5 ms·
There is at least one known exception: neutrinos from a supernova. (Don't get too excited, this doesn't contradict Einstein, as we'll see.) In the hot, dense co
by internet_person 7y ago
There is at least one known exception: neutrinos from a supernova. (Don't get too excited, this doesn't contradict Einstein, as we'll see.) In the hot, dense core of a supernova, photons will scatter around for a while before escaping. Neutrinos, which interact much less often than photons, and travel also more or less at the speed of light, get out basically right away. The difference can be as much as a few hours! Of course it's the high-energy photons that are more dangerous, so the neutrinos are really more like an early-warning system.
See e.g.: https://en.wikipedia.org/wiki/SN_1987A https://en.wikipedia.org/wiki/SN_1987A
- oAlbe 7y agoThat's still not an exception though. Neutrinos escape first by virtue of the fact that they don't interact with matter and don't bounce around, while light does. They aren't travelling faster than light, just travelling a shorter distance.
- xmprt 7y agoThe question wasn't about how fast neutrinos can travel but whether we can detect something before we see it.
- onetimemanytime 7y agoSo x event happened 550,000 years ago and the radiation from it might kill us. You say that we may get a warning from neutrinos before the harmful stuff kills us?
- chrischen 7y agoBut we detect things with particles other than just light.
- saberdancer 7y agoThis is very misleading. In fact, neutrinos are not going faster than speed of light (c), they are going faster than photons that are emitted from the supernova. Not just that, but lights when it passes through a medium slows down depending on it's refractive index (speed of light in water is about 225 000km/h while in vacuum it's 300 000km/h). This is important distinction as recently we had an uproar when it looked like neutrinos are slightly faster than c (in the end, it was a measurement error). You can observe effects of particles going faster than speed of light in a medium if you look at photographs of Cherenkov radiation.
- Erlich_Bachman 7y agoThat comment never wrote that neutrinos were faster than the speed of light?
- pavs 7y agoNo, but he did write "There is at least one known exception", the misleading part.
- Lukas_Skywalker 7y agoI'm sure it's a typo, but for others: speed of light is 300'000 m/s in vacuum, not km/h.
- Cyberspy 7y agoIt's not a typo - it's 299,792,458 m/s - approx 300,000,000 m/s or 300,000 km/s
- lmilcin 7y agoThe correct way to say it is that the speed of light is the speed of causality only in vacuum. In any medium the speed of light is slower but the causality or other fields (for example gravity field) that are not impeded by matter can and will propagate faster than the speed of light.
- blueprint 7y agoWhere does there exist a vacuum? How does a particle or its environment measure the particle's traversal of a truly empty space?
- tromp 7y ago> in vacuum it's 300 000km/h 300 000 km per second
- mcdevilkiller 7y ago
- throwaway2048 7y agoIts possible to exceed the local speed of light in many classes of material. https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation