Penrose: WMAP Shows Evidence of ‘Activity’ Before Big Bang

[Grep]

Here's some strange stuff coming from Penrose... An article on Universe Today:
http://www.universetoday.com/79750/penrose-wmap-shows-evidence-of-‘activity’-before-big-bang/

And the paper:
http://arxiv.org/abs/1011.3706

Okaaaay... Granted, I need to actually pore over the actual paper, but that's some conclusions! I think I'll file this under "interesting but highly speculative." It's going to take a lot before I toss out inflation, let me tell you.

This seem as implausible to you guys as it does for me? Either way, I guess the paper should be interesting reading.

 

[Chalnoth]

Hmmm, could definitely use some more investigation. However, I strongly suspect that getting the instrument beam slightly wrong could produce the same effect.

 

[phyzguy]

It's a fascinating idea. Penrose' "outrageous hypothesis" is that the phase of exponentially accelerating expansion at the end of a lambda-dominated universe (like the one we appear to live in) is the same as the exponentially accelerating expansion that happens during inflation. His idea is that eventually all matter disappears and that the universe contains only massless particles. Once this happens, the universe "loses all measure of scale" and somehow things get re-scaled from the extremely large to the extremely small, leading to a cyclic universe. It's this last bit that I have trouble grasping. Does anyone have a better feel for how this could happen? I'm not sure whether this data(the circles) is meaningful or not, but at this stage I wouldn't dismiss it out of hand.

 

[bapowell]

There is zero statistical analysis in that paper.

 

[granpa]

http://arxiv.org/pdf/1011.3706v1

The clearest observational signal of CCC (Conformal cyclic cosmology) results from numerous supermassive black-hole encounters occurring within clusters of galaxies in the aeon previous to ours. These encounters should yield huge energy releases in the form of gravitational radiation bursts. From the perspective of our own aeon (see [3]), these would appear not in the form of gravitational waves, but as spherical, largely isotropic, impulsive bursts of energy in the initial material in the universe, which we take to be some primordial form of dark matter, the impulse moving outwards with the speed of light up to our last-scattering surface (see Fig. 1).

The effect of such an energy burst would be to provide an outward kick to this initial material of the early universe

The effect may be compared with what happens when a supernova burst encounters a cloud of gas.

As viewed from the perspective of our present location in space-time, the most immediately distinctive effect on the CMB of this energy burst would be a
circular (or annular) region, perhaps slightly distorted, over which the temperature variance would be anomalously low.

Those points in the CMB sky which are centres of circles whose depth (the amount by which its temperature variance is lower than the mean) is at least 15μK are noted, these deviating greatly from the Gaussian expectation with a significance of up to 6σ, i.e. probability 10^-7. (The peaks of high variance are of no importance, as these can result from numerous irrelevant effects.) It is found, very remarkably, that all low-depth circles are also centres of other such circles. We note that points which are simultaneously centres of n circles of around that depth would occur, with Gaussian data, only with the far smaller probability of~10^-7n.

this picture provides a serious problem for inflationary cosmology

 

[Cold Winter]

Here's some strange stuff coming from Penrose... An article on Universe Today:
http://www.universetoday.com/79750/penrose-wmap-shows-evidence-of-‘activity’-before-big-bang/

And the paper:
http://arxiv.org/abs/1011.3706

Okaaaay... Granted, I need to actually pore over the actual paper, but that's some conclusions! I think I'll file this under "interesting but highly speculative." It's going to take a lot before I toss out inflation, let me tell you.

This seem as implausible to you guys as it does for me? Either way, I guess the paper should be interesting reading.

Only if you think that its practical to assume that the big bang came from nothing. That "something" lead up to the big bang would seem quite reasonable to me. A completely sterile "beginning" for the big bang might be the more improbable...

 

[bcrowell]

I gave a talk on this for students at my school recently. Penrose has a popular-level book out on the topic, which came out a few months before the publication of this claimed observation. Here http://www.Newton.ac.uk/webseminars/pg+ws/2005/gmr/gmrw04/1107/penrose/ is a talk Penrose gave at Cambridge in 2005 on the topic.

If this is right, then it's certainly a huge discovery. There are at least two pretty big problems, however.

(1) Penrose's model requires some mechanism by which 100% of the massive particles in the universe get recycled into photons or other massless radiation. Black holes can do a lot of this, but there will inevitably be a few lonely hydrogen molecules that never fall into a black hole. Therefore one of the predictions of the model is that there is some novel particle physics going on. In the video of the 2005 talk, you can see that he posits the existence of charged particles lighter than an electron. Various particle physicists pointed out to him that this really isn't possible. (E.g., low-energy photons would interact with matter by pair production, and we observe that that doesn't happen.) By the time he published the popular book, he'd change this to a prediction that all massive particles simply lose their rest mass very, very slowly. This is disappointing, because it means he's stepped back from making testable predictions. "Very, very slowly" can be as slowly as you like, i.e., too slowly to measure, and therefore this aspect of the theory isn't falsifiable.

(2) The other problem is that it's not clear whether the claimed circular patterns are real. Penrose's co-author, the experimentalist on the new paper, is Gurzadyan. Gurzadyan got the WMAP and Boomerang collaborations to give him data. He is not part of those collaborations, but he has a ton of papers on CMB on arxiv, seems to be a heavy hitter in the field. The thing that makes me cautious is that the WMAP and Boomerang collaborations have not jumped on the bandwagon. If they really believed the statistical significance of the result, presumably they'd want their names on this extremely exciting result. Penrose's book also describes a grad student who worked on searching for such patterns in the data, and the book makes it sound like that search was inconclusive. If that grad student (and his advisor) believed in the patterns presently being claimed by Gurzadyan and Penrose, then there's no way in hell that this paper would go out without the grad student's name on them as a co-author; he definitely contributed to the work, and if he believed in the result, his name would be on there.

 

[71STARS]

When you begin with wrong data, you can expound on this wrong data with inconceivable results. Do you believe in the Big Bang? What if there was no single atom explosion? What if there was an atom that became a huge Mother Sun? Can data show that Suns shed a part of themselves continuously until they reach a maximum sustainable size? Since the accretion theory is unexplainable for creating Suns (which was an outcropping of the Big Bang Theory), then when will a new creation theory be given credence? In the Beginning surely entails Pure Hydrogen. If there was Void-Friction-Spark-Matter, how would it be possible for anyone to conjure up the exact environment "before the Big Bang"? There has to be a "sequence of events"; however, Man is not privy to what created Pure Hydrogen, in my humble opinion. Supposition and theory is good, but only based on logic.

 

[Chalnoth]

When you begin with wrong data, you can expound on this wrong data with inconceivable results. Do you believe in the Big Bang? What if there was no single atom explosion? What if there was an atom that became a huge Mother Sun? Can data show that Suns shed a part of themselves continuously until they reach a maximum sustainable size? Since the accretion theory is unexplainable for creating Suns (which was an outcropping of the Big Bang Theory), then when will a new creation theory be given credence? In the Beginning surely entails Pure Hydrogen. If there was Void-Friction-Spark-Matter, how would it be possible for anyone to conjure up the exact environment "before the Big Bang"? There has to be a "sequence of events"; however, Man is not privy to what created Pure Hydrogen, in my humble opinion. Supposition and theory is good, but only based on logic.

This post demonstrates a profound ignorance of the big bang theory. Please educate yourself before pontificating on that which you have no understanding.

 

[bcarpent1228]

I gave a talk on this for students at my school recently. Penrose has a popular-level book out on the topic, which came out a few months before the publication of this claimed observation. Here http://www.Newton.ac.uk/webseminars/pg+ws/2005/gmr/gmrw04/1107/penrose/ is a talk Penrose gave at Cambridge in 2005 on the topic.

If this is right, then it's certainly a huge discovery. There are at least two pretty big problems, however.

(1) Penrose's model requires some mechanism by which 100% of the massive particles in the universe get recycled into photons or other massless radiation. Black holes can do a lot of this, but there will inevitably be a few lonely hydrogen molecules that never fall into a black hole. Therefore one of the predictions of the model is that there is some novel particle physics going on. In the video of the 2005 talk, you can see that he posits the existence of charged particles lighter than an electron. Various particle physicists pointed out to him that this really isn't possible. (E.g., low-energy photons would interact with matter by pair production, and we observe that that doesn't happen.) By the time he published the popular book, he'd change this to a prediction that all massive particles simply lose their rest mass very, very slowly. This is disappointing, because it means he's stepped back from making testable predictions. "Very, very slowly" can be as slowly as you like, i.e., too slowly to measure, and therefore this aspect of the theory isn't falsifiable.

The talk was very good, thank you for the link. The Penrose book is also quite good, i especially enjoyed his views on relativity - although the Penrose concept of a "popular level" book is not the normal Greene, Wheeler, Susskind "popular level"

In the Q&A session a question was raised concerning the conformal representation; Penrose replied that more work is required to (1)to derive general relativity and (2)to possibly introduce mass into the conformal equations.

From that comment i surmised that the "mass-less" particle requirement is necessary for his current conformal formulation but may not be required for CCC.

 

[Chalnoth]

I talked about this with some of the guys at work, and the basic consensus was that we think that it's probably a failure to properly account for the statistical properties of the CMB.

Basically, when doing a pixel-based analysis like this, you need to take into account the correlations between pixels. Our models of the CMB predict a very specific pattern of correlations between pixels that depends only upon the separation between pixels. Given a theoretical model of the CMB, it is pretty straightforward to calculate what these correlations should be. There are also other instrumental effects that induce other correlations between pixels that can be really nasty to deal with, but are in principle necessary to get a proper accounting of the measurement error in this sort of analysis.

But there is no mention of this covariance in the paper, which is a strong indication that they did no such analysis, which means they're probably just seeing a normal feature of the CMB.

 

[bcrowell]

But there is no mention of this covariance in the paper, which is a strong indication that they did no such analysis, which means they're probably just seeing a normal feature of the CMB.

Interesting point. Well, the paper is extremely schematic in general. They don't really say anything substantive about the analysis. Way too early to tell anything. I also wonder about the effects of removing all of the features like the effect of the galactic disk.

 

[Chalnoth]

Interesting point. Well, the paper is extremely schematic in general. They don't really say anything substantive about the analysis. Way too early to tell anything. I also wonder about the effects of removing all of the features like the effect of the galactic disk.

Well, the claim of 6-sigma significance for an observable effect in the WMAP maps that deviates from the standard cosmology should most definitely raise anybody's suspicions. People have been looking for deviations from the standard cosmology since the WMAP first-year release, and have been unable to confirm any of them at reasonable significance. See this paper by the WMAP team, for instance:
http://arxiv.org/abs/1001.4758

So given the history of looking for anomalies in the WMAP data, the finding of a new anomaly with such extraordinary significance should be treated as an extraordinary claim. And extraordinary claims require extraordinary evidence. Until that evidence is presented, it should be treated with quite a bit of skepticism.

Anyway, turns out this sort of analysis is right up my alley, but it would take a fair amount of work to actually do the analysis carefully myself, and I'm not sure if I want to spend the time to do that. I'm just that skeptical that there isn't anything here.

 

[TrickyDicky]

Anyway, turns out this sort of analysis is right up my alley, but it would take a fair amount of work to actually do the analysis carefully myself, and I'm not sure if I want to spend the time to do that. I'm just that skeptical that there isn't anything here.

This is the scientific spirit at its highest. Fortunately someone else will do it, so no great harm for science.

 

[71STARS]

This post demonstrates a profound ignorance of the big bang theory. Please educate yourself before pontificating on that which you have no understanding.

My education is quite profound regarding the Big Bang Theory due to the fact that I would disagree with this well-established scenario. 1.

If the elements were not produced in the explosion that created the universe, where were they produced? It seemed that there was only one other possibility: the cores of stars. [end quote by Barry Parker "Einstein's Brainchild." 2.

We simply do not know yet whether there was a beginning of the universe, and so the origin of space-time remains in terra incognita." [end quote by George Smoot "Wrinkles in Time." 3.

Scientists have calculated that one 10tothe36 second (equivalent to one million-million-million-million-million-millionth of a second) after the Big Bang, the universe was the size of a pea, and the temperature was 10 billion million million million degrees C/18 billion million million million degrees F. One second after the Big Bang, the temperature was about 10 billion degrees C/18 billion degrees F. [end quote by the 1999 Scientific American Desk Reference.]
As for the accretion theory which had to be an outcropping for the Big Bang Theory to work, the formation of a Sun by the condensing action of a cloud of gas and dust has never to this day been able to be explained in detail.
Finally, it must be remembered that in 1949, the great physicist Enrico Fermi concluded only Hydrogen and Helium could have come from the Primordial Atom explosion. This is in direct opposition to the stated temperature calculations which at "1 billion degrees Centigrate permitted Protons and Neutrons to form into complex nuclei at 180 seconds immediately after the explosion."
There should be no fear in addressing a new theory, Penrose included.

 

[Grep]

This is the scientific spirit at its highest. Fortunately someone else will do it, so no great harm for science.

You know, people don't have infinite time to do things. You've got to prioritize ideas by how likely you think they are to pay off. It's frankly none of your business what he does or does not want to spend time on. Your comment was rather rude and sarcastic.

 

[bcrowell]

Well, the claim of 6-sigma significance for an observable effect in the WMAP maps that deviates from the standard cosmology should most definitely raise anybody's suspicions. People have been looking for deviations from the standard cosmology since the WMAP first-year release, and have been unable to confirm any of them at reasonable significance. See this paper by the WMAP team, for instance:
http://arxiv.org/abs/1001.4758

Well, this doesn't raise any suspicions in my mind at all, in and of itself. You've got a big data-set, and they're claiming a *correlation* of a type that nobody had looked for previously.

Six sigma actually isn't necessarily a strong claim of statistical significance in this context. In a big data-set, you expect to see a few large fluctuations. These circles are parametrized by three variables. Out of all the combinations of these three parameters, you should expect to see a few for which the signal gets big. It's not immediately obvious that six sigma is bigger than should be expected. They claim that the effect doesn't show up in their simulated version of the CMB. However, the simulated version doesn't need to have the amount of "photoshopping" that the real data do.

 

[Chronos]

My education is quite profound regarding the Big Bang Theory due to the fact that I would disagree with this well-established scenario. 1. "If the elements were not produced in the explosion that created the universe, where were they produced? It seemed that there was only one other possibility: the cores of stars. [Barry Parker "Einstein's Brainchild."] 2. "We simply do not know yet whether there was a beginning of the universe, and so the origin of space-time remains in terra incognita." [George Smoot "Wrinkles in Time."] 3. "Scientists have calculated that 10e-36 second (equivalent to one million-million-million-million-million-millionth of a second) after the Big Bang, the universe was the size of a pea, and the temperature was 10 billion million million million degrees C/18 billion million million million degrees F. One second after the Big Bang, the temperature was about 10 billion degrees C/18 billion degrees F." [ 1999 Scientific American Desk Reference.]
As for the accretion theory which had to be an outcropping for the Big Bang Theory to work, the formation of a Sun by the condensing action of a cloud of gas and dust has never to this day been able to be explained in detail. Finally, it must be remembered that in 1949, the great physicist Enrico Fermi concluded only Hydrogen and Helium could have come from the Primordial Atom explosion. This is in direct opposition to the stated temperature calculations which at "1 billion degrees Centigrate permitted Protons and Neutrons to form into complex nuclei at 180 seconds immediately after the explosion."
There should be no fear in addressing a new theory, Penrose included.

Feel free to attack any specifics you object to in BBT. Please include the math you relied upon to justify your objections. Hand waving is not pursuasive.

 

[foolosophy]

I do hope that everyone in here realizes that Roger Penrose is the only physicist on the planet that shoudnt be questioned

He is not from this planet

Only Roger Penrose can publish a giant book called "road to reality" and get away with it

 

[twofish-quant]

This is the scientific spirit at its highest. Fortunately someone else will do it, so no great harm for science.

Or it's quite possible (and actually IMHO much more likely) that someone else has already done it, found nothing, and since they found nothing there was no reason to publish.

One other thing is that just because someone is freaking brilliant in one area doesn't mean that they have any clue in some other part of physics.

 

[twofish-quant]

I do hope that everyone in here realizes that Roger Penrose is the only physicist on the planet that shoudnt be questioned

Penrose is a good example of why "brand name" shouldn't count for much in science. He's come up with some really, really brilliant stuff. He also comes up with stuff that is pure crackpot nuttery (microtubules).

 

[Greg Bernhardt]

Let's get this nice thread back on track if we can.

 

[marcus]

If anyone is interested there are some earlier threads on the general topic of Penrose's Conformal Cyclic Cosmology.
E.g. one started 8 September which has quite a bit of discussion:
https://www.physicsforums.com/showthread.php?t=427567

Bcrowell started another ("more on Penrose's Conformal Cyclic...") in late October, with some very interesting points:
https://www.physicsforums.com/showthread.php?t=442740

This earlier thread has links to video of Penrose presenting his Cyclic Cosmology idea to general audience, and also to an excellent slide+audio presentation. The Penrose talks are informative, but there is no discussion in the thread, only links:
https://www.physicsforums.com/showthread.php?t=236682

My personal take is that the ideas here are highly conjectural and there is no need to get emotionally heated about any of it. Unless you like argument for argument sake. We just have to wait and see. Bcrowell already made the point that since WMAP team itself hasn't shown interest the odds are that the statistics weren't convincing and this one isn't going to catch on. But we don't need to lay odds or try to pick winners/losers---we can simply wait for things to sort themselves out.

 

[hadsed]

Also an interesting article I read earlier posted below. It looks like the author of this blog feels pretty strongly about criticisms made by Penrose on inflation. I'd like to know what other experts think.

http://motls.blogspot.com/2010/11/penroses-ccc-cosmology-is-either.html

 

[Chronos]

Roger Penrose has somewhat a history of shooting from the hip just to see if anything falls out of the sky. He has earned this right by contributing numerous important ideas and papers over the years. I don't think this particular idea is especially promising, but, it could be.

 

[Chalnoth]

Also an interesting article I read earlier posted below. It looks like the author of this blog feels pretty strongly about criticisms made by Penrose on inflation. I'd like to know what other experts think.

http://motls.blogspot.com/2010/11/penroses-ccc-cosmology-is-either.html

Motl may have some important insights here, but I'm extremely turned off by his patently ridiculous views on entropy, which he takes the time yet again to mention in this post.

Anyway, there has been enough discussion at work on this that I've decided I'll do some analysis on this after all. Hopefully it won't take more than a day to do the simple check I want to do :)

 

[bapowell]

In following a friend's thread of Facebook, Dave Spergel chimed in and had the following to say,

"...I fear that he has detected the fact that the noise in the WMAP maps vary spatially. The noise is less near the ecliptic pole and there is a circle of low variance around the pole. If you look at his circle centers they are near the NEP and SEP. Since there are no equations in the paper and no discussion of spatially varying noise, I strongly suspect that they did not realize this in their analysis."

To which Glenn Starkman replied,

"As David implied, one would expect increased amplitude not decreased variance. But leaving the theory prediction aside, one could test David's hypothesis that the circles are all in the low-noise (ecliptic polar) part of the sky."

Also, apparently Amir Hajian has conducted the same study using a one-point function as an unbiased estimator and did not come to the same conclusion as Penrose.

 

[Chronos]

I don't find that particularly surprising. Why would anyone expect selection effects to be less pronounced along the ecliptic, as opposed to the poles?

 

[Chalnoth]

I'm pretty sure these are real features in the CMB, but they're features that you expect to see in a plain Gaussian realization. I made the same sort of plot with a plain Gaussian random realization of the CMB:

Sorry if the plot's a bit big. Anyway, unless Penrose and Gurzadyan decide to do a proper covariance analysis, as opposed to their current handwaving one, the fact that we expect to see similar sorts of structures in plain Gaussian random realizations shows that there probably isn't anything interesting going on here.

 

[Lievo]

I made the same sort of plot with a plain Gaussian random realization of the CMB:

Very good. A clear indication that these plots are not convincing by itself, or at least that the 6-sigma claim came from wrong assumptions. However Gurzadyan and Penrose added a much more interesting claim.

It is found, very remarkably, that all low-depth circles are also centres of other such circles.

Too bad there's so little flesh on the bones. Would you say this is true as well in your random realization of the CMB?

 

[Chalnoth]

Very good. A clear indication that these plots are not convincing by itself, or at least that the 6-sigma claim came from wrong assumptions. However Gurzadyan and Penrose added a much more interesting claim.

Too bad there's so little flesh on the bones. Would you say this is true as well in your random realization of the CMB?

Well, I didn't explicitly look for low-variance circles. I just looked for low-temperature spots, and made plots like they made around them, then grabbed one that looked interesting.

But I don't think their analysis actually determines whether they are concentric or not. They just looked at a bunch of different centers and picked ones that looked interesting (presumably with some sort of search algorithm for finding interesting ones). It was, in other words, the same analysis I did on the simulated map (though I did limit mine to a mere 10 spots with low temperature centers).

 

[Lievo]

I don't think their analysis actually determines whether they are concentric or not.

I don't think either, but wouldn't be the smart move to do?

I did limit mine to a mere 10 spots with low temperature centers

Sure, they need to show more before one spend weeks on that. However, did your quick look reveals that any of these 10 plots that includes 1 maybe-concentric-thing also includes several?

You know, I see why one may expect to see something like that even in random reconstruction, but I don't see why one should expect to always see several when there is at least one. Or do you see a reason?

 

[Chalnoth]

I don't think either, but wouldn't be the smart move to do?

Sure, they need to show more before one spend weeks on that. However, did your quick look reveals that any of these 10 plots that includes 1 maybe-concentric-thing also includes several?

You know, I see why one may expect to see something like that even in random reconstruction, but I don't see why one should expect to always see several when there is at least one. Or do you see a reason?

Don't really see a reason, no.

Basically, I think it just comes down to the physics of the CMB. The most simple model for the CMB is that you have a bunch of waves on the sky, and each wave draws its amplitude from a random Gaussian distribution that only depends upon the wavelength.

In mathematical terms, it's the statement that:

$$P(a_{\ell m}) \propto e^{-a_{\ell m}a^*_{\ell m} \over 2C_\ell}$$So here's the question: if I have a random distribution where the variables are independent in harmonic space, what does that mean for real space?

Well, as long as $C_\ell$ is non-constant, the real space distribution will also be Gaussian, but highly correlated. The covariance matrix becomes:

$$\sum_\ell {2\ell + 1 \over 4\pi} C_\ell P_\ell(\cos \theta_{ij})$$

Here $P_\ell(\cos \theta)$ are the Legendre polynomials. I'm not sure it would be useful to go into detail about what these are, but the most important consideration is this: the entire covariance matrix is just a function of $\theta_{ij}$. What is this parameter?

This is the angle across the sky between pixel $i$ and pixel $j$.

This means that different pixels on the sky are very highly correlated, and they are correlated by an amount that depends upon the angle of separation between them. Fundamentally this means that when you're binning up the pixels on the sky, the number of degrees of freedom is much smaller than the number of pixels in the bins. So with fewer random variables to average things out, you expect much larger variations from the expectation based just upon the number of pixels and assuming those pixels are independent.

Furthermore, by looking specifically at circles on the sky, which are a constant angle from some central point, you're exacerbating the visibility of any effect here because all pixels in each ring will have the same amount of correlation with the central pixel.

 

[Lievo]

Chalnoth, this is a very clear explanation of why the reported features could be by chance. But of course proving that there is truly nothing requieres some statistical testing. I was thinking at one test one could do (or that the authors could have done...), I wonder if you agree with the idea.

Suppose you count the number of 'concentric' features (min-max higher than, maybe, 10^-5K), automatically for each point of both real and randomly reconstructed CMB. Then you could plot the distribution of the points exhibiting more than 1, 2, ... n waves. If it's true that there is no anormality in the number of 'concentric' feature at some points in the CMB, then you could prove it by showing that real and sham distribution are the same even when considering the points with several 'concentric' features. What do you think?

 

[Chalnoth]

Chalnoth, this is a very clear explanation of why the reported features could be by chance. But of course proving that there is truly nothing requieres some statistical testing.

Yes, absolutely. I just don't see much of any reason to do that. His theoretical justification for this sort of feature is flimsy at best, and the default assumption is just that it isn't there. If he really believes it, let him do the work. I spent one morning on it, not really willing to spend much more.

The real difficulty here that mucks things up tremendously is instrument noise. Basically, it is currently impossible on most machines to store the instrumental noise covariance matrix for the whole sky at the resolutions of interest (these are nside=512 maps, where the instrument noise covariance stored in single precision would be 36 Terabytes).

It may be possible to compute and store only the instrument noise covariance for the patch of interest, but that would require some mapmaking, and mapmaking is not my strong suit.

Without pursuing the full noise covariance matrix in addition to the CMB covariance, we will never know for sure whether any deviation we do detect from normal CMB behavior (if any) is actually just instrument noise or some real deviation.

There's also the additional problem of the foreground signals, which will contaminate things and nobody knows how to simulate properly.

These are relatively small details, mind you, but they would all have to be taken into account to ensure that what deviations are seen (which there probably would be some) are real.