Lambda-CDM theory - Woo or not?

[Michael Mozina]

Very well.

First, this is the most basic fact about inflation. If you don't know it, you know nothing about the topic.

"Knowing" the dogma exists and "believing it" are two entirely different things.

Odd that someone so totally ignorant would start a thread ridiculing the experts in the field, isn't it?

If you could produce this effect in a lab, or power my car with this stuff, there wouldn't be anything to ridicule. Since it only seems to occur in math formulas, and is shy around a lab, and no consumer products use inflation for anything, it's not particularly convincing.

Now for the math: take a scalar field and couple it to gravity.

[latex]${\cal L} = -(1/2) \partial_\mu \phi \partial^\mu \phi - V(\phi) + R$[/latex], where R is the Ricci scalar curvature for the expanding metric [latex]$ds^2 = -dt^2 + a(t)^2 d \vec x^2$[/latex]. You can immediately verify that if [latex]$V'(\phi_0) = 0$[/latex] for some \phi_0, then [latex]$\phi(t,x) = \phi_0$[/latex] is a solution to the equations of motion. If there are no other sources of energy around, one then immediately gets a solution [latex]$a(t)=e^{H t}$[/latex] where the space grows exponentially with time ([latex]$H^2=(8 \pi G_N/3) V(\phi_0)$[/latex]).

Now, the proper energy density on this solution is simply [latex]$T^0_0 = V(\phi_0)$[/latex] (you can derive this by varying the scalar field part of the lagrangian with respect to the metric). And that's it - we're done. The energy is constant.

This analysis is completely general - it applies to the Higgs (which is obvious, by the way - if the energy in the Higgs condensate redshifted, the expansion history of the universe over the last 10 billion years or so would be completely and totally different than it is) and to every other scalar field.

So, you now have three choices:

1) find a mistake in the math (good luck with that)

2) admit you were wrong, and explain to us why you came in with guns blazing mocking a topic you're so totally ignorant of, or

3) run away and hide.

Which will it be?

It won't be number three. You'll have to let me chew on your response when I have free time today before I comment further.

 

[Michael Mozina]

OK, is there a way you can provide a verbal description of how "you increase the volume by a factor of 10 and add no more particles to the condensate," and you "maintain a constant density."? Is there some analogy that a non-physicist might grasp? I'm not doubting the validity of your demonstration (I have no way to do so); I am merely interested.

The short answer is no, there isn't a way to describe this verbally. These sorts of "tricks" only work in math formulas. They never work in the lab.

 

[Michael Mozina]

Hi Michael Mozina
Controlled lab environments are nice to have.

But it sounds like you are suggesting that no useful science can be done by observation of the universe because the universe is not a controlled environment.

That is not what I'm trying to suggest. I don't really have a problem with the idea that the universe isn't controllable. I have a problem with attempting to claim inflation or DE has some influence on the universe if you can't even make them show up in a laboratory experiment here on Earth. If they don't show up here, why should I believe they have some influence somewhere "out there" in space?

The fact that the universe is big, varied, full of stuff and uncontrolled gives plenty of useful science. A large number of uncontrolled experiments where the universe sets the parameters can be as useful as a large number of controlled experiments where a scientist sets the parameters.

An observation is not an "experiment". You can slap math to "magic fairies", tinker with it till it fits some distant observation, and yet that will still not demonstrate that "magic faeries did it". There's a problem with even trying to call that an "experiment" in fact because it cannot possibly be used to demonstrate the existence of faeries, even if the math "fits" the observation.

The universe may miss some parameter sets - on the other hand the universe may apply a set of parameters that a scientist might not think of.

Ok, so how would we decide which ideas have merit if not based upon empirical testing. How would you falsify my magic faeries based on an uncontrolled observation, assuming my math worked out correctly?

I don't have any problem with the industry using *known* forces of nature to attempt to "explain" distant observations. Even if their ideas are 'wrong', they are at least rooted in real physics. When they simply make stuff up (like inflation) I get squeemish. If it doesn't show up here on Earth, what makes you think it exists anywhere or ever existed? Do you see my point at least?

I realize that we can't control objects in space, but it makes no sense to attempt to explain these things based on things that don't show up in empirical experiments, just as it would make no sense for me to create a mathematical theory about the influences of invisible faeries on objects in space. The math isn't going to satisfy or resolve the basic skepticism in the existence of faeries.

 

[Tubbythin]

The short answer is no, there isn't a way to describe this verbally. These sorts of "tricks" only work in math formulas. They never work in the lab.

That should be "These sorts of "tricks" only work in our observations of the Universe and in maths formulas".

 

[GreedyAlgorithm]

Don't threads like this belong in the CT forum?

 

[Tubbythin]

That is not what I'm trying to suggest. I don't really have a problem with the idea that the universe isn't controllable. I have a problem with attempting to claim inflation or DE has some influence on the universe if you can't even make them show up in a laboratory experiment here on Earth. If they don't show up here, why should I believe they have some influence somewhere "out there" in space?

Why should cosmological phenomena show up in a lab? Your demands are about as ridiculous as those of an evolution denier who refutes evolution with "well we've never seen a monkey turn into a human in a lab".

An observation is not an "experiment". You can slap math to "magic fairies", tinker with it till it fits some distant observation, and yet that will still not demonstrate that "magic faeries did it". There's a problem with even trying to call that an "experiment" in fact because it cannot possibly be used to demonstrate the existence of faeries, even if the math "fits" the observation.

Then you must reject all notions of cosmology and astronomy.

Ok, so how would we decide which ideas have merit if not based upon empirical testing. How would you falsify my magic faeries based on an uncontrolled observation, assuming my math worked out correctly?

See what other observations you can make which would could either support/disprove your theory.

I don't have any problem with the industry using *known* forces of nature to attempt to "explain" distant observations. Even if their ideas are 'wrong', they are at least rooted in real physics. When they simply make stuff up (like inflation) I get squeemish. If it doesn't show up here on Earth, what makes you think it exists anywhere or ever existed? Do you see my point at least?

Nope. The idea that inflation is just made up is, in fact, just made up. (I'm not saying tis right or wrong here. Just that the idea that Alan Guth suddenly went "Inflationdidit" and everyone else went "Of course. Lets just accept this answer" is utterly ridiculous.)

I realize that we can't control objects in space, but it makes no sense to attempt to explain these things based on things that don't show up in empirical experiments, just as it would make no sense for me to create a mathematical theory about the influences of invisible faeries on objects in space. The math isn't going to satisfy or resolve the basic skepticism in the existence of faeries.

If it were the case that observation is of no scientific use then you might have a point. But it isn't and you don't.

 

[Ziggurat]

That is not what I'm trying to suggest. I don't really have a problem with the idea that the universe isn't controllable. I have a problem with attempting to claim inflation or DE has some influence on the universe if you can't even make them show up in a laboratory experiment here on Earth. If they don't show up here, why should I believe they have some influence somewhere "out there" in space?

If you had a clue about the theory, you'd realize that the densities are far too low to have a measurable effect except over very large volumes.

Do you believe Einstein's general relativity is basically correct? None of its effects are observable in a lab experiment here on earth, even today. And for esseintially the same reason: the effects are too small on these length scales and at mass densities. Gravity bending space? What utter nonsense! You can't show me curved space in a lab! Why should I believe it could be curved "out there" in space?

An observation is not an "experiment"

True. But it's still science. And it's still how Newton arrived at his universal law of gravity.

You can slap math to "magic fairies", tinker with it till it fits some distant observation, and yet that will still not demonstrate that "magic faeries did it".

That's not any different than a controlled experiment.

Ok, so how would we decide which ideas have merit if not based upon empirical testing.

You can test a theory with observations. That's what Newton did.

How would you falsify my magic faeries based on an uncontrolled observation, assuming my math worked out correctly?

Again, how is that situation any different from an experiment? Either the model is falsifiable or it is not. If it is not falsifiable, then experiments don't help. If it is falsifiable, then observations can falsify it. For practical reasons it may be easier to come up with experiments that could falsify a model than observations, but that's not an intrinsic limit of any sort.

And you never mentioned whether or not your magic faeries model is falsifiable. If it is, then it could indeed be scientific. Hell, it could even be correct (which, BTW, is not the same thing). If it is not, then it's not science. But then, your entire line of argumentation suggests that you don't really understand the meaning of the term. But my own argument may have been in vain, because you may be equally clueless about what falsifiability means.

 

[ben m]

That is not what I'm trying to suggest. I don't really have a problem with the idea that the universe isn't controllable. I have a problem with attempting to claim inflation or DE has some influence on the universe if you can't even make them show up in a laboratory experiment here on Earth. If they don't show up here, why should I believe they have some influence somewhere "out there" in space?

And when you find that simple-Earth-experiments can't exactly reproduce something you see in space---what are you going to do? Give up? File a complaint with God? "I expected you to make the Big Bang using only forces that appear below the TeV scale. You did it wrong."

You're also making a dumb mistake in thinking that inflation is an extremely "unnatural" thing for Nature to do. You're wrong. It just so happens that inflation is *not* something that the quark, lepton, electroweak, fields do; it's not something that the hypothetical Higgs field or axion field "naturally" do. It *is* something that the inflaton field naturally does.

 

[Perpetual Student]

...

Do you believe Einstein's general relativity is basically correct? None of its effects are observable in a lab experiment here on earth, even today. And for esseintially the same reason: the effects are too small on these length scales and at mass densities. Gravity bending space? What utter nonsense! You can't show me curved space in a lab! Why should I believe it could be curved "out there" in space?

...

Now, that is a great analogy! I'll be interested in his response.

 

[Skwinty]

Now, that is a great analogy! I'll be interested in his response.

Maybe the National Ignition Facility will provide some more reason to believe later this year.

 

[Tubbythin]

And when you find that simple-Earth-experiments can't exactly reproduce something you see in space---what are you going to do? Give up? File a complaint with God?

. That made me laugh.

 

[Michael Mozina]

Very well.

First, this is the most basic fact about inflation. If you don't know it, you know nothing about the topic. Odd that someone so totally ignorant would start a thread ridiculing the experts in the field, isn't it?

Now for the math: take a scalar field and couple it to gravity.

Ok, I should get some time this afternoon to look at your math, but let's start with some basics. You gave me *NOTHING* in terms of units. Start there. Secondly, please explain why you are "coupling" your "condensate" to anything external to the condensate. That sounds like the "trick" right there. Are you saying the condensate has mass and therefore a gravity field, or are you trying to gain mass/energy through this process somehow?

 

[Michael Mozina]

That should be "These sorts of "tricks" only work in our observations of the Universe and in maths formulas".

No, it only works in math trickery. In the real world, nothing retains near constant density over multiple exponential increases in volume. You evidently confuse "observation" and "interpretation".

 

[Michael Mozina]

Now, that is a great analogy! I'll be interested in his response.

My response is that I do in fact keep an open mind to quantum gravity theories, and other "options" as it relates to 'explaining' gravity. On the other hand I have no doubt that "gravity" exists in nature. I can jump up and down and 'experience' it for myself. I am in fact a great fan of GR, but not with all the metaphysical baggage that's been stuffed into Lambda-"blunder" theory as Einstein would have called it.

There is truth in the fact that several elements of GR theory cannot be demonstrated here on Earth. It is also true that Newtons formulas work just fine for interplanetary space travel. I guess the best way I could respond is to say that "keep an open mind" as it relates to the math, but I have no doubt at all in the existence of "gravity" in nature.

It is truly bizarre from my perspective that something like gravity, which can be "experienced" here on Earth is still being compared to something like "inflation"" that defies every law of physics and acts like no other vector or scalar field in nature. (Yes I know this is still in dispute, but I will demonstrate my point before this thread is done).

 

[sol invictus]

OK, is there a way you can provide a verbal description of how "you increase the volume by a factor of 10 and add no more particles to the condensate," and you "maintain a constant density."? Is there some analogy that a non-physicist might grasp? I'm not doubting the validity of your demonstration (I have no way to do so); I am merely interested.

I'll try.

First, you shouldn't think of the inflaton background (or the Higgs condensate) as being made of particles. Particles are the excitations on top of the condensate, not the condensate itself. So the question isn't sensible.

Imagine a guitar string, fixed at each end. That string has a series of vibrational modes - the fundamental, where only the ends are motionless, the first harmonic, where the ends and the center are still, the second, where the ends and the points 1/3 and 2/3rd of the way are still, etc. Now suppose it's impossible to ever keep the string from vibrating in those modes. No matter how hard you try, it's always vibrating a little bit in every one of those modes, with the same amplitude in each. Its total energy is given by a sum over all the modes - it's just the total number of modes times the energy in each (if it bothers you that the number is infinite, just suppose there's a shortest wavelength, and the modes smaller than that don't vibrate).

Now double the length of the string. What happens to the total energy? It doubles - for every mode which existed before there are now two, but the amplitudes (and the shortest wavelength) are just as before. So the energy density in the vibrations is exactly the same as it was before you doubled.

Scalar condensates are like that - the only feature they have is an energy density. It's impossible to change the density by expanding the space, because the condensate is featureless - it looks exactly the same when you zoom in on it. It's similar to not being able to tell by looking how far you are from an infinite plane if you have no other reference point. A collection of particles is not like that, because they are particles - they have a spacing, and the spacing gets larger when you blow up the space.

 

[Michael Mozina]

Why should cosmological phenomena show up in a lab?

Why wouldn't they? We're living in part of the cosmos aren't we?

Your demands are about as ridiculous as those of an evolution denier who refutes evolution with "well we've never seen a monkey turn into a human in a lab".

Er, no. Micro evolution has been well documented in nature. Hox genes show that even macro-evolutionary changes are possible in a single generation. These issues aren't even in the same league as something like inflation that never shows up anywhere.

Then you must reject all notions of cosmology and astronomy.

Yep.

See what other observations you can make which would could either support/disprove your theory.

That is utterly illogical. If I can't demonstrate that faeries are real, and have some affect on nature, slapping on some math formulas, and pointing at the sky isn't going to make faeries appear in the sky! Gah!

Nope. The idea that inflation is just made up is, in fact, just made up.

If that were so, you could empirically demonstrate it exists in nature, like you can empirically demonstrate EM fields exist in nature. The fact you can't do that is evidence that it is in fact "made up". In fact I can even tell you the name of the individual that made it up. His name is Alan Guth.

(I'm not saying tis right or wrong here. Just that the idea that Alan Guth suddenly went "Inflationdidit" and everyone else went "Of course. Lets just accept this answer" is utterly ridiculous.)

No, that's pretty much exactly how it went down. It took time of course, but no consumer product runs on inflation does it?

If it were the case that observation is of no scientific use then you might have a point. But it isn't and you don't.

Observation can be helpful in deciding which theories have merit. They can't help us demonstrate that faeries exist in nature and have some affect on distant objects.

 

[Michael Mozina]

I'll try.

First, you shouldn't think of the inflaton background (or the Higgs condensate) as being made of particles.

Translation: My idea doesn't work if you actually use real particles and real fields because the moment you do that it becomes obvious that there would be less of them per cubic meter if you increased the volume by a factor of ten.

 

[Ziggurat]

There is truth in the fact that several elements of GR theory cannot be demonstrated here on Earth.

NO aspects of GR can be demonstrated here on earth.

It is truly bizarre from my perspective that something like gravity, which can be "experienced" here on Earth is still being compared to something like "inflation"" that defies every law of physics

It is truly bizarre from my perspective that something like gravity, which can be "experienced" here on Earth is still being compared to something like curved space that defies every law of geometry.

You have no consistency.

 

[sol invictus]

Ok, I should get some time this afternoon to look at your math

Sure, whatever.

, but let's start with some basics. You gave me *NOTHING* in terms of units. Start there.

Units? What are you talking about?

Secondly, please explain why you are "coupling" your "condensate" to anything external to the condensate.

In the simplest cases it's coupled to gravity only - and that's enough for this.

That sounds like the "trick" right there. Are you saying the condensate has mass and therefore a gravity field, or are you trying to gain mass/energy through this process somehow?

A condensate can't have mass - that makes no sense. I guess that's another word you don't know the meaning of.

Am I gaining energy through what process? If you mean the expansion of space, then no - the total energy is exactly constant, because the increase in total energy in the condensate is precisely compensated for by a increase in the magnitude of the (negative) gravitational potential it produces - as it must be, since it's a solution to Einstein's equations.

 

[sol invictus]

Translation: My idea doesn't work if you actually use real particles and real fields because the moment you do that it becomes obvious that they there would be less of them per cubic meter if you increased the volume by a factor of ten.

It's not my idea, Michael - it was Einstein's. This is a basic part of general relativity. Do you not believe in that either? After all, it's impossible to test in a lab...

And as I told you, particles do decrease in density when you expand the space. Condensates do not, because they are not particles. Sometimes two different things behave differently - I guess that's a hard concept for you to grasp?