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

End of the Universe

  1. Mar 9, 2007 #1
    I have been thinking about this for a while. Most theories don't make a lot of sense to me. What makes sense is that the universe will end in light. because light is being given off always and shot off into the end of space then it will never come back to hit another solid and be transferred into another form of energy. So unless there is something to bounce off of at the edge of the universe then it should end with a lot of light and some gas.
  2. jcsd
  3. Mar 9, 2007 #2


    User Avatar

    Staff: Mentor

    Why does there need to be an end to the universe? It is a tough concept to wrap your mind around, but if you get into a plane, you can fly around the earth in any direction and never reach an end. Apply that concept in 3 dimensions instead of 2.
  4. Mar 9, 2007 #3
    Well how could the energy from the light that goes beyond the universe every be brought back into any other type of energy. I'm assuming that the universe has a finite amount of energy.
  5. Mar 9, 2007 #4


    User Avatar

    Staff: Mentor

    I don't understand the question. Why would the energy need to change into another type of energy?

    It may be moot, in any case, as the universe's expansion makes it impossible for a photon to actually travel around the universe completely. Again, imagine the plane but this time on an expanding earth. The plane moves forward, but is actually moving away from its starting point in either direction.
  6. Mar 9, 2007 #5
    What I am saying is that the energy from the stars eventually burn up and stop giving off light. After the sun is gone the only thing left of it was the light that it gave off. And once the light goes towards the end of the universe it will never hit anything else. It will always be light. The earth and planets would be pulled into the sun and would eventually be gone too.
  7. Mar 9, 2007 #6
    <first post on here, hi everyone!>

    As stated already there's no 'end' to the universe per se, you seem to be dismissing curvature. Also light wouldn't travel for ever in the way you're describing, not only will it get absorbed by other matter et.c but it follows a geodesic, i.e it follows the curvature of spacetime. You may need to do some background reading on GR, and some basic principles of cosmology.

    You seem to be visualizing the universe as though it's within another arena, as though it has a boundary or edge, but that isn't the accepted cosmological view, the universe is 'where', there's no outside of the universe. Not sure if that helps at all ?
  8. Mar 10, 2007 #7


    User Avatar
    Science Advisor
    Gold Member

    Not even photons can escape the observable universe. The question is moot.
  9. Mar 10, 2007 #8

    there are many holes in that argument- and they are all black (^__-)
  10. Mar 10, 2007 #9


    User Avatar
    Science Advisor

    To make any speculation about the future evolution of the universe is an extreme extrapolation based on the observational data we have today. That being said and accepted, if the universe expands forever and it accelerates the expansion (as we assume it will happen), then it will reach asymptotically a state of no change, or thermal death, that you could regard as its "end". In this state it will actually contain photons (light) and some gas (other elementary particles). However, they will be so diluted that space will be nearly empty. You can read about the end of an universe with accelerated expansion here.
    Last edited: Mar 10, 2007
  11. Mar 11, 2007 #10
    From what I know:

    1. The Big Crunch Theory...

    Results in gigantic black holes before the end of the universe.

    2. The Speeding Up Theory...

    Universe will continue to expand due to dark matter.

    The answer to your question...

    The light will probably be reflected off or absorbed by dust, and will eventually have a (limit to infinity) wavelength.
  12. Mar 11, 2007 #11
    The universe's potential energy gets converted into photons in one way or another. The light released by starts has little or no effect on other star system s because of vast distances between them. Therefore we can assume the light from stars will travel in all directions ad infinitum, long after the host starts are dead.

    So I agree, ultimately, if the universe has no boundaries, and has finite energy, the light will be all that's left, plus chunks of matter unable to release more energy. That's one possible scenario. But we don't know enough about dark matter, energy.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook