News. It’s all politics and disease and protests and stuff, right? But when a whole branch of science is having a crisis. For me? Tha...
News. It’s all politics and disease and protests and stuff, right? But when a whole branch of science is having a crisis. For me? That’s news.
Got 10 minutes? I’ll explain it, but if you only got one minute?
Cosmology is having an actual crisis right now. But the very word ‘crisis’ has a very specific meaning to scientists. It may not mean what you think it means.
When scientists describe having ‘tensions’ within a field of study they mean ‘we have a problem with the data but the solution is fairly obvious, we just need to sort it out”.
If they have issues with the data but there isn’t an obvious solution? Then it’s a ‘problem’. Cosmology has had tensions and problems in it for ages.
But the moment you have to accept that maybe long settled ideas could be wrong and the very foundation stones of the subject could be producing flawed results?
Then it’s a crisis.
Cosmology therefore is having such a crisis right now. And, literally, may have to trash decades of work and start over.
What’s going on?
Allow me try to explain
(I’m an Astrobiologist by training not a cosmologist, so I invite any and all Cosmologists to happily pop up in comments and laugh at how badly I explain things. Go for it. I mean given the potential of the issues you guys face- you need something to stop you falling into despair)
So first- gotta say it for those who don’t know the exact definition; what is Cosmology? Technically it is one of the branches of astronomy; it is the study of the age and evolution of the universe and trying to work out how the universe all started and where it’s going.
They‘re cool nerds.
We dig them.
See traditionally Cosmologists had a nice way of estimating the age of the universe. This was the method used by Hubble and the great founding fathers of Cosmology. I could give you the technical explanation- but let’s keep it real simple.
Hubble standard candle
Imagine a candle. A special type of candle. One that burns and produced consistent light. Something that is the same brightness no matter what.
This is the ‘standard candle’. So if you can measure it’s apparent brightness to you, you can measure the distance between you and the candle.
Now, cosmologists DO NOT actually use candles. That would be silly. But they do use certain light sources in the night sky to measure by, and we call these a ‘standard candle’ (as opposed to ‘Cepheid variant stars’ or ‘type 1a supernova’ which is a mouthful but the technically correct name).
So now we get distance and can work on the size of the universe. But it doesn’t help with getting the age. Luckily the universe is moving.
We can tell if stuff is moving towards us or away from us by measuring the blue shift if it’s moving towards us or the red shift if it’s moving away (light slips into the blue or red spectrum if the object moves fast enough).
By measuring the brightness of these objects in the observable sky we can calculate their distance and, by measuring the red shift in the light, the speed at which they are moving away from us. And then?
You can mentally rewind time and end up with a date when it was all smooshed together based upon speed and distance (aka speed equals distance over time)
Extrapolate this data across the night sky?
We get a rough estimate as to the age of the universe.
Barebones that’s roughly how it’s done (yes it is way more complicated than this, and involves more mathematics and physics, but this is just an overview).
So we had this standard candle way of judging the age of the universe and it gave us things like the Hubble Constant (or ‘the not very constant constant’, as boy has it been adjusted since Hubble first proposed it). But bottom line this gave us a scientifically valid date for the age of the universe.
Roughly it was 14.5 billion years old.
Still with me? Cool.
Meanwhile, as time has passed we developed radio telescopes and that technology has opened up huge areas of discovery and really furthered Cosmology.
Eventually using this technology, we got around to measuring the radiation echo of the Big Bang itself. We call this the Cosmic Microwave Background (CMB) and we realised that we needed to observe from outside our atmosphere to get proper data from it.
This in turn led to three satellites designed specifically to picture the CMB; first COBE, then WMap, and finally, Planck.
And the way we get an age of the universe out of the CMB is to say;
Right, if THIS is what the Big Bang has left us, given our best estimate of the contents, structure and expansion of the universe, then what age of the universe does that model spit back out at us.
Around 13.7 billion years old.
This is ALSO a scientifically valid date for the age of the universe.
So we had two perfectly sound and scientifically accurate ways to measure the age of the universe.
Only, as you can see, there was a SLIGHT problem.
The numbers didn’t match.
The two methods produced two differing answers:
The standard candle method (looking at ‘local’ supernova say) gave us an age of about 14.5 billion years.
While the CMB gave us around 13.7 billion years.
It don’t seem like much, but it’s actually important.
