John Carlos Baez on Nostr: Wow! You may have looked through polaroid glasses and seen how the Sun reflecting off ...
Wow! You may have looked through polaroid glasses and seen how the Sun reflecting off water looks different depending on how you turn your head. That's because the electric and magnetic fields in light are able to wave back and forth in different directions, so there are different kinds of light: different 'polarizations'.
Now for the cool part:
In 1971 the physicist Stephen Adler predicted that in extremely strong magnetic fields, the speed of light depends on its polarization. And now this effect may have been seen near a 'magnetar': a young neutron star that's spinning around and has an extremely strong magnetic field, a hundred million times stronger than any man-made magnet.
You might be shocked, because you know that the speed of light in a vacuum is constant. But an extremely strong magnetic field is far from a vacuum! A magnetar's magnetic field has an energy density that corresponds to a mass density over 10,000 times that of lead. The magnetic field of a magnetar would be lethal even at a distance of 1,000 kilometers - and at a distance of halfway from Earth to the Moon, a magnetar could wipe information from the magnetic stripes of all credit cards on Earth.
https://arxiv.org/abs/2509.19446https://www.nature.com/articles/s41586-026-10859-z?linkId=63101551Published at
2026-08-06 11:46:13 CESTEvent JSON
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"content": "Wow! You may have looked through polaroid glasses and seen how the Sun reflecting off water looks different depending on how you turn your head. That's because the electric and magnetic fields in light are able to wave back and forth in different directions, so there are different kinds of light: different 'polarizations'. \n\nNow for the cool part:\n\nIn 1971 the physicist Stephen Adler predicted that in extremely strong magnetic fields, the speed of light depends on its polarization. And now this effect may have been seen near a 'magnetar': a young neutron star that's spinning around and has an extremely strong magnetic field, a hundred million times stronger than any man-made magnet.\n\nYou might be shocked, because you know that the speed of light in a vacuum is constant. But an extremely strong magnetic field is far from a vacuum! A magnetar's magnetic field has an energy density that corresponds to a mass density over 10,000 times that of lead. The magnetic field of a magnetar would be lethal even at a distance of 1,000 kilometers - and at a distance of halfway from Earth to the Moon, a magnetar could wipe information from the magnetic stripes of all credit cards on Earth.\n\nhttps://arxiv.org/abs/2509.19446\n\nhttps://www.nature.com/articles/s41586-026-10859-z?linkId=63101551",
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