Sixth Sense

Harys Dalvi

November 2022

Florida may be the lightning capital of the US, but New England has tried to compensate with its doorknobs. It seems every other time I've opened a door in November, I've gotten a static shock. Sometimes I can physically see a flash of lightning from the shock, especially when it's dark.

North Florida winters have this to some extent as well. Last winter I got in the habit of flicking doorknobs before opening them so I wouldn't have to bother pulling my hand back when the inevitable shock came. Around the same time, in my physics E&M class, there was once a live demo with a Van de Graaf generator. I thought I could feel the electric field in the room as it powered up.

This got me thinking: can humans detect electric fields? Some research has proposed cellular mechanisms for detection of electric fields [2], but this is likely minor compared to our main five senses. On the other hand, I might have an explanation for human detection of electric fields corroborated by a few days of anecdotal evidence.

Feeling Electric

It's well known that the vapor pressure of water is less in cold air. This means that there's less water to keep you electrically neutral as you build up charge by walking around. Something about the material of my jacket seems particularly prone to building up static electricity. One day I set my jacket down indoors and I could feel an electric field emanating from it.

This was the perfect opportunity to figure out why it is that I think I can feel electric fields. As I moved closer to the jacket, I could feel my hairs drawn towards it. This is probably the explanation for that electric, tingling sensation of an electric field. (Some research [3] seems to back up my conclusion.)

After that, when I had to open the door, I felt the same thing. I knew I was in for the shock of my life, so I decided not to touch the doorknob directly. Instead, I held my phone and moved it close to the doorknob. Eventually, I heard a loud click and saw a bolt of electricity rush between the doorknob and my phone. Even though I wasn't touching the doorknob directly, I felt a static shock in my fingers. Once the charges had neutralized, I couldn't feel the electric field anymore. This anecdotal evidence seems to confirm my theory.

The next question is, is it me or the doorknob that has a charge imbalance, or both? Any of those options would explain this effect because charged objects can attract even neutrally charged objects. For example, if you bring a positively charged object near a neutrally charged object, the electrons in the neutrally charged object will be drawn towards the positively charged object. This will create an asymmetry in the neutrally charged object, allowing it to feel an electrostatic attraction.

Another question is, is this an accumulation of positive or negative charge? Kite-flying Benjamin Franklin famously chose our modern charge convention, which is confusing because electrons are negatively charged but do most of the work in moving electricity around. This is a hard question to answer, because the motion of positive charges one way is almost indistinguishable from the motion of negative charges the other way. One way to distinguish them is known as the Hall effect [4]. Unfortunately, even if humans can detect electric fields, I doubt they can detect something like the Hall effect.

Feeling Magnetic

In a few languages, such as Guugu Yimithirr in Australia, people don't use prepositions such as “in front” and “to the right of”; instead, they use only the cardinal directions north, south, east, and west [5]. So instead of saying there is a kangaroo behind you, they might say there is a kangaroo to your west. Does this represent an underlying human detection of a magnetic field?

In order for a magnetic field to have an effect, there must be moving charges. One example is water: because oxygen is more elecronegative than hydrogen, the oxygen of a water molecule tends to be slightly negatively charged while the hydrogens tend to be the opposite. This makes a moving water molecule, as in blood or the brain, kind of a mini magnet. This is the principle behind MRI machines.

But can we feel it? While we have hairs to feel electric fields, a magnetic field can only make the water molecules in our body point in a particular direction. People usually go about their day without caring which direction their water molecules are pointing in. It isn't something that can really be felt.

If that's the case, then how do migrating birds detect the magnetic field of the Earth? The exact details have been difficult to work out, but one theory suggests that a pair of charged proteins in the eye act as a magnet which then sends signals to the brain through the optic nerve [6].

Feeling Heavy

Can humans feel gravitational fields? This is a surprisingly deep question. At the physiological level, the answer seems to be a clear yes. Stereocilia in the ear bend with gravity based on the position of your head, allowing you to detect the orientation of your head relative to the ground [1]. This means that you can feel which way is up and which way is down even if you can't see or feel the floor. This really is like a sixth sense because it involves a specialized neurological signaling pathway just like the other senses.

However, if you were falling, the stereocilia in your ear would be falling at the same rate. Because of that, rather than feeling gravity, you would feel weightless. The sense of falling would instead come from air resistance on your feet and from seeing the ground come closer with your eyes.

In fact, such a thought experiment was part of what led Einstein to develop the general theory of relativity. If you are falling in an elevator, you can't tell if the elevator is falling due to gravity or if it's quickly accelerating downwards. This led to the idea that gravity isn't a force at all, and instead is an illusion created by the bending of spacetime. From a biological sensing perspective, the (very indirect) implication is that when stereocilia detect orientation, it's really due to lack of the normal force and not gravity itself.

Feeling Strong

I really don't think there's any way for humans to feel the strong force or the weak force.

Feeling Warm

One thing I know humans can feel is warm weather, and I'm feeling the difference. I'm also glad to have a strong candidate explanation for how humans can feel electric fields. Now that I'm back in hot and humid South Florida, I'll enjoy feeling them less often. The forecast is clear of lightning here, but New England doorknobs have started to feel like stormclouds, waiting for a chance to strike.

References

1. Vander's Principles of Physiology (Widmaier, Raff, & Strang, 15^th edition) ^
2. Scientists explain how you can 'feel' electrical fields (K. G. Orphanides, Wired) ^
3. Perception of local DC and AC electric fields in humans (Chapman et al., 2005) ^
4. Hall Effect (C. R. Nave, HyperPhysics, Georgia State University) ^
5. Guugu Yimithirr Cardinal Directions (John B. Haviland, 1988) ^
6. How Migrating Birds Use Quantum Effects to Navigate (Peter J. Hore, Scientific American, 2022) ^