In a famous scene in X2 (of the first cinematic X-Men films), Magneto uses his magnetic powers to rip the iron out of somebody's body, before going on a rampage using the iron like a bullet.
Of course, the movie goes to great pains to show that the reason Magneto is able to do this is because the security guard had been injected with iron beforehand. Nevertheless – as people have been asking on Reddit – is it possible for a really strong magnet to affect your blood?
First off, while we know blood contains iron, we also know that magnets can't rip the iron from your blood. If it could, that would happen every time somebody stepped into an MRI machine, and they probably wouldn't still be in use. But that doesn't mean that strong magnets don't affect your blood. In fact, a technique used for measuring brain activity inside MRI machines relies on the fact that they do.
Your blood is not ferromagnetic, or magnetic in the same way that people usually understand magnetism. However, it does have very weak magnetic properties.
Oxyhemoglobin is weakly diamagnetic, meaning it is slightly repelled by a magnetic field, while deoxyhemoglobin is paramagnetic, or slightly attracted to a magnetic field. It is this that allows us to measure brain activity using MRI machines.
"The reason fMRI is able to detect [changes in the brain] is due to a fundamental difference in the paramagnetic properties of oxyHb and deoxyHb," Radiopaedia explains.
"Deoxygenated haemoglobin is paramagnetic whereas oxygenated haemoglobin is not, and therefore the former will cause local dephasing of protons, and thus reduce the returned signal from the tissues in the immediate vicinity."
As suggested on Reddit, if you scaled up the magnet say to that of magnetars, "you're going to have a bad time". Everything is a little magnetic, including the tissues in your body, and will respond to a magnetic field if it's strong enough. But your body will levitate like a frog in the 90s long before the doctor is forced to issue a death certificate listing the cause of death as "blood shot at a big magnet".
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