Lambda-CDM theory - Woo or not?

[sol invictus]

So when we talk about the big bang/inflation etc, ALL we mean is our visible universe?

Generally it is assumed for simplicity that the universe is close to homogeneous everywhere, based on the fact that the part of it we can observe is (on large scales). However that assumption is not necessary, and probably not true.

By 'multiverse' do we mean the other visible universes? Would there have been multiple bangs?

That term refers to models in which the universe on large scales is very inhomgeneous, and regions with very different physics can exist simultaneously in neighboring regions.

If so, this is rather difficult for me to understand. We observe our universe expanding, extrapolate back in time, and get to the grapefruit. Fine. But suppose we are (instantaneously) transported 7 billion light years in a certain direction, and observe again. I imagine we will observe the same properties, extrapolate back in time, and get to the grapefruit. But this grapefruit overlaps with the other grapefruit we've observed. 7 billion light years or so worth of it. Assuming we could do this on to infinity, then we have an infinite number of overlapping grapefruits... isn't this a bit of a problem?

Why is it a problem?

 

[dogjones]

Generally it is assumed for simplicity that the universe is close to homogeneous everywhere, based on the fact that the part of it we can observe is (on large scales). However that assumption is not necessary, and probably not true.

Why do you think it probably isn't true? Is it because infinity implies infinite variety?

That term refers to models in which the universe on large scales is very inhomgeneous, and regions with very different physics can exist simultaneously in neighboring regions.

Wow, interesting. I thought it was something to do with other 'dimensions' or something rather than if you travel long enough in a straight line you may hit another universe (assuming inhomogenousness (inhomogenuity?)).

Why is it a problem?

Well, the BB assumes we started out as a singularity, yes? But can a singularity be of infinite size?

 

[Dancing David]

mumble mumble, smaller infinity, mumble mumble

 

[DeiRenDopa]

[...]

Well, the BB assumes we started out as a singularity, yes? But can a singularity be of infinite size?

(bold added)

That's the (or one) popular misconception.

'The Big Bang' may be described more precisely as the application of GR (General Relativity) plus the Standard Model (of particle physics, which incorporates our understanding of the electroweak force and the strong force, together with the specifics of various particles) plus some modest extensions (inflation and dark energy, in some form or other) to the (observable) universe as a whole; and somewhat more narrowly to 'running the clock backwards'.

As such it does NOT incorporate, or even hint at, what the physics of the Planck regime is ... i.e. how does stuff behave where the mutual contradiction between GR and QM becomes intolerable (or, if you prefer, there's no quantum theory of gravity, or similar). This means that the clock stops at ~10^-43s ... and in practice considerably before then too, because the Standard Model (plus its 'safe' extensions) ceases to be applicable (at around ~10^-30s??).

The only thing 'the singularity' (or any singularity) tells us is that the physics we know, today, is incomplete; i.e. there are circumstances (regions of parameter space) where it must remain mute.

 

[dogjones]

Cool. So, assuming infinite homogenousness, running back in time to, say, ~10^-43s, we get a massively compressed yet infinitely extended Planck regime, which (going forward again) inflates outward into a larger infinity?

The school/popular textbooks should get rid of the 'all the matter in the universe was once compressed into an area smaller than a pinhead' thing anyway.

 

[dogjones]

mumble mumble, smaller infinity, mumble mumble

 

[sol invictus]

Why do you think it probably isn't true? Is it because infinity implies infinite variety?

For several different reasons. Essentially, because it would require an mechanism - i.e. there is no reason for it to be true a priori - and there isn't one (inflation doesn't suffice).

Wow, interesting. I thought it was something to do with other 'dimensions' or something rather than if you travel long enough in a straight line you may hit another universe (assuming inhomogenousness (inhomogenuity?)).

Sometimes those other regions can have a different number of (large) dimensions . Otherwise, no.

Well, the BB assumes we started out as a singularity, yes? But can a singularity be of infinite size?

Yes, it can - at least in the sense that the size is infinite at all times t>0, so if you define the size at the singularity as a limit it's infinite. But as DRD says, we can't trust classical gravity (or any theory we understand) under those conditions anyway.

The school/popular textbooks should get rid of the 'all the matter in the universe was once compressed into an area smaller than a pinhead' thing anyway.

Well, the "observable" part gets arbitrarily small. And in models with finite volume, the volume does go to zero as t->0. And in models with curvature, the radius of curvature also goes to zero. So it's not exactly wrong - it's just an example of what happens when you try to explain something fairly complex and technical in simple terms.

 

[Michael Mozina]

And that sentence doesn't disagree with what these guys are saying, that you think it does is telling.

Did you read the sentence before it?

Only waves that can fit multiples of half a wavelength between the surfaces resonate, leaving non-resonating frequencies suppressed.

So you end up with "waves" and a "lack thereof", or a "higher" and "lower" density of such waves. There is no "negative pressure". It's just lower density of standing waves resonating on the inside and a higher density of such waves on the outside, hence the plates are "pushed" together.

On the wikipedia page it takes this basic premise, then derives the formula for the pressure between the plates from that premise. And the result is a negative pressure.

It is simply the result of a "pressure differential", nothing more, nothing less. The equations is a mathematical "oversimplification" of what occurs at very small distances, and what occurs at the level of quantum physics.

You've said you agree with the wiki page, but you've said that that pressure formula is incomplete, so please show where the derivation is wrong, or show how the basic premise from the source which you chose is wrong.

The equations are not "wrong" anymore than Chapman's equations were "wrong" in terms of the energy it predicts. They are simply "oversimplifications" of what is a very complex system.

Doesn't the fact that the sources that you yourself choose only support your position if you take one or two sentences out of the whole but other sentences in those same sources undermine you tell you anything at all?

Doesn't the fact you folks entirely ignored that physics link and it's *exact same explanation* tell me something too? I'm afraid you're unwilling to hear what you do not wish to hear, or see what you do not wish to see in terms of those graphics and you are fixated only on a couple of words in that Wiki article, and ignoring that physics link I provided entirely. How did you rationalize that behavior? Isn't that just pure denial?

 

[Michael Mozina]

http://physicsworld.com/cws/article/news/32380

Here's the whole paragraph.

The quantum Casimir effect comes about because a vacuum always contains fluctuating electromagnetic fields.

In other words, it's not "empty" at all, but rather it is "full of" fluctuating fields of energy.

Normally these fluctuations are roughly the same everywhere, but two close conducting surfaces set “boundary conditions” that limit the number of allowed field frequencies between them. Only waves that can fit multiples of half a wavelength between the surfaces resonate, leaving non-resonating frequencies suppressed. The result is that the total field inside a gap between conductors cannot produce enough pressure to match that from outside, so the surfaces are pushed together.

This is a perfectly accurate description of the process. The plates are pushed together because the pressure on the outside of the plates is "greater than" the pressure inside the plates. There's no mystery here. He goes on to explain a *repulsive* process which you again you all simply utterly ignore because it rains on your parade.

 

[Ziggurat]

http://physicsworld.com/cws/article/news/32380

Notably absent is any actual math to calculate forces or pressures. This is an article aimed at the mainstream reader. Why would you assume they wouldn't dumb down the description?

But here's an interesting little bit from elsewhere in the article, describing this classical analogue:

And, like the quantum Casimir effect, two close surfaces in such a liquid set boundary conditions, this time by preferring to be in contact with one of the substances over the other. To fulfil these conditions, the surfaces attempt to surround a single region of the preferred substance by drawing together.

Why, that sounds like a description of negative pressure!

 

[GeeMack]

Doesn't the fact you folks entirely ignored that physics link and it's *exact same explanation* tell me something too? I'm afraid you're unwilling to hear what you do not wish to hear, or see what you do not wish to see in terms of those graphics and you are fixated only on a couple of words in that Wiki article, and ignoring that physics link I provided entirely. How did you rationalize that behavior? Isn't that just pure denial?

But you see, Michael, since you've demonstrated time and time again that you don't have the slightest clue about the science of physics, your interpretation of the links and articles and pretty little pictures becomes irrelevant. You don't understand the physics, and consequently you aren't able to understand the comments people here are making in response to your silly ideas. It's a vicious cycle, I know, but you started out wrong, you're still wrong, and if history is any indicator, you'll continue to be wrong.

 

[ben m]

In other words, it's not "empty" at all, but rather it is "full of" fluctuating fields of energy.

Yes! Right! We're almost there! Now just apply the well-known definition of pressure, P = -dE/dV to a system which has a constant energy density, as you've now learned that empty space has. Apply the equations of General Relativity---look, energy density is right in there---to a vacuum which has a constant energy density. You will get (a) negative pressure and (b) an accelerating expansion of the universe.

That was the whole point of bringing Casimir into this discussion: inflation and "dark energy" are just what you expect when you allow the vacuum to have an energy density due to fluctuations.

 

[The Man]

http://physicsworld.com/cws/article/news/32380

Here's the whole paragraph.


In other words, it's not "empty" at all, but rather it is "full of" fluctuating fields of energy.



This is a perfectly accurate description of the process. The plates are pushed together because the pressure on the outside of the plates is "greater than" the pressure inside the plates. There's no mystery here. He goes on to explain a *repulsive* process which you again you all simply utterly ignore because it rains on your parade.

Did you miss this part?

The critical Casimir effect has the same underlying principle, but is a classical phenomenon that arises in a mixed liquid close to its critical point — the point, defined by a threshold temperature and pressure, beyond which the gas and liquid phases are indistinguishable. A mixed liquid taken towards its critical point gradually begins to separate into regions of its constituent substances, the size and shape of which fluctuate like the quantum fields in a vacuum. And, like the quantum Casimir effect, two close surfaces in such a liquid set boundary conditions, this time by preferring to be in contact with one of the substances over the other. To fulfil these conditions, the surfaces attempt to surround a single region of the preferred substance by drawing together.

So they are speaking of a “classical phenomenon” that is analogous to the Casimir effect in that it depends on boundary conditions. The difference is in this example the “mixed liquid” is not at it’s zero point energy as the vacuum field in the Casimir effect is, that is the critical factor you seem to be ignoring. This “classical phenomenon” is also dependent on the “critical point” of the mixed liquid where it can begin a phase transition. That too is analogous to the effects in cosmological inflation resulting from a phase transition of the Higgs field.

 

[Michael Mozina]

Notably absent is any actual math to calculate forces or pressures. This is an article aimed at the mainstream reader. Why would you assume they wouldn't dumb down the description?

The explanation of pressure is not being "dumbed down", you just don't like the implication of his statements because they agree with everything I've told you.

But here's an interesting little bit from elsewhere in the article, describing this classical analogue:

Why, that sounds like a description of negative pressure!

No, that sounds like you're reaching now for anything at all to prop up your otherwise falsified belief system. It is relatively easy to understand how a constant quantum bombardment on all surfaces, can create unequal "pressure" on the sides of the plates, and can cause them to be "pushed" together or pushed apart. What (physically) however would cause "negative pressure" to form on *any* side of *any* plate?

The only thing happening in a Casimir experiment is a "pressure difference" between various sides of the plates. There is no area in that chamber that experiences "negative pressure" because the whole thing takes place in a *POSITIVE PRESSURE ENVIRONMENT* in the first place! Hoy.

The denial quotient around here is pretty much off scale at this point. You folks do not want to admit or embrace the notion that it can be "repulsive" as well as attractive, and therefore you simply ignore every physics, and explanation I've provided.

Talking with creationists is never rewarding, and I can see that talking with *this* group of "creationists" isn't going to be any different. The only thing that is different is you have a somewhat older creation date that you can't justify via empirical physics any more than any other creationist. Belief in your creation story requires a pure act of "faith" on the part of believer.

 

[Ziggurat]

No, that sounds like you're reaching now for anything at all to prop up your otherwise falsified belief system. It is relatively easy to understand how a constant quantum bombardment on all surfaces, can create unequal "pressure" on the sides of the plates, and can cause them to be "pushed" together or pushed apart. What (physically) however would cause "negative pressure" to form on *any* side of *any* plate?

So it seems like you're back to categorically denying the existence of negative pressure under any circumstance.

Get back to me when you figure out how to define pressure. Right now, you're just beclowning yourself.

 

[Michael Mozina]

But you see, Michael, since you've demonstrated time and time again that you don't have the slightest clue about the science of physics, your interpretation of the links and articles and pretty little pictures becomes irrelevant.

You have demonstrated time and time again that you are not actually interested in finding the "truth" and therefore your opinions of me, the articles and the pretty pictures is irrelevant. You aren't interested in truth.

 

[Michael Mozina]

So it seems like you're back to categorically denying the existence of negative pressure under any circumstance.

No, I said there was no such thing as "negative pressure in a vacuum" as Guth required from his vacuum to make his magical inflation theory work correctly. I also pointed out to you that the Casmir effect can be "repulsive", not simply attractive, and you all simply ignored that giant problem with your "interpretation" of the process. Denial of fact and misrepresentation of my statements isn't helping your case, it's just making you look bad IMO.

 

[Michael Mozina]

Did you miss this part?

No. Did you miss that part about it being "repulsive" as well as "attractive" depending on the conditions?

 

[edd]

No, I said there was no such thing as "negative pressure in a vacuum" as Guth required from his vacuum to make his magical inflation theory work correctly. I also pointed out to you that the Casmir effect can be "repulsive", not simply attractive, and you all simply ignored that giant problem with your "interpretation" of the process. Denial of fact and misrepresentation of my statements isn't helping your case, it's just making you look bad IMO.

Errrr.... we were using the argument that it can be repulsive as well as attractive to demonstrate that your understanding of its physics was deeply lacking.

 

[Michael Mozina]

(bold added)

That's the (or one) popular misconception.

'The Big Bang' may be described more precisely as the application of GR (General Relativity) plus the Standard Model (of particle physics, which incorporates our understanding of the electroweak force and the strong force, together with the specifics of various particles) plus some modest extensions (inflation and dark energy, in some form or other) to the (observable) universe as a whole; and somewhat more narrowly to 'running the clock backwards'.

As such it does NOT incorporate, or even hint at, what the physics of the Planck regime is ... i.e. how does stuff behave where the mutual contradiction between GR and QM becomes intolerable (or, if you prefer, there's no quantum theory of gravity, or similar). This means that the clock stops at ~10^-43s ... and in practice considerably before then too, because the Standard Model (plus its 'safe' extensions) ceases to be applicable (at around ~10^-30s??).

The only thing 'the singularity' (or any singularity) tells us is that the physics we know, today, is incomplete; i.e. there are circumstances (regions of parameter space) where it must remain mute.

Even if you "stop" prior to a "singularity", you end up with a concentrated amount of mass that is surrounded by a gigantic event horizon from which no material at all should ever escape. How large do you figure the event horizon might have been around this "near singularity thingy" once it gets down to something that is smaller than a breadbox?