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Author Topic: Can light run out of energy?  (Read 6792 times)

James Howard

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Can light run out of energy?
« on: 21/05/2010 10:30:03 »
James Howard asked the Naked Scientists:
   
This question is based on an assumption..

The energy that light has that propels it through space is I presume finite, meaning that there is a limit to the distance to which a light emitting object can shine.

If so, what happens when it runs out of energy? What's left?
I'm thinking about the Sun and its influence.

What do you think?
« Last Edit: 21/05/2010 10:30:03 by _system »


 

Offline Vern

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Can light run out of energy?
« Reply #1 on: 21/05/2010 13:57:36 »
The present thinking is that light does not lose energy as it propagates through space. Many of us think it should. If light did lose energy as it moves through space we would need to rethink all the expanding universe notions we now embrace.
 

Offline syhprum

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Can light run out of energy?
« Reply #2 on: 21/05/2010 16:35:30 »
Provided light propergates thru empty space the only way it loses energy is if the space thru which it is travelling is in fact expanding.
The light that started its journey some 13 billion odd years ago with an energy equivalent to 10^4 degrees has now degraded due to expansion of space to a energy equivalent of 2.73 degrees.
On human time scales there is no loss of energy other than when light interacts with matter en route.
 

Offline Murchie85

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Can light run out of energy?
« Reply #3 on: 23/05/2010 23:26:45 »
I don't pretend to know a lot about this subject as I have yet to study it deeper in my physics course although I can mention a few things I know that may help clarify.

Firstly light that is emited from a star such as our sun will come in many wavelenghts and thus have different amounts of energy, for example blue carries more energy that red light. Considering the first law of thermodynamics in that energy can not be created or destroyed we can assume that the light will only loose or gain energy in interactions with matter (such as a gas cloud in which energy can be transfered from the photon to the gas).

I am not to sure about the next bit but light does not exactly stop, there is minimum level of energy associated with photons and its propagation is associated with the oscilations of the electromagnetic fields. So in theory a photon can travel indefinitely with no energy loss unless there is matter for which it to react with.
 

Offline Atomic-S

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Can light run out of energy?
« Reply #4 on: 24/05/2010 07:49:22 »
The matter is complicated if General Relativity must be considered, which it must, if gravity is significant. Specifically, due to the gravitational time dilation, light having a certain frequency as seen where leaving a gravitating body, will have a lesser frequency when far away from it (as observed at that location) because it is keyed to its original timeframe, which looks slower from a distant location. The number of photons is, apparently, conserved; but inasmuch as the energy of a photon is proportional to frequency, the energy detected at a distant point will be less than what would be detected near the source. It should be pointed out that this energy is not lost irretrievably: if the light then heads in to another gravitating body, it will regain (as seen by an observer there) frequency and energy.
 

Offline JP

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Can light run out of energy?
« Reply #5 on: 24/05/2010 09:11:27 »

 Considering that each future event, losses a potential, 1/2 or some magnitude lesser,
 of the prior event, as the event cascades? (iterations → ∞)

 for example where at any given moment of iteration, in the x domain, Y=0 , X → 0 and will never reaching zero reference,  or visa verse of in the event X and Y → 0 and either never reach the value of zero
 
 Well anyway: the events of the loss of light energy never reaches zero. This might count for the far, far... ∞ far off,  light emission ∞ly showing up in view as time passes relative to the speed of light. Think of it as a spherical dispersion and in any given line of sight there is that photon entity. Hubble deep space stare?


You lost me here.  Light doesn't have to only lose half its energy when interacting with something.  It can lose all its energy and be absorbed.  I think the answers and responses are all about if light traveling in space (and not hitting matter) loses its energy just because time has passed. 

Quote
.  space, light and time are infinite! Umm, 3rd dimension, 4th dimension and 5th dimension, the numerical ratio of a right triangle! Amazing toying with, relating identities of unrelated natures with no proved association. Redefining the word Fantasy?
.

What do 3rd, 4th and 5th dimensions have to do with it?   ???
 

Offline JP

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Can light run out of energy?
« Reply #6 on: 25/05/2010 04:38:05 »
  If the theory of dark matter is supported, which I believe it is!
  Though explanation of the results caused by astronomical refractive lensing.
  Since dark matter makes up for the rest of visually absence of solid matter in the universe.
Can it be safe to say, that light is constantly interacting with matter

Light "loses its energy just because time has passed?"
Energy, in the realm of space, needs a load component to drain or deplete
Time does not have this characteristics.
 .

Space-time is curved by gravity and light moves through space-time, so in that sense, it is interacting with matter constantly.  Dark matter has a fancy name, but its really just matter.  It doesn't really have anything to do with the question about light moving through empty space, far from matter interactions, which was the point of the question, I believe.

Symantics:
3rd dim is space
4th is time
5th is considered light
.
No, the 5th dimension isn't considered light.  Dimensions have a very precise physical and mathematical meaning.  "Light" isn't a dimension.

OK get rid of the hypothetical (1/2) and we partially agree. This is helping me to cover my initial bases
Lose its total energy? Only to the naked eye.
I say the energy amplitude approaches zero and never gets there. Through the hyperbolic function, (x)= 1/x
Plotting the function of (x), as x → ∞; (Y) never reaches zero because x never reaches infinity.
That is the reason Hubble's Deep Space Stare, discovered more spots of light at a the farthest reaches.
I believe that there will be more behind that in the far future relative to Light speed vs space-time
Yes, I think you're right.  The intensity of light reaching us from most spherical sources (and stars tend to be spheres) decreases like 1/r2, where r is the distance to us from the object.  That means that things very far away are very faint.  There are, of course, exceptions to this--some objects like pulsars or gamma ray bursts emit a beam of radiation that dies off much more slowly with distance.  Finally, in the future, we'll probably see fewer objects, because the expansion of the universe is carrying things away from us faster than light.
« Last Edit: 25/05/2010 04:45:19 by JP »
 

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Can light run out of energy?
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