Notices
Results 1 to 12 of 12
Like Tree1Likes
  • 1 Post By Physicist

Thread: Age of the universe

  1. #1 Age of the universe 
    Junior Member Udoka Esther's Avatar
    Join Date
    Jan 2014
    Location
    nigeria
    Posts
    5
    How do we know the age of the universe?Isn't it possible that there exists light that's so far away,that it hasn't gotten here yet?
    Happy
    Reply With Quote  
     

  2. #2  
    Senior Member
    Join Date
    Jun 2014
    Posts
    551
    Quote Originally Posted by Udoka Esther View Post
    How do we know the age of the universe?Isn't it possible that there exists light that's so far away,that it hasn't gotten here yet?
    It's computed from measuring several cosmological parameters and using general relativity to predict the age of the universe. It's described in Wiki
    Age of the universe - Wikipedia, the free encyclopedia
    Reply With Quote  
     

  3. #3  
    Senior Member
    Join Date
    Mar 2014
    Posts
    236
    We don't actually "know" the age of the Universe - there are just estimations based on theories and observances, and sure there may be light from distances to far away that it has not reached us yet. One of the problems I 'see' is that when we see light from distant places (stars, or what have you) the things eminating the light may not even exist any longer.

    Actually, I have a question on this too. Doesn't light eventually completely dissipate and cease to be? I have always heard that electromagnetic waves dissipate with the inverse of the square of the distance.
    Reply With Quote  
     

  4. #4  
    Senior Member
    Join Date
    Jun 2014
    Posts
    551
    Quote Originally Posted by Mayflow
    Actually, I have a question on this too. Doesn't light eventually completely dissipate and cease to be? I have always heard that electromagnetic waves dissipate with the inverse of the square of the distance.
    Two things happen; (1) the photon density become less and less dense as time goes on and (2) it's energy decreases through cosmological redshift as it moves through the universe so after a few billion years its energy is extremely small.
    Reply With Quote  
     

  5. #5  
    KJW
    KJW is offline
    Super Moderator
    Join Date
    Jun 2013
    Posts
    861
    Quote Originally Posted by mayflow View Post
    One of the problems I 'see' is that when we see light from distant places (stars, or what have you) the things eminating the light may not even exist any longer.
    How is that a problem?
    A tensor equation that is valid in any coordinate system is valid in every coordinate system.
    Reply With Quote  
     

  6. #6  
    Senior Member
    Join Date
    Mar 2014
    Posts
    236
    Quote Originally Posted by KJW View Post
    How is that a problem?
    Because it makes me wonder where all the energy went. If the law of conservation of energy holds true, it must still be around somewhere.
    Reply With Quote  
     

  7. #7  
    Senior Member
    Join Date
    Oct 2013
    Location
    UK
    Posts
    997
    Mayflow, most of the light went past us. Why do you think it doesn't exist anymore?
    Reply With Quote  
     

  8. #8  
    Senior Member
    Join Date
    Mar 2014
    Posts
    236
    Quote Originally Posted by Jilan View Post
    Mayflow, most of the light went past us. Why do you think it doesn't exist anymore?
    I didn't think the energy doesn't exist anymore but it may not still exist in the form of light. A lot of it we won't probably see because it disperses so the intensity at any one place is lessened. Some I think will be transformed into other energies. Maybe like chemical energy as in plants or maybe heat. Maybe some other forms of energy. Maybe even electrical like in solar panels.
    Reply With Quote  
     

  9. #9  
    Senior Member
    Join Date
    Jan 2013
    Posts
    362
    Quote Originally Posted by mayflow View Post
    We don't actually "know" the age of the Universe - there are just estimations based on theories and observances,
    That's what science is all about, Mayflow. That's how it differs from random people just asserting uninformed opinions.

    and sure there may be light from distances to far away that it has not reached us yet. One of the problems I 'see' is that when we see light from distant places (stars, or what have you) the things eminating the light may not even exist any longer.
    I'll add my request to that of others: Why is this a problem for calculating the age of the universe? In fact, what knowledge do you have of how science has calculated the age of the universe, and how would the death of some object in the past affect that calculation?

    I have always heard that electromagnetic waves dissipate with the inverse of the square of the distance.
    You are using the word "dissipate" in too loose a way. The inverse-square law has nothing to do with "dissipation" of energy. It's merely a geometric consequence of energy conservation, not loss. If waves are spreading out uniformly without energy loss, then the energy density must go as the inverse square of distance, because the surface area of a sphere grows as the square of distance. Otherwise, energy would not be conserved.
    Reply With Quote  
     

  10. #10  
    Senior Member
    Join Date
    Jun 2014
    Posts
    551
    Quote Originally Posted by Mayflow
    One of the problems I 'see' is that when we see light from distant places (stars, or what have you) the things eminating the light may not even exist any longer.
    If a star explodes then the energy of the exploding start is conserved. You thought that was a problem because when asked you responded by saying

    Quote Originally Posted by Mayflow
    Because it makes me wonder where all the energy went. If the law of conservation of energy holds true, it must still be around somewhere.
    What must still be around? The energy of the star/source of energy? If so then regardless of what that is energy will be conserved. The sun gives of energy in many forms, some of which is light. The processes which go on inside the star which releases the energy in the form of kinetic energy of sub atomic particles including photons. The laws of thermodynamics ensures that energy will be conserved in all of these processes.
    mayflow likes this.
    Reply With Quote  
     

  11. #11  
    Senior Member Boing3000's Avatar
    Join Date
    Jan 2013
    Location
    Belgium
    Posts
    194
    Quote Originally Posted by tk421
    The inverse-square law has nothing to do with "dissipation" of energy. It's merely a geometric consequence of energy conservation, not loss.
    If a may high-jack a question here, for any radiating source, there is a point when statically you would not fine anymore a unit of Planck energy per unit of increasing surface.
    What is that distance for a star like the sun ?
    Reply With Quote  
     

  12. #12  
    Senior Member
    Join Date
    Jan 2014
    Location
    out there
    Posts
    306
    Where is the energy from "old" light going?

    Is the Universe Leaking Energy? by Tamara M. Davis in Scientific American July 2010.

    The article was scanned or otherwise reproduced in http://www.physics.uq.edu.au/downloa...iAm_Energy.pdf.
    Reply With Quote  
     

Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •