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astrophysics rambling social commentary

Stretching Conventional Wisdom Too Far

Today found me reading an article (https://phys.org/news/2019-10-giant-radio-galaxies-defies-conventional.html) about research into the far distant universe.

In this case the research was “New research on giant radio galaxies defies conventional wisdom”.

The article begins with this summation:

Conventional wisdom tells us that large objects appear smaller as they get farther from us, but this fundamental law of classical physics is reversed when we observe the distant universe.

https://phys.org/news/2019-10-giant-radio-galaxies-defies-conventional.html

Now I understand conventional wisdom (CW) and why it would tell us that: CW operates within the scope of human scale thinking that has obtained since time immemorial to us humans. And yes things that are further away do appear smaller.

But CW appears to have suffered arrested development sometime in the 19th century (the era of Classical Physics) – before we discovered:

  • that light takes time to cover distances.  So the further away something is from us the light we see from it comes from further back in time.
  • that almost everything in the universe is moving away from us at increasing rates of speed the further it is.
  • that this universe we live in was once a small thing that experienced a Big Bang and expanded enormously (and still appears to be expanding)

My own version of CW knows these things and takes them into account. So when I read that opening paragraph I was a bit perplexed – why would anyone with the same basic cosmology education I got think that the things we see very far out there, from very long ago, would not appear to be larger?

Confused?

Let’s see if my basic logic can help you follow this . . .

We think the universe is about 13.6 Billion Years old (13.6 GY) .
This also means that the edge of the visible universe is 13.6 GLY (Billion Light Years) from us.
That means when we see some object or structure 10 GLY from us the light was emitted 10 GY ago when the universe was just 3.6 GY old.

Good so far? (if not go back, reread and rethink about that – we’ll wait for you 🙂

Okay – this is where it gets interesting.

The universe is expanding.
Hubble was the first to discover that there was more universe our there than just what we saw in our galaxy. That the nebulae were actually other galaxies outside our own Milky Way.
He measured the spectra of their light and found that these were shifted towards the Red end of the spectrum.
He noticed that when he measured the red shifts of objects at inter galactic scales the further the object was from us the more red shift it had.
Meaning not only that these things are moving away from us (otherwise there would be no shift in the spectrum) BUT the ones further away are moving away faster than the closer ones.

Eventually we worked out that this is because the universe is expanding and has been since the beginning it apparently had.
One way to think about it is that measuring stick that once crossed the universe is still there but the gradations on its scaling are getting smaller in size and larger in number. (much the same as a dollar from 50 years ago is still a dollar today but due to inflation how much you can buy with it has shrunk – in both case we call this inflation)

At a very very early stage of the universe the structures formed occupied a certain fraction of the size of the actual universe.

At the age of 3.6 GY the universe was 3.6G LY in radius.
And let’s say that a large galaxy of 500,000 LY in size had formed and a monster black hole at its centre had been spewing and feeding the huge polar lobe structures we now know that they form.

These lobes are typically larger than the galaxy that spawned them. So let’s say these grow to 750K LY in size. Two of them plus the galactic bulge between could span 2 Million LY.

In a 7.2 GLY diameter universe 2 Million LY is a fraction of 2/7200 or 2.78×10^-10. That is the size and fraction of the size of the universe it was when if formed 10 GY ago.

Moving forward in time to Now.

The universe has expanded to 27.2 GLY diameter. This is approx. 3.778 times the size it used to be 10 GY ago.

All the structures that existed 10GY ago that do NOT have a strong gravity well to hold all their parts close in have also expanded in size.

So the galaxies themselves might have enough mass within them to keep most of their masses within their gravity wells . . . the ejected stuff further outside the well’s mouth will be subject to this universal expansion.

In the cases of Radio Galaxies the lobes of radio emitting gases and plasma may well fit in this category.

So lobes that were 750K LY in diameter would have grown to 2,833 LY in diameter after 10G years of expansion.

If you buy into the expanding universe you have to also buy that structures evolved Billions of years in the past cannot fail to appear larger now than old-style Conventional Wisdom would suggest.

When you look at the Wikipedia article (https://en.wikipedia.org/wiki/Radio_galaxy) on radio galaxies you will find this: “The largest radio galaxies have lobes or plumes extending to megaparsec scales”

A parsec is just over 3.262 LY. A mega parsec is 3.262 Million Light Years.

If we took our example radio galaxy and moved its birth back to 1 Billion Years in the life of the universe (12.6 GY ago) the expansion by now would have been 27.2 times instead of 3.7. So the 750LY lobes would appear to be 10.2LY across now.

Back when I was 12 years old (mid 60s) I learned about Hubble and the Red Shift and the expanding universe. Without benefit of a calculator I could still come up with a size and age of 12.5 GLY size and 12.5 GY age. Admittedly rough calculations by a child but this is how I’ve learned to think about the universe.


Why is that decades have passed – we’re even in a new millennium now – and that child has grown into a gray haired man but still our Conventional Wisdom is stuck somewhere before my grandparents were born?

Perhaps that is part of the problem our society appears to have in relating to science and technology. If you sound like you’re a scientist or know science you’re some kind of ‘elite’ and that’s a bad thing in the current political climate pervading society.

The idea that scientific fact and theory are being relegated to being ‘just another opinion with as much credence as the opinions of politicians and snake oil salesmen and charlatans’ scares the crap out of me.

Back when the Khmer Rouge emptied the cities they had a purge of \intellectuals’. Anyone who wore glasses was automatically branded an intellectual and sent to camps to be worked to death. Why? Because they could read . . .

When I see the wholesale discarding of science and scientists in favour of political expedience; denial of evidence based predictions because they prescribe hard-to-do solutions; I have to ask how did we come to this?

People want the world to make sense.

If the brightest brains tell them the world is so strange that they would not understand it even if they could understand the science all they hear is: you’re too stupid to understand this stuff – leave it to us. (which implies a classification-by-smarts system where the scientists are smarter and therefore in a higher class)

I know most scientists aren’t out to lord it over the normal people but that’s one possible take-away that non-science people get.

In better times they might get other, less negative, take-aways . . . but not now. Now there’s so many ‘alternative truths’ floating about being spouted by ‘truth tellers’ it would be very hard for the uneducated to filter out the crap from the facts. And most of those sources push some form of the negative take-away. Reinforce the idea that you cannot trust science and scientists. And most of those web denizens are engaged in reaching out to the non-science-people in the world. Like most media outlets they make money from the eyeballs and views and clicks they garner. So the more egregious and outlandish or scary the claims they make the more money they make. Truth is secondary.

A good education is pretty much free on the web as well . . . why most do not avail themselves of it is another issue.

I wasn’t trying to be preachy – just scratching an itch.