Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Dark Matter / Dark Energy

  1. Jul 9, 2010 #1
    If Dark Matter and Dark Energy are so abundant wasn't to be expected that they should be found on Earth?

    We can find elements such as uranium on our planet, which is one of the rarest elements fused on Stars, Dark Matter being estimated to account for roughly 20% of the total mass of the universe and Dark Energy about 70%, shouldn't we expect to find it on Earth, the Moon, Mars or orbiting the Sun?
     
    Last edited: Jul 9, 2010
  2. jcsd
  3. Jul 9, 2010 #2

    mathman

    User Avatar
    Science Advisor

    Dark matter and dark energy are all around. However neither seems to interact with ordinary matter so they are essentially undetectable.
     
  4. Jul 9, 2010 #3
    So how can we ever prove/disprove their existence?
     
  5. Jul 10, 2010 #4
    Some stars move at speeds that should rip the galaxy apart; there is not enough measured mass to supply the gravity needed to hold the galaxy together.

    These high rotational speeds suggest that the galaxy contains more mass than was calculated. Scientists theorize that, if the galaxy was surrounded by a halo of unseen matter, the galaxy could remain stable at such high rotational speeds.

    source: http://www.eclipse.net/~cmmiller/DM/
     
    Last edited by a moderator: Apr 25, 2017
  6. Jul 10, 2010 #5

    Janus

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Dark matter would be evenly distributed as a halo around the galaxy and due to its properties, wouldn't "clump" together like planets and stars do.

    To paint a picture of what I mean, imagine that 4 times the entire mass of the solar system where spread out uniformly in a sphere with the radius of the Oort cloud. You would end up with a density of 4.56e-9 kg/ km³.

    In other words, the entire volume of the Earth would contain ~5000 kg of dark matter at this density. And this would be spread out evenly throughout the entire Earth. Compare this to the 35,709 metric tons of Uranium processed per year from just the upper layers of the Earth's crust.

    And this vastly overestimates the density of dark matter in the galaxy. There may be a lot of it, but it is spread very thinly.
     
  7. Jul 10, 2010 #6

    nicksauce

    User Avatar
    Science Advisor
    Homework Helper

    Meanwhile, the "mass" of dark energy in the earth would be about 10 milligrams.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook