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Give Me Some Perspective: Size of Universe?

  1. Jun 23, 2014 #1
    I still can't quite grasp the scale and size of our universe. Can you guys give the basic facts?

    Size of universe?
    Number of stars?
    Number of galaxies?
    Size of our own planet/sun in comparison to others in existence?

    Thanks very much! :approve:
  2. jcsd
  3. Jun 23, 2014 #2


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    There are many videos available on youtube about the size of the universe. Here's one:

    Its appropriate to mention the Blake poem here:

    Last edited by a moderator: Sep 25, 2014
  4. Jun 23, 2014 #3


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    Last edited by a moderator: May 18, 2015
  5. Jun 23, 2014 #4


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    Just keep in mind that there are two ways "universe" is used. First, the observable universe, which has a defined finite and bounded size and second "the universe" which is everything including all that is outside the observable universe and has no defined size ... might be finite and unbounded or might be infinite.

    Sometimes you'll see "universe" used when "observable universe" is what is meant, to it's a good idea to be careful about usage.
  6. Jun 23, 2014 #5


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  7. Jun 23, 2014 #6


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    Or, as Douglas Adams puts it:

  8. Jun 23, 2014 #7


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    The universe is much, much larger than necessary. It's all just an incredible waste of space. :grumpy:
  9. Jun 23, 2014 #8


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    1) Observable universe is roughly 45 billion light years in proper radius.

    2) Roughly 10^22-10^24 stars in the observable universe.

    3) Roughly 200 billion to 1 trillion galaxies in the observable universe.

    4) Our planet is roughly 1/10 the radius of Jupiter, meaning 1000 Earths will fit in Jupiter. Again Jupiter is roughly 1/10 the radius of the Sun, meaning 1000 Jupiters will fit in the Sun, or 1,000,000 Earths will fit in the Sun. The Sun is roughly an average sized star, there are very many smaller stars and some far larger stars.

    The largest stars out there are probably about 60-200 times more massive than the Sun. However, for stars not on the main sequence, the giant stars can develop a very large envelope of gas indeed (kind of like a huge atmosphere). The super giant stars, made up of high mass stars who have turned giant, can be up to roughly 200-1,000 times larger in radius than the Sun.

    But one should note that much of this size is a diffuse (quite diffuse) atmosphere.
  10. Jun 23, 2014 #9


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    Just wait. Somebody will come along shortly, complaining that the universe isn't big enough.
  11. Jun 23, 2014 #10


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    The vastness of the universe is trivial compared to the smallness of the planck length. The midpoint between the two is about 7 nanometers - roughly the middle of the x ray spectrum.
  12. Jun 23, 2014 #11


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  13. Jun 23, 2014 #12
    There is no video or image out there that can put into context just how unimaginably large the observable universe is. Our brains are simply not wired to comprehend the distance or size of these objects. Here is a taster though.

    It takes light about 8 and a half minutes to travel from the sun to earth. 8 and a half minutes at 186,000miles per second, now that is a pretty long distance right? Now "try" to wrap your head around this. The closest star to our own is 4.2light years away. 4.2years at 186,000miles every single second, or to put it in numbers that you still won't understand, 24.7trillion miles.

    24.7trillion miles or 4.2light years and we are barely left the doorstep. If you were to compare this to a distance on Earth, you'd be about half an inch ouside your door with the rest of the world still to be explored.

    There may be some physicists out there who can actually grasp just how far 24.7trillion miles is but for the most part, it's a meaningless number, anything further is even more meaningless.
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