A study on how turtles navigate using the Earth’s magnetic field
unc.edu
unc.edu
Mostly I think they're just cute, which is by itself a perfectly valid reason for an animal to be your favorite, but I've always been fascinated by their ruggedness. It's not weird for a turtle to live to 100 years old, and it feels like they can survive just about anything.
Having a built-in GPS just makes them even cooler.
Put me on some winding singletrack in the woods, or driving around an unfamiliar part of town, and I'll remember an imaginary map of where I've been and which directions I've turned, and be able to tell you where north is all day. If I forget, there are context clues everywhere - it's late afternoon here in Michigan so the sun is setting in the southern sky, pointing south-southwest. I'm currently in a windowless manufacturing facility, but I know where the front door is and I remember that's on the west side of the building, so I'm facing east. It helps a lot that many roads and buildings are indexed to be precisely aligned with the compass. It also helps that my Garmin GPS watch has a built-in compass, so if I ever need to shoot a bearing precisely, I train and recalibrate this sense of direction.
But if you put a blindfold on me, sit me down on an office chair, spin it around for a couple minutes as you wheel me down the hall and into an unfamiliar room...after I have finished retching, I hypothesize that I'd have no sensation to tell me where north is.
I appreciate the author's study design here - the source PDF [1] and linked website [2] describe feeding the turtles in the same pool, but exposing them to varied magnetic fields by surrounding the pool in a giant Helmholtz coil. It's not as if they flew the turtles alternately to New Hampshire and to the Gulf of Mexico, which might leave lots of context clues in light or smell or taste, but as if they effectively teleported them to an identical pool of water with slightly different magnetic fields.
[1] https://www.nature.com/articles/s41586-024-08554-y.epdf?shar...
[2] https://oceanweb.sites.oasis.unc.edu/www.unc.edu/depts/ocean...
The true compass would be if you could be blinded, walked through some turns, and you could still pick up north, having no idea about how you got into the surroundings.
Real test would be spin around in a dark room without any cues can you pick out true north.
I'd just sit for like 5-10 minutes at a time every day doing that until I got "bored" by the skill. Not necessarily sure if it's something you can practice as I know there's actual brain structural differences that can determine whether you have this skill and how advanced it is, and I'd imagine it's potentially harder to rewire your brain for this as an adult.
Or if you meant what you wrote, then fairly safe to rule out magnetism from being involved! (I suspect it's not involved either way, but I don't know anything)
(Explanation of the difference between true and magnetic norths: https://www.rmg.co.uk/stories/topics/true-north-magnetic-nor... )
I don't know if its rare? I think most people just never held a magnet against their face.
> I don't know if its rare? I think most people just never held a magnet against their face.
If it were not rare, and simply because most people haven't held a magnet against their nose, people would definitely feel it during an MRI scan, since those are much much much stronger than any regular magnet. An MRI will rip a nose piercing right out of you, a regular magnet you'd have around the home couldn't do that.
I don’t think they comprehend just how strong an MRI is. You don’t need to be inside the machine for it to be the strongest magnetic field you’ve experienced, that’s likely true if you’re in the room nearby. Sure it falls as the square of the distance, but those suckers are big. https://www.youtube.com/watch?v=kLjxhuybFWo
For comparison earths magnetic field is ~50 microtesla vs an MRI at 200,000 to 7,000,000, with 1.5 million microtesla (aka 1.5 T or 15,000 gauss) being common.
If simply waving weak magnetic fields in people’s faces were enough for anything close to 1% of people to notice then it would be common knowledge at this point.
When the signal is strong enough you don’t need careful experiments to pick out the difference. IE the rest of the universe outside of earth isn’t made of antimatter because our telescope’s aren’t on fire. https://what-if.xkcd.com/114/
In electromagnetic fields both an electric field and a magnetic field are produced. They are orthogonal to one another (in 2D with 2 vectors this is perpendicular, orthogonal is when the vector is in a different dimension with respect to multiple reference dimensions). So, detection of a magnetic field could be based on the detection of this orthogonal electric field in the presence of a magnetic field. Highly sensitive electrical detection cells triggered by a magnetic field would be orientation specific, because the more "out of orientation" the less strong the signal.
Also, we could easily have chalked this effect up to a "weird side effect" of metallic taste during MRI[0] which would be more pronounced when the head is moved during the MRI[1].
