The rarest event ever recorded

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 aln 25 Apr 2019

https://www.independent.co.uk/life-style/gadgets-and-tech/news/dark-matter-...

Cool science and that, but I don't get something in this report. It says the event observed was the end result of a process more than a trillion times the age of the universe. So a process that started before the universe existed? 

Pan Ron 25 Apr 2019
In reply to aln:

Incomprehensible really.  All I can suggest is trying DMT, which can feel pretty close to those kinds of figures much of the time.

And I hope I wasn't the only bloody-minded person, so determined not to disable my ad-blocker, electing instead to read this one line at a time between the big bad "Disable your ad-blocker" box and the top of the screen.

 DaveHK 25 Apr 2019
In reply to aln:

Has my old mate Tom bought a pint?

OP aln 25 Apr 2019
In reply to Pan Ron:

In the past I've experienced some of the associated molecules but never the pure breakthrough. Of course with that, 'the past' has no meaning. I'm not sure what you mean about ad-blockers etc, I didn't see any of that when I looked at the article. 

Post edited at 21:02
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Deadeye 25 Apr 2019
In reply to Pan Ron:

It's nice science... but that's a horrible article.  It mangles the explanation of what's happening and why it's significant.

Do science journalists have any background in science?

 LGraham 25 Apr 2019
In reply to aln:

The ‘trillion times the age of the universe’ thing is the half-life of the decay of xenon-124. The half-life is how long it’ll take for half of some group of items to do something on average, some of the items will do it faster, some will do it slower. This animation shows it quite well https://en.wikipedia.org/wiki/Half-life#Probabilistic_nature

Post edited at 21:09
OP aln 25 Apr 2019
In reply to LGraham:

Yeah I get what a half-life is, I think. But trillions?

 Tom Valentine 25 Apr 2019
In reply to Pan Ron:

Thanks for the tip. Useful for us time -rich types.

 Philip 25 Apr 2019
In reply to aln:

> Yeah I get what a half-life is, I think. But trillions?

https://en.m.wikipedia.org/wiki/Double_electron_capture

In this case the probability of the decay is very much a function of the probability of the capture event.

OP aln 25 Apr 2019
In reply to Philip:

> In this case the probability of the decay is very much a function of the probability of the capture event.

So it didn't take trillions of years to happen?

 Philip 25 Apr 2019
In reply to aln:

No. I thought you said you understood half life, so only linked the reason the value is so high. It's rare,  but not that rare.

 David Alcock 25 Apr 2019
In reply to aln:

No. Just that the complete decay process will take about a trillion times longer than the current age of the universe. Xenon 124 half life of roughly 10^22 = universe 10^10 * trillion 10^12. So yeah, the chance of witnessing this event is unbelievable. 

 Philip 25 Apr 2019
In reply to David Alcock:

Not really. 1300kg of Xenon 124 =6e27 atoms. Xenon 124 is 0.095% abundance.

N(t)=N(0).0.5^(t/T½)

230 decays per year. Must be hard to observe and therefore potentially not all are detected.

http://m.wolframalpha.com/input/?i=%280.00095*6.3e27%29*%281-%280.5**%281%2...

 SenzuBean 26 Apr 2019
In reply to aln:

> So it didn't take trillions of years to happen?


Half-life can be thought of a bit like a lottery. If you keep buying the same numbers every week, it will take on average 11.2 million years to win the lottery. What the scientists did, was get a metric crapton of lottery tickets together (they got 1.3 tons of xenon atoms - suffice to say this is a lot of xenon atoms), so they could increase their chances to win the lottery within a few months, instead of 11.2 million years.

cb294 26 Apr 2019
In reply to Philip:

The trick with these kinds of experiment is distinguishing the couple of hundreds of real events from the millions or more of similar looking background events. There is a delicate tradeoff to be made between avoiding false positives (absolutely essential, as you do not want to make your later conclusions based on these) and not having too many false negatives, i.e. you still have too see something at all.

This is essentially the opposite to, say, cancer or HIV screening, where false positives are OK(ish), as you can always exclude them later, but missing one patient would have huge consequences. 

The message from this observation is that confidently detecting this decay event (which due to the huge number of Xenon atoms present was always expected to happen) gives the scientists a benchmark for how sensitive their experimental setup has become, and at which level they can therefore expect to observe or exclude the events they are really looking for.

CB

 David Alcock 26 Apr 2019
In reply to Philip:

I woke in the night thinking about that sum! 

 Philip 26 Apr 2019
In reply to cb294:

Actually I assumed they only had a single signal. But it seems they detected 126 of these in 2 years - 1156 expected.

(it's actually 3200 kg Xenon, so I corrected the calculation https://www.wolframalpha.com/input/?i=(0.00095*(6e23*3200000%2F124))*(1-(0.5**(2%2F(1*1.8e22)))) )

What they are finding is both the x-ray and the related Auger electron, the mismatch between the observed and the expected could be noise on either detector - detecting a single quantum event is pretty impressive, to get two related even more so.

 Philip 26 Apr 2019
In reply to David Alcock:

> I woke in the night thinking about that sum! 

No where near as much panic as I had when I temporarily assumed I didn't have a suitable calculator in my house.

 Jamie Wakeham 26 Apr 2019
In reply to David Alcock:

> Just that the complete decay process will take about a trillion times longer than the current age of the universe.

I'm afraid that's not how half life works.  The half life is the time you would expect to wait for half the radioactive nuclei to decay. 

Decay is spontaneous, and random, but also predictable.  Picture 1000 dice (I actually do this with classes - it's great fun).  They 'decay' if they come up with a six, and are then removed from the experiment.  Their decay is spontaneous (nothing external controls whether a die decays or not); it's random (I can't point at any particular die and say that it'll be next to decay); but it's predictable (I know that more or less one sixth of the remaining dice will decay on each throw).

After each throw, 5/6 of the dice remain.  The 'half life' of this experiment is how many throws do I need to get to 50 dice - or how many times must I multiply 100 by 5/6 to get to 50.  It's about 3.5 throws.  After 7 throws I'm at 25; after 10.5 throws I'm at 12-ish, after 14 throws I'm at 6-ish.  It's meaningless to ask how long it would take to get rid of all the dice, though, because at very low numbers random chance dominates (ie I might get lucky and not throw a six for ages).

So, if the half life of Xe-124 is 1.8e22 years, that means I would have to wait for 1.8e22 years just for half of them to have decayed.

Phil, I'm getting different numbers to you: 1300kg Xe = 10500 moles = 6.3e23 molecules, and at 0.095% abundance that's 6.0e20 molecules of xe-124.  Lambda = ln2/halflife = 3.85e-23 per year.

Activity = lambda x N = 0.023 events / year, or one event / 50 years.  Have I missed something..?

Edit - bugger - just saw you've corrected the mass.  But we're still disagreeing by a few orders of magnitude.

As mentioned above, the really hard thing here is that detecting it is almost impossible - the only things you can look for are a pair of neutrinos (almost indetectable) and the characteristic emission of photons from outer electrons dropping in to fill the gaps created by the absorbed electrons (that's what they actually recorded).

Post edited at 13:57
 Philip 26 Apr 2019
In reply to Jamie Wakeham:

Your N is wrong, should be 1.5e25

You were out by 4 orders of magnitude, your error appears when you applied the 0.095%, looks like you applied it twice.

All of this is rather boring, would have been more exciting to find it breaks the standard model, apparently neutrinos are emitted.

Post edited at 14:36
XXXX 26 Apr 2019
In reply to Deadeye:

> Do science journalists have any background in science?

Why would they? They're journalists. Do political editors need to be old mps? 

And the answer is some do. 

 Jamie Wakeham 26 Apr 2019
In reply to Philip:

D'oh.  I think I typed in Avogadro's number wrongly!

Yes, electron capture gives off a neutrino, so this double process must give off two - not that we'd be able to detect them.  I'd love to see the standard model broken, mostly because it's dull to teach - it's a long string of "this happens, because <complicated quantum thing that I can't explain properly at A level>, but this doesn't happen, because <different complicated quantum thing that I also can't explain at A level>".  With really bright pupils I take the time to talk about uncertainty governing the time that virtual particles can exist for, but most pupils have already gone tharn by that point.

 Philip 26 Apr 2019
In reply to XXXX:

> Why would they? They're journalists. Do political editors need to be old mps? 

No put they do usually have a politics degree.

Science journalism is probably bad because a science graduate who ends up in journalism isn't going to be the best scientist (stays in science or takes the cash and goes in to finance). They probably know nothing about the field.

Take the Science editor of the BBC, 2nd class geography degree from Durham. No wonder their reporting it so poor.

XXXX 26 Apr 2019
In reply to Philip:

Actually I think the level of science journalism is really high. I think your suggestion that only failed scientists become science journalists is insulting.

1
 Philip 26 Apr 2019
In reply to XXXX:

> Actually I think the level of science journalism is really high. I think your suggestion that only failed scientists become science journalists is insulting.

I didn't say failed, I said not the best.

Please pay more attention so that you don't misrepresent my views.

 Robert Durran 26 Apr 2019
In reply to Philip:

> Science journalism is probably bad because a science graduate who ends up in journalism isn't going to be the best scientist.

I doubt being a good actual scientist is a necessary qualification for being a good science journalist; I expect what is really needed is a talent for journalism and just sound scientific literacy.

> Take the Science editor of the BBC, 2nd class geography degree from Durham. No wonder their reporting it so poor.

Really? I think it is generally very good and their programming excellent.

Post edited at 21:05
 Pero 26 Apr 2019
In reply to Deadeye:

> It's nice science... but that's a horrible article.  It mangles the explanation of what's happening and why it's significant.

> Do science journalists have any background in science?

Science journalists are journalists, not scientists. 

 Pero 26 Apr 2019
In reply to XXXX:

> Actually I think the level of science journalism is really high. I think your suggestion that only failed scientists become science journalists is insulting.

It depends what you mean by "high level".  For example, suppose a study is done, which has a 95% confidence level of supporting a current theory.  A scientific view of this might be that the study is perfectly compatible with the current theory.  But, a journalist who reported it that way might be considered a poor journalist, as there is no story in that.

A journalist, however, might produce a story along the lines that the data cast doubt on the current theory.  That might even be considered "good" journalism.

In fact, you could make a case that good journalism implies bad science.


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