Comment by thayne

Comment by thayne a day ago

17 replies

The title is... odd.

White dwarfs and neutron stars are generally considered "dead stars", since they no longer have active fusion processes. But they do radiate from energy left over from the star's "death". (Mostly thermal energy for a white dwarf, for neutron stars there is also a lot in angular momentum and the spinning magnetic field.) In theory, they will eventually radiate all of their energy away and become black dwarfs or cold neutron stars, but IIRC, that would take longer than the current lifetime of the universe.

GuB-42 a day ago

I second that. A more accurate title would be "Only black holes emit Hawking radiation".

AFAIK everything above above absolute zero radiates, which effectively means that everything radiates. Black holes would be an exception if it wasn't for Hawking radiation.

In addition, (stellar) black holes are dead stars. Or at least, that's one way to see them.

  • tbrownaw 18 hours ago

    > AFAIK everything above above absolute zero radiates, which effectively means that everything radiates.

    What really matters is temperature relative to surroundings. Something at the same temperature as everything around it won't lose any net energy to radiation.

    • jfengel 18 hours ago

      And black holes are much colder then their surroundings, i.e. the Cosmic Microwave Background. And they will be for trillions of years.

      • dr_dshiv 11 hours ago

        Do you mean singularities are much colder? Because everything outside of that is super hot, no?

        • jfengel 8 hours ago

          We can only talk about the surface. The surface emits basically no radiation at all. The amount of Hawking radiation it emits is practically non-existent. It's truly black.

          The temperature inside could be anything. You could well be inside a black hole right now.

          Even if we were inside one we couldn't really talk about the temperature of the singularity. The singularity is a divide-by-zero error. It probably doesn't physically exist at all, and whatever does exist is beyond our ability to model.

jpmattia 8 hours ago

> The title is... odd.

Not if you know the reputation of John Baez: Anyone familiar with him or his writings would know without hesitation that he understands black-body and E&M radiation, so his choice of title is clearly meant to be provocative.

It says to the reader "I wonder what he means?" To this reader, I'll also say that he delivered a terrific blog post.

  • nothrabannosir 7 hours ago

    > It says to the reader "I wonder what he means?"

    This has become affectionately known as “click bait”.

    No disrespect to the pedigree of the clearly distinguished author.

    • jpmattia 7 hours ago

      Perhaps, but "Mathematical Physicists HATE when authors make THIS ONE ASSUMPTION!!1!" would be more click baity. I took it more as Baez writing for his physics audience.

      • nothrabannosir 6 hours ago

        Purely out of pedantic interest: is that a meaningful distinction, or is it just the same thing for a different audience? I'm reminded of chess youtubers who give similarly "click baity" titles to their videos which are only click bait to people who watch chess videos. Isn't it the same?

        All the power to them by the way. It's the crushing power of the algorithm. No hard feelings, just something I've been wondering.

        • jpmattia 5 hours ago

          Well, you got me thinking about "What exactly is clickbait?"

          So full disclosure: I've directly interacted with John Carlos Baez only in social media, with the topics as disparate as music and observational astronomy. My own QFT & GR background is grad course level but with little actual usage in my career. (I've done more solid-state + high-speed electronics work, with a bunch of programming as well.) With that background, and turning the pedantry dial up to 11:

          To me, one distinguishing element of clickbait is that the post is ultimately disappointing. The usual M.O. for clickbait is that the website needs eyeballs for advertising, so they beef up a headline of an uninteresting article with the expectation of getting extra monetization compared to an honest headline.

          I would venture a guess that he doesn't actually care about monetization, or really even extra clicks, with this post. The screenshot with the big red X through the popsci article sets the expectation pretty quickly, and the tone of the rest of the post is really a rant that mediocre science made it into PRL and then into the popular science literature. He explicitly calls out the popsci journalists for laziness, but in a clever (I'm pretty sure Mark Twain would approve of his name being taken in vain) and erudite (correct use of the subjunctive) way.

          Would I have clicked on the title without seeing the authorship johncarlosbaez.wordpress.com? Maybe but I doubt it. There is so much bad popsci physics out there that I'm pretty trained to ignore obviously inadequate headlines. So on a scale of 1-10, I'd rate the click-baityness of the headline no more than a 3. He got me to click, but only because I knew it was his post.

          As for others, the set of people who understand that Hawking radiation exists has nearly 100% overlap with those who know that black bodies and spinning magnets radiate, so for those folks who are in the set who are also unfamiliar with the author, perhaps it's more clickbaity.

          [edit: And I can't believe you got me to write that many words on the clickbait philosophy. Have I been baited? :) ]

      • thayne 4 hours ago

        > I took it more as Baez writing for his physics audience.

        I have a degree in Physics with an emphasis in Astronomy, and my thought on reading the title was "that's absurd". Even if you somehow infer that "radiate" specifically means "emit hawking radiation" which I don't know how you would without more context, "dead stars" generally is considered to include black holes, which do emit hawking radiation.

        • jpmattia 4 hours ago

          I wrote in the other reply:

          > As for others, the set of people who understand that Hawking radiation exists has nearly 100% overlap with those who know that black bodies and spinning magnets radiate, so for those folks who are in the set who are also unfamiliar with the author, perhaps it's more clickbaity.

          So according to my theory, you must in the set that understands Hawking radiation + black bodies + E&M, but not in the set familiar with Baez.

          I worked hard on my theory, please don't let me down and be a counterexample. :)

alienbaby 15 hours ago

The article itself explains the title quite well.

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