1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How large a mass would it be if all matter was collected together

  1. Jul 21, 2013 #1
    If we say collected all matter in the universe and made one giant lump?
  2. jcsd
  3. Jul 21, 2013 #2


    User Avatar
    Gold Member

    Since it is not known whether the universe is infinite or not, and if finite what size it is, your question cannot be answered.
  4. Jul 21, 2013 #3
    Hi, okay, I never thought about that. How about if we restrict the size of the universe to what is observable.

    Also this is kind of a sub question. If the universe is infinite would the mass of the universe be infinite? Or should I ask this in a fresh thread? I am kind of new here so still discovering the etiquette of the forum.
  5. Jul 21, 2013 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    This is vague even IF we know the total mass of the universe. Why? Because you have not defined the density of this final mass.

    1 gram of lead has a smaller volume than 1 gram of Styrofoam, simply because the lead has a higher density than Styrofoam. So you simply can't say let's collect all the mass and then ask what is the volume, because that volume depends very much on how compact the final object becomes.

  6. Jul 21, 2013 #5
    Thanks, I seem to have got myself in a spot of bother with asking this as I am not a physicist nor clever in physics but just interested in physics as something of an on going interest that I am learning about.
    It is just that I read somewhere that if all the matter in the known universe was compressed into a single mass with no spaces between the atoms of the matter it would be about the size of a large beach ball.

    I just wanted some clarity on that.
  7. Jul 21, 2013 #6
    I hope you didn't get this from this video:


    If so, please don't believe anything that the video tells you. It's complete and utter rubbish.
  8. Jul 21, 2013 #7


    User Avatar

    Staff: Mentor

    Wherever you read that.... don't go back there. :smile:

    And seriously, the responses that you are getting here ("What's the density?" "All the matter in what what volume" "Did you think about...") are a good starting point for appreciating the difference between science and the insipid blather that comes from so much of the pop-sci press and new-age pseudo-sages.
  9. Jul 21, 2013 #8
    No I didn't get it from that video source think it was some internet article I came across. So I suppose my question has not a valid answer at least in real science. Besides when I think about it, if so much matter was clumped together it would ultimately become a black hole due to its gravity and all the matter would become a dimensionless singularity.

    I hope I am correct at least there. Thank you who have responded for clearing some things up for me, much appreciated.
  10. Jul 21, 2013 #9


    User Avatar

    Staff: Mentor

    Perhaps not, but you're much more on the right track by thinking about it this way.

    It's likely that our best current theories (General Relativity and Quantum Mechanics) won't make accurate predictions under such unimaginably high densities; so it may be that something other than the dimensionless singularity suggested by GR will happen. But we don't know what that might be; finding a theory of quantum gravity that will tell us is an important unsolved problem.
  11. Jul 21, 2013 #10
    Thanks taken on board. :)
  12. Jul 21, 2013 #11
    As you condense matter you get to the point where you have a black hole. The volume of a black hole is defined as the volume of the sphere defined by it's event horizon. If we assume this to be a Schwarzschild radius then the radius is proportional to the mass, and therefore the density is proportional to the inverse square of the mass. The more mass you have the less dense you can make it.

    I was going to go ahead and perform the calculation for the Schwarzschild radius for the estimated mass in the observable universe but it appears that someone beat me to it. Per the Wikipedia article on Schwarzschild radius the radius would be about 10 billion light years. http://en.wikipedia.org/wiki/Schwarzschild_radius
  13. Jul 21, 2013 #12
    You ave certainly given me some food for thought and some personal research. I wouldn't of guessed that the event horizon radius of a black hole of all the matter of the observable universe to be so large but I need to remember the observable space in our universe is 14 or so billion light years radius in all directions so space is a lot lot larger.
  14. Jul 22, 2013 #13
    Try 46 billion light years. Add to that the fact that the further away you look the longer ago it was and the more dense it was.
  15. Jul 23, 2013 #14


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I'm surprised that the black hole would be such a significant percentage of the size of the observable universe?
  16. Jul 23, 2013 #15


    User Avatar
    Gold Member

    Yeah, I'm with you. I was really startled the first time I saw this calculation. Turns out supermassive black holes, if you count "density" as the mass divided by the volume inside the Event Horizon are REALLY incredibly lightweight per unit volume and the "size" (again, based on the radius of the EH) gets ridiculously large as the mass increases.
  17. Jul 23, 2013 #16
    That video that Micromass added is so good... that it should have aired on comedy central.

    Anyway as to the OP , the only thing I can say is that the internet is extremely full of crap, possibly the dirtiest place in the whole world.There are two things , either if you are a starter take a trusted webpage like ones from universities or forums like these or just a good book , and if you know something and have a good enough background you can read the internet but you will probably have to sort out atleast 50% of what you read.
    That's how I did.before I cam here at PF I was reading up on many sites just to check how wrong and misleading people can get.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook