You can prove a theory

Yes, you can prove a theory

You just have to be very careful about how you define "proof" and "theory". Which sounds silly, but it isn't really. If you accept that reality is an illusion, and/or that our senses cannot be trusted or give information which is always unreliable, that we cannot ever really know what reality is like, then it's true you can't prove a theory. But in that case you can't even have true facts either, only things which (at best) can be assigned probabilities.

But this is not typically how most of us think or how science normally works either. It operates under the assumption that we can actually objectively measure the world, even if our information about it is not complete. Our measurements do represent reality in some way. They may occasionally be wrong or people may lie about them and deceive us, but this is the exception rather than the rule. Thus, under this assumption, it is perfectly possible to measure things we may consider to be absolute, true facts. The only way to say the Earth is flat is to invoke a massive conspiracy theory and/or our memories are being constantly manipulated. This isn't wrong, but it isn't science.

Once you allow absolute facts, you also allow provable theories. Evolution has been proven to occur, the Earth has been proven to be roughly spherical. These are both theories, in that they tell us how the world works, and facts, in that they are known to be true. They have varying degrees of predictive power, and you have to specify precisely under what conditions they should occur - but if those conditions are indeed replicated precisely, then evolution will always happen and gravity will always operate.

It's true that most of the time things are not always so black and white - most theories are varying shades of grey. But the absolute extremes - the definitely true and the definitely false - do happen. "Alternative facts" are indeed simply lies.

https://astrorhysy.blogspot.com/2017/02/you-cant-not-prove-it-wasnt-me-who.html

QA2 training

Today's ALMA QA2 training was relatively painless. Oh, it's a silly, badly-organised process in which files are given helpful labels like, "uid__Xf43e_2016.SB.00982.ms.split.cal" or worse, "textfile.txt", and finding the relevant information is like reading a dictionary when you know the meaning of the word but not the word itself.... BUT at least each individual step is not that bad. To tackle every possible eventuality you'd have to have years and years of experience, but that isn't going to happen most of the time. It's just a matter of writing a sensible set of ordered instructions (and using a Linux environment which FFS lets you minimise windows !)... there's light at the end of the tunnel and it's not an oncoming train.

So here is a short visual guide to observing with ALMA. Totally 100% accurate.

Not amused

Imagine, if you will, an enormous online technical manual from which you need to extract a few key points. Some of these are easily visible but most are hidden in obscure hyperlinks. You can control+f but not search the entire site in any way. Some points are labelled in an obvious way but others require reading and understanding to extract the relevant detail. You'll need at least a dozen different pages from which to extract all the information, but maybe not all at the same time and you can't minimize windows or have multiple desktops (because frak you, that's why). Some information can't be extracted directly from the manual but only by running a series of long, complicated tasks which then require you to check yet more extremely long web pages that are incredibly poorly-labelled and use a program which just plain doesn't work for no reason. The result of all this is access to data which doesn't interest you and you're not allowed to use in any case, and the absolute best you can hope for is that someone will eventually write you a thank-you email.

That's what ALMA QA2 is like.

Nope nope nope.

TMI

I will never, ever again fall back on the old adage, "in the age of information, ignorance is a choice". Anyone quoting that has never read the ALMA CASA cookbook. Or the example training PDF. And the less said about the vast, stupendous data reduction wiki, the better.

In the age of information overload, I need more tea. Much more tea.

QA2 begins

This week I'm in Garching learning ALMA QA2 (quality assessment level 2) procedures. All we have to do is determine if the data have the correct sensitivity and resolution. Which is like saying that in order to go to the Moon, all you have to do is build a big enough rocket...

Preparing for the VLA

So I've submitted my "scheduling blocks" to the VLA to get better resolution images of these optically dark hydrogen clouds in the Virgo cluster. With Arecibo they are single pixels : we get their maximum size and direct measurements of their position, mass and velocity width, but that's all. That's enough to say, "these little buggers are very interesting", but not enough to determine what the hell they actually are. We can run simulations for years and years, but we'll never really know without more data.

These observations will get us resolution that's about 4x better than Arecibo - not a huge gain, but potentially enough to distinguish between possible explanations. Given their mass we can work out a lower size limit at which they should have a density high enough to form stars - if they're close to that we'll know if we've caught them at a strange phase in their evolution just before they ignite star formation. In that case we might consider searching for molecular hydrogen. Or they might be more extended, rotating objects which could be stable on long timescales, in which case that's probably a Nature paper. Tonnes of stuff we can potentially get from this.

Of course, we'd like even better resolution, but that's not so easy. Interferometers like the VLA have sensitivity effects that single-dishes like Arecibo just don't have - making them (in some situations) far worse than due to the difference in collecting area. So their sensitivity to diffuse gas is ~100-1000x lower, and while these clouds were detected at Arecibo in 5 minutes of observations, we've requested 2 hours for each one at the VLA. Even then, since we don't know the true structure of the clouds, we're not guaranteed to detect anything. Fingers crossed...

Reading the VLA observing guide and links therein has been a less than fun affair, much like reading an old computer manual. Great if you need reference info, not so good if you need to learn stuff for the first time. The sheer amount of information is mmmmwwwaaaaaarrrgh. It takes a lot of getting used to the different terminologies : "scheduling block" really mean "observing script", "resource file" really means "telescope configuration file". I wouldn't say these are particularly intuitive labels and it makes mentally processing the information very much harder than it needs to be.

On the positive sides, the observing preparation tool is very nice. It's a simple, reasonably intuitive GUI webpage rather than a scripting language like Arecibo uses (though Arecibo does have an interactive GUI for doing the observations too). And even better, the NRAO helpdesk is genuinely very, very helpful, responding to my inept inquires in a few hours and in great detail.

And so now we play the waiting game, until the data arrives and I have to learn how the heck to process it.