# Thread: Age of the universe

1. 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?

2. Originally Posted by Udoka Esther
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

3. 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.

4. 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.

5. 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.
How is that a problem?

6. Originally Posted by KJW
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.

7. Mayflow, most of the light went past us. Why do you think it doesn't exist anymore?

8. Originally Posted by Jilan
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.

9. Originally Posted by mayflow
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.

10. 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

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.

11. 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 ?

12. 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.

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