# physics question how fast does something produce light.

**URL:** <https://boards.straightdope.com/t/physics-question-how-fast-does-something-produce-light/229647>\
**Category:** Factual Questions\
**Created:** [February 17, 2004, 12:37pm UTC](https://boards.straightdope.com/t/physics-question-how-fast-does-something-produce-light/229647 "2004-02-17T12:37:24Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![swansont](https://avatars.discourse-cdn.com/v4/letter/s/5fc32e/32.png) [@swansont](https://boards.straightdope.com/u/swansont)\
**Post date:** [February 21, 2004, 4:44pm UTC](https://boards.straightdope.com/t/physics-question-how-fast-does-something-produce-light/229647/21 "2004-02-21T16:44:30Z")

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> [@billy](#):
>
> The question that should be asked is, after photons have joined, for example in a laser beam, is it possible to extract a photon, that carries the same energy it started with, or in other words, since the photons interact with each other, do they smear to together and lose thier individual energy, and simply grab the same amount back from the stream when they hit something, or do they hold on to the energy the whole time?

The photons don’t join together, like cars on a train. The photons don’t really interact with each other.

If you do an experiment that measures the wave behavior of your light, you’ll see wave behavior. If you do something that measures particle behavior, you’ll see photons. What it’s doing when you aren’t measuring, you really can’t say.

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**Author:** ![billy](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@billy](https://boards.straightdope.com/u/billy)\
**Post date:** [February 21, 2004, 7:09pm UTC](https://boards.straightdope.com/t/physics-question-how-fast-does-something-produce-light/229647/22 "2004-02-21T19:09:16Z")

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> [@swansont](#):
>
> The photons don’t really interact with each other…
> 
> …What it’s doing when you aren’t measuring, you really can’t say.

I’m not saying you’re wrong 'cause I don’t really know myself but wave front theory(wavelets) works on assumptionm that the leading egde of the light can always be assumed to be made of tiny points sources of wave that just happen to interfere constructively only in the dircetion of the beam and destructively all other directions, doen’t this assume the photons are interacting with eachother?

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