The question ‘how old is the universe’ is actually the off shoot from another question ‘what speed is the universe expanding’ as you need one to calculate the other. The two methods we had use to measure the speed at which the universe was expanding was giving us differing answers, which leads to speculation as to where the start date is.
This is not really new news. The above has led to some debate within Cosmological circles for a wee while. There was ‘tension’ between the two sets of data but this was NOT a crisis. Why?
Well we allowed for error; and the errors in our measurements allowed us to see that the two methods could overlap. Which is why everyone kinda assumed the precise age was probably somewhere in the middle, so hence the nice easy statement ‘the universe is about 14 billion years old’.
A few years pass.
Then the tensions start becoming problems as we began to get better at measuring things; improvements in telescopes, in software, in computational abilities, in more precise instruments to measure the CMB have meant that the error’s in those measurements have been reduced and reduced...
And still they do not overlap. So now have a problem.
In 2019 just before all the madness of 2020 there was a gathering of cosmologists in California to attend a conference called ‘Tensions between the the early and late universe’. During the opening key note speech it was admitted- Cosmology was in crisis.
In a nutshell the differing ages of the universe was based on 100% certain data and basically threw up some big questions:
Is the universe expanding at different rates in different places? If so, how the hell does it do that?
DID the universe experience periods of slowing down and then speeding up in its expansion (after the cosmic inflationary period)?
Above all:
How can we reconcile the CMB data with the Standard Candle data?
So with this as the background we come to the recent bombshell.
Three cosmologists decided to go back to basics and re-analyse the CMB data from the Plank satellite (which produced the best data on the CMB). But this time they allowed a couple of different parameters in their model vary.
Why is this important?
Well, one of the things that the models used to analyse the CMB data always kept the same was the geometry of the universe.
Universal geometry 101
Yep. Come for dank memes, end up talking about cosmic geometry. Welcome to Imgur...
Basic simplified way to get this:
The universe is either Flat, Open or Closed.
We are taking the actual geometry of space itself.
No, we are not talking about the curves/shape of space/time caused by mass as Einstein described in General Relativity, we are talking about the physical geometry of space in the universe.
How we should calculate stuff.
If we say that we should use a ‘flat’ geometric design what that means is if I send two parallel beams of light out in a straight line into space, they will never EVER converge and meet. They just run in straight lines forever parallel to one another.
If we say the universe is ‘closed’ it means the two parallel beams of light will eventually meet. How? Well look at the the surface of a sphere (aka the globe). If we send out two beams of light they will move apart (like the lines longitude start together at the poles but are parallel and seperate to one another at the equator) but we know if you travel along then far enough they converge either at the other Pole. That is an example of a ‘closed’ space.
No, it doesn’t mean that the universe is spherical in shape but we use a sphere as it makes it easier for our brains to visualise it.
If we say the universe is ‘open’ then the situation would be like the lines of longitude at the Poles- we would fire them parallel but they would soon diverge, and rather than move together at some pole, would keep growing further and further apart.
So you have the three models for the geometry of the universe- flat, open and closed. Got it? Awesome.
Right back to the narrative...
So our three cosmologists decided to allow the CMB data have a varied parameter; instead of looking at it and assuming the universe was flat, they picked up on recent evidence that suggested the universe was closed.
And that’s fine. We could probably accept that the universe is in some way closed; that’s not the issue.
The issue is- what does changing that parameter do to all the other parameters we use in our model of the universe.
So first the good news- they solved something. Why judging data from far away does not match the local data. In a flat universal model we have differences and can’t explain it. But if we say the universe is closed?
Hey presto- it works. We know why. It’s a closed universe. The local data WILL be different from the background data.
So that’s all good right?
Nope because when we solve THAT problem what we now face is that the values you then derive, for example, the age of the fricken universe, end up being even worse than before.
According to this?
The universe is 18 billion years old.
Like a whole extra 4/5 billion years unaccounted for.
Arse.
They also discovered that using this method, the faction of matter in the universe rockets up from 25% to 50%. Which is a huge change also.
These are proper scientists here now folks. The study and the results isn’t the issue (a single study is just that, it proves nothing). And it has led to quite some debate (and quite some snark) on cosmological based forums.
What most upset some was the genuine worry that the study would be picked up by non experts (like me), who would write up non technical explanations (like this), offer childishly simplified descriptions of complex mathematics (see above) and then sensationalise the events for fake internet points (see the clickbait title to this whole thing).
