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Existance of universe?

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  1. Aug 10, 2015 #1
    How the scientists are determining that a galaxy exist & many galaxies also there. How they find the universe? without seeing with our eyes, a human being can never ever judge the things. but in the existance of other galaxies & universe how they came to conclusion by the telescopes & advanced technologies results.Thanks in advance!!
     
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  3. Aug 10, 2015 #2

    PeterDonis

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    If we only accepted the existence of things we could see with our unaided senses, we would have to abandon most of what we know. We accept the existence of many, many other galaxies, and other distant objects in the universe, for the same reason we accept the existence of microorganisms, or atoms, or subatomic particles, or the Earth's iron core, or fusion reactions inside the Sun and other stars--because we have good indirect evidence for all those things, even though we can't directly perceive them with our unaided senses.
     
  4. Aug 10, 2015 #3

    mfb

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    Did you ever see me with your own eyes? Probably not. Do you question my existence? Or the existence of all the other 7 billion humans on Earth you never saw?
    Our eyes are not good tools for science - they are nice if you want to walk around without bumping into anything, if you want to see predators and prey and so on, but they are very limited in many aspects. Tools allow us to measure things that the eye cannot see, or cannot see directly.
     
  5. Aug 10, 2015 #4
    It's amazing when you think of how much we know and how far we can look in the universe and how much we can learn from this one little rock with water on it. I'm sure we still have many discoveries and events to witness that will make our heads explode once we find them.
     
  6. Aug 11, 2015 #5
    What you mean to say is that you humans can't judge something it doesn't understand, but our brains are very skilled at gather and organizing information and science is the tool we use to do it logically. Our telescopes are technology, but so are your eyes, crafted by evolution.

    And we can see other galaxies and the furthest reaches of the universe. This is Hubble Deep Field, these galaxies are currently billions of light years from us, and are seen by the telescope how the existed in the very early stages of our universe.
    DetailWF4.gif

    We can see even further back in microwave light. This is the edge of the universe, but remember when you talk about an edge, you are also talking about time. This picture is the universe when it was about 300,000 years old. We can't see further back than that, it's not a limitation of our technology either. It's a limitation imposed on us by a universe that has a finite speed of light and a beginning of time.
    cosmic-microwave-background.jpg
     
  7. Aug 11, 2015 #6
    Can you tell me the radius of the universe?
     
  8. Aug 11, 2015 #7
    Extrapolating backwards and taking redshift into account The observed CMB light was emitted 13.7 billion years ago.
    So 13.7 billion light years is the radius of the observable Universe at that time.
    The 'big bang' (whatever it was) occurred not long before that in the scale of cosmological time
    Since the regions of space which emitted that light have been expanding (moving away from us) since then, they are now more distant.
    Our current best theories place them at around 46 billion light years distant.
     
    Last edited: Aug 11, 2015
  9. Aug 11, 2015 #8
    No, I can tell you the radius of the observable universe according to current calculations: about 46 billion light years. It's unknown if the universe even has a finite size.
     
  10. Aug 11, 2015 #9

    PeterDonis

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    No, that's not correct. When the CMB was emitted, the scale factor was about 1000 times smaller than it is now, so the radius of the observable universe was about a 1000 times smaller than it is now. It's about 46 billion light-years now, as you and newjerseyrunner agree, so it was about 46 million light-years when the CMB was emitted.
     
  11. Aug 11, 2015 #10

    mfb

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    I would like to highlight the difference between two types of "radius" here: the numbers above are the radius of the observable universe - the part we can see in visible (or previously visible) light. We know the universe has to be larger than that - light couldn't propagate freely before, but gravity could, and a small universe evolves differently than a larger universe. Different models lead to different lower limits on the size of the total universe, but for sure it is much larger than the part we can observe. It could be infinite in size.
     
  12. Aug 11, 2015 #11
    newjerseyrunner, post: 5195386, member: 553315"]What you mean to say is that you humans can't judge something it doesn't understand, but our brains are very skilled at gather and organizing information and science is the tool we use to do it logically. Our telescopes are technology, but so are your eyes, crafted by evolution.

    (sniped rest of quote)

    "You humans..." Is there something you would like to disclose about yourself? :approve:

    On a more serious note, our brains/minds have allowed us to create instruments to extend our senses and extract information from the results. Thats how we know about the universe.
     
    Last edited: Aug 11, 2015
  13. Aug 11, 2015 #12
    The telescopes are instruments, not unlike a pair of binoculars. We know they work because you can look through a binocular at something that is too far away and then walk up to it to verify that they do in fact work. We can also check objects illuminated by radio or by x-ray light, the bones in an x-ray are indeed accurate representations. Maybe microscopes like particle accelerators are not quite so obvious, but the original question was simply about viewing through telescopes.
     
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