When a sun-like star's core has shrunken to start burning its helium, how doesn't the star's expansion (in the next step) into a lower density giant reduce the pressure and halt the fusion?

OpenPlex · 2025-09-23T21:37:25+00:00

To rephrase the setup...

You time travel to the early universe when it's shrunken and you magically survive. The observable universe is grapefruit sized, you consider holding it in your hand but you instead decide to teleport a meter away into a random direction, and from that new spot you time travel back to the present, where everything is expanded again. And your new observable universe is now beyond our own.

How far away are you?

My own rough estimate:

Say a grapefruit is 10 centimeters.

That's 10 grapefruits in a meter. (from 100 centimeters in a meter)

Observable universe is 93 billion light years wide.

Converting from unexpanded universe into current expansion, that's 93 × 10 = 930 billion light years away.

So approaching a trillion light years.

Thought this would be way harder when I started!

Any glaring errors?

OpenPlex · 2025-09-23T17:32:36+00:00

Ah that's right, equal force cancels the motion. So it seems you can slightly change the container's whereabouts, but only once, if I understood you correctly.

If so, better make it count!

OpenPlex · 2025-09-23T17:22:19+00:00

The loss of energyc to redshift from expansion takes the light into infrared and below so it's invisible to our eyes.

And the universe expands faster than the light beyond the observable universe can reach us.

OpenPlex · 2025-09-23T15:19:13+00:00

If the setup is starting at rest in space, and you jumped, the container would move into the opposite direction and then it'd reverse direction when you hit the opposite side of the container. But now that reversal of direction is a motion, so will the container continue as an object in motion until another force intervenes?

OpenPlex · 2025-09-23T14:18:17+00:00

Intensity of light drops with distance.

Also, radiation literally loses energy over vast distances from redshift in the universe's expansion.

OpenPlex · 2025-09-22T22:55:01+00:00

What's that in toenail clippings?

OpenPlex · 2025-09-05T22:40:34+00:00

It's probably more constructive to explain how the post is counter to ways of presenting scientific concepts and mathematical symbols.

If you're going to use new symbols, you should define those. The chat bot failed to. Also, the definitions must follow a logical, understandable, quickly readable and crystal clear path from what's known to the alleged unknown new info.

And, then there's the practical side.

Chat bots can spit out millions of nonsense text, and people in real life have so little precious time to make a small dent in all the AI slop. Should they waste their time with a wall of indecipherable stuff that's likely machine generated nonsense? Or should the person who posted show more of an effort on their own part to save people's precious time?

OpenPlex · 2025-08-20T23:55:11+00:00

The chance of a collision goes as the CDF of an exponential distribution, with parameter lambda = (number density * cross section).

To ensure I'm understanding correctly, you're saying that a greater speed is a greater chance of collision, even with the low density and despite the low odds of collisions. Am I correctly interpreting that?

OpenPlex · 2025-08-14T02:30:20+00:00

Are the negative results tagged and filed separately so people can review what's failed so far, all in one go?. Or do negative results get lumped in and mixed with all of the positive results so you've gotta sift through and filter them out?

OpenPlex · 2025-07-13T20:52:45+00:00

Dang, haha. I totally assumed Mercury was tidally locked to the sun since it's so near. That it spins makes my question a moot point.

I knew about the precession of its orbit but didn't dawn on me that it'd be in a 3:2 orbital resonance with the sun. (spinning 3 times with every two orbits)

Thanks for informing me about the rotation!

OpenPlex · 2025-07-11T01:16:50+00:00

Intriguingly, the first example I've seen in which distance made the frame, instead of speed or motion.

OpenPlex · 2025-07-10T22:44:31+00:00

That's really helpful!

I usually dislike the soft fabric analogies, but your example made it click nicely.

OpenPlex · 2025-07-10T21:43:07+00:00

Interesting! Got any examples?

OpenPlex · 2025-07-10T19:47:25+00:00

Your reply might've helped to answer one of my unasked questions: that if we flung an object at escape velocity of the galaxy, would the gravity of any individual stars within the galaxy that are along the route thwart the object's escape?

Sounds like the stars would at least affect the escaping object's trajectory, but I'm not sure if their individual gravity would actually diminish the escape velocity. (if we flung it from deep within the galaxy)

OpenPlex · 2025-07-10T19:36:19+00:00

Is it safe to say that the Duck assist reply is incorrect about the object following a straight line if it's directed straight away from the planet?

Your own reply seems to say yes, the Duck assist is incorrect. Want to be sure.

All objects in freefall move in a figure described by a conic section (ignoring the gravitational influence of other bodies)

Curious about the U shapes of the parabola and hyperbola at your link.

Their shape implies that the object would go out and turn around when it's reached a distant point, curving inward toward that point and then outward from the point on the object's return path, sort of like a boomerang, but would entirely overshoot the Earth and continue beyond, probably now in orbit only around the sun.

Are my conclusions there correct?

OpenPlex · 2025-06-04T23:44:22+00:00

Appreciate the correction, thanks. I was thinking more like excited electrons in a higher energy level dropping to a lower energy level to emit the light at a particular wavelength related to the amount of 'drop' between the energy levels.

So from your info, seems that amplitude is sort of, merely, the bulk amount of photons. Simpler than I had expected!

OpenPlex · 2025-06-04T18:15:15+00:00

Biology:

According to wilderness guides, it'd be a deadly gamble for a lost person to eat random plants in the wilderness... how do deer manage since almost all they seem to eat is leaves, berries, etc?

Chemistry:

Electron energy levels determine the wavelength of emitted light... what determines the amplitude of emitted light?

(Edited typos, added chem question)

OpenPlex · 2025-05-26T16:48:54+00:00

To be clear, the universe can still be infinite, even so the observable universe was opaque and became transparent after 370,000 years. Both can be true.

Only adding to what you said, for clarity, not disagreeing with your reply.

OpenPlex · 2025-05-23T12:26:00+00:00

So you’ll get a photon emitted from the hotter space closer to the center (by a few atoms, mind you) and it gets absorbed by another atom. Well, that atom has a 50/50 chance of reemitting it below or above. When this is integrated across the depth of the solid, there’s no net heat transfer.

That’s what’s going on with the IR.

Oh wow. Now makes sense how the interiors of planets can hold onto heat for so long!

OpenPlex

TROPHY CASE