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I have no formal education in cosmology or astronomy, with the exception of a single Intro to Astronomy course I took a couple years ago and which caused me to start asking a lot of questions. Although I'm familiar with almost none of the mathematics behind modern cosmology, I am acquainted with many of the its general concepts, and my gut (no convoluted ideas or reasonings, merely my gut, which I have more faith in than anything) leads me to be extremely skeptical of many of its most fundamental assertions. I have several questions that would be difficult to ask in a cohesive manner in a single post, so I'll start by asking one fairly simple question and see where the discussion can go from there, and hopefully get some idea of just how much I do or do not understand:

Briefly, what is the most important evidence that the universe is expanding? What is the most important evidence that this expansion is accelerating?

Nick,

You'd get better answers from multiple experts by posting your questions to http://www.bautforum.com/

Very briefly, though,

1.The red-shift of the light coming from remote galaxies is a measure of how fast they seem to be receeding from us. More remote galaxies are more red-shifted than nearby ones -- i.e. distant galaxies are receeding more rapidly than those closer to us. To first approximation, this increase of speed of recession with distance is consistant with a constant speed of expansion.

2. Most "type 1" supernovae result in almost identical light output. They can be seen and measured at greater distances than most other "yardsticks.". Knowing how bright they really are and meauring how bright they appear to be yields reasonably accurate distances to the galaxies they're in. Graphing these distances versus those galaxies' redshifts shows that the more nearby of them are receeding faster than would be the case if the expansion were linear. i.e. it is accelerating.

Selden,

SNIa is certainly NOT the BEST evidence for the acceleration of the cosmic expansion. It was the first.

The acceleration is usually expressed in the non-vanishing of the so-called dark-energy fraction, Omega-Lambda.

Here is a typical display summarizing the state of the art.
What makes the acceleration a fact beyond doubt is the COINCIDENCE of completely independent data. Note of course the crucial impact of CMB (Cosmic Microwave background, WMAP)!



Bye Fridger

PS: For a long time there was much criticism about the SNIa evidence. Notably, since we only know that SNIa are "standard bombs" NOW. But the evidence that is crucially used to argue for the accelerated expansion refers to SN's at HIGH z , i.e in the far past. Nobody has any solid arguments about the universality of the SN light curves to within a few percent for such "old" SN's.

As the registration-confirmation e-mail for the Bad Astronomy forum seems to have been dispatched from one of the more distant galaxies, and as I am sure the members of this forum are more than qualified to have this discussion, I think I'll keep it here. Thanks, though, Selden; that's clearly a very good forum.

Now, concerning the redshifts of galaxies:
I understand that the primary means for determining distances at the scale of galaxies is by measuring apparent magnitudes of certain standard candles. This seems like a fairly foolproof method, as the biggest assumption therein, by my reasoning, is that the physics of, say, a cepheid, or a supernova, are the same in other galaxies as they are here. I also understand enough of spectroscopy and basic electromagnetism to have full faith in the measurements of redshifts.

Thus, I do believe that our measurements of distances to galaxies are more or less accurate, and that the measurements of the redshifts associated with these galaxies are also accurate. I believe, therefore, that there is indeed a correlation between distance and redshift.

I am also fully acquainted with the simple concept of doppler shift, and its use to measure radial velocities of celestial objects. Therefore, I can easily see how, especially to a seasoned astronomer used to attaching redshifts to radial velocities (such as, say, Edwin Hubble), the data would suggest that distant galaxies are receding at speed.

However, this assumption, which is apparently held to be law by the astronomical community at large, seems extremely weak to me, and here's why: what I see in a correlation between distance and redshift is just that: a correlation between an object's redshift and its distance. I have a good-science habit of always asking "Are there any other possibilities?" and stemming from that, my instict, from the first time I ever came to understand this correlation, has been to wonder "Is it possible that light becomes redshifted simply by traveling long distances?" Or, another way to put it: "Is it possible that all light loses energy over time or over distance travelled through space?"

This question was suggested to me quite naturally by a distance-redshift correlation, and its hard for me to believe that it has never occurred to anyone else. However, the question has stuck with me for a long time because I have never been able to find a good answer. As I said, I have very little formal education in these subjects, and I am quite limited in the free time I have to address the question myself, so I may just have not looked hard enough. However, in all my perusings, I have noticed a disturbingly complete absence of any kind of serious discussion on this question, or anything that could be remotely related to it. Does space - specifically, outer space - have an effect on the energy of light? Nobody seems to care. Obviously its an important question concerning Hubble's law.

Also, theoretically, if we assume that the truth of the matter is indeed that the redshift is due simply to time spent traveling, and not to radial velocity of the source, there are then several direct implications that I find very interesting and, furthermore, neatly agree with some of my other more rebellious feelings in a way that smacks of truth, as well as perhaps pointing towards better understandings of dark matter and dark energy.

Any thoughts?

Just two comments :

1- the second interpretation you're describing (about the redshift dependant on distance, which may be caused by a kind of "photon fatigue" in its course through a space filled with dust and gas) was already discussed a long time ago in the physics community, and it was rejected. It is conficting with the conservation of energy in some ways I wont describe.

2- There's a lot of misconceptions about the redshift of far away galaxies which are always conveyed by the scientific popularizers and journalists : it ISN'T a Doppler effect at all ! Doppler shift is caused by moving sources of light and the relative wavelenght difference is dependant on velocity in this case. On average, the distant galaxies AREN'T moving, locally (there are some subtleties I wont describe for now). It is actually space itself, between us and the far away galaxies, which is stretching with time, and which gives us the illusion that the galaxies are moving away (locally, they are stationary !). The redshift of distant galaxies isn't a Doppler effect, but a consequence of the expansion of space itself. It's dependant on distance, and not on velocity (so it's not a Doppler effect).

Nick wrote: Or, another way to put it: "Is it possible that all light loses energy over time or over distance travelled through space?"

Does space - specifically, outer space - have an effect on the energy of light? Nobody seems to care. Obviously its an important question concerning Hubble's law.
?

Yes, space DO have an effect on the energy of a photon : during its expansion, space is stretching the wavelenght of the photons. This is exactly the source of the redshift we see.

Formally, in some way, it is a kind of "photon fatigue", with a clear interpretation under the General Relativity theory.

For a critics concerning deep space objects and red shift see below:

http://en.wikipedia.org/wiki/Halton_Arp

Cham wrote:1- the second interpretation you're describing (about the redshift dependant on distance, which may be caused by a kind of "photon fatigue" in its course through a space filled with dust and gas) was already discussed a long time ago in the physics community, and it was rejected. It is conficting with the conservation of energy in some ways I wont describe.

One of my deepest scientific principles is to always assume that there is something more out there that nobody knows anything about yet. This assumption is based primarily on history, as it would have saved a great many highly intelligent and qualified scientists from looking like fools in the textbooks, not just a long time ago, but throughout the entire course of scientific history. I would be interested to know what reasons were ultimately given for rejecting my hypothesis of distance red-shifting, as merely calling upon conservation of energy is woefully insufficient. As I stated before, there are several interesting direct implications resulting from this hypothesis, one of which is clearly that there must be something causing it that nobody knows about yet and that the energy lost must be going somewhere. This much would not be at all difficult for me to accept. I could easily come up with ten different theories off the top of my head that would require a lot of technical arguments to refute.

One such rough theory, just as an example, is that the energy given up by all the light that moves across the vast reaches of space collects in some mysterious form, the effects of which, coincidentally, are only just beginning to be noticed by astronomers, and subsequently causing a lot of confusion and headaches...

Cham wrote:2- There's a lot of misconceptions about the redshift of far away galaxies which are always conveyed by the scientific popularizers and journalists : it ISN'T a Doppler effect at all ! Doppler shift is caused by moving sources of light and the relative wavelenght difference is dependant on velocity in this case. On average, the distant galaxies AREN'T moving, locally (there are some subtleties I wont describe for now). It is actually space itself, between us and the far away galaxies, which is stretching with time, and which gives us the illusion that the galaxies are moving away (locally, they are stationary !). The redshift of distant galaxies isn't a Doppler effect, but a consequence of the expansion of space itself. It's dependant on distance, and not on velocity (so it's not a Doppler effect).

I should have put it that way originally, as I was actually aware, somewhere inside my noggin, that this was the actual current explanation of the redshift. It is one of the more difficult concepts, which I suppose naturally makes it easier for me to forget about. As a side question, I should like to clarify my understanding of this theory: The way I understand it, all space expands, but because of gravity, the expanding space between, say, the Earth and the Moon, is quickly overtaken by their mutual attraction. I think of it as a kind of sliding action powered by gravity. This understanding comes from a lot of guesswork, though, so if a brief clarification is possible it would be appreciated.

Anyway, replacing the doppler-shift explanation with relativistic expanding space does little to mitigate my skepticism. If anything it makes me more skeptical, as follows:

Cham wrote:Yes, space DO have an effect on the energy of a photon : during its expansion, space is stretching the wavelenght of the photons. This is exactly the source of the redshift we see.

Formally, in some way, it is a kind of "photon fatigue", with a clear interpretation under the General Relativity theory.

This is obviously the point where my ability to argue breaks down, as I do not understand the vast amounts of complicated mathematics used to come to the current theory of the universe, and it would be impossible for me to refute any arguments stemming from that math. However, there are a few things I do understand that if anything only increase my doubt, the first of which is that the current theory of the universe is based on vast amounts of complicated mathematics: so were epicycles.

Epicycle models provided extremely accurate predictions, but only once they were worked and modified and basically intellectually manhandled into agreement with observations. I admit I may be making a big leap here because of my unfamiliarity with the mathematics involved, but I've definitely gotten the impression a similar process has occurred with current cosmological theory. And I also understand that, just as epicycle models always ended up carrying slight discrepencies or incosistencies, every single "modern" cosmological model thus far has proven to be fundamentally flawed in some way. I'm no math-whiz, but I know enough math to know that when you've got the right formula there are no flaws. How am I not supposed to be skeptical of almost everything I hear concerning modern cosmology when I know there's something wrong about it?

Before Hubble discovered his law, were the mathematics of relativity theory consistently showing that space expands? Or were the coeffecients modified to produce such a result sometime afterwards? And be honest.

Just thought I'd mention that this is a fascinating discussion
concerning the expansion of the universe and the red-shifting of light.

Dr. Schrempp? Martin? Can you gentleman continue here? I am very
much enjoying the dialog and am even learning some things here.

Please keep it up.

Nick? Thanks for starting this conversation. Extremely interesting.

Thanks, Brain-Dead

Nick wrote:Before Hubble discovered his law, were the mathematics of relativity theory consistently showing that space expands? Or were the coeffecients modified to produce such a result sometime afterwards? And be honest.

There occured many ironic situations during the development of physics, and the expansion of space is one of them. It just happened that Einstein's General Relativity theory PREDICTED the expansion of the universe 10 years BEFORE Hubble made his observational discovery. Back in 1915, Einstein realised that his theory was telling something about global expansion. Even him refused to accept it, so he introduced his cosmological constant just to stop that expansion. It's only after Hubble announced the results of his observations (around 1925) that Einstein said "I made my biggest blunder", since he refused to accept what his own theory was telling. Predicting on paper alone that the whole universe should be expanding was certainly the most impressive achievement in Science. It was the greatest PREDICTION, in all mankind history, literally !

And about that epicycles comparison : it's a very wrong comparison. The epicycles were used at Ptolemy's time just to explain a physically simple problem : planets moving around a star, as seen from a planet perspective. Now, modern physics is getting very complicated and sophisticated just because it's now able to describe and explain MUCH more natural phenomenons. Physics theories are now GLOBAL, so it's very clear why they're also getting so much complicated and mathematical : they're able to describe more complicated situations than just planets moving around a star. The epicycles analogy is thus very unfair.

And actually, it's the whole reverse : globally, physics is getting SIMPLER ! Okay, this isn't obvious at first when you have to study all the maths, but physics is really going simpler. Gravitation, as an example, is MUCH simpler in General Relativity theory than in newtonian theory ! According to Newton, gravity is a very mysterious force traveling instantaneously at distance, through vacuum, space is the arena, time is another thing, etc, while they are all unified in General Relativity : space-time geometry IS gravity ! How can it be simpler ?

EDIT : Personally, I have an extremely strong confidence in General Relativity (almost at the faith level, actually !). As Einstein himself once said : it CANNOT be wrong, or else, I'll be very sorry for the Lord !

Cham wrote:

Nick wrote:Before Hubble discovered his law, were the mathematics of relativity theory consistently showing that space expands? Or were the coeffecients modified to produce such a result sometime afterwards? And be honest.

...

And about that epicycles comparison : it's a very wrong comparison. The epicycles were used at Ptolemy's time just to explain a physically simple problem : planets moving around a star, as seen from a planet perspective. Now, modern physics is getting very complicated and sophisticated just because it's now able to describe and explain MUCH more natural phenomenons. Physics theories are now GLOBAL, so it's very clear why they're also getting so much complicated and mathematical : they're able to describe more complicated situations than just planets moving around a star. The epicycles analogy is thus very unfair.

And actually, it's the whole reverse : globally, physics is getting SIMPLER ! Okay, this isn't obvious at first when you have to study all the maths, but physics is really going simpler. Gravitation, as an example, is MUCH simpler in General Relativity theory than in newtonian theory ! According to Newton, gravity is a very mysterious force traveling instantaneously at distance, through vacuum, space is the arena, time is another thing, etc, while they are all unified in General Relativity : space-time geometry IS gravity ! How can it be simpler ?

EDIT : Personally, I have an extremely strong confidence in General Relativity (almost at the faith level, actually !). As Einstein himself once said : it CANNOT be wrong, or else, I'll be very sorry for the Lord !

Indeed. Epicycles does worked one by one just for the single planet under observation. That is, from the epicycles of Venus the astronomer cannot predict the movement of Mars, for example; as in the Newtonian mechanics it's possible. There weren't a general predictive framework with which the astromers were to relate the planet's movements, simply because they haven't a dynamics, or the wrong one fulfilled by religious precepts; just a kynematics to save the phenomenon.

I would like to clarify a few things concerning my own views:
First of all, I do believe, in principle, in both quantum mechanics and relativity, which I understand encompass more or less the entirety of the "complicated math" we are referring to. I am not so naive as to think it could possibly be a coincidence that so much observational data has been corroborated by these two theories. (Again, I don't actually know how much data it is, but I understand it is...sizeable, to say the least.) What this tells me is that, at the very least, modern cosmology has indeed hit upon the truth, somehow. However, I am totally unconvinced that this is proof that any of its practitioners really understand how the theories are able to reflect the truth. Newtonian mechanics is an excellent case study: Newton's equations were not just lucky guesses that happened to work perfectly everywhere they were applied (at first). They were the product of mountains of observation and interpretation and a lifetime devoted to science, and, indeed, they reflect reality in a fundamental way. I find it hard to believe that the principle of conservation of energy - which I doubt anyone here would seriously try to challenge - could have been realized before a concept like "equal and opposite reaction" was introduced to the world. Assuming hypothetically that general relativity is perfectly correct and the ultimate truth (not even a necessary assumption, but it makes the argument more clear), I would argue that Newton got nothing wrong in his equations, he was only wrong in assuming that they were the ultimate truth and that there was nothing more to it. Can you not, by inserting whichever variables are necessary to describe the conditions on the surface of the Earth and in the vicinity of the Sun, effectively produce Newton's exact equations from those of relativity? Newton's mistakes were of a totally different class from those of, say, the supporters of epicycles, who simply had no idea what they were talking about. Is it not possible that the accuracy of the mathematics used currently is really due to some even greater process that nobody knows about yet, as was the case with Newton?

I have at this point done the following: compared you ("you" denoting all who would defend modern cosmology against my ideas) to the believers in epicycles, compared you to the believers in Newtonian mechanics, and then stated that those two types of people are completely different. To clear up this little inconsistency, let us recognize that in reality, the situation with modern cosmology is, of course, somewhat different from that of either epicycles or Newtonian mechanics during their respective era's of prominence. (I would expect many of you would be eager to point this out as well, as would be perfectly valid.) In the case of modern cosmology, it appears to me that there is such a vast range of phenomena which the current theories attempt to explain all at once, that it is entirely possible that both kinds of misunderstanding could be contained in modern models: some things are not fully understood or are not being approached from the right direction, although much of their nature is already manifest in your equations somehow, as was the case with Newton. On the other hand, there could at the same time be many phenomena you simply do not understand and are completely unqualified to talk about at this point, as was the case with epicycles. Something that has always struck me as a likely candidate for the latter group, for example, would be gamma-ray bursts.

Forgive me for using the term "you" so much; it is mainly for the purpose of brevity, which I'm having a hard enough time with already.

I could elaborate even further on some of my reasons for remaining skeptical in the face of all the evidence for current theory, but it would be tedious and time consuming, and my arguments would probably start getting quite weak quite quickly. As I am obviously the skeptic in the room here (and everywhere else I go I'm sure), it is important that I have some idea of what other possibilities could exist, if I'm going to presume that the current explanation of things is incorrect. I have no theories; I do not know nearly enough about actual observations to warrant any attempt at replacing inflationary cosmology. I do have ideas of things that should be considered, though, and areas of study that could be fruitful:

I am sure many of you are familiar with the concepts of complex systems, and of emergent behaviors and structures. I have only fairly recently come to an understanding of these ideas, and they have proved to be the most astoundingly beautiful and powerful concepts I have ever come across. Everything I understand about nature - things from astronomy, chemistry, mechanics, particle physics (a little), economics, human geography, psychology and neurology, etc. - are all direct results of complex systems. Most impressive of all, for which reason I state this subject seperate from those in that list, are biology and all its related fields, which at their very foundation are based on the mechanisms of complex systems. Life, which I'm sure we all agree is quite unique among all known natural phenomena, is an emergent behavior of the universe, and every living thing is an emergent structure at every level down to the molecules. Yet it shares this property with all other natural phenomena: the formation of a star is nothing short of an emergent process, as is the seperation of oil and water in a flask, or the development of a mega-metropolis around certain naturally sheltered harbors. My ideas concerning this subject are not yet fully mature, but it appears to me quite likely that every action, every structure and object that exists or ever will exist in the universe, and thus even the universe itself, emerges naturally from collections of more fundamental yet equally emergent structures and behaviors.

I have done a lot of personal work on dimensions as well, and ever since I was in tenth grade I have been convinced that dimensions were a key to understanding the universe, as the possibilities they present are so completely limitless. I have struck upon what to me is an extremely interesting concept that ties the general idea of "other dimensions" to my much more solid understanding of complex system, and so I propose that scale can be thought of as a dimension, distinct from space and time and providing the means by which those two classes of dimensions interact.

Finally, just as a though experiment, I have tried to come up with my own idea of what the general nature of the universe as a whole might be. It has been argued that the universe is finite and it has been argued that it is infinite. It has been argued that it is static, it has been argued that it is open, and argued that it is closed. It has been argued that it is cyclical. It has been argued that it is one of many. What I currently believe to be the most likely description is that the universe is infinite, in every direction, in time, space, and scale (and what-have-you), and that it is constantly changing itself and reinventing itself through the natural process of complexity. The universe has never before been the way it is now, in the infinity of the past, and it never will be again, in the infinite future. At some point, perhaps, the nature of stars and of galaxies and of atoms and of electrons will no longer be meaningful anywhere in the universe, and entirely new phenomena will have replaced them, only to be themselves replaced an era later.

I have much more to say, but I'm getting sick of writing at the moment and if I was reading this I'd probably be getting sick of that too. I'll fit other things in neatly where I can later, I expect. I would like to finish by asking if anyone could give me their interpretation of a fact that I stated earlier: that there is clearly something wrong with current models. I believe it could almost be made a definition of mathematics that, as I said before, when you've got the right formula EVERYTHING works! If you are describing your universe with two theories that mathematically don't add up, at least one of them is wrong. It's just wrong. There is something wrong about it. I seem to take this fact much more seriously than most folks, but it certainly seems important to me when it comes to searching for the truth.

Cham wrote:Gravitation, as an example, is MUCH simpler in General Relativity theory than in newtonian theory ! According to Newton, gravity is a very mysterious force traveling instantaneously at distance, through vacuum, space is the arena, time is another thing, etc, while they are all unified in General Relativity : space-time geometry IS gravity ! How can it be simpler ?

I'm probably gonna regret this, but you've peaked my incessant
curiosity once again there Martin...

Are you saying that from everything we know, gravity is the same
everywhere? It IS a mysterious force, is it not? I realize that gravity is
the weakest force in nature (assuming that I really understand ANY of
this stuff), but why is Newton wrong?

I mean, when you get to black holes, gravity suddenly becomes
the strongest force in nature doesn't it?

Thanks, Brain-Dead

BobHegwood wrote:Are you saying that from everything we know, gravity is the same
everywhere? It IS a mysterious force, is it not? I realize that gravity is
the weakest force in nature (assuming that I really understand ANY of
this stuff), but why is Newton wrong?

I mean, when you get to black holes, gravity suddenly becomes
the strongest force in nature doesn't it?

Gravity isn't of the same strenght everywhere, of course not. It depends on the proximity to the source. Gravity is a manifestation of the space-time curvature and it isn't a "real force", unlike all the other interactions of nature (the electric force acting on an electron, say). We still use the word "force" in the case of gravity, but this is just a word without a real meaning in this case, and which is used to simplify discussions. If space-time was "flat" (no curvature of the space-time geometry), as in euclidian geometry, there wouldn't be any gravitational force at all, according to General Relativity.

You may be interested to read this small page, about the geometrical interpretation of gravity :

http://www.bun.kyoto-u.ac.jp/~suchii/apple.html

Usually, i.e. in "normal" circumstances, curvature of space-time is low (gravity is weak). For example, a simple elementary particle produces a slight deformation (curvature) of the space-time around it, so its gravitational influence appears to be insignificant to other particles. All the other forces of nature (electromagnetic, nuclear, etc) are MUCH stronger in this case. But if you place alot of mass-energy in a given location of space (a pack of neutrons to form a pulsar, say), you may generate a huge deformation of the space around (curvature = gravity). Gravity may then become the dominant force to an observer, depending on the distance where the observer stands relative to the source of gravity.

There's a kind of irony in the case of gravity : it's the weakest interaction of all, as defined at the microscopic level(*) (until we discover some new ones, of course), but it's also the ultimate strongest force of all, at the macroscopic level. Gravity is the queen of all interactions currently known, especially since she's universal and acting on everything(**).

From Misner, Thorne and Wheeler :

Motto of Electromagnetism : "I count all charges"
Motto of Gravity : "I weigh up all that is"

________________
(*) Actually, gravity may also becomes the strongest force of all, at a fondamental sub-microscopic level. The sub-micro and macro levels may join in some still unknown way. But this is an aspect I don't want to discuss here.

(**) This universality is what makes gravity geometric in nature. It is a consequence (or the origin, depending on the point of view) of the famous "principle of equivalence" of Einstein.

Well I appreciate that explanation...

Was good reading, and I THANK you for it.

Take care, Brain-Dead

Very interesting topic. To throw a new angle at this discussion there is this stuff called Dark Matter DM http://en.wikipedia.org/wiki/Dark_matter. Not saying that wikipedia is the final answer but it pop-up first in google.

I attended a presentation at Stanford Linear Accelerator a few months ago on the subject. It was the first time I was exposed to DM. There is another phenomenon called Dark Energy DE which is even stranger that DM. DE was not even discussed. Here is the LINK
http://home.slac.stanford.edu/pressreleases/2006/20060821.htm to the presentation.

Nick, you have an interesting POV and I like you (maybe even more) I am short on the math side. From what I understand DM and DE is were some of the latest and most interesting research is current happening.

Who knows what the research in DM and DE will validate or show false. My guess is it could also shed light (no pun) on the red shift and expansion theory.

Didn't Dark Energy have something to do with Einstein's "Biggest
Blunder?" If I recall correctly, he had to "fudge" his equations to
account for the acceleration of the universe or some such.

Any elucidations here? Nick? Martin?

Again THANKS for this illuminating discussion.

Take care, Brain-Dead (Who IS by the way, very MUCH interested in
this ongoing topic.)

Who'da THUNK it, eh?

Complexity teach just how the things aren't neither monist nor dualist, where the monism is that of great unified theory and the dualism the actual state of the art (gravity vs qed). This latter is date back to Aristotle with own tenet "you cannot think the matter without a form" otherwise with the form alone no reason could be assigned to the matter, and this shouldn't logic. After a long run, nowadays the matter are atoms and subparticles (field's manifestations) and the form is the gravitation (space-time manifestations). If we need some sort of platonic monism, in my opinion would be the gravitation to blend the quantum mechanics, nor the contrary. Said this, for what concern "two theories that mathematically don't add up", mind at the waving theory of light and the corpuscolar theory of the light: both doesn't add up much more, nevertheless weren't both wrong. So, the theory of complexity didn't tell what is wrong in "something", just that this "something" is far to be simple and riductive.

BobHegwood wrote:Didn't Dark Energy have something to do with Einstein's "Biggest
Blunder?" If I recall correctly, he had to "fudge" his equations to
account for the acceleration of the universe or some such.

Any elucidations here? Nick? Martin?

Again THANKS for this illuminating discussion.

Take care, Brain-Dead (Who IS by the way, very MUCH interested in
this ongoing topic.)

Who'da THUNK it, eh?

Dark energy = quintessentia > flogist > calorics > ether

Fenerit wrote:Dark energy = quintessentia > flogist > calorics > ether

HUH
Well, I'll probably stick my foot in my mouth here but.......
Please forgive me if some of what I post here is in error. 1. I'm not a mathematician and 2. Formally, I only watched or audited a couple of Intro to astronomy classes. The Infinite Frontier and Project Universe.
Anyhow, I read earlier in this thread that red shifts were due to expansion of space.
I think there are also other reasons for observed red-shifts. I think that velocities are being observed in clusters and this is the reason that the search for dark matter and dark energy was started. Without dark matter and dark energy the theory of gravity also breaks down. On a galactic scale, the outer stars are orbiting the galaxy too fast for the amount of matter observed.
Galaxies in clusters are moving to fast (according to red shifts) for the amount of matter observed in the cluster system.
Since dark matter or dark energy does not radiate at any detectable wavelength, only it's effect can be seen. So is it really there or is this a patch for all our current theories? I believe the latter. I think that dark matter is supposed to account for 90% of the universe. I don't know if I can believe that.
How did I do? Any errors?
cartrite

Not too bad, cartrite

Well Einstein himself admitted first the possibility of Dark Energy via the introduction of an (undetermined), so-called cosmological constant Lambda in his famous equations (in the framework of general relativity).

When Dark Energy (or correspondingly the accelerated expansion of the Universe) was actually discovered (from type Ia Supernovae data), it came as a big surprise. So no systematic searches for Dark Energy beforehand.

The confidence in the presence of Dark Energy increased massively once the /independent/ evidence came from the WMAP (and earlier) Cosmic Microwave Data (CMD). See my summary plot higher up in this thread.

As to Dark Matter, you got it quite correctly. The original arguments came indeed from the (outer) rotation curves of galaxies that massively disagree with standard gravity. Meanwhile we have much better independent evidence from the so-called "bullet event"

http://chandra.harvard.edu/photo/2006/1e0657/
http://www.celestiaproject.net/forum/viewtopic ... tter#89453

Here "micro lensing" is used to establish an "atlas" of Dark matter, while Chandra X-rays are exploited to separately display the hot /luminous/ matter component in the so-called "bullet cluster" that was formed after the collision of two large clusters of galaxies,

The DarkMatter story is particularly HOT, since Elementary Particle Physics beyond the Standard Model offers VERY natural Dark Matter candidate particles that can be confirmed at the forthcoming LHC collider (CERN/Geneva) possibly already end of 2008...

So far some comments from the professional front

Cheers,
Fridger