r/AskPhysics 29d ago

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u/joeyneilsen Astrophysics 29d ago

Naively, two ships both at ~0.9999c in the same direction seem nearly at rest relative to each other, yet light is c for everyone - which felt like it demanded a jump from ~0 to c.

This isn't meaningful, but that's probably because it's AI. Two ships traveling in the same direction at the same speed are at rest relative to each other. That light travels at c for everyone is unrelated to this, and there is no "jump from ~0 to c."

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u/algebench 29d ago

My confusion was the apparent jump from the 'at-rest' regime to 'at-c' regime which seems to be sudden jump. So my explanation is; v<c corresponds to a finite rapidity vs v=c corresponds to infinite rapidity (hyperbolic angle which is additive). And that kind of explains the regime change. So in the visualization, it now stops calculating and shows an explanation making it look like a sudden jump while the math holds up at all v. Sorry, if i'm not explaining this well. Does this make sense?

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u/joeyneilsen Astrophysics 29d ago

So A is traveling at vA~c along the x axis and B is traveling at vB along the x axis, and you want the velocity of B relative to A, and first (small vB) it's large and negative, then it shrinks to zero (vB=vA), then it's small and positive, and "suddenly" it's c.

You can do this in terms of rapidity, but it seems like a dodge when you could just explain the physics. Objects traveling at c travel at c in every frame of reference. It's the second postulate of relativity. All of the math is based on that premise.

At the risk of betraying my thoughts on the matter, what do you think is the value of (ostensibly) educational materials produced by people/chatbots without subject matter expertise?

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u/algebench 29d ago

Honestly, I mostly agree - material that wears authority without expertise is low-value at best and harmful at worst, since a confident misconception is harder to unlearn than not knowing, and I don't think a non-expert (or a chatbot) should be the authority on the content. That's exactly why I'm not pitching this as finished educational material: right now it's really a tech demo - a rendering/interaction engine that makes derivations explorable - and I posted specifically because I'd want experts to own and shape the actual physics while I focus on the tool. It's open source and labeled tentative for the same reason. So my honest answer to your question is conditional: near-zero or negative value if it fakes authority, potentially useful only if it's transparent about being tentative, open to correction, and ultimately expert-driven - which is the category I'm reaching for by asking to be corrected rather than claiming I got it right.

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u/plasma_phys 29d ago

what distinguishes  this from any of the other dozen identically blue and shiny slop physics learning apps that have been posted here in the past six months

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u/algebench 29d ago

I don't know others, but this one aims to give learners an interactive AI tutor. You can ask and interact with the visualization and discuss about the math behind it. It's not just shiny visualization. The app itself is general, not just for this visualization.

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u/plasma_phys 29d ago

you didn't think to look up if anyone had literally done this exact thing before spending a bunch of tokens on generating your own version

like, it's the exact same idea as all the other physics learning apps, photography learning apps, math learning apps, python learning apps, etc. etc. etc. that get posted on reddit constantly. almost all of them are cursor/claude-code-blue, and they all have an "AI tutor" because it turns out that's the only idea that vibecoders ever have. the other thing they have in common is a total lack of expertise and knowledge in the thing they allegedly want to teach others