Unruled Notebook

Cats are worshiped by Egyptians. Cats are blogged on Fridays. Even cat’s downfall is analyzed in feline pesematology. Nevertheless, in this part of terra firma, cats crossing your path is considered a bad omen.

You step out of the house on an important errand, and a cat crosses your path; you (are made to) promptly stop, turn around and get back into home. You wait for sufficient time inside your home, drinking a cup of water before some one elderly checks the road and prompts when everything is auspicious again for you to get back on the road.

The “reasons” for considering cat crossing your path as a bad omen are many, with new ones given on the spur everyday. Let me give here the “scientific” one given to me some years back. It goes like this: Cats sense magnetic fields and since they do, they should be magnetic or at least capable of influencing magnetic fields. So, when they cross in front of you, cats influence the local geomagnetic field, which in turn manifest as a bad omen for you. Of course, this “scientific reason” wasn’t meant to be believed, but was given to make me think “what if” and in the process, not mind actually doing what the elders of the family asked me to do, i.e the routine in the previous paragraph, when I cross path with a cat.

Flash-forward. There is a recent Physics Today article on Magnetoreception in animals by Sönke Johnsen and Kenneth J. Lohmann that states

the idea that animals can detect Earth’s magnetic field has traveled the path from ridicule to well-established fact in little more than one generation. Dozens of experiments have now shown that diverse animal species, ranging from bees to salamanders to sea turtles to birds, have internal compasses.

If you have access to the magazine, read the nice article. We shall proceed with a summary on magneto reception research.

It has been observed that many animals possess means for detecting magnetic fields. The familiar one for us is perhaps the pigeon but even sharks and salamander possess magnetoreception. However, it is not yet clear how exactly animals sense the magnetic field. Finding this mechanism is a current research area of sensory biology.

Three mechanisms of sensing magnetic fields are proposed so far in animals. Electro-magnetic induction, ferri-magnetism and radical pair reactions that are influenced by magnetic fields. All three proposed mechanisms are capable of obtaining information from the weak geomagnetic field (varies between 30 to 60 microteslas). However, with the exception of magnetotactic bacteria, no mechanism has been conclusively established.

Sharks and rays possess magneto-induced electroreception. A conducting rod, when moved through a magnetic field is induced with a charge distribution, based on the Lorentz force. However, due to the weakness of the geomagnetic field, it requires a highly sensitive receptor for sensing the field. Sharks seem to possess such a receptor in the form of long canals filled with a high conducting jelly, with the canals beginning at tiny pores in the skin surface and ending at a depth at the ampullae made of cells that are capable of detecting very small voltage differences (~ 2 micro volts/meter).

[Image Source: Physics Today, March 2008, p.29, Magnetoreception in Animals]

With such a sensitive receptor – to quote from the above PT article

[..] magnetoreception using induction (for sharks) is theoretically possible. Depending on its compass direction, a shark or ray moving horizontally through the ocean at 1 m/s (about 2 miles per hour) could generate a voltage gradient at the receptor as high as 25 µV/m, well above the detection threshold.

There are several other complications and debates about electroreception serving as a means for magnetoreception in sharks, which I shall skip for the moment. They are all adequately explained in the above article.

However, barring pigeons and bacteria, it is yet to be established that such magnetoreception techniques are present in terrestrial animals. To quote from the PT article

[..] electromagnetic induction appears unlikely to be a widespread mechanism for magnetoreception because only elasmobranchs are known to have the extreme electrical sensitivity required. Most animals with electroreceptors have electric thresholds two to five orders of magnitude higher—too high for magnetoreception. For example, the electric fish Eigenmannia (glass knifefish), a relatively electrosensitive animal, would need to swim at 400 mph (nearly 180 m/s) to detect Earth’s field using induction.

So, to answer my doubt about cats and their magnetoreception or ability to influence the geomagnetic field, I would conclude they just can’t do it. Assuming that cats possess such electroreceptive organs (which is yet to be established) like sharks with similar electric thresholds (highly unlikely) and their 2 miles/hour travel speed, cats crossing my path should do so at about a meter per second.

That is, when they do cross in front of me, I would be unaware that they did.