# Can a ray of light be destroyed? **URL:** \ **Category:** Factual Questions\ **Created:** [December 29, 2004, 1:23am UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037 "2004-12-29T01:23:12Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![CrazyFoo](https://avatars.discourse-cdn.com/v4/letter/c/e79b87/32.png) [@CrazyFoo](https://boards.straightdope.com/u/CrazyFoo)\ **Post date:** [December 29, 2004, 1:23am UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/1 "2004-12-29T01:23:12Z")
Sorry if this has been covered. I did a search and couldnt find it. Once light travels from the sun to the earth, does that ray of light live forever? Just speeding around the universe at 186,000 miles a second? Or does it eventually diminsh, wear out and die? Regards ---
**Author:** ![dotchan](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@dotchan](https://boards.straightdope.com/u/dotchan)\ **Post date:** [December 29, 2004, 1:59am UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/2 "2004-12-29T01:59:37Z")
I suppose eventually they lose so much energy that they just stop existing. (IIRC, Heisenberg’s uncertainty principle can also be expressed as a function of energy and time.) ---
**Author:** ![HMS\_Irruncible](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hms_irruncible/32/7394_2.png) [@HMS\_Irruncible](https://boards.straightdope.com/u/HMS_Irruncible)\ **Post date:** [December 29, 2004, 2:04am UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/3 "2004-12-29T02:04:06Z")
> [@CrazyFoo](#): > > Sorry if this has been covered. I did a search and couldnt find it. > > Once light travels from the sun to the earth, does that ray of light live forever? Just speeding around the universe at 186,000 miles a second? > > Or does it eventually diminsh, wear out and die? > > Regards It wears out and dies, and darned if it always doesn’t happen right after the warranty expires. Seriously… when a photon of light encounters matter, it comes to an end. It is absorbed and radiated as either a different photon of light, or some other type of energy. There’s another active thread on this right now with some nice analogies, but I can’t be arsed to dig it up. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [December 29, 2004, 7:22am UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/4 "2004-12-29T07:22:50Z")
> [@CrazyFoo](#): > > Sorry if this has been covered. I did a search and couldnt find it. > > Once light travels from the sun to the earth, does that ray of light live forever? Just speeding around the universe at 186,000 miles a second? > > Or does it eventually diminsh, wear out and die? > > Regards There’s no such thing as a ray of light. The waves in the electromagnetic field from a point generating source have lower amplitudes farther from the source, but it’s the mode of vibration in spacetime of the field _as a whole_ which is a photon. Nothing really dissipates or diminishes. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [December 29, 2004, 9:22am UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/5 "2004-12-29T09:22:01Z")
The wavelength increases as the universe is expanding, so that would indicate a loss of energy, maybe more like a lose of entropy, as your not suppose to be able to loose energy. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [December 29, 2004, 1:34pm UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/6 "2004-12-29T13:34:11Z")
> [@kanicbird](#): > > The wavelength increases as the universe is expanding, so that would indicate a loss of energy, maybe more like a lose of entropy, as your not suppose to be able to loose energy. Um, entropy only goes up. You know, one of those _other_ laws of thermodynamics than conservation of energy? The wavelength gives the energy _density_, and the expansion increases the volume, thus conserving energy. ---
**Author:** ![CrazyFoo](https://avatars.discourse-cdn.com/v4/letter/c/e79b87/32.png) [@CrazyFoo](https://boards.straightdope.com/u/CrazyFoo)\ **Post date:** [December 29, 2004, 2:36pm UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/7 "2004-12-29T14:36:32Z")
Do photons come in different sizes? I see the sun as a giant nuclear reactor in the sky, shotting down light beams to earth (photons) Do these photons vary in size depending on the pulse? Or are they always the same size? Thank you ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [December 29, 2004, 3:57pm UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/8 "2004-12-29T15:57:57Z")
You may be interested in this thread: [What happens to photons?](http://boards.straightdope.com/sdmb/showthread.php?t=293867) The “size” of a photon is about its wavelength. But photons are not hard, with a well-defined edge. Photons are squishy. 🙂 ---
**Author:** ![Joe\_Random](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)\ **Post date:** [December 29, 2004, 4:01pm UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/9 "2004-12-29T16:01:22Z")
> [@CrazyFoo](#): > > Do photons come in different sizes? From what I understand, photons don’t really **have** a property that could correctly be called “size”. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [December 29, 2004, 11:52pm UTC](https://boards.straightdope.com/t/can-a-ray-of-light-be-destroyed/282037/10 "2004-12-29T23:52:21Z")
Back to the OP, we know we can see the farthest galaxies, quasars, and other early universe objects. Those photons have been traveling effectively as far as photons can go in our observable universe. They have not faded out or lost energy (despite the efforts of some who wish to believe that the redshift is caused by something other than distance and relative speed). So, unlike diamonds, photons are forever.