Genady

Nothing. The discussion between @Lorentz Jr and @Markus Hanke has moved to GR and then to SR some time ago.

Right! But I've expected the microbial answer and that's why have specified animal organs in the OP. It didn't help, though. Yes, this might be a fundamental obstacle. If we designed a pump for moving blood around, aka heart, it would certainly have a few wheels in it. Dawkins: Why Don't Any Animals Have Wheels? | Live Science:

From your link: I wonder, why. The OP question refers to a variety of wheels used in a variety of human designed mechanisms.

That was the subject of the OP question. There are wheels in microbial world, but not in macroscopic world of animal organs. Why? For clarity: What about it? This:

Animal organs. I am not sure there is a problem, yet. OP just states a fact.

Wheels are ubiquitous in human designed mechanisms but absent in animal organs. Why is it so?

This is not SR. This is a wordplay.

Right. The slowdown of aging is not physical as long as they are in transit. Only when they meet again, their ages can be physically compared. The result is the consequence of the entire history between their separation and their meeting. There are two different worldlines with two different lengths. The acceleration is just an indication of the difference. If the histories are different, why to expect the outcome to be the same?

I think it is more than this, it determines who ages more. Let's say A is on Earth and B is in the spaceship. When B reaches the turning point, it doesn't turn, but instead A accelerates to a faster relative speed and catches up with B somewhere behind that point. Then it will be B who has aged more, right?

The difference is that the spaceship accelerates while Earth does not.

Why is this straightforward question a brain teaser or puzzle?

An active ball joint mechanism (ABENICS) enhanced by interactions of spherical gears: https://ieeexplore.ieee.org/ielx7/8860/9556521/9415699/supp1-3070124.mp4?arnumber=9415699

I see that one can find spirals here and there. I don't see that they are favored.

About 15 years ago I watched an MIT seminar on issues in cosmology. A professor leading it has offered his prediction that in 10 years we will know what dark matter is and we will know that dark energy doesn't exist. 15 years later, we don't know much more than we did then, do we?

What is it?

Is it a cosmological comoving frame, the one where CMB is isotropic?

Separation?

Oh, sorry, I've misunderstood your reply then. We are on the same page

Why do you expect it to be different? Everything else in Nature is like this, too. Look at biological evolution, for example. The principle is nice and simple, descend with modification and selection, but the result is messed and convoluted.

Yes, I think it is our only hope. The pictures which @Lorentz Jr refers to as ontological (deep, intuitive) are and will be human based, shaped by human experience. The rest of the picture can be painted mathematically. Moreover, the flexibility and adaptability of human mind will allow to bend our human intuition to accommodate the mathematical extensions to some degree.

Yes. There is some loss in the dark matter also because of gravitational radiation going away when its particles accelerate and decelerate, but that is many orders of magnitude smaller than the loss to collisions in the normal matter.

You are right. Changing of a shape from sphere to disk does not accelerate the rotation. The reduction in the diameter does. The original cloud of dust and gas is thousands of times larger than the galaxy.

These shapes and the rotation are a natural result of gravitational collapse of the cloud of dust and gas which had a higher density of matter than surrounding space. No. You can find an overview of these processes and related ideas here: Galaxy formation and evolution - Wikipedia

No inheritance of property or genes? Otherwise, it seems that opportunity is not equal from the start.

Is it?