51 replies to this topic

[chubtoad]

http://www.nature.co.../040712-12.html

Hawking changes his mind about black holes

Mark Peplow
Physicist plans to pay up on long-standing bet.
Stephen Hawking has admitted he was wrong.
The eminent physicist Stephen Hawking has conceded that information can escape from black holes after all. The idea has been gaining popularity with physicists for some time, but the fact that Hawking, a pioneer of black-hole theory in the 1970s, has finally accepted it is something of a watershed.

[jonathan2111]

I'm interested in the phrase ..."information can escape from black holes...". Are we quite sure we know what information really is?

I don't think people really understand what information is at all. They think they do, but they do not.

Jonathan

[eternaltraveler]

what are the general points Stephen Hawking changed his mind about. I cannot access the article.

[jonathan2111]

There's an article here:
http://www.cnn.com/2....blackholes.ap/
and another here:
http://news.bbc.co.u...ech/3897989.stm

So I wonder what the information he is talking about tells you, and I wonder how it can be decoded.

Jonathan

[kevin]

Hi Johnathan..

Although not at all well versed in information and complexity theory.. I find it VERY intriguing.

http://www.imminst.o...470

[stormheller]

Well, that makes sense. If a black hole is an imploded star from our own universe, then there ain't any way for information to go through to some other universe. I guess those sci-fi freaks had better stop reading Michael Moorcock's 'multiverse' junk.
I believe that the 'information' that he is talking about is the stuff that makes matter into the shape of YO' AZZ. That's information. Anything that ain't pure matter is information. Heck, even the makeup of a proton, atom, electron, quark or whatever is information.

[el_excellencicc]

it, seems that scientists now have some evidence of a bh breaking-up universe most dense-matter .. a: neutron-star - to cite; Physorg ~

[biknut]

Pushing the Limit: Black Hole Spins at Phenomenal Rate
By Jeanna Bryner
Staff Writer
posted: 20 November 2006
09:39 am ET


X-ray vision has brought astronomers closer than ever to completel characterizing a black hole, a place where strange things happen.

Astronomers measured the spinning speed of three black holes, finding that one rotates at a breakneck 950 times per second, nearing its theoretical rotation limit of 1,150 spins a second. The black hole lies within the constellation Aquila (the Eagle) about 35,000 light-years from Earth.

The finding represents an important step toward understanding these invisible objects.

Mass and spin

When any mass, such as a star, becomes more compact than a certain limit, its own gravity becomes so strong that the object collapses to a singular point, a black hole. The spin of a star is thought to translate into spin of a black hole that forms from the star's collapse. With its mass much more compact, the spin rate ought to be phenomenal, much like a skater pulls in his arms to increase speed when performing a pirouette.

While astronomers have calculated the masses of more than a dozen black holes, spin-speed measurements have remained elusive. Until now, the spin rate of only one other black hole has been accurately measured, according to the researchers.

"Ever since the community figured out many years ago how to measure black hole mass, measuring spin has been the holy grail in this field," said Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass.

Powerful tug

A black hole's gravity, at a distance, behaves like that of a star of the same mass. If the Sun were to suddenly become a black hole, for example, its gravitational effect on Earth would not change.

“When you take a black hole and you try putting an object into orbit around it, you have no trouble if you’re doing it at a large distance,” said CfA's Ramesh Narayan.

But as swirling matter gets closer to a black hole, it starts orbiting faster and faster until it reaches the jaws of the dark behemoth. Just before the gas and dust get devoured, the matter heats up to millions of degrees, unleashing jets of X-rays.

The scientists, led by McClintock and Narayan, used NASA's Rossi X-ray Timing Explorer satellite data to measure this radiation and calculate the area of this disk of radiation (seen in images as a bright-white ring around the black center).

“Before, [the matter] was swirling around, happily, very slowly just spiraling in, and then it reaches this radius and then bang, it just freefalls into the black hole,” Narayan told SPACE.com.

Inside this radius, the gas is falling in so quickly it doesn’t send out much radiation.

Spin speed

The faster a black hole spins, the smaller its critical radius. That’s because when a black hole is spinning, it drags space-time around with it. So if surrounding matter is spinning in the same direction as the black hole, it gets tugged along due to this so-called frame-dragging effect. “The space is being pulled, so it’s helping the particle go around, so it’s able to hang on much closer to the black hole,” Narayan explained.

“If a particle is going around a black hole in the same direction as the spin of the black hole, then it turns out that it can be comfortable. It’s able to find a circular orbit even at much smaller radii,” Narayan explained.

They found two of the black holes spin at less than 50 percent of their maximum rates, while the black hole called GRS1915+105, which has 14 times the mass of the Sun, rotates between 82 and 100 percent of its maximum spin speed.

Each black hole is part of what's called an X-ray binary system, in which two objects orbit each other with gas from one—a normal star like the Sun—getting pulled toward the black hole.

http://space.com/sci...khole_spin.html

[Infernity]

Information= pure state of energy, unconstructed to a greater element but to a form.

-Infernity

[xanadu]

I hadn't seen this thread before though I think Lazarus gave a link to it in the other thread. Of course information can leave a black hole. Obviously by measuring the gravity of a BH you thereby know how much mass is contained inside. That is info. If gravity waves can be created and measured, then any kind of info could be sent to the outside world.

What I don't understand is how they can say a BH consists of a point singularity. I don't believe it's a point. A point is an absolute and you end up dividing by zero which is undefined or equal to infinity. If it did contract to a point then the spin would have to be a whole lot more than 1000 rps or so. If you go from a radius of 100,000 miles to 1 mile then you get a corresponding increase in rotation. Of course practical effects would dilute that, friction and so on. But, if you contract all the way to a mathmatical point, then the rotation would approach infinity unless someone can give a better explanation. Some of the rotational energy might be turned into heat or some other form as the matter collapses. I think it will turn out that matter shrinks down to a very small size but not to a point.

Another thing I don't get is this space dragging effect they talk about. That seems to be saying that a gravitational field has a special effect when it turns. Maybe it does but I'd like to know how they decided that. Probably a theory but it would be nice to know how they got there. Don't tell me it's just too complicated to explain. I have noticed that those who truely understand something seem to have no trouble explaining the basic concepts in clear form. Those with a lesser understanding give a much more complicated explanation and those without a clue give out only bafflegab. I don't have a clue about some things but I try to avoid giving a bable type answer. I'll just say I don't know. When I see an explanation that is overly complex, I figure they don't completely understand it. When it comes out completely unintelligable then they either haven't bothered to explain their terms or it's another bafflegab job.

[bgwowk]

Good questions, xanadu. If we can get through this, it will explain just about everything that's been bothering you about black holes and cosmology generally. Here's the deal:

What made Einstein one of the greatest physicists who ever lived was his theory of General Relativity. It wasn't Special Relativity, the photoelectric effect, understanding brownian motion, although those were great accomplishments themselves. His greatest theory-- the greatest and most important development in physics since Maxwell's Equations of electicity of magnetism --was General Relativity.

General Relativity starts with a set of simple assumptions about the laws of physics, such as invariance of the laws of physics under certain observer conditions. From these assumptions, Einstein derived a set of equations that relate space and time to mass (techically, mass-energy). What makes this theory amazing, and a step beyond Newton, is that General Relativity predicts the existence of gravity as a consequence of the simple assumptions it is based on. When something known in physics can be predicted by simple and general assumptions, that is a sign of progress!

The equations of General Relativity predict that gravity actually differs from Newtonian gravity, but only by a subtle amount under ordinary conditions. These predicted subtle differences immediately explained a long-standing puzzle in astronomy, which was the precession of the orbit of Mercury, which unlike Newton's theory, General Relativity predicted precisely. General Relativity was further validated by measurements of star light bending around the eclipsed sun a few years after Einstein published the equations. General Relativity has since been validated in numerous more ways, not the least of which are General Relativistic corrections in Gobal Positioning Systems used by thousands (millions?) of people everyday. The "theory" of General Relativity is now established physical reality in the same sense than Maxwell's "theory" of electricity and magentism is established. (In fact, it's now known that Einstein's Special Theory of Relativity is embedded in Maxwell's equations.)

So what does this all have to do with Black Holes and Cosmology? Black holes are specific solutions to Einstein's equations of General Relativity. Different types of black holes, rotating, non-rotating, charged, uncharged, are different solutions to Einstein's equations. All the weird stuff that black holes do, like how rotating black holes cause "frame dragging", dual event horizons, ring-shaped singularity, etc. are predictions of Einstein's equations. These properties aren't "what-if" theories pulled out of a hat. They are what everything we know about space, time, and mass predicts. For black holes not to have these properties would mean serious overhaul of physics.

Cosmological theories of the origin and future of the universe are what you get when you apply everything we know about space and time (the equations of General Relativity) to all the mass in the universe. In cosmology there is more uncertainty than there is about black hole physics because there are more unknown values of parameters to be filled in. But for a given set of conditions, the structure and evolution of the universe is sharply constrained by General Relativity.

General Relativity is not the last word in the same way the Newtonian gravity wasn't the last word. In particular, a more general quantum theory of gravity is still needed. Newtonian gravity is dramatically wrong in the vicinity of dense objects like black holes. Similarly, it is expected by physicists that General Relativity becomes dramatically wrong deep inside black holes in the vicinty of the singularity. Only a finished theory of quantum gravity will explain the true nature of singularities.

[xanadu]

Yes, that's nice bgwowk but the statement that something is a solution to Einstien's equations does not explain the principles involved. What you have written would make a good introduction to a book on the subject. What I was looking for was the next level of explanation which goes from established facts demonstrated by his work and extends from that to how it applies to BH's in specific circumstances, for example. A good simple explanation of how mass affects light would be to say it bends space (and time) around it and light follows space and only seems to bend. Then a level of complexity greater than that would go into the actual math and how you calculate the warping of space, the terms involved and so on. Once you have the concept you may or may not be interested in how exactly they derived it but that part is interesting too.

I think you really summed up the state of our knowledge on the subject when you said this:

Only a finished theory of quantum gravity will explain the true nature of singularities.

So basicly no one knows the answers right now. We don't know if a BH is really a point or something close to a point. What gets me is when theories are presented as facts without any notice to the reader that these theories have not been verified. We know that Einstien's work has been verified and many predictions based on his work have been verified. What we don't know is if all such predictions will turn out to be observed in nature. Things like hawking radiation are said to be facts but facts can be verified and this has not yet been. Things like the current belief in the expansion or expansion at FTL rates of the universe are presented as known facts. These things rest in part on assumptions like red shift being a solid and reliable way to measure distances and speed. We talked about that before and I guess you didn't like my alternate theory. However, it does seem to be true that any errors in our assumptions would have a drastic effect on our understanding of what goes on in the universe. I think you might agree with that much.

[bgwowk]

What I was looking for was the next level of explanation which goes from established facts demonstrated by his work and extends from that to how it applies to BH's in specific circumstances, for example.

Plenty has been written about black holes on the Web and in books by General Relativity experts. If you want to know mathematically where the predictions come from, you would need to learn tensor calculus, and begin working through Misner, Thorne, Wheeler or Wald. That is very non-trivial. But if you want to question what experts say General Relativity predicts, that is the level of expertise you must reach to question them.

Here's the important point to understand, and that I fear you may be missing: "Theory" in science means a model of reality. Some theories, which is to say some models, are very well established. General Relativity is one of them. The truth and predictive power of General Relativity extends far beyond observed facts. The theory itself is now an established fact. In other words, the theory can be used to confidently predict all sorts of things even though they have not been directly observed. The only place the model is expected to break down is at very small scales.

So basicly no one knows the answers right now.

Be careful not to generalize statements of specific limitations of a theory to statements of general ignorance. The inadequacy of General Relativity for dealing with phenomena at length scales less than 10**-35 meters does not give license to question results of the theory at larger scales.

What we don't know is if all such predictions will turn out to be observed in nature.

Some theories are so well-established, and based on such primary assumptions, that if predictions turn out to be wrong, a revolution in physics must follow. The default assumption is therefore that predictions of well-established models are correct.

Things like hawking radiation are said to be facts but facts can be verified and this has not yet been.

Hawking radiation is expected to be real because quantum theory predicts it, and because it neatly solves a long-standing problem with the thermodynamics of black holes. It's one of those things that would make physics more complicated were it not true. So the default assumption is that it exists.

Things like the current belief in the expansion or expansion at FTL rates of the universe are presented as known facts. These things rest in part on assumptions like red shift being a solid and reliable way to measure distances and speed. We talked about that before and I guess you didn't like my alternate theory. However, it does seem to be true that any errors in our assumptions would have a drastic effect on our understanding of what goes on in the universe. I think you might agree with that much.

Yes, assumptions are key ingredients. But ALL assumptions must be understood, and most importantly *how they fit together*. Current models of cosmology are based on more than just Red Shift observations. The Red Shift, type 1A supernova distance calibrations, CMB measurements, General Relativity, and other stuff I don't even know all fit together like pieces of a puzzle. If you say one of those pieces is different than generally-accepted, you have to understand the other pieces well enough to explain how they also can be different so the whole thing still fits together without contradictions. Frankly neither one of us knows enough physics and cosmology to propose alternative models. Not by a long shot.

[xanadu]

bg, you are preaching again along the usual themes of accepting what scientists say, that we or at least I should not be questioning them and so on. No new info in your last post, just the usual stuff. I was hoping you could tell us how the predictions made about BH's related to Einstien's work. If you don't know, that's no shame, probably none of us understand that part either.

Frankly neither one of us knows enough physics and cosmology to propose alternative models. Not by a long shot.

I don't think anyone needs a long string of letters after their name or recognition in order to propose theories. To verify your theory, that is another thing entirely. But, scientists have not verified much if any of the latest beliefs either. It's not much of a stretch to think that previously unknown and unmeasured properties of space or even the weak gravitational effect I theorised could have a red shifting effect over great distances. This would mean that those far galaxies are not as far away as we thought and are not moving away as fast as we thought either. Poof, there goes inflation that was supposed to be going on right now.

Hawking radiation is expected to be real because quantum theory predicts it, and because it neatly solves a long-standing problem with the thermodynamics of black holes. It's one of those things that would make physics more complicated were it not true. So the default assumption is that it exists.

Now you are being specific. Can you show us that quantum theory does predict it or are you taking someone else's word for that? I'm probably asking for too much but you did make that statement.

It has been said that BH's have charge. I assume this means electrical charge. How can electrical charge exist on a BH when electromagnetic radiation can not escape the EH? This would apply to electrostatic fields as well as light etc. I'll give you an out, you can say it exists due to conditions outside the EH if you want to go that route. I suspect you will dodge this question as well and go back to attacking me but I hope you won't.

No one still has come up with any reason why the universe would not be a black hole. It clearly had the density needed to create one near the time of the big bang. And what about before the big bang? If it was at any time a BH, how could it reverse the process? No one knows but if we accept the big bang theory, then we accept that the universe should be a BH.

[bgwowk]

xanadu wrote:

No new info in your last post, just the usual stuff. I was hoping you could tell us how the predictions made about BH's related to Einstien's work. If you don't know, that's no shame, probably none of us understand that part either.

As I said, black holes and their properties are solutions to Einstein's field equations.

I don't think anyone needs a long string of letters after their name or recognition in order to propose theories.

You don't need a string of letters. You need to understand the field you are theorizing about. In modern physics, that means knowledge of advanced mathematics, past theory, and pertinent empirical findings. It's usually the case that people who have this requisite background accumulate letters after their name while acquiring it. There have been exceptions. Einstein himself was not a PhD when he wrote his three 1905 papers that changed the whole field of physics. But he had mastered the material he was talking about.

Where theories of the universe are concerned, such as whether the universe is a "black hole", you cannot propose such ideas without knowledge of General Relativity. You must be able to write an equation expressing your theorized universe, and show that it is a solution to Einstein's field equations, and further show that any free parameters in the equation, such as mass density, are consistent with what is empirically known. Just saying, "I think the universe is a black hole" is not science. Without recourse to a mathematical description within the framework of General Relativity, "black hole" isn't even defined!

It's not much of a stretch to think that previously unknown and unmeasured properties of space or even the weak gravitational effect I theorised could have a red shifting effect over great distances. This would mean that those far galaxies are not as far away as we thought and are not moving away as fast as we thought either. Poof, there goes inflation that was supposed to be going on right now.

Remember what I said about knowing ALL the pieces and how they fit together? Red Shift is not and has never been a direct measure of distance. Rather than explain this, I'm going to try something new. I'm going to ask you to explain the connection between Red Shift and distance, and how the connection was made. Furthermore, since you are challenging the 1998 result showing that expansion is accelerating, you also need to explain how the 1998 measurements changed that connection. Finally, having established that background, you need to explain how your alternative theory changes the conclusion that expansion is accelerating.

There is no need for me to try and answer your new questions about Hawking radiation and electric charge. In the course of learning sufficient General Relativity to be able to formulate a new theory of the universe and call it "your" theory, you should be able to answer such questions yourself. If you believe you are knowledgeable enough to theorize about frontiers of physics, which I am not, then you should be able to answer any of these basic questions better than I can.

Edited by bgwowk, 23 November 2006 - 09:18 AM.

[xanadu]

There is no need for me to try and answer your new questions about Hawking radiation and electric charge.

That sums up your post. Not that you are unable to answer these questions, perish the thought. It's just that I'm not worthy of the explanation.

As I said, black holes and their properties are solutions to Einstein's field equations.

Because someone told you this? You constantly imply you know things which induces people to ask you questions. I toss out questions to the world in general and you reply with statements that imply you know the answer but you never really give it. It would be nice to see someone explain just how these things relate and not in a dumbed down way but in a clear conceptual way. I suppose I could do my own research. I guess I'm just too lazy and would rather tap someone else's knowledge. Maybe one day I'll look into it more.

Rather than explain this, I'm going to try something new. I'm going to ask you to explain the connection between Red Shift and distance, and how the connection was made.

I've never claimed to be the one with the answers, I've been mostly asking questions. I will take a stab at it rather than ducking or evading and you can then pick apart my reply. Sound fair enough?

Red shift is the apparent change in frequency of light that is received from great distances away. This light comes from galaxies, quasars and so on which are very distant from the earth. We know the light is shifted in frequency toward the red because we know that elements, gold for example, have a certain spectral pattern. When we see the spectral signature for gold or helium etc we know it's present in a star. When we see this pattern but the frequencies are shifted toward the red or blue, we don't think it's a new element, we believe it's the same element but with a shift, in this case, a red shift. The reason for the shift is believed to be a doppler like effect much like sound becoming higher in frequency as the souce approaches the listener and lower as it moves away. By measuring red shift we know how fast the object emmiting the light is moving away from us. We have noticed that red shift seems to vary closely with the distance from us to the star or galaxy. From that we assume the red shift is an accurate measurement of distance as well as speed. Notice the assumption built into that.

It's a big subject and I'm sure I could do a quick search and find a lot more info rather than just off the top of my head. It is a very good subject and maybe we should have a new thread for it. My thinking is that if there is any other factor that influences red shift, then these speed and implied distance measurements are going to be off, maybe way off. That is the essence of my theory and yes it would be better if I had some calculations of how this works. It would be better still if I had some referrence to Einstien's work that seemed to fit in. I'm not denying that would be good and would fit into the mold and would bring more serious consideration, without a doubt. Without a doubt that would take a lot of work and may not get anywhere.

Theories, including those which are presently accepted did not start out as equations usually. They started as concepts which seemed to fit the observed phenomena, in many cases. I'm sure you can find other cases in which it was the opposite. Sometimes solutions to equations end up finding the effects in nature later on such as with much of Einstien's work. But, it most often starts with a concept and then we look for something to back it up and then later find how it relates to something else and write equations for it. Then sometimes we find new implications which stem from that work rather than from the basic concepts.

[xanadu]

There is no evidence that this is the case

The large and excessive amounts of red shift observed needed some explanation so they came up with inflation. New space is supposed to be appearing all the time. There is no evidence of that happening except the excessive red shift. It's kind of circular logic. Rather than proposing "dark energy" which has never been observed and saying the universe is expanding faster than light, the theories I proposed are rather tame and unassuming in comparison. That doesn't prove they are correct but Occam's razor shows my theory is the less preposterous. Always assume the simplest explanation if two equally valid theories exist. If you put food out at night and the next morning it's gone, it might be unicorns who ate it or maybe racoons. Don't assume unicorns unless the simpler theories have not panned out.

[Lazarus Long]

Rather than proposing "dark energy" which has never been observed and saying the universe is expanding faster than light, the theories I proposed are rather tame and unassuming in comparison.

Dark matter has been observed and its presence supports the premise of dark energy and they can, and are testing for the presence dark energy as well. These are not unassailable hypotheses like string theory but significantly testable ones, whose results will have important repercussions to our future understanding one way or the other.

Also no one is saying the universe is still expanding faster than light, only that it did in the moments following the Big Bang and that is because the present laws of physics as we understand them do not apply to the conditions that would have existed in those few moments. Even long after that period matter was still forming and collapsing into more discrete gravitational fields that later become stars and bodies as well as galaxies etc but that is much later after the inflation rate has slowed down to well below C as I have understood the theory.

[xanadu]

Dark matter has been observed and its presence supports the premise of dark energy and they can, and are testing for the presence dark energy as well. These are not unassailable hypotheses like string theory but significantly testable ones, whose results will have important repercussions to our future understanding one way or the other.

We weren't talking about dark matter at the moment and I happen to agree it does exist. Not that we really have "observed" it as such but we see it's pull and it's hard to come up with an alternate theory to explain it though I'm sure I could crank one out if you insisted.

Yes, they are looking for dark energy but haven't found any. Are you of the faith that it will be found? Maybe it will, I'm just saying there is a very real possibility it won't or something different will be found and they will try to say that's what they meant. It's supposed to have a repulsive effect on matter, isn't it? I thought that energy had weight, if so, then why wouldn't this dark energy have detectable gravity or is that what they are looking for right now?

I had heard that far parts of the universe were moving away from us at greater than light speed according to one theory or another. It was said that you could never visit any place in it that was farther than the hubbel distance, I think they called it. It was in one of these threads. I just think my explanation is a little more likely than the unicorn type explanations we've been getting. I do not hypothesise FTL expansion nor near light speed expansion. I do not theorise any new space being created at a rapid clip. Maybe it is, maybe all that's true. Maybe there are unicorns, I don't know. I'm just saying my theories do not require belief in any such things.

[xanadu]

I just happened to think that you are probably saying that dark matter will turn out to be dark energy or be related to it. Is that part of what you are saying?

[Lazarus Long]

Dark matter and dark energy are still related by E=MC2

Yes, they are looking for dark energy but haven't found any. Are you of the faith that it will be found? Maybe it will, I'm just saying there is a very real possibility it won't or something different will be found and they will try to say that's what they meant. It's supposed to have a repulsive effect on matter, isn't it? I thought that energy had weight, if so, then why wouldn't this dark energy have detectable gravity or is that what they are looking for right now?

I suggest you not confuse weight and mass as energy does not actually have mass but is convertible to mass, again in accord with General Relativity. As such energy can be influenced by gravity but that does not in itself mean it possesses mass except that most forms of particles associated with energy do possess some mass.

I do not operate on faith though hunches do have value as long as they are understood as the beginning and not the end of the process.

Also the Dark Energy should be detectable to our science so we are not dealing with an idea that is untestable and I believe that is a part of the purpose of both some cosmological experiments underway and also some of the objectives of the Cern, Large Hadron Collider .

Also Dark energy is not clustered but distributed throughout much of the universe which suggests its effects would be measurable by things like the acceleration rate of the universe not by the impact on specific regions of space. However the exception might be in close proximity to very large masses like Black Holes. But we are still a long way from deciphering all the information that is emanating from the regions near but outside the Event Horizon.

Nonetheless we are rapidly getting closer to definitive answers and the desire for faith is only relevant to its use as a motivation for constructive conjecture for the design of valid test models.

[bgwowk]

xanadu wrote:

From that we assume the red shift is an accurate measurement of distance as well as speed. Notice the assumption built into that.

There is no such assumption in the 1998 conclusion that expansion has varied with time, and is now accelerating. None! If you had done as I asked, and explained how the 1998 conclusion was drawn, you would know that.

You admit that you could learn more by studying these matters further. What I'm trying to tell you is that such study is an absolute prerequisite to even begin thinking about alternative explanations for observations. You can't offer alternative explanations for observations when you still haven't stated the observations that need to be explained.

Because someone told you this?

It is because of comments like that that I have little interest in continuing this discussion. You greet answers with incredulity or dismissal, and then complain that not enough questions are being answered, or answered in sufficient depth. The process is a farce.

[bgwowk]

Also no one is saying the universe is still expanding faster than light, only that it did in the moments following the Big Bang and that is because the present laws of physics as we understand them do not apply to the conditions that would have existed in those few moments.

Laz, you might want to brush up a bit on these matters. This article is excellent,

http://www.sciam.com...47&chanID=sa008

especially page 3.

In fact galaxies beyond the Hubble distance do recede from us at faster than the speed of light. That's true even without inflation, and is a standard result of General Relativity applied to a large universe. Relativity is not violated by this kind of FTL travel because it's still true that no object can overtake a light beam if they start at the same place at the same time.

[xanadu]

It is because of comments like that that I have little interest in continuing this discussion.

Ho hum. I'm still waiting for you to explain something but all I get is statements like that and your expressions of belief that what you were told must be true. If you aren't going to grace us with any more of your wisdom, I for one will manage to get by. It is ironic but fitting that the one who dodged almost all of my questions and gave evasive answers to most of the rest is not satisfied with the answers I gave him. Not complete enough was it? Oh dear.

LL wrote:

Dark matter and dark energy are still related by E=MC2

You make huge assumptions here. First you assume dark matter is indeed ordinary matter then you assume dark energy exists and that it is ordinary energy. It may be but you've assumed a lot there.

energy does not actually have mass but is convertible to mass, again in accord with General Relativity. As such energy can be influenced by gravity but that does not in itself mean it possesses mass except that most forms of particles associated with energy do possess some mass.

I think you are splitting hairs here. The energy contained in a system has mass and displays gravity effects associated with it. Are you saying that the mythical dark energy does not possess mass? Are you saying it's a dynamic form of energy or is it radiant? Of course no one knows because it has not been found, detected or anything else. It has been theorised about as an explanation for the apparent FTL expansion of the universe that both you and bg are fervent believers in. I've never said that was false but I've shown alternate explanations that assume a lot less fantastic things than the standard current theory. I would ask bg how the universe can expand FTL without inflation but he would just intone that "Einstien's equations say so" without saying how and that tells us nothing so I will not bother to ask.

[Lazarus Long]

(xanadu)

LL wrote:

Dark matter and dark energy are still related by E=MC2

You make huge assumptions here. First you assume dark matter is indeed ordinary matter then you assume dark energy exists and that it is ordinary energy. It may be but you've assumed a lot there.

Not much of an assumption since that is why they could detect Dark Matter in the first place; because it conforms to General Relativity and bends light due to its gravity and ability to warp space/time but no I am not saying it is *normal* matter to suggest that it must conform to the conservation of mass/energy rules or that it is convertible to *dark* energy in accord with GR.

Xanadu why do you assume that so much is unknown and assumed when the extent and rate of accruing knowledge is unparalleled and unprecedented in all of human history?

Brian I am still reading the article and it is helpful but I have some questions I will bring up later. I see what you mean about the issue of SR Red Shift versus the Doppler Red Shift and to a certain extent I guess I am a victim of what the article refers to when astronomers have kind of mislead me. Nonetheless the issue of detecting a sort of after image of the objects beyond the Universal Event Horizon so that inflation causes them to appear to be moving faster than light is still somewhat a mathematical construct assuming an absolute value for Hubble's Constant. This may be but there are some questions around this hypothesis.

Also I found the part about inflation exceeding the speed of light and still accelerating interesting. So what is the inflation rate and how much faster does it need to go before the big rip?

[eternaltraveler]

So what is the inflation rate and how much faster does it need to go before the big rip?

Depends what is really meant by the big rip. On a very large scale the big rip is happening already. This is evident by portions of the universe receding from us beyond the speed of light. For a smaller scale, say, our own galaxy to be torn apart the rate of the acceration of the expansion would have to increase to the point where it is greater than the inward acceleration due to gravity. For something like our own planet to be torn apart that means the rate of acceration of expansion would have to be around 9.8 m/s^2. A hell of an increase to say the least from where it is now around 10^ -35 m/s (if I remember correctly which I probably don't ) )

[xanadu]

Not much of an assumption since that is why they could detect Dark Matter in the first place; because it conforms to General Relativity and bends light due to its gravity and ability to warp space/time but no I am not saying it is *normal* matter to suggest that it must conform to the conservation of mass/energy rules or that it is convertible to *dark* energy in accord with GR

I wasn't disputing the existance of dark matter, just it's nature. I do not accept dark energy and will not until some proof is shown.

Xanadu why do you assume that so much is unknown and assumed when the extent and rate of accruing knowledge is unparalleled and unprecedented in all of human history?

If there was proof of this dark energy the proof would be shown. Not just shown but paraded through the streets in chains. The belief that the universe is expanding FTL rests heavily on assuming red shift is reliable over long distances. This is an assumption. Dark energy was invented to explain the paradox of the red shift. I know Einstien used the term first but he retracted his belief in it. As for us having so much knowledge, that could be said about any point in history. We always knew a lot more than we did before but that has never stopped us from being very wrong about some things. It's easy to laugh at past mistakes and think that we are not believing equally false things today but that would be a huge assumption. Man will continue to err as long as he is human. But from our errors comes truth, little by little. We haven't found it all yet and will continue to make errors along the way.

[bgwowk]

Laz wrote:

Also I found the part about inflation exceeding the speed of light and still accelerating interesting. So what is the inflation rate and how much faster does it need to go before the big rip?

We need to get our concepts clear. Inflation and expansion are not the same thing. Expansion is the general process of the universe getting bigger that's been going on since the Big Bang. The concept of expansion (including superluminal expansion beyond the Hubble distance) is as old as Big Bang theory, and predates the idea of inflation by half a century.

The rate of expansion of the universe is now known to have varied over time, and is now slightly accelerating. This was discovered in 1998, and has since been confirmed in several different ways. The fact of this acceleration is what is called Dark Energy. The nature of Dark Energy (in other words, exactly what is causing the acceleration) is still the subject of theoretical speculation.

Inflation is a specific mechanism of extremely rapid expansion that is now believed to have operated during the early moments of the Big Bang. It was first developed in 1980, and now has strong evidence supporting it. Inflation may or may not still be happening. It is one of the candidate explanations for Dark Energy.

The Big Rip is the idea that perhaps 50 billion years from now, accelerating expansion will push star systems, stars, planets, and even atoms apart. It's gotten a lot of press because it's so melodramatic, but it's actually now almost ruled out by recent data from the Cosmic Microwave Background measurements by the WMAP probe announced this year.

Edited by bgwowk, 25 November 2006 - 04:14 AM.

[bgwowk]

xanadu wrote:

If there was proof of this dark energy the proof would be shown. Not just shown but paraded through the streets in chains.

For Heaven's sake, the existence of Dark Energy has been established by at least four independent methods.

http://physicsweb.or...es/world/17/5/7

Why not read and learn?

[biknut]

I thought this news report meant they had found proof of Dark Matter for the first time?

http://chandra.harva...ess_082106.html