Posted by Brajeshwar 1 day ago
It would be really amazing if we were able to know if both chiralities are equally represented in the space. Apart from the life itself it is astonishingly interesting how life evolved to be monochiral.
Think about trying to “evolve” a glove that fits perfectly on both hands yet is also specific and does not accidentally fit onto non-hands… it would be much harder and less likely than evolving one that only fits left or only right hands.
Spontaneous chemical reactions that make the things we find in space never had to physically fit into a machine like a key into a lock, so both chiral isomers are equally likely to form.
I wonder if planets revolve around stars cw vs ccw evenly distributed.
(and could these kinds of things be related?)
Depends on whether you view it from one side or the other, no? Or, how do you define which side of a planetary system is the "top"?
The rotation vector is associated with another, which is angular momentum. The reason why there's all kinds of spinny stuff in a solar system, or a galaxy, is that the massive objects jointly conserve the total angular momentum of the blob of dust that the system coalesced from.
Neutrinos are another beast, they have a preference for one direction of their spin quantum number:
https://neutrinos.fnal.gov/mysteries/handedness/
In fact you could use the spin of neutrinos to say that the sign convention for rotation is not arbitrary.
Consider the following. You and I are standing on opposite sides of a pane of glass. I spin a wheel parallel to the pane of glass and we both observe it. From my side of the glass the wheel is spinning clockwise. From your point of view (because you are seeing the opposite side of the wheel) it is spinning counterclockwise.
Whether a given rotation is clockwise or counterclockwise depends entirely on your reference frame - they really don't have a robust definition that doesn't depend on the pov of the observer.
There is a really excellent and clear description of the problem and solution to this that is employed in classical mechanics here[1] but if you only care about the solution, by convention we employ the right hand rule. If you and I both agree a common direction in the plane of rotation of the wheel say parallel to the floor off to the side (whichever side doesn't matter but for one of us it will be to the left and the other right), point our right hand index finger in that direction (called r hat or the direction of radial motion) and curl our two smallest fingers in the direction of rotation of the wheel, our thumbs will be pointing parallel with one another. This would be called n hat (normal motion), and is the direction of any vectors which are the cross product of two vectors in the plane of rotation of the wheel. As a bonus if you make your right hand middle finger perpendicular to the index finger you have theta hat (tangential motion). Now even though you and I can't agree whether the wheel is spinning clockwise or counterclockwise we have three identical basis vectors and can use these to form a common polar coordinate system to describe this rotating system.
This is true for most of the other planets also and they orbit in the same plane.
And this is true for most stars in the galaxy and the rotation of the galaxy itself too.
So it's pretty much all counter-clockwise.
If you define North to be "the pole that if it's on the top then things rotate counterclockwise" and that's consistent then that's equivalent to the definition of an orientable Euclidian space I think, and I'm glad that's the case for our universe because things would be mighty weird if it weren't. You could shift your breakfast around the table and it would come back as a mirror image of itself.
Joking aside as I understand it any orientable 3-d space admits two orientations, which are defined by the choice of the surface normal n. If you do it the way I said in a sibling post with the right-hand rule then n is pointing paralel to the axis of the Earth with positive in the direction of the North pole, the rotation is counterclockwise from that perspective and everything is groovy. But we could equally use our left hand, our thumb would point South and the rotation of the Earth would be clockwise. In that case we are choosing to orient using the other possible surface normal (-n).
So it shouldn't be surprising stuff is for the most part moving in the same direction. It's surprising when something isn't, probably because it was hit by some body changing its angular velocity.
The same goes for the alignment of equators.
From https://news.ycombinator.com/item?id=41873531 :
> "Chiral Colloidal Molecules And Observation of The Propeller Effect" https://pmc.ncbi.nlm.nih.gov/articles/PMC3856768/