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Ethan Siegel just posted a detailed response to this. https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-df0a131d7b95 https://medium.com/star

by tericho 12y ago

Ethan Siegel just posted a detailed response to this. https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-df0a131d7b95 https://medium.com/starts-with-a-bang/yes-virginia-black-hol...

anigbrowl 12y ago
That was written in February (how could you miss this? it's literally the very first thing at the top of the page) and doesn't mention either of this paper's authors. The article discusses a closely related but nevertheless quite different topic.
- tericho 12y ago
  Was directed there from his Twitter feed where he seems to offer it as a response. "There's been a story going around that it's been proven that black holes don't exist. Yes, they do. <link>" https://twitter.com/StartsWithABang/status/514885248916938754 https://twitter.com/StartsWithABang/status/51488524891693875... Edit: Re-reading my original comment I see my choice of words was poor.
  - anigbrowl 12y ago
    Perhaps he hasn't read the paper we're talking about :-)
scott_s 12y ago
I don't think that is a response to this work. That is dated February 1. He links to this paper's author, Laura Mersini-Houghton, but he links to a paper and blog post of hers from January. Reading that blog post (http://backreaction.blogspot.com/2014/01/if-it-quacks-like-black-hole.html http://backreaction.blogspot.com/2014/01/if-it-quacks-like-b...), what she says seems to be in contradiction with the more recent paper she wrote (http://arxiv.org/abs/arXiv:1409.1837 http://arxiv.org/abs/arXiv:1409.1837). In her blog post from January, she says: "What Hawking is saying is essentially that he believes that a matter collapse only leads to a temporary apparent horizon but not to an eternal event horizon. That is an opinion which is shared by many of his colleagues (including me) and there is nothing new about this idea whatsoever." But in her more recent paper, she says: "More specifically, we find that collapsing stars slow down their collapse right outside their horizon, while substantially reducing their mass through Hawking radiation. ... The star never crosses its horizon, so neither unitarity nor causality are violated, thereby solving the longstanding information loss paradox. This investigation shows that universally collapsing stars bounce into an expand- ing phase and probably blow up, instead of collapsing to a black hole." I am not a physicist, but when I read those two statements, they are in contradiction. The first statement says to me: it may not be an absolute horizon, but it is a horizon. The second statement says to me: actually, we never reach any horizon. So I think that the more recent statement means that she has changed her conclusions based on her recent work.
- aruggirello 12y ago
  I'm confused here. The mere existence of an event horizon - albeit a temporary one - should make a black hole! So "More specifically, we find that collapsing stars slow down their collapse right outside their horizon," by implying that a horizon DOES exist, simply doesn't cut it. Am I missing something?
  - scott_s 12y ago
    I believe that's using the concept of a horizon. For an object of a particular mass, we can use our theory to tell us where the event horizon would be, if it collapses past that point. My understanding of this recent paper is that they are saying: it won't collapse past that point.
deleted 12y ago
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imaginenore 12y ago
> If we want to escape its gravitational pull, we’d need to accelerate ourselves up past the escape velocity, or the speed necessary to climb out of the gravitational potential well that Earth’s mass creates. We can (and have) accomplished this, in fact, but it would take a speed of around 11.2 km/s (or 0.004% the speed of light) to make it so. This whole paragraph is wrong. You don't need to move at the escape velocity to leave our planet, you can move as slow as you wish, as long as you have enough fuel. Escape velocity is just a minimum velocity of a fuel-less projectile enough to leave the gravitational pull.

by tericho 12y ago

Ethan Siegel just posted a detailed response to this. https://medium.com/starts-with-a-bang/yes-virginia-black-holes-exist-df0a131d7b95 https://medium.com/starts-with-a-bang/yes-virginia-black-hol...

anigbrowl 12y ago

That was written in February (how could you miss this? it's literally the very first thing at the top of the page) and doesn't mention either of this paper's authors. The article discusses a closely related but nevertheless quite different topic.

tericho 12y ago
Was directed there from his Twitter feed where he seems to offer it as a response. "There's been a story going around that it's been proven that black holes don't exist. Yes, they do. <link>" https://twitter.com/StartsWithABang/status/514885248916938754 https://twitter.com/StartsWithABang/status/51488524891693875... Edit: Re-reading my original comment I see my choice of words was poor.
- anigbrowl 12y ago
  Perhaps he hasn't read the paper we're talking about :-)

scott_s 12y ago

I don't think that is a response to this work. That is dated February 1. He links to this paper's author, Laura Mersini-Houghton, but he links to a paper and blog post of hers from January. Reading that blog post (http://backreaction.blogspot.com/2014/01/if-it-quacks-like-black-hole.html http://backreaction.blogspot.com/2014/01/if-it-quacks-like-b...), what she says seems to be in contradiction with the more recent paper she wrote (http://arxiv.org/abs/arXiv:1409.1837 http://arxiv.org/abs/arXiv:1409.1837). In her blog post from January, she says: "What Hawking is saying is essentially that he believes that a matter collapse only leads to a temporary apparent horizon but not to an eternal event horizon. That is an opinion which is shared by many of his colleagues (including me) and there is nothing new about this idea whatsoever." But in her more recent paper, she says: "More specifically, we find that collapsing stars slow down their collapse right outside their horizon, while substantially reducing their mass through Hawking radiation. ... The star never crosses its horizon, so neither unitarity nor causality are violated, thereby solving the longstanding information loss paradox. This investigation shows that universally collapsing stars bounce into an expand- ing phase and probably blow up, instead of collapsing to a black hole." I am not a physicist, but when I read those two statements, they are in contradiction. The first statement says to me: it may not be an absolute horizon, but it is a horizon. The second statement says to me: actually, we never reach any horizon. So I think that the more recent statement means that she has changed her conclusions based on her recent work.

aruggirello 12y ago
I'm confused here. The mere existence of an event horizon - albeit a temporary one - should make a black hole! So "More specifically, we find that collapsing stars slow down their collapse right outside their horizon," by implying that a horizon DOES exist, simply doesn't cut it. Am I missing something?
- scott_s 12y ago
  I believe that's using the concept of a horizon. For an object of a particular mass, we can use our theory to tell us where the event horizon would be, if it collapses past that point. My understanding of this recent paper is that they are saying: it won't collapse past that point.

deleted 12y ago

[deleted]

imaginenore 12y ago

> If we want to escape its gravitational pull, we’d need to accelerate ourselves up past the escape velocity, or the speed necessary to climb out of the gravitational potential well that Earth’s mass creates. We can (and have) accomplished this, in fact, but it would take a speed of around 11.2 km/s (or 0.004% the speed of light) to make it so. This whole paragraph is wrong. You don't need to move at the escape velocity to leave our planet, you can move as slow as you wish, as long as you have enough fuel. Escape velocity is just a minimum velocity of a fuel-less projectile enough to leave the gravitational pull.