Hopefully it is clear now why "I think lots of people would have noticed it" is not a great argument against the possibility of humans evolving the detection of magnetic fields. Please let me know if I can clarify anything.
It’s obviously false, but I’m curious why you assume it would be the case.
As to your example, that’s well known even with only 1 in 20 people experiencing it, thus demonstrating my point.
1) The people operating the MRI are outside the magnetic field.
2) The patient in the MRI is oriented such that the magnetic field is directed from head to toe (where the effect on sensing apparatus in place which might detect earth's magnetic field while standing or sitting would be approximately zero, no matter the magnetic strength).
3) Instructions for the patient in the MRI are to remain as still as possible to reduce imaging noise. So, most patients do not move their head much at all.
I'm sorry you seem to be unwilling to even consider the physics, and apparently didn't bother to look at the second reference. I am also sorry that I am having trouble explaining concepts that most biomedical engineers readily understand as the reasons why "but MRI!" is not a valid argument. Regardless, I hope you have a wonderful weekend.
That’s not how magnetic fields work. It’s not some sci-fi force field that cuts off instantly, the field drops off quickly but it doesn’t disappear. Which is why as mentioned in your second link workers noticed the effect.
> unwilling to even consider the physics
Again, you’re seemingly unaware of the actual physics involved.
MRI’s operate via two different electromagnets which create magnetic fields. A really strong one which is on 24/7, and a separate field which is turned off and on in operation and thus doesn’t correlate with earths magnetic field.
So when you walk up to the machine you’re “in” the same giant field just as when you’re inside the machine (or even sitting in some other room in the hospital if we want to be pedantic). This is why it’s relatively common for chairs etc to be yanked across the room and smack into the machines.
And thus, if people could directly sense the orientation of earths magnetic field, being anywhere near an MRI would be a really obvious and novel experience.
When you walk up to the machine it's not turned on. Then non-participants go to the small enclosed control room and then the magnet is activated. Every time you respond you reveal how little you know about MRI and weaken your case. You should stop while you are behind.
Also, you should lookup faraday cage. They're like magic to someone who has never heard of them, and they're used in MRI control rooms.
I feel sorry for your apparent inability to accept you might be ignorant about anything. I hope you grow out of it one day. Enjoy your weekend, I won't be responding again.
False. MRI: https://mriquestions.com/is-field-ever-turned-off.html
Permanent magnet scanners are permanently "on" by definition.
Resistive electromagnet scanners, in theory, can be turned on and off. However, it may take 30-60 minutes for their magnetic fields to stabilize after being off and hence they are generally left continuously on during daily operations. To save electricity, they are usually turned off or have their power levels reduced after hours.
Superconducting scanners remain on at all times as long as superconducting temperatures are maintained. The main field may be ramped down for servicing in a controlled manner with minimal loss of cryogens in about 30 minutes and restored in a few hours, but this is performed only occasionally. In the event of an emergency, all superconducting scanners have a "quench" button that releases liquid helium into the atmosphere and turns their fields off within a few seconds. Dumping that helium is inherently expensive and only done in a serious emergency.
“Faraday cages cannot block stable or slowly varying magnetic fields, such as the Earth's magnetic field (a compass will still work inside one).” https://en.wikipedia.org/wiki/Faraday_cage
> then the magnet is activated
A magnet not THE primary one. Here’s a reasonable though simplified explanation of why there’s multiple magnets involved: https://www.youtube.com/watch?v=NlYXqRG7lus
Anyway, it’s clear you have many fundamental misunderstandings so I can see how you’d come to such wildly inaccurate conclusions.
> it's impossible for any humans to be able to take advantage of the effect at lower field strengths.
The actual literature investigating the effect describes why it doesn’t work on earths magnetic field.
Maybe this source will clue you in as to why your understanding of MRI is fundamentally flawed:
https://pmc.ncbi.nlm.nih.gov/articles/PMC4632105/
Good luck buddy.
But wallow in your ignorance, it brings a little dark joy knowing I am simply better than you in a real tangible way.
You’re unable to erase signs of your failure, and as long as HN lasts anyone can know my dominance.
All it takes is learning how the fundamental forces of the universe work.
Ok, in this context having a friend who works in medical imaging was useful, but that’s just a trivial matter.
Our dogs do that. There's a building we used to go up with six elevators. Three on each side of the hallway facing each other. Without hesitation the dogs will pick the correct direction to go coming out of the elevator. Whereas I always had to check because it all looks the same and depending on which side the elevator is on you have to turn left or right.
It's like they have an innate sense of where they are.
My apartment building has identical elevator lobbies. I thought my dog was smart by not leaving the elevator on seemingly identical incorrect floors. But actually I think she just knows what home smells like.
I would attribute part of it to practice, because when I was younger I spent a lot of times in the woods where you can easily get turned around following animal trails and skirting around obstacles, and finding your way back out accurately was extremely helpful.
Can't remember where I first heard about this, I think it may have been a Malcolm Gladwell book, but in any case if you search you can find lots of articles on the topic.
Interesting, I just barely listened to a Radiolab episode about magnetoreception in birds today [1]. The mechanism is thought to be cryptochrome, a type of protein that exhibits quantum effects when exposed to blue light [2]. The RadioLab story mentioned this mechanism was first proposed in the 70s (I think?) and it was heresy at the time a didn’t get published. Now there’s a SciAm article about it [3], and lots of blog posts. I wonder why this isn’t mentioned? Isn’t there a pretty good chance the mechanism is the same?
* edit: BTW while listening to the podcast I was reminded of Haidinger’s Brush [4] - the fact that many humans can see polarization, once they know what to look for. I wonder if it’s potentially related to navigation since the polarization effect is strongest at 90 degrees from the sun… i.e., generally north and south, in the morning and evening, for much of the earth.
[1] https://radiolab.org/podcast/quantum-birds
[2] https://en.wikipedia.org/wiki/Cryptochrome#Magnetoreception
[3] https://www.scientificamerican.com/article/how-migrating-bir...
Learned magnetic map cues and two mechanisms of magnetoreception in turtles. Nature (2025).
https://doi.org/10.1038/s41586-024-08554-y
https://www.nature.com/articles/s41586-024-08554-y
Full text: https://rdcu.be/d9CgI (shortened link as provided on the page below)
( Provided by the lab's 'Publications' page: https://lohmannlab.web.unc.edu/research-publications/ )
This paper is claiming something different, something to do with a particular magnetic field having a behavioral association.
Lot of question marks and need for some more context. Why would turtles evolve the dancing behavior? Does it have to do with the kind of food they eat and how they get that food? No, turtles did not evolve like dogs to dance and do tricks for food.
The paper (which is here [0] by the way, they failed to provide a link in the article) indicates that these turtles have been known to orient themselves using magnetic fields. The new finding is that they're also able to use magnetic fields as a map -- they can identify a location based on its specific magnetic fields. And apparently, the "mapping" involves a different neurobiological mechanism from the "orientation".
At least that's what I've been telling folk. NewScientist I'm certain.
Something like miniscule tugging of the shell in certain directions being felt?
The magnetic field is sensed by the magnetic forces that act on the magnetite crystals, much in the same way as we sense gravity and acceleration by the forces that act on the otoliths in our inner ear.
While in turtles it has not been identified how they sense the magnetic field, one of the possibilities is that they also use magnetite crystals located somewhere, at least for one of the two kinds of magnetic senses identified in them.
More likely, this might be the same as the mechanism which exists in birds, who can effectively see the Earth's magnetic field in their eyes, although an internal magnetic detection system present in animals would be much more interesting. See https://royalsocietypublishing.org/doi/10.1098/rsif.2019.029.... Birds essentially perceive the Earth's magnetic field through a chemical process in the receptors for red and green light in their eyes, and are believed to have special cells in their beak, brain stem, and possibly their vestibular system as well. It can be disrupted fairly easy by magnetism or different wavelengths of light.
There are obvious other strange implications of this as well, although I'm not sure how much real evidence there is to support them. For instance, there are many concerns about the effects of EMF exposure, as well as that EMF can affect plant life. There is research on magnetic and electric brain stimulation as well. At the most out-there level, there is the research into remote viewing and things like telepathy. So, to whatever extent this actually exists, there are interesting implications for the phenomenological experience of other forms of animal life.
Regardless, it is interesting to see research that is actually showing new and intriguing things regarding different forms of perception (I guess this is arguably ESP, or at least a new sense) that are not complete crank nonsense. I've always felt like my sense of direction was a sort of 6th sense; I guess it really could be.
Wasn’t such a molecule found in bird’s eyes?
[1] https://en.wikipedia.org/wiki/Magnetoreception#Proposed_mech...
[2] https://www.scientificamerican.com/article/how-migrating-bir...