# Does the speed of light still = c...when NOT observed?

**URL:** <https://boards.straightdope.com/t/does-the-speed-of-light-still-c-when-not-observed/1026499>\
**Category:** Factual Questions\
**Created:** [January 9, 2026, 4:09am UTC](https://boards.straightdope.com/t/does-the-speed-of-light-still-c-when-not-observed/1026499 "2026-01-09T04:09:15Z")\
**Posts on this page:** 4\
**Page:** 2

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [January 10, 2026, 2:02pm UTC](https://boards.straightdope.com/t/does-the-speed-of-light-still-c-when-not-observed/1026499/21 "2026-01-10T14:02:23Z")

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Gluons, too, but there are reasons why free gluons never propagate significant distances.

Also possibly (as in, we haven’t ruled it out) the lightest of the neutrinos. It’d be kind of weird if one neutrino is massless while the others have mass, but then again, it’s kind of weird that photons are massless while the Z has mass.

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**Author:** ![EnolaStraight](https://avatars.discourse-cdn.com/v4/letter/e/41988e/32.png) [@EnolaStraight](https://boards.straightdope.com/u/EnolaStraight)\
**Post date:** [January 10, 2026, 4:13pm UTC](https://boards.straightdope.com/t/does-the-speed-of-light-still-c-when-not-observed/1026499/22 "2026-01-10T16:13:59Z")

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Yes. This was the point I was trying to make.

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**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\
**Post date:** [January 10, 2026, 5:03pm UTC](https://boards.straightdope.com/t/does-the-speed-of-light-still-c-when-not-observed/1026499/23 "2026-01-10T17:03:24Z")

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> [@Exapno\_Mapcase](#):
>
> What does QM say about the constant speed of light?

I read somewhere that quantum mechanics does not explain the speed of light but instead assumes it.

I can’t find the link to what I read though so grain of salt and all that.

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**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\
**Post date:** [January 10, 2026, 6:17pm UTC](https://boards.straightdope.com/t/does-the-speed-of-light-still-c-when-not-observed/1026499/24 "2026-01-10T18:17:39Z")

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> [@EnolaStraight](#):
>
> Yes. This was the point I was trying to make

Sure, and as above, this notion of “observable” is not really the same as in the QM sense of observing some phenomena at subatomic scales.

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