<p>In summary "no, why would it?"</p>

<p>If the universe continues to expand, then the photon will experience ongoing cosmological redshift, so it's wavelength (as measured by an observer moving with the general "flow" of galaxies in that part of the cosmos, will get longer, its energy lower, and it will, accordingly become more difficult to detect.</p>

<p>We can detect today photons emitted about 380 000 years after the big bang. At the time they were infrared light, but redshift has stretched them to microwave wavelengths today. </p>

CC BY-SA 4.0
2019-07-30T08:33:29.720Z
Although the peak wavelength of the CMB (when it was emitted) was in the near infrared, it had a significant component in the visible spectrum, as you can see in the spectrum diagram [here](https://physics.stackexchange.com/a/133943/123208). That answer also shows what it would have looked like (orange).
PM 2Ring
CC BY-SA 4.0
2019-07-29T14:50:32.047Z
2019-07-29T14:50:32.047Z
Steve Linton
<p>What happens with a photon when it moves ouit of a galaxy into the 'infinity void', where there's nothing but 'darkness'? Does the photon decay in the end when there are no interactions?</p>

CC BY-SA 4.0
2019-07-28T04:00:08.120Z
light quantum = photon?
Mike G
CC BY-SA 4.0
2019-07-29T03:57:44.437Z
Edited question.
Yurii Kosiak
CC BY-SA 4.0
2019-07-29T04:57:06.677Z
The photon is more accurately defined as a wave if it doesn't hit anything.  The wave expands theoretically forever, though is loses energy both by the inverse square law (frequency) and by the expansion of space (stretches the wavelength).  There may be some kind of ultimate plank limit where the photon/wave is no longer detectible, but that would take a long time to get that far.    So, ultimately the "photon" becomes undetectable if it travels far enough and if the expansion of space is universal.    Does that answer your question?
userLTK
CC BY-SA 4.0
2019-07-29T08:20:46.200Z
Edited title a little
Steve Linton
CC BY-SA 4.0
2019-07-29T12:03:00.417Z
@userLTK Thank you. Is there some method to detect and observe this kind of photons?
Yurii Kosiak
CC BY-SA 4.0
2019-07-29T12:36:45.743Z
Of course - stick a detector out there and it will detect them. Like the way we can detect photons from other galaxies - they just keep on going until the interact with something
Rory Alsop
CC BY-SA 4.0
2019-07-30T08:36:41.640Z
What do you mean by "infinity void"? There are certainly large voids in the observable universe, but they're finite.
PM 2Ring
<light><quantum-mechanics>
What is the final destiny of a photon?
Yurii Kosiak
# What is the final destiny of a photon?

(Asked by: username_0 on 2019-07-26)

What happens with a photon when it moves ouit of a galaxy into the 'infinity void', where there's nothing but 'darkness'? Does the photon decay in the end when there are no interactions?

**Tags:** light, quantum-mechanics

> **Comments:**
> **username_1**: light quantum = photon?  
> **username_0**: Edited question.  
> **username_2**: The photon is more accurately defined as a wave if it doesn't hit anything.  The wave expands theoretically forever, though is loses energy both by the inverse square law (frequency) and by the expansion of space (stretches the wavelength).  There may be some kind of ultimate plank limit where the photon/wave is no longer detectible, but that would take a long time to get that far.    So, ultimately the "photon" becomes undetectable if it travels far enough and if the expansion of space is universal.    Does that answer your question?  
> **username_3**: Edited title a little  
> **username_0**: @username_2 Thank you. Is there some method to detect and observe this kind of photons?  
> **username_4**: Of course - stick a detector out there and it will detect them. Like the way we can detect photons from other galaxies - they just keep on going until the interact with something  
> **username_5**: What do you mean by "infinity void"? There are certainly large voids in the observable universe, but they're finite.  

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## 1 answers

### Answer by username_3 on 2019-07-29. Score: 5 | Accepted answer

In summary "no, why would it?"

If the universe continues to expand, then the photon will experience ongoing cosmological redshift, so it's wavelength (as measured by an observer moving with the general "flow" of galaxies in that part of the cosmos, will get longer, its energy lower, and it will, accordingly become more difficult to detect.

We can detect today photons emitted about 380 000 years after the big bang. At the time they were infrared light, but redshift has stretched them to microwave wavelengths today.

> **Comments:**
> **username_5**: Although the peak wavelength of the CMB (when it was emitted) was in the near infrared, it had a significant component in the visible spectrum, as you can see in the spectrum diagram [here](https://physics.stackexchange.com/a/133943/123208). That answer also shows what it would have looked like (orange).  

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