Spontaneous Energy Loss in Light

Les Sleeth

Gold Member
2,142
2
I have a question I hope someone can help me with. Does light ever spontaneously lose energy? What I mean is, would, say, an infrared wave be traveling along and suddenly shift to microwave radiation, and maybe later to a radio wave, without any outside influences having affected it? If external influences do cause EM to lose energy, what natural circumstances would do that?

Thanks in advance for anyone's help.
 
Last edited:
A

Alexander

Guest
I never heard about LOSS of energy (=frequency) by a photon.
 
30
0
Loss of energy?

Light can loose energy but it depends on the medium. Wave spontaneously doesn't loose or gain energy. If that's the case we would have radiowaves from X ray machines and Gamma rays from radio stations. Only time photons loose energy is when they collide with a particle
 
Last edited:

Les Sleeth

Gold Member
2,142
2
So I might assume then, that if the universe were to expand eternally, any light that's ever been emitted and not colliding with a particle will continue forever at the same frequency?
 
30
0
Yeah and No! most likely

Remember tired light theory. The wavelengths of the all photons lost energy through interactions with matter en route to earth. This means that almost all photons that interact with earth must have atleast once collided with a matter or even a particle. So it's extremly rear you find a photon not collide with a matter continuing at their original frequency. I beleive you will never find a photon not come in contact with matter ever since they have been emmited. If at all a photon never comes in contact with matter it should continue to move in the same frequency that they have been emitted. But let's wait till astrophysicists tell their ideas. Matter of fact Universe is expanding and galaxies are moving farther away from each other.
 

drag

Spectral Anomaly
Science Advisor
1,046
0
Greetings !
Originally posted by LW Sleeth
So I might assume then, that if the universe were to expand eternally, any light that's ever been emitted and not colliding with a particle will continue forever at the same frequency?
Compared to the Universe as a whole - yes.
BUT, to us, being inside the Universe, the
frequency of EM waves decreases due to the
Universal expansion. An example is the Cosmic
Microwave Background Radiation. Shortly
after the BB the CMBR was EXTREMELY energetic
but then as the Universe expanded the frequency
and hence energy of these waves decreased until
it reached its current microwave frequency
spectral range (and it will keep decreasing).

Live long and prosper.
 
30
0
drag: really?

So you are saying as the universe expands the frequency decreases?
 
A

Alexander

Guest
Re: Yeah and No! most likely

Originally posted by anil
Remember tired light theory. The wavelengths of the all photons lost energy through interactions with matter en route to earth. This means that almost all photons that interact with earth must have atleast once collided with a matter or even a particle.
Not true. It simply means that you are in moving differently than the source reference system (Doppler effect as a mathematical coordinate transformation result).
 
A

Alexander

Guest
Originally posted by LW Sleeth

I was thinking about that because I wonder if there are lower states of energy possible for light than that of a radio wave, and if so, what might light be like in its absolute lowest state of energy.

Obviously only speculation is possible about most of that, but I thought if light had ever been observed spontaneously dropping to a lower energy state, that might be clue. [/B]
Lower than radiowave state is still radiowave (just with lower frequency: 1000000 Hz, 60 Hz, 0.00001 Hz). No additional speculations needed.
 
30
0
Oh...ok!

So in reality a photons cannot loose all of it's energy?
 

Integral

Staff Emeritus
Science Advisor
Gold Member
7,161
54
Photons exist due the change in energy created when an electron changes orbitals. Likewise all photons cease to exist when they induse the reverse transition within an atom. Thus photons are pure energy, they are our conceputalization of how atoms exchange energy, this is the case for all photons. So do not attempt to consider photons with out some understanding of the nature of atoms.
 
A

Alexander

Guest
Re: Oh...ok!

Originally posted by anil
So in reality a photons cannot loose all of it's energy?
Nope. Energy concerves.
 

Les Sleeth

Gold Member
2,142
2
Originally posted by Integral
So do not attempt to consider photons with out some understanding of the nature of atoms.
:frown:
 

Tom Mattson

Staff Emeritus
Science Advisor
Gold Member
5,453
21
Originally posted by Integral
So do not attempt to consider photons with out some understanding of the nature of atoms.
I don't think all that is necessary. Sure, atomic transitions emit light, but that is not the only source. There is also Brehmssrahlung, which is readily understandable without the gory details of atomic physics.
 

marcus

Science Advisor
Gold Member
Dearly Missed
24,650
781
Re: drag: really?