Guilty as charged your honour.
But let me be clear- I am not saying the universe is 18 billion years old. That is NOT the crisis.
No what is causing the crisis is the implications of the methods used for the study.
It basically questions the parameters of all our readings of the CMB. And this now presents Cosmologists with a dilemma.
They don’t know if they are precise or not or accurate or not.
Because of the discrepancy between so many other local measurements of the age of the universe, as well as other properties of the universe they have to conclude that they have a serious problem.
So there IS a bit of a crisis.
With three possible explanations:
1- these guys have made a huge mistake (which is fine but doesn’t get rid of the fact that Cosmology is in crisis anyway)
2-there is new physics here. The kind we have never thought off. We need hypothesise and explain it.
(To be blunt... no. This is really the most unlikely solution as the authors themselves here are quick to point out, you can get these results and remain happily within general relativity).
3-there is something deeply wrong with the data. Or the analysis of the data. A systemic failure in our models and our understanding of the CMB. That there is a problem in the systems we used to study the CMB that is effecting ALL our results.
Ouch.
Folks have been looking but haven’t found anything, but think about it- there is so much in the pipeline that could be wrong. We have to now triple check everything. The issue could lie in the actual observations themselves. Or from how we recorded the data. Or how we compiled the data.
There could be a flaw, a human flaw, in something and if there is, then it could be utterly turning all the answers/data we get from the CMB into junk, and basically everything we have been doing with the CMB will have something wrong with it.
It’s fair to say, no one wants this option.
It also has to be said that my conclusions are also clickbait sensationalism and that babbling about ‘new discoveries’ is exactly the kind of nonsense Cosmology does NOT need right now.
And cosmologists would be right in feeling resentful at me right now. I’m implying that until this issue is resolved, any work done based on the existing CMB data will have doubt cast on it because of this issue.
And THAT is not the kinda thing you say in a room full of cosmologists. You are going to get your head kicked in (verbally, usually by someone pointing out that ‘CMB lensing, BAO, weak lensing, and direct distance ladder measurements have NOT been taken into effect’ and I know nothing... NOTHING!)
But... whichever way you look at it. Cosmology IS having some very calm but very interesting debates right now.
In the end if nothing else the study demonstrated that the authors ‘don't believe that the Universe is closed but claiming now that the universe is flat with a precision below 0.5% it is also quite premature’.
And that IS a significant thing.
Basically one of three things will happen I think:
1- someone repeats their experiment and goes ‘aha! They got X wrong and the data now shows the universe isn’t 18 billion years old’
(Looking forward to that)
2- Someone (or many someone’s) goes ‘aha! We found it! We were reading the CMB data all wrong because of X so we need to recalculate stuff again...’
(also... Looking forward to that also)
3- no one says ‘aha!’ More and more non experts start talking about this.
(No cosmologist wants to see this, not because of any desire to silence anyone but folks like me are NOT experts and we dumb things down, and eventually some ‘science editor’ (I use the term loosely) in some newspaper picks up on some looney tunes idea and publishes a version of the debate which sticks in folks mind and the public’s perception is screwed and cosmologists have to spend years correcting folks...)
And it must be said that Cosmology is VERY prone to the media picking up some wild nasty comment and running with it.
Proof? In 1949 on a radio interview with the BBC, Sir Fred Hoyle, a brilliant Cosmologist, was trying to put forward his newly created idea for the formation of the universe (the steady state theory), and he dismissed the idea he thought was nonsense (that the universe had come from a single starting point); to him the data did NOT support the evidence and so he coined a term to dismiss the theory and make it sound stupid.
He called it the ‘big bang’ theory, with the words said with raised eyebrows in a mocking way.
(Exact quote: ‘Earlier theories... were based on the hypothesis that all the matter in the universe was created in one Big Bang at a particular time in the remote past”)
That’s how it is with Cosmology. You make a jokey sweeping generalisation about stuff, and the whole world picks up on it. And uses it without understanding the masses of debate that went before.
So that’s it in a nutshell. A very brief overview of the current crisis in Cosmology.
Which basically just means the universe is about 14 billion years old.
Give or take a few billion years.
Possibly.
We ain’t 100% sure right now.
(And remember- the ONLY reason I focused on the age of the universe in the above is that it’s a backdoor way into talking about ‘how fast is the universe expanding’ which is really what the focus is)
No comments