70 replies to this topic

[xanadu]

LL wrote:

"Actually expansion is not slowing, it's accelerating according to most of the recent data and the reason is attributed to dark matter. The current Nobel for physics was awarded over this discovery."

I will admit I have not kept up with things in recent years. Can you tell me how or why dark matter would cause the universe to accellerate it's expansion? You admit not all the data supports this view "according to most of the recent data"

Jay wrote:

"Logically follows? An object blasted from the surface of the earth at greater than escape velocity will slow as it pulls away from the earth, yet it doesn't logically follow that it will slow and fall back to earth. Is this the type of logic you use when studying physics?"

We are talking about the expansion of the universe, not escaping from a planetary body. There are places you can go other than earth, there is no place other than the universe to go to. I submit that your logic in this case is faulty.

bgwowk wrote:

"According to Guth, inflation *at a minimum* predicts that the whole universe is 10**23 times larger (about a TRILLION TRILLION times larger) than the visible universe. The even wilder large numbers apparently come from calculations by Andrei Linde based on models of chaotic inflation."

So the theorists are all over the map and this is to be taken seriously? 10^1000 parsecs is so much larger than the size by Guth that the difference is a number that does not relate to our universe at all. I really don't think you want to stay with that larger number. You might as well say this universe is infinite. I know there is a difference but how could you define the difference in terms that mean anything?

I read your wikipedia definition of decoherence and am not convinced at this point. The definition seemed very vague and more philosophical than practical. Wikipedia is not a solid souce of info, IMO. Then there is this statement of yours:

"For example, if QM predicts that a double slit experiment will give rise to two observers each seeing a different result, but never able to communicate with each other because of decoherence, and you can subjectively be only one of them, how do you handle the other observer that QM predicts? "

You are saying that classical QM makes these prediction? I don't think it does. And why would the two observers not be able to communicate with each other? I'm interested in theories that relate to reality, not theories that just relate to more theory. If you can't make testable predictions with a theory, it is of no use. One guy's wild theory gives a huge size to the universe and the next person's theory gives a size so much larger that it's basicly infinite. Then someone else's theory says even wilder things. What is the difference between those theories and my theory that pixies are responsible for physical phenomenon? My theory isn't testable either.

[bgwowk]

Xanadu, all I've tried to do is give you a few examples of how real theories constructed by real physicists (respected experts published in cosmology and quantum mechanics) suggest that there is much to reality beyond our eyesight. Your responses indicate that you understand neither the depth of knowledge that goes into such theories, or the difference between model building based on simple axioms versus cooking up fairy tales. If you don't understand the difference between dark matter, dark energy, or competing interpretations of quantum mechanics, yet believe you have the background to scold QM experts and cosmologists while putting forth your own theories, I submit that you don't know what you don't know. And I, frankly, don't know where to begin.

[jaydfox]

"Logically follows? An object blasted from the surface of the earth at greater than escape velocity will slow as it pulls away from the earth, yet it doesn't logically follow that it will slow and fall back to earth. Is this the type of logic you use when studying physics?"

We are talking about the expansion of the universe, not escaping from a planetary body. There are places you can go other than earth, there is no place other than the universe to go to. I submit that your logic in this case is faulty.

You stated that if the universe's expansion was slowing, then it "logically follows" that it will stop and then contract. I simply presented a simple and easy to understand example where something can slow but not stop. Unless you're using some unorthodox version of logic, it's yours that's faulty. It is of course possible that if the universe's expansion is slowing, then it will stop, but it doesn't logically follow.

[jaydfox]

What is the difference between those theories and my theory that pixies are responsible for physical phenomenon? My theory isn't testable either.

I generally find that it's impossible to debate intellectually with someone who can say something so asinine with a straight face (well, I assume you had a straight face; after all, I can only see the words you typed).

In religious debates, I suppose one could get away with it more easily (e.g., comparing the idea of whether there is a God to the idea that there is an invisible pink unicorn on Pluto that rules the universe), but in physics, it just takes away any credibility you might otherwise be striving to have. It's not Brian's fault that you are ignorant as to the mathematics and physical interpretations of both theory and experiment, with regards to quantum mechanics, general relativity, and cosmology in general. He's trying to be helpful; you're just being rude and arrogant out of ignorance. I apologize if this sounds ad hominem, but I'm just being blunt.

[xanadu]

Jay, you have nothing to say so I won't waste any more time on you.

bgwowk wrote:

"Xanadu, all I've tried to do is give you a few examples of how real theories constructed by real physicists (respected experts published in cosmology and quantum mechanics) suggest that there is much to reality beyond our eyesight"

I've seen only statements that the universe is a certain size, statements about decoherence and nothing to back up any of those theories. I notice that you ignore most of my questions.

"Your responses indicate that you understand neither the depth of knowledge that goes into such theories,..."

All you've done is state the theories, you have given no practical examples nor any of the background to them. You state things and expect everyone to already know and agree with what you are talking about. If you want to educate or inform us, why not explain things rather than simply saying that's the way it is? I'm here to learn, I'm sure many others are as well. Most or all of us have no idea what you are talking about with many of the things you have said. Unlike them, I will ask the hard questions and if that reveals ignorance, then so be it. If you understand your stuff, you should be able to explain it to some degree.

"...or the difference between model building based on simple axioms versus cooking up fairy tales."

If your models do not predict reality, then they are of no more use than the fairy tales.

"If you don't understand the difference between dark matter, dark energy, or competing interpretations of quantum mechanics, yet believe you have the background to scold QM experts and cosmologists while putting forth your own theories, I submit that you don't know what you don't know. And I, frankly, don't know where to begin"

Which QM experts and cosmologists have I scolded? Are you a cosmologist? I don't believe I've scolded anyone but I do ask the tough questions. Why do you state things that you believe few if any of us understand if you refuse to take the time to explain yourself? The fact that these "competing" theories are in fact competing indicates that even the experts do not agree. Why then should we agree?

I'm not sure that anyone thoroughly understands dark matter or dark energy. Much of the so called dark matter could simply be dust and gas not visible to our telescopes. Some of it might be black holes including micro black holes. Some of it may be matter in another dimension or another phase that does not interact with ordinary matter except by gravitation. What is your explanation of it? People say a vacuum has energy in it. Theories say that matter is being formed continuously. Have any of these theories been validated and if so, how. I am here to learn, many other are here for the same reason. If you have knowledge, then share it.

[bgwowk]

"You can ignore the result (predicted new observers that can't be observed) as irrelevant for any practical purpose."

Is the part I bolded the Copenhagen interpretation, or is that something else further?

Yes, it is the modern Copenhagen Interpretation as I understand it. Bear in mind that orthodox Copenhagen Interpretation doesn't even permit observers to be modeled quantum mechanically; there is always a Heisenberg "cut" between the observer and the observed. Orthodox Copenhagen also says that wavefunctions collapse instantaneously. I think it's fair to say that nobody takes either of these ideas seriously anymore. The utility of QM to cosmology and quantum computing has required that the observer issue be confronted, and decoherence has provided a much more satisfictory solution to the measurement problem than instantaneous wavefunction collapse. To the extent Copenhagen survives, it survives with decoherence as the mechanism of wavefunction collapse. Many Worlders (and Consistent Histories) people simply note that you get the same observable predictions without assuming wavefunction collapse. You do however get a vast profusion of predicted unobservable realities, which many people find philosophically objectionable. So they impose wavefunction collapse to get rid of them.

By the way, the Wikipedia material on QM interpretations is actually quite good to my eye based on my limited study of this subject. While there is junk to be found on Wikipedia, technical subjects usually only attract contributors educated enough to contribute good content.

[knite]

It does lead to all kinds of conjecturing and fun-thought doesnt it? Like, what if its because the stuff that we cant see on the other side of the stuff we can see is acting on our small corner, or what if its just the universe wrapping around on itself, and the pieces of the universe are pulling eachother from (apparently) the other side of the universe. Oh how entertaining would that be....personally I like the latter, something romantic about the universe coming to an end, versus the sad heat death.

[xanadu]

Gee, it seems that no one wants to answer any tough questions, least of all bgwowk. It's much easier to talk about philisophical things and stuff that can't be proven one way or the other. I ask for practical examples and get no response. I ask a variety of questions relevent to things discussed and get insults and evasions. Now it's a conspiracy of silence. Let me go back and refresh your memory about some of the tough questions that were posed

how or why dark matter would cause the universe to accellerate it's expansion?

(10^1000 parsecs) You might as well say this universe is infinite. I know there is a difference but how could you define the difference in terms that mean anything?

I asked why decoherence would mean that the double slit experiment would lead to 2 observers who are never able to communicate with each other?

I gave my explanation for dark matter and asked bgwowk for his.

These questions and others have not elicited any answers nor attempts at answers from any of our "experts" in residence. The tone and attitude of the response was that I was too much of a peasant for bgwowk to waste his time on. And the many others following this discussion who would assumably be interested in the answers as well? They are out of luck too. This thread has gotten many many views lately. BTW, I suspect that wikipedia entry on decoherence was authored by our bgwowk himself

If you are going to run and hide pretending not to see the questions, I will leave you alone. I believe the emperor has no clothes.

[jaydfox]

We'll take this in steps:

(10^1000 parsecs) You might as well say this universe is infinite. I know there is a difference but how could you define the difference in terms that mean anything?

If you don't understand the difference between very large numbers and infinity, then perhaps you should educate yourself. There are a number of good primers on the subject. I suggest this one:
http://www.scottaaro...bignumbers.html

[Lazarus Long]

(xanadu)

LL wrote:

"Actually expansion is not slowing, it's accelerating according to most of the recent data and the reason is attributed to dark matter. The current Nobel for physics was awarded over this discovery."

I will admit I have not kept up with things in recent years. Can you tell me how or why dark matter would cause the universe to accellerate it's expansion? You admit not all the data supports this view "according to most of the recent data"

I apologize for not replying sooner but I have been very busy in the real world and have had no time for the internet at all. I will likely not reply immediately to most things for the time being and that leads me to an important point. You said:

You admit not all the data supports this view "according to most of the recent data"

Respectfully, this is not about semantics. More than a sufficient amount of data is in to dispel the classical notions of expansion; the closed universe model is history. The reasons the universe appears open and not likely to decelerate and collapse are the subject of very serious debate but the universe IS accelerating, not slowing down and it has been doing so for the last 6 billion years (coincidentally since about the time period our planet formed.)

Second, I wrote fast and didn’t add Dark Energy as well. In fact while Dark Matter is important it is pretty much accounted for as a minor factor and the real driving force of the acceleration we clearly observe is what physicists call dark energy.

You may want to review a considerable amount of data collected by the Chandra telescope and well as WMAP.
http://chandra.harva...004/darkenergy/

A galaxy cluster is comprised on hundreds of galaxies embedded in a cloud of extremely hot gas and dark matter. Dark matter, an invisible and unknown type of material, is postulated to hold clusters together. X-ray observations have the unique ability to determine the ratio of the mass of the hot gas and the mass of the dark matter in a cluster. The observed values of the gas fraction depend on the assumed distance to the cluster.
Because galaxy clusters are the largest bound structures in the Universe, they are thought to represent a fair sample of the matter content in the universe. If so, the ratio of hot gas and dark matter should be the same for every cluster. Using this assumption, the distance scale can be adjusted to determine which one fits the data best. These distances show that the expansion of the Universe was first decelerating and then began to accelerate about six billion years ago.

Many scientists attribute the driving force behind cosmic acceleration to dark energy a strange form of energy that acts like repulsive gravity. It could be due to extra dimensions of space, or possibly it is an indication that modifications of Einstein's theory are needed.

Assuming that dark energy is responsible for the acceleration, combining the Chandra results with observations of the cosmic microwave background radiation indicates that dark energy makes up about 75% of the Universe, dark matter about 21%, and visible matter about 4%. The Chandra observations agree with results from the Hubble Space Telescope (HST) and other optical telescopes, which first showed evidence for an accelerating expansion of the Universe. Chandra's independent verification helps to strengthen the case for cosmic acceleration.

The new Chandra results suggest that the dark energy density may be constant. If so, the Universe would continue expanding forever, with galaxy groups and clusters spreading further and further apart. The Chandra data also allow for the possibility that the dark energy may be increasing slowly with time. In this case, the cosmic acceleration would increase until, at a far distant time, galaxies, stars, planets and even atoms will eventually be torn apart in what has been termed "The Big Rip."

In just the last few months a fascinating experiment that used light traveling to us from supernovae at great distance and emulating an earlier experiment done to confirm GRT, came in pretty conclusively to prove the presence of dark matter by how it bent light when passing by a galaxy on its way to us.

The results of these and many more observations appear to suggest the universe is proportioned as stated in the quote above thus:



The why and how of this observed fact is subject to debate but the fact that the universe is accelerating is not and this has now been confirmed from multiple independent sources of measure. I am sorry if that upsets some people’s cosmological view but that is not the point. The point is that more and more the closed universe model is being overruled in favor of the open one.

Before getting all upset about these ideas and worrying about whether or not we here are expert, folks may instead check out pages like these for themselves:
http://www.astro.ucl...mology_faq.html

http://physicsweb.or...s/news/6/11/7/1

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

http://physicsweb.or...es/news/7/2/4/1

And since this thread is about the sheer size of the universe, here is a map that has been generated by recent data from the WMAP satellite.

http://map.gsfc.nasa.gov/m_mm.html

And this represents the most recent time-line analysis of the age and shape of space/time.


(BTW this graph does not suggest that the universe is a funnel; it is a time-line that reflects [airquote] inflation [/airquote] as a 2 dimensional ring or disk along a chronological order)

Please everyone rather than seeking a conflict, those who do not want to agree with these conclusions and interpretations of the data owe it to themselves to become updated on what has been one of the most revolutionary decades in the modern history of cosmology. The orbital telescopes have revolutionized our ability to model the universe on a scale only equal to the impact of Galileo’s lenses and Tycho Brahe’s data.

[xanadu]

Jay, clearly there is a difference between large numbers and infinity. I asked for a definition of the difference that would make sense. What difference is there between the two that matters at all to us? As I pointed out, the number of atoms in the known universe is likely less than 10^100 so 10^1000 is a nonsense number that does not relate to anything we can measure, count or deal with. It is for all practical purposes, infinite.

Lazarus, thank you for the response. That was a well thought out and extremely well annotated reply. It had many links which I will be perusing. I assume you have already read the links and know something about this subject. What is your explanation for the fact or belief that the universe began accelerating expansion 6 billion years ago and how did scientists determine this?

"Because galaxy clusters are the largest bound structures in the Universe, they are thought to represent a fair sample of the matter content in the universe. If so, the ratio of hot gas and dark matter should be the same for every cluster. Using this assumption, the distance scale can be adjusted to determine which one fits the data best."

There seem to be a lot of assumptions at work. If any of them are incorrect, it would throw off a lot of other calculations. Dark energy seems to have been invented to explain this apparent acceleration of expansion. Is there any independent evidence of dark energy? Dark matter's existance has been verified by things such as the rotation and behavior of stars and galaxies. We don't totally understand what it's composed of but it's existence is indisputable. That or gravity works in ways we don't as yet understand. I'm not saying this theory of dark energy and expansion is wrong, I'm looking at the underpinnings for weak links. Saying there is a form of energy that causes repulsion that it's something we can't see or measure just to justify the apparent expansion sounds like a weak link. At one time, our best scientists thought heat was a form of liquid that flowed from one object to another. It seemed to fit the data.

If the universe was a tiny size at one time, then presumably everything that now exists was present in that tiny form. How then could dark energy have suddenly formed a mere 6 billion years ago? Was it not present at the beginning? Our universe at the beginning would have to have been a black hole by definition. It's mass would have been great enough to close space even though it was or seemed to be expanding. When then did it stop being a black hole or did it ever stop?

I realise there may be no answers to many of these questions. I want to get people thinking about things and I hope to learn what new advances and observations have been made. At least you have been forthcoming with what you know.