Lambda-CDM theory - Woo or not?

[Tim Thompson]

Random Dark Dumbness

And that's the really pathetic truth. No mention of physics anywhere, no reference as to why any specific model of dark energy must be wrong.

That is like asking me to demonstrate that every possible definition of "God" is necessarily false. How can every potential variation of something that's never been show to haven an effect on a real experiment be shown to be "false" Tim?

That's just plain stupid. No, as a matter of fact, it is nothing like that at all. There are specific, published hypotheses as to what dark energy might be in terms of natural phenomena. If you don't know what those hypotheses are, and you are unwilling to address them in particular, then you have nothing informative to say on the topic.

Because "dark energy" is by definition the "anything" which is responsible for the accelerated expansion of the universe.

Tim, it's like a theist claiming God energy is by definition anything which is responsible for the accelerated expansion of the universe, therefore God energy (and God) exist by definition.

OK, fine. So if I call it "dark energy" that means that dark energy (and therefore dark) exist by definition. I don't think anyone reading this will have any serious problem with the defined existence of dark, do you? After all, dark, unlike God, is quite tangible, and easily demonstrated in controlled laboratory experiments. Hey, you don't suppose it was just some random accident that the words used in this case actually are "dark energy" and not "God energy"?

But in responding to me, Mozina completely ignored my comments about the 4 known forces or about observation. Why might that be? Like I said before, even though we may not know what dark energy is, we can know (and do know) what it is not, and we know this through the time honored scientific process known as observation.

That's just simply a false statement. You do *NOT* know what the actual cause is, ...

Hang on a minute. Now I said, "Like I said before, even though we may not know what dark energy is, ...", and then you said, "That's just simply a false statement. You do *NOT* know what the cause is.". So, you agree with me that I don't know what the cause of dark energy is, but insist that it is nevertheless a false statement? That's some pretty good stuff you're smokin' dude, did you bring enough for everybody?

... it has nothing to do with "dark energy" because dark energy isn't "real" and does not exist in nature.

Really? I should think that anything with enough oomph to push the entire universe around must have a lock on that "real" thing (you do remember, don't you, that the name of the thing that pushes the entire universe around is "dark energy", right?).

It's a term you use to essentially "cover up" your own ignorance in the final analysis and allow you to do math problem where you can include impotent invisible dark gods that make up all but 4 percent of your entire theory.

No it's not. It's a name. A name. Next you will be telling us that some kid was named "Joe" so his parents could cover up the fact that they don't really know anything about kids. Sheesh.

Sorry, I'm simply unimpressed.

Hey, I'm with you on that one. You really are about as unimpressive as it gets.

You guys complained because the best "bang" theory from a PC/EU orientation was off by something like 15 percent, but you're off by a whopping 96 percent without "fudging the numbers".

Who's "you guys"? I wasn't part of that conversation and have no idea what you are talking about. I thought PC/EU theory were steady states and denied the bang altogether.

You don't even know what you can rule out unless you start by *ASSUMING* a "closed" system in some way (a creation event in other words).

No Way Ho Say. Whether or not the universe is a closed system (which strikes me as a pretty reasonable assumption, really) and whether or not there was a creation event are independent concepts. And in any case, the assumption of a "creation event" is not a bad assumption either, since all we know about cosmology thus far is certainly consistent with that assumption. So what's the big deal?

It actually doesn't fly if you don't assume the house is locked. You and ben should talk about which empirical players can be ruled out if the doors are not locked.

You should show us the controlled laboratory experiment which supports your assertion that the universe is exposed to influences from outside the universe. If you can't do that, then by your own standard of "empirical", your claim is not empirical, and is as you would say, a figment of your imagination.

And finally ...

The problem is completely and entirely your own fault (collectively). Your industry never starts with "ordinary English".

OK, I get it. You think it's our own fault that we don't dumb things down to your level of dumbness. I respectfully disagree. If you can't climb up to our collective level of smartness (and there seem to be a lot of people who have managed that around here), that's your fault, not ours.

 

[Perpetual Student]

Obviously, it would take a lot of energy to accelerate the whole universe. However, my limited knowledge of physics would never have led me to guess that the amount of energy could be more than the all the mass in the universe. Can anyone direct me to a source for the rational and the mathematical derivation demonstrating that dark energy must comprise 74% of the mass-energy of the universe?

 

[Tim Thompson]

Cosmological Parameters II

Can anyone direct me to a source for the rational and the mathematical derivation demonstrating that dark energy must comprise 74% of the mass-energy of the universe?

The original paper does deal with this in some detail: Riess, et al., 1998. They present the math fairly completely. Also see the book Cosmology by Steven Weinberg (Oxford University Press, 2008), chapter 1.5 "Dynamics of Expansion". There are 3 key fundamental parameters, Ω_M (the mass fraction), Ω_λ (the vacuum energy fraction), and H₀ (the Hubble constant). These parameters (and several more that occasionally crop up) are defined & derived in Weinberg's book. Naturally, the Riess, et al., paper assumes you already know what they are, but they do a good job explaining how they arrive at their derived values. It is a probability argument based on deriving multiple parameters simultaneously and deciding which family of parameters best fits the observational data set. There are a number of papers since then which repeat that exercise (or one similar to it), always arriving at the same conclusion. All of the papers I list in my earlier post Empirical Evidence for Dark Energy repeat the fit of cosmological parameters to the data. Hope that helps.

 

[Perpetual Student]

The original paper does deal with this in some detail: Riess, et al., 1998. They present the math fairly completely. Also see the book Cosmology by Steven Weinberg (Oxford University Press, 2008), chapter 1.5 "Dynamics of Expansion". There are 3 key fundamental parameters, Ω_M (the mass fraction), Ω_λ (the vacuum energy fraction), and H₀ (the Hubble constant). These parameters (and several more that occasionally crop up) are defined & derived in Weinberg's book. Naturally, the Riess, et al., paper assumes you already know what they are, but they do a good job explaining how they arrive at their derived values. It is a probability argument based on deriving multiple parameters simultaneously and deciding which family of parameters best fits the observational data set. There are a number of papers since then which repeat that exercise (or one similar to it), always arriving at the same conclusion. All of the papers I list in my earlier post Empirical Evidence for Dark Energy repeat the fit of cosmological parameters to the data. Hope that helps.

Thanks, I will look at the above sources. I was hoping for some straightforward demonstration, calculating the energy needed to accelerate an object (like a galaxy cluster, or a volume of space?), then converting it to its equivalent mass and seeing the relationship to the amount of mass (or space?) being accelerated. Would this not be a reasonable approach to this question?

 

[Perpetual Student]

This comment from Wikipedia gives us some sense of the total magnitude of dark energy:

"The nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense — roughly 10−29 grams per cubic centimeter — it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 74% of universal density, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant. Both models include the common characteristic that dark energy must have negative pressure."

Perhaps the kind of mathematical approach I describe above is meaningless, since it "uniformly fills (all) space."

 

[Tim Thompson]

Energy and the Accelerated Expansion III

Would this not be a reasonable approach to this question?

I don't think so, though I am near the limit of my own knowledge here. The problem is that calculating the energy that way tells you what you need to accelerate something through space, whereas in the expanding universe cosmology, it is the space itself doing the moving. That changes things considerably.

There is also the problem that energy described as you have is strictly observer dependent. Consider the kinetic energy, (1/2)MV², where the velocity is relative to the observer. So the kinetic energy is also relative to the observer. Now if we ask the question about the universe as a whole, with respect to what "observer" do we compute an energy, and what does it really mean cosmologically to do so anyway? It may be that our friend Sol Invictus could be more enlightening about now.

 

[sol invictus]

Thanks, I will look at the above sources. I was hoping for some straightforward demonstration, calculating the energy needed to accelerate an object (like a galaxy cluster, or a volume of space?), then converting it to its equivalent mass and seeing the relationship to the amount of mass (or space?) being accelerated. Would this not be a reasonable approach to this question?

Something like that should work. Choose an origin for coordinates (maybe it's the center of the Milky Way). Your test galaxy cluster is at some radial distance from that origin, and it's accelerating outwards at some rate. By "Gauss' law", only the mass and dark energy inside the sphere defined by that radius and origin can affect the motion of the test cluster.

Since the cluster is accelerating outwards, we know immediately that the effect of the dark energy inside that sphere is larger than the effect of the mass.

To be more quantitative we need an equation that relates the two forces; there's a simple one we can try. I don't have time to type it up now, so I'll just say how to do it. There's some amount of gravitational potential energy inside the sphere due to the mass (just use the Newtonian formula for that). The derivative of that energy with respect to radius gives us an attractive force on the cluster. By the same token the derivative with respect to radius of the amount of dark energy inside that sphere gives a repulsive force. Their sum should give the observed acceleration.

That ought to work to at least a factor of 2 (and in fact I suspect is better than that). To be more accurate you'd need general relativity.

 

[Michael Mozina]

Something like that should work. Choose an origin for coordinates (maybe it's the center of the Milky Way). Your test galaxy cluster is at some radial distance from that origin, and it's accelerating outwards at some rate. By "Gauss' law", only the mass and dark energy inside the sphere defined by that radius and origin can affect the motion of the test cluster.

Since the cluster is accelerating outwards, we know immediately that the effect of the dark energy inside that sphere is larger than the effect of the mass.

To be more quantitative we need an equation that relates the two forces; there's a simple one we can try. I don't have time to type it up now, so I'll just say how to do it. There's some amount of gravitational potential energy inside the sphere due to the mass (just use the Newtonian formula for that). The derivative of that energy with respect to radius gives us an attractive force on the cluster. By the same token the derivative with respect to radius of the amount of dark energy inside that sphere gives a repulsive force. Their sum should give the observed acceleration.

That ought to work to at least a factor of 2 (and in fact I suspect is better than that). To be more accurate you'd need general relativity.

You would essentially need mass and/or charge attraction to something *OUTSIDE* of this physical universe. Of course you'd have to give up that whole creation concept to get there, but I guess that's the whole purpose of creating "dark energy" in the first place.

 

[Michael Mozina]

This comment from Wikipedia gives us some sense of the total magnitude of dark energy:

Oh this should be fun:

"The nature of this dark energy is a matter of speculation.

IOW, the actual *CAUSE* is unknown and the term "dark energy" is nothing more than a placeholder term for human ignorance, like 'ignorant energy".

It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity.

Translation: We don't know what actually drives acceleration, but somehow it miraculously interacts with gravity.

Since it is not very dense — roughly 10−29 grams per cubic centimeter — it is hard to imagine experiments to detect it in the laboratory.

I gotta believe that's a typo because 10-29 grams of mass/energy seems like quite a bit for a cubic centimeter. How could you even miss that much mass/energy?

Dark energy can only have such a profound impact on the universe, making up 74% of universal density, because it uniformly fills otherwise empty space.

It sounds positively like an expanding aether theory when you put it that way.

The two leading models are quintessence and the cosmological constant. Both models include the common characteristic that dark energy must have negative pressure."

And there we go with the need for magic negative pressure from a vacuum. Then again it could be an *EXTERNAL* influence, but we can't talk about that because that screws up the whole creation story.

Perhaps the kind of mathematical approach I describe above is meaningless, since it "uniformly fills (all) space."

It's only meaningless because the claim itself is meaningless. There is no such thing as "negative pressure" in a "vacuum". Guth made up that concept. You could have something *REAL* that was *PULLING* on the mass from the *OUTSIDE*, but then all we need is external mass and/or charge attraction and we have no need for a 'negative pressure" anything, let alone "dark energy". Ooops.

 

[W.D.Clinger]

Oh this should be fun:



IOW, the actual *CAUSE* is unknown and the term "dark energy" is nothing more than a placeholder term for human ignorance, like 'ignorant energy".

That's pretty much what numerous people here have been trying to tell you.

I gotta believe that's a typo because 10-29 grams of mass/energy seems like quite a bit for a cubic centimeter. How could you even miss that much mass/energy?

Had you consulted the Wikipedia article on dark energy^WP, you'd have discovered that the equivalent density is 10^-29 g/cm³. (When text is copied and pasted, superscripting is usually lost. For one thing, the web browser knows nothing about JREF's markup language.)

Avogadro's number is approximately 6×10²³, so 10^-29 g/cm³ is gravitationally equivalent to about 6 hydrogen atoms per cubic meter. That's considerably less than the matter density of intergalactic space, but considerably greater than the matter density of galactic voids. In other words: dark energy dominates matter only within the voids, so it only shows up in large-scale observations where voids dominate visible matter.

 

[Ziggurat]

It's only meaningless because the claim itself is meaningless. There is no such thing as "negative pressure" in a "vacuum". Guth made up that concept.

That would sound a lot more convincing if you could even define what pressure means. But of course, we've been through this before, and you can't define pressure. You don't actually know what it even means.

 

[ben m]

IOW, the actual *CAUSE* is unknown

Yes, for the 10,000th time. That's the usual difference between "current exciting science topic" rather than "something that Lord Rayleigh solved 120 years ago and is now considered boring"

and the term "dark energy" is nothing more than a placeholder

Well, it's a name for the HYPOTHESIS. "dark energy" is a better name for this hypothesis which than "hypothesis 1980.305b", don't you think? It is, after all, a hypothesis about a form of energy density which, among other properties, does not emit or absorb light, i.e. it's dark.

term for human ignorance, like 'ignorant energy".

No, it's not. It's a name for this specific hypothesis---the dark energy hypothesis, which posits that the cause of the acceleration is a new form of energy density associated with empty space. An alternative hypothesis, the "cosmic void" hypothesis, posits that the cause of the acceleration is a perfectly-spherical shell of matter centered on Earth. An alternative hypothesis, now ruled out, was called the "grey dust" hypothesis. An alternative hypothesis was called the "varying speed of light" hypothesis.

Note that we're equally "ignorant" (in your definition) of dark energy, of any giant void, of any grey dust, and of any variation in the fundamental constants. But they get different names, see? The dark energy hypothesis is not "let's take whatever the hell we misunderstand and call it dark energy". It's "let's hypothesize that space has this specific property". Different hypotheses get different names.

 

[Reality Check]

You would essentially need mass and/or charge attraction to something *OUTSIDE* of this physical universe. Of course you'd have to give up that whole creation concept to get there, but I guess that's the whole purpose of creating "dark energy" in the first place.

Still totally ingnorant about cosmology, Michael Mozina. For yet another time:

There is no creation event in the Big Bang theory. Thus it is not a creation theory. It is a theory about the evolution of an already existing universe.
​

You are displaying even more ignorance and demostrating to the world that you cannot learn.
Also dark energy has nothing to do with your delusion of a creation event in Big Bang theory. Dark energy (as you seem to agree !) is the placeholder (accepted term) for whatever is the cause of the measured acceleration in the rate of expansion of the universe.

Also there is nothing outside of the physics universe - you mean outside of the observable universe.

Also "charge attraction" (electromagnetism I assume) from sources outside the observable universe will not effect matter because the observable universe is neutral on tiny scales.

 

[Tim Thompson]

What is "dark energy", really? II

IOW, the actual *CAUSE* is unknown and the term "dark energy" is nothing more than a placeholder term for human ignorance, like 'ignorant energy".

That's pretty much what numerous people here have been trying to tell you.

Quite amazing. Mozina has gone out of his way to belittle & insult everybody who has said what he himself has just said. I think that Mozina should now publicly call himself stupid, just to make it fair. After all, that's what he has been calling me and everybody else, despite our saying exactly what he just said.

 

[Michael Mozina]

Quite amazing. Mozina has gone out of his way to belittle & insult everybody who has said what he himself has just said. I think that Mozina should now publicly call himself stupid, just to make it fair. After all, that's what he has been calling me and everybody else, despite our saying exactly what he just said.

I think it's just plain stupid that you created a 'religion' out of your ignorance and created a dark energy god that supposedly makes up 3/4ths of the universe Tim. All you actually know is that you're utterly and completely clueless as to the actual cause of the acceleration. That's all you can be sure of. You don't know it involves (internal) energy. You don't know if that energy is actually "dark" either. Your alleged "properties" are purely arbitrary as far as you know. You might as well have called the cause the ''dark Krishna energy"". None of your words my have anything at all to do (empirically) with the acceleration you observe. Your dark energy "traits" are purely arbitrary.

 

[Ziggurat]

You don't know if that energy is actually "dark" either.

Actually, that's the one thing we are sure of.

Your alleged "properties" are purely arbitrary as far as you know.

Nope. There are only two properties the model requires: darkness and density. The darkness part is obvious: we can't see it, so if it exists, it's dark. And the density comes from fits of General Relativity to observations. There's nothing arbitrary about either of those properties.

You might as well have called the cause the ''dark Krishna energy"".

A rose by any other name...

None of your words my have anything at all to do (empirically) with the acceleration you observe.

The equations sure as hell do.

But then, you wouldn't know that, being math-phobic. Oh, and you also have your own peculiar definition of "empirical" which doesn't match standard usage.

 

[ben m]

None of your words my have anything at all to do (empirically) with the acceleration you observe. Your dark energy "traits" are purely arbitrary.

"dark energy" refers to a hypothesis that empty space has an constant or nearly-constant energy density of 10^-29 g/cm^3

1) The trait "10^-29 g/cm^3" is not arbitrary; that's the quantity that you need to plug into the source term in GR to get the observed acceleration. If you plug in a larger number you get more acceleration than observed. If you plug in a smaller number you get less acceleration than observed.
2) The trait "energy" is not arbitrary; energy is the only thing you *ever* plug into the source term in GR.
2a) The use of GR is not arbitrary. If you want a non-GR or modified-GR way of explaining the acceleration, you're not talking about the dark energy hypothesis any more, but rather about some other hypothesis.
3) The trait "constant" is not arbitrary; various hypotheses about non-constant energies have been proposed, but (except for the slowest-changing versions) they have been disproven by observation. The "constant" version is the one that agrees with the cosmology.
4) The "dark" is not arbitrary. If it were a light-emitting or light-absorbing substance, we'd know about it already.

Don't bother with the "IT'S A UNEMPIRICAL RELIGION BECAUSE YOU DON'T EVEN ARBITRARY MAGIC IN THE LAB VOODOO PLASMA RELIGION DOGMA RELIGION GOD GOD PONIES" response again, please. Read my post and address what it says.

For example, do you think that "a constant density of non-energy that absorbs light" is a good alternative hypothesis for the observed acceleration?

 

[GeeMack]

I think it's just plain stupid that you created a 'religion' out of your ignorance and created a dark energy god that supposedly makes up 3/4ths of the universe Tim.

But since nobody has actually done that, your claim that they have makes you a liar, Michael.

All you actually know is that you're utterly and completely clueless as to the actual cause of the acceleration. That's all you can be sure of.

Well that seems pretty close to a personal insult. Your continued incivility is noted.

You don't know it involves (internal) energy. You don't know if that energy is actually "dark" either. Your alleged "properties" are purely arbitrary as far as you know.

Well it is reasonable to suggest that some sort of energy is involved in the cause of an observed effect which entails acceleration. But if you have a suggestion that doesn't involve any sort of energy, you sure have been awfully darned tight lipped about it. Funny how you have a habit of lying about everyone else's hypotheses, yet when it comes to offering any rational alternative, nothing.

You might as well have called the cause the ''dark Krishna energy"". None of your words my have anything at all to do (empirically) with the acceleration you observe. Your dark energy "traits" are purely arbitrary.

Empirically we understand that there is an accelerated expansion of the Universe. It is accepted that the effect, empirically demonstrated, has a cause. Dark energy is the name given to the cause because it doesn't emit or reflect any light, and it is reasonable to suggest that some sort of energy might be involved in the acceleration. So, your claim that the traits are arbitrary is a lie. Another lie. Imagine that!

And meanwhile, aside from your incessant lies and arguments from incredulity and ignorance, you've offered what in the way of an alternative explanation? Oh that's right. Not a damned thing.

 

[Perpetual Student]

sol invictus

To be more quantitative we need an equation that relates the two forces; there's a simple one we can try. I don't have time to type it up now, so I'll just say how to do it. There's some amount of gravitational potential energy inside the sphere due to the mass (just use the Newtonian formula for that). The derivative of that energy with respect to radius gives us an attractive force on the cluster. By the same token the derivative with respect to radius of the amount of dark energy inside that sphere gives a repulsive force. Their sum should give the observed acceleration.

So, I've been trying to get a feel for this proceedure.
Since we need to calculate the mass of the dark energy in the sphere:
Would one intergate the rate of acceleration with respect to the radius then multiply that by the total mass of the sphere, then subtract the gravitational potential energy in the sphere, then finally divide this result by c² to get the mass of the dark energy in the sphere?

 

[Reality Check]

A rose by any other name...

We have all been here, done that when Michael Mozina demonstrates yet again (and again and again) his persistent inability to learn .
For example (w.r.t. inflation)

Yes it is testable.
So is

• "Satanflation"
• "Carflation"
• "Dogflation"
• "MichaelMozinaflation"
• "Xmanflation"
• etc. etc. etc.
• and of course the scientific inflationary theory ("inflation" in MM-speak) which has actually been tested and passed.

This post in another thread (Are you aware that you are displaying the symptoms of a crank? ) has a list of the evidence that you are providing us of your crack-pottery.

Now we have:

• The delusion that changing the word that is used to describe something changes what is described.
  As Shakespeare said: A rose by any other name would smell as sweet.
  A Godrose smells as sweet as a rose.
  A Satanrose smells as sweet as a rose.

...