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

Do particles without a rest mass bend spacetime?

  1. Dec 26, 2009 #1
    Hi guys,

    simple question I have:

    Do particles without a rest mass (including EM radiation) cause spacetime to bend? Or only those with a rest mass have gravity?
     
  2. jcsd
  3. Dec 26, 2009 #2
    Yes, all forms of energy contribute to the curvature of spacetime.

    Although the role of vacuum energy is still under debate ;)
     
  4. Dec 26, 2009 #3
    Ok, so, the higher Energy the higher local spacetime curvature. Therefore gamma rays bend spacetime more than i.e. radio waves, right?

    If so, then there is a lot of energy out there radiated in the course of the Universe's history. Is there any estimate of how much energy is out there in form of radiation versus matter? Just wondering if this has been included in the "Dark matter" problem explanations? If a large fraction of Universe's energy is out there in form of invisible radiation and it still has a gravitation effect it could account for a lot of the "too much gravity" problem.
     
  5. Dec 26, 2009 #4

    Dale

    Staff: Mentor

  6. Dec 26, 2009 #5
    Thanks, I see that this also explained my problem from my other post where an object could become a black hole if you passed fast enough close to it :).

    Although, I still cannot buy that gravity waves phenomenon. To me existence of gravity waves implies that the energy from a gravity field can vary with a distance (in a wave-like pattern) and therefore not obey the strenght to be measured inversely proportional to the square of the distance rule.
     
  7. Dec 26, 2009 #6

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    The universe does not consider our likes and dislikes.

    I should point out that one can apply your exact same objection to electromagnetic waves.
     
  8. Dec 26, 2009 #7
    But unlike electromagnetic waves, the gravity waves have never been observed. And that's where a personal objection can sneak in ;)
     
  9. Dec 26, 2009 #8

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    That's a different objection. Furthermore, you have to qualify it still further, in that gravity waves have not been directly observed. The rate of energy loss seen in the orbital decay of PSR B1913+16 matches exactly one's expectations from gravitational radiation.
     
  10. Dec 26, 2009 #9
    Wow, I didn't know about this, thanks for pointing this out. Off to study more.
     
  11. Dec 26, 2009 #10

    jtbell

    User Avatar

    Staff: Mentor

    More precisely, the curvature of spacetime at a point is determined by the stress-energy tensor at that point, whose components depends on both energy and momentum.
     
  12. Dec 26, 2009 #11

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    There was a time when the universe was dominated by radiation rather than matter. You can pretty much get this from simple scaling arguments: http://www.lightandmatter.com/html_books/genrel/ch04/ch04.html#Section4.2 [Broken] See section 4.2.2, example 5.
     
    Last edited by a moderator: May 4, 2017
  13. Dec 26, 2009 #12
    Yes, according to the Big Bang theory that was until the CMBR event. But before that was most of the radiation absorbed and re-emited again. So more specifically I would be interested in a matter/radiation estimate after the CMBR event. I guess there is a lot of "flying mass" since just our Sun according to https://www.physicsforums.com/showthread.php?t=238006 looses 4,200,000,000 kilograms of mass to energy every second!

    And this mass is traveling (and bending spacetime) to all directions from every star there is. I would certainly love to see a model of a galaxy that takes this energy distribution into account and see what effect it has on rotational speed of stars in the galaxy.
     
    Last edited by a moderator: May 4, 2017
  14. Dec 26, 2009 #13

    bcrowell

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You're mixing up two different things here: (1) the time when the universe became transparent to radiation, and (2) the time when radiation stopped being the dominant form of mass-energy.

    http://relativity.livingreviews.org/Articles/lrr-2001-1/ [Broken]

    Virtually none. The rotational speed of a star is determined by conservation of angular momentum combined with its moment of inertia. Neither of these is changed signficantly by emission of radiation.
     
    Last edited by a moderator: May 4, 2017
  15. Dec 26, 2009 #14
    I thought both were equal. So when did the (2) happen?

    Sorry, I meant the orbiting speed of stars around the centre of their galaxy. You know, the current problem is that unlike the planets in our solar system, the stars (or any observable objects like hydrogen clouds) in most of galaxies do not reduce their galaxy orbiting speed with distance from their galaxy centre. Instead it stays more or less the same from core to the outer edges. To explain this requires existence of the gravitational pull of the dark matter. The idea I am exploring is if some of the "dark matter effect" is not due to the gravity of energy in form of radiation coming from the galaxy?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook