Is ΛCDM considered "speculative?"

[Schneibster]

I notice that no one is discussing ΛCDM cosmology here. Is this considered "speculative," or do most folks here just not know about it?

[mathematic]

I notice that no one is discussing ΛCDM cosmology here. Is this considered "speculative," or do most folks here just not know about it?

I am not sure what you mean by speculative. Maybe there just hasn't been anything new in this subject recently.

[Schneibster]

I saw that there is a debate going on about whether some topics are "mainstream" or "speculative," both in a sticky, and in an announcement as well. Just trying to get along; if ΛCDM cosmology is considered "speculative" here I didn't want to offend.

 

Lambda-CDM is currently being called the "Standard Model of Cosmology." I'm quite surprised not to find it a major subject of conversation with all the interesting baryon acoustic oscillation observations, and interesting large cosmic structure and large cosmic void discoveries that have happened over the last year.

 

I guess you don't discuss cosmology here much.

 

Frankly I haven't found anyplace that does yet.

 

Also I'm surprised there isn't any discussion of ΛCDM cosmology on the Cosmo Basics sticky thread.

 

It's kind of like going to an astronomy site and they don't know the phases of the Moon.

Edited February 18, 2014 by Schneibster

[ajb]

The Lambda CDM model is not considered speculative, there is lots of evidence for it. Right now people are looking at deviations from the model in the power spectrum of the CMBR. In particular, the non-Gaussian element of it. This is outside my area of expertise and so I can't tell you exactly the current situation here.

 

And I always point people towards the Lambda CDM model when they propose their own cosmology. Is it common knowledge on this site, I don't know as we always get wacky cosmologies suggested here.

[Schneibster]

Good. I'll be able to help some there, at least conceptually. One of the nice things about nonisotropies in the CMBR is that after they show you the numbers you can look at the whole-sky spectrum (or a piece of it) and see the ripples at that scale.

 

How about inflation?

[ajb]

How about inflation?

Lambda CDM + inflation seems to fit the data very well. I would say that most cosmologists accept that at the moment.

[Schneibster]

I would agree with that assessment.

 

How do you feel about the assertion that lambda drove the inflation?

 

And have you heard of "Eternal Inflation?"

 

Or the "cosmic landscape" or "string theory landscape?"

Edited February 20, 2014 by Schneibster

[ajb]

How do you feel about the assertion that lambda drove the inflation?

 

I don't think there is any reason to think the two are directly related as the energy scales involved are different. The early period of inflation and the current acceleration of the expansion of the Universe are usually thought of as separate phenomena. Or at least, that is what the last cosmologist I asked said.

 

Or the "cosmic landscape" or "string theory landscape?"

I am aware of the string landscape.

[Schneibster]

I don't think there is any reason to think the two are directly related as the energy scales involved are different. The early period of inflation and the current acceleration of the expansion of the Universe are usually thought of as separate phenomena. Or at least, that is what the last cosmologist I asked said.

 

Leonard Susskind thinks they are, and unless they've changed their minds Alex Vilentkin and Andre Linde agree with him. That's the inventor of the original string theory, and two cosmologists. OTOH the argument is not simple. So it's a bit too much for this thread. I just want to be sure we're all agreed this isn't "speculative."

 

Your argument about energy scales is the first time I've heard a plausible argument against it, however, so that's interesting and you can expect I'll follow up.

 

Should I conclude you've never heard of Eternal Inflation?

Edited February 20, 2014 by Schneibster

[Airbrush]

How about telling us what Lamba CDM means, for us non-experts. Or do you only converse with experts?

[Schneibster]

Lambda Λ is the cosmological constant in the Einstein field equation: G_μν + Λg_μν = (8πG_newton/c⁴)T_μν

 

It's the dark energy.

 

And I will always attempt to explain things at a lower level if requested. I don't believe in "scoring points" off people because they didn't take advanced math in gradeschool. Just ask. I like helping non-experts. I'm still closer to them than to the physicists.

Edited February 21, 2014 by Schneibster

[Strange]

And CDM is cold dark matter. Of course, apart from being cold (i.e. not moving at very high velocities) and dark (not interacting via the electromagnetic force, and possibly not the weak force either) we don't know what it is.

 

So Lambda-CDM is basically a description of the universe based on general relativity (specifically, the Friedmann–Lemaître–Robertson–Walker (FLRW) metric) with the addition of dark matter to explain the dynamics of galaxies and galaxy clusters (and various other things) and dark energy to explain the accelerating expansion.

[Schneibster]

And CDM is cold dark matter.

 

Yes, And the rest is correct too.

 

To give folks who are perhaps a bit more physics-oriented the idea, the majority of cosmologists are calling ΛCDM "The Standard Model of Cosmology." A small minority of astrophysicists think that's overambitious but the majority of cosmologists and astrophysicists are good with it.

I'll be firing up an argument in Modern Physics about the tension between XENON and XENON II, and DAMA/LIBRA and CDMS and CDMS II before too long. I don't believe in coincidences, for example DAMA/LIBRA, CDMS, and CDMS II all having the same systematic error and it not being a systematic error due to an undiscovered property of xenon.

 

But this is, again, not a conversation for Astronomy and Cosmology.

Edited February 21, 2014 by Schneibster

[ajb]

I just want to be sure we're all agreed this isn't "speculative."

I would say that the idea that the early phase of inflation and the current phase are related is speculative. But that is okay, modern physics at the edge of our understanding is by its nature speculative. The difference with the "speculations" section of this forum is that the idea that they could be linked was not just made up, but came from current understanding of physics.

 

Your argument about energy scales is the first time I've heard a plausible argument against it, however, so that's interesting and you can expect I'll follow up.

It has been a while since I asked any experts about it, it is quite possible people change their opinion regularly!

 

Should I conclude you've never heard of Eternal Inflation?

Yes, this is the idea that at least parts if the Universe could still be in the inflationary epoch. I don't know if this is in favor with cosmologists at the moment or not. Cosmology is not my area of expertise

[Schneibster]

Totally cool, ajb, I am going to really enjoy running stuff past you. I am already starting to read the books that have this stuff in them, so as I recall these ideas there will be more to say!

 

And I know a lot of cosmology, including Eternal Inflation and the echoes in the CMBR, as well as the large scale structure. So we're going to bounce a bunch of good stuff back and forth.

 

My next project is to figure out how to have multiple quotes. It's probably obvious but it's late to me, and I'm going to bed. Tomorrow.

Edited February 21, 2014 by Schneibster

[ajb]

Totally cool, ajb, I am going to really enjoy running stuff past you. I am already starting to read the books that have this stuff in them, so as I recall these ideas there will be more to say!

Give us a list of the books you are using.

 

The one I like for a good introduction to cosmology is Liddle's An Introduction to Modern Cosmology. It requires a good understanding of undergraduate physics, but not any quantum field theory or general relativity. It is a good place to get the basics.

[Schneibster]

I have amassed my cosmology from many sources.

 

I will give you the library as I have time. My major sources have been Heinz Pagels (whose premature death I bitterly regret), Brian Greene, Kip Thorne, Stephen Hawking, and Leonard Susskind, with major assists from Isaac Asimov's non-fiction History of Physics and Feynman's Lectures in Physics, commonly called "The Red Books." Some of the physics I learned in the EE curriculum served me well and most of the math certainly did.

 

It's a bit late this evening. Perhaps a partial one tomorrow, and a complete one the next day. If I'm motivated.

[MigL]

Just started working my way through Liddle's book AJB, as time permits.

I do tend to believe as Shneibster seems to, that all forms of expansion/inflation are driven by dark energy/cosmological constant-lambda/negative pressure/vacuum energy. Not that I can prove it, just a 'gut feeling'.

Not so sure about Linde's eternal inflation. Seems if universes were inflating from Planck scales to macroscopic all around us, there would be some observational consequences.

[Schneibster]

Actually Guth invented Eternal Inflation but Linde certainly did a great deal of work on it.

 

As far as consequences, they appear to be in the CMBR written across the sky for those with radiotelescopes to see.

 

Carry on.

Edited February 21, 2014 by Schneibster

[MigL]

In the CMBR? How?

The CMBR is very isotropic across the sky ( one part in one thousand or better if I recall ) except for the slight blue shift in the Milky Way's direction of travel and red shift in the opposite, and the best substitute for a universal frame we can ever hope to have.

I would think small universes inflating would have a huge effect on the CMBR unless shielded behind an event horizon.

The large spherical ( ? ) voids separated by filaments and walls of galaxy clusters are not areas of inflation as they can be explained by quantum fluctuations before the inflation of our universe 13.7 Byrs ago.

[Schneibster]

In the CMBR? How?

 

We can see echoes in the CMBR of the inflations of other universes "near" ours at its inception. This is years old, maybe even a decade. Do you need an article on it? It's not very hard to find. But I'll go find one if you can't.

Edited February 22, 2014 by Schneibster

[ajb]

In short, the details of the tiny fluctuations in the CMBR temperature fit very well with that predicted by inflationary models. I don't think we are at a stage to rule out specific models of inflation, but rather right now we now that a generic model fits well.

 

You should look up the Planck telescope.

You can read a little more about this on my blog.

[Strange]

 

We can see echoes in the CMBR of the inflations of other universes "near" ours at its inception. This is years old, maybe even a decade. Do you need an article on it? It's not very hard to find. But I'll go find one if you can't.

 

Are you talking about the ideas of Laura Mersini-Houghton? These are not widely accepted, so your statement seems a little "definite".

[Schneibster]

http://www.technologyreview.com/view/421999/astronomers-find-first-evidence-of-other-universes/

 

contains news recent discoveries (last October) on this front. This is what I'm talking about.

 

Incidentally it seems Roger Penrose was involved and made the discovery simultaneously with another person.

Edited February 22, 2014 by Schneibster

[Strange]

Yes, that is what Mersini-Houghton is claiming supports her multiverse theory. This is not widely accepted, so you should be careful about presenting this as if it were "fact". Even the article you link to is full of caveats about the tentative nature of the results.

 

And Penrose's idea is a bit different: he claims there is evidence of a "big bounce"; echoes of an earlier universe before the big bang. Again, neither the results nor the theory are generally accepted.