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How scientists have measured universe?

  1. Apr 9, 2015 #1
    Nothing can exceed the speed of light so how can scientists can tell us about 1000s of light years away of our location in the universe ? I mean what instruments have they used for it ? Waves? ( what kind of waves ? ).
  2. jcsd
  3. Apr 9, 2015 #2


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    We look at the light and other forms of EM radiation (and in a few cases particles such as neutrinos) that have been emitted from these objects. There is, of course, a significant time-delay between the actual emission of the EM radiation and the time we detect it. For example, when we look at the closest star system, Alpha Centauri, we are seeing it as it was about 4 years ago since it is about 4 light-years away. When we look at the Andromeda galaxy we are seeing it as it was about 2 million years ago. The further away an object is from us, the longer it takes for light to reach us. So as we look into the far distance, we are seeing further into the past.
  4. Apr 9, 2015 #3


    your answer was satisfying . as this universe has been around for

    13.82 billion years so we must have the farthest stars and galaxies even farther than 13 billion light years because the universe is expanding now what is farthest place or star or galaxy known to us and how far is that ? it's obvious that no
    boundary is determined for the universe to have .
  5. Apr 9, 2015 #4
    The beginning of the universe, 13.8 billion years was found by the redshift that galaxies emit. This redshift indicates that the universe is expanding and based on this expansion rate, distance and with Hubble's Constant, we found the age of the universe. Simply stating, the redshift was what allowed us to find the age, not light's travel through the universe. We didn't find the age by seeing how far light travelled but by redshift. As far as my understanding goes.
  6. Apr 9, 2015 #5


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    You are correct. The maximum light travel time, aka how long light has been traveling, is about 13 billion years. Light traveling this long was emitted during something called recombination, which was the point in time that the universe cooled enough for nuclei to combine with electrons and become a transparent gas. Prior to this point in time the universe was filled with a plasma, which easily responds to light waves, scattering and absorbing them. Because of this, the universe was entirely opaque to EM radiation. Light emitted in one area could only travel a very short distance before being scattered or absorbed. Once recombination occurred, this plasma turned into a transparent gas, and the light that was emitted during this event is now seen as the Cosmic Microwave Background Radiation. It used to be visible light, but has been redshifted into the microwave range. It's important to understand that while we cannot see 'past' this 'primoridal light barrier' (because the light that was emitted prior to this time was immediately absorbed and can therefor never reach us) it is not a physical barrier. There is almost certainly much, much more universe past this.

    The material that emitted the CMB is now about 46 billion light years away thanks to expansion, though it was much closer at the time of recombination and has been receding from our area of space ever since.

    See here for more: http://en.wikipedia.org/wiki/Recombination_(cosmology)
    And: http://en.wikipedia.org/wiki/Cosmic_microwave_background
  7. Apr 9, 2015 #6


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    Not quite. The expansion muddles things. The light from the stuff that's furthest took about 13.8 billion years to reach us. But that light was emitted from matter that was, at the time, about 42 million light years away. Today, that matter is about 46 billion light years away.
  8. Apr 22, 2015 #7
    very confused now, so how big is the universe now in 2015 earth year?
  9. Apr 22, 2015 #8


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  10. Apr 22, 2015 #9


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    As Chalnoth says, the observable universe has a radius of 46 billion light years.
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