129 points | by Brajeshwar5 days 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.
PS: I mean both as in separate ecosystems. Not arguing that one organism could contain both.
Less critical things outside of central carbon metabolism often do evolve different stereoisomers in different species, or even the same species. For example, the large macrocyclic antibiotic molecules sometimes evolve to flip sterochemistry, creating a new antibiotic.
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/
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"?
Sure, the names CW/CCW don't matter. But I first have to determine an orientation for each star system, to look at it to see if it is spinning CW or CCW. If I don't, then we cannot decide which way it's spinning, since it's spinning CW from one view, but CCW from another.
E.g., let's say I orient each star system in the galaxy such that it appears to be spinning CW: then by definition, all star systems appear to spin CW. I could choose the other method, and now all star systems spin CCW, despite nothing in the universe changing. I could orient them randomly, and it'd be 50/50. But that tells us nothing: we're sampling how we orient the system to sample it, not any innate quality of the universe.
That is, the entire question, to me, is how do you pick a frame of reference, since there seems to be nothing upon which to pin a frame of reference to.
https://en.wikipedia.org/wiki/Frame_of_reference
You are looking for some sort of absolute reference. A "frame" of reference is arbitrary and relative. It's something you just make up and the rules which you made up apply only relatively and within that frame.
When you look at a paper map, it says North on it, pointing to the "top" of the page. That north is not the real North. It points in whatever random direction the paper happens to be pointing. The paper is a frame of reference, and that "north" only applies relative to everything else on that paper.
If you turn the paper 90 degrees, North no longer points "up" relative to your eyes (although, now it may point "up" relative to my eyes since I am not you but standing next to you).
So that particular instance of "north" is arbitrary. There is no higher or more absolute reference that it is based on.
You pick any direction you want and call it "north", because you can lay that paper down on a table in any direction you want. And it doesn't matter what direction you picked. There is nothing special about "up relative to my eyes" because your eyes point in a random direction. Your eyes and the table and the paper are all somewhere on the surface of a sphere called Earth for one thing, your eyes and the paper might be pointing in any direction at all in 3d space simply by being anywhere on the surface of a sphere. Let alone that the sphere is rotating and travelling in an orbit which itself is in a larger orbit etc etc.
The distribution of celestial objects is full of uniqueness. It's one huge fingerprint. So it is possible to pick identifiers. You can pick objects and then recognize them later from their positions relative to other objects, like finding the north star by recognizing the big dipper.
You can pick any 3 stars and say "For the purposes of the next 5 minutes, let's call this star A and this star B and this star C. A is the north pole, B is the south pole, C is 12 o-clock or 0 degrees, and degrees count up clockwise when looking from north to south."
Congratulations. You just created a coordinate system that you can apply to the entire imagined universe. All other objects can be described in relation to this reference.
That is a frame of reference. There is no "north", you just picked a random direction and said "This is north. Now, relative to that, what directions do the axis of rotations of all other objects point?"
Probably for this question and really all others, it makes more sense to use a rule that "north" for any object is always described relative to it's own direction of rotation. IE rather than saying "this solar system rotates CCW", what you measure is the angle of each objects own local "north" relative to the universal north you made up. Each objects own local "north" would be pointing up from a clock face matching it's rotation.
It does not matter at all which objects you picked for A, B, and C. All that matters is that you use those same points and relationship rules for all subsequent measurements.
(Also since everything, including A, B, and C, are always moving, there is a 4th point of reference which is some arbitrary single point in time)
And for the purpose of the question about random distribution, it does not matter what direction you happened to pick to call north, because we don't care what the directions of all other objects are called, or what they refer to, only are they distributed randomly or is there a bell curve, or some other non-random plot?
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.