# Can light propagate backwards in time?

**URL:** <https://ask.igwn.org/t/can-light-propagate-backwards-in-time/1343>\
**Category:** Uncategorized\
**Created:** [June 24, 2025, 3:04am UTC](https://ask.igwn.org/t/can-light-propagate-backwards-in-time/1343 "2025-06-24T03:04:32Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Shan909](https://yyz1.discourse-cdn.com/flex031/user_avatar/ask.igwn.org/shan909/32/510_2.png) [@Shan909](https://ask.igwn.org/u/Shan909)\
**Post date:** [June 24, 2025, 3:04am UTC](https://ask.igwn.org/t/can-light-propagate-backwards-in-time/1343/1 "2025-06-24T03:04:32Z")

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I was reading Kip Thorne’s book on the science behind interstellar and a phrase there stuck with me.  
“What happenes inside the event horizon? Time is so extremely warped there that if flows in a direction you would have thought was spatial: it flows downwards towards the singularity. That downward flow in fact is why nothing can escape a black hole.”

Now for me this is a new method of thinking about why nothing escape’s the event horizon as my viewpoint was stuck with gravity and speed light barrier at the event horizon. But if we think that time is flowing onwards linearly, that raises some questions.

The biggest of all is, does this mean light can travel backwards in time?  
Surely nothing comes out of a black hole, but the visual models that I have seen show that the light rays get stuck at the event horizon when released from inside. Or even if they are not travelling from inside the black hole to the horizon but simply holding stationary at that point in space. Does this not mean that they travel backwards in time by conjunction? As the time keeps flowing onwards but the light rays hold still, until they fade out from hawking radiation or dissipation that is.

 ![1000113950](https://canada1.discourse-cdn.com/flex031/uploads/gwosc/original/1X/20fdcc64cb4afbc3abcd59ad7c83c4e8e630968b.jpeg)

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**Author:** ![bhurren](https://avatars.discourse-cdn.com/v4/letter/b/db5fbb/32.png) [@bhurren](https://ask.igwn.org/u/bhurren)\
**Post date:** [October 2, 2025, 6:06pm UTC](https://ask.igwn.org/t/can-light-propagate-backwards-in-time/1343/2 "2025-10-02T18:06:50Z")

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not sure about the answer to this directly, but here is another question, would the photon traveling backwards in time be an ‘anti’ photon, if there is such a thing?

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**Author:** ![Julian](https://yyz1.discourse-cdn.com/flex031/user_avatar/ask.igwn.org/julian/32/408_2.png) [@Julian](https://ask.igwn.org/u/Julian)\
**Post date:** [October 25, 2025, 1:40am UTC](https://ask.igwn.org/t/can-light-propagate-backwards-in-time/1343/3 "2025-10-25T01:40:17Z")

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> **[Negative time observed in photon-atom interaction – Physics World](https://physicsworld.com/a/negative-time-observed-in-photon-atom-interaction/)**
>
> Researchers find that a photon can spend a negative amount of time in an excited atomic state while passing through a cloud of atoms

> **[Scientists observe 'negative time' in quantum experiments](https://phys.org/news/2024-12-scientists-negative-quantum.html)**
>
> Scientists have long known that light can sometimes appear to exit a material before entering it—an effect dismissed as an illusion caused by how waves are distorted by matter.