Only a very few of those mentions are about handedness though, and they show no tendency for right handedness among norther hemisphere critters. In fact they even give evidence for our own right handedness to be hemisphere independent seeing as our close and tropical cousins appear to have right handed tendencies.
Brain laterality aside, there has been plenty of observation that most animals seem to exhibit individual paw/hoof/whatever preferences. Your veterinarian will probably tell you that your cat or dog may be right or left pawed. Cecil covering this:
Is there such a thing as a left handed cat
Cecil offers one commonly stated reason why a paw preference may be better than being ambidextrous:
It is quite common for individual animals to have a preference for one side or the other. It is fairly common for the preference to be biased one way or the other across an entire species. Humans have a stronger bias than most (probably because there’s an advantage to everyone using the same tools). But there’s no particular pattern for which species is biased which way.
As to the three symmetries C, P, and T: So far as we can tell, the strong force, electromagnetism, and gravity all three respect all three symmetries individually (and thus also any combination of them). The weak force doesn’t respect C or P by itself at all, but respects the combination CP almost perfectly: That is, if you take a valid reaction between two particles, replace all of the particles with their antiparticles, and take the mirror image of it, then you have another valid reaction. But even CP isn’t perfectly respected by the weak force: The antiparticle-and-mirrored reaction will be valid, but might proceed at a slightly different rate, by perhaps one part in a thousand (and it is this asymmetry that allows for an actual answer to the question). CPT, meanwhile, should be obeyed by everything: If you take a valid reaction, replace the particles with antiparticles, mirror-flip it, and run the tape backwards, then you have another valid reaction that runs at exactly the same rate.
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However, magnetic field is arbitrary, i.e. labeling the north and south poles of a magnet (or a planet) is arbitrary.
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Hang on. Are you telling me that if I induce a magnet in an electric field, the resulting magnet will have the cathode end pointing north half the time, and the anode end pointing north half the time? That there is no relationship between the orientation of iron atoms in an electric field and the polarity of the resulting compass?
If it comes to that, can’t I construct a compass with an electromagnet?
No, I meant historically, we arbitrarily picked which direction we define as the direction of the magnetic field. It’s defined as the direction of field lines from the N pole to the S pole of a magnet, but that’s defined by the direction of earth’s magnetic field; it could just as easily have been the other way.
If you take every diagram about magnetic fields and reversed all the arrows indicating magnetic field direction, the diagrams will still be correct - except all the right-hand rules become left-hand rules. You can’t send a message to the alien explaining which convention we use.
The whole problem with N-S poles is that we named them from the map directions on the Earth. Why could we do this? Because the Earth has a magnetic field, and that is how compasses work. But there is nothing intrinsic about a planet’s magnetic filed. Not all planets even have them. And ours does becuse of the geo-dynamo effect of circulating conductive fluid inside. Which is why the entire thing becomes self referential.
The reason we can talk about N-S poles is because there are circulating currents in the Earth. So we have defined the poles of a permanent magnet relative to the direction of an electric current. Trying to then define direction of electric current relative to the permanent magnet is simply using the magnet as a proxy for comparing the direction of your experimental current to the direction of the current inside the Earth. So you haven’t won. You are defining a direction via another unknown direction.
Worse, the direction of the Earth’s magnetic field reverses from time to time, and as I hinted 800,000 years ago was the other direction. So if you were talking via a time portal to a being on the Earth 800,000 years ago, you couldn’t be assured of conveying left versus right correctly.
hey y’all,
i’m a longtime lurker here and while I enjoy a good in depth discussion about molecular polarity as much as the next guy/gal, I think youre making this too hard. they are humanoid, and have an understanding of our anatomy and can read our words, the fact that the back of the left hand resembles the first letter of the left word should be enough of a coorelation to start with
I’m still not getting this.
Which of these statements is incorrect
-
We can tell our alien how to construct a circuit with the same meaning of anode and cathode as we use on Earth.
-
We tell the alien to construct a magnet by placing molten iron in the field generated by that circuit.
-
We tell the alien that the north pole is the pole of the magnet that was closest to the anode during formation.
-
So the resulting magnet north and south poles are not at all arbitrary. They are referenced to an anode and a cathode, which are objectively defined.
-
We can then tell the alien that their planetary south pole is the pole that the north pole of the magnet faces towards
-
That allows me to define a south pole as the one which the anode end of the magnet faces.
Put in simple terms, I tell the aliens to paint the anode end of their magnet red. That means that the red end of the magnet will face towards the north pole of their planet. If I then take that magnet to Earth, the red end of the magnet will face towards the north poles of the Earth.
That means that a compass constructed this way is universal. If we have two people holding a compass made in this way, they will always agree on the direction to the north pole. And because we can construct such a compass with no reference to any object that we can both see, that means that we can agree on which pole is the south pole. It’s not arbitrary.
This one:
There is no reason to believe their planet has a magnetic field, if it does, no reason to think that the part of the map they represent as “up” is the same as the North magnetic pole. Heck, it is only an approximation on the Earth. And the Earth’s field can and does periodically reverse.
