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A 'small black hole'?!?!?! How big exactly is a large black hole?… - CERisE's Testing for L

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August 13th, 2006


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02:46 am
A 'small black hole'?!?!?! How big exactly is a large black hole? And how are they not exactly the same size?

Apart from this (and something else that annoyed me less, but I've forgotten), Questionable Content seems like a pretty decent webcomic.

(16 comments | Leave a comment)

Comments:


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From:theswede
Date:August 13th, 2006 10:01 am (UTC)
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The distance from the center of the black hole to the event horizon varies with the mass of the black hole. If you want details, read Hawking. He knows a thing or two about those babies. And no, black holes are not all the same size.
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From:level_head
Date:August 13th, 2006 12:08 pm (UTC)
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He's thinking, of course, of the diameter of the "singularity" itself. But indeed, the size of black holes is sometimes given as the size of the event horizon as you say.

Usually, though, they just give the mass.

Here's some information on these babies. They definitely exist -- and the small ones would give off a LOT of Hawking radiation.

But mass is how you sort them out. Because, of course, measuring the singularity itself is ... pointless. ];-)

===|==============/ Level Head
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From:testing4l
Date:August 13th, 2006 12:19 pm (UTC)
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I'm shocked! A reference to wikipedia! ; )

The bit about equating elementary particles to black holes was something I hadn't come across before. It's an intriguing idea if it pans out. It'd be interesting to start a movement to ban micro black holes (a la DHMO) considering how extremely dangerous they are. ; )
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From:tehschkott
Date:August 13th, 2006 07:48 pm (UTC)
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is wikipedia now "out"?
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From:relsqui
Date:August 13th, 2006 08:08 pm (UTC)
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The people who think it's a bad resource because anyone is free to mess it up have become more vocal recently, in my experience; I guess you could call that "out." Having no problem at all with it myself, I still wouldn't use it as a reference for a research paper or anything else that really requires accuracy. level_head makes a point of knowing what he's talking about, so I think testing4l was surprised that he used a potentially unreliable (albeit fairly reliable in practice) resource.
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From:testing4l
Date:August 13th, 2006 11:01 pm (UTC)
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Not really. It's a playful jab at level_head. He is, in my opinion, a little too untrusting of wikipedia. He's very vocal about it -- and with good reason -- so I really couldn't resist. 8)
[User Picture]
From:tehschkott
Date:August 13th, 2006 11:34 pm (UTC)
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arent' arguments against wikipedia also arguments against open source?

(open source = built in error checking with community)

[User Picture]
From:theswede
Date:August 13th, 2006 12:39 pm (UTC)
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Who uses the term "black hole" as a substitute for "singularity of a black hole" in common speech? Sven is hardly trying to convey precise scientific information in a peer reviewed publication, making it rather harsh to hold him to standards of that level.
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From:level_head
Date:August 13th, 2006 01:00 pm (UTC)
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Who uses the term "black hole" as a substitute for "singularity of a black hole" in common speech?

As nearly as I can tell, everyone. But I think you just phrased it backward; I agree with your point.

And "small" is an attribute of some black holes.

We're in agreement here.

===|==============/ Level Head
[User Picture]
From:theswede
Date:August 13th, 2006 01:30 pm (UTC)
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As near I can tell, the singularity would be the Kantian object, and "black hole" would refer to the collection of properties which actually can be meaningfully discussed outside of purely formal systems. But that is rather more nitpicky than one actually has to be in common speech.
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From:testing4l
Date:August 13th, 2006 11:14 pm (UTC)
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It is harsh and exacting. I'm willing to accept that. I make a point of correcting people when they say "centrifugal force" in everyday speech.

The only reason it really bothers me is the next line about using that line to pick up "hot lady physicists". If you're going to do that, one would expect precision and exacting care in the phrasing. It seems kind of like using naive set theory in a discussion of paradoxes with a maths person.

But -- again -- that's my opinion from where I sit.
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From:theswede
Date:August 14th, 2006 05:07 am (UTC)
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Sven did not say - or obviously from his response ever contemplate - that. An emo kid with no education what so ever in physics, working as an office bitch, with a sarcasm quotient which defies the ozone layer said that.
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From:testing4l
Date:August 13th, 2006 12:09 pm (UTC)
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You're referring to the Schwarzschild radius which is different than the way I took that strip to mean.

It is true that the radius differs depending on mass, but referring to the "black hole" and intending the event horizon is just plain sloppy terminology. If you're going to discuss the black hole as a discrete thing, then one must discuss the singularity itself which is necessarily of infinitesimal volume -- the event horizon is merely a property, not the thing itself.

And so, with that in mind (and the implied evidence that I've taken some time to look into these things myself), I repeat my claim.
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From:theswede
Date:August 13th, 2006 12:38 pm (UTC)
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That you take the strip to mean something else than pretty much every other human on the planet does isn't anyone's problem but yours. The humorous abstract concept of a human being powered by a small black hole and thus being able to eat tremendous amounts of food works very well. Indeed, I fail to see why you have any kind of problem with it.

"Black hole" is a collection name to the entire, well, black hole. Not to the singularity alone; that is merely one part of a black hole. The event horizon is, indeed, a property of a black hole. As is its mass. As is its size, however one wishes to measure it (mass, radius, comic value etc.).
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From:level_head
Date:August 13th, 2006 01:06 pm (UTC)
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Forgive me, my friend, but I must side with TheSwede here. Because of the information boundary properties of the event horizon, anything within that radius is considered to be "inside" the black hole.

And nothing emerges but Hawking radiation (if that), which was never inside anyway.

===|==============/ Level Head
[User Picture]
From:wyrdfae
Date:August 14th, 2006 04:45 pm (UTC)
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I like questionable content..esppecially the kitties
Twisp and catsby are better but rare
http://www.penny-arcade.com/comic/search?keyword=catsby

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