Expansion of space and dark matter

  1. question 1. i need some help understanding this. it is proven that the universe is infinitely expanding correct? what is the exact reason for that?

    question 2. i have a couple questions on dark matter. does dark matter give off its own gravity bending space-time, im assuming ?
  2. jcsd
  3. Drakkith

    Staff: Mentor

    1. It is believed that the universe is expanding and that it will continue. Is it PROVEN? There IS evidence, which is why we believe this, but to say it is proven is kind of iffy. It's better to say that the current evidence combined with our currrent understanding of physics supports the idea that the universe is expanding. The reason for the expansion is currently unknown. There are several hypothesized things such as dark energy that might explain it, but we currently don't know.

    2. From our current theory on dark matter, it DOES interact through gravity. Meaning that it does have gravity like normal matter does. This is supposedly the reason why galaxies are held together, as the amount of matter that is visible to us currently doesn't seem to be enough to hold everything together. That and other discrepencies as well.
  4. bcrowell

    bcrowell 6,240
    Staff Emeritus
    Science Advisor
    Gold Member

    By "reason," do you mean what is the evidence, or what is the physical mechanism that people invoke to explain the observations?
  5. so, a possible theory would be that dark matter gives off a repulsive force that is expanding the universe?
  6. yes the evidence
  7. Drakkith

    Staff: Mentor

    No, that is Dark Energy. Dark matter interacts through gravity and pulls stuff in like normal matter does.
  8. Drakkith

    Staff: Mentor

    One of the biggest points in evidence is the increasing amounts of redshift as we look at things further and further away from us.
  9. very good explanation thank you
  10. DaveC426913

    DaveC426913 16,350
    Gold Member

    As Drakkith points out, DM has an attractive force, just like regular matter.

    Indeed, DM was initally hypothesized as an explanation of an observed larger gravitational attraction than expected. (i.e. the gravitational effect was observed first and, without any explanation forthcoming, it was thus proposed that there was some extra matter floating about that could not be seen - i.e. dark).
  11. without dark matter would light still bend in space?
  12. Drakkith

    Staff: Mentor

    Yes. Gravity from normal matter bends light. One of the first experiments to prove Einsteins theories on relativity was measuring the bending of light around the sun.
  13. very well sir. another question for you. If Newtons third law states that every reaction has an equal and opposite reaction , would it be possible for everything a black hole intakes it would spew out somewhere else maybe a white hole ?
  14. DaveC426913

    DaveC426913 16,350
    Gold Member

    1] That is a misapplication of Newton's Law.

    2] We know that the infalling matter of a black hole does not go anywhere. We know this because we can measure the BH's gravity, which is in direct correlation with the amount of matter there.
  15. bcrowell

    bcrowell 6,240
    Staff Emeritus
    Science Advisor
    Gold Member

    There is also a second, independent source of information from the CMB anisotropy, and it confirms the nonzero cosmological constant.
  16. Firstly let it be known that I am a total philistine. I dropped out of community college before I even got an AA so don't let my ignorance offend you who is reading this.

    In response to the certainty that the matter in blackholes does not go anywhere -- Ok, so from my limited understanding according to Einstein, gravity waves travel along the fabric of spacetime at the speed of light i.e. the sun disappears, it would take approx 8 minutes (or what have you) for the gravitational effects to be felt. Does a black hole warp spacetime to an infinite degree? Are we necessarily able to interpret the goings on of a black hole beyond a certain extent in that warping? In my mind I'm seeing that when spacetime is warped/stretched it takes longer for the gravitational wave to travel along it to an outside point and be "observed" It almost sounds like I'm asking whether or not gravity affects itself which sounds bizarre to me now that I think about it.

    That aside, I found this thread on google because I was searching for information on dark matter. I had the thought "What if mass isn't what warps spacetime, but an already warped spacetime is what attracts/pools mass?" I made the assumption that if this were the case there would be places where spacetime was warped but there would be no observable mass because there simply wasn't any nearby matter to "pool" into the warp in spacetime, so I started looking into dark matter.

    Once again, I apologize for my ignorance. I'm simply an unemployed drunkard with a computer.
  17. Theget welcome to the forum. I think it is good that you and others ask questions. Perhaps the various threads already here may help?
  18. Sorry, I should've looked through the forum before replying.
  19. There is none proof of 1. What exists are observations that is currently expanding.

    I think that you confound dark matter with dark energy
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