If you simply tell them that the red end the magnet defines their North Pole, you still haven’t won, as they have no useful direction defined to compare it to.
There is absolutely nothing intrinsic about a planet having a magnetic field or in which direction it points. or for how long it does point. Our sun has a field that reverses every 11 years. Mars has an utterly weird magnetic field, essentially none in one hemisphere, and very weak in the other. Imagine you are trying the conversation with someone on Mars, without having any knowledge of the Martian magnetic field.
This step is wrong. The resulting magnet is not aligned with the anode/cathode; rather, it is perpendicular to the electrical current. The only way to define the north pole of the magnet is to say “if the anode is directly above the cathode, and the magnet is between you and the current flow, the north pole is the right side of the magnet.”
(Or is it the left? I always get this confused.)
Error
An electromagnet is usually made in the form of a helix, so the north end will be closer to either the anode or the cathode. Which one? Well, that depends on whether it’s a right-handed helix or a left-handed one, and now we’re right back to defining left and right again.
You are completely missing the point. No offence, but I’m not going to spend time correcting the misapprehension. You need to re-read what I posted. None of what you posted above has any relevance to what I have written.
SD records go back only to 1973, so cut us a break here.
Maybe. I think we are both reading past one another. Everything I wrote is quite relevant, it all depends upon when you resolve the OP’s question.
It remains arbitrary. You have told the alien that there is a point on their planet that we can call South. By symmetry there is a point that we can call North. So what? You could do this in any manner you like. What does this knowledge gain them? What you are unable to do is to take this definition and turn it into a left versus right distinction without additional knowledge about the planet. Even if we allow a planet that has a similar geo-dynamo to ours, you don’t know how the currents are circulating. So you remain with the problem that all you have done is provide a way of labeling the poles, but not one of working any further.
You don’t need to work this though with another planet. Try this with the Earth and a time portal. Spin the dial on the portal to an unknown time in the last say 5 million years. Try your technique. Can you tell the person at the other end of the portal how to tell left from right? You don’t know the date at the other end of the portal.
This one.
The magnetic field will be clockwise around current in a straight wire, and straight inside a coil or inductor. In either case you’ll have to define “clockwise” for the aliens to determine north from south, and therefore right from left, with this experiment. Which you can’t do without the distinction between right and left to begin with.
Yup. Just occurred to me as well.
It is impossible to convey which is the N and S.
You can wind an appropriate solenoid that you can be consistent with. Take a wire, point it out from you. Drop it over the former to the ground. Loop it back towards yourself, up and over again. Make a nice solenoid.
Now send a current though the wire. Generates a nice magnetic field. We can enforce the direction of the current in many ways, from electro-chemistry up to electron flow in a vacuum tube.
Place some steel in the solenoid. Lots of current, magnetizes the steel. OK, now how do you tell the alien which end is N? You can’t. The solenoid is facing left right. Unless you can convey the left versus right direction you can’t do it.
The same problem arises if you face the solenoid any other direction. You just move the step of defining direction to the direction of wire winding.
Maybe I’m overcomplicating this by referring to the planetary poles, which I thought was the simple option. Let’s start from basics and see if you can point out the flaw in my reasoning.
- Construct a Faraday cage with no external magnetic field.
- In that cage, construct a simple circuit. Basically, give instructions to lay out the circuit on the floor in a rectangular configuration. Place the power source closest to a wall and the anode furthest from the observer.
The result will resemble on of these badly drawn diagrams, where ^ represents the direction of current flow:
_____________
| |^
| |^
-_ |^
_ |^
+| |^
| |^
| |^
| |^
| |^
| |^
| |^
_________________
_________________
^| |
^| |
^| |
^| _-
^| _+
^| |
^| |
^| |
^| |
^| |
^| |
_________________
- Melt some iron, place it in a rectangular mould. Lay it at right angles to the circuit wire:
_________________
| |^
| |^
-_ |^
_ |^
+| |^
| |^
| |^
| ______|_________
| | Molten iron |
| |________________|
| |^
| |^
| |^
| |^
| |^
_________________
_________________
^| |
^| |
^| |
^| _-
^| _+
^| |
^| |
^| |
________|______________ |
| Molten iron ||
|_______________________||
^| |
^| |
^| |
_________________
- Close the circuit and let it run while the iron cools.
As a result of this, we will have created a magnet, possibly a weak one, but with no external fields we will have a magnet.
And because of the left hand rule, the right hand side of this magnet will be the south pole.
We don’t need to actually use the word right hand at this stage. We just need to agree that if we allowed this iron bar to pivot on its long axis inside a magnetic field, the left hand side would point towards what we humans call the south magnetic pole.
Or to say the same thing without using left or right, if we painted the anode side of the magnet blue, the blue side would face east.
Do you see a problem with this?
If this is all correct we can move on to the next step.
The whole issue is, the aliens don’t know which side of a magnet we call the south pole. You are in a circular argument: the “south” pole of a magnet is the side the left side of the magnet points to. And “left” is the side that has the “north” magnetic pole.
Aah, OK, I see now, thanks for the explanation.