Black Holes 'Do Not Exist,' Contends Physicist

SpaceAdmiral writes "Nature reports that, according to a physicist at the Lawrence Livermore National Laboratory in California, 'It's a near certainty that black holes don't exist.' George Chapline argues that the collapse of massive stars is more likely to lead to dark energy stars. These dark energy stars behave somewhat like a black hole outside of the surface, but the negative gravity inside could cause matter to 'bounce back out again.'"

Comments

Theory tug of war

[selectspec]

This idea that "singularities" don't really exist has been around for a few years now. The idea is that a very small bubble forms that is unable to compress into a singularity because of the "dark energy" concept of reverse-gravity. However, the new theories that "dark energy" really doesn't exist, and that the expansion of the universe can be explained by the negative higgs field + spacetime ripples of the early inflation of the universe run contrary to this "no black hole" concept.

So what did this dudes?

[cuerty]

What did they do?: http://science.slashdot.org/article.pl?sid=05/03/1 7/1541230&from=rss

Dark energy stars?

[TrekkieGod]

From the article:

Over the past few years, observations of the motions of galaxies have shown that some 70% the Universe seems to be composed of a strange 'dark energy' that is driving the Universe's accelerating expansion

Ah, but I at least one theory exists that says dark energy isn't really needed.

Not there's anything wrong with having different theories, we'll let observational data sort it out later. Could a physicist around here explain how these proposed dark energy stars could explain the expansion of the universe if they behave exactly like black holes outside the event horizon?

This is likely wrong.

[Artifakt]

The researcher is claiming that his theory accounts for both dark matter and dark energy, as well as some observations like x-ray bursts from the cores of active galaxies.
Conventional theory doesn't tie dark matter to dark energy at all. If the popularizations hadn't used the word dark in both cases, the two concepts would easily be completely unrelated.
Several candidates for dark matter are very conventional forms of matter, such as neutrinos or even plain old neutronium, which don't need an exotic explanation. Others involve particles we have produced in accelerators or theorize on the basis of data we have obtained ever since the 1940's.
Dark Energy, o.t.o.h., is something very different. The evidence for it is all very recent, and the theories proposed are all well outside the standard model for Cosmology.
Thinking we even need a single theory to explain both only makes sense if you can first disprove the more conventional explanations for dark matter.

Nitpick:

[Otto]

An object does not have to reach escape velocity to escape a planet's gravitational pull.

You're partly right. You can NEVER escape a planet's gravitational pull. It just keeps pulling, no matter how far you go. ;)

Escape velocity is the inital speed needed for a ballistic object to ensure that the gravitational pull of the planet will never be able to bring it to a complete stop, relative to the planet. As you move away from the planet, the gravitational force weakens. If you can move away faster than the force can slow you down, then the gravity of the planet can never stop you. That's the escape velocity.

However, for a rocket (or other powered device) to escape a planet's gravitational pull, as the GP said, all it has to do is provide enough vertical thrust to provide a positive acceleration. That acceleration does not have to accelerate it to the escape velocity - in fact, you could adjust it to compensate for the falling gravitational pull and so maintain a constant velocity of whatever you want, and (if you have sufficient power/fuel) you'll still escape.

In theory, you're partly correct here. If you could overcome gravity to provide a 1 foot per second squared upward accelleration, then yeah, you'd get to outer space. Eventually. It'd take one hell of a lot of fuel though, because you're only barely overcoming gravity. It's not actually *possible* because no ship exists that can do that and also have enough fuel to do it.

Any acceleration larger than gravity will get you there eventually if you assume enough fuel. And as gravity drops off due to distance, eventually you'll be travelling faster than escape velocity for the given height you happen to be at. And then you're free.

That doesn't work for a black hole because all of that is based on Newtonian mechanics, which do not apply in the large gravitational fields close to the event horizon. There, you must use General Relativity, which is counter to our everyday common sense view of the world (precisely because on our scales, it's irrelevant). I don't know enough about GR to demonstrate why this is, however.

The main reason is similar to the above: You don't have enough fuel. And not just because the technology doesn't exist, but because inside the event horizon, the acceleration due to gravity is so high that even light itself isn't moving fast enough to go "up". No amount of acceleration will let you make any forward progress at all, because you cannot possibly give it enough speed to exceed the speed of light. So you can't even go up at 1 foot per second, you can only go down.

To put it another way, inside the event horizon, space is bent in such a way that moving away from the singularity is no longer an available option.

Outside the event horizon, the normal, simple, equations still apply, more or less. The gravity is high, but the concept is the same. With a higher gravity comes a higher escape velocity, that's all. Also time dilation, but that's rather irrelevent to this discussion. ;)