda is our closest galactic neighbor. In any local neighborhood of galaxies you may find two or three moving closer to one another, orbiting one another, even coliding with one another. So when cosmologists talk of an expanding universe, they are speaking on the macro level - overall - in general.
  • Apr 25 2012: As I understand it, the galaxies are showing a 'red shift' which indicates light retreating so although it was retreating X millions/billions of light years ago, it showed us that it was moving away from us. However, I have heard that the Andromeda Galaxy is actually getting closer to us - because it is showing a 'blue shift'. I don't know how that fits in to the idea that everything is moving apart.
  • Apr 25 2012: I'm glad you asked this question because it is something I've wondered also and it is so counter-intuitive and contradictory to what we hear that there must be an explanation unknown to both of us that makes sense.

    The farther away one peers into the universe, the further back in time one is looking. The logical deduction is, if those farthest objects are moving away faster than the objects closer to us (as observed by their red shift), then the rate of expansion was greater in the distant past than it was in the more recent past. And a casual observer would resonably conclude that the expansion is slowing down. So why are we told just the opposite?

    Any physicists want to answer this question? What's the logic?
    • thumb
      May 2 2012: Try this...
      Exponential growth! Example:
      1. |-|--|---|----|...
      2. |--|----|------|--------|...
      3. |----|--------|------------|----------------|...
      4. |--------|----------------|------------------------|------------------------------------|...
      The vertical lines " | " are set markers from a base and are galaxies. At each step the distance between each marker has been doubled. And you can clearly see the amount the last marker (Lets say the edge of the universe) is getting is faster and further away at each step than the ones nearer the base line.

      So the Red-Shift between each galaxy gets more the further you look out. This is not the only thing that is happening - Dark Energy is a constant 'Push' and is the force that is driving the speed-up of the expansion of the universe.

      How that helps. :)
      • May 3 2012: Not sure that explanation answers the principle question, David, which is: how do we consider the age of the universe at the distances at which we measure red shift?
        • thumb
          May 13 2012: Opps... no it doesn't... I typed my explaination in to the wrong box - This was meant for another place and another question on the site :D
    • thumb
      May 13 2012: While it is true that the further one looks out in to the Universe, the further one sees back in time. However, this doesn't mean that we are seeing the Red Shift of the light at the time that it left those objects.

      The colours of the light that left those distant objects is/was 'Normal' in colour when it left. It is only shifted on it's way here by the expansion of the universe.