3 ms·

Most people haven't been in an MRI, either. I only know about their existence from TV.

Retric 2y ago
That doesn’t really matter here. ~300k people in the US get an MRI per year (significantly more are near the things) and they have been around since the 1970’s. 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/ https://what-if.xkcd.com/114/
- daveguy 2y ago
  Let me break it down for you. 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. [0] https://mriquestions.com/metallic-taste.html https://mriquestions.com/metallic-taste.html [1] https://pubmed.ncbi.nlm.nih.gov/17969179/ https://pubmed.ncbi.nlm.nih.gov/17969179/
  - Retric 2y ago
    Sure, you can clarify why you think someone walking up to and then getting inside an MRI would only experience a specific orientation? 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.
    - daveguy 2y ago
      Apparently you have not had an MRI or studied MRI. 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.
      - Retric 2y ago
        > The people operating the MRI are outside the magnetic field. 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.
        daveguy 2y ago
        Oh good, they noticed the effect too. It's almost as if many people experience the effect, but somehow to you it's impossible for any humans to be able to take advantage of the effect at lower field strengths. 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.

That doesn’t really matter here. ~300k people in the US get an MRI per year (significantly more are near the things) and they have been around since the 1970’s. 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/ https://what-if.xkcd.com/114/

daveguy 2y ago
Let me break it down for you. 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. [0] https://mriquestions.com/metallic-taste.html https://mriquestions.com/metallic-taste.html [1] https://pubmed.ncbi.nlm.nih.gov/17969179/ https://pubmed.ncbi.nlm.nih.gov/17969179/
- Retric 2y ago
  Sure, you can clarify why you think someone walking up to and then getting inside an MRI would only experience a specific orientation? 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.
  - daveguy 2y ago
    Apparently you have not had an MRI or studied MRI. 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.
    - Retric 2y ago
      > The people operating the MRI are outside the magnetic field. 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.
      - daveguy 2y ago
        Oh good, they noticed the effect too. It's almost as if many people experience the effect, but somehow to you it's impossible for any humans to be able to take advantage of the effect at lower field strengths. 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.