Thread

1. haitchfivee · 1790354524 · focus · HN ↗

   My nitpick is with something the author said in passing about Hawking. Yes, around 1970 Hawking and the scientific community at large still used to believe nothing could escape a black hole, and between 1971 and 1973 Hawking along with Penrose and others expanded their evolving understanding and consequences of of Albert Einstein's breakthrough work.

   But then Hawking argued back the opposite case, which in simple terms means that some things can, indeed, escape an event horizon. In fact, name dropping Hawking just to mention his views as they stood before his 1973 work, and his 1974 model of Hawking radiation seems dangerously incomplete journalistic reporting.

   In 1974 Hawking formulated what we now know as Hawking Radiation, which is the *exact opposite* of what was previously believed about the impossibility of anything coming back from a black hole. Whilst still not conclusively proven as a physical fact, this did win him the Special Fundamental Physics Prize in 2013. specifically for his discovery of Hawking radiation from black holes and his deep contributions to quantum gravity and quantum aspects of the early universe.

   1. metalliqaz · 1790357182 · focus · HN ↗

      Please correct my understanding as I am not a scientist, but why do you assert that Hawking radiation "escapes" or "comes out of" a black hole? Nothing crosses the event horizon. Isn't it more correct to say that Hawking radiation is produced by the extreme warping of the spacetime very near the event horizon, and the black hole shrinks to conserve the energy? Black holes can also shrink as gravitational waves are produced, but we don't say that the waves "escape" the black hole.

      1. rhdunn · 1790361541 · focus · HN ↗

         My understanding is that Hawking radiation is where:

         1. a particle/anti-particle pair is created at the event horizon;

         2. the particle is on the outside edge of the event horizon, so "escapes" the black hole;

         3. the anti-particle is on the inside edge of the horizon, so decreases the size of the black hole due to particle/anti-particle annihilation (with a corresponding particle on the inside of the black hole).

         1. metalliqaz · 1790362861 · focus · HN ↗

            This is often used as an explanation in pop-sci materials, but it isn't particularly accurate, IIRC.

            For example, Hawking radiation is always photons, with the wavelength corresponding to the size of the black hole. That isn't explained purely by virtual particles.

            Also, for that explanation to work, it would always have to be an anti-matter particle that is selected to cross the event horizon, and I don't see how that would be the case.

            1. auntienomen · 1790364749 · focus · HN ↗

               Minor quibbles: Hawking radiation has a blackbody spectrum, so we get a variety of wavelengths, with a peak determined by the size of the hole. The outgoing particles should eventually include any kind of particle that can be created in the Standard Model, not just photons and gravitons.

Unofficial Hacker News client; not affiliated with Y Combinator.