From Nature: Black holes 'do not exist'

Ben Owen
Ben Owen
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RE: But this new theory is

Message 9927 in response to message 9926

Quote:
But this new theory is not yet finished. (I´think Ben Owen is working on it, so maybe next year or so ;-) )

'Fraid not. That would be a tall order.

Now that I'm in this thread, I should say something about that article. I didn't want to trash it without coming up with something instructive to say as well.

Don't believe everything you read in Nature. It is a very respectable journal in some fields, like x-ray astronomy, but in gravity the saying is that Nature publishes only papers that are demonstrably wrong. About once a decade they mess up and let a good gravity paper through, but I doubt that this is that paper. It sounds like the authors aren't familiar with some pretty old and classic results.

The business about black holes looking like "stuck stars" is a relic of the days when relativity was mostly studied by mathematicians, who tend to idealize equations and abhor dirtying them with real numbers. (So are white holes, for that matter.) The idealized black hole of the Schwarzschild solution is indeed static, as Mark Forester mentioned earlier in this thread. Formally you can't use it to describe a collapsing star, which is dynamic.

But a star that has collapsed most of the way has become a small perturbation on the Schwarzschild solution. Perturbation theory tells you that such perturbations (differences from Schwarzschild) die away exponentially with time. If you are a grungy physicist who deals in numbers, you can work out that the half-life of a perturbation (as seen by a distant observer) is about a millisecond for a typical black hole formed by stellar collapse. So in real life situations where we are looking at things like Cyg X-1 millions of years after collapse, they have become for all practical purposes indistinguishable from static black hole solutions. Unless they have gobbled up another star or so within the last fraction of a second. This was worked out in the 1960s.

The moral of the story is that exact solutions don't exist. But that's not limited to relativity - remember those massless springs and frictionless blocks from freshman homework? And inexact solutions are often close enough.

If the Nature paper postulates some form of matter that will stiffen up at high density to prevent collapse just outside the Schwarzschild radius, it comes up against a result from the 1970s. Any matter that obeys special relativity - which has been tested every day for decades in particle accelerators - has to have the sound speed less than the speed of light. In that case there is a maximum mass that it can support before it collapses on itself (it's about three solar masses for anything that at low density looks like ordinary matter). That part of the result depends on general relativity, but in a very robust way that doesn't care about quantum mechanics, Hawking radiation, etc.

Hope this helps,
Ben

Tony I
Tony I
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Hey Michael, You really

Hey Michael,

You really need to read the reply from Ben Owen, and then read, slowly and with some thought, Stephen Hawking. Be sure you understand 1.)Hawking Radiation 2.) Virtual particle pairs 3.) Black hole 'evaporation'

You get that stuff down young man, and you can come back here and debate with the best of 'em.

Good luck

michael
michael
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i hate being proved wrong,

i hate being proved wrong, espesailly by like 5 people

Matt3223
Matt3223
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hate being proved wrong?????

hate being proved wrong????? i can understand that........but then, how does one learn?

try this out, follow what the scientists do.........make all your statements or thoughts in the form of a theory. And you can also make "theoretical" statements in the form of questions too.

This way, you are inquiring of other people. Testing ideas. Whether or not you think you already know the answer. Nobody has to know that.

Theories and statements in the forms of questions..............watch out when making declarations. You might very well get proved wrong.

;)

MarkF
MarkF
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I wanted to add an obsevation

I wanted to add an obsevation about the time it takes a test particle to fall through the even horizon of a static black hole. For the test particle the time is finite. A distant observer receiving a signal from the test paricle would see the test particle's clock slowing down as the test particle approached the event horizon and never quite reaching the instant at which the test particle crosses the event horzion.
This seeming contradiction between the observations of two different observers viewing the same event is one of things that makes the study of GR so facinating and difficult. I say seeming contradiction because this calculation is only a first approximation. The mistake is in extrapolating to results to far.

As we seem to have some very knowledgable people on this thread I wanted to ask a question. What ever happened the to the Binary Black Grand Challange project?

Ben Owen
Ben Owen
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Folks, I forgot to mention

Folks,

I forgot to mention something very important when I talked about how all the perturbations (deviations from the final stationary solution) of a black hole die off exponentially with a short half life. They don't just disappear. In fact, most of a generic perturbation (that is, one that's not specially contrived to avoid it) is radiated as gravitational waves.

These waves are not long-lived periodic signals like Einstein@Home is looking for. They do have a fairly well-defined period (or several periods if several harmonics are excited), but they are definitely not long-lived. The half-life of the perturbations is proportional to the black hole mass (all else being equal), and even if we look at the supermassive black holes weighing hundreds of millions of solar masses in the middle of big galaxies, the half-life is less than an hour. So they would sound like a bell ringing and then fading out, and they're usually called ringdown signals.

LIGO is searching for these ringdowns, as well as other types of signals. Since they're short (a fraction of a second for "ordinary" stellar black holes, which are the ones with frequencies in the LIGO band) they're not too computationally intensive to search for, which is why Einstein@Home is not doing them. But they are expected after two black holes merge or a black hole eats a neutron star. And a detection of one would give a pretty precise measurement of the final black hole mass and spin.

The big problem with ringdown signals is actually that lots of other things can make them. Like servo loops. The idealized picture of laser beams bouncing between mirrors in an "L" is a cartoon. The real mirrors are hooked up to all kinds of servos to prevent various bad things from happening, like the "light saber incident" which I'll tell you about some other time. If you hit a servo loop the right way, it moves the mirrors in a way that looks like a ringdown in the output.

So all the servo voltage data is cross-checked against potential gravitational wave signals. So are microphones, magnetometers, seismometers, and a lot of other things. There are something like 17,000 channels of housekeeping data in addition to the one channel for the "gravitational wave" signal, which is actually one output of a certain photodiode.

That 14MB data file you get is actually a very small fraction of the whole picture. Down and dirty, but that's how real science works.

Hope this helps,
Ben

Ben Owen
Ben Owen
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RE: What ever happened the

Message 9933 in response to message 9931

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What ever happened the to the Binary Black Grand Challange project?

The Grand Challenge itself, which was a sort of consortium of many research groups, is no more. But all the former members, and then some, continue to work on developing binary black hole simulations. Actually, there has been a lot of progress recently. Last year Bernd Bruegmann's group made the first simulation of a complete orbit, and within the last couple of months Frans Pretorius (sorry no press release link) has gone further, maybe enough to estimate the gravitational waves.

Hope this helps,
Ben

hockeyguy
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Do we have an update on this

Message 9934 in response to message 9933

Do we have an update on this article? I think it is a very intersting alternative to blackholes. I think it makes more sense too.

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