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If photons don’t ‘experience time’ how do they experience space? (kbin.social)

submitted 1 year ago by [email protected] to c/[email protected]

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I have read that since photons have no valid reference frame they don’t experience time. They move through space at c so no time value, in essence.

But space and time are the same in relativity and space obviously affects photons ie they experience eachother. Photons redshift over distance and time, as the most obvious example.

So how is it that a photon can’t “experience time” yet it experiences space? Why isn’t redshifting over X ly considered experiencing time already?

I’m just a layman so I’m having a hard time reconciling a photon not experiencing time due to not having a valid reference frame; but that just doesn’t affect its deal with space? It gets a valid reference frame in space then?

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[–] [email protected] 3 points 1 year ago (1 children)

It's a bit more easily understood if you look at a space-time diagram, but essentially it kind of boils down to the speed of an object through space and the speed of an object through time are related and they must add up to 1. So if you're traveling at 50% the speed of light through space, then you're traveling at 50% the speed through time compared to an object at rest. So if you're traveling at 100% the speed of light through space, you're traveling at 0% through time, or not at all.

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago) (1 children)

I’ve read about this but it kind of loses me since it’s such an abstract model of what’s going on. It treats each dimension as equal but like, time certainly seems distinct from the 3 spatial dimensions too.

I know it’s legit and a proper way of understanding it though just nitpicking since it leaves me with a sense of fuzziness like, maybe a gross oversimplification?

Granted I know it’s only meant to explain what’s happening in a predictable way not actually address the nature of these values which I guess is what I naturally lead into wondering about

[–] [email protected] 3 points 1 year ago

I found this channel (Science Asylum) really helpful in explaining things very simply. He uses space-time diagrams in this video to explain how gravity is an emergent property of time and how the two are linked together.

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago) (1 children)

Redshift depends on the observer, so photons do not "experience" redshift until they are detected in an ordinary reference frame.

Furthermore, I'm not sure there is a good way to define the "experience" of a photon. Photons simply move through space until they interact with matter, and matter is never in the same reference frame as light.

[–] [email protected] 1 points 1 year ago

Yeah I figure “experience” is sort of ambiguous and pop science-y, but it’s how I’ve usually had it explained.

That redshift depends on the observer is obvious now that you point it out and profound too since yeah, I suppose they’re not developing across space in the way I imagined.

This makes me wonder about a potential universe with nothing except photons/radiation in it. They’d just.. never change? Even though they could do things like affect spacetime they pass through or interfere with eachother?

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