Originally posted by anil
So you are saying as the universe expands the frequency decreases?
Anil, this is true.

this post of yours did not get a response in the thread.
You were replying to what Drag said about some very old light that has declined in frequency and quantum energy over the years:

Drag said:
[[...the
frequency of EM waves decreases due to the
Universal expansion. An example is the Cosmic
Microwave Background Radiation. Shortly
after the BB the CMBR was EXTREMELY energetic
but then as the Universe expanded the frequency
and hence energy of these waves decreased until
it reached its current microwave frequency
spectral range (and it will keep decreasing).]]

So you said "does the frequency really decrease as space
expands" and yes indeed it does. The frequencies in the
CMBR have declined by a factor of 1000.

Space stretching out makes their wavelengths longer and
that lowers their frequency by the same factor. Space
has expanded by a factor of 1000 since those photons were emitted
and so their wavelengths are 1000 times longer and
their frequencies correspondingly lower.

That light which drag was talking about is believed to be
almost as old as the universe----having been emitted only
some 300 thousand years into its history.

interesting stuff, i think
 

marcus

Science Advisor
Gold Member
Dearly Missed
24,650
781
Re: Anil's question about light losing energy

Originally posted by anil
So in reality a photons cannot loose all of it's energy?
Maybe not all, without being absorbed, but a photon can lose 999/1000 of its energy and there are
trillions of photons in the space around us which have already done that----Cosmic Microwave Background photons.

Someone already replied to this post, but in a misleading way, suggesting that a photon can NOT lose any energy because
of something called "energy conservation" but this is untrue.
They CAN lose nearly all their energy.

In principle one can lose everything but a tiny remnant like a millionth of its energy. Or even all but a billionth. This is simply with the expansion of space---not by interacting or being absorbed by anything.
 

marcus

Science Advisor
Gold Member
Dearly Missed
24,650
781
Originally posted by Integral
Photons exist due the change in energy created when an electron changes orbitals. Likewise all photons cease to exist when they induse the reverse transition within an atom. Thus photons are pure energy, they are our conceputalization of how atoms exchange energy, this is the case for all photons. So do not attempt to consider photons with out some understanding of the nature of atoms.
Radiowaves are a form of light which is made by antennas.

Shall I not attempt to consider photons unless I have made a study of antennas?

X-rays and radiowaves are forms of light. X-rays are not made by orbital-change in atoms but by a beam of electrons hitting the wall and having to stop abruptly.

I think I must understand abrupt stopping before I try to understand light.:smile:

It seems that light has something to do with the acceleration and deceleration of charge---electrons in particular.

Changes in momentum---maybe there are changes in momentum inside atoms when they emit and absorb light.

Might be understandable in a general way without studying atoms specifically.
 

Les Sleeth

Gold Member
2,142
2
Re: Re: drag: really?

Originally posted by marcus
The frequencies in the CMBR have declined by a factor of 1000. Space stretching out makes their wavelengths longer and
that lowers their frequency by the same factor. Space
has expanded by a factor of 1000 since those photons were emitted and so their wavelengths are 1000 times longer and
their frequencies correspondingly lower. . . . interesting stuff, i think
Is this true? I'm unfamiliar with it . . . . could you recommend something I might read to get up to speed about it? I agree, intersting stuff, to me anyway.
 
Last edited:

Les Sleeth

Gold Member
2,142
2
Originally posted by Tom
There is also Brehmssrahlung, which is readily understandable without the gory details of atomic physics.
Brehmssrahlung? . . . I'll do a Google search and read up on it.

EDIT: No hits at Google . . . is that the correct spelling?
 
Last edited:
472
0
Re: Re: drag: really?

Originally posted by marcus
So you said "does the frequency really decrease as space
expands" and yes indeed it does. The frequencies in the
CMBR have declined by a factor of 1000.

Space stretching out makes their wavelengths longer and
that lowers their frequency by the same factor. Space
has expanded by a factor of 1000 since those photons were emitted
and so their wavelengths are 1000 times longer and
their frequencies correspondingly lower.
Wait, just only 1000 times?? 13billion lightyears radius that was once singularity, expanded just 1000 times?
And, if even photon looses energy due to expansion, then anything should loose energy to expansion. Or, even, which is first, expansion causing loss of energy, or loss (dissipation) of energy causing expansion?

LW, google for bremsstrahlung
